JP2017040588A - Nuclear reactor facility - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to detect water leakage using a drain sump even when a core catcher is installed in a containment.SOLUTION: According to an embodiment, a nuclear reactor facility comprises: a core catcher 21 disposed below a reactor pressure vessel within a containment and holding a core molten substance during a core meltdown accident; a water filling pipe supplying cooling water for cooling the core molten substance within the core catcher 21 during the core meltdown accident; a drain sump 20 disposed below the core catcher 21 within the containment and storing leak water leaking from the reactor pressure vessel at normal time; a core catcher cover 22 disposed to cover an upper portion of the core catcher 21 below the reactor pressure vessel within the containment and having a cover through hole 43 formed to pass through the core catcher cover in a vertical direction; and a drain pipe 40 for communicating the cover through hole 43 with the drain sump 20 within the containment.SELECTED DRAWING: Figure 2

Description

  Embodiments described herein relate generally to a nuclear reactor facility including a core catcher and a drain sump.

  In a normal water-cooled nuclear reactor, if cooling water is lost due to the stoppage of water supply to the reactor pressure vessel or the breakage of piping connected to the reactor pressure vessel, the reactor water level drops and the core is exposed. Cooling may be insufficient. Assuming such a case, the reactor is automatically shut down in response to a water level lowering signal, and the core is submerged and cooled by injecting coolant using an emergency core cooling system (ECCS), and a core melting accident is performed. It is designed to prevent it.

  However, although the probability is very low, it can be assumed that the emergency core cooling device does not operate and water injection devices for other cores cannot be used. In such a case, the core is exposed due to a decrease in the reactor water level, and sufficient cooling is not performed, and the fuel rod temperature rises due to decay heat that continues to occur after the reactor shuts down, eventually leading to core melting. It is possible.

  When such a situation occurs, the high-temperature core melt melts into the lower part of the reactor pressure vessel, and further melts and penetrates the bottom of the reactor pressure vessel and falls onto the floor in the reactor containment vessel. The core melt heats the concrete stretched on the reactor containment floor, reacts with the concrete when the contact surface reaches a high temperature, generates a large amount of noncondensable gases such as carbon dioxide and hydrogen, and melts and erodes the concrete. To do. The generated non-condensable gas increases the pressure in the containment vessel and may damage the containment vessel. Also, the boundary of the containment vessel may be damaged by melting and erosion of concrete. The structural strength of the container may be reduced. As a result, if the reaction between the core melt and concrete continues, the reactor containment vessel will be damaged, and radioactive materials in the reactor containment vessel may be released to the external environment.

  By the way, water leakage (drain) from a reactor pressure vessel during normal operation is guided to a drain sump provided at the bottom of the reactor containment vessel, and the water leak is detected by a detector in the drain sump. In such a reactor facility, if the core melt enters the drain sump, the area of the upper surface of the core melt is small compared to the volume of the core melt. Even if it does, there is a possibility that the temperature of the core melt does not decrease and erosion of the drain sump bottom continues.

  In addition, a core catcher may be installed in the lower part of the reactor containment vessel as a countermeasure for preventing the progress of an event in which the core melt falls through the bottom of the reactor pressure vessel. The core catcher has a function of receiving and holding the core melt that has melted and dropped through the bottom of the reactor pressure vessel. The decay heat generated from the core melt drives the water-steam density difference in the cooling channel provided at the bottom of the core catcher and the cooling by the water from the upper surface of the molten core deposit received in the core catcher. Heat is removed by natural circulation of water formed as force.

  It has been considered that the core catcher is provided with a cover for preventing damage caused by falling objects in the event of an accident. However, as described above, there is a drain sump at the bottom of the reactor containment vessel. Even when a core catcher is installed, it is necessary that water leaks to the drain sump during normal operation.

  In order to make the core catcher and the water leak detection function of the drain sump coexist, there is a method of providing a water leak detection floor above the core catcher (Patent Document 1). With this structure, it is possible to detect water leakage at the upper part of the core catcher. In addition, in order to provide a core catcher and a core catcher cover in an existing nuclear reactor, it is considered that a part of the pedestal concrete needs to be cut to secure an installation space.

