Method for constructing a buried nuclear facility

Abstract

The invention relates to a method for constructing a buried nuclear facility at a site (10), comprising a well (12) excavated into the ground (14, 16) and defining a bottom (12a) at a given depth relative to the ground surface, and an opening (12b, 12b1, 12b2) located at the ground surface surrounding the well. The method comprises the following phases: - constructing a protective slab (D1, D2; D; 230) for protection against external threats over an area (Zcd) of the ground surface, referred to as the slab construction area, located adjacent to the opening (12b, 12b1, 12b2) of the well; - constructing a reactor building (B1, B2) inside the well (12), wherein the construction phases of the protective slab (D1, D2; D; 230) and the reactor building (B1, B2) are carried out in parallel.

Description

Description Title of the invention: METHOD OF CONSTRUCTING A BURIED NUCLEAR FACILITY Technical Field

[0001] The present invention relates to the field of buried nuclear installations. Prior art

[0002] We know, in particular from document WO 2018 / 204081, a nuclear installation in which a boiling water nuclear reactor containment vessel is housed in a silo built into the ground and rests on the bottom of the silo. The silo is closed at its upper part by a concrete cover to protect the nuclear reactor against external impacts and explosions.

[0003] According to current construction methods used to build such an underground nuclear facility, very generally, the first step is to excavate the ground to pour a foundation at the bottom and create a silo. A reactor building is then built inside the silo by erecting concrete walls. The nuclear reactor containment vessel and its components (primary circuit) are installed inside the reactor building, which is then closed. Once the various equipment external to the reactor building (e.g., cooling sources as indicated in document WO 2018 / 204081) is installed, the silo is sealed at its upper part with a concrete cover.

[0004] The order of the construction sequences identified above imposes an overall schedule for the construction of the nuclear facility.

[0005] In view of the above, it would be useful to design a method for constructing an underground nuclear facility that would save time in the overall construction schedule of the facility. Statement of the invention

[0006] The invention thus relates to a method for constructing a nuclear installation buried on a site, the site comprising a well dug in the ground so as to define a bottom, at a given depth relative to the surface of the ground, and an opening located substantially at the level of the surface of the ground surrounding the well, characterized in that the method comprises the following construction phases: - the construction of at least one protective slab against external aggression on an area of ​​the ground surface, called the construction zone, which is arranged next to the opening of the well, - the construction of at least one reactor building inside the shaft, the construction phases of said at least one protective slab and said at least one reactor building being carried out in parallel.

[0007] According to the aforementioned method, said at least one protective slab which is entirely arranged on the construction zone is built on this zone (before being shifted from this zone to above the opening of the shaft in order to completely seal it) while the construction of said at least one reactor building is in progress. This means that one does not wait for the completion of the construction of said at least one reactor building in the shaft, and even less for the installation of all the components and equipment internal to the shaft, to construct said at least one protective slab, unlike the conventional method used in the aforementioned prior art document. The construction phases of said at least one protective slab and said at least one reactor building overlap in time, which thus provides the above construction method with a considerable time saving on the overall construction schedule of the installation.The construction phase of said at least one protective slab may begin before that of said at least one reactor building, or at the same time, or even after. In addition, by constructing said at least one slab on the construction zone located next to the opening of the shaft (at a distance from the opening) and then transporting it above the opening of the shaft, the construction operations or phases of the installation are facilitated. In particular, once constructed next to the shaft, said at least one slab only has to be translated over a few tens of meters to be placed on the opening of the shaft, so as to seal it. completely. The at least one slab is constructed close to the well so that it can be moved with minimal effort to the well (this would not be the case if the at least one slab had to be moved over too great a distance, such as several hundred meters). It is therefore not necessary to bring an already constructed slab from a distant site and place it on the well.

[0008] According to other possible characteristics: -the method comprises a phase of construction of one or more pieces of equipment or buildings on said at least one protective slab, the phase of construction of equipment(s) or building(s) starting during the phase of construction of said at least one reactor building and while said at least one protective slab (D1, D2; D; 230) is on the slab construction zone which is located next to (at a distance from) the peripheral edges defining the opening of the shaft; the construction of (auxiliary) equipment(s) or building(s) is possible as soon as said at least one protective slab is finished (in one piece or in half-slabs, or even in more than two slab elements); this allows considerable time to be saved on the overall construction schedule (overall assembly time) compared to a situation where this or these pieces of equipment or buildings would be constructed only after the installation of said at least one slab on the opening of the shaft;it should be noted that when the slab is formed of several slab elements (two or more half-slabs), the or each piece of equipment or building is constructed on a single slab element which supports it, i.e. no piece of equipment or building is constructed straddling two slab elements; -the equipment or buildings constructed on said at least one protective slab are configured to provide support functions for the operation of the nuclear reactor and the entire nuclear installation and, as such, they are called 'auxiliary' equipment or buildings as opposed to so-called 'main' equipment or buildings which provide nuclear safety functions and which are positioned buried inside the shaft; in other words, they are equipment or buildings located above said at least one protective slab against external attacks and which may be subject to external attacks to the extent that the functions necessary for the safety of the reactor which they perform, in cases of degraded or accidental situations, are redundant with the safety functions of the reactor of the equipment or buildings located under said at least one slab; - the equipment or buildings constructed on said at least one protective slab comprise at least one of the following elements: a nuclear installation control room, a building providing ventilation functions, a building providing cooling functions, a room containing control and command cabinets for operating support and electricity production functions, an instrumentation room, a high-current electrical distribution room, a low-current electrical distribution room and batteries / inverters, a valve and exchanger room, a first-aid diesel engine room; - the construction phase of said at least one reactor building comprises the installation of at least one nuclear reactor enclosure and, optionally, at least one nuclear fuel storage pool; the nuclear fuel storage pool may alternatively be arranged next to the reactor building(s), in the shaft, in particular in an area of ​​the shaft adjacent to that housing the reactor building(s); during this construction phase, the enclosure and, optionally, the pool may be constructed in the shaft (before sliding of said at least one slab) and not only installed in the latter; -the construction phase of said at least one reactor building comprises the construction, on the one hand, of a wall or several walls surrounding said at least one nuclear reactor enclosure and, optionally, said at least one nuclear fuel storage pool and, on the other hand, of a roof covering the wall(s) so as to enclose, inside said at least one reactor building, said at least one nuclear reactor enclosure and, optionally, said at least one nuclear fuel storage pool; the nuclear fuel storage pool may alternatively be arranged next to the reactor building(s), in the shaft and therefore not be enclosed in a reactor building; -the construction method includes a phase of sliding said at least a protective slab, from the slab construction zone (at a distance from the opening of the shaft) to the right of the opening of the shaft, so that said at least one protective slab completely closes the shaft by being placed above said at least one reactor building at the end of the shifting; it will be noted that when one or more pieces of equipment or buildings are constructed (at least partially) on said at least one protective slab before its shifting, said at least one slab is thus shifted with the piece(s) of equipment or building(s) that it supports and which rest only on it; - the construction method comprises, after the phase of shifting said at least one protective slab, a phase of fitting out an intermediate space, called a technical gallery, between said at least one protective slab and said at least one reactor building; the technical gallery is inscribed in the diameter of the shaft; the technical gallery serves in particular to connect together a lower part of the installation housed in the shaft (reactor building) and an upper part located on said at least one protective slab, and serves in particular to connect together the prefabricated networks of these two parts by allowing the passage of various connections (cables, pipes, etc.) between these parts; -the construction method includes the construction phase of a single slab or two half-slabs (slab elements), or even more than two half-slabs or slab elements on the slab construction area which are slid one after the other up to the right of the shaft opening, then assembled with each other so as to completely close the shaft at the end of slidability (the slab thus acts as a separation barrier between the space above and the space below the slab); the use of two or more half-slabs makes it possible to reduce the weight of the load to be slidable and therefore to size the slab moving system accordingly, which simplifies the design of the installation and the slidability operations;this is particularly advantageous when one or more equipment or buildings are constructed on the half-slabs because, in the end, the loads to be shifted per half-slab are lower than if the same equipment or buildings were constructed on a single slab; - the sliding phase of said at least one protective slab takes place at the end of construction of said at least one reactor building; thus, time continues to be saved on the overall schedule compared to a situation where one would wait for the complete completion of the construction of said at least one reactor building before constructing above the reactor building said at least one protective slab and, in particular, before constructing above the reactor building said at least one protective slab and its possible equipment and / or buildings; - the phase of shifting said at least one protective slab takes place after the installation of said at least one nuclear reactor enclosure and, optionally, of said at least one nuclear fuel storage pool and the construction of the wall(s) and roof of said at least one reactor building; after shifting said at least one protective slab, it is in fact difficult to put such components in place in the well; - said at least one protective slab is placed at the opening of the shaft so that it can be removed later in the event of modification or dismantling of the nuclear installation; - when the shifting phase is completed, the construction phase of equipment(s) or building(s) continues on said at least one shifted protective slab; this again allows time to be saved on the overall construction schedule of the installation; - when the shifting phase is completed, the construction phase of said at least one reactor building continues, in particular inside the shaft; - prior to the start of the construction phase of said at least one reactor building, the construction method comprises the construction in the shaft of one or more vertical walls bordering the interior of the shaft; it will be noted that the construction of the shaft and its vertical walls may be carried out before the construction of said at least one protective slab; - said at least one protective slab is shifted to the right of the opening of the well so as to come into vertical support: directly on an embankment arranged at the outer periphery of the well, a bellows device being arranged vertically between said at least one protective slab and the vertical wall(s) bordering the interior of the well, or directly on the vertical wall(s) bordering the interior of the well, or indirectly on the vertical wall(s) bordering the interior of the well by by means of a damping joint device and / or directly on one or more supports arranged externally relative to the vertical wall(s) bordering the interior of the well; - the vertical well has a general rectangular, square or circular shape according to a view taken in a horizontal plane; -the construction method comprises a phase of construction of a turbine building on an area of ​​the ground surface surrounding the shaft, called the turbine building construction area and may also comprise the construction of other buildings; the turbine building construction area may be arranged opposite the slab construction area with respect to the shaft or at another location; the phase of construction of a turbine building may also take place during one and / or the other of the phases mentioned above in order to save time on the overall construction schedule.

[0009] The invention also relates to a buried nuclear installation obtained by the construction method set out above, according to one or more of the aspects mentioned above, or even according to all the aspects. Brief description of the drawings

[0010] Other characteristics and advantages will appear during the description which follows, given solely as a non-limiting example and made with reference to the appended drawings, in which:

[0011] [Fig. 1] Figure 1 is a schematic view of a possible example of a site for the installation of a buried nuclear installation according to a possible embodiment of the invention;

[0012] [Fig. 2] Figure 2 is a schematic perspective view from above of a first phase of a construction method according to one embodiment of the invention;

[0013] [Fig. 3] Figure 3 is a view similar to that of Figure 2 illustrating a second phase of the construction method according to an embodiment of the invention;

[0014] [Fig. 3A] Figure 3A is a partial schematic perspective view from above of two half-slabs spaced longitudinally apart from each other;

[0015] [Fig. 3B] Figure 3B is a partial schematic view in vertical cross-section showing the through openings of a half-slab and also a representation of a technical gallery;

[0016] [Fig. 4] Figure 4 is a view similar to that of Figure 3 illustrating a third phase of the construction method according to an embodiment of the invention;

[0017] [Fig. 5] Figure 5 is a schematic view in vertical longitudinal section illustrating the third phase of the construction method of Figure 4;

[0018] [Fig. 5A] Figure 5A is an enlarged partial schematic view, in vertical cross-section, of a possible longitudinal guidance system for a half-slab;

[0019] [Fig. 6] Figure 6 is a view similar to that of Figure 4 illustrating a fourth phase of the construction method according to an embodiment of the invention;

[0020] [Fig. 7] Figure 7 is a view similar to that of Figure 4 illustrating a fifth phase of the construction method according to an embodiment of the invention;

[0021] [Fig. 7A] Figure 7A is an enlarged partial schematic view of a connection zone between two half-slabs according to a possible embodiment;

[0022] [Fig. 7B] Figure 7B is a schematic perspective view from above of two half-slabs joined together;

[0023] [Fig. 7C] Figure 7C is an enlarged partial schematic view of an area of ​​the buried nuclear facility of Figure 7 located between a protective half-slab and the walls bordering the shaft according to a possible embodiment of the invention;

[0024] [Fig. 7D] Figure 7D is a partial schematic view illustrating the support of the protective slab according to an alternative embodiment;

[0025] [Fig. 7E] Figure 7E is a partial schematic view illustrating the support of the protective slab according to another variant embodiment;

[0026] [Fig. 7F] Figure 7F is a partial schematic view illustrating the support of the protective slab according to another variant embodiment;

[0027] [Fig. 7G] Figure 7G is a partial schematic view illustrating the support of the protective slab according to another variant embodiment;

[0028] [Fig. 8] Figure 8 is a schematic vertical sectional view illustrating the buried nuclear installation of Figure 7;

[0029] [Fig. 9] Figure 9 illustrates, in a vertical sectional view, another possible embodiment of a buried nuclear installation;

[0030] [Fig. 10] Figure 10 illustrates, in a horizontal sectional view, another possible embodiment of a buried nuclear installation;

[0031] [Fig. 11] Figure 11 illustrates, in top view, a possible embodiment of a circular underground nuclear installation under construction;

[0032] [Fig. 12] Figure 12 illustrates, in a vertical sectional view, the installation of Figure 11 after the slab shifting phase;

[0033] [Fig. 13] Figure 13 illustrates, in top view, a schematic variant of a possible configuration of buried nuclear installations;

[0034] [Fig. 14] Figure 14 illustrates, in top view, another schematic embodiment of a possible configuration of buried nuclear installations;

[0035] [Fig. 15] Figure 15 illustrates, in top view, another schematic embodiment of a possible configuration of buried nuclear installations. Description of the embodiments

[0036] The invention which is described below with reference to the attached drawings relates to different possible embodiments of a method of constructing a new architecture of a buried nuclear installation on a site.

[0037] As shown very schematically in Figure 1, a site 10 for the installation of a buried nuclear installation comprises a well or pit vertical 12 which has been dug (excavation phase) into a soil or terrain 14 to a predetermined depth, for example of the order of 30-35m using conventional excavation techniques and equipment. These dimensions may however vary.

[0038] This well 12 comprises, at a lower end, a bottom 12a and, at an upper end, an opening 12b of dimensions substantially equal to those of the bottom. In this embodiment, the earth which is removed during the formation of the well is, for example, used to form one or more embankments 16 arranged around the opening 12b of the well, thus forming an elevation relative to the surface of the ground 14. This arrangement can serve as a barrier against flooding. It will be noted that the presence of embankments is optional, the earth removed during excavation being able to be transported elsewhere. However, in the present embodiment, the embankment(s) 16 are present around the opening 12b of the well and it is considered that the opening 12b of the well is located substantially at the level of the upper surface of the embankment(s) surrounding the opening 12b.This upper surface can therefore be considered as the 'ground surface' which surrounds the opening 12b within the meaning of the invention. In the case where there is no backfill(s), everything which will be described subsequently applies directly to the level of the ground surface 14 surrounding the opening of the well (fig. 1).

[0039] The height or depth of the shaft 12 is defined between the opening 12b and the bottom 12a of the shaft and is chosen in order to be able to house entirely inside the shaft all the elements making up the buried part of the nuclear installation which will be described later (reactor building, technical gallery, possible nuclear fuel storage pool, etc.), taking into account the height of the base that will be formed at the bottom of the shaft. The shaft 12 may have any general shape following a horizontal section (perpendicular to the vertical plane of Figure 1) and, for example, may adopt a generally rectangular, square, circular section, etc. Generally speaking, the components of the buried part of the nuclear installation are located at a height which is lower than that of the ground surface and / or that of the lower surface of the embankment.In the present embodiment, the well has for example a rectangular section but the elongated dimension of the well is deliberately not. shown in Figure 1 which is a schematic diagram. The elongated shape will be visible in the following figures.

[0040] Then, several vertical walls are formed against the inner earth walls 19a, 19b of the well so as to border the useful interior space of the well. Only two vertical walls 18a, 18b are shown in Figure 1 while the well of rectangular section has four. These vertical walls 18a, 18b bordering the useful interior space of the well are, for example, cast walls well known to those skilled in the art (reinforced concrete walls cast in the ground). These walls are generally anchored in the ground by prestressed anchor rods.

[0041] These walls serve to absorb the pressure of the earth surrounding the well and to ensure a seal (barrier) inside the well, particularly against water that may infiltrate the surrounding earth. This sealing barrier may be supplemented by another barrier comprising a waterproofing membrane. Depending on the geometry of the well, a single wall (well with a circular section) or several vertical walls (well with a square, rectangular section, etc.), for example molded, may be considered.

[0042] As shown in Figure 1, the ground surface (here it is the upper surface of the embankment(s) 16) surrounding the opening 12b of the shaft comprises, close to this opening (but at a distance from it), on one side of the shaft, a Zed zone dedicated to the construction of a protective slab for the future buried nuclear installation. The proximity of the Zed zone to the shaft must be understood as a reasonable distance to allow the horizontal sliding of the protective slab from this zone to the opening of the shaft without causing excessive forces as would be the case if it were necessary to transport a slab over several hundred meters. This is therefore a distance which is of the order of magnitude of the largest horizontal dimension of the slab (length of a rectangle, diameter of a disc, etc.) and, in practice, which is greater than this largest dimension.For example, a single slab of generally rectangular shape may have a length of approximately 40m, which will define the end of the Zed construction zone that is furthest from the well, for example at a distance from the well of at least 40m, or even around 45 to 50m. This slab has the function, in particular, of protecting the installation against attacks. external, such as falling objects (e.g., airplanes) or external explosions. The protective slab is generally made of reinforced concrete. Alternatively, the slab can be constructed of prestressed concrete or made using a composite construction with a lower facing consisting of a stiffened steel sheet fixed and welded to the slab to which flexible connectors are welded.

[0043] The Zed zone is a construction area that is prepared before the construction of the protective slab, for example by creating a platform on which the slab will be built. This preparation phase can take place after the construction of the shaft walls described above or, in parallel, during the construction of the shaft walls.

[0044] Furthermore, the ground surface (here it is the upper surface of the embankment(s) 16) surrounding the opening 12b of the shaft may include, near this opening, on another side of the shaft which is opposite the side hosting the Zed zone, a Zcbt zone dedicated to the construction of a turbine building (optional) intended to accommodate a turbo-alternator. It should be noted, however, that the nuclear installation may also (or alternatively) be used to produce thermal energy to supply a heating network. The two Zed and Zcbt zones are arranged on either side of the opening 12b of the shaft following the same longitudinal alignment (X axis). The foundation work for the turbine building is carried out in the Zcbt zone and may take place during the preparation work for the Zed construction area of ​​the protective slab.It should be noted that the Zcbt zone can be arranged in another way and not necessarily in alignment with the Zed zone and the well in the case where, with the aligned configuration, the building containing the turbo-alternator would hinder the sliding of the protective slab.

[0045] The well 12 comprises, at its lower end, a raft 12c constituting the bottom of the well on which the various elements / components of the buried installation which will be housed inside the well will be installed. This raft is put in place in a known manner after the excavation of the well and the formation of the diaphragm walls. An injected bottom may prove necessary to limit the inflow of water from the bottom if the ground is permeable.

[0046] We will now describe in more detail, with reference to Figures 2 to 7, different construction phases of a possible example of a method for constructing an underground nuclear installation comprising, for example, two reactor buildings and where the protective slab is, for example, formed of two half-slabs. It should be noted, however, that everything that will be described (like everything that has just been described above) applies, in particular, to the construction of an installation comprising a single reactor building with a single protective slab above, or even two protective half-slabs above (in the case where one seeks to reduce the weight of the loads to be shifted due to a large reactor building) or even more than two reactor buildings with as many protective slabs as reactor buildings (or with more protective slabs than reactor buildings), and with a shaft of any shape (rectangular, square, circular, etc.).If several wells are to be constructed, the positioning of the preparation areas for the protective slab(s) must be studied on a case-by-case basis.

