CA2816494C

CA2816494C - Nuclear power plant

Info

Publication number: CA2816494C
Application number: CA2816494A
Authority: CA
Inventors: Kazuaki Kito; Masao Chaki; Masaya Ohtsuka; Kenichi Katono; Akinori Tamura
Original assignee: Hitachi GE Nuclear Energy Ltd
Current assignee: Hitachi GE Nuclear Energy Ltd
Priority date: 2012-05-29
Filing date: 2013-05-24
Publication date: 2016-03-15
Anticipated expiration: 2033-05-24
Also published as: CA2816494A1; JP2013246117A

Abstract

A suppression chamber provided with vent pipes whose upper ends are positioned above a core in a reactor pressure vessel (RPV) is formed in a primary containment vessel (PCV) surrounding the RPV. A steam discharge connection pipe having an open/close valve is connected to a core shroud surrounding the core in the RPV above the core. A feed water connection pipe having an open/close valve is communicated with a downcommer in the RPV. The steam discharge connection pipe and the feed water connection pipe are opened into an upper drywell in the PCV. After an occurrence of a severe accident accompanied by a station blackout, cooling water is collected in the PCV, and the cooling water is supplied to the core through the feed water connection pipe, and the cooling water discharged from the core and including steam is discharged to the upper drywell by the steam discharge connection pipe.

Description

TITLE OF INVENTION
NUCLEAR POWER PLANT
BACKGROUND OF THE INVENTION
[Technical Field]
The present invention relates to a nuclear power plant and more particular to a nuclear power plant suitable for application to a boiling water nuclear power plant.
[Background Art]
A nuclear power plant, for example, a boiling water nuclear power plant needs to remove decay heat generated in a core even after an operation stop of the boiling water nuclear power plant. Generally, a part of water in a reactor pressure vessel, and a suppression pool installed at a lower portion in a primary containment vessel is pulled out from the reactor pressure vessel and the suppression pool. The pulled-out water is cooled by seawater in a heat exchanger, and the cooled water is returned to the reactor pressure vessel and the suppression pool. As a result, the aforementioned generated decay heat is removed. As necessary, water is pulled out from the suppression pool and a condensate storage tank installed outside the primary containment vessel, and the water is

- 2 -pressurized by a pump and is supplied to the reactor pressure vessel. Thus, the core can be always maintained in the water-immersed state (core flooding).
Such a cooling system uses a motor driven pump to pull out water from the reactor pressure vessel, suppression pool, and condensate storage tank and draw up seawater for cooling. Therefore, the operation of the cooling system needs a power source. When an abnormal event such as a stoppage of the power transmission to the reactor from the outside occurs, the emergency generator installed in the nuclear power plant starts and operates these cooling systems.
On the other hand, a core cooling system that can achieve the core flooding and removal of the decay heat in the event of a stoppage of the power transmission to the nuclear power plant from the outside is proposed in Japanese Patent Laid-open No. 2011-137709.
The nuclear power plant described in FIG. 1 of Japanese Patent Laid-open No. 2011-137709 includes a primary containment vessel and a reactor pressure vessel disposed in the primary containment vessel. A
drywell and a suppression chamber are formed in the primary containment vessel. The reactor pressure vessel is disposed in the drywell and the drywell and suppression chamber are separated from each other. The

- 3 -suppression chamber is disposed in a lower portion of the primary containment vessel. The drywell includes an upper drywell and a lower drywell. An opening formed in an upper end of a vent pipe is communicated with the upper drywell and positioned above an upper end of the core in the reactor pressure vessel. A lower end portion of the vent pipe is soaked in cooling water filled in a suppression pool formed in a bottom portion of the suppression chamber. A main steam pipe for introducing steam to a turbine is connected to the reactor pressure vessel and a steam discharge pipe with an equalizing valve is connected to the main steam pipe.
Generally, the equalizing valve installed in the steam discharge pipe is closed. An equalizing core cooling system pipe to which an automatic opening valve is installed is connected to the reactor pressure vessel at a lower position than the upper end of the vent pipe soaked in the cooling water in the suppression pool.
Generally, the automatic opening valve is closed.
A cooling water pool filled with cooling water is disposed outside the primary containment vessel and is installed on a top of the primary containment vessel. A
heat exchanger is installed in the cooling water pool and is disposed in the cooling water of the cooling water pool. A steam sucking pipe opened to the upper -

- 4 -drywell is connected to the heat exchanger and a drain pipe connected to the reactor pressure vessel is also connected to the heat exchanger.
When a pipe (for example, the main steam pipe) connected to the reactor pressure vessel is broken in the primary containment vessel, the equalizing valve and automatic opening valve are opened, and water is injected into the primary containment vessel up to the position of the upper end of the vent pipe in the primary containment vessel. The cooling water in the reactor pressure vessel is heated by the decay heat generated in the core and turns into steam. The steam is discharged to the upper drywell through the main steam pipe and steam discharge pipe. On the other hand, the cooling water collected up to the upper end of the vent pipe in the primary containment vessel flows into the reactor pressure vessel through the equalizing core cooling system pipe and cools the core. The steam generated in the reactor pressure vessel is discharged to the upper drywell and the cooling water in the primary containment vessel is supplied into the reactor pressure vessel, so that the core flooding can be maintained.
The steam discharged from the reactor pressure vessel to the upper drywell is introduced to the heat . - 5 -exchanger installed in the cooling water pool through the steam sucking pipe and is cooled and condensed by the cooling water in the cooling water pool. The condensed water generated by this condensation is returned into the reactor pressure vessel through the drain pipe. The decay heat generated in the core, finally, is discharged into the outside environment due to boiling of the cooling water in the cooling water pool.
As a method of realizing the core flooding, as described in Japanese Patent Laid-open No. 2011-58866, there is a method available of raising the top of the suppression chamber than the upper end position of the core in the reactor pressure vessel, installing a gravity driven cooling system pool on the top of the suppression pool, and injecting the cooling water in the gravity driven cooling system pool into the reactor pressure vessel when a severe accident occurs. In Japanese Patent Laid-open No. 2011-58866, the top of the suppression chamber is higher than the upper end position of the core in the reactor pressure vessel, so that the cooling water is easily collected in a drywell existing between the suppression chamber and the reactor pressure vessel.
[Citation List]

-[Patent Literature]
[Patent Literature 1] Japanese Patent Laid-open No.

[Patent Literature 2] Japanese Patent Laid-open No.

