JP5690202B2 - Nuclear decay heat removal equipment - Google Patents

Description

  The present invention relates to an apparatus for removing decay heat generated as a result of nuclear fuel collapsing after stopping a nuclear fission chain fission reaction in a nuclear reactor.

  An example of an apparatus for removing decay heat generated after the reactor is shut down is described in Patent Document 1 and Patent Document 2. In Patent Document 1, one end of a heat pipe is immersed in cooling water in a reactor pressure vessel so that the other end of the heat pipe is exposed to the outside of the reactor pressure vessel and the other end is surrounded. An apparatus is described in which a heat radiating duct is provided and a gate valve is provided at the entrance and exit of the heat radiating duct. Then, unexpected accidents and natural disasters occur, and the reactor's main cooling system and emergency cooling system (hereinafter referred to as ECCS) do not operate, or the power supply for operating them fails or is lost. When the temperature of the cooling water in the reactor pressure vessel rises, the above-mentioned gate valve is opened and the heat radiating duct is communicated with the outside air, so that one end of the toe pipe functions as an evaporator and the other end is condensed. It is comprised so that it may function as a part. Therefore, according to the invention of Patent Document 1, when the gate valve is opened in the emergency of the nuclear reactor as described above, the heat pipe can be operated to dissipate the heat of the cooling water into the atmosphere. Even if it does not operate, it is said that the nuclear reactor can be reliably cooled to prevent nuclear fuel melting accidents.

  Patent Document 2 discloses an apparatus in which a heat exchanger that transfers heat generated in a reactor core from a coolant in a reactor pressure vessel to another coolant (so-called secondary system) and a heat pipe are combined. The apparatus is configured to dissipate decay heat generated in the core into the atmosphere after the reactor is shut down. Specifically, the above heat pipe is of a loop type, and a part of the pipe is disposed inside the reactor pressure vessel, so that a part of the pipe is heated inside the reactor pressure vessel. The cooling water and the working fluid sealed in the heat pipe are configured to function as a heat exchanger that causes heat exchange. Then, the working fluid vaporized by heat exchange flows through the main steam pipe connected to a part of the pipe via the steam drum, is supplied to the steam turbine, and is then condensed by the condenser. ing. The working fluid condensed in the condenser is made to flow through the water supply pipe and the cooling water side pipe by a pump and supplied to the other part of the pipe immersed in a pool provided above the reactor containment vessel. It has come to be. A water supply drum is provided at a connection portion between the water supply pipe and the cooling water side pipe, and the water supply drum is also connected to a part of the pipe, and the condensed working fluid passes through the water supply drum to the pipe. It is designed to be refluxed in part. The steam drum is also communicated with other portions of the pipe via a steam side pipe. In addition, a valve is provided in each of the main steam pipe and the water supply pipe, and each of the valves causes an emergency stop (ie, reactor scram) by rapidly inserting a control rod into the core. Accordingly, the flow is closed and the flow of the working fluid in the main steam pipe and the water supply pipe is blocked. That is, when the nuclear reactor is scrammed, a part of the pipe functions as an evaporation part, and the other part of the pipe functions as a condensing part. Therefore, according to the invention described in Patent Document 2, when the reactor is scrammed, the loop heat pipe can be operated to remove the decay heat from the core. There is no need to use it, and it is said that it can be a highly reliable device without failure.

JP 58-1118988 JP-A-1-172800

  As described above, the device described in Patent Document 1 uses a heat pipe to remove decay heat, and the heat pipe is configured to operate only when the reactor is scrammed. Yes. However, in the configuration described in Patent Document 1, unless a large number of heat pipes are installed around the nuclear fuel, there is a possibility that the decay heat after the nuclear reactor is scrammed cannot be sufficiently removed. On the other hand, as described in Patent Document 2, in the configuration using the loop heat pipe, the vapor flow and the liquid flow of the working fluid do not face each other, so that the amount of heat transport increases accordingly. Therefore, the use of a loop heat pipe is advantageous for removing decay heat. However, in the configuration described in Patent Document 2, a pump is used to recirculate the condensed working fluid to the evaporating unit. Therefore, when the pump fails, the evaporating unit is forcibly liquid-phase working fluid. Will not be supplied. As a result, in the configuration described in Patent Document 2, dryout may occur due to decay heat, and the loop heat pipe may not operate. In addition to this, even if a loop heat pipe is used, in order to sufficiently remove the decay heat immediately after the reactor is scrammed, if the loop heat pipe with a large heat transport amount is not installed, the heat There may be a shortage in transport volume.