JP 2009-145135 A

  As a known technique, there is one having a function of cooling and holding a core melt by a core catcher in a core melting accident while maintaining a water leak detection function required for a drain sump by providing a water leak inspection floor. However, there are concerns such as failure due to earthquakes, loss of function due to floor damage, and lack of reliability due to lack of water leakage detection results. Further, in existing reactors, the space below the reactor containment vessel is narrow and there are interferences, so the floor installed on the core catcher should be as thin as possible and have a small amount of material.

  The embodiment of the present invention has been made in view of the above circumstances, and an object of the present invention is to enable water leak detection using a drain sump even when a core catcher is installed in a nuclear reactor containment vessel.

  In order to achieve the above object, a nuclear reactor facility according to an embodiment includes a nuclear reactor pressure vessel that accommodates a core, a nuclear reactor containment vessel that contains the nuclear reactor pressure vessel, and the atomic reactor within the nuclear reactor containment vessel. A core catcher that is disposed below the reactor pressure vessel and holds the core melt in the event of a core melting accident, and is disposed below the core catcher in the reactor containment vessel and normally leaks water from the reactor pressure vessel. A drain sump to be stored; a core catcher cover which is disposed so as to cover the upper side of the core catcher below the reactor pressure vessel and has a through-hole penetrating vertically; the cover through-hole and the drain sump; And a drain pipe communicating therewith.

  According to the embodiment of the present invention, water leakage detection using a drain sump can be performed even when a core catcher is installed in a nuclear reactor containment vessel.

1 is an overall vertical sectional view of a nuclear reactor facility according to a first embodiment of the present invention. FIG. 2 is a vertical sectional view of main parts of the nuclear reactor facility of FIG. 1. FIG. 3 is a partial perspective view of the drain pipe of FIG. 2. It is a perspective view of the partial drainage pipe member which comprises the drainage pipe of the nuclear reactor installation which concerns on the 2nd Embodiment of this invention. It is a fragmentary sectional perspective view of the drain pipe of the nuclear reactor installation which concerns on the 3rd Embodiment of this invention. It is a fragmentary sectional perspective view of the drain pipe of the nuclear reactor equipment which concerns on the 4th Embodiment of this invention.

  Hereinafter, an embodiment of a nuclear reactor facility according to the present invention will be described with reference to the drawings. Here, the same or similar parts are denoted by common reference numerals, and redundant description is omitted.

[First Embodiment]
FIG. 1 is an overall vertical sectional view of a nuclear reactor facility according to a first embodiment of the present invention. FIG. 2 is a sectional view of a principal part of the nuclear reactor facility of FIG. FIG. 3 is a partial perspective view of the drain pipe of FIG.

  The reactor facility according to this embodiment is a boiling water nuclear power plant, and a reactor core 11 is accommodated in a reactor pressure vessel 10. The reactor pressure vessel 10 is disposed in the reactor containment vessel 12. The internal space of the reactor containment vessel 12 includes a dry well 13 that accommodates the reactor pressure vessel 10 and a wet well 15 that accommodates the pressure suppression pool 14. The dry well 13 and the pressure suppression pool 14 communicate with each other through a vent pipe 16.

  The reactor pressure vessel 10 is supported by a cylindrical pedestal 17 made of concrete and having an open top. A pedestal bottom 18 made of concrete is formed at the bottom of the pedestal 17. In the dry well 13, a space surrounded by the pedestal 17 and below the reactor pressure vessel 10 and above the pedestal bottom 18 is referred to as a pedestal space 19. A wet well 15 is formed around the pedestal 17.

  A part of the pedestal bottom 18 is dug to form a drain sump 20. In the drain sump 20, a detector for detecting water leakage (not shown) is arranged.

  A core catcher 21 is disposed on the pedestal bottom 18. A core catcher cover 22 is disposed so as to cover the upper surface of the core catcher 21.

  In the event of an accident, a water injection pipe 23 for supplying cooling water from outside the reactor containment vessel 12 to above the core catcher cover 22 is provided, and a water injection valve 24 is provided in the pedestal space 19 in the middle of the water injection pipe 23. .

  The core catcher 21 has a structure that can hold and cool the core melt falling through the bottom of the reactor pressure vessel 10 in the event of a core melting accident. The core catcher 21 is made of a heat-resistant material that is not melted by the heat of the core melt. The core catcher 21 is formed at the core melt receiver 30 that opens upward, and below and outside the core melt receiver 30, and cooling water And a flowing cooling water channel 31. The upper surface of the core melt receiving part 30 has a low center and is inclined so as to increase toward the outer periphery. The outer peripheral wall 32 of the core catcher 21 has a cylindrical shape extending along the inner periphery of the pedestal 17.

  The cooling water (including water vapor) in the cooling water flow path 31 descends from the outer peripheral portion 33 along the outer peripheral wall 32 of the core catcher 21 as shown by an arrow A in FIG. To the bottom center 35, rising from the bottom center 35, and rising toward the outside along the inclined surface of the core melt receiver 30. Furthermore, it rises along the outer periphery of the core melt receiving part 30, rises to the upper end of the core catcher 21, and then descends the outer peripheral part 33 again.

  A drain pipe 40 extending in the vertical direction is disposed at the center in the horizontal direction of the core catcher 21. The lower end of the drain pipe 40 is supported by the pedestal bottom 18. The core catcher cover 22 has a disk shape extending horizontally. The load of the core catcher cover 22 is supported by the upper end of the outer peripheral wall 32 of the core catcher 21, and a part of the load is also supported by the drain pipe 40.

  A cover through hole 43 extending vertically is formed at a portion where the core catcher cover 22 contacts the upper end of the drain pipe 40, and the lower end of the cover through hole 43 communicates with the upper end of the drain pipe 40. The drain pipe 40 penetrates the horizontal center of the core catcher 21 in the vertical direction. Near the lower end of the drain pipe 40, a lower end flow hole 44 is formed on the side surface, and a bottom channel 45 reaching the drain sump 20 is formed below the bottom of the core catcher 21. That is, a drainage path is formed from above the core catcher cover 22 through the cover through hole 43, through the drainage pipe 40, and further through the bottom channel 45 to the drain sump 20.

As shown in FIG. 3, the drain pipe 40 has a double pipe structure, and includes an inner pipe 41 and a cladding pipe 42 that is disposed outside the inner pipe 41 and reinforces its strength. The inner tube 41 is made of a high melting point ceramic such as ZrO ₂ or Al ₂ O ₃ , for example. The cladding tube 42 is made of a metal such as stainless steel or carbon steel. The drain pipe 40 may have an elliptical shape, a rectangular shape, or the like in addition to a circle. A flow path 46 is formed in the inner tube 41.

  As another example of the structure of the drain pipe 40, the inner pipe 41 may be made of a metal such as stainless steel or carbon steel, and the cladding pipe 42 may be made of a high melting point ceramic. Further, even if the drain pipe 40 does not have a double pipe structure, it may be a pipe made of a homogeneous material as long as the heat resistance and the structural strength are sufficient.

If the configuration of the present embodiment is used, even when the core catcher 21 is installed in a nuclear reactor in which the drain sump 20 is present in the concrete of the pedestal bottom 18 existing on the floor of the reactor containment vessel 12, as in the existing nuclear reactor, During normal operation, water leakage can be discharged to the drain sump 20. In addition, by appropriately designing the inner diameter of the drain pipe 40, the core melt can be solidified in the process of flowing through the flow path 46 in the drain pipe 40 when the core melt has infiltrated in a severe accident. In addition, when the drain pipe 40 is made of ZrO ₂ , even if it is in direct contact with the hot core melt at the time of a severe accident, it is not easily eroded, so the drain pipe 40 breaks and the core melt flows from the damaged part. , Has the effect of preventing discharge to the drain sump 20. Furthermore, the structural strength of the core catcher 21 and the core catcher cover 22 can be increased by using the drain pipe 40 as a support.

  As shown in FIG. 2, a plurality of struts 70 are arranged between the upper surface of the core melt receiver 30 and the lower surface of the core catcher cover 22. The strut 70 is made of a heat-resistant material that is not melted by the heat of the core melt in the event of a core melting accident. The column 70 supports a part of the load of the core catcher cover 22 and transmits the load to the core melt receiver 30. Thereby, the core catcher cover 22 is supported more reliably.

  Note that a neutron absorber (not shown) may be applied to the drain pipe 40, or a neutron absorber may be mixed into the inner tube 41 or the cladding tube 42 of the drain tube 40. Thereby, after the core melt is held by the core catcher 21, an effect of preventing the recriticality of the nuclear fuel component which is feared to be generated can be obtained.

  In the example shown in FIGS. 1 and 2, the drain pipe 40 is disposed approximately at the center in the horizontal direction of the core catcher 21. However, the drain pipe 40 may be disposed near the outer periphery of the core catcher 21.

[Second Embodiment]
FIG. 4 is a perspective view of a partial drainage pipe member constituting a drainage pipe of a nuclear reactor facility according to the second embodiment of the present invention.

  In the second embodiment, the drain pipe 40 (see FIG. 2) is configured by connecting a plurality of partial drain pipe members 50 divided in the longitudinal direction. Other configurations are the same as those of the first embodiment.

  As shown in FIG. 4, a male screw 51 is formed at the first end (upper end) in the axial direction of the partial drainage pipe member 50, and at the second end (lower end) opposite to the first end. A female screw 52 is formed. By draining the male screw 51 and the female screw 52 of the plurality of partial drainage pipe members 50 to each other, the drainage pipe 40 similar to the drainage pipe 40 of the first embodiment is formed. Each partial drainage pipe member 50 may have a double pipe structure similar to the drainage pipe 40 in the first embodiment.

  As a modification of this embodiment, instead of a structure in which the male screw 51 and the female screw 52 are screwed together, a structure in which the convex portion and the concave portion are fitted to each other is also possible. That is, a convex portion protruding in the axial direction is provided at the first end portion in the axial direction of the partial drainage pipe member 50, and a concave portion recessed in the axial direction is provided at the second end portion in the axial direction of the partial drainage pipe member 50. Thus, these convex portions and concave portions may be fitted to each other.

  Further, as the partial drainage pipe member 50, an elbow type or T-shaped partial drainage pipe member (not shown) can be used in addition to the straight pipe structure shown in FIG. Various structures, such as a part, a merge part, and a bent part, can be realized.

  If the configuration of the present embodiment is used, similarly to the first embodiment, it is possible to discharge water leakage to the drain sump 20 during normal operation and to prevent the molten core from flowing into the drain sump 20 during severe accidents. Moreover, the drain sump 20 can be provided with a water leakage detection function as before.

  Moreover, even if the carrying-in space of an existing nuclear reactor etc. is restricted, the components which comprise the drainage pipe 40 can be easily carried in manually by the drainage pipe 40 installation position. As a result, the construction period at the site can be shortened. In addition, by using an L-shaped partial drainage pipe member in part, avoiding interference and by using an elbow-type partial drainage pipe member, the drainage pipe 40 is guided and connected to an appropriate connection destination. be able to. In addition, when a T-shaped partial drain pipe member is used and connected to another partial drain pipe member, there is an effect of increasing the structural strength.

[Third Embodiment]
FIG. 5 is a partial cross-sectional perspective view of a drain pipe of a nuclear reactor facility according to a third embodiment of the present invention. This embodiment is a modification of the first embodiment, and a net 60 made of a heat-resistant material is fixed midway in the flow path 46 of the drain pipe 40. A plurality of obstacle members 61 made of a heat-resistant material are disposed between the upper end in the flow path 46 of the drain pipe 40 and the net 60. The obstruction member 61 is, for example, gravel and has a size that does not pass through the net 60. The mesh 60 and the obstruction member 61 have heat resistance to such an extent that they do not melt due to the heat of the core melt when in contact with the core melt at the time of the core melting accident.

  According to the configuration of the present embodiment, when the core melt enters from the flow path 46 inlet of the drain pipe 40 in a severe accident, since the pressure loss is large, the advance speed of the core melt is slow. Therefore, it has the effect of shortening the distance required for the core melt to solidify. In particular, since the solidification distance when the core melt enters from the upper entrance of the flow path 46 of the drain pipe 40 can be shortened, an effect of reducing the risk of the core melt flowing out to the drain sump 20 can be obtained.

[Fourth Embodiment]
FIG. 6 is a partial cross-sectional perspective view of a drain pipe of a nuclear reactor facility according to a fourth embodiment of the present invention. This embodiment is a modification of the first embodiment, and a reduced flow portion 65 is formed in the lower part of the drain pipe 40. The flow path of the flow reducing portion 65 has a smaller flow area than the flow path 46 above the flow reducing portion 65, and the flow path area is rapidly reduced at the upper end of the reduced flow portion 65. The contracted portion 65 is located in the bottom center 35 of the core catcher 21 shown in FIG.

  In addition, it is good also as a structure where the metal rib (not shown) which protrudes toward an inner flow path was engage | inserted in the inner surface of the flow reduction part 65, for example. Cooling at the contracted flow portion 65 is promoted by this rib.

  According to this embodiment, when the core melt flows into the contracted portion 65 in the flow path 46 in the drain pipe 40 at the time of a severe accident, the pressure loss here is large, so that the infiltration rate is reduced. be able to. Further, since cooling water exists in the bottom center 35 (FIG. 2) at the time of the core melting accident, the heat removal performance with respect to the core melt that has entered the reduced flow portion 65 is improved, and the distance required for the core melt to solidify is increased. Has the effect of shortening. Furthermore, by providing a heat transfer promoting structure such as a metal rib around the contracted flow portion 65, the cooling effect can be enhanced and the solidification distance of the core melt can be shortened. Thereby, the effect of reducing the risk that the core melt flows into the drain sump 20 is obtained.

[Other Embodiments]
The features of the above embodiments can be combined in various ways. For example, the structure in which the plurality of partial drainage pipe members 50 described as the second embodiment are joined to each other in the longitudinal direction can also be adopted in the configuration of the third or fourth embodiment. Further, as the structure of the drain pipe 40, the upstream side may have the structure of the third embodiment, and the downstream side may have the structure of the fourth embodiment.

  As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 10 ... Reactor pressure vessel, 11 ... Core, 12 ... Reactor containment vessel, 13 ... Dry well, 14 ... Pressure suppression pool, 15 ... Wet well, 16 ... Vent pipe, 17 ... Pedestal, 18 ... Pedestal bottom, 19 ... Pedestal space, 20 ... Drain sump, 21 ... Core catcher, 22 ... Core catcher cover, 23 ... Water injection pipe, 24 ... Water injection valve, 30 ... Core melt receiver, 31 ... Cooling water flow path, 32 ... Outer wall, 33 ... Outer periphery 34, bottom part, 35 ... bottom center, 40 ... drain pipe, 41 ... inner pipe, 42 ... cladding pipe, 43 ... cover through-hole, 44 ... bottom end flow hole, 45 ... bottom channel, 46 ... channel, 50 ... Partial drainage pipe member, 51 ... Male screw, 52 ... Female screw, 60 ... Net, 61 ... Obstruction member, 65 ... Constriction part, 70 ... Post

Claims (5)

A reactor pressure vessel containing the reactor core;
A reactor containment vessel for housing the reactor pressure vessel;
A core catcher that is disposed under the reactor pressure vessel in the reactor containment vessel and holds the core melt in the event of a core melting accident;
A drain sump that is disposed below the core catcher in the reactor containment vessel and normally collects water leaked from the reactor pressure vessel;
A core catcher cover which is arranged so as to cover the upper side of the core catcher below the reactor pressure vessel and has a cover through hole penetrating in the vertical direction;
A drain pipe communicating the cover through hole and the drain sump;
A nuclear reactor facility characterized by comprising:   The drain pipe includes an inner pipe and a cladding pipe that covers the outer side of the inner pipe, and one of the inner pipe and the cladding pipe is made of ceramics, and the other is made of metal. The nuclear reactor facility according to claim 1 or 2, wherein:   The nuclear reactor equipment according to claim 1, further comprising a plurality of obstacle members made of a heat-resistant material and disposed in the drain pipe.   The atom according to any one of claims 1 to 3, wherein the drain pipe includes a contracted portion in which a flow path is reduced in the middle from the cover through hole to the drain sump. Furnace equipment.   The nuclear reactor equipment according to any one of claims 1 to 4, wherein the drain pipe contains a neutron absorber.

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