[0047] As shown in perspective in Figure 2, the preparation of the Zed construction area involves the construction of a reinforced concrete platform Ptf 1 which is here positioned in alignment (axial or longitudinal direction X) with the largest dimension (length) of the rectangular shape of the horizontal section of the well and centered in relation to the median longitudinal axis of this rectangle. The Ptf 1 platform has a generally rectangular shape in top view in order to accommodate the two protective half-slabs along its length.

[0048] Furthermore, two guide / slip beams L1 and L2, parallel to each other and aligned along the longitudinal axis X, are arranged symmetrically to each other on the Ptf 1 platform. These beams L1 and L2, generally made of reinforced concrete, are for example anchored in the ground each by means of vertical piles p1, p2 (foundation piles) regularly spaced along the X axis. These beams will serve as support for the protective half-slabs during their translational movement towards the shaft and, for this purpose, can be equipped, on their upper face, with plates made of a material having a low coefficient of friction with stainless steel, for example ipalen. Plates for example made of stainless steel can be fixed on the face lower half-slabs and will come into contact with the plates, for example in ipalen, of the stringers.

[0049] During this preparatory phase of the construction method, it is also planned to set up a displacement system to move by sliding the two half-protection slabs D1, D2 from their construction zone or area Zed to their final position for closing the shaft, above the shaft opening, once they have been constructed. This same displacement system can also be applied to a single protection slab or to more than two slab elements.

[0050] For example, a system for moving the two protective half-slabs may comprise, on the side of the shaft opposite the side where the construction zone Zed is located, one or more supports firmly anchored in the ground (or fixed to the head of the diaphragm wall) and one or more motorized mechanical traction devices fixed to the support or supports and exerting a tensile force on cables firmly attached to each half-slab. More particularly, the vertical section of Figure 5, which is a view of the construction site at a more advanced stage of construction than in Figure 2, shows a support formed by an anchor block M1, a hydraulic cable jack V1 mounted on the block M1, a traction cable or strand Ca1 attached at one end to the jack V1.The traction cable Ca1 extends longitudinally above the shaft and through the half-slab D1 which is closest to the shaft (a tube or sheath is for example put in place, during construction, in the thickness of the half-slab, at mid-height of the latter and it extends over the entire longitudinal dimension of the half-slab) to emerge at its opposite end outside the half-slab D1. The emerging end of the cable is for example equipped with an anchor head which can be fixed to a load distribution plate (passive anchor A1) secured to the face of the protective half-slab D1 which is opposite the shaft. It is planned to duplicate this arrangement with two anchor blocks, two jacks and two traction cables to exert a balanced longitudinal traction on the half-slab. Furthermore, a longitudinal guidance system can be provided on each stringer in order to avoid any deviation during the translation of the half-slab and in particular the. across it. Alternatively, a system using cables and one or more winches can be used.

[0051] Figure 5A represents an enlarged partial view, in vertical cross-section relative to the longitudinal axis X of shifting of Figure 5, of the displacement system and the guidance system of a half-slab D1 on the side of the shifting beam L2 (not visible in Figure 5). Thus, the traction cable Ca2 (symmetrical to the cable Ca1 of Figure 5) crosses the falling peripheral edge forming a skirt R1 of the half-slab D1 in the length thereof. The shifting beam L2 is equipped, on its upper face, with one or more plates Pi made of a material having a low coefficient of friction with stainless steel, for example ipalen and, one or more plates or sheets Pa, for example stainless steel, are fixed on the lower face of the edge R1 of the half-slab and arranged in contact with the lower plate(s) Pi. Furthermore, a support post Ps is partially anchored in the ground and fixed to the shifting beam L2.The support post Ps carries, in its unburied part and on its internal face oriented towards the edge R1 of the half-slab, a guide rail rg which is in contact with the external face of the edge R1 and serves to guide the longitudinal shifting / translation movement of the half-slab. A symmetrical arrangement is provided on the other part of the edge R1 of the half-slab arranged above the shifting beam L1 of figure 5. Other longitudinal guidance systems can alternatively be envisaged to guide the half-slab D1 (and the other half-slab D2) and thus avoid any non-longitudinal movement of the latter.

[0052] In parallel with these operations, the construction of the foundation of the turbine building on the construction area Zcbt can be carried out (fig. 2) by first constructing, for example, a reinforced concrete platform Ptf2, here aligned along the longitudinal axis X, and on which, for example, a slab Dbt is built to serve as a floor for the turbine building. The turbine building is generally positioned close to the reactor building in order to reduce as much as possible the length of the steam pipes that must reach the turbine building. The layout of the turbine building is however planned so as not to hinder the future sliding of the half-slabs D1 and D2.

[0053] In parallel with the operations of preparing the half-slab construction area, the construction of at least one reactor building inside the shaft begins, which saves time on the overall construction schedule of the installation since construction tasks are thus carried out in parallel. In this example embodiment, the construction of two reactor buildings B1 and B2 begins by first constructing the walls, for example made of reinforced concrete, of the reactor buildings which are visible in Figure 2 and rest on the base 12c, namely two large longitudinal walls parallel to each other 20 and 22, two smaller transverse walls 24 and 26 arranged along the length of the shaft, as well as a separating transverse wall halfway between the walls 24 and 26.It will be noted that a third longitudinal wall (not visible in Figure 2 but which will be represented in particular in Figures 7D and 7E described later under the reference 27), parallel to the two longitudinal walls 20 and 22, is constructed in the shaft between the wall 22 and the cast wall of the shaft which is located on the front face of the shaft in Figure 2 (this wall of the shaft is referenced 18c in Figures 7D and 7E). The space delimited between the wall 22 and this third wall 27 is used for example for the construction of a zone of the shaft which is arranged adjacent to the zone of the shaft where the reactor buildings are housed and which may include a vertical handling zone and include one or more stairs, equipment ancillary to the operation of the reactors, or even one or more nuclear fuel storage pools.

[0054] The longitudinal wall 22 is pierced in its thickness, near each of its two opposite longitudinal ends, so as to locally provide an opening 01.1 and 02.1 which, each, connects the interior of the corresponding reactor building B1, B2 with the space adjacent to this building along the wall 22. This opening (called buffer) is permanently closed during operation of the reactor (by means of a sliding or pivoting door not shown) and opened only to evacuate or bring in equipment.

[0055] Figure 3 illustrates a more advanced phase of the construction method where the construction of the two protective half-slabs D1 and D2 begins on the construction zone / area Zed provided for this purpose. The Zed zone is subdivided into two sub-zones or secondary areas distant from each other along the longitudinal direction X and each concrete half-slab is built on one of the two separate sub-zones or secondary areas, each being positioned above one of the two guide beams L1 and L2, symmetrically with respect to the other half-slab. A longitudinal space is left free between the two half-slabs. Each protective half-slab is generally made of reinforced concrete. Alternatively, each half-slab can be built of prestressed concrete or made using a mixed construction with a lower facing consisting of a stiffened steel sheet onto which flexible connectors are welded. It should be noted that the construction parallel to the longitudinal axis X, of a second "line" of construction of an underground nuclear installation can be envisaged as will be described later.

[0056] Figure 3A shows, in a perspective view from above (enlarged compared to the view in Figure 3), the two protective half-slabs D1, D2 (without the other elements of Figure 3), each on their secondary construction area. The half-slabs are thus constructed at a distance from each other and each have a free end face fa1, fa2 facing each other. These two faces fa1, fa2 will be mechanically joined / assembled with each other to form a single slab as explained further on with reference to Figure 7A. As shown in Figure 3A, a peripheral edge R1, R2 is arranged respectively on the lower face of each half-slab D1, D2 and extends vertically downwards in the manner of a skirt or a falling edge.

[0057] Each half-slab D1, D2 has openings which are made through its thickness in order to allow the passage of cables, pipes, equipment and people (for stair access) according to the opening(s) concerned. In figures 3 and 3A an opening T1, T2 offset laterally with respect to the longitudinal median axis of each half-slab is present. This opening is intended to form a hopper which will be used later for maintenance or handling and which will be arranged above the handling area located between the longitudinal wall 22 and the non-visible front wall of the shaft (wall 27 in figures 7D and 7E). Other through openings are arranged at separate locations in each half-slab on which buildings will be constructed as will be seen later. Each of these openings are used for the passage of cables, pipes, etc. (various connections) between the building located above the half-slab and the reactor building located under the half-slab via a technical gallery located between the half-slab and the reactor building and which will be described later.

[0058] Figure 3B is a schematic vertical sectional view of a half-slab Di (along its smallest dimension) showing for example two through openings Di 1 and Di2 (a greater number of openings can be envisaged in a variant if the number of buildings increases) arranged respectively in line with future buildings constructed on the half-slab and an opening Ti, arranged on one side of the half-slab, acting as a hopper and which is for example closed by a hatch ti shown in the two positions in Figure 3B. After having selectively put in place the various connections through each opening Di 1 (e.g.: pipes), Di2 (e.g.: cables), the latter is sealed in a manner known to those skilled in the art, in particular to ensure sealing and fire protection.

[0059] Furthermore, each half-slab D1, D2 has footprints r1.1, r1.2, r2.1, r2.2 (figs. 3 and 3A) of the rails of an overhead crane which will be used later to move various equipment on the slab and in particular for maintenance above the handling hoppers T1, T2.

[0060] Meanwhile, the construction of the two reactor buildings B1 and B2 continues with the installation, in each building, for example of an intermediate slab di 1 , di2 (fig. 3) which is pierced in its central part with an opening 01 , 02 in order to accommodate a nuclear reactor enclosure. At the same time, the free space defined between the longitudinal wall 22 of the buildings B1 , B2 and the third longitudinal wall not visible in figure 3 is arranged, for example, by construction of two multi-story structures S1 , S2 each against the part of the wall of one of the two reactor buildings and which are, for example, stairs, platforms for access to certain instruments or equipment necessary for controlling the operation of the reactor(s). The two structures S1 , S2 are separated from each other by a transverse wall 32 which divides the free space into two compartments C1 , C2 each dedicated to a reactor building.

[0061] According to an alternative embodiment not shown here, a nuclear fuel storage pool may be constructed / installed, for example, in the above-mentioned space / compartment, adjacent to the area of ​​the shaft accommodating the two reactor buildings, along the wall 22, extending on either side of the intermediate transverse wall 28 (along the areas occupied by the two reactor buildings). Alternatively, two nuclear fuel storage pools may be constructed / installed, for example, in the above-mentioned space. Each pool is arranged adjacent to one of the two reactor buildings and is dedicated to the latter. As with the construction of the building(s), the construction / installation of the pool(s) in the shaft is carried out in parallel with the construction of the protective half-slabs next to the shaft.

[0062] At the same time, construction of a turbine building 30 begins (fig. 3).

[0063] Figure 4 illustrates an even more advanced phase of the construction method in which the construction of one or more facilities or buildings begins on each half-slab of protection that has been constructed on the construction area.

[0064] This or these pieces of equipment or buildings are configured to provide support functions for the operation of the nuclear reactor and the entire nuclear facility and, as such, are called 'auxiliary' equipment or buildings as opposed to so-called 'main' equipment or buildings which provide nuclear safety functions and which are positioned buried inside the shaft. In other words, these are pieces of equipment or buildings located above the slab and which may be subject to external attacks to the extent that the functions necessary for the safety of the reactor that they perform, in degraded or accidental cases or situations, are redundant with the reactor safety functions of the equipment or buildings located below the slab.

[0065] This or these equipment or buildings constructed on each half-protection slab may include at least one of the following elements: a nuclear installation control room, a building providing ventilation functions, a building providing cooling functions, a room containing control and command cabinets for operating support and electricity production functions, an instrumentation room, a high-current electrical distribution room, a low-current electrical distribution room and batteries / inverters, a valve and exchanger room, a first-aid diesel engine room.

[0066] In Figure 4, half-slab D1 thus supports two buildings b1.1 and b1.2, while half-slab D2 supports two buildings b2.1 and b2.2. In this embodiment, buildings b1.1, b1.2, b2.1 and b2.2 are respectively an auxiliary building providing cooling functions, an auxiliary building providing ventilation functions, an auxiliary emergency diesel engine room and a plant control room. Generally, each half-slab supports the entire weight of the equipment / buildings built on it.

[0067] During the construction of the equipment and / or buildings on a half-slab or on the half-slabs, the construction of the two reactor buildings B1 and B2 continues with the construction of a nuclear reactor enclosure E1, E2 of known type in each of the buildings.

[0068] When each enclosure is completed (figs. 4 and 5), a roof (not shown) is put in place, for example by pouring a concrete slab, above each reactor building B1, B2, resting on the walls of the building so as to cover and close the entire building. The roof of each reactor building is placed at a distance from the opening 12b of the shaft in order to provide, above the roof, a free space where a technical gallery will be arranged between the roof concerned and the half-slab which will be placed above. As each half-slab is built and topped with buildings, independently from one half-slab to the other, and each reactor building is also built independently of each other, the roof of reactor building B2 is not necessarily put in place at the same time as the roof of reactor building B1 (moreover, enclosure E2 is not necessarily completed at the same time as enclosure E1).The roof of reactor building B2 can be installed after that of reactor building B1.

[0069] Two staircases 34, 36 are for example each constructed in one of the two compartments C1, C2 arranged along the longitudinal wall 22 of the buildings B1, B2, next to the corresponding structure S1, S2. These staircases 34, 36 are arranged for example each at a location which will be situated under the hopper T1, T2 of each half-slab.

[0070] Construction of turbine building 30 can continue during this construction phase (Fig. 4).

[0071] Figure 6 illustrates a subsequent phase of the construction method during which the protective half-slab D1 (constructed with the equipment(s) and / or buildings at least partially constructed on it) is shifted longitudinally / horizontally (along the X axis) using the movement and guidance systems described above with reference to Figures 5 and 5A (in Figure 6 this movement system is not shown for the sake of clarity). This movement is carried out from the secondary area of ​​the construction zone Zed to the right of the part 12b1 of the shaft opening located above the roof of the reactor building B1 (Fig. 5), passing above the part 12b2 of the shaft opening located above the roof of the reactor building B2. The shifting is carried out over a distance of several tens of meters and, for example, over a distance greater than twice the length of the half-slab.Thus, the half-slab D1 partially seals the shaft by being placed above the reactor building B1 at the end of the shifting operation (fig. 6) and also extending above the compartment C1 (zone adjacent to the reactor building B1). The half-slab D1 can rest on the diaphragm walls of the shaft defined above or be placed in support in different ways as will be seen later. The shifting phase of the first half-slab D1 takes place at the end of the construction phase of the reactor building B1 while the main tasks of building construction have been completed.

[0072] For example, the roof of reactor building B2 can be put in place after the first half-slab D1 has been slid but before the second half-slab D2 has been slid. Similarly, while the first half-slab D1 is being slid, construction of the buildings on the second half-slab D2 can continue, as can the construction of containment E2 if these have not been completed.

[0073] It should be noted that during this shifting phase, the construction of reactor building B1 is not yet completely complete and various small pieces of equipment (e.g. ventilation, cabling, tests, etc.) remain to be installed.

[0074] Figure 7 illustrates a subsequent phase of the construction method during which the second protective half-slab D2 (constructed with the equipment(s) and / or buildings at least partially constructed on it) is shifted longitudinally / horizontally (along the X axis), at the end of the construction phase of the reactor building B2 (the remarks made above concerning the shifting of the half-slab D1 with respect to the construction of the building B1 apply here) by implementing the displacement system described above with reference to Figures 5 and 5A (in Figure 7 this displacement system is not shown for the sake of clarity). This displacement is carried out from the secondary area of ​​the construction zone Zed to the right of the part 12b2 of the shaft opening located above the roof of the reactor building B2 (Fig. 5).Thus, half-slab D2 partially seals the shaft by being placed above reactor building B2 at the end of the shifting operation (fig. 7) and also extending above compartment C2 (area adjacent to reactor building B2). Half-slab D2 rests on the lower structure in the same way as half-slab D1. With the two protective half-slabs thus positioned, opening 12b of the shaft is completely sealed. The anchor blocks can then be demolished. It should be noted that when the two half-slabs D1 and D2 rest on the heads of the diaphragm walls, lateral stops made of reinforced concrete can, for example, be made around the entire periphery of the shaft by being connected to the diaphragm walls in order to laterally block the slab formed by the two half-slabs on these walls. Furthermore, a seal is created between the external peripheral surface of the slab and the diaphragm walls.

[0075] Alternatively, the half-slab sliding operation can be carried out on an air cushion using, for example, so-called APS modules of the Freyssinet system, which are air-cushion sliding supports arranged under each half-slab. More specifically, the air-cushion sliding supports can be arranged between the lower faces of the two longitudinal edges or skirts of the slab or each half-slab and the upper face of the two sliding beams (the coefficient of friction is very low, around 1%). Figure 5A illustrates where these sliding supports can be positioned.

[0076] In the position of Figure 7, the half-slab D2 is arranged against the half-slab D1 and the two half-slabs are mechanically joined / assembled with each other, for example by keying, in order to mechanically form a single protective slab while ensuring continuity of the mechanical resistance of the slab at the junction or connection zone between the half-slabs (to do this, the reinforcement or reinforcement must be continuous at this zone). Figure 7A illustrates a possible example of mechanical assembly between the half-slabs D1 and D2. This figure is an enlarged partial view of a mechanical connection zone between the two half-slabs. The connection between the two half-slabs D1 and D2 can be achieved by providing a keying zone Zcl between these half-slabs.The half-slabs are installed by providing a keying width greater than the overlap length of the longitudinal reinforcements which are located in the lower layer a1 i and a2i and in the upper layer a1 s and a2s of the half-slabs. The longitudinal reinforcements of each slab element (half-slab) overlap with the longitudinal reinforcements of the other slab element. Several layers of upper and lower reinforcements are required for each slab element but only one layer of upper reinforcement and one layer of lower reinforcement are shown for each slab element on the schematic diagram in Figure 7A to facilitate understanding. The longitudinal reinforcements in the other direction and the shear reinforcements are also installed (see schematically the perpendicular reinforcements a3i and a3s in the figure).In addition, temporary Cfp formwork can be fixed under the slab elements and the concreting of the keying zone is then carried out in order to mechanically connect the two slab elements. The temporary Cfp formwork is removed and removed a few days after concreting the keying zone. It should be noted that other solutions can be considered to ensure the continuity of the longitudinal reinforcement: couplers, welding of the bars.

[0077] Figure 7B illustrates the slab obtained after assembling the two half-slabs D1, D2, for example as explained in the embodiment described above, but which can be obtained in a different manner not described in detail here.

[0078] The slab obtained after assembly of the two half-slabs D1, D2 is a protective slab against external attacks on the well and thus protects the components of the installation which are entirely housed in the well.

[0079] Generally, each half-slab is installed so that it can be removed later in the event of dismantling of the installation (at the end of its life) or even in the event of a major modification thereof, for example to carry out major maintenance work in terms of the safety and operation of the installation. For example, the replacement of one or more steam generators may justify such an operation. The configuration of the slab which allows it to be removed later (i.e. after installation to seal the shaft) is linked to the fact that it is a slab resulting from the assembly of two half-slabs (or even more than two half-slabs in a variant not shown) and which thus becomes a single slab formed from a single piece which can be slid out of the shaft in the aforementioned axial / longitudinal direction X in order to clear the shaft opening.It should be noted that this axial / longitudinal displacement / slip of the slab follows the opposite slip path to that associated with the installation of the slab during the construction of the facility. The same is true for a single slab that is homogeneous in its construction.

[0080] It should be noted that during the shifting phase of half-slab D2, the construction of reactor building B2 is not yet fully completed and various small pieces of equipment (e.g. ventilation, cabling, testing, etc.) remain to be installed. Furthermore, during this shifting phase of half-slab D2, the construction of the auxiliary buildings on half-slab D1 can continue if it is not yet complete. Similarly, after shifting half-slab D2, the construction of the auxiliary buildings on half-slab D2 can continue if it is not yet complete. However, it should be noted, in general, that the shifting of the half-slabs can be carried out at a varying degree of progress in the construction of the buildings on the half-slabs. Depending on the needs and the approach followed, one can, for example, seek to construct as many buildings as possible on each half- slab (maximum prefabrication of the buildings), while also carrying out in parallel the maximum fabrication in the reactor building (and in the containment) concerned before proceeding with the slipping of the corresponding half-slab. According to another approach, the buildings are partially constructed on each half-slab (at an adequate stage of progress of the intermediate construction) while the major construction works of the reactor building (and containment) concerned are carried out, then the corresponding half-slab is slipped above the part of the corresponding shaft opening. The finishing works of the reactor building (and containment) concerned are then carried out by introducing in particular the missing equipment and materials through the maintenance hoppers of the half-slabs.

[0081] Furthermore, during the shifting phase of the two half-slabs, the construction of the turbine building 30 can continue and be completed when the shifting phase is finished (fig. 7). Alternatively, the construction of the turbine building 30 can be completed before any shifting and therefore independently of any constraint.

[0082] Construction of the underground nuclear facility shown in Figure 7 is largely complete, with only some finishing work remaining.

[0083] As briefly mentioned above, the protective slab joining the two half-slabs D1 and D2 can be arranged in vertical support directly on the embankment(s) 16 of Figure 1 located at the outer periphery of the shaft, so that the weight of the slab does not rest directly on the upper edges, also called heads, of the vertical walls of the shaft, in particular the vertical walls 18a, 18b. Thus, the protective slab is mechanically independent of the buried structure and in particular the walls 18a, 18b, which means that in the event of vibration of the slab (for example under the impact of an object external to the installation), the vibrations generated at the slab will be transmitted to the embankment(s) and damped by the earth and will therefore not be transmitted to the buried structure via the vertical walls of the shaft.

[0084] It should be noted, however, that the mechanical independence mentioned above does not mean that the slab and the vertical walls of the shaft, in particular 18a, 18b, do not cannot be in indirect mechanical contact with each other, as described below with reference to Figure 7C, or in direct mechanical contact with each other as is the case in Figures 7E and 7G described below. For the sake of simplification, the buildings constructed on the half-slabs are not shown in Figures 7C-7G. In the configurations of Figures 7D-7G an embankment 16 is present. However, the protective slab does not rest on it but is arranged adjacent to the embankment, against it, while being distinct from it. In the figures, the slab extends in height substantially at the same height as the embankment so as to form an upper surface flush with that of the embankment. However, the slab may be higher or lower than the embankment depending on the configurations envisaged. The above applies to the different modes and variants of the present description.

[0085] Figure 7C is a partial enlarged view of the area between a half-slab (e.g. D2) of the slab and the head 18a1 of the wall 18a and shows the presence, between these two elements, of a bellows device 42 with a thick rubber wave of known type, arranged substantially vertically. This device 42 rests on the entire perimeter of the heads of the vertical walls of the well. This perimeter here takes a rectangular shape but it can take a square, circular shape, etc., depending on the geometry of the cross-section of the well. The device 42 is for example connected to the heads of the walls, as well as to the lower surface Si2 of the slab (on an area which is in geometric correspondence with the heads of the walls, in particular 18a, 18b, directly above them) by respective fixing members f1, f2.In this embodiment, the edges of the bellows device 42 are, all around, fixed, for example, by stainless steel slats which compress them, these stainless steel slats themselves being fixed in the concrete by spaced anchor studs. The bellows device 42 makes it possible to ensure sealing between the two spaces e1 and e2 which it separates: space e1 corresponds to the useful space inside the well and in which the various elements / components of the buried installation are arranged and space e2 corresponds to the space adjacent to the backfill(s) 16 (not visible in FIG. 7C). Tl

[0086] It should be noted that with such an arrangement the intermediate space formed by the technical gallery G which will be described below with reference to figure 8 can be isolated in terms of ventilation thanks to this rubber wall 22. It is thus possible to create a slight depression (-5 or -10 mm of CE) thanks to this specific ventilation function. The depressions can be identical to those which will be in place in the reactor building outside the enclosure, thus ensuring continuous confinement for the spaces subject to confinement under the slab.

[0087] An alternative embodiment is shown in Figure 7D along a vertical section plane perpendicular to the section plane of Figure 7C and which shows the vertical walls 18c, 18d bordering the well which are adjacent to the perpendicular walls 18a, 18b of Figures 1 and 7C. Figure 7D shows the protective half-slab D1 which is connected to the vertical walls bordering the well, in particular 18c, 18d, by means of a flexible joint device 42'. In this alternative, the protective half-slab D1 bears vertically directly on one or more supports 44 arranged externally relative to the vertical walls, in particular 18c, 18d, bordering the interior of the well. More particularly, the protective half-slab D1 comprises one or more peripheral edges R jointly forming a skirt which extends vertically from the external periphery of the lower surface Si1 away from the latter.As shown in Figure 7D, the skirt R1 rests on one or more supports 44 such as stringers which are supported by piles or soles 46 anchored vertically in the ground at a distance from the vertical walls bordering the interior of the well.

[0088] According to another variant embodiment shown in figure 7E, the protective half-slab D1 rests vertically directly on the vertical wall(s) (e.g.: 18c, 18d) bordering the well, by means of a skirt R1 similar to that of figure 7D.

[0089] As illustrated in Figures 7D and 7E, the respective walls facing the reactor building B1 and the shaft may be joined or joined.

[0090] As shown in Figures 7D and 7E, the respective walls facing the reactor buildings and the shaft are close to each other, leaving as little space as possible between them, without however being linked mechanically between them. The embodiment variants of figures 7D and 7E described above illustrate such an arrangement with the walls of reactor building B1 (the same applies to the walls of reactor building B2), here wall 20, and the walls of the opposite shaft, here wall 18d. The same applies to the walls not shown in figures 7D and 7E but shown for example in figures 1 and 2, namely wall 26 of reactor building B1 and the opposite wall 18b of the shaft (for building B2, this is wall 24 opposite wall 18a of the shaft). The longitudinal wall 27 externally bordering the area adjacent to the reactor buildings is also close to the opposite wall 18c of the shaft.

[0091] According to an alternative embodiment of the installations of figures 7D and 7E, the walls of the reactor building are spaced horizontally from the vertical walls bordering the shaft so as to provide a space between the respective facing walls. These facing walls, spaced apart from each other, are not mechanically connected to each other so as not to create a mechanical connection through which mechanical forces / vibrations would be likely to pass.

[0092] Figures 7F and 7G illustrate such arrangements in which respectively the respective walls of the reactor building B1' (wall 20' and the two other adjacent walls that are perpendicular and not visible in Figures 7F and 7G) and the walls facing the shaft (wall 18d and the two other adjacent perpendicular walls 18a and 18b, not visible in Figures 7F and 7G) are spaced horizontally from each other as explained above. The longitudinal wall 27' externally bordering the area of ​​the shaft adjacent to the reactor buildings is also facing the wall 18c of the shaft. In the examples illustrated in Figures 7F and 7G the dimensions of the space between the facing walls have been deliberately exaggerated for the purposes of explanation. This may be a useful technical space to allow inspection by maintenance personnel, or even by cameras. In practice, this space can be about 1.5 to 2m wide.The vertical supports of the protective half-slab in Figures 7F and 7F correspond respectively to the supports in Figures 7D and 7E.

[0093] Everything previously described in relation to Figures 7C-7G also applies to the other half-slab D2 and to the reactor building concerned. B2, B2', as well as a single slab. The same applies to a configuration with more than two half-slabs. The following figures 8 to 12 illustrate various buried nuclear installations that have been built using the method described above.

[0094] Figure 8 illustrates the buried nuclear installation 10 comprising the two reactor buildings B1 and B2 of Figures 2 to 7 in a longitudinal vertical sectional view (X axis). For the sake of simplification, the buildings constructed on the two half-slabs and described above are not shown here.

[0095] Each reactor building B1, B2 is closed at its upper part by a roof 31, 33 and the protective slab which is formed by the two half-slabs D1, D2 assembled together at their junction J defines, with the two facing roofs which it completely covers, a technical gallery G. Each roof here is a reinforced concrete slab of simple structure, which means that it has a sufficient thickness of reinforced concrete to ensure its resistance under all the stresses to which it may be subjected. This slab can alternatively be a mixed steel-concrete slab.

[0096] Each buried reactor building B1, B2 encloses, with its vertical walls and its roof, the corresponding nuclear reactor enclosure E1, E2 which here has a circular shape and rounded at its upper part in order to withstand internal pressure in the event of an explosion. The protective slab formed by the two half-slabs D1, D2 rests for example by its vertical peripheral edge forming a skirt R on the walls bordering the shaft (e.g.: 18a, 18b in figure 8). Alternatively, one of the configurations of figures 7C-7G can be applied here.

[0097] Technical gallery G is used in particular to connect a lower part of the installation housed in the shaft (reactor building containing a reactor enclosure) and an upper part located on the protective half-slabs (auxiliary buildings, in particular those defined above) and is used in particular to connect the prefabricated networks of these two parts by allowing the passage of various connections (cables, pipes, etc.) between these parts. In other words, technical gallery G forms a vertical intermediate space ensuring the circulation of people and the routing of cables, conduits and other equipment or any other component serving as a connection between the two. upper and lower parts defined above. Figure 3B already partially described above illustrates a possible configuration of the technical gallery G between an upper slab or half-slab Di (the auxiliary building(s) are not shown for the sake of simplicity for the purposes of the presentation) and the lower roof T of the corresponding reactor building. In this figure, the openings Di 1 and Di2 made in the thickness of the slab or half-slab Di are used for the selective passage of pipes (Di1) and electrical cables (Di2) and other connecting elements not shown (for example through other through openings not shown) between the auxiliary building(s) built on the slab or half-slab Di and the technical gallery G, then between the latter and the reactor building below through corresponding openings Oi 1, Oi2 made in the roof T of the building.It should be noted, for example, that the electrical cables passing through the Di2 opening are connected to a UT (processing unit) collector equipment and that other electrical cables leave this equipment to pass through the Oi2 opening in the roof for connection to equipment in the reactor building. Generally speaking, the connections are made in a sectorized manner by making separately (and for example, staggered in time) the connections between the area above the slab or half-slab and the technical gallery, on the one hand, and the connections between the area below the slab or half-slab and the technical gallery, on the other hand, unlike making the connections simultaneously to connect the area above to the area below after completion of these areas.It should be noted in particular that part of the connection links for equipment housed in the auxiliary buildings can be put in place when the buildings are being constructed on the slab or half-slab, before it is moved above the shaft, which also provides an undeniable time saving.

[0098] Advantageously, one of the advantages of the technical gallery is that it provides flexibility to the construction method by carrying out assembly in several segments and not assembly in one go, at the end (when the upper and lower zones are more or less fixed in their construction), with the additional risk of causing delays if modifications are to be made to the various connections. In the event of a modification being made, the advantage of having a segmentation in three parts (technical gallery, part above above the technical gallery and part below the technical gallery) is to avoid having to redo the entire circuit (piping, cables, etc.) since only the part of the circuit concerned by the modification can be modified (e.g.: the part of the electrical wiring circuit between the top of the slab and the technical gallery).

[0099] The nuclear facility has high compactness and limited footprint by arranging the nuclear facility in several vertically superimposed levels and the functional intermediate space G completes this arrangement and further improves the compactness of the facility.

[0100] In the present embodiment, the nuclear reactor is of the PWR type, that is to say that it uses pressurized water technology. Such a reactor may comprise mainly inside the sealed enclosure, in a known manner, a primary circuit which comprises: - a reactor vessel containing in particular the fuel elements and the control rods, -one or more steam generators, - primary pumps ensuring a loop circulation of the primary fluid which travels through the fuel elements of the reactor vessel by recovering the thermal energy released by the nuclear reaction and circulates in the primary part of the steam generators, where a heat exchange takes place between the primary fluid and the secondary part of the steam generators in order to produce steam at the top of said steam generators. The steam thus produced is evacuated from the steam generators through the steam pipes of a secondary circuit which passes through the walls of the enclosure and carries it to one or more turbines outside the shaft to turn it or them and thus produce, at the alternator output, electric current distributed on a high-voltage electrical network. The primary circuit also includes a pressurizer which has a primary circuit regulation function.

[0101] Furthermore, independently of the previous preferred embodiment, the buried nuclear installation according to the invention can be applied to any other nuclear technology such as one of the following technologies: BWR, HTR, with powers adapted to the SM R model (“Small Modular Reactor” in Anglo-Saxon terminology) For example, the powers can range from 50MWe to N x50MWe, with N greater than 1 and, for example, N can take values ​​between 1 and 8, or even greater than 8. According to another example, the powers can range from 100MWe to N xl OOMWe, with N greater than 1 and, for example, N can take values ​​between 1 and 8, or even greater than 8.

[0102] Each nuclear reactor enclosure E1, E2 rests on the base 12c which may have, in its central part located under the reactor vessel, a recess or cut-out 12d, 12c2 (footprint of a volume) directed downwards and which may be excavated to possibly install a device there to deal with any accident occurring around, on or in the vessel. It should also be noted that each enclosure is not suspended from an upper part of the reactor building such as the roof thereof. The reactor building itself is also not suspended from an area located at the top of the shaft. The above applies to all the modes and variants described in this description.

[0103] Each reactor building B1, B2 may also comprise a horizontal intermediate slab di1, di2 (shown in FIG. 3 already described) which is secured to the vertical walls of the building, namely the walls 20, 22, 26, 28 for building B1 and the walls 20, 22, 24, 28 for building B2. The intermediate slab di1, di2 extends horizontally from these walls so as to radially surround the nuclear reactor enclosure E1, E2, without however coming into contact with it. This slab is arranged at a level or a height along the vertical of the building which represents an intermediate position between the raft 12c and the roof 31, 33. This intermediate slab is arranged parallel to the raft 12c, above and at a distance from it.

[0104] Everything that has just been explained concerning this method of implementation and in particular the arrangement of the installation with the technical gallery also applies to the methods described above or below.

[0105] As shown in Figure 9, another buried nuclear facility 10' comprises a single reactor building B in vertical section along a Y direction which is perpendicular to the longitudinal direction (X axis) along which the slab single protection D has been slid, from its construction area located next to the opening of the shaft in which the buried reactor building B is built and housed entirely, to above this shaft to completely close its opening. For the sake of simplification, the buildings built on the slab and which are similar to those described above and built on the two half-slabs are not shown here but they are all built on the same slab (as a variant, the buildings which are built on slab D may differ at least in part from the buildings built on the two half-slabs). It should be noted, however, that slab D can alternatively be slid along the Y direction of Figure 9.

[0106] In Figure 9, the protective slab D against external attacks rests directly, via its falling peripheral edge R, on the heads of the molded walls bordering the well and of which only the walls 18c, 18d are shown. These walls each have a peripheral rim forming an external shoulder, here 18c1 and 18d 1 . This arrangement can also be applied to any of the embodiments already described. Alternatively, one of the configurations of Figures 7C-7G can be applied here.

[0107] As already described with reference to Figure 8, the reactor building B encloses, with its vertical walls, here 20' and 22' (the other two walls which are perpendicular are not shown in this view) and its roof 35, the nuclear reactor containment E which is for example analogous to any of the nuclear reactor containments E1, E2. A technical gallery G' is arranged between the slab D and the roof 35, as for Figure 8. Access to the technical gallery G' can be achieved via the stairs (not visible in Figure 9) which are arranged in the zone Z of the shaft which is adjacent to the zone housing the reactor building. Although this is not visible in Figure 8, access to the technical gallery G can also be achieved via stairs housed in the zone of the shaft adjacent to that(these) of the reactor buildings.

[0108] The nuclear reactor enclosure E rests on the base 12c' which may have, in a manner not shown in Figure 9, in its central part located under the reactor vessel, a recess or cut (footprint of a volume) directed downwards and which may be excavated to possibly install a device to deal with any accident occurring around, on or in the tank.

[0109] The reactor building B may also comprise a horizontal intermediate slab di (analogous to one of the slabs di 1 , di2 of figure 8) which is integral with the vertical walls of the building, namely the walls 20', 22' and the other adjacent ones not shown. The intermediate slab di extends horizontally from these walls so as to radially surround the nuclear reactor enclosure E, without however coming into contact with it. This slab is arranged at a level or a height along the vertical of the building which represents an intermediate position between the raft 12c' and the roof 35. This intermediate slab is arranged parallel to the raft 12c', above and at a distance from it.

[0110] As shown in Figure 9, a maintenance zone or shaft Z is arranged in shaft 12' (adjacent zone) located next to reactor building B, between the vertical wall 22' of the building and the parallel wall 27' of the installation which is opposite the wall 18d of shaft 12'. An opening O made in the lower part of wall 22' connects zone Z with the interior of the reactor building. This opening O (called buffer) is permanently closed during operation of the reactor (by means of a sliding or pivoting door not shown) and opened only to evacuate or bring in equipment. The zone and the opening have the same characteristics as those of openings 01.1, 02.1 of Figure 2 and compartments C1, C2 of Figures 3 and 4.Opposite this opening O, another opening O' (called a buffer) is provided in enclosure E, which is permanently closed during operation of the reactor (by means of a sliding or pivoting door, not shown). A hopper t is provided in the thickness of slab D at the right angle to zone Z and plays the same role as hoppers T1 and T2 in figures 3 and 4.

[0111] As shown in Figure 10, another buried nuclear installation 100 comprises a single reactor building B in vertical section along the longitudinal direction (X axis) along which the single protective slab D has been shifted, from its construction area located next to the shaft in which the reactor building B is constructed and housed, to above this shaft to seal completely its opening. For the sake of simplification for the purposes of the presentation, the buildings constructed on the slab and which are analogous to those described above and constructed on the two half-slabs are not represented here. It should be noted, however, that the slab D can alternatively be shifted in a direction perpendicular to the longitudinal direction (X axis).

[0112] As for the mode of figure 9, the reactor building B comprises walls (e.g.: 124, 126), here at a distance from the walls of the shaft (e.g.: 18a, 18b) and a roof 135 which, together, enclose a nuclear reactor enclosure E3, surrounded by an intermediate slab di3 fixed on one side to the wall 124. The enclosure E3 rests, like the whole of the building B, on the raft 112c and may also comprise a recess 112d. A technical gallery G3 is arranged between the slab D and the roof 135, as for figures 8 and 9.

[0113] Alternatively, one of the configurations of Figures 7C-7G may apply here.

[0114] The installation 100 of Figure 10 also includes a PECN nuclear fuel storage pool, of known type, which is supported by the base 112c and on which the intermediate slab di3 also rests. Here the PECN pool is arranged inside the reactor building.

[0115] However, in a variant not shown, the pool is arranged outside the reactor building, for example in an area of ​​the shaft which is adjacent to the area housing the building, such as the area which includes zone Z of Figure 9.

[0116] According to a variant not shown of the installation of Figure 8, such a nuclear fuel storage pool is arranged in an area of ​​the shaft adjacent to the area of ​​the shaft accommodating the two reactor buildings. More particularly, the nuclear fuel storage pool can be arranged between the two compartments C1 and C2 of Figures 3 and 4, partially encroaching on the area occupied by each of them, on either side of the wall 32.

[0117] Figures 11 and 12 illustrate a method of constructing a buried nuclear installation 200 according to another embodiment where the well 212 dug in the ground has a horizontal section of circular shape (well of generally cylindrical shape), as does the reactor building B' which is housed there and the slab of protection 230 also has a generally circular shape (in horizontal section) to adapt to the general shape of the well opening.

[0118] Figure 11 is a plan view of the installation 200 under construction along a horizontal section and shows, on the left-hand side, the slab 230 under construction on a construction zone or area Zed' and, on the right-hand side, the shaft 212 (generally cylindrical in shape) of circular cross-section with a wall, for example a diaphragm 218 of annular cross-section which borders the interior of the shaft. The reactor building B' also has a circular shape and contains a nuclear reactor enclosure E' as described above. These circular and annular shapes have the advantage of better resisting thrusts coming from the outside (the earth in the case of the shaft) and overpressures (internally, coming from the enclosure or the reactor building). In particular, the diaphragm wall 218 of annular shape (in cross-section) works like a ring compressed by the thrust of the earth which is directed radially relative to the diaphragm wall.The diaphragm wall 218 is self-stable and the number of anchors of the wall in the ground is thus reduced, which in particular simplifies the design and construction. It will be noted that the wall 218 more generally has a cylindrical crown shape according to a three-dimensional view and the internal space of the well which is bordered by the wall 218 occupies a cylindrical shaped space.

[0119] In this embodiment, a nuclear fuel storage pool PECN' (optional) is arranged inside the reactor building B' but off-center relative to the enclosure E', as illustrated in Figure 11. The installation 200 also comprises, inside the reactor building B', a zone Z' forming a handling shaft and which is also off-center relative to the enclosure E', as well as a zone Z”, also off-center, in which a staircase is arranged to connect the different vertical levels of the shaft 212, from the base 212c to the upper protective slab.

[0120] As for the embodiment described with reference to figures 1 to 7, the protective slab 230 is constructed on the Zed' area, with auxiliary buildings on top (at least partially constructed on the slab before it is shifted), while the reactor building B' is being constructed in the shaft. Everything described above with reference to Figures 2 to 7 regarding the sequencing in time of the different construction phases (in particular, order and duration of the phases in relation to each other) of the half-slabs and the reactor building applies here to slab 230 and reactor building B' and will not be repeated.

[0121] In figures 11 and 12, the Zed' area comprises a Ptf platform, like the Ptf 1 platform in figure 2 (if the ground condition requires it), and two guide / slip beams L1', L2' mounted on piles p anchored in the ground (again, depending on the ground condition), similar to the beams L1 and L2 in figures 2 to 7 and their anchor piles.

[0122] On the left side of Figure 11 (top view), several equipment / buildings b3.1, b3.2, b3.3 have been built (more or less completely, depending on the degrees of completion that vary according to the needs and the approach followed, as already explained above) on slab 230 during the construction of the reactor building in the shaft. For example, buildings b3.1, b3.2, b3.3 are respectively, an auxiliary building providing cooling functions, an auxiliary building providing ventilation functions and a plant control room. Other equipment / buildings can of course be built on the slab instead of these buildings or in addition.An opening T similar to the openings T1 and T2 of the two half-slabs of figures 3, 4 and 6 is also arranged in the thickness of the slab 230 to fulfill the same function and in particular to serve as a hopper at the right of the handling zone Z' of the shaft 212 (right part in figure 11), when the slab will be put in place above the shaft.

[0123] Figure 11 illustrates in top view (horizontal section) a possible general shape for the protective slab 230 which must close the upper opening 212b of the well 212 (figures 11 and 12). As shown in figure 11, the slab 230 has a generally circular shape with dimensions corresponding to those of the opening 212b to be covered. The slab 230 comprises, at two diametrically opposite zones of its circumference, two external radial extensions 230a and 230b, here symmetrical with respect to each other, which each start from two diametrically opposite portions 230c, 230d of the circular circumference of the slab to each end with a flat face (cut or beveled) 230a.1 and 230b.1. The two flat faces 230a.1 and 230b.1 are parallel to each other and each form a lateral peripheral edge which is intended to cooperate with the guide beam located below (fig. 11) to transport by sliding the protection slab 230, from its construction zone Zed' to a position located above the opening of the well (fig. 12). The system for moving the slab 230 is substantially identical to that described with reference to figure 5 and comprises for example similar elements: two jacks V1, two blocks M1, two traction cables Ca1 crossing the external radial extensions 230a and 230b in their length and fixed to the faces of these extensions which are opposite the well. The shifting takes place over a distance greater than the external diameter of the slab, but which does not exceed several slab diameters in this case to facilitate handling of the slab.

[0124] The left part of figure 12 illustrates the slab 230 constructed with the auxiliary equipment / buildings above, before shifting and the right part of this figure illustrates this same slab 230 with its buildings, after shifting, in the position of closing the opening 212b of the shaft, above the roof 235 of the reactor building B'.

[0125] In general, figures 11 and 12 repeat most of the elements described with reference to figures 8 to 10, with different references and which will not be described again here, namely in particular the raft 212c, the intermediate slab di4, the roof 235, the technical gallery G4 between the roof 235 and the slab 230. In the present embodiment, the gallery occupies a circular space in top view and not a rectangular one as in the previous embodiments but it retains the same functionalities and advantages as previously in another form.

[0126] In the present embodiment, the protective slab 230 is shown bearing directly on the wall 218 which is spaced from the wall 220 of the reactor building B'. However, the different arrangements described with reference to FIGS. 7B to 7F are also applicable here.

[0127] According to an alternative embodiment not shown, the reactor building can adopt a general shape of square (horizontal) cross-section fitting inside the internal space of circular (horizontal) cross-section of the well (bordered by the annular wall 218).

[0128] According to another embodiment variant not shown, the shaft retains a circular (horizontal) cross-section which is divided into two separate compartments each forming a surface occupying a semicircle and a reactor building of circular, square or rectangular (horizontal) section occupies each of the two semicircles. This variant can be adapted to low-power technologies, for example of the order of 100 MWe each, to avoid a diameter which would be too large for the upper protection slab if the reactors were of larger dimensions).

[0129] According to yet another embodiment variant not shown, the well having a rectangular or square shape is configured to house a single large reactor building and two half-slabs or more than two half-slabs are used to seal the well in order to reduce the weight of the load to be skidded which would be much higher with a single slab.

[0130] According to other embodiments, several buried nuclear installations can adopt different configurations with several wells which are arranged, for example, in the general shape of a square, rectangle or circle.

[0131] Thus, for example, Figure 13 shows two parallel lines 300, 302 for the construction of buried nuclear installations, with on each line the construction of two installations 304, 306 (for line 300) and 308, 310 (for line 302). In this configuration, the installations 304 and 308 are built in parallel along the two parallel construction lines 300, 302. The same applies to the installations 306 and 310. The protective slabs 304a, 308a which are built on preparation zones or areas located next to the shafts concerned are slid in parallel directions and in the same direction until the shafts 304b, 308b are respectively sealed. The sliding of the slabs 306a, 310a which are built on preparation zones or areas located next to the wells concerned until the wells 306b, 310b respectively are closed is carried out in the opposite direction.In this configuration, the wells are, for example, circular and the slabs square. The wells. could, however, have a square shape. Alternatively, the slabs can be circular with circular shafts. The number of construction lines for buried nuclear facilities can, however, vary and, for example, be reduced to one line or be more than two lines depending on the needs.

[0132] Figure 14 illustrates a configuration in which circular slabs are slid to circular-shaped shafts in a general cross or diagonal arrangement. The protection slabs 404a, 406a, 408a and 410a which are built on preparation zones or areas located next to the shafts concerned are slid along the axes 400, 402 which intersect and represent the construction lines until the shafts 404b, 406b, 408b, 410b respectively are closed. The protection slabs 404a and 406a (resp. 408a and 410a) are slid in opposite directions to each other along the same construction line. Alternatively, the slabs and shafts may be square in shape.

[0133] Depending on the morphology of the land and its occupation during the construction phases, the configurations described above may be appropriate. The method of constructing an underground nuclear facility involving one or more slabs built next to (at a distance from) one or more shafts (possibly with auxiliary buildings built on top while the slab(s) are still next to the shaft(s)) while one or more reactor buildings are built in the adjacent shaft(s) offers maximum adaptability depending on the morphology of the land and its occupation during the construction phases.

[0134] It should be noted that other alternative configurations can be considered by varying the construction line arrangements and the shapes of the protection slabs and wells, as well as the number of slabs and wells.

[0135] Generally speaking, the parallel construction of underground nuclear installations is very advantageous in terms of planning, especially when there is a multiplication of wells in order to increase power.

[0136] It should be noted that one or more turbine buildings can be placed between the construction lines, whether they are parallel to each other (fig. 13) or crossed (fig. 14).

[0137] Figure 15 illustrates an alternative configuration to that of Figures 2, 3, 4, 6 and 7 in which a rectangular-shaped shaft 500 (similar to shaft 12) is arranged along a construction line 502 aligned with the longitudinal axis X mentioned in the previous figures. In this configuration, shaft 500 is intended to house two reactor buildings such as reactor buildings B1 and B2 of the previous figures. The protective half-slabs D1' and D2', for example identical to half-slabs D1 and D2 (in particular those illustrated in Figure 3A), are each constructed on a preparation / construction area adjacent to the area of ​​the shaft opening that the slab is supposed to cover, namely area 500a for half-slab D1' and area 500b for half-slab D2'.Thus, the shifting of each half-slab is carried out over a reduced distance compared to that over which the half-slabs D1 and D2 are shifted since each half-slab D1', D2' only has to cover the distance which separates it from the adjacent shaft as well as the length of the shaft area to be covered, which represents a distance greater than the longitudinal dimension of a half-slab but which may, for example, be less than twice this dimension. Everything concerning the description of the method in figures 2, 3, 4, 6 and 7 also applies here, with some adaptations linked to the different positioning of the half-slabs.

[0138] The features and advantages mentioned above in relation to the method of constructing a buried nuclear installation involving one or more slabs constructed next to one or more shafts (possibly with auxiliary buildings constructed on them while the slab(s) are still next to the shaft(s)) while one or more reactor buildings are constructed in the adjacent shaft(s) apply equally to all the modes and variants described above (in particular those illustrated in Figures 13 to 15) and will not be repeated.

