BURIED NUCLEAR FACILITY WITH VERTICAL ARRANGEMENT

Abstract

Underground nuclear installation (10), comprising: - a vertical shaft (12) having, at a lower end, a bottom (12c) and, at an upper end, an opening (12b), - at least one reactor building (26) housed in the shaft, - and which contains at least one nuclear reactor containment building (30) enclosed within said at least one reactor building (26), and / or at least one spent nuclear fuel pool housed in the shaft, - at least one protective slab (20) against external hazards which seals the opening (12b) of the shaft, extending in particular above said at least one reactor building, - one or more pieces of equipment or buildings (b1-b4) arranged on said at least one protective slab (20). Figure for the abbreviation: Fig. 3.

Description

Title of the invention: BURIED NUCLEAR FACILITY WITH VERTICAL ARRANGEMENT technical field

[0001] The present invention relates to the field of buried nuclear installations. Previous technique

[0002] A nuclear installation is known, notably from document WO 2018 / 204081, in which a containment building for a boiling water nuclear reactor 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] In view of the above, there is a need to create a new architecture for a high-compact underground nuclear installation. Description of the invention

[0004] The invention thus relates to an underground nuclear installation comprising: -a vertical well having a bottom at one lower end and an opening at one upper end, -at least one reactor building housed in the shaft, - at least one nuclear reactor containment building enclosed within said at least one reactor building, -and / or at least one nuclear fuel storage pool housed within the well, - at least one protective slab against external aggressions which seals the well opening by extending in particular above said at least one reactor building, -one or more pieces of equipment or buildings arranged on said at least one protective slab.

[0005] The aforementioned installation allows, by arranging on said at least one protective slab one or more pieces of equipment or buildings, in particular of an auxiliary type in relation to the reactor building (main building) located under the protective slab, to limit the ground footprint of the installation and thus to increase its compactness.

[0006] According to other possible characteristics: -the equipment or building(s) located 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; -the equipment or building(s) located on said at least one protective slab include at least one of the following elements: a control room the nuclear installation, a building providing ventilation functions, a building providing cooling functions, a room containing control and command cabinets for operational support and electricity production functions, an instrumentation room, a high-voltage electrical distribution room, a low-voltage electrical distribution room and batteries / inverters, a valve and heat exchanger room, a first-rescue diesel engine room; other equipment or buildings may be arranged on said at least one slab protecting against external aggressions in addition to or instead of some of the aforementioned equipment or buildings; this additional equipment or buildings may perform functions different from those identified above; it should be noted that depending on the nuclear technologies envisaged, appropriate redundancies may be required; -said at least one reactor building includes a roof which covers said at least one nuclear reactor containment and / or said at least one nuclear fuel storage pool, said at least one protective slab extending in particular above the roof and at a distance from it so as to provide between them a technical gallery which constitutes an intermediate space;said at least one reactor building and the technical gallery are arranged under said at least one protective slab and the equipment or building(s) are arranged on said at least one protective slab, resulting in an architecture with an improved compact vertical arrangement divided into three parts, namely a lower part housed in the shaft, an upper part located on the protective slab and an intermediate part (technical gallery) housed in the shaft between the upper and lower parts and which serves to connect these two parts, and in particular the prefabricated networks of the latter; ; -the installation includes one or more vertical walls bordering the inside of the well, said at least one protective slab being in vertical support: directly onto an embankment placed at the outer periphery of the shaft, a bellows device being arranged vertically between said at least one protective slab and the vertical wall(s) bordering the interior of the shaft, or directly onto the vertical wall(s) bordering the inside of the well, or indirectly onto the vertical wall(s) bordering the inside of the well via a damping seal and / or directly on one or more supports arranged externally relative to the vertical wall(s) bordering the inside of the well; -said at least one reactor building includes one or more vertical walls which are spaced horizontally from the vertical wall(s) bordering the inside of the well or attached to the wall or vertical walls bordering the inside of the well; -said at least one nuclear reactor containment structure is supported by at least one support slab resting on the bottom of the shaft and / or said at least one nuclear fuel storage pool is supported by at least one support slab resting on the bottom of the shaft; -said at least one support slab is either connected to, or separated from, the wall(s) of the reactor building by one or more peripheral isolation joints or by a space between said at least one support slab and the wall(s) of the reactor building; - the installation includes, adjacent to a zone of the well in which said at least one reactor building is housed, at least one other zone of the well which forms in particular a vertical handling zone capable of being put into communication with the zone of said at least one reactor building; -said at least one protective slab includes a hopper which is located in an area of ​​said at least one protective slab located above said at least another area of ​​the well; - said at least one nuclear fuel storage pool is located adjacent to said at least one reactor building, and is, for example, located in the vertical handling shaft or in another space adjacent to said at least one reactor building; - said at least one protective slab is formed of one slab or two half-slabs which are fixed to each other; the use of two or more half-slabs makes it possible to reduce the weight of the load to be moved from a construction area of ​​the half-slabs located near the shaft to the shaft and therefore to size the slab movement system accordingly, which simplifies the construction of the installation and the moving operations, as well as the energy consumption of the moving operations; this is particularly advantageous when one or more pieces of equipment or buildings are built on the half-slabs and therefore increase the weight of the load to be moved; - said at least one protective slab is configured to be able to be removed later in the event of modification or dismantling of the nuclear installation; - the vertical shaft has a general rectangular or circular shape according to a view taken in a horizontal plane. Brief description of the drawings

[0007] Other features and advantages will become apparent in the following description, given solely by way of non-limiting example and with reference to the accompanying drawings, on which:

[0008] [Fig-1] Fig. 1 is a schematic view of a possible example of implementation of an underground nuclear installation according to an embodiment of the invention;

[0009] [Fig.2] The [Fig.2] is a simplified enlarged schematic view of the buried nuclear installation of the [Fig.1], following a vertical section, according to a possible embodiment of the invention;

[0010] [Fig.3] The [Fig.3] is a view of the buried nuclear installation of the [Fig.2] in a vertical cross-section plane parallel to that of the [Fig.2];

[0011] [Fig.3A] The [Fig.3A] is a partial schematic view in vertical cross-section showing the through openings of a slab and also a representation of a technical gallery;

[0012] [Fig.4A] The [Fig.4A] is an enlarged partial schematic view of an area of ​​the buried nuclear installation of the [Fig.1] located between the protective slab and the walls bordering the shaft, showing a flexible joint provided between these two elements, according to a possible embodiment of the invention;

[0013] [Fig.4B] The [Fig.4B] is a partial schematic view illustrating a support of the protective slab according to an alternative embodiment;

[0014] [Fig.4C] The [Fig.4C] is a partial schematic view illustrating a support of the protective slab according to another embodiment variant;

[0015] [Fig.4D] The [Fig.4D] is a partial schematic view illustrating a support of the protective slab according to another embodiment variant;

[0016] [Fig.4E] The [Fig.4E] is a partial schematic view illustrating a support of the protective slab according to another embodiment variant;

[0017] [Fig.5] The [Fig.5] illustrates, following a vertical cross-sectional view, another possible embodiment of an underground nuclear installation;

[0018] [Fig.5A] The [Fig.5A] is a partial schematic perspective top view of two half-slabs for protection against external aggressions, spaced longitudinally apart from each other;

[0019] [Fig.5B] The [Fig.5B] is an enlarged partial schematic view of a connection zone between two half-slabs for protection against external aggressions according to a possible embodiment;

[0020] [Fig.5C] The [Fig.5C] is a schematic perspective top view of two half-slabs of protection against external aggressions joined together;

[0021] [Fig.6] Fig.6 illustrates, following a vertical cross-sectional view, another possible embodiment of an underground nuclear installation;

[0022] [Fig.7] Fig.7 illustrates, following a horizontal cross-sectional view, another possible embodiment of an underground nuclear installation;

[0023] [Fig.8] Fig.8 illustrates, in top view, a possible embodiment of a circular buried nuclear installation under construction;

[0024] [Fig.9] The [Fig.9] illustrates, following a vertical cross-sectional view, the installation of the [Fig.8] after the sliding of the protective slab against external aggressions. Description of the implementation methods

[0025] The invention which is described below with reference to the attached drawings relates to different possible embodiments of a new buried nuclear installation architecture.

[0026] As schematically represented in [Fig.1], an underground nuclear installation 10 comprises a vertical shaft 12 dug into a soil 14 to a predetermined depth, for example of the order of 30-35 m using conventional excavation techniques and equipment.

[0027] This well 12 comprises, at a lower end, a bottom 12a, and, at an upper end, an opening 12b with dimensions substantially equal to those of the bottom. In this embodiment, the earth removed to form the well is, for example, used to form one or more embankments 16 arranged around the opening 12b of the well, thus creating a raised area relative to the ground surface 14. This arrangement can serve as a barrier against flooding.

[0028] The height or depth of the shaft 12 is defined between the opening 12b and the bottom 12a of the shaft and is chosen to accommodate within the shaft all the components of the buried part of the nuclear installation 10, which will be described later, taking into account the height of the foundation slab that will be formed at the bottom of the shaft. The shaft 12 can have any general shape along a horizontal section (perpendicular to the plane of [Fig. 1]) and, for example, can have a generally rectangular, square, circular, etc., cross-section.

[0029] The function of these walls is to resist the pressure of the earth surrounding the well and to ensure a watertight seal (barrier) for the interior of the well, particularly against water that could infiltrate the surrounding soil. This watertight barrier can be supplemented by another barrier incorporating a waterproofing membrane. Depending on the geometry of the well, a single wall (well with a circular cross-section) or several vertical walls (well with a square, rectangular, etc. cross-section), for example, cast-in-place walls, can be used. In a well with a rectangular cross-section, for example, four walls are provided to delimit the usable interior space of the well.

[0030] As shown in [Fig. 1], the underground nuclear installation 10 comprises at least one protective slab 20 against external threats to the shaft, such as falling objects (e.g., aircraft) or external explosions. For the sake of simplicity in the following explanation, said at least one protective slab 20 is considered herein to be a single protective slab 20. However, everything concerning the underground nuclear installation of the invention also applies to a protective slab that is formed of several slabs, and for example of two half-slabs as will be seen later in another embodiment. This protective slab 20 is positioned above shaft 12 and extends horizontally so as to completely seal the shaft opening 12b. The general shape of the slab 20 is adapted to the shape of the horizontal section of the shaft opening 12b and, in this embodiment, the general shape of the slab 20 is rectangular (however, the general shape may take other forms depending on the shape of the shaft opening and, for example, a circular shape). The protective slab 20 is generally made of reinforced concrete. Alternatively, the slab may be constructed of prestressed concrete or using a composite construction with a lower facing consisting of a stiffened steel sheet to which flexible connectors are welded.

[0031] In the embodiment illustrated in [Fig. 1], the protective slab 20 is positioned vertically, resting directly on the backfill 16 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 the heads, of the walls 18a, 18b. Thus, the protective slab 20 is mechanically independent of the buried structure and, in particular, of the walls 18a, 18b. This 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 level of the slab will be transmitted to the backfill and damped by the earth, and will therefore not be transmitted to the buried structure via the walls 18a, 18b. The protective slab 20 is preferably configured so that it can be removed later in the event of a major modification or dismantling of the installation 10.The slab's configuration, which allows for its subsequent removal (i.e., after installation to seal the well), is linked to the fact that it is either a single, homogeneous slab that can be slid out of the well's area to clear the well opening (the sliding occurs along an axial direction parallel to the longer dimension of the rectangular slab), or a slab resulting from the assembly of two or more half-slabs, thus becoming a single, continuous slab that can also be slid out of the well along the aforementioned axial direction to clear the well opening. It should be noted that this movement / sliding of the slab follows the reverse path of that associated with its installation during the construction of the facility.

[0032] It should be noted, however, that the mechanical independence mentioned above does not mean that the slab 20 and the walls 18a, 18b cannot be in indirect mechanical contact with each other, as described later with reference to [Fig.4A], or in direct mechanical contact with each other, as is the case in Figures 4C and 4E also described later.

[0033] Figures 2 and 3 are enlarged views of an underground nuclear installation similar to that of [Fig. 1] but remain schematic for the purposes of this explanation. However, the support of the protective slab 20 differs from that of [Fig. 1] since The slab 20 is supported vertically directly on the vertical wall(s) 18a, 18b bordering the shaft, by means of a skirt or peripheral edge 20b extending downwards from the lower face 20a of the slab. The skirt 20b rests directly on the tops of the walls (only walls 18a, 18b are shown in this section), each of which has a peripheral rim forming an external shoulder, such as that 18a2 of wall 18a. It should be noted that the following description applies to all embodiments and variants and, in general, is not limited to the vertical support method of the protective slab.

[0034] As shown in [Fig. 2], the well 12 includes, at its lower end, a foundation slab 12c forming the bottom of the well on which the various elements / components of the buried installation will be installed. This foundation slab was installed in a known manner after the well excavation (an injected base may be necessary to limit water ingress from the bottom if the ground is permeable).

[0035] The underground nuclear installation 10 here comprises a reactor building 26 housed in shaft 12 and resting on the foundation slab 12c. It should be noted that several reactor buildings can be installed in shaft 12, as will be seen later in the description of other embodiments.