  The present invention has been made paying attention to the above technical problems, and effectively and sufficiently removes decay heat generated by a nuclear reactor without requiring power equipment or a power source for operating the power equipment. An object of the present invention is to provide a so-called passive decay heat removal apparatus for a nuclear reactor.

  In order to achieve the above object, the invention of claim 1 includes a nuclear fuel that undergoes a nuclear fission reaction, and a cooling water that is immersed in the nuclear fuel and heated by the heat accompanying the chain fission reaction to be vaporized. In a reactor decay heat removal apparatus comprising: a reactor pressure vessel having a control rod for controlling the chained fission reaction; and a core cooling device for cooling the nuclear fuel by cooling the cooling water. A gravity-type cooling water injection water tank that is provided above the water surface of the cooling water inside the reactor pressure vessel and stores a predetermined amount of other cooling water therein, and its gravity-type cooling water injection A water supply pipe that communicates a water tank with the reactor pressure vessel, and is provided in the middle of the water supply pipe. An on / off valve for water supply that is opened when the temperature of the cooling water becomes equal to or higher than a predetermined temperature by stopping the operation of the core cooling device. And a pressure equalizing pipe for equalizing the pressure in the space in the gravity-type cooling water injection water tank to the internal pressure of the reactor pressure vessel.

  According to a second aspect of the present invention, in the first aspect of the invention, the gravity-type cooling is performed after a predetermined time has elapsed after the water supply opening / closing valve is opened or when the water supply opening / closing valve is opened. As the other cooling water stored in the water injection tank is supplied to the inside of the reactor pressure vessel, the temperature of the cooling water inside the reactor pressure vessel becomes equal to or lower than another predetermined temperature. A reactor decay heat removal apparatus comprising a loop heat pipe that operates in some cases to dissipate the decay heat into the atmosphere.

  According to a third aspect of the present invention, in the first or second aspect of the invention, the loop heat pipe includes a working fluid that changes phase, an evaporation unit that heats and vaporizes the working fluid, and the vaporized working fluid. A condensing part for condensing the vaporized working fluid by dissipating the heat of the gas, a steam pipe for flowing the working fluid vaporized in the evaporation part toward the condensing part, and a working fluid condensed in the condensing part A liquid return pipe that flows toward the evaporation section, a reservoir that stores the working fluid, a connection pipe that communicates the reservoir with the liquid return pipe, and the connection pipe or the connection pipe in the liquid return pipe. A main valve that regulates the flow of the working fluid and is provided closer to the evaporation unit than the communicating portion, the evaporation unit is arranged to be able to transfer heat to the reactor pressure vessel, and the condensing unit is Previous The main valve is disposed above the reactor pressure vessel and exposed to the atmosphere, and the main valve is disposed after a predetermined time has elapsed since the opening of the water supply on / off valve, or the water supply on / off valve is The temperature of the cooling water inside the reactor pressure vessel is determined in advance by supplying the other cooling water that has been opened and stored in the gravity-type cooling water injection water tank to the inside of the reactor pressure vessel. A reactor decay heat removal apparatus configured to be opened when the temperature is lower than another temperature.

  The invention of claim 4 is the invention according to any one of claims 1 to 3, wherein a shroud for supporting the nuclear fuel and a jet pump for flowing the cooling water are provided inside the reactor pressure vessel, The evaporation section includes a plurality of pipes disposed between the shroud or the jet pump and the reactor pressure vessel, a first header for communicating one end of the pipes with the liquid return pipe, and the pipes A second header that communicates the other end of the gas pipe with the steam pipe, and the working fluid is configured to be vaporized by being heated by the decay heat in each header and each pipe. Is a decay heat removal device for a nuclear reactor.

According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the water supply pipe is communicated with a lower portion of the reactor pressure vessel, and the uniform pipe is connected to an upper portion of the gravity-type cooling water injection water tank. A reactor decay heat removal apparatus characterized in that the reactor pressure vessel side communicates with the water supply opening / closing valve in the water supply pipe.

