A nuclear facility and a passive safety method in a nuclear facility

Abstract

According to a first aspect of the present disclosure, there is provided a nuclear facility with a flooding network associated with an operational pool placed in an operational hall (100) More specifically the nuclear facility features a condensation surface (101, 102), a first operational pool, and a first collector (131) all contained in the operational hall (100). The first collector is for collecting condensate off the condensation surface (101, 102). The nuclear facility also features a first flooding conduit (151), which connects respective volumes of the first collector (131) and the first operational pool (110). The nuclear facility further also features a flooding liquid source (180) for selectively flooding the first collector (131) to establish a phase-changing circulation of fluid along a recirculation flow path between the first operational pool (110), the condensation surface (101, 102), the first collector (131), and the first flooding conduit (151).

Description

A NUCLEAR FACILITY AND A PASSIVE SAFETY METHOD IN A NUCLEAR FACILITYFIELD

[0001] The present disclosure relates to nuclear facilities. In particular, the present disclosure relates to managing removal of heat, such as decay heat, in operational pools, such as reactor pools or spent fuel pools, found in operational halls, such as reactor halls or spent fuel halls, of nuclear facilities.BACKGROUND

[0002] Several different solutions are known in the art for removal of decay heat from operational pools found in nuclear facilities. Conventional solutions rely on long term water inventories for injecting water from a secure source to an operational pool, particularly a reactor pool or spent fuel pool, during an emergency. Conventional systems are dependent on sophisticated active control systems for ensuring the presence of a sufficient amount of water in an operational pool during an emergency.

[0003] It is an object of the present proposal to provide a useful alternative to the prevailing art that is more passive and less prone to fail than conventional systems for controlling sufficient water levels in an operational pool during an emergency. It is a particular object of certain embodiments to address the long-term cooling challenges associated with multi-unit operation of small modular reactors (SMR) in a shared reactor hall.SUMMARY

[0004] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0005] The present disclosure introduces, as a first concept, a nuclear facility with a flooding network associated with operational pools placed in an operational hall. More specifically the nuclear facility features a condensation surface, a first operational pool, and a first collector all contained in the operational hall. The first collector is for collecting condensate off the condensation surface. The nuclear facility also features a first flooding conduit, which connects respective volumes of the first collector and the operational pools. The nuclear facility further also features a recirculation flow path between the operationalpools, the condensation surface, the first collector, and the first flooding conduit to establish a phase-changing circulation of fluid along the recirculation flow path.

[0006] The present disclosure introduces, as a second concept, a passive safety method for promoting heat removal of a first operational pool contained an operational hall of a nuclear facility. The method involves establishing a phase-changing circulation of fluid along a replenishment flow path formed at least in part by the first collector, which collects condensate off a condensation surface of the operational hall, a first flooding conduit, which leads fluid from the first collector to the operational pools, the operational pools, and the inner surface of the operational hall.

[0007] Certain specific variants of the disclosed concepts may include one or more than one feature from the following itemized list:- the recirculation flow path is formed at least in part by the first operational pool, the condensation surface, the first collector, and the first flooding conduit,- the first collector is flooded with liquid to establish a phase-changing circulation of fluid along a replenishment flow path formed at least in part by the first collector,- the condensation surface is or is formed at least in part by a ceiling surface or an inner wall surface,- the condensation surface is or is formed at least in part by a floor surface,- the flooding conduit is configured to connect said volumes selectively,- the replenishing flow path is a closed or open flow path,- the flooding liquid source is configured to selectively flood the intermediate space via the first collector and first flooding conduit,- the flooding liquid source is a bespoke liquid reservoir external to the operational pool(s),- the nuclear facility comprises a platform around the operational pool(s),- the platform is sloped towards the collector(s),- the operational pool is a reactor pool or a spent fuel pool,- the nuclear facility comprises a dry well provided into the operational hall,- the nuclear facility comprises a first pool enclosure provided into the operational hall,- the first pool enclosure forms the first operational pool at least in part,- the first pool enclosure defines the water volume of the first operational pool,- the first pool enclosure is provided into the dry well,- an intermediate space is formed between the dry well and the pool enclosure,- the first pool enclosure is provided into the dry well such that no air gap is formed between the dry well and the pool enclosure,- the flooding liquid source is configured to selectively flood the water volume of the first operational pool via the first collector, first flooding conduit, and intermediate space,- the flooding liquid source is connected to the first collector with a flooding liquid source conduit,- the flooding liquid source is selectively connected to the first collector with a flooding liquid source conduit,- an outlet of the flooding liquid source conduit is set higher than an inlet of the first flooding conduit- the first flooding conduit leads to the first operational pool,- an outlet of the flooding liquid source conduit communicates with the first collector,- the inlet of the first flooding conduit is set higher than the maximum liquid level of the first operational pool under normal operation,- the outlet of the first flooding conduit to the first operational pool is set higher than the nominal liquid level of the first operational pool under normal operation,- the nuclear facility comprises a first sump for storing some of the fluid collected by the first collector,- the nuclear facility comprises a first sump conduit connecting the first sump to the first collector,- the first sump conduit connects the first sump to the bottom section of the first collector,- an inlet of the first sump conduit at the first collector is set higher than the outlet of the first sump conduit at the first sump,- the nuclear facility comprises a plurality of such operational pools,- the plurality of operational include a second operational pool provided adjacent to the first operational pool inside the operational hall with aligning normal operating fluid levels,- the nuclear facility comprises a plurality of such collectors,- the plurality of collectors includes a second collector,- the second collector opposes the first collector inside the operational hall,- the second collector is configured to collect condensate off the condensation surface,- the nuclear facility comprises a respective plurality of drainage conduits for connecting the collectors to the operational pools,- the plurality of drainage conduits comprises a second flooding conduit, which connects respective volumes of the second collector and the second operational pool,- the flooding liquid source is configured to flood all operational pools at once via the respective collectors,- the operational hall is a reactor hall or a spent fuel hall,- the operational hall forms an air-tight boundary for the air space defined by the operational hall,- the recirculation flow path formed at least in part by the air space defined by the operational hall,- the recirculation flow is natural,- the nuclear facility is a small modular nuclear reactor facility,- the operational hall is a reactor hall housing a plurality of reactor pools.

[0008] Considerable benefits may be gained with the novel proposition.

[0009] The collectors and conduits form a novel flooding network that seeks to ensure that evaporated water from the overheated pool returns to the pool without unnecessary loss of water volume. By flooding the collectors, a connected vessels' system is created. Once the water starts to evaporate due to reactor overheating, the condensation of the vapor happening on the envelope of the building is collected in the collectors, thus making the connected vessels' system to compensate the missing water in the affected pool(s).BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In the following certain exemplary embodiments are described with reference to the accompanying drawings, in which:FIGURE 1 illustrates a schematic cross-sectional view of a passive safety system in a nuclear power facility under normal operation;FIGURE 2 illustrates a schematic top-elevation view of the system of FIGURE 1 ;FIGURE S illustrates a schematic cross-sectional elevation view of the system of FIGURE 1 during an emergency;FIGURE 4 illustrates a schematic top-elevation view of the system of FIGURE 3;FIGURE 5 illustrates a cross-sectional perspective view of the system of FIGURE 1 ;FIGURE 6 illustrates a partial cross-sectional side view of the collector and sump of the system of FIGURE 5 under normal operation;FIGURE 7 illustrates a partial cross-sectional side view of the collector and sump of the system of FIGURE 5 during an emergency;FIGURE 8 illustrates a partial cross-sectional side view of the collector and operational pool of the system of FIGURE 5 under normal operation, andFIGURE 9 illustrates a partial cross-sectional side view of the collector and operational pool of the system of FIGURE 5 during an emergency.EMBODIMENTS

[0011] As will become apparent hereafter, the disclosed embodiments provide for a setup for maintaining water levels in a nuclear facility to ensure sufficient cooling in an overheating event. The proposed embodiments involve various return paths for evaporated water to replenish the pool for minimizing loss of water volume.

[0012] FIGURE 1 illustrates an exemplary operational hall 100 of a nuclear facility on a schematic level. The nuclear facility may be a small modular nuclear reactor facility with an operational hall used as a reactor hall housing one or several reactor pools. According to a particular embodiment, the nuclear facility is configured to produce district heat.

[0013] The illustrated operational hall 100 houses two operational pools 110, 120. More particularly, the exemplary operational hall 100 is a reactor hall with two reactor pools. It should be noted, however, that two reactor pools 110, 120 are illustrated only by way of example and that the embodiments herein described are equally applicable to other operational halls as well as to other pools in number and type found in nuclear facilities, such as spent fuel halls with one or more spent fuel pools, respectively. For the sake of clarity, the following description will explain exemplary embodiments in the illustrated context of reactor pools. One or more than one of these reactor pools may contain one or more than one nuclear reactor cores enclosed in a pressure vessel. In other words, nuclear reactors may be submerged into the reactor pools.

[0014] The reactor hall 100 has ceilings, walls, and / or other enveloping structures that define an internal air space. These enveloping structures and, if an HVAC system is used, also the HVAC system, preferably form an air-tight boundary to the internal air space.

[0015] The reactor pools 110, 120 are formed by pool enclosures 112, 122 that are embedded into dry wells 111 , 121 at the bottom of the reactor hall 100. While optional, it is preferable to separate the pool enclosures 112, 122 from the dry wells 111 , 121 by an intermediate space 113, 123 there between. The intermediate space 113, 123 serves the purpose of facilitating protection equipment against seismic shock and / or maintenance. Additionally or alternatively the intermediate space 113, 123 may be used to provide an extended grace period to revert the configuration of the system in case of spurious unintentional actuation of the system, thus preventing extended grace period before there is any affectation to the pool enclosure 112, 122.

[0016] The reactor hall 100 also houses one or more than one collector 131 , 132 for collecting condensate off one or more than one condensation surface. In the illustrated example the reactor hall 100 houses two collectors 131 , 132 arranged peripherally as condensation gutters. It would, however, also be possible to use only one collector 131 to serve several operational pools 110, 120. As is custom, the reactor hall 100 features elevated platforms for technicians to walk on aside the reactor pools 110, 120. FIGURE 1 shows a collector platform 102a between the collectors 131 , 132 and reactor pools 110, 120 and a pool platform 102b between the reactor pools 110, 120. The platform system formed by the individual sections of platform is preferably inclined towards the pool 110, 120 or collector 131 , 132 so as to avoid standing water on the reactor hall floor. In other words the platform system 102a, 102b forms a floor surface 102. It should be noted that also the floor surface 102 may attract some condensation. As the floor surface 102 forms or may form part of the condensation surface, inclination is advised. In FIGURE 1 said inclination is shown on the collector platforms 102a, which are tilted towards the collectors 131 , 132. These platforms are elevated above the assumed water level of the collectors 131 , 132 and reactor pools 110, 120.

[0017] The collector 131 , 132 is connected to the adjacent reactor pool 110, 120 with a conduit for selectively flooding the reactor pool 110, 120 with water accumulated into the collector 131 , 132. FIGURE 1 shows two such conduits, namely a first flooding conduit 151 , which connects the first collector 131 to the first reactor pool 110, and a second flooding conduit 152, which connects the second collector 132 to the second reactor pool 120. The flooding conduits 151 , 152 are sloped towards the reactor pool 110, 120, meaning that the inlets of the flooding conduits 151 , 152 at the collector 131 , 132 are elevated in respect to the outlet at reactor pool 110, 120. The inlets of the flooding conduits 151 , 152 at the collector 131 , 132 are set higher than the nominal water level of the collectors 131 , 132 during normal operation. This means that the flooding conduits 151 , 152 will only flood the reactor pools 110, 120, when the water level of the collector131 , 132 exceeds the nominal water level enough to reach the inlet of the flooding conduit 151 , 152. Accordingly, the reactor pool 110, 120 will be selectively flooded upon first flooding the collector 131 , 132.

[0018] FIGURE 1 also shows an optional flooding conduit valve 154, 155 provided to the flooding conduit 151 , 152 for extra flooding control. Flooding of pools 110, 120 may be controlled by opening and closing the flooding conduit valves 154, 155 irrespective of the water level in the collectors 131 , 132. Additionally, the flooding conduit valves 154, 155 may be useful for servicing. The conduit valves 154, 155 could be replaced with other means of controlling water flow in flooding conduits 151 , 152, such as removable plugs or any other foreseeable mechanisms.

[0019] The water volumes of the collectors 131 , 132 and pools 110, 120 are connected into a flooding network by the flooding conduits 151 , 152 that also form part of the flooding network. A flooding liquid source 180 is connected to the flooding network to adjust the amount of water contained in the flooding network. More particularly, the flooding liquid source 180 may be set to inject a single pre-determined amount of water into the flooding network. FIGURE 1 shows a water reservoir as an example of such a flooding liquid source 180. While the water reservoir may be external to the reactor hall 100, it may set up in practically any location, such as inside, above, or even below the reactor hall 100 provided that an additional pressure source is provided. By releasing the contents of the water reservoir into the flooding network, the system is flooded, whereby no further adjustment of the water level is required.

[0020] Alternatively, the flooding liquid source 180 may be provided as a pressurised water line. For practical reasons, however, an external water reservoir elevated in respect to the collector is preferred because it will not take up space in the reactor hall and because it does not require an additional pressure source. It is to be understood that even if the flooding liquid source 180 would be provided inside the reactor hall 100, it would be a volume separate from the operational pools 110, 120.

[0021] The flooding liquid source 180 is connected to the flooding network by a flooding liquid source conduit 153. In the embodiment shown in FIGURE 1 the outlet of the flooding liquid source conduit 153 is set to pour into the collector 131 . This outlet is set higher than the nominal water level of the collector 131 and higher than the inlet of the flooding conduit 151 communicating with the operational pool 110. The flooding liquid source conduit 153 could alternatively be connected to any one or all other parts of the flooding network, such as the second collector 132 or to any one or all of the operational pools 110, 120. To control the selective release of the liquid contained in the floodingliquid source 180 the flooding liquid source conduit 153 is equipped with a flooding liquid source valve 156. In the simple example depicted in the FIGURES only one valve 156 is needed as the flooding liquid source 180 is connected to only one part of the flooding network, namely to the first collector 131. However, if more than one part of the flooding network is to be flooded, it may be preferable to add valves to those parts, which are to be flooded separately.

[0022] FIGURE 2 provides for a wider overview of the exemplary nuclear facility in a top elevation view. FIGURE 2 reveals how the collectors 131 , 132 are arranged on lateral sides of the elongated reactor hall 100 with operational pools 110, 120 placed in the center. FIGURE 2 also shows that both operational pools 110, 120 are connected to both collectors 131 , 132 with flooding conduits 151 , 152.

[0023] FIGURE 2 further reveals the presence of a sump 141 connected to the collector 131. While certain embodiments may feature only a single sump, the illustrated embodiment involves two sumps 141 , 142 for serving the elongated reactor hall 100. A first sump 141 is provided at one end, namely one longitudinal end, of the reactor hall 100 between collectors 131 , 132 that flank opposing lateral ends of the reactor hall 100. The first sump 141 is connected to the first and second collector 131 , 132 with a sump conduit 161 , 162. Similarly, a second sump 142 is provided at the other longitudinal one end of the reactor hall 100 opposing the first sump 141 and between collectors 131 , 132 flanking the lateral ends. The second sump 142 is connected to the first and second collector 131 , 132 with a sump conduit 163, 164. The placement and number of the sumps 141 , 142 with respect to each other and / or to the collectors 131 , 132 may be varied.

[0024] FIGURE 5 shows the placement of the first sump 141 from a more illustrative perspective. FIGURE 5 demonstrates how the sump 141 is placed relative to the collector 131 to act as the lowest elevation of the flooding network. A sump 141 is optional and may added to ultimately collect water that has accumulated in the collector 131 due to normal operation leakages in the operational hall, so that the water can be pumped out during normal operation. The sump 114 is not required for the operation of the flooding network. However, with aid of the sump 141 , the collector 131 may be designed as relatively shallow. FIGURE 5 also shows that the sump conduit 161 connects the sump 141 to the bottom region of the collector 131 and is inclined towards the sump 141. In the illustrated embodiment the inlet of the sump conduit 161 is placed on the bottom of the sump 131 but placement above the bottom point is also foreseeable. The sump 141 may have a pump (not illustrated) for pumping out any normal drainage that is collected in the flooding network.

[0025] There is a considerable degree of freedom in the design of the sumps as long as the placement and size of the sumps does not interfere with the operation of the flooding network. This means that the shape and volume of the sump may be varied provided that the size of the sump is taken into consideration in designing the volume of the flooding liquid source 180 so as to reach the nominal flooding level, which will be discussed here after. It is also preferable to place the sump above the minimum height needed for the operational pool 110, 120 to cool the heat source, e.g. reactor or spent fuel. This prevents inadvertent drainage of water from the operational pool towards the sumps to avoid dangerous reduced inventory in the pool.

[0026] FIGURE 5 also shows the optional presence of an auxiliary volume 170. In the present context the auxiliary volume 170 represents any additional cavity that could be present in the operational hall that may collect condensation. The auxiliary volume 170 may be added to a relatively low elevation in respect to a flooding level, which will be discussed here after. While the depth and dimensions of such an auxiliary volume 170 are not decisive for the operation of the flooding network, connections to such a volume are preferably designed to avoid stagnation of water in the auxiliary volume 170. To make sure that any condensate that has crept into the auxiliary volume 170 is drained, the auxiliary volume 170 is preferably connected to the collector 131 , 132 with an auxiliary volume conduit 171. The auxiliary volume 170 may, depending on its function, be set up to be dry or partially or fully filled with water. By way of example the auxiliary volume 170 may be used as a decontamination pit, which is intended to be kept dry.

[0027] Let us now examine operation of the nuclear facility 100 during normal operation, which is depicted in FIGURES 1 , 2, 5, 6, and 8 that show relative heights of conduits and water levels within the flooding network.

[0028] As is shown in FIGURES 1 , 2, 5, 6, and 8, water level in the operational pools 110, 120 is kept at a nominal water level 205. FIGURE 8, however, illustrates that the water level in the operational pool 110, 120 may, under normal operation, fluctuate between a minimum water level 206 and a maximum water level 204 with the nominal water level 205 found there between. It should be understood that water is in this context disclosed as an example of any liquid pooled for operating a nuclear facility. In other words, water may in this context be equated with any liquid used in a nuclear process, for storing spent fuel in or for any other pooled application in a nuclear facility.

[0029] FIGURES 6 and 8 also show an exemplary respective height set up between the conduits leading to and from the collector 131 as well as to the sump 141 and operational pool 110, respectively. The outlet of the flooding liquid source conduit 153 isset lower than the inlet and / or higher than the outlet of the flooding conduit 151. When comparing heights or elevations of inlets and outlets of various conduits, the measurement is taken at the center point of the opening of said inlet or outlet. The outlet of the flooding liquid source conduit 153 is, on the other hand, set lower than the nominal level of flooding liquid source 203, i.e. the water level intended to be reached after flooding, and / or higher than the maximum water level 204 of the first operational pool 110 under normal operation. As the flooding conduit 151 is slanted towards the operational pool 110, the inlet is set higher than the outlet thereof. It is to be noted that the outlet of the flooding conduit 151 is set higher than the nominal water level 205 of the operational pool 110. To promote homogeneous increase of water level in the collector 131 before the water reaches the inlet of the flooding conduit 151 , it is preferable that the outlet of the flooding liquid source conduit 153 to the collector 131 is set to a lower height than the inlet of the flooding liquid source conduit 153.

[0030] In the state depicted by FIGURE 6, all water accumulated in the collector 131 has been lead into the sump 141 , wherein the water level in the flooding network does not reach the bottom of the collector 131 but, rather, the sump conduit 141. The depicted water level is to be expected in a real-life application, where only little water is condensed during normal operation. In such a case, the water level does not reach the inlet of the flooding conduit 151 .

[0031] In the state depicted by FIGURE 8, water level in the operational pool 110 is at its nominal level 205. This means that all water of the operational pool 110 is contained in the water volume of the pool enclosure 112 with no water passing to the intermediate space 113 between the dry well 111 and the pool enclosure 112 nor to the flooding conduit 131 , 132. Additionally, all water of the flooding network is kept between collector 131 and sump 141 , and no water is transferred to the dry well through the flooding conduit 151.

[0032] With the nuclear facility running normally, the collectors 131 , 132 are relatively empty, which is depicted in FIGURE 2 that shows the collectors 131 , 132 and sumps 141 , 142 in a light colour and the operational pools 110, 120 in a dark colour to represent the degree of filling. The same is shown in FIGURE 1 , which shows that the flooding liquid source 180 is full and ready to be deployed.

[0033] Let us then examine operation of the nuclear facility 100 during emergency operation that is depicted in FIGURES 3 and 4, which show the general operation of the flooding network, and in FIGURES 7 and 9, which that show relative heights of conduits and water levels within the flooding network.

[0034] The flooding network is flooded by releasing the water from the flooding liquid source 180 by opening flooding liquid source valve 156. With the flooding liquid source valve 156 open, water flows through the flooding liquid source conduit 153 to fill the first collector 131. FIGURE 3 shows the flooding liquid source 180 partly depleted. Water is then distributed to the second collector 131 via sump conduits 161 , 162, 163, 164 and sumps 141 , 142 as well as to the operational pools 110, 120 via flooding conduits 151 , 152. If the flooding network features flooding conduit valves 154, 155 in the flooding conduits 151 , 152, these valves must be left open or opened during flooding. FIGURE 4 shows an overall view of the flooding network in a flooded state with all components depicted in a dark color to indicate a high degree of filling.

[0035] FIGURE 7 shows the state of the collector 131 and sump 141 in such an emergency state. Both the collector 131 and the sump 141 are filled up to the nominal level of flooding 203, which above the maximum water level 204 of the first operational pool 110 under normal operation but below the pool platform level 201 collector platform level 202 so as to not submerge the platform 102a, 102b.

[0036] FIGURE 9 shows the state of the collector 131 and operational pool 110 in such an emergency state. Both the collector 131 and the operational pool 110 are filled up to the nominal level of flooding 203. In the design shown in FIGURE 9, the outlet of the flooding conduit 131 opens up to the intermediate space 113. Alternatively, the outlet of the flooding conduit 131 could be devised to bridge over the pool enclosure 112, as is shown in FIGURE 1. Either way, flooding of the flooding network will raise the water level enough to exceed the pool enclosure 112. Now the water level in the operational pool 110 exceeds the maximum water level 204 of the first operational pool 110 under normal operation, whereby the water flows over the edge of the pool enclosure 112 to fill the intermediate space 113 directly (embodiment of FIGURE 9) or indirectly (embodiment of FIGURE 1 ). As can be understood, now the volume of the flooding network is filled, whereby water connects the collectors 131 , 132, sumps 141 , 142, and operational pools 110, 120 together via the flooding network.

[0037] FIGURE 3 shows the principle of the resulting water replenishment mechanism during such an emergency state. In the illustrated example, the first operational pool 110 is a reactor pool, which contains an abnormal amount of heat to be dissipated from the reactor core. The heat source heats up the water contained in the reactor pool 110 inducing evaporation of the water, which is depicted with curved lines in the air space of the reactor hall 100. The reactor hall 100 features several surfaces interfacing the internal air space that form a condensation surface 101 for the water vaporto condense against. In the illustrated example the ceiling of the reactor hall 100 is identified as the condensation surface 101 but, in practice, there may be other additional surfaces that attract condensation, such as the walls or any other superstructures on top of the reactor pool 110. As condensation accumulates on the condensation surface 101 , it eventually starts flowing down toward the collector 131 , 132, which is placed at the periphery of the downward sloping condensation surface 101. Once the condensation reaches the collector 131 , 132, it replenishes the water volume of the reactor pool 110 via the flooding network. In the example of FIGURE 3, the collected condensation flows from the condensation surface 101 to the collector 131 and via the flooding conduit 151 to the reactor pool 110.

[0038] Overall it is preferable to set the inlets and outlets of the flooding network such that any normal drainage collections never reach a height that could let water run through flooding network, particularly through the flooding conduits 151 , 152 towards the operational pool 110, 120. If there are several operational pools 110, 120, it is preferable to ensure that, during operation, the flooded elevation is the same in all the connected volumes of the flooding network.

[0039] After the root cause of the emergency has been removed, normal operations may be resumed by removing excess water from the system. Restoration of the normal state may be performed by pumping out water from the flooding network with pumps (not illustrated) provided in the sumps or intermediate space, for example.

[0040] In view of the above it may be summarized that the flooding network is set up to establish a phase-changing recirculation flow path of water. Once the flooding network has been flooded by the flooding liquid source 180, the recirculation flow path formed part by the following components of the flooding network: the condensation surface 101 , the collector 131 , 132, the flooding conduit 151 , 152, and the operational pool 110, 120. If the nuclear facility includes more than one collector, flooding conduit, or operational pool, also one or more than one of these components may participate in the forming of the flooding network. Optionally, the air space, which is formed under the envelope of the operational hall 100 and through which water traverses in vapor form, may be seen as forming part of the recirculation flow path.

[0041] The novel concept of forming a phase-changing recirculation flow path of water inside an operational hall 100 of a nuclear facility finds use in a passive safety method for promoting heat removal of an operational pool 110 contained in such operational hall 100. In such a method a collector 131 is flooded with liquid to establish a phase-changing circulation of fluid along a replenishment flow path formed at least in partby the collector 131 , which collects condensate off an inner surface 101 of the operational hall 100, a flooding conduit 151 , which leads fluid from the first collector 131 to the operational pool 110, the operational pool 110, and the inner surface 101 of the operational hall 100.

[0042] The embodiments herein described may be varied in several ways.

[0043] For example, the first pool enclosure may be provided into the dry well 111 such that no air gap is formed between the dry well 111 and the pool enclosure 112.

[0044] In the illustrated embodiments the condensation surface is formed by the inner surface of the operational hall, which is shown to include at least the wall and ceiling surfaces as well as the floor surfaces. The inner space of the operational hall may include further structures, on which moisture condensates. These structures are preferably set such that the condensate flows off to the collectors. The operational hall may additionally or alternatively include an intentional condensation structure, such as a lid or deflector, set up to attract moisture rising from the operational pool and to lead the moisture to the collector. Such a lid may, for example, take the form of a slanted canopy over the operational pool.

[0045] The embodiments herein shown involve an open replenishing flow path across the internal airspace of the operational hall. It could, however, be possible to force the vapor rising from the operational pools to follow a certain path towards the condensation surface 101 , 102. According to one embodiment, the operational hall comprises ducting provided into the internal airspace to guide evaporated steam onto the condensation surfaces, thus closing the recirculation flow path to follow a pre-determined route.

[0046] The disclosed recirculation of condensate occurs naturally through evaporation, convection, and condensation. The recirculation could alternatively be assisted by fans blowing in the intermediate space, wicks on the condensation surface, or other facilitators.

[0047] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0048] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.

[0049] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0050] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0051] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0052] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwiseexplicitly stated. Furthermore, it is to be understood that the use of "a" or "an", i.e. a singular form, throughout this document does not exclude a plurality.REFERENCE SIGNS LIST

Claims

1. CLAIMS:

1. A nuclear facility comprising:- an operational hall (100),- a condensation surface (101 , 102) contained in the operational hall (100), and- a first collector (131 ) contained in the operational hall (100) and configured to collect condensate off the condensation surface (101 , 102), characterized by:- a plurality of operational pools (110, 120) contained in the operational hall (100) and by- a plurality of flooding conduits (151 , 152), which connects respective volumes of the first collector (131 ) and the plurality of operational pools (110, 120) to a flooding network to selectively connect respective volumes of the first collector (131 ) and operational pools (110, 120) together.

2. The nuclear facility according to claim 1 , wherein the nuclear facility comprises a recirculation flow path for phase-changing circulation of fluid, which recirculation flow path is formed at least in part by:- the plurality of operational pools (110, 120),- the condensation surface (101 , 102),- the first collector (131 ), and- the plurality of flooding conduits (151 , 152).

3. The nuclear facility according to claim 1 or 2, wherein the nuclear facility comprises a flooding liquid source (180), which is configured to selectively flood the first collector (131 ) to establish the phase-changing circulation of fluid along the recirculation flow path.

4. The nuclear facility according to any one of the preceding claims, wherein the condensation surface (101 , 102) is or is formed at least in part by a ceiling surface or an inner wall surface.

5. The nuclear facility according to any one of the preceding claims, wherein the flooding conduits (151 , 152) are configured to connect said volumes selectively.

6. The nuclear facility according to any one of the preceding claims, wherein the recirculation flow path is a closed or open flow path.

7. The nuclear facility according to any one of the preceding claims, wherein the flooding liquid source (180) is configured to selectively flood the intermediate space (112) via the first collector (131 ) and first flooding conduit (151 ).

8. The nuclear facility according to any one of the preceding claims, wherein the flooding liquid source (180) is a bespoke liquid reservoir external to the operational pools (110, 120).

9. The nuclear facility according to any one of the preceding claims, wherein the nuclear facility comprises a platform (102a, 102b) around the operational pools (110, 120) and sloped towards the collector(s) (131 , 132).

10. The nuclear facility according to any one of the preceding claims, wherein one or more than one of the plurality of operational pools (110, 120) is a reactor pool or a spent fuel pool.11 . The nuclear facility according to claim 10, wherein a nuclear reactor enclosed in a pressure vessel is submerged into the reactor pool.

12. The nuclear facility according to any one of the preceding claims, wherein:- the nuclear facility comprises dry wells (111 , 121 ) provided into the operational hall (100) and wherein- the nuclear facility comprises pool enclosures (112, 122) provided into the operational hall (100), which pool enclosures (112, 122): o form the plurality of operational pools (110, 120) at least in part and o define the water volume (114, 124) of the plurality of operational pools (110).

13. The nuclear facility according to claim 12, wherein the pool enclosures (112, 122) are provided into the dry wells (111 , 121 ) such that an intermediate space (113, 123) is formed between respective dry wells (111 , 121 ) and pool enclosures (112, 122).

14. The nuclear facility according to claim 12, wherein the pool enclosures (112, 122) are provided into the dry wells (111 , 121 ) such that no air gap is formed between the dry wells (111 , 121 ) and the pool enclosures (112, 122).

15. The nuclear facility according to claim 13, wherein the flooding liquid source (180) is configured to selectively flood the water volumes (114, 124) of the operational pools (110, 120) via the first collector (131), flooding conduits (151 , 152), andintermediate spaces (113, 123).

16. The nuclear facility according to any one of the preceding claims, wherein:- the flooding liquid source (180) is connected, particularly selectively connected, to the first collector (131 ) with a flooding liquid source conduit (153) and wherein- an outlet of the flooding liquid source conduit (153), which communicates with the first collector (131 ), is set higher than inlets of the flooding conduits (151 ), which lead to the respective operational pools (110, 120).

17. The nuclear facility according to claim 16, wherein inlets of the flooding conduits (151 , 152), which lead to the operational pool (110), are set higher than the maximum liquid level (204) of the operational pools (110, 120) under normal operation.

18. The nuclear facility according to claim 16 or 17, wherein outlets of the flooding conduits (151 , 152) to the operational pools (110, 120) are set higher than the nominal liquid level (205) of the operational pool (110) under normal operation.

19. The nuclear facility according to any one of the preceding claims, wherein:- the nuclear facility comprises a plurality of sumps (141 , 142) for storing some of the fluid collected by the first collector (131 ),- the nuclear facility comprises sump conduits (161 , 162, 163, 164) connecting the sumps (141 , 142) to the first collector (131 ), preferably to the bottom section of the first collector (131).

20. The nuclear facility according to claim 19, wherein inlets of the sump conduits (161 , 162, 163, 164) at the first collector (131) is set higher than the outlet of the sump conduits (161 , 162, 163, 164) at the sumps (141 , 142).21 . The nuclear facility according to any one of the preceding claims, wherein the operational pools (110, 120) are provided adjacent to each other inside the operational hall (100) with aligning normal operating fluid levels.

22. The nuclear facility according to claim 21 , wherein:- the nuclear facility comprises a plurality of such collectors, including a second collector (132) opposing the first collector (131 ) inside the operational hall (100),- the second collector (132) is configured to collect condensate off thecondensation surface (101 , 102), and wherein- the nuclear facility comprises a respective plurality of drainage conduits for connecting the collectors to the operational pools, including a second flooding conduit (152), which connects respective volumes of the second collector (132) and the second operational pool (120).

23. The nuclear facility according to claim 21 or 22, wherein the flooding liquid source (180) is configured to flood all operational pools at once via the respective collectors.

24. The nuclear facility according to any one of the preceding claims, wherein the operational hall (100) is a reactor hall or a spent fuel hall.

25. The nuclear facility according to any one of the preceding claims, wherein the operational hall (100) forms an air-tight boundary for the air space defined by the operational hall (100).

26. The nuclear facility according to any one of the preceding claims, wherein the recirculation flow path is formed at least in part by the air space defined by the operational hall (100).

27. The nuclear facility according to any one of the preceding claims, wherein the recirculation flow is natural.

28. A passive safety method for promoting heat removal of a plurality of operational pools (110, 120) contained in an operational hall (100) of a nuclear facility, the method comprising establishing a phase-changing circulation of fluid along a recirculation flow path formed at least in part by:- the first collector (131 ), which collects condensate off a condensation surface (101 , 102) of the operational hall (100),- a plurality of flooding conduits (151 , 152), which lead fluid from the first collector (131) to the plurality of operational pools (110, 120),- the plurality of operational pools (110, 120), and- the inner surface (101 ) of the operational hall (100).

29. The method according to claim 28, wherein the nuclear power facility is that defined in any one of the preceding claims 1 to 27.

30. The method according to claim 28 or 29, wherein the phase-changing circulation offluid is established by flooding the first collector (131 ).31 . The method according to claim 28, 29, or 30, comprising flooding the plurality of operational pools (110, 120) contained in the operational hall (100) at once.

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