[0036] In this embodiment, the reactor building 26 comprises one or more vertical walls (depending on the building's geometry). If the building has a rectangular or square horizontal cross-section, it will necessarily have several walls (as is the case here with the rectangular shape), whereas it may have only one wall if it has a circular horizontal cross-section (cylindrical shaft). The reactor building 26 also includes a roof 28 that rests on the top of the wall(s) (depending on the configuration) to cover the building, thus defining an enclosed space within it. In the example described, the reactor building 26 has a rectangular horizontal cross-section and comprises four vertical walls, of which only two, 26a and 26b, opposite each other, are shown in [Fig. 2], the other two adjacent vertical walls being perpendicular and not visible here. The walls of the reactor building 26 rest on the foundation slab 12c.Roof 28 is a simple reinforced concrete slab, meaning it has sufficient thickness of reinforced concrete to ensure its resistance under all the stresses to which it may be subjected. This slab could alternatively be a composite steel-concrete slab.

[0037] The walls of reactor building 26 (wall 26a and the two other adjacent perpendicular walls not visible in [Fig. 2]) are positioned opposite the vertical walls bordering the shaft (wall 18a and the two other adjacent perpendicular walls 18c and 18d, not visible in [Fig. 2] but visible in Figures 4B-4E described later), close to each other, leaving as small a space between them as possible (this space is, however, not visible in the figures 2 and 3), without however being mechanically linked together, so as not to create a mechanical link through which mechanical forces / vibrations could be transmitted.

[0038] As shown in Figures 2 and 3, the protective slab 20 is positioned above the roof 28 of the reactor building 26, at a distance (vertically) from it, so as to create a vertical space between them that serves as a technical gallery G, the floor of which is formed by the roof 28. Depending on the length of the gallery, this space allows, in particular, the movement of people and the routing of cables, conduits, and other equipment or any other component serving as a link between, on the one hand, the buildings that are external to the buried part of the installation, in particular those mounted on the protective slab 20, and, on the other hand, the interior of the reactor building and, in fact, up to the reactor containment building. In other words, the technical gallery G forms an intermediate space between the reactor building and the space located on the slab and occupied by auxiliary buildings and equipment, which will be described later.Access to the technical gallery G can be gained via the stairs (visible in [Fig.2]) which are located in the shaft area adjacent to the area housing the reactor building.

[0039] The horizontal dimensions of the slab (in the length shown in [Fig.2] but also in a horizontal direction perpendicular to the plane of this figure) are greater than those of the roof 28 which stops at the level of the upper edges or heads of the walls 26a, 26b of the reactor building 26. The slab extends horizontally in particular above a space or area of ​​the shaft which is adjacent to the area of ​​the shaft in which the reactor building is housed and which will be described later.

[0040] The reactor building 26 contains, within the enclosed space delimited by its vertical walls 26a, 26b (and the two adjacent perpendicular vertical walls not visible in [Fig. 3]) and its horizontal roof 28, at least one nuclear reactor containment structure. In the present embodiment, only one nuclear reactor containment structure 30 is housed within the reactor building 26. The containment structure has a rounded shape at its upper part to resist internal pressure.

[0041] In the present embodiment, the nuclear reactor is of the PWR type, i.e., it uses pressurized water reactor technology. Such a reactor may include, primarily within the sealed containment 30, in a known manner, a primary circuit comprising: - a reactor vessel containing, in particular, the fuel elements and control rods, - one or more steam generators, - primary pumps ensuring a closed-loop circulation of the primary fluid which flows through the fuel elements of the reactor vessel Recovering the thermal energy released by the nuclear reaction, the fluid circulates in the primary section of the steam generators, where heat exchange occurs between the primary fluid and the secondary section of the steam generators to produce steam at the top of said steam generators. The steam thus produced is discharged from the steam generators through the steam pipes of a secondary circuit that passes through the walls of containment structure 30 and carries it to one or more turbines outside the well. There, it drives the turbine(s) to produce, at the alternator output, electrical current distributed to a high-voltage power grid.

[0042] The primary circuit also includes a pressurizer which has, in particular, a function of regulating the primary circuit.

[0043] It should be noted that the walls bordering the well, the walls of the building and the roof 28 have much lighter structures than that of the wall of the enclosure 30, which makes it possible not to affect the integrity of the enclosure in the event that one of the previous elements is projected against the enclosure 30.

[0044] Furthermore, regardless 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 power outputs adapted to the SMR model (Small Modular Reactor). By way of example, power outputs can range from 50 MWe to N x 50 MWe, 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, power outputs can range from 100 MWe to N x 100 MWe, with N greater than 1 and, for example, N can take values ​​between 1 and 8, or even greater than 8.

[0045] The foundation slab 12c has been designed to include a support slab 32 on which the nuclear reactor containment 30 rests. The support slab 32 may have, in its central part located under the reactor vessel, a recess or excavation 32a (imprint of a volume) extending downwards. The foundation slab 12c may be excavated to potentially install a device to address any accident occurring around, on, or within the vessel. It should be noted that the foundation slab 12c and the support slab 32 may constitute a single reinforced concrete structural element.

[0046] As shown in Figures 2 and 3, the reactor building 26 may also include a horizontal intermediate slab 34 which is integral with the vertical walls of the building (26a and 26b in Figures 2 and 3 and the two other adjacent perpendicular vertical walls). The intermediate slab 34 extends horizontally from these walls so as to radially surround the nuclear reactor containment 30, without, however, coming into contact with it, as shown in [Fig. 2]. This slab 34 is positioned at a level or elevation along the vertical of the building which represents an intermediate position between the support slab 32 and the roof 28. This intermediate slab 34 is arranged parallel to the support slab 32 and the roof 28, and at a distance from them.

[0047] Figure 2 also illustrates, on the right-hand side of the underground installation 10, an IZ zone adjacent to the area containing the reactor building 26, which is located inside the shaft but separate from that building. This IZ zone is delimited between the wall 26b of the building and an opposite wall of the installation, designated PI, which is located opposite the wall 18b bordering the shaft. The IZ zone forms an internal compartment within the shaft in which a staircase 36 can be located, allowing personnel to move between the lower and upper parts of the shaft (including access to the level of the protective slab).

[0048] In [Fig. 3] (cross-section parallel to that of [Fig. 2]), another zone Z2, adjacent to the zone containing the reactor building 26, is arranged between the wall 26b of the building and the opposite wall PI, which is located opposite the wall 18b bordering the shaft. Zone Z2 forms a vertical handling shaft that provides access, in particular, to the support slab 32 located at the bottom of the shaft. The protective slab 20 extends above the reactor building and the adjacent zones Z1 and Z2. As shown in this figure, an opening O (called a cover), which is permanently closed during reactor operation (by means of a sliding or hinged door not shown) and opened only to remove or re-enter equipment, is provided in the vertical wall 26b of the reactor building to connect the handling shaft Z2 to the interior of the reactor building.Opposite this opening O, another opening O' (called a buffer) is provided in the enclosure 30, which is permanently closed during reactor operation (by means of a sliding or pivoting door not shown).