[0139] Generally speaking, buried nuclear installations according to certain embodiments of the invention may comprise two or more reactor buildings, thus making it possible to have smaller reactor cores providing less power (e.g. 50 or 100 MWe) than that of a larger installation with greater power (e.g. 800 MWe, or even higher powers). For example, to provide a power of 800 MWe, a buried nuclear installation according to the invention can be configured according to four wells of 200MWe each, each well being able to produce 2x100MWe or 1 x200MWe.

[0140] The power modularity offered by these smaller installations also comes with a simplification of installations and a reduced implementation cost compared to a larger power installation.

[0141] Generally speaking, regardless of the embodiment or variant described above, the construction method according to the invention makes it possible to significantly reduce the overall construction schedule for an underground nuclear installation during the construction phase which occurs after the preparation of the ground and before the cold and hot tests of the installation and the criticality tests. During this construction phase, different tasks or operations are carried out in parallel, which provides a considerable saving of time.

[0142] In particular, the construction of one or more slabs or slab elements on a construction area adjacent to the shaft may begin while the shaft is in its excavation phase and / or subsequently during various civil engineering operations carried out for the construction of the shaft. The slab construction may continue during the construction of one or more reactor buildings in the shaft or the slab construction may begin only after the shaft is finished and, thus, begin almost simultaneously with the construction of one or more reactor buildings in the shaft. During the construction of one or more reactor buildings in the shaft, one or more equipment and / or auxiliary buildings are at least partially constructed on the slab or slabs or slab elements arranged next to the shaft.

[0143] The sliding of the slab(s) or slab element(s) above the shaft may take place after the largest equipment and components have been constructed or installed in the shaft, particularly in the reactor building(s) (in particular the roof of the building(s) must have been installed). Once the slab(s) or slab element(s) have been moved into the final position for sealing the shaft, the internal construction and the various internal arrangements within the shaft may continue, particularly using the gallery technique arranged between the slab(s) or slab element(s) closing the shaft and the roof of the reactor building(s) for the installation, in a segmented manner over time, of the various connections (electrical cables, pipes, etc.) between the auxiliary equipment / buildings supported by the slab(s) or slab element(s) and the equipment and components of the reactor building(s). This is achieved by installing connections between the auxiliary buildings and the technical gallery, on the one hand, and between this technical gallery and the equipment and components of the reactor building(s), on the other hand. The order in which these connection installation sequences are carried out may vary.The level of prefabrication can be pushed, which will allow the installation of modules that will facilitate installation in the different areas, thus bringing considerable time savings in addition to the gains already obtained by the method and construction sequences described above.

[0144] It should be noted that the equipment or buildings arranged on the half-slabs, or on the slab if it is a single slab, may take other forms and perform other functions than those described above depending on the nuclear technology envisaged.

Claims

Claims

1. Method for constructing a buried nuclear installation on a site (10), the site comprising a shaft (12) dug into the ground (14, 16) so as to define a bottom (12a), at a given depth relative to the ground surface, and an opening (12b, 12bl, 12b2) located substantially at the level of the ground surface surrounding the shaft, characterized in that the method comprises the following construction phases: - the construction of at least one protective slab (DI, D2; D; 230) against external aggressions on an area (Zed) of the ground surface, called the slab construction area, which is arranged next to the opening (12b, 12bl, 12b2) of the shaft, - the construction of at least one reactor building (Bl, B2) inside the shaft (12), the construction phases of said at least one protective slab (Dl, D2; D; 230) and of said at least one reactor building (Bl, B2) being carried out in parallel.

2. Method of constructing a buried nuclear installation according to claim 1, characterized in that the method comprises a phase of constructing one or more equipment or buildings (bl.l, bl.2, b2.1, b2.2; b3.1, b3.2, b3.3) on said at least one protective slab (Dl, D2; D; 230), the phase of constructing equipment(s) or building(s) starting during the phase of constructing said at least one reactor building (Bl, B2) and while said at least one protective slab (Dl, D2; D; 230) is on the slab construction zone (Zed).

3. Method of constructing a buried nuclear installation according to the preceding claim, characterized in that the equipment or buildings (bl.1, bl.2, b2.1, b2.2; b3.1, b3.2, b3.3) constructed on said at least one protective slab (Dl, D2; D; 230), are configured to provide support functions for the operation of the nuclear reactor and the entire nuclear facility.

4. Method of constructing a buried nuclear installation according to claim 2 or 3, characterized in that the equipment or buildings constructed on said at least one protective slab (DI, D2; D; 230) comprise at least one of the following elements: a nuclear installation control room (b2.2; b3.3), a building providing ventilation functions (bl.2; b3.2), a building providing cooling functions (bl.1; b3.1), a room containing control and command cabinets for operating support and electricity production functions, an instrumentation room, a high-current electrical distribution room, a low-current electrical distribution room and batteries / inverters, a valve and exchanger room, a first-aid diesel engine room (b2.1).

5. Method of constructing a buried nuclear installation according to one of the preceding claims, characterized in that the construction phase of said at least one reactor building (B1, B2) comprises the installation of at least one nuclear reactor enclosure (El, E2; E; E3; E') and, optionally, at least one nuclear fuel storage pool (PECN; PECN').

6. Method of constructing a buried nuclear installation according to the preceding claim, characterized in that the construction phase of said at least one reactor building (B1, B2; B; B3; B') comprises the construction, on the one hand, of a wall or several walls (20, 22, 24, 26, 28; 20', 22'; 124, 126; 220) surrounding said at least one nuclear reactor enclosure (El, E2; E; E3; E 7) and, optionally, said at least one nuclear fuel storage pool (PECN; PECN') and, on the other hand, a roof (31, 33; 35; 135; 235) covering the wall(s) so as to enclose, inside said at least one reactor building, said at least one nuclear reactor enclosure and, optionally, said at least one nuclear fuel storage pool.

7. Method of constructing a buried nuclear installation according to one of the preceding claims, characterized in that the construction method comprises a phase of sliding said at least one protective slab (DI, D2; D; 230), from the slab construction zone (Zed) to the right of the opening (12b, 12bl, 12b2) of the shaft, so that said at least one protective slab (DI, D2; D; 230) completely closes the opening of the shaft by being arranged above said at least one reactor building (Bl, B2; B; B3; B 7) at the end of the shift.

8. Method of constructing a buried nuclear installation according to the preceding claim, characterized in that the construction method comprises, after the phase of shifting said at least one protective slab (DI, D2; D; 230), a phase of fitting out an intermediate space, called a technical gallery, between said at least one protective slab and said at least one reactor building (Bl, B2; B; B3; B').

9. Method of constructing a buried nuclear installation according to claim 7 or 8, characterized in that the construction method comprises the phase of constructing a single slab (D; 230) or two half-slabs (DI, D2) on the slab construction zone which are slid one after the other up to the right of the opening (12b, 12bl, 12b2) of the shaft, then assembled with each other so as to completely close the opening of the shaft at the end of slid.

10. Method of constructing a buried nuclear installation according to one of claims 7 to 9, characterized in that the phase of shifting of said at least one protective slab (DI, D2; D; 230) takes place at the end of the construction phase of said at least one reactor building (Bl, B2; B; B3; B').

11. Method of constructing a buried nuclear installation according to claim 6 and according to one of claims 7 to 10, characterized in that the phase of sliding said at least one protective slab (DI, D2; D; 230) takes place after the installation of said at least one nuclear reactor enclosure (El, E2; E; E3; E 7 ) and, optionally, said at least one nuclear fuel storage pool (PECN; PECN 7 ) and the construction of the wall(s) and roof of said at least one reactor building (B1, B2; B; B3; B 7 ).

12. Method of constructing a buried nuclear installation according to one of claims 7 to 11, characterized in that said at least one protective slab (DI, D2; D; 230) is placed in line with the opening (12b, 12bl, 12b2) of the well so as to be able to be removed subsequently in the event of modification or dismantling of the nuclear installation.

13. Method of constructing a buried nuclear installation according to one of claims 2 to 4 and according to one of claims 7 to 12, characterized in that, when the shifting phase is completed, the phase of construction of equipment(s) or building(s) (bl.1, bl.2, b2.1, b2.2; b3.1, b3.2, b3.3) continues on said at least one shifted protective slab (DI, D2; D; 230).

14. Method of constructing a buried nuclear installation according to one of claims 7 to 13, characterized in that, when the shifting phase is completed, the construction phase of said at least one reactor building (B1, B2; B; B3; B 7 ) continues.

15. Method of constructing a buried nuclear installation according to one of the preceding claims, characterized in that, prior to the start of the construction phase of said at least one reactor building (B1, B2; B; B3; B 7 ), the construction method comprises the production in the well (12) of one or more vertical walls (18a-d; 218) bordering the interior of the well.

16. Method of constructing a buried nuclear installation according to one of claims 7 to 12 and according to the preceding claim, characterized in that said at least one protective slab (DI, D2; D; 230) is slipped to the right of the opening of the well so as to come into vertical support: - directly on an embankment (16) arranged at the outer periphery of the well, a bellows device (42) being arranged vertically between said at least a protective slab (DI, D2; D; 230) and the vertical wall(s) (18a-d) bordering the interior of the well, or - directly on the vertical wall(s) (18a-d) bordering the interior of the well, or - indirectly on the vertical wall(s) (18a-d) bordering the interior of the well by means of a damping joint device and / or - directly on one or more supports (44, 46) arranged externally relative to the vertical wall(s) (18a-d) bordering the interior of the well.

17. Method of constructing a buried nuclear installation according to one of the preceding claims, characterized in that the vertical shaft (12; 12'; 112; 212) has a generally rectangular, square or circular shape according to a view taken in a horizontal plane.

18. Method of constructing a buried nuclear installation according to one of the preceding claims, characterized in that the construction method comprises a phase of constructing a turbine building (30) on an area (Zcbt) of the ground surface surrounding the well, called the turbine building construction area.

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