SUMMARY OF THE INVENTION
[Technical Problem]
Since the cooling system described in Japanese Patent Laid-open No. 2011-137709 includes the steam discharge pipe connected to the main steam pipe with the equalizing valve, the equalizing core cooling system pipe connected to the reactor pressure vessel and having the automatic opening valve, the steam sucking pipe opened to the upper drywell and connected to the heat exchanger in the cooling water pool, and the drain pipe connected to the reactor pressure vessel and connected to the heat exchanger, even if a loss-of-coolant accident occurs, as described above, the core is covered with water, and the fuel assembly in the core can be cooled, and the decay heat generated in the core can be discharged from the cooling water pool into the outside environment.
However, even if a severe accident should occur and furthermore, a station blackout should occur, the cooling ability of the fuel assembly in the core is desired to increase.
An object of the present invention is to provide a nuclear power plant capable of increasing cooling ability of fuel assemblies in a core even if an accident should occur.
[Solution to Problem]
Certain exemplary embodiments can provide a nuclear power plant comprising: a reactor pressure vessel having a core loaded with a plurality of fuel assemblies and a core shroud surrounding said core and forming a circular cooling water path between said reactor pressure vessel and said core shroud; a primary containment vessel surrounding said reactor pressure vessel and forming internally a drywell in which said reactor pressure vessel is disposed, and a suppression chamber separated from said drywell; a liquid surface forming member having an upper end disposed above an upper end of said core installed in said primary containment vessel for forming a liquid surface of cooling water collected in said drywell formed in said primary containment vessel above said core; a steam discharge pipe; and a cooling water feed pipe, wherein one end portion of said steam discharge pipe is connected to said core shroud in said reactor pressure vessel and is in communication with a region in said core shroud above said core, a first open/close valve is mounted to said steam discharge pipe, and another end portion of said steam discharge pipe penetrates said reactor pressure vessel and opens in said drywell formed in said primary containment vessel outside said reactor pressure vessel; and wherein one end portion of said cooling water feed pipe is connected to said reactor pressure vessel and is in communication with said circular cooling water path, another end portion of said cooling water feed pipe opens in said drywell formed in said primary containment vessel, said one end portion and said another end portion of said cooling water feed pipe are positioned below an upper end of said liquid surface forming member, and a second open/close valve is mounted to the cooling water feed pipe.
Since the steam discharge pipe where the one end portion thereof is connected to the core shroud in the reactor pressure vessel and is communicated with the region in the core shroud above the core, and the another end portion penetrates the reactor pressure -vessel and opens in the primary containment vessel outside the reactor pressure vessel, and the cooling water supply pipe where the one end portion thereof is connected to the reactor pressure vessel and is communicated with the tubular cooling water path, the another end portion opens in the primary containment vessel, and the one end portion and the another end portion are positioned below the upper end of the liquid surface forming member are included, even if an accident should occur, the cooling water collected in the primary containment vessel is supplied to the core through the cooling water feed pipe with the second open/close valve opened at the time of the accident and the circular cooling water path in the reactor pressure vessel and cools the fuel assemblies in the core. The cooling water heated in the core is discharged from the region in the core shroud above the core, and from the steam discharge pipe with the first open/close valve opened at the time of the accident into the primary containment vessel outside the reactor pressure vessel.
The flow rate of the cooling water supplied from the circular cooling water path into the core can be increased due to the installation of the aforementioned cooling water feed pipe and steam discharge pipe and the cooling ability of the fuel assemblies in the core -=

can be improved.
[Advantageous Effect of the Invention]
According to the present invention, even if an accident should occur, the cooling ability of the fuel assemblies in the core can be increased.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a structural diagram showing a nuclear power plant according to embodiment 1, which is a preferable embodiment of the present invention.
FIG. 2 is a structural diagram showing a nuclear power plant according to embodiment 2, which is another preferable embodiment of the present invention.
FIG. 3 is a structural diagram showing a nuclear power plant according to embodiment 3, which is other preferable embodiment of the present invention.
FIG. 4 is a structural diagram showing a nuclear power plant according to embodiment 4, which is other preferable embodiment of the present invention.
FIG. 5 is a structural diagram showing a nuclear power plant according to embodiment 5, which is other preferable embodiment of the present invention.
FIG. 6 is a structural diagram showing a nuclear power plant according to embodiment 6, which is other preferable embodiment of the present invention.

-FIG. 7 is a structural diagram showing a nuclear power plant according to embodiment 7, which is other preferable embodiment of the present invention.
FIG. 8 is a structural diagram showing a nuclear power plant according to embodiment 8, which is other preferable embodiment of the present invention.
FIG. 9 is a structural diagram showing a nuclear power plant according to embodiment 9, which is other preferable embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The embodiments of the present invention will be explained below.
[Embodiment 1]
A nuclear power plant according to embodiment 1 which is a preferable embodiment of the present invention will be explained by referring to FIG. 1. The nuclear power plant of embodiment 1 is a boiling water nuclear power plant.
A boiling water nuclear power plant 1 of the present embodiment is provided with a reactor pressure vessel 2, a primary containment vessel 6, a cooling pool 13, a heat exchanger 15, a steam discharge connection pipe 20, and a feed water connection pipe (a cooling water feed pipe) 22. A core 3 loading a plurality of fuel assemblies (not shown) is disposed in the reactor pressure vessel 2. A cylindrical core shroud 4 enclosing the core 3 is installed in the reactor pressure vessel 2. A circular downcommer (a circular cooling water path) 5 is formed between the core shroud 4 and the reactor pressure vessel 2.
A drywell and a suppression chamber 9 are formed in the primary containment vessel 6 and the drywell and the suppression chamber 9 are separated from each other.
The reactor pressure vessel 2 is disposed in the drywell. The drywell includes an upper drywell 7 and a lower drywell 8. The lower drywell 8 is formed below the reactor pressure vessel 2 and is surrounded by the suppression chamber 9. A suppression pool 10 filled with cooling water is formed in the suppression chamber 9. A plurality of vent pipes 11 penetrate the top of the suppression chamber 9, are mounted to this top and are extended from the upper drywell 7 into the cooling water in the suppression pool 10. An opening formed in an upper end of each of the vent pipes 11 is opened to the upper drywell 7. The lower portion of each of the vent pipes 11 is soaked in the cooling water in the suppression pool 10 and steam discharge outlets 12 formed in each of the vent pipes 11 is disposed in the cooling water in the suppression pool 10. The opening -formed in the upper end of each of the vent pipes 11 is disposed above the upper end of the core 3. A water injection pipe 37 communicated with the upper drywell 7 is connected to the primary containment vessel 6. An open/close valve 38 is installed in the water injection pipe 37.
A main steam pipe 35 is connected to the reactor pressure vessel 2, penetrates the primary containment vessel 6 and is connected to a turbine (not shown) coupled with a generator (not shown) installed in a turbine building (not shown). Isolation valves 36A and 36B are installed in the main steam pipe 35 inside and outside the primary containment vessel 6.
The steam discharge connection pipe 20 penetrates the reactor pressure vessel 2, is disposed in the reactor pressure vessel 2 and is connected to the core shroud 4 at a position above the upper end of the core 3 by crossing the downcommer 5. The steam discharge connection pipe 20 is joined to the reactor pressure vessel 2 by welding and the interval between the steam discharge connection pipe 20 and the reactor pressure vessel 2 is sealed by the welding. An opening formed in one end of the steam discharge connection pipe 20 existing in the reactor pressure vessel 2 is opened in the region in the core shroud 4 above the core 3. The opening (steam discharge outlet) at the other end of the steam discharge connection pipe 20 is connected to the upper drywell 7. An open/close valve 21 is installed in the steam discharge connection pipe 20 outside the reactor pressure vessel 2.
One end of the feed water connection pipe 22 is connected to the reactor pressure vessel 2 and an opening formed at the one end of the feed water connection pipe 22 is communicated with the downcommer

5. An opening at the other end of the feed water connection pipe 22 is communicated with the upper drywell 7. An open/close valve 23 is installed in the feed water connection pipe 22. The connection position of the one end of the feed water connection pipe 22 to the reactor pressure vessel 2 and the opening position at the other end of the feed water connection pipe 22 are positioned below the opening formed in the upper end of the vent pipes 11 and above the upper end of the core 3. In the present embodiment, the opening position at the other end of the steam discharge connection pipe 20 is positioned below the upper end of the vent pipes 11. The connection position of the steam discharge connection pipe 20 to the core shroud 4 may be disposed above the upper end of the vent pipes 11 in the state that the opening position at the other end of the steam discharge connection pipe 20 is positioned below the upper end of the vent pipes 11.
In the present embodiment, the connection position of the steam discharge connection pipe 20 to the core shroud 4 is disposed at the same position as the connection position of the feed water connection pipe 22 to the reactor pressure vessel 2 in the axial direction of the reactor pressure vessel 2. However, the connection position of the steam discharge connection pipe 20 to the core shroud 4 may be disposed above the connection position of the feed water connection pipe 22 to the reactor pressure vessel 2.
The cooling water pool 13 is installed outside the primary containment vessel 6 in a reactor building (not shown) where the primary containment vessel 6 is installed. Cooling water 14 is filled in the cooling water pool 13. A steam discharge outlet 24 is formed at an upper end portion of the cooling water pool 13. The heat exchanger (stem condenser) 15 is disposed in the cooling water of the cooling water pool 13. A steam supply pipe 16 communicated with the upper drywell 7 above the upper end of the vent pipes 11 and connected to the primary containment vessel 6 is connected to the heat exchanger 15 and is connected to one header portion (referred to as a first header portion) (not shown) of the heat exchanger 15 to which each one end of a plurality of heat exchanger tubes of the heat exchanger 15 is connected. One end of a drain pipe 17 is connected to a bottom of another header portion (referred to as a second header portion) (not shown) of the heat exchanger 15 to which other end of each heat exchanger tube of the heat exchanger 15 is connected.
The drain pipe 17 penetrates the primary containment vessel 6, is disposed in the upper drywell 7 and other end of the drain pipe 17 is connected to the reactor pressure vessel 2. The drain pipe 17 is communicated with the downcommer 5 in the reactor pressure vessel 2.
An open/close valve 18 is installed in the drain pipe 17 in the upper drywell 7. The drain pipe 17 is joined to the primary containment vessel 6 by welding in the penetration and the interval between the drain pipe 17 and the primary containment vessel 6 is sealed. One end portion of a non-condensable gas discharge pipe 19 is connected to an upper end portion of the second header portion of the heat exchanger 15. The non-condensable gas discharge pipe 19 is disposed in the upper drywell 7 while penetrating the primary containment vessel 6, and other end of the non-condensable gas discharge pipe 19 reaches inside the suppression camber 9 and is soaked in the cooling water of the suppression pool 10.

_ The cooling water pool 13, the heat exchanger 15, the steam supply pipe 16, the drain pipe 17, and the non-condensable gas discharge pipe 19 configure a steam condensation apparatus that condenses steam in the upper drywell 7.
Although not shown, isolation valves are respectively installed in the steam supply pipe 16 in the neighborhood of the primary containment vessel 6, the drain pipe 17 inside and outside the primary containment vessel 6 in the neighborhood of the primary containment vessel 6, and furthermore, the non-condensable gas discharge pipe 19 inside and outside the primary containment vessel 6 in the neighborhood of the primary containment vessel 6.
The open/close valves 18, 21, and 3 are closed during normal operation of the boiling water nuclear power plant 1. Steam generated in the core is supplied to the turbine through the main steam pipe 35 during normal operation and rotates the turbine. The generator is rotated by the rotation of the turbine and power is generated. The steam exhausted from the turbine is condensed by a condenser (not shown) and the water obtained by the condensation, as feed water, is supplied to the reactor pressure vessel 2 through a feed water pipe (not shown).

Assume that a very severe accident in which a pipe connected to the reactor pressure vessel 2 is broken during operation of the boiling water nuclear power plant 1 and further a station blackout occurs has occurred. At this time, the open/close valves 18, 21, and 3 are totally opened by electricity supplied from the battery.
The operation of the boiling water nuclear power plant 1 is stopped due to the aforementioned occurrence of the severe accident. By the occurrence of the severe accident, the hot cooling water in the reactor pressure vessel 2 turns into steam and the steam is discharged to the upper drywell 7 through the broken place of the aforementioned pipe. This steam is discharged into the cooling water in the suppression pool 10 from the steam discharge outlet 12 through the vent pipes 11 and is condensed. The rise of the inner pressure of the primary containment vessel 6 is suppressed due to the condensation of the steam.
A part of the steam discharged to the upper drywell 7 through the broken place is introduced into the first header portion of the heat exchanger 15 through the steam supply pipe 16 communicated with the upper drywell 7 and flows into each heat exchanger tube of the heat exchanger 15. The steam is cooled and -condensed in the heat exchanger tubes by the cooling water 14 in the cooling water pool 13. The condensed water generated by the condensation of the steam is discharged from each heat exchanger tube to the second header portion of the heat exchanger 15 and furthermore, is introduced to the downcommer 5 in the reactor pressure vessel 2 through the drain pipe 17. The condensed water introduced into the reactor pressure vessel 2 is introduced to the core 3 and is used to cool the fuel assembles loaded in the core 3.
Non-condensable gas (for example, nitrogen gas) filled in the primary containment vessel 6 flows in the steam supply pipe 16 along with steam and is introduced to the heat exchanger 15. The non-condensable gas is collected at the upper portion in the second header portion of the heat exchanger 15, so that it flows in a non-condensable gas discharge pipe 19 from the second header portion and is discharged into the cooling water of the suppression pool 10 in the suppression chamber 9.
If there exists steam flowing accompanying the non-condensable gas, the steam is condensed by the cooling water of the suppression pool 10. The non-condensable gas discharged into the cooling water in the suppression pool 10 rises in the cooling water and is collected in a wetwell that is space formed above the liquid surface of the cooling water in the suppression pool 10.
After the occurrence of the severe accident, when the hose of a water supply car (not shown) is connected to the water injection pipe 37 and the open/close valve 38 is opened by electricity supplied from the battery, the cooling water supplied from the water supply car is injected into the primary containment vessel 6 through the water injection pipe 37. The water injection is executed until a water surface is formed at the position of the upper end of the vent pipes 11 in the primary containment vessel 6. The water supply up to the predetermined level is executed while monitoring water level measured by a water level gauge (not shown) installed in the primary containment vessel 6. The vent pipes 11 with the upper end positioned above the core 3 are a liquid surface forming member for forming the liquid surface of the cooling water collected in the primary containment vessel 6 above the core 3. The vent pipes 11 which are a liquid surface forming member prevent the cooling water collected in the primary containment vessel 6 from flowing into the suppression chamber 9. By doing this, the liquid surface of the cooling water collected in the primary containment vessel 6 can be formed above the core 3, thus as described later, the core flooding, and the supply of the cooling water to the core 3 through the feed water connection pipe 22 can be executed.
Even after the operation stop of the boiling water nuclear power plant 1 due to the occurrence of the severe accident, the cooling water in the core 3 is heated by heat (decay heat) generated by decay of a nuclear fuel material included in a nuclear fuel assembly loaded in the core 3, and steam is generated.
This steam is discharged from the core 3 into the region in the core shroud 4 above the core 3, and is discharged from the region into the upper drywell 7 outside the reactor pressure vessel 2 through the steam discharge connection pipe 20. While the cooling water is injected from the water injection pipe 37 into the primary containment vessel 6 and the steam discharge outlet of the steam discharge connection pipe 20 is positioned above the liquid surface of the cooling water collected in the primary containment vessel 6, the steam passing through the steam discharge connection pipe 20 is discharged to the upper drywell 7 and is introduced to the heat exchanger 15 through the steam supply pipe 16. And, the steam is cooled and condensed by the cooling water 14 in the cooling water pool 13. The condensed water generated by the condensation is introduced into the downcommer 5 by the drain pipe 17.
The temperature of the cooling water 14 in the cooling water pool 13 rises due to condensation of the steam introduced to the heat exchanger 15 through the steam supply pipe 16. For this reason, a part of the cooling water 14 becomes steam and is discharged into the outside environment from the steam discharge outlet 24 of the cooling water pool 13. The water level of the cooling water 14 in the cooling water pool 13 lowers by to this steam discharge. Cooling water is supplied from the water supply car to the cooling water pool 13 as well to prevent this water level reduction.
When the water injection into the primary containment vessel 6 by the water injection pipe 37 is performed continuously, the steam discharge outlet of the steam discharge connection pipe 20 is soon submerged into the cooling water collected in the primary containment vessel 6. After the steam discharge outlet of the steam discharge connection pipe 20 is submerged into the cooling water, the steam discharged from the inside of the core shroud 4 through the steam discharge connection pipe 20 is discharged into the cooling water collected in the primary containment vessel 6 and is condensed by the cooling water.

When the liquid surface of the cooling water collected in the primary containment vessel 6 by water injection becomes higher than the height of the opening at the other end on the side of the upper drywell 7 of the feed water connection pipe 22, the cooling water is supplied to the downcommer 5 in the reactor pressure vessel 2 through the feed water connection pipe 22. The cooling water supplied to the downcommer 5 is introduced to the core 3 and cools the fuel assemblies in the core 3. Since the pressure loss of the steam discharge connection pipe 20 is very small, the water level of the cooling water in the reactor pressure vessel 2 is almost equal to the water level of the injected cooling water in the primary containment vessel 6 or becomes higher than the water level of the injected cooling water in the primary containment vessel 6 by the water level pushing-up effect by the steam generated by the core 3. Eventually, the water level in the reactor pressure vessel 2 rises up to the position of the upper end of the vent pipes 11, so that the core flooding can be maintained.
Further, since the connection position of one end of the feed water connection pipe 22 with the reactor pressure vessel 2 is positioned above the upper end of the core 3, even if a severe accident occurs, the water -level in the reactor pressure vessel 5 is held above the connection position of one end of the feed water connection pipe 22 with the reactor pressure vessel 2, that is, above the upper end of the core 3. For this reason, the connection position of the one end of the feed water connection pipe 22 with the reactor pressure vessel 2 may be disposed below the upper end of the core 3, though it is desirable that it is disposed above the upper end of the core 3. The opened end to the upper drywell 7 which is the other end of the feed water connection pipe 22 may be disposed below the upper end of the core 3.
The steam discharge connection pipe 20 is connected to the core shroud 4, thus in the present embodiment, the flow rate of the cooling water to be supplied to the core 3 can be increased as explained below.
The cooling water in the core 3 is heated by the decay heat generated in the fuel assemblies loaded in the core 3 and the temperature of the cooling water rises. Further, part of the cooling water is boiled and turns into steam. Therefore, the density of the cooling water in the core shroud 4 which is high in temperature and includes steam becomes lower than the density of the low-temperature cooling water in the downcommer 5 supplied from the feed water connection pipe 22. In =

such a state, the cooling water in the downcommer 5 supplied from the feed water connection pipe 22 goes down and the cooling water in the core shroud 4 goes up, so that the flow of cooling water passing through the downcommer 5, the core 3, and the region in the core shroud 4 above the core 3 in this order from the feed water connection pipe 22 and moving to the steam discharge connection pipe 20 is formed. Furthermore, the cooling water (warm water) whose temperature has risen by being heated in the core 3 and in which the steam generated because part of the cooling water was boiled is included, can be flowed out into the region where the cooling water in the primary containment vessel 6 is collected through the steam discharge connection pipe 20. In consequence, in the present embodiment, after the occurrence of the severe accident, the cooling water quantity supplied to the core 3 can be increased as compared with the case in Japanese Patent Application 2011-137709 that only steam is discharged from the steam discharge pipe with the equalizing valve which is connected to the main steam pipe, and the fuel assemblies in the core 3 can be cooled earlier and surely.
Furthermore, the cooling water which went up in the core 3 and has been discharged into the region in the core shroud 4 above the core 3 is discharged into the region where the cooling water in the primary containment vessel 6 is collected from the steam discharge connection pipe 20, so that the cooling water surely passes through the core 3 and even when the inside diameter of the steam discharge connection pipe 20 is small, the fuel assemblies in the core 3 can be easily cooled.
To use the aforementioned effect at its maximum, the height of the connection portion of the steam discharge connection pipe 20 with the core shroud 4 should be equal to the height of the connection portion of the feed water connection pipe 22 with the reactor pressure vessel 2 or should be made higher than the height of the latter connection portion.
The heat quantity held by cooling water including steam discharged into the region where the cooling water in the primary containment vessel 6 is collected through the steam discharge connection pipe 20 from the inside of the core shroud 4 is transmitted to the cooling water collected in the primary containment vessel 6 because the discharged cooling water is cooled by the cooling water collected in the primary containment vessel 6 and furthermore the steam included in the discharged cooling water is cooled by the cooling water collected in the primary containment vessel 6. Therefore, the discharge of the cooling water including the steam from the steam discharge connection pipe 20 is continued, thus the temperature of the cooling water collected in the primary containment vessel 6 rises slowly. The cooling water whose temperature was raised does not boil but generates steam. This steam is discharged to the upper drywell 7 above the liquid surface of the cooling water collected the primary containment vessel 6, and as described above, is supplied to the heat exchanger 15 through the steam supply pipe 16. The steam in the heat exchanger tubes of the heat exchanger 15 is condensed by the cooling water 14 in the cooling water pool 13. The condensed water generated by the condensation is returned to the downcommer 5 in the reactor pressure vessel 2 through the drain pipe 17. This condensed water is introduced to the core 3 together with the cooling water supplied by the feed water connection pipe 22 and is used to cool the fuel assemblies in the core 3.
The temperature of the cooling water (the cooling water collected in the primary containment vessel 6) supplied from the feed water connection pipe 22 is low at an early stage of start of the supply to the reactor , pressure vessel 2 by the feed water connection pipe 22.
The cooling water collected in the primary containment vessel 6 is heated by the cooling water including steam, that has been discharged from the reactor pressure vessel 2 through the steam discharge connection pipe 20, and the temperature of the cooling water rises in the course of time and finally becomes a saturated temperature. The condensed water discharged from the heat exchanger 15 through the drain pipe 17 to the downcommer 5 becomes slightly lower in temperature than the saturated temperature of the cooling water collected in the primary containment vessel 6 because a design margin is provided for the heat removal quantity at the time of design of the heat exchanger 15.
Therefore, after considerable time elapses from the occurrence of a severe accident and after the temperature of the cooling water collected in the primary containment vessel 6 rises up to the neighborhood of the saturated temperature, the temperature of the condensed water discharged from the heat exchanger 15 becomes lower. In this case, the density of the cooling water in the downcommer 5 with which the condensed water was mixed becomes high and the flow rate of the cooling water supplied to the core 3 is increased, so that the cooling ability of the fuel assemblies is increased.
As described above, the decay heat generated in the fuel assemblies loaded in the core 3 is transmitted to the cooling water 14 in the cooling water pool 13 and boils the cooling water 14. The steam generated by the boiling of the cooling water 14 is discharged into the outside environment through the steam discharge outlet 24, thus the decay heat generated in the fuel assemblies is discharged into the outside environment.
As described above, the cooling water collected in the primary containment vessel 6 evaporates, though the steam generated by the evaporation is condensed by the heat exchanger 15 and becomes condensed water. This condensed water is returned to the core 3 and is discharged into the cooling water collected in the primary containment vessel 6 by the steam discharge connection pipe 20. Therefore, even if the cooling water collected in the primary containment vessel 6 evaporates, the water level of the cooling water in the primary containment vessel 6 is hardly changed.
The boiling water nuclear power plant 1 of the present embodiment includes the steam discharge connection pipe 20 extending outside the reactor pressure vessel 2 connected to the core shroud 4 and the feed water connection pipe 22 connected to the ' reactor pressure vessel 2 and communicated with the downcommer 5, thus even if the aforementioned severe accident accompanied with the station blackout occurs, the core flow rate supplied to the core 3 can be increased and the cooling ability of the fuel assemblies in the core 3 can be enhanced.
Further, since in the present embodiment, the non-condensable gas discharge pipe 19 connected to the second header portion of the heat exchanger 15 is inserted into the suppression chamber 9, the non-condensable gas moves due to the different pressure between the upper drywell 7 and the suppression chamber 9, and when the rate of the non-condensable gas is high, the steam in the upper drywell 7 can be condensed by the heat exchanger 15 while discharging the non-condensable gas into the suppression chamber 9.
[Embodiment 2]
A nuclear power plant according to embodiment 2 which is another preferable embodiment of the present invention will be explained by referring to FIG. 2. The nuclear power plant of embodiment 2 is a boiling water nuclear power plant.
A boiling water nuclear power plant lA of the present embodiment has a structure that in the boiling water nuclear power plant 1 of embodiment 1, the drain pipe 17 are not connected to the reactor pressure vessel 2 but is extended to the bottom of the lower drywell 8. The other structures of the boiling water nuclear power plant lA are the same as those of the boiling water nuclear power plant 1.
In the present embodiment, if the severe accident accompanied with the station blackout described in embodiment I occurs, the steam of the upper drywell 7 is introduced to the heat exchanger 15 by the steam supply pipe 16, similarly to embodiment 1 and is condensed in the heat exchanger tubes of the heat exchanger 15 by the cooling water 14 in the cooling water pool 13. The condensed water generated by the condensation is discharged to the lower drywell 8 through the drain pipe 17.
The present embodiment can obtain each effect generated in embodiment 1. Since the condensed water generated by the heat exchanger 15 is discharged to the lower drywell, in the present embodiment the cooling water can be collected up to the upper end of the vent pipes 11 in a shorter period of time than in embodiment 1 at the time of injection into the primary containment vessel 6 from the water injection pipe 37. This makes the supply of cooling water to the downcommer 5 by the feed water connection pipe 22 start earlier than in ' embodiment 1. Further, in the present embodiment, the installation of the open/close valve 18 onto the drain pipe 17 is unnecessary.
[Embodiment 3]
A nuclear power plant according to embodiment 3 which is another preferable embodiment of the present invention will be explained by referring to FIG. 3. The nuclear power plant of embodiment 3 is a boiling water nuclear power plant.
A boiling water nuclear power plant 1B of the present embodiment has a structure that in the boiling water nuclear power plant 1 of embodiment 1, the primary containment vessel 6 is replaced with a primary containment vessel 6A made of steel and the cooling water pool 13, the heat exchanger 15, the steam supply pipe 16, the drain pipe 17, and the non-condensable gas discharge pipe 19 are eliminated. In a boiling water nuclear power plant including a reactor having small thermal power, the wall surface of the primary containment vessel 6A can be used as a cooling surface instead of the heat exchanger 15 by use of the primary containment vessel 6A made of steel. The other structures of the boiling water nuclear power plant 1B
are the same as those of the boiling water nuclear power plant 1.

In the boiling water nuclear power plant 1B, if the severe accident accompanied with the station blackout described in embodiment I should occur, the steam heat in the upper drywell 7 can be discharged outside the primary containment vessel 6A through the primary containment vessel 6 made of steel. By doing this, the steam condenses on an inner surface of the primary containment vessel 6A. The condensed water generated by the condensation of the steam drops down to the lower drywell 8 and is collected in the lower drywell 8 similarly to embodiment 2.
The present embodiment can obtain each effect generated in embodiment 2. Since the present embodiment can eliminate the steam condensing apparatus that condenses the steam in the upper drywell 7 and that includes the cooling water pool 13, the heat exchanger 15, the steam supply pipe 16, the drain pipe 17, and the non-condensable gas discharge pipe 19, the nuclear power plant can be made more compact than in embodiment 1.
[Embodiment 4]
A nuclear power plant according to embodiment 4 which is another preferable embodiment of the present invention will be explained by referring to FIG. 4. The nuclear power plant of embodiment 4 is a boiling water nuclear power plant.
A boiling water nuclear power plant 1C of the present embodiment has a structure that in the boiling water nuclear power plant 1 of embodiment 1, a gravity-driven water injection system is added and the water injection pipe 37 with the open/close valve 38 is eliminated. Furthermore, the boiling water nuclear power plant 1C forms an operation floor 29 in an upper portion in the primary containment vessel 6 and a plurality of connection paths 30 which are blocked by a rupture valve (not shown) and penetrate through the operation floor 29 are formed in the operation floor 29.
The other structures of the boiling water nuclear power plant 1C are the same as those of the boiling water nuclear power plant 1. The primary containment vessel 6 in the present embodiment is a primary containment vessel made of steel as with the primary containment vessel 6 of embodiment 3.
The gravity-driven water injection system used by the boiling water nuclear power plant 1C includes a dryer separator pool 25 filled with cooling water 26 and a water injection pipe 27 with an open/close valve 28. The dryer separator pool 25 is formed in the operation floor 29, which is disposed above the reactor pressure vessel 2 and is mounted to the inner surface of the primary containment vessel 6. The dryer separator pool 25 filled with the cooling water 26 is disposed above the core 3, concretely, above the reactor pressure vessel 2. The water injection pipe 27 is connected to a bottom of the dryer separator pool 25 and furthermore, is connected to the reactor pressure vessel 2 and is communicated with the downcommer 5. In the dryer separator pool 25, the cooling water quantity necessary to be collected up to the upper end of the vent pipes 11 in the primary containment vessel 6 and the cooling water quantity necessary to be stored up to the upper end position of the vent pipes 11 in the reactor pressure vessel 2 are kept. The operation floor 29 on which the connection path 30 blocked by the rapture valve is formed separates the upper drywell 7 from an operation floor space 31 formed above the operation floor 29 during the normal operation of the boiling water nuclear power plant 1C.
In the present embodiment, if a severe accident accompanied with a station blackout should occur, steam is discharged from a broken place of a pipe connected to the reactor pressure vessel 2 to the upper drywell 7 and the pressure of the upper drywell 7 rises. The rapture valve for blocking each connection path 30 raptures due to the pressure rise of the upper drywell 7 and the steam in the upper drywell 7 is discharged into the operation floor space 31 through each connection path 30. The pressure in the upper drywell 7 lowers by the discharge of the steam into the operation floor space 31. The steam discharged to the upper drywell 7 is discharged and condensed in the cooling water of the suppression pool 10 through the vent pipes 11. Further, part of the steam discharged to the upper drywell 7 is condensed by the heat exchanger 15 in the cooling water pool 13, similarly to embodiment 1 and is supplied to the reactor pressure vessel 2 as condensed water.
At the time of occurrence of the severe accident, the boiling water nuclear power plant 10 is brought to an emergency shutdown and electricity from the battery is supplied to the open/close valves 21, 22, and 28, thus these open/close valves are opened. The cooling water 26 in the dryer separator pool 25 is injected into the downcommer 5 in the reactor pressure vessel 2 through the water injection pipe 27, and the core 3 is flooded, and the fuel assemblies in the core 3 are cooled. The cooling water ascends in the core 3 and cools the fuel assemblies, and then is discharged to the upper drywell 7 outside the reactor pressure vessel 2 through the steam discharge connection pipe 20. Part of the cooling water 26 injected into the downcommer 5 from the dryer separator pool 25 is discharged to the upper drywell 7 through the feed water connection pipe 22. The cooling water discharged from the steam discharge connection pipe 20 and the feed water connection pipe 22 falls on the lower drywell 8 and is collected upward in the primary containment vessel 6 from the bottom of the lower drywell 8. When the liquid surface of the cooling water collected in the primary containment vessel 6 soon reaches the upper end of the vent pipes 11, the cooling water 26 in the dryer separator pool 25 is used up, and the injection of the cooling water 26 from the dryer separator pool 25 into the reactor pressure vessel 2 is stopped. At this time, the liquid surface of the cooling water in the reactor pressure vessel 2 is formed above the core 3 and becomes almost equal to the height of the upper end of the vent pipes 11. In the state that the liquid surface of the cooling water collected in the primary containment vessel 6 has reached the upper end of the vent pipes 11, the cooling water collected in the primary containment vessel 6, similarly to embodiment 1, is supplied to the core 3 through the feed water connection pipe 22 and the downcommer 5 and cools the fuel assemblies in the core 3. The cooling water heated by the decay heat generated by the fuel assemblies and including steam generated in the fuel assemblies, is discharged and cooled in the cooling water collected in the primary containment vessel 6 through the steam discharge connection pipe 20.
The steam condensing apparatus that includes the cooling water pool 13, the heat exchanger 15, the steam supply pipe 16, the drain pipe 17, and the non-condensable gas discharge pipe 19 and condenses the steam in the upper drywell 7 condenses the steam in the upper drywell 7 and supplies the condensed water to the reactor pressure vessel 2, similarly to embodiment 1 in the present embodiment.
The present embodiment can obtain each effect generated in embodiment 3. In the present embodiment, when a severe accident occurs, water can be immediately injected into the reactor pressure vessel 2 by the gravity-driven water injection system, thus the cooling of the fuel assemblies in the core 3 can be executed earlier. Further, since in the present embodiment, the cooling water injected into the reactor pressure vessel 2 by the gravity-driven water injection system is supplied to the core 3 through the downcommer 5 and is discharged outside the reactor pressure vessel 2 through the steam discharge connection pipe 20 and the feed water connection pipe 22, cooling water can be collected in the primary containment vessel 6 while cooling the fuel assemblies in the core 3 by the discharged cooling water.
In the present embodiment, when the primary containment vessel 6 is a primary containment vessel made of concrete, the thermal conductivity is low (the thermal conductivity of concrete is low) when compared with a primary containment vessel made of steel, so that the steam condensing apparatus including the cooling water pool 13, the heat exchanger 15, the steam supply pipe 16, the drain pipe 17, and the non-condensable gas discharge pipe 19, which is used in embodiment 1, needs to be installed.
[Embodiment 5]
A nuclear power plant according to embodiment 5 which is another preferable embodiment of the present invention will be explained by referring to FIG. 5. The nuclear power plant of embodiment 5 is a boiling water nuclear power plant.
A boiling water nuclear power plant 1D of the present embodiment has a structure that in the boiling water nuclear power plant 1C of embodiment 4, the water injection pipe 27 of the gravity-driven water injection system is not connected to the reactor pressure vessel 2 but is extended to the bottom of the lower drywell 8.
Although not shown in FIG. 5, the boiling water nuclear power plant 1D has the steam condensing apparatus that condenses the steam in the upper drywell 7 and that includes the cooling water pool 13, the heat exchanger 15, the steam supply pipe 16, the drain pipe 17, and the non-condensable gas discharge pipe 19 which are installed in embodiment 1. The other structures of the boiling water nuclear power plant ID are the same as those of the boiling water nuclear power plant 1C.
In the present embodiment, if a severe accident accompanied with a station blackout should occur, an open/close valve 28 is opened and the cooling water 26 in the dryer separator pool 25 is discharged to the lower drywell 8 through the water injection pipe 27.
The present embodiment can obtain each effect generated in embodiment 1. Furthermore, in the present embodiment, the cooling water 26 in the dryer separator pool 25 is discharged to the lower drywell 8 through the water injection pipe 27, thus cooling water can be collected in the primary containment vessel 6 up to the upper end position of the vent pipes 11. In the present embodiment, the open/close valve 28 can be changed to a fusion valve and the reliability of the operation of the open/close valve 28 can be improved.

=

[Embodiment 6]
A nuclear power plant according to embodiment 6 which is another preferable embodiment of the present invention will be explained by referring to FIG. 6. The nuclear power plant of embodiment 6 is a boiling water nuclear power plant.
A boiling water nuclear power plant 1E of the present embodiment has a structure that in the boiling water nuclear power plant 1 of embodiment 1, the connection portion of the steam discharge connection pipe 20 with the core shroud 4 and the steam discharge outlet of the steam discharge connection pipe 20 are disposed above the upper end of the vent pipes 11.
Although not shown in FIG. 6, the boiling water nuclear power plant 1E has the steam condensing apparatus that condenses the steam in the upper drywell 7 and that includes the cooling water pool 13, the heat exchanger 15, the steam supply pipe 16, the drain pipe 17, and the non-condensable gas discharge pipe 19 which are installed in embodiment 1. The other structures of the boiling water nuclear power plant lE are the same as those of the boiling water nuclear power plant 1.
In the present embodiment, if the severe accident accompanied with the station blackout which is described in embodiment 1 should occur, similarly to , embodiment 1, the fuel assemblies in the core 3 are cooled, and furthermore, the steam of the upper drywell 7 is condensed by the aforementioned steam condensing apparatus and is supplied to the downcommer 5 of the reactor pressure vessel 2. The cooling water in the downcommer 5 such as the cooling water supplied through the feed water connection pipe 22 is supplied to the core 3 and cools the fuel assemblies, and is discharged from the core 3 in the state including steam, and is discharged into a vapor phase portion of the upper drywell 7 above the liquid surface of the cooling water collected in the primary containment vessel 6, through the steam discharge connection pipe 20. The cooling water discharged from the steam discharge connection pipe 20 falls into the cooling water collected in the primary containment vessel 6. The steam included in the cooling water discharged from the steam discharge connection pipe 20 is introduced in the steam supply pipe 16 and is condensed in the heat exchanger 15. The generated condensed water is introduced into the reactor pressure vessel 2 from the heat exchanger 15.
The present embodiment can obtain each effect generated in embodiment 1. In the present embodiment, the cooling water including the steam passing through the steam discharge connection pipe 20 is discharged , into the vapor phase portion of the upper drywell 7, so that resistance of the steam discharge outlet of the steam discharge connection pipe 20 due to the water head of the cooling water collected in the primary containment vessel 6 disappears, and the flow rate of the cooling water including the steam discharged outside the reactor pressure vessel 2 from the inside of the core shroud 4 is increased. As a result, the flow rate of the cooling water supplied to the core 3 is increased and the cooling ability of the fuel assemblies in the core 3 can be improved more than in embodiment 1.
If the steam discharge outlet of the steam discharge connection pipe 20 is positioned above the upper end of the vent pipes 11, the connection portion of the steam discharge connection pipe 20 to the core shroud 4 may be positioned below the upper end of the vent pipes 11. Even such a structure can eliminate the resistance of the steam discharge outlet of the steam discharge connection pipe 20 due to the water head of the cooling water collected in the primary containment vessel 6 and improve the cooling ability of the fuel assemblies in the core 3 more than in embodiment 1.
[Embodiment 7]
A nuclear power plant according to embodiment 7 which is another preferable embodiment of the present invention will be explained by referring to FIG. 7. The nuclear power plant of embodiment 7 is a boiling water nuclear power plant.
A boiling water nuclear power plant 1F of the present embodiment has a structure that in the boiling water nuclear power plant lE of embodiment 6, a circular partition plate (partition member) 32 is added.
Although not shown in FIG. 7, the boiling water nuclear power plant 1F has the steam condensing apparatus that condenses the steam in the upper drywell 7 and that includes the cooling water pool 13, the heat exchanger 15, the steam supply pipe 16, the drain pipe 17, and the non-condensable gas discharge pipe 19 which are installed in embodiment 1. The other structures of the boiling water nuclear power plant 1F are the same as those of the boiling water nuclear power plant 1E.
The outside overall periphery of the partition plate 32 is attached to the suppression chamber 9 and the inside overall periphery of the partition plate 32 is attached to the reactor pressure vessel 2. Such a partition plate 32 separates the upper drywell 7 and the lower drywell 8 from each other.
The present embodiment can obtain each effect generated in embodiment 1E. In the present embodiment, the upper drywell 7 is separated from the lower drywell 8 by the partition plate 32, so that if the severe accident accompanied with the station blackout described in embodiment 1 should occur, the cooling water injected into the primary containment vessel 6 by the water injection pipe 37 is collected above the partition plate 32. Therefore, in the present embodiment, the quantity of cooling water necessary to collect up to the upper end position of the vent pipes 11 in the primary containment vessel 6 can be made less than that quantity in embodiments 1 and 1E. Therefore, the feed start point of time of cooling water to the downcommer 5 by the feed water connection pipe 22 becomes earlier than in embodiments 1 and 1E.
In the aforementioned embodiments 1, 3, 4, and 6 and embodiments 8 and 9 which will be described later, the partition plate 32 may be installed.
[Embodiment 8]
A nuclear power plant according to embodiment 8 which is another preferable embodiment of the present invention will be explained by referring to FIG. 8. The nuclear power plant of embodiment 8 is a boiling water nuclear power plant.
A boiling water nuclear power plant 1G of the present embodiment has a structure that in the boiling water nuclear power plant lE of embodiment 6, an upper end surface of the suppression chamber 9 is disposed above the upper end of the core 3 and the cooling water outlet of the water injection pipe 37 is disposed right above the interval between the inner side wall of the suppression chamber 9 and the reactor pressure vessel 2.
The opening formed in the upper end of each vent pipe 11 mounted to the top of the suppression chamber 9 and communicated with the upper drywell is disposed at the upper surface of the suppression chamber 9. Although not shown in FIG. 8, the boiling water nuclear power plant 1G has the steam condensing apparatus that condenses the steam in the upper drywell 7 and that includes the cooling water pool 13, the heat exchanger 15, the steam supply pipe 16, the drain pipe 17, and the non-condensable gas discharge pipe 19 which are installed in embodiment 1. The other structures of the boiling water nuclear power plant 1G are the same as those of the boiling water nuclear power plant 1E.
In the present embodiment, if the severe accident accompanied with the station blackout which is described in embodiment 1 should occur, the cooling water supplied through the water injection pipe 37 is injected between an inner side wall of the suppression chamber 9 and the reactor pressure vessel 2 from the cooling water outlet of the water injection pipe 37.
The cooling water is collected from the bottom of the lower drywell 8 up to the upper end surface of the suppression chamber 9. When the liquid surface of the cooling water collected in the primary containment vessel 6 reaches the upper end surface of the suppression chamber 9, the injection of the cooling water from the water injection pipe 37 is stopped.
The suppression chamber 9 that the position of the upper end surface is positioned above the core 3 is a liquid surface forming member for forming the liquid surface of the cooling water collected in the primary containment vessel 6 above the core 3. The suppression chamber 9 that the position of the upper end surface is positioned above the core 3 and that is a liquid surface forming member prevents the cooling water collected in the primary containment vessel 6 from flowing in the suppression chamber 9. By doing this, the liquid surface of the cooling water collected in the primary containment vessel 6 can be formed above the core 3 and as mentioned in embodiment 1, the flooding of the core 3 and the supply of cooling water to the core 3 through the feed water connection pipe 22 can be performed.
The present embodiment can obtain each effect generated in embodiment 1E. In the present embodiment, the cooling water from the water injection pipe 37 is injected inside the inner side wall of the suppression chamber 9, thus before the liquid surface of the cooling water collected in the primary containment vessel 6 is positioned above the upper end of the core 3, the quantity of the cooling water injected into the primary containment vessel 6 can be reduced.
[Embodiment 9]
A nuclear power plant according to embodiment 9 which is another preferable embodiment of the present invention will be explained by referring to FIG. 9. The nuclear power plant of embodiment 9 is a boiling water nuclear power plant.
A boiling water nuclear power plant 1H of the present embodiment has a structure that in the boiling water nuclear power plant lE of embodiment 6, a cylindrical partition wall 33 enclosing the reactor pressure vessel 2 is installed on the upper end surface of the suppression chamber 9 and the cooling water outlet of the water injection pipe 37 is disposed right above the interval between the partition wall 33 and the reactor pressure vessel 2. An upper end of the cylindrical partition wall 33 is positioned above the core 3. Although not shown in FIG. 9, the boiling water nuclear power plant 1G has the steam condensing apparatus that condenses the steam in the upper drywell 7 and that includes the cooling water pool 13, the heat exchanger 15, the steam supply pipe 16, the drain pipe 17, and the non-condensable gas discharge pipe 19 which are installed in embodiment 1. The other structures of the boiling water nuclear power plant 1G are the same as those of the boiling water nuclear power plant 1E.
In the present embodiment, if the severe accident accompanied with the station blackout which is described in embodiment 1 should occur, the cooling water supplied through the water injection pipe 37 is injected between the cylindrical partition wall 33 and the reactor pressure vessel 2 from the cooling water outlet of the water injection pipe 37. The cooling water is collected from the bottom of the lower drywell 8 up to the upper end surface of the partition wall 33.
When the liquid surface of the cooling water collected in the primary containment vessel 6 reaches the upper end surface of the partition wall 33, the injection of the cooling water from the water injection pipe 37 is stopped.
The cylindrical partition wall 33 that the position of the upper end is positioned above the core 3 is a liquid surface forming member for forming the liquid surface of the cooling water collected in the primary containment vessel 6 above the core 3. The partition wall 33 that the position of the upper end is positioned above the core 3 and which is a liquid surface forming member prevents the cooling water collected in the primary containment vessel 6 from flowing in the suppression chamber 9. By doing this, the liquid surface of the cooling water collected in the primary containment vessel 6 can be formed above the core 3 and as mentioned in embodiment 1, the flooding of the core 3 and the supply of cooling water to the core 3 through the feed water connection pipe 22 can be performed.
The present embodiment can obtain each effect generated in embodiment 1E. In the present embodiment, the cooling water from the water injection pipe 37 is injected inside the partition wall 33, so that before the liquid surface of the cooling water collected in the primary containment vessel 6 is positioned above the upper end of the core 3, the quantity of the cooling water injected into the primary containment vessel 6 can be reduced.
The primary containment vessel 6A made of steel used in embodiment 3 can be applied to each reactor pressure vessel of the boiling water nuclear power plants lA and 1C to 1H. In this case, the steam condensing apparatus that condenses the steam in the upper drywell 7 and that includes the cooling water pool 13, the heat exchanger 15, the steam supply pipe 16, the drain pipe 17, and the non-condensable gas discharge pipe 19 can be eliminated.
[REFERENCE SIGNS LIST]
1, 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H : boiling water nuclear power plant, 2 : reactor pressure vessel, 3 :
core, 4 : core shroud, 5 : downcommer, 6, 6A : primary containment vessel, 7 : upper drywell, 8 : lower drywell, 9 : suppression chamber, 11 : vent pipe, 13 :
cooling pool, 15 : heat exchanger, 16 : , 17 : , 18, 21, 23, 28 : open/close valve, 19 : non-condensable gas discharge, 20 : steam discharge connection pipe, 22 :
feed water connection pipe, 25 : dryer separator pool, 27 : water injection pipe, 29 : operation floor, 32 :
partition plate, 33 : partition wall.

Claims

WHAT IS CLAIMED IS:

1. A nuclear power plant comprising:
a reactor pressure vessel having a core loaded with a plurality of fuel assemblies and a core shroud surrounding said core and forming a circular cooling water path between said reactor pressure vessel and said core shroud;
a primary containment vessel surrounding said reactor pressure vessel and forming internally a drywell in which said reactor pressure vessel is disposed, and a suppression chamber separated from said drywell;
a liquid surface forming member having an upper end disposed above an upper end of said core installed in said primary containment vessel for forming a liquid surface of cooling water collected in said drywell formed in said primary containment vessel above said core;
a steam discharge pipe; and a cooling water feed pipe, wherein one end portion of said steam discharge pipe is connected to said core shroud in said reactor pressure vessel and is in communication with a region in said core shroud above said core, a first open/close valve is mounted to said steam discharge pipe, and another end portion of said steam discharge pipe penetrates said reactor pressure vessel and opens in said drywell formed in said primary containment vessel outside said reactor pressure vessel; and wherein one end portion of said cooling water feed pipe is connected to said reactor pressure vessel and is in communication with said circular cooling water path, another end portion of said cooling water feed pipe opens in said drywell formed in said primary containment vessel, said one end portion and said another end portion of said cooling water feed pipe are positioned below an upper end of said liquid surface forming member, and a second open/close valve is mounted to the cooling water feed pipe.

2. The nuclear power plant according to claim 1, comprising:
a steam condensing apparatus including a cooling pool, a steam condenser installed in said cooling pool, a steam supply pipe connected to said primary containment vessel above said upper end of said liquid surface forming member and in communication with said drywell, and a drain pipe connected to said steam condensing apparatus, extending in said primary containment vessel, and introducing condensed water generated by said steam condensing apparatus into said primary containment vessel.

3. The nuclear power plant according to claim 2, wherein said drain pipe is connected to said reactor pressure vessel and is in communication with said circular cooling water path.

4. The nuclear power plant according to claim 2, wherein said drain pipe is opened in said primary containment vessel.

5. The nuclear power plant according to claim 1, wherein said primary containment vessel is a primary containment vessel made of steel.

6. The nuclear power plant according to claim 1, comprising:
a gravity-driven water injection system connected to said reactor pressure vessel.

7. The nuclear power plant according to claim 1, comprising:
a gravity-driven water injection system, wherein a water injection pipe of said gravity-driven water injection system is opened in said drywell.

8. The nuclear power plant according to claim 1, wherein an opening formed in said other end portion of said steam discharge pipe is disposed below said upper end of said liquid surface forming member.

9. The nuclear power plant according to claim 1, wherein an opening formed in said other end portion of said steam discharge pipe is disposed above said upper end of said liquid surface forming member.

10. The nuclear power plant according to claim 1, comprising:
a partition member attached to said reactor pressure vessel and said suppression chamber, wherein said drywell is separated into two regions by said partition member.

11. The nuclear power plant according to claim 1, wherein said liquid surface forming member is any of said vent pipes whose upper ends are positioned above said core, said suppression chamber whose upper end surface is positioned above said core, and a partition wall whose upper end is positioned above said core, surrounding said reactor pressure vessel.

12. The nuclear power plant according to claim 2, wherein said liquid surface forming member is any of said vent pipes in communication with said drywell, reaching a suppression pool in said suppression chamber, and whose upper ends are positioned above said core, said suppression chamber whose upper end surface is positioned above said core, and a partition wall whose upper end is positioned above said core, surrounding said reactor pressure vessel.