[0049] A hopper 40 is, for example, provided in the protective slab 20 directly above at least one of the two zones Z1 and Z2 adjacent to the reactor building zone 26. This hopper 40 is permanently closed but can be opened when it is necessary to access the space below, and in particular to carry out maintenance operations via the handling shaft Z2, such as, for example, to remove and re-enter components or elements of the nuclear reactor containment via the same route. The reactor containment 30 has an opening (not shown), called a buffer, which should ideally be positioned opposite the sliding door 01 closing the opening (of the reactor building).

[0050] As shown in figures 2 and 3, one or more pieces of equipment or buildings are arranged on the protective slab 20.

[0051] This equipment or these buildings are configured to provide support functions for the operation of the nuclear reactor and the entire nuclear installation and, as such, are called 'auxiliary' equipment or buildings, as opposed to the so-called 'primary' equipment or buildings, which perform nuclear safety functions and are located underground inside the well. In other words, these are equipment or buildings located above the protective slab against external hazards and which may be subject to external hazards insofar as the functions necessary for reactor safety that they perform, in degraded or accidental situations, are redundant with the reactor safety functions of the equipment or buildings located below the slab.

[0052] This equipment or these buildings are built on the protective slab and may include at least one of the following: a nuclear installation control room, a building providing ventilation functions, a building providing cooling functions, a room containing control and command cabinets for operational support and electricity production functions, an instrumentation room, a high-voltage electrical distribution room, a low-voltage electrical distribution room and batteries / inverters, a valve and exchanger room, a first-aid diesel engine room.

[0053] In the embodiment shown in Figures 2 and 3, the slab 20 supports an auxiliary building bl forming a control room for the installation and, in the background, three auxiliary buildings b2, b3, and b4, which are respectively an auxiliary building providing cooling functions, an auxiliary building providing ventilation functions, and an auxiliary diesel engine room. It should be noted that the slab can obviously support other equipment or auxiliary buildings, in addition to or replacing at least some of those already described.

[0054] It should be noted that through-openings (not shown in the figures) can be provided at different locations within the slab, in its thickness, opposite which the auxiliary buildings mentioned above are constructed. Each of these openings serves for the passage of cables, pipes, etc. (various connections) between the auxiliary building located above the slab and the reactor building located below the slab via the technical gallery located between the slab and the reactor building and through-openings (not shown in the figures) provided in the roof of the reactor building for the passage of these various connections.

[0055] Fig. 3A is a schematic vertical cross-sectional view of a Di slab for protection against external aggressions (along its smallest dimension) showing, for example, two through openings D1 and Di2 (a larger number of openings can be envisaged in a variant if the number of buildings increases) arranged respectively, at the location of future buildings constructed on the slab and an opening Ti, located on one side of the slab, acting as a hopper and which is, for example, closed by a hatch ti shown in both positions in [Fig. 3A]. After selectively installing the various connections through each opening Dil (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 watertightness and fire protection (at least 2 hours). It should be noted that the above also applies to a half-slab in the case where the protective slab is formed of two half-slabs. [Fig. 3A] illustrates a possible configuration of the technical gallery G between the upper slab (or half-slab) Di (the auxiliary building(s) are not shown for the sake of simplicity) and the lower roof T of the corresponding reactor building.In this figure, the openings Dil and Di2, cut into the thickness of the slab (or half-slab) Di, serve as selective passageways for piping (Dil) and electrical cables (Di2), as well as other connecting elements not shown (for example, through other through-openings not shown), between the auxiliary building(s) constructed on the slab (or half-slab) Di and the technical gallery G, and then between the latter and the reactor building below, through corresponding openings Oil and Oi2 in the roof T of the building. Note, for example, that the electrical cables passing through opening Di2 are connected to a UT (treatment unit) collector, and that other electrical cables run from this unit through the roof opening Oi2 for connection to equipment in the reactor building.In general, connections are made in a sector-based manner by 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 the simultaneous making of connections to link the area above to the area below after completion of these areas.

[0056] In the event of a modification to be made, the advantage of having a segmentation into three parts (technical gallery, part above the technical gallery and part below the technical gallery) is to avoid having to redo the entire circuit (pipes, cables...) since it is possible to modify only the part of the circuit concerned by the modification (ex: the part of the electrical wiring circuit between the top of the slab and the technical gallery).

[0057] The new architecture described above provides high compactness and a limited footprint by arranging the nuclear installation on several vertically superimposed levels, arranging on said installation at least one protective slab, one or more pieces of auxiliary equipment or buildings, and at least one underground reactor building. (in the shaft) located below said at least one protective slab. Preferably, the technical gallery is constructed in the shaft, above said at least one reactor building and below said at least one protective slab in order to complete this arrangement and further improve the compactness of the installation.

[0058] Figure 4A is a partial enlarged view of the area between slab 20 and the top 18a of wall 18a of Figure 1 and shows the presence, between these two elements, of a bellows device 22 with a thick rubber corrugation of a known type, arranged in a substantially vertical manner. This device 22 rests on the entire perimeter of the wall tops 18a, 18b. This perimeter is rectangular here, but it can be square, circular, etc., depending on the geometry of the (horizontal) cross-section of the well. The device 22 is, for example, connected to the wall tops, as well as to the lower surface 20a of slab 20 (in an area that corresponds geometrically with the wall tops 18a, 18b, directly above them) by respective fastening members 24a, 24b.In this embodiment, the edges of the bellows device 22 are fixed all around, for example, by stainless steel strips which compress them, these stainless steel strips being themselves fixed in the concrete by spaced anchor bolts. The bellows device 22 ensures a seal between the two spaces El and E2 that it separates: space El corresponds to the usable 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 16 (not visible in [Fig. 4A]).

[0059] It should be noted that with such an arrangement the intermediate space formed by the technical gallery G described above with reference to figures 2 and 3 is isolable in terms of building ventilation thanks to this rubber wall 22. It is thus possible to create a slight depression (-5 or -10mm CE) thanks to this specific ventilation function.

[0060] According to an alternative embodiment shown in [Fig. 4B], the protective slab 20' is connected to the vertical walls 18c, 18d bordering the shaft (these two walls are adjacent and perpendicular to the two walls 18a, 18b of [Fig. 1]) by means of a flexible joint device 22'. In this alternative embodiment, the protective slab 20' is vertically supported directly on one or more supports 23 arranged externally relative to the vertical walls 18a, 18b bordering the interior of the shaft. More particularly, the slab 20' has one or more peripheral edges 20b' jointly forming a skirt that extends vertically from the outer periphery of the lower surface 20a' away from it. As shown in [Fig.4B], the skirt 20b' rests on one or more supports 23 such as stringers which are supported by piles or footings 25 anchored vertically in the ground at a distance from the vertical walls 18a, 18b bordering the inside of the shaft. .

[0061] According to another embodiment shown in [Fig.4C], the protective slab 20” is supported vertically directly on the vertical wall(s) 18c, 18d bordering the shaft, by means of a skirt 20b” similar to the skirt of [Fig.4B].

[0062] As illustrated in Figures 4B and 4C described above, the respective walls facing reactor building 26 and the well can be contiguous or adjoining.

[0063] According to an alternative embodiment of the installations shown in Figures 4B and 4C, the walls of reactor building 26 are horizontally spaced from the vertical walls bordering the shaft so as to create a gap between the respective facing walls. These facing walls, spaced apart from each other, are not mechanically connected to avoid creating a mechanical link through which mechanical forces / vibrations could be transmitted. The space thus created can be a useful technical space for inspection by maintenance personnel, or even by cameras. In practice, this space can have a width of approximately 1.5 to 2 meters.

[0064] Figures 4D and 4E illustrate such arrangements in which the respective walls of reactor building 26' (wall 26a' and the two other perpendicular adjacent walls not visible in Figures 4D and 4E) and the walls facing the shaft (wall 18d and the two other perpendicular adjacent walls 18a and 18b, not visible in Figures 4D and 4E) are respectively spaced horizontally apart from each other as explained above. The vertical supports of the protective slab in Figures 4D and 4E correspond respectively to the supports in Figures 4B and 4C.

[0065] It will be noted that the arrangements described above between the respective walls facing the reactor building 26, 26' and the shaft also apply to the mode described above concerning the vertical support of the protective slab 20 on the embankment 16 ([Fig.l]).

[0066] Fig. 5 represents a vertical cross-sectional view of a new configuration of an underground nuclear installation 10' according to another embodiment in which two reactor buildings 26.1 and 26.2 are housed in the shaft 12', adjacent to each other and separated from each other by an internal transverse wall 26.12. Each reactor building is, for example, identical to the other, as well as to the reactor building 26 already described.

[0067] As shown in [Fig. 5], the walls bordering the shaft (only the parallel walls 18a' and 18b' are visible) surround the two buildings 26.1 and 26.2. The walls (not visible) that are perpendicular to walls 18a' and 18b' are elongated relative to the corresponding walls in Figures 2 and 3 in order to accommodate two reactor buildings 26.1 and 26.2 side by side, each containing two nuclear reactor containment structures 30.1 and 30.2. As in the configuration of Figures 2 and 3, each nuclear reactor containment structure rests on a support slab 32', which is common to both containment structures and analogous to the support slab 32 in [Fig. 2]. The support slab 32' thus presents, in each of the parts located under a reactor vessel 30.1, 30.2, a recess or excavation 32a.l, 32a.2 (imprint of a volume) which extends downwards, identically to the recess 32a of figures 2 and 3.

[0068] As with Figures 2 and 3, areas (not visible in [Fig.5]) which are analogous to the ZI and Z2 areas of Figures 2 and 3 are arranged adjacent to each of the well areas containing one of the two reactor buildings 26.1 and 26.2.

[0069] In [Fig. 5], the protective slab 20.2 is formed of two protective half-slabs 20.2a and 20.2b which are fixed to each other at their junction 20.2c located approximately vertically below the inner wall 26.12 separating the two reactor buildings. The fixing can be achieved using known techniques and, for example, the two protective half-slabs 20.2a and 20.2b can be keyed to each other or joined together by overlapping reinforced concrete bars or by reinforced concrete bars connected by sleeves (couplers) in reserved areas which are concreted in a second phase, after the reinforcement bars have been joined.

[0070] Figure 5A shows, in a top perspective view, the two protective half-slabs 20.2a and 20.2b (without the other elements of Figure 5 for clarity) separated from each other along a longitudinal direction X, for example in a position where each half-slab is on its construction area or zone near the shaft (not shown here). The half-slabs are thus constructed at a distance from each other and each has a free end face fal, fa2 opposite each other. These two faces fal, fa2 are intended to be mechanically joined / assembled to form a single slab as explained later with reference to Figure 5B. As shown in [Fig.5A], a peripheral edge RI, R2 is provided respectively on the underside of each half-slab 20.2a, 20.2b and extends vertically downwards in the manner of a skirt or a dropped edge.

[0071] Each half-slab 20.2a, 20.2b may have openings cut through its thickness to allow the passage of cables, pipes, equipment, and personnel, depending on the opening(s) concerned. In [Fig. 5A], an opening T1, T2, offset laterally from the longitudinal median axis (parallel to the X-axis) of each half-slab, is present. This opening is, for example, intended to form a hopper that will be used later for maintenance or handling and will be located above the shaft or handling area situated along the reactor building. Other through-openings (not shown here) may be provided at separate locations on each half-slab on which auxiliary buildings are constructed. Each of these openings serves for the passage of cables, pipes, etc.(various connections) between the equipment or building located above the half-slab and the reactor building located below the half-slab via the gallery. technical system located between the half-slab and the reactor building and through openings (not shown in the figures) provided in the roof of the reactor building for the passage of these different connections.

[0072] Furthermore, each half-slab 20.2a, 20.2b may have impressions rl.1, rl.2, r2.1, r2.2 (figs. 5A and 5C) 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.

[0073] In the position shown in [Fig. 5] (the half-slabs are positioned above the opening 12b' of the shaft), half-slab 20.2a is placed against half-slab 20.2b and the two half-slabs are mechanically joined / assembled to each other, for example by keying, in order to mechanically form a single protective slab, ensuring continuity of the slab's mechanical resistance at the junction or connection zone 20.2c between the half-slabs. To achieve this, the reinforcement or bracing must be continuous at this zone.

[0074] Figure 5B illustrates a possible example of a mechanical connection between the half-slabs 20.2a and 20.2b. This figure is a partial, enlarged view of a mechanical connection zone between the two half-slabs. The connection between the two half-slabs 20.2a and 20.2b can be achieved by providing a keying zone Zcl between these half-slabs. The half-slabs are installed with a keying width greater than the overlap length of the longitudinal reinforcement in the lower layer a1i and a2i and the upper layer als and a2s of the half-slabs. The longitudinal reinforcement of each slab element (half-slab) overlaps the longitudinal reinforcement of the other slab element.Several layers of top and bottom reinforcement are required for each slab element, but only one top and one bottom layer are shown for each slab element in the schematic diagram in [Fig. 5A] for ease of understanding. Longitudinal reinforcement in the opposite direction and shear reinforcement are also placed (see schematically the perpendicular reinforcements a3i and a3s in the figure). In addition, temporary formwork Cfp can be fixed under the slab elements, and the keyway is then concreted to mechanically connect the two slab elements. The temporary formwork Cfp, which, for example, rests on the reactor roof (previously installed), is removed and taken down, for example, a few days after the keyway has been concreted.It should be noted that other solutions can be considered to ensure the continuity of the longitudinal reinforcement: couplers, welding of bars.... .

[0075] Figure [5C] illustrates the slab 20.2 obtained after assembly of the two half-slabs 20.2a, 20.2b, for example as explained in the embodiment described below. above, but which can alternatively be obtained in a different way not described in detail here. Slab 20.2 of [Fig. 5] is, for example, the one shown in [Fig. 5C] without the auxiliary buildings bl'-b4' for the sake of clarity. Certain construction details may vary between the slab in [Fig. 5C] and that in [Fig. 5], notably the position and number of through-openings in each half-slab for the maintenance shafts and for the auxiliary building(s), the presence or absence of the rails ri.l-r2.2 and their position...

[0076] The slab 20.2 obtained after assembly of the two half-slabs 20.2a, 20.2b is a protective slab against external aggressions to the well and thus protects the components of the installation housed in the well 12'.

[0077] Generally, each half-slab is placed above the shaft after the reactor building roof slab has been constructed, in such a way that the complete slab (e.g., the slab in [Fig. 5C]) can be removed in one piece later, in the event of dismantling the installation (at the end of its service life) or even in the event of modifications to the installation, for example, to carry out major maintenance work affecting the safety and operation of the installation. For example, the replacement of one or more steam generators may justify such an operation.The slab's configuration, which allows it to be removed later (i.e., after installation to seal the shaft) as a single unit, is due to the fact that it is a slab resulting from the assembly of two half-slabs (or even more than two half-slabs in an unshown variant). This creates a single, continuous slab that can be slid out of the shaft along an axial / longitudinal X direction to clear the shaft opening. It should be noted that this axial / longitudinal movement / sliding of the slab follows the reverse sliding path of the slab's installation during the construction of the installation. The same applies to a single slab with a homogeneous construction.

[0078] Furthermore, each reactor building is closed at its upper part by a roof 28.1, 28.2 ([Fig. 5]), and the protective slab 20.2 defines, with each of the opposite roofs, a technical gallery G' larger than the technical gallery G of Figures 3 and 4. More specifically, each half-slab 20.2a, 20.2b located above the roof 28.1, 28.2 of the corresponding reactor building forms a part of the technical gallery G' with the latter, along its length. An intermediate slab 34.1, 34.2 can be provided in each of the reactor buildings 26.1, 26.2, in a manner analogous to the intermediate slab 34 of Figures 2 and 3.

[0079] In this embodiment, each half-slab 20.2a, 20.2b supports one or more auxiliary equipment or buildings as explained above with reference to Figures 2 and 3.

[0080] More specifically, in [Fig. 5], the half-slab 20.2a supports a building Auxiliary building bl' forms a control room for the installation and an auxiliary diesel engine room b2', while the half-slab 20.2b supports two auxiliary buildings b3' and b4', which are respectively an auxiliary building providing ventilation and cooling functions and an auxiliary building providing cooling functions. It should be noted that each half-slab can obviously support other equipment or auxiliary buildings, in addition to or replacing at least some of those already described.

[0081] Everything described above also applies in this embodiment where two reactor buildings are housed in the well and will therefore not be repeated.

[0082] Figure 6 illustrates, in vertical section, another embodiment of an underground nuclear installation 100 which differs mainly from the embodiment shown in Figures 2 and 3 by the presence of a nuclear fuel storage pool, identified in the figure by the acronym PECN, located in a zone Z2” of the shaft adjacent to the zone where the reactor building 126 is located. The elements corresponding to the embodiment shown in Figures 2 and 3 and which are repeated here are preceded by the number “1 and, in principle,” will not be described again. The PECN pool rests on the same support slab 132 as the nuclear reactor containment 130. A roof 128 extends here over the reactor building 126 and the adjacent zone LT'. It should be noted that the arrangement of the roof over the zone Z2” may be only local, extending over the PECN pool, but without extending across the entire LT' zone.

[0083] As shown in [Fig. 6], an opening O' (called a buffer), which is permanently closed during reactor operation (by means of a sliding or hinged door not shown), is provided in the vertical wall 126b of the reactor building 126, which separates the interior of the building from the adjacent area LT'. The opening O' is opened only to access the interior of the reactor building when the removal of material(s) and / or the introduction of new material(s) are necessary. The protective slab 120 extends over the reactor building 126 and the area Z2'' adjacent to it, and therefore over the PECN pool. As in the configuration of Figures 2 and 3, a similar technical gallery G" is provided between the roof 128 and the protective slab 120.

[0084] Furthermore, one or more auxiliary equipment or buildings are arranged on the protective slab 120 as explained above with reference to figures 2 and 3.

[0085] In the embodiment shown in [Fig. 6], the slab 120 supports an auxiliary building bl” forming a control room for the installation and, in the background, three auxiliary buildings b2”, b3” and b4” which are respectively an auxiliary building providing cooling functions, an auxiliary building providing functions of ventilation and an auxiliary diesel engine room. It should be noted that the 120 slab can obviously support other equipment or auxiliary buildings, in addition to or as a replacement for at least some of those already described.

[0086] It should be noted that through-openings are provided at distinct locations in the slab, within its thickness, opposite which the auxiliary buildings mentioned above are constructed. Each of these openings serves for the passage of cables, pipes, ... (various connections) between the auxiliary building located above the slab and the reactor building located below the slab via the technical gallery G“ located between slab 120 and reactor building 126 and through-openings (not shown in the figures) provided in the roof of the reactor building for the passage of these various connections.

[0087] Everything described above also applies in this embodiment and will not be repeated.

[0088] Figure 7 illustrates, in a horizontal cross-sectional view (top view), another embodiment of an underground nuclear installation 200 analogous to the underground nuclear installation 10' of Figure 5. The difference between these two embodiments lies in the presence of a spent fuel pool PECN' in an area of ​​shaft 12" that is adjacent to the area of ​​the shaft housing the two reactor buildings 26.1 and 26.2. This pool is located in line with wall 126.12, which separates the two reactor buildings, and is adjacent to each of the two buildings, as it extends on both sides of this wall. This intermediate position between the two buildings allows fuel elements from either of the reactors in containment buildings 130.1 and 130.2 to be stored in this pool.In addition, in an alternative variant not shown, two pools could be provided, each in an area adjacent to a reactor building and dedicated to that building.

[0089] Similar to the arrangement of the zones in [Fig. 5], Installation 200 includes zones Z1” and Z2” (vertical handling shafts) located adjacent to the shaft area containing reactor building 126.1. Likewise, Installation 200 includes other zones Z1”' and “LT” (vertical handling shafts) located adjacent to the shaft area containing reactor building 126.2. Zones Z1” and Z2” and zones Z1”' and “LT” are arranged symmetrically with respect to the intermediate position of the PECN’ pool located between them. Each of the zones has, for example, the same functions as the corresponding zone in the preceding figures.

[0090] As with the arrangement of [Fig.5], the installation 200 includes a slab (not shown) formed of two half-slabs on each of which auxiliary equipment or buildings are constructed.

[0091] Everything described above also applies in this embodiment and will not be repeated.

[0092] Figures 8 and 9 illustrate an underground nuclear installation 300 according to another embodiment.

[0093] The right-hand side of [Fig. 8] is a plan view of the installation along a horizontal section of shaft 312. The section shows the elements located beneath the protective slab, the outlines of which appear transparent above the shaft. Shaft 312 (generally cylindrical in shape) has a circular cross-section with a wall, for example a diaphragm wall, 318, of annular cross-section bordering the inside of the shaft. The reactor building 326 also has a circular shape and encloses a nuclear reactor containment 330 as described above. These circular and annular shapes have the advantage of better resisting external pressures (from the earth in the case of the shaft) and internal overpressures (from the containment or the reactor building). In particular, the annular diaphragm wall 318 (in cross-section) acts as a ring compressed by the earth pressure directed radially with respect to the diaphragm wall.The diaphragm wall 318 is self-supporting, thus reducing the number of tiebacks anchoring the wall to the ground, which simplifies design and construction. It should be noted that the wall 318 generally has a cylindrical crown shape in three-dimensional view, and the internal space of the shaft, which is bordered by the wall 318, occupies a cylindrical shape.

[0094] In this embodiment, a nuclear fuel storage pool (PECN) can be located inside the reactor building 326 but offset from the containment 330, as illustrated in [Fig. 8]. The installation 300 may also include a Z3 area forming a handling shaft, which is also offset from the containment 330, as well as an offset Z4 area containing a staircase 336 providing access between the different levels of the shaft 312, from the foundation slab 312c to the protective slab 320, visible only in [Fig. 9].

[0095] Figure 9 is a vertical cross-sectional view along section plane AA of Figure 8 and shows an arrangement similar to that of Figure 6. The entire reactor building 326 and containment structure 330 are supported by the same support slab 332, and the spent fuel pool (PECN) is also supported by the same support slab 332. It should be noted that in a circular configuration, it is simpler to use only one circular support slab. Providing two separate (independent) support slabs, one to support the reactor building 326 and the other to support the spent fuel pool (PECN), as positioned in Figure 8, would require removing part of the circular slab to accommodate the slab supporting the pool. which would affect the integrity of the support slab of reactor building 326 and could weaken this support slab.

[0096] On the contrary, when the well has a general rectangular (in section) or even square shape, and accommodates at least one reactor building and an adjacent pool, it may be more suitable, and in particular more economical, to have two independent support slabs.

[0097] In general, figures 8 and 9 include most of the common elements described with reference to the previous figures and which will not be described again here, namely in particular the foundation slab 312c, the recess 312cl (optional), the support slab 332, the intermediate slab 334 (optional), the roof 328, the technical gallery G'” between the roof 328 and the slab 320. In the present mode, the gallery occupies a circular space in top view and not a rectangular one as in the previous modes.

[0098] According to an alternative embodiment not shown, the reactor building can adopt a general shape of square cross-section (horizontal) fitting inside the internal space of circular cross-section (horizontal) of the well (bounded by the circular wall 318).

[0099] According to another embodiment not shown, the shaft retains a circular (horizontal) cross-section which is here divided into two distinct compartments, each forming a surface occupying a semicircle, and a reactor building with a circular, square or rectangular (horizontal) cross-section occupies each of the two semicircles. This variant can be adapted to low-power technologies, for example on the order of 50 or 1000W each, to avoid a diameter that would be too large for the upper protective slab if the reactors were larger.

[0100] In the present mode, the protective slab is shown resting directly on the wall 318 and the wall 318 is separated from the wall 326a of the reactor building 326. However, the different arrangements described with reference to Figures 4A to 4E are also applicable here.

[0101] It should be noted that the protective slab (and each half-slab) of the various installations described above with one or more reactor buildings can be supported in different ways, as described above with reference to figures 4A to 4E.

[0102] Generally, underground nuclear installations according to certain embodiments of the invention may comprise two or more reactor buildings, as shown in Figures 5 and 7, thus allowing for smaller reactor cores providing less power (e.g., 50 or 1000 MWe) than a larger, higher-power installation (e.g., 800 MWe, or even higher power outputs). For example, to provide 800 MWe of power, An underground nuclear installation according to the invention can be configured with four wells of 200MWe each, each well being able to produce 2x100MWe or 1x200MWe.

[0103] The power modularity offered by these smaller installations is also accompanied by a simplification of installations and a reduced implementation cost compared to a larger power installation which can however benefit from the effect of standardization and repetition.

[0104] The left-hand side of [Fig. 8] illustrates, in a top view (horizontal section), a possible general shape for the protective slab 320 that is to close the upper opening 312b of the shaft 312 (Figures 8 and 9). As shown in [Fig. 8], the slab 320 has a generally circular shape with dimensions corresponding to those of the opening 312b to be covered. The slab 320 has, at two diametrically opposed areas of its circumference, two external radial extensions 320a and 320b, here symmetrical to each other, each originating from two diametrically opposed portions 320c, 320d of the circular circumference of the slab and each terminating in a flat face (cut or beveled edge) 320a.1 and 320b.1. The two flat faces 320a. 1 and 320b.1 are parallel to each other and are used to move the protective slab 320 to a position above the opening of the shaft 312 by sliding, from a Zed zone shown on the left side of [Fig.8] which is located outside the shaft but close to it. .

[0105] The two flat faces 320a.1 and 320b.1 each form a dropped lateral peripheral edge, one of which is visible on the left part of [Fig.9].

[0106] In the embodiment of Figures 8 and 9, the protective slab 320 is for example constructed on the Zed area or zone, with auxiliary buildings such as those described above on top (at least partially constructed on the slab before its sliding), while the reactor building 326 is under construction in shaft 312.

[0107] On the left side of [Fig. 8] (top view), several pieces of equipment / buildings b3.1, b3.2, b3.3 were constructed on slab 320 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 control room for the installation. Other pieces of equipment / buildings can, of course, be constructed on the slab in place of at least some of these buildings or in addition to them. An opening T can also be provided in the thickness of slab 320, notably to serve as a hopper at the handling area Z3 of shaft 312 (right side in Figures 8 and 9), when the slab is placed over the shaft.

[0108] The protective slab 320 can be slid from its construction zone Zed to a position located above the well opening 312b using, for example two parallel guide stringers L1, L2 ([Fig.8]) intended to cooperate each with a lateral peripheral edge dropped from one of the two flat faces 320a.1 and 320b.1 of the slab.

[0109] A system for moving the slab 320 by translation comprises, for example, two jacks VI, two blocks M1 to which the jacks can be fixed and to which two traction cables Cal are attached, the cables passing through the external radial extensions 320a and 320b of the slab along their length and being fixed to the faces of these extensions opposite the well (anchorage A1). Alternatively, the sliding operation of the half-slabs 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 of each half-slab and the upper face of the two sliding stringers (the coefficient of friction is very low, on the order of 1%).

[0110] The right-hand side of [Fig. 9] illustrates the slab 320 with its auxiliary equipment / buildings, after sliding, in the position of sealing the shaft opening 312b, above the roof 325 of the reactor building 326. As with the previous configurations, the installation thus configured has a compact vertical arrangement with the reactor building(s) in the shaft and below the protective slab (half-slab) and the auxiliary equipment / buildings above the slab. The compactness is further improved with the technical gallery located between the protective slab (half-slab) (above) and the reactor building(s) (below).

[0111] It should be noted that the sliding of slab 320 just described can be applied to the other slabs or half-slabs described above with reference to the preceding figures, even if their shape is different. The sliding principle remains the same.

[0112] 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

Demands

1. Underground nuclear installation (10; 10'; 100; 200; 300), comprising: - a vertical shaft (12) having, at a lower end, a bottom (12c) and, at an upper end, an opening (12b), - at least one reactor building (26) housed in the shaft, - at least one nuclear reactor containment building (30) enclosed within said at least one reactor building (26), and optionally at least one spent nuclear fuel pool (PECN; PECN'; PECN”) housed in the shaft, - at least one protective slab (20; 20'; 20"; 120; 320) against external aggressions which completely seals the opening (12b) of the shaft by extending in particular above said at least one reactor building, - one or more pieces of equipment or buildings (bl-b4) arranged on said at least one protective slab (20; 20'; 20"; 120; 320).

2. Underground nuclear installation according to claim 1, characterized in that the equipment or building(s) (bl-b4) arranged on said at least one protective slab (20; 20'; 20''; 120; 320) are configured to provide support functions for the operation of the nuclear reactor and the entire nuclear installation.

3. Underground nuclear installation according to claim 1 or 2, characterized in that the equipment or building(s) (bl-b4) arranged on said at least one protective slab (20; 20'; 20''; 120; 320) comprise at least one of the following: a nuclear installation control room, a building providing ventilation functions, a building providing cooling functions, a room containing control and command cabinets for operational support and electricity production functions, an instrumentation room, a high-voltage electrical distribution room, a low-voltage electrical distribution room and batteries / inverters, a valve and heat exchanger room, a first-rescue diesel engine room.

4. An underground nuclear installation according to any one of the preceding claims, characterized in that said at least one building reactor (26) includes a roof (28) which covers said at least one nuclear reactor containment (30) and optionally said at least one nuclear fuel storage pool (PECN; PECN'; PECN”), said at least one protective slab (20; 20'; 20”; 120; 320) extending in particular above the roof and at a distance from it so as to provide between them a technical gallery (G; G'; G”; G'”).

5. A buried nuclear installation according to any one of the preceding claims, characterized in that it comprises one or more vertical walls (18a-d) bordering the interior of the shaft, said at least one protective slab (20; 20'; 20") being vertically supported: - directly on a backfill (16) disposed at the outer periphery of the shaft, a bellows device (22) being arranged vertically between said at least one protective slab and the vertical wall(s) (18a-d) bordering the interior of the shaft, or - directly on the vertical wall(s) (18a-d) bordering the interior of the shaft, or - indirectly on the vertical wall(s) (18a-d) bordering the interior of the shaft via a damping joint device (22') and / or - directly on one or more supports (23, 25) disposed externally relative to the vertical wall(s) (18a-d) bordering the inside of the well.

6. Underground nuclear installation according to the preceding claim, characterized in that said at least one reactor building (26) comprises one or more vertical walls (26a, 26b) which are horizontally spaced from the vertical wall(s) (18a-d) bordering the interior of the shaft or attached to the wall or vertical walls bordering the interior of the shaft.

7. Underground nuclear installation according to any one of the preceding claims, characterized in that said at least one nuclear reactor containment (30) is supported by at least one support slab (32) resting on the bottom of the shaft and optionally said at least one nuclear fuel storage pool (PECN; PECN'; PECN") is supported by at least one support slab (32) resting on the bottom of the shaft.

8. Underground nuclear installation according to claims 6 and 7, characterized in that said at least one support slab (32) is either connected, or separated from the wall(s) of the reactor building by one or more peripheral isolation joints or by a space between said at least one support slab and the wall(s) of the reactor building.

9. A buried nuclear installation according to any one of the preceding claims, characterized in that it comprises, adjacent to a zone of the shaft in which said at least one reactor building (26) is housed, at least one other zone of the shaft which forms in particular a vertical handling zone capable of being made communicable with the zone of said at least one reactor building.

10. Underground nuclear installation according to the preceding claim, characterized in that said at least one protective slab (20; 20'; 20"; 120; 320) comprises a hopper (40) which is located in an area of ​​said at least one protective slab located above said at least one other area of ​​the shaft.

11. Underground nuclear installation according to any one of the preceding claims, characterized in that said at least one nuclear fuel storage pool (PECN; PECN'; PECN") is disposed adjacent to said at least one reactor building (26).

12. Underground nuclear installation according to any one of the preceding claims, characterized in that said at least one protective slab is formed of a slab (20; 20'; 20"; 120; 320) or of two half-slabs (20.2a, 20.2b) which are fixed to each other.

13. Underground nuclear installation according to any one of the preceding claims, characterized in that said at least one protective slab (20; 20'; 20"; 120; 320) is configured to be able to be removed later in the event of modification or dismantling of the nuclear installation.

14. A buried nuclear installation according to any one of the preceding claims, characterized in that the vertical shaft (12; 12'; 12"; 312) has a general rectangular or circular shape according to a view taken in a horizontal plane.

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