  According to the first aspect of the present invention, the gravity-type cooling water injection water tank for storing other predetermined amount of cooling water is provided above the water level of the cooling water in the reactor pressure vessel. The gravity-type cooling water injection water tank is communicated with a reactor pressure vessel by a water supply pipe, and a water supply opening / closing valve is provided in the water supply pipe. The on-off valve for water supply is a case where the nuclear fission reaction is controlled by the control rod and the operation of the nuclear reactor is stopped, and the nuclear fuel generates decay heat due to its collapse. When the temperature of the cooling water in the reactor pressure vessel becomes equal to or higher than a predetermined temperature by stopping, it is configured to be opened. In addition to this, the pressure in the space portion of the gravity type cooling water injection water tank is made equal to the internal pressure of the reactor pressure vessel by the pressure equalizing pipe. For this reason, only the head pressure of other cooling water stored in the gravity-type cooling water injection water tank acts on the on-off valve for water supply. Therefore, the temperature of the cooling water can be reduced because the reactor is stably shut down or scrammed and the existing core cooling system does not operate, or the reactor is scrammed and the power supply for operating the core cooling system is lost. When the temperature rises above a predetermined temperature, the water supply opening / closing valve can be automatically opened. Then, other cooling water stored in the gravity-type cooling water injection water tank can be supplied from the gravity-type cooling water injection water tank to the inside of the reactor pressure vessel by the water head pressure. That is, when the temperature of the cooling water rises due to decay heat generated after the reactor is shut down, the cooling water is supplied from the gravity-type cooling water injection water tank to the inside of the reactor pressure vessel without using a power device such as a pump. The nuclear fuel that is supplied and generating decay heat can be immersed in the cooling water, whereby the nuclear fuel can be cooled and the decay heat immediately after the reactor shutdown can be effectively removed. Further, since the cooling water is supplied by the water head pressure, the cooling water can be caused to flow inside the reactor pressure vessel by the liquid flow, thereby also effectively cooling the nuclear fuel. From the above, it is possible to provide a so-called completely passive decay heat removal device that does not require power equipment or a power source for operating the power equipment.

  According to the invention of claim 2, in addition to the effect similar to the effect of the invention of claim 1, the loop heat pipe for dissipating the decay heat into the atmosphere is provided, In the reactor pressure vessel after a predetermined time has elapsed since the opening of the on-off valve, or when other cooling water is supplied from the gravity-type cooling water injection water tank into the reactor pressure vessel. It is configured to operate when the temperature of the cooling water becomes equal to or lower than another predetermined temperature. That is, since the loop heat pipe does not operate during so-called normal operation of the nuclear reactor, heat loss during normal operation can be prevented. On the other hand, in the so-called emergency as described above, after the decay heat immediately after shutting down the reactor is removed to some extent by other cooling supplied from the gravity cooling water injection water tank, the loop heat pipe is automatically When activated, the remaining decay heat can be dissipated into the atmosphere. In other words, the loop heat pipe can be automatically activated after the cooling water inside the reactor pressure vessel has been cooled to some extent by the sensible heat of other cooling water stored in the gravity cooling water injection water tank. Thus, the cooling water inside the reactor pressure vessel can be continuously cooled. In addition, since a loop heat pipe is used, the amount of heat transport can be increased as compared with the case of using a normal heat pipe. As a result, the number of loop heat pipes used for heat transport of decay heat can be reduced, and the size of itself can be reduced. Therefore, the material cost, installation cost, etc. which are used for such a cooling device can be suppressed.

  According to the invention of claim 3, in addition to the effect similar to the effect of the invention of claim 1 or 2, the evaporation part of the loop heat pipe is connected to the reactor pressure vessel so that heat can be transferred, and the condensation part Is exposed above the reactor pressure vessel and in the atmosphere. Further, the liquid return pipe of the loop heat pipe and the reservoir storing the working fluid are communicated with each other by a connection pipe, and a main valve is provided in the connection pipe. The main valve is supplied with other cooling water into the reactor pressure vessel after a predetermined time has elapsed since the opening of the water supply opening / closing valve or from the gravity cooling water injection water tank. Thus, it is configured to be opened when the temperature of the cooling water in the reactor pressure vessel becomes equal to or lower than another predetermined temperature. That is, during the normal operation of the nuclear reactor, almost all the working fluid is stored in the reservoir, the condensing unit, the liquid return pipe, and the like, and the loop heat pipe does not operate. Therefore, it is possible to prevent heat loss during normal operation. In contrast, in an emergency such as that described above, after removing the decay heat immediately after the reactor shut down to some extent, the main valve automatically opens and the working fluid stored in the reservoir is supplied to the evaporation section. The loop heat pipe is activated. Since the evaporation part is thermally connected to the reactor pressure vessel, the nuclear fuel and the cooling water can be cooled by transporting the decay heat by the latent heat of the working fluid and dissipating it to the atmosphere.

  According to the invention of claim 4, in addition to the same effect as that of any one of the inventions of claims 1 to 3, the shroud or cooling water in which the evaporating part supports the nuclear fuel inside the reactor pressure vessel is provided. A plurality of pipes disposed between the jet pump to be flown and the reactor pressure vessel; a first header for communicating one end of each of the pipes with a liquid return pipe; and the other end of the pipes for steaming A second header communicated with the pipe, and the working fluid is heated by decay heat in each header and each pipe and is vaporized. Therefore, it is possible to effectively remove the decay heat and cool the nuclear fuel and the cooling water.

  According to the invention of claim 5, in addition to the effect similar to the effect of any one of the inventions of claims 1 to 4, the water supply pipe is communicated with the lower part of the reactor pressure vessel, and the uniform pipe is cooled by gravity type cooling. The upper part of the water injection tank is connected to the reactor pressure vessel side with respect to the on-off valve for water supply in the water supply pipe. Therefore, the internal pressure of the gravity-type cooling water injection water tank, more specifically, the pressure in the space can be made equal to the internal pressure of the reactor pressure vessel. As a result, the pressure acting on the water supply on / off valve can be limited to the water head pressure at which other cooling water stored in the gravity-type cooling water injection water tank is generated. In an emergency, other cooling water can be supplied into the reactor pressure vessel using the head pressure of the other cooling water stored in the gravity-type cooling water injection water tank. In addition, it is possible to prevent the supply of other cooling water from stopping due to a decrease in the internal pressure accompanying the supply of other cooling water from the gravity-type cooling water injection water tank. In addition, the gravity-type cooling water injection tank can be made airtight with respect to the outside thereof, and therefore, radioactive substances can be contained.

It is a figure which shows typically an example of a structure at the time of applying the decay heat removal apparatus which concerns on this invention to a boiling water reactor. It is sectional drawing which follows the II-II 'line | wire shown in FIG. It is a figure which shows an example of a structure of an evaporation part in three dimensions. It is a figure which shows typically an example of a structure of the nuclear reactor which can apply this invention.

  The decay heat removal apparatus according to the present invention can be provided in a nuclear reactor that generates steam by causing a chain fission reaction in nuclear fuel and operates a turbine with the steam to generate electric power. The reactor may be a boiling water reactor (BWR) or a pressurized water reactor (PWR) that is generally known in the art, and can be applied to any reactor. The nuclear fission chain fission reaction is controlled by absorbing the number of neutrons generated by the nuclear fuel radioactive decay by the control rod, but even after the chain fission reaction is stopped by the control rod Radiates and generates heat (hereinafter referred to as decay heat).

  In the present invention, the decay heat can be removed even when the power equipment or the power source for operating the power equipment is lost. More specifically, the decay heat removal apparatus according to the present invention includes a gravity-type cooling water injection water tank that removes a relatively high temperature decay heat, and a loop heat pipe that removes a relatively low temperature decay heat. It has. First, the gravity-type cooling water injection tank will be described. The gravity-type cooling water injection tank is a tank for storing cooling water separately from the cooling water filled in the reactor pressure vessel. The water tank is provided outside the reactor pressure vessel, and the bottom of the water tank is above the liquid level of the cooling water filled in the reactor pressure vessel during the so-called normal operation of the reactor. Is provided. The gravity-type cooling water injection water tank is communicated with the reactor pressure vessel by a water supply pipe. The water supply pipe is provided with a water supply on / off valve. This water supply on / off valve can be used, for example, when a nuclear reactor is scrammed and a power supply for operating an existing main cooling device or ECCS fails or power is lost. When these devices do not operate, or when the temperature of the cooling water in the reactor pressure vessel exceeds a predetermined temperature due to the failure of these devices, the device is configured to automatically open. be able to. Therefore, by opening the water supply opening / closing valve, other cooling water stored in the gravity-type cooling water injection water tank can be supplied to the inside of the reactor pressure vessel. Further, the internal pressure of the water tank, specifically, the pressure in the space portion above the water tank is made equal to the internal pressure of the reactor pressure vessel by the pressure equalizing pipe. In the present invention, the normal operation of the nuclear reactor means a state in which power generation can be performed by appropriately controlling the chain fission reaction of nