Molten core material handling system for SMR in event of severe accident

Abstract

A molten core material handling system for an SMR in the event of a severe accident, according to an embodiment of the present invention, comprises: a U-shaped wall unit attached to a lower outer wall of a reactor vessel at a predetermined interval to transfer heat generated from nuclear fuel of a core disposed in a lower portion of the reactor vessel; a U-shaped cooling water storage space in which cooling water is filled between the lower outer wall of the reactor vessel and the U-shaped wall unit; and a pressure release valve configured to open and close the U-shaped cooling water storage space at the upper end of the U-shaped wall unit, and thus the core molten material handling system can perform initial in-vessel retention (IVR) in the event of a severe SMR accident, and can secure a time in which, in the event of a severe accident, a molten core material is caught, by means of the cooling water tank that surrounds the lower part of the reactor provided with a PRD, in the lower part of the reactor or the inside of the cooling water tank, and shutdown cooling can be smoothly performed by other passive or active safety equipment.

Description

SMR core meltdown response system in case of a severe accident

[0001] The present invention relates to an in-vessel retention system for SMR core material in the event of a severe accident, and more particularly, to an SMR core material response system in the event of a severe accident that performs initial in-vessel retention (IVR) of the internal core material in the event of an SMR core material accident, and secures time for the core material to be caught in the lower part of the reactor or inside the coolant tank surrounding the lower part of the reactor equipped with a PRD (Pressure Relief Damper) and for smooth shutdown cooling to be performed by other passive or active safety equipment.

[0002] Currently, SMRs are under development or have been completed both domestically and internationally, aiming to innovatively enhance safety by incorporating various passive safety features. Korea Hydro & Nuclear Power (KHNP) is also planning an innovative SMR with a core damage frequency (CFD) of 1e-9.Ry.

[0003] NuScale, currently considered the most advanced SMR reactor type, has 12 modular 50 MW reactors, producing 600 MW of power. To ensure passive safety in the event of a major accident, it adopted a design in which the containment building (in the form of a steel vessel) containing the reactor is placed in a large water tank and a cooling water pool.

[0004] This structure is difficult to maintain periodically in the cooling water tank, requires a lot of effort to manage the quality of the cooling water in the tank, and requires a secondary facility to store all the water during periodic planned preventive maintenance, making the management system complex. It is also very cost-effective as a facility to prepare for a serious accident with a low probability.

[0005] All SMRs (small modular reactors) currently under development at home and abroad are being developed with a focus on improving safety. However, despite the existence of various safety shutdown systems, there are no specific measures developed to prevent the external leakage of molten core material within the SMR reactor in the event of a serious accident with a very low probability.

[0006] Typical large commercial nuclear power plants have various countermeasures in place to prevent direct reaction between the core melt and the concrete floor of the lower cavity of the reactor building to prevent loss of reactor building integrity in the event of a severe accident. A representative example of this is the core catcher, which collects, retains, and cools the core melt in the lower cavity of the reactor building by supplying cooling water.

[0007] However, all previously developed core catchers are installed in a wide space outside the reactor. Therefore, in SMRs without a containment building or designed to be in close contact with the reactor vessel, installation of existing core catchers is impossible.

[0008] The present invention has been devised to solve such problems, and the purpose of the present invention is to provide an SMR core melt response system in the event of a severe accident, which performs initial in-vessel retention (IVR) of the internal core melt in the event of a severe accident of an SMR, and secures time for the core melt to be caught in the lower part of the reactor or inside the coolant tank by the coolant tank surrounding the lower part of the reactor equipped with a PRD (Pressure Relief Damper) and for smooth shutdown cooling to be performed by other passive or active safety equipment.

[0009] According to one embodiment of the present invention, a SMR core meltdown response system in the event of a severe accident is characterized by including a U-shaped wall portion attached to the lower outer wall of a reactor vessel at a predetermined interval so as to transfer heat generated from nuclear fuel of a core disposed at the lower portion of the reactor vessel, a U-shaped coolant storage space filled with coolant between the lower outer wall of the reactor vessel and the U-shaped wall portion, and a pressure relief valve configured to open and close the U-shaped coolant storage space at the upper portion of the U-shaped wall portion.

[0010] A system for dealing with SMR core melt in a severe accident according to one embodiment of the present invention can perform initial in-vessel retention (IVR) of internal core melt in the event of a severe accident of an SMR.

[0011] According to one embodiment of the present invention, a system for dealing with SMR core melt in the event of a severe accident can secure time for core melt in the event of a severe accident to be caught by a cooling water tank surrounding the lower part of the reactor equipped with a PRD (Pressure Relief Damper) or inside the cooling water tank, and for smooth stop cooling to be performed by other passive or active safety equipment.

[0012] Figure 1 is a perspective view of a typical SMR reactor.

[0013] Figure 2 is a cross-sectional view of Figure 1;

[0014] Figure 3 is a schematic diagram showing the direction of coolant flow inside the general SMR reactor of Figure 2.

[0015] Figure 4 is a drawing illustrating heat transfer in the lower part of a typical SMR reactor vessel, and

[0016] Figure 5 is a drawing explaining a system for dealing with SMR core meltdown in the event of a major accident according to one embodiment of the present invention.

[0017] The present invention will be described in more detail with reference to the drawings below.

[0018] The attached drawings are merely examples provided to more specifically explain the technical idea of ​​the present invention, and therefore the idea of ​​the present invention is not limited to the attached drawings.

[0019] Additionally, the attached drawings may be exaggerated in size and spacing to illustrate the relationship between each component.

[0020] Referring to FIGS. 1 to 5, a system (1) for dealing with SMR core meltdown in a severe accident according to one embodiment of the present invention is described.

[0021] FIG. 1 is a perspective view of a typical SMR reactor, FIG. 2 is a cross-sectional view of FIG. 1, FIG. 3 is a schematic diagram showing the direction of coolant flow inside the typical SMR reactor of FIG. 2, FIG. 4 is a drawing explaining heat transfer in the lower part of a typical SMR reactor vessel, and FIG. 5 is a drawing explaining an SMR core meltdown response system in a severe accident according to one embodiment of the present invention.

[0022] As shown in FIGS. 1 and 2, a typical SMR reactor (10) is configured to include a reactor vessel (11), a core (12), a steam generator (13), a reactor coolant pump (14), a pressurizer (15), a core support barrel (17), and a control rod drive device (18).

[0023] The reactor vessel (11) can form the exterior of the SMR reactor (10).

[0024] The reactor vessel (11) may be a pressure vessel made of carbon steel material to load nuclear fuel and allow a chain nuclear fission reaction to occur safely.

[0025] The reactor vessel (11) may be composed of an upper vessel body (11a), a lower vessel body (11b), and a reactor head (11c).

[0026] The upper container body (11a) may be formed in a cylindrical shape. The upper container body (11a) may be formed to be open in the vertical direction.

[0027] The upper container body (11a) may have a receiving space for receiving a steam generator (13).

[0028] The lower vessel body (11b) may be formed in a cylindrical shape. The reactor vessel (11) may be formed to have a vertical length longer than its diameter.

[0029] A hemispherical lower head can be mounted on the lower part of the lower container body (11b).

[0030] The reactor head (11c) may be connected to a flange using stud bolts to cover the upper portion of the upper vessel body (11a). A control rod drive device may be mounted on the exterior of the reactor head (11c) for inserting or withdrawing control rods that control the nuclear fission reaction rate.

[0031] The primary system is a system that cools the core (12) by directly transferring heat from the core (12) by circulating the reactor coolant, which is the primary system fluid. The primary system includes a steam generator (13), a reactor coolant pump (14), a pressurizer (15), etc.

[0032] A secondary system is a system that maintains a pressure boundary with the primary system and generates electricity using heat transferred from the primary system. The secondary system is equipped with a turbine and a generator, which generates electricity.

[0033] The core (12) is placed at the bottom of the reactor vessel (11). The core (11) is where nuclear fuel is loaded and may be composed of a nuclear fuel assembly.

[0034] Inside the reactor vessel (11), a core support barrel (17), which is an internal structure that can be separated from each other, can be installed.

[0035] The core support barrel (17) is designed to support the nuclear fuel from below.

[0036] The interior of the reactor vessel (11) is filled with primary system fluid, and heat received from the core (12) is transferred to the secondary system fluid in the steam generator (13).

[0037] A plurality of nozzles are formed to penetrate the reactor vessel (10) in the thickness direction. A steam generator (13) and a reactor coolant pump (14) can be installed in the plurality of nozzles.

[0038] The reactor coolant pump (14) can be installed on top of the steam generator (13).

[0039] The impeller of the reactor coolant pump (14) is connected to the electric motor via a rotating shaft. As the electric motor operates, the impeller rotates to circulate the reactor coolant.

[0040] The steam generator (13) may be located above the core (12). The steam generator (12) may be located higher than the core (12).

[0041] A plurality of steam generators (13) can be arranged spaced apart from each other in the circumferential direction inside the reactor vessel (10).

[0042] As shown in Fig. 3, the core support barrel (17) and upper guide structures (not shown) such as the shroud and riser can form a circulation path of the reactor coolant inside the reactor vessel (10).

[0043] A circulation path can be formed to move from the core (12) to the steam generator (13) through the core support barrel (17) and the upper guide structure.

[0044] The reactor coolant rises along the circulation path in the core (12) and can flow into the upper part of the steam generator (13).

[0045] According to this configuration, the reactor coolant of the primary system circulates in the order of the core (12), the reactor coolant pump, the steam generator (13), and the core (12), and the heat generated in the core (12) can be transferred to the steam generator (13).

[0046] The steam generator (13) may be configured in a once-through spiral shape. The steam generator (13) may be configured with a shell and spiral heat transfer tubes. The reactor coolant may be configured to flow to the outside of the heat transfer tubes, and the secondary feedwater may be configured to flow to the inside of the heat transfer tubes.

[0047] Referring again to Figure 2, the lower part of the steam generator (13) is connected to the water supply system through the water supply pipe (13a), and receives water from the water supply system.

[0048] A water supply valve is installed in the water supply pipe (13a), so that the water supply pipe (13a) can be opened and closed.

[0049] The upper part of the steam generator (13) is connected to the turbine system through a steam pipe (13b), and supplies steam generated in the steam generator (13) to the turbine system.

[0050] Likewise, a steam valve is installed in the steam pipe (13b), so that the steam pipe (13b) can be opened and closed.

[0051] In normal operation of an SMR reactor, feedwater is supplied from the feedwater system to the steam generator (13) through the feedwater pipe (13a), and the steam generator (13) generates steam using the heat transferred from the core (12). The steam is supplied to the turbine system through the steam pipe (13b), and the turbine system generates electricity using the supplied steam.

[0052] Although not shown, the SMR reactor (10) may further include a shroud and / or riser to control the flow of coolant.

[0053] As illustrated in FIGS. 4 and 5, a severe accident SMR core meltdown response system (100) according to one embodiment of the present invention includes a U-shaped wall portion (110) attached to the lower outer wall of the reactor vessel (11) at a predetermined interval so as to transfer heat generated from nuclear fuel of the core (12) disposed at the lower portion of the reactor vessel (11), a U-shaped coolant storage space (130) filled with coolant between the lower outer wall (11a) of the reactor vessel (11) and the U-shaped wall portion (110), and a pressure relief valve (150, PSD; Pressure Relief Valve) configured to open and close the U-shaped coolant storage space at the upper portion of the U-shaped wall portion (110).

[0054] The above pressure relief valve (150) is installed in a plurality, preferably 4 to 8, facing each other at the upper end of the U-shaped cooling water storage space (130), and may include a first pressure relief valve (151) installed at the first upper end (131) and a second pressure relief valve (153) arranged at the second upper end (133) opposite to the first upper end (131).

[0055] The first pressure relief valve (151) is configured to open into the U-shaped cooling water storage space (130), and the second pressure relief valve (153) can be operated to open out of the U-shaped cooling water storage space (130).

[0056] The above pressure relief valve (150) can be installed circumferentially spaced apart from each other between the U-shaped wall portions (110) installed close to the lower outer wall of the reactor vessel (11) with respect to the lower outer wall of the reactor vessel (11).

[0057] When the above SMR reactor (10) is in normal operation, the U-shaped coolant storage space (130) is filled with water and is in a standby state, and when the core melt is relocated to the lower part of the reactor in the event of a severe accident, a direct heat transfer reaction can begin with the water filled in the U-shaped coolant storage space (130).

[0058] In the event of a serious accident, when the heat of the core melt is transferred and the water in the U-shaped coolant storage space (130) boils, the first pressure relief valve (151) is configured to open into the U-shaped coolant storage space (130), and the second pressure relief valve (153) is operated to open out of the U-shaped coolant storage space (130), so that a natural cooling path can be formed from the inside to the outside.

[0059] That is, the U-shaped cooling water storage space (130) forms a cooling water tank, and in normal times, the inside is maintained filled with water, but in the event of a serious accident, the water inside can flow in one direction due to the heat transfer temperature from the atom (a certain temperature and evaporation of water in the cooling water tank and generation of corresponding pressure).

[0060] At this time, the containment vessel (170) outside the SMR reactor (10) may already be filled with water by a cooling water pump (180) such as an emergency core cooling system or a shutdown cooling system, and the temperature of the core melt may be lowered and physically blocked by the cooling water filled between the SMR reactor (10) and the containment vessel (170) so that it does not leak out of the reactor.

[0061] In the event of a serious accident, the core melt surrounds the lower outer wall (11a) of the reactor vessel (11) and can be caught by the U-shaped coolant storage space (130) that functions as a coolant tank by having a pressure relief valve (150) at the upper end (131).

[0062] According to one embodiment of the present invention, a system (100) for dealing with a severe accident in an SMR core meltdown can provide a coolant tank having a double-layer structure formed by a U-shaped coolant storage space (130) formed by a U-shaped wall portion (110) attached to the lower portion of a reactor vessel (11) of an SMR reactor (10) and a containment vessel (170) outside the SMR reactor (10).

[0063] Not only can coolant be filled between the lower outer wall (11a) of the reactor vessel (11) and the U-shaped wall portion (110), but a sacrificial material layer (120) can also be placed.

[0064] Accordingly, it is possible to prevent the core molten material, which is about 2,500°C, from accumulating and gradually melting the reactor vessel (11) and containment vessel (170) made of carbon steel, which have a melting temperature of about 1,800°C.

[0065] A mixture of concrete or ceramic components and tungsten (melting point 3,500°C) can be used as the sacrificial material constituting the above sacrificial material layer (120).

[0066] The above cooling water is filled with boric acid water instead of water, so that recriticality can be prevented by the boric acid water in case the lower part of the reactor vessel (11) melts.

[0067] A system for dealing with SMR core melt in a severe accident according to one embodiment of the present invention can perform initial in-vessel retention (IVR) of internal core melt in the event of a severe accident of an SMR.

[0068] According to one embodiment of the present invention, a system for dealing with SMR core melt in the event of a severe accident can secure time for the core melt to be caught in the lower part of the reactor or inside the coolant tank by the coolant tank surrounding the lower part of the reactor equipped with a PRD in the event of a severe accident, and for smooth stop cooling to be performed by other passive or active safety equipment.

Claims

1. A SMR core meltdown response system in the event of a severe accident, comprising: a U-shaped wall portion attached to the lower outer wall of a reactor vessel at a predetermined interval so as to transfer heat generated from nuclear fuel of a core placed at the lower portion of the reactor vessel; a U-shaped coolant storage space filled with coolant between the lower outer wall of the reactor vessel and the U-shaped wall portion; and a pressure relief valve configured to open and close the U-shaped coolant storage space at the upper portion of the U-shaped wall portion.

2. In paragraph 1, The above pressure relief valve is installed close to the lower outer wall of the reactor vessel at the upper part of the U-shaped coolant storage space, and is a severe accident response system for SMR core meltdown, in which 4 to 8 valves are installed facing each other and spaced apart from each other in the circumferential direction.

3. In paragraph 1, The above pressure relief valve includes a first pressure relief valve installed at a first upper portion among the upper portions and a second pressure relief valve installed at a second upper portion opposite the first upper portion. A severe accident SMR core meltdown response system in which the first pressure relief valve is configured to open into the U-shaped coolant storage space, and the second pressure relief valve is operated to open out of the U-shaped coolant storage space.

4. In paragraph 3, The above U-shaped coolant storage space is normally filled with water inside, and in the event of a severe accident, the water inside flows in one direction due to the heat transfer temperature from the SMR reactor vessel, and the SMR core meltdown response system in which coolant is filled in the containment vessel outside the SMR reactor through the emergency core cooling system or the shutdown cooling system.

5. In paragraph 1, A SMR core meltdown response system in case of a severe accident, which provides a coolant tank having a double-layer structure formed by a U-shaped coolant storage space formed by the U-shaped wall portion added to the lower part of the reactor vessel and the SMR reactor external containment vessel.

6. In paragraph 1, A severe accident SMR core meltdown response system further including a sacrificial material layer between the lower outer wall of the reactor vessel and the U-shaped wall section.

7. In paragraph 6, The above sacrificial material layer uses a mixture of concrete or ceramic components and tungsten, and the above cooling water contains boric acid water. It is a SMR core meltdown response system in the event of a severe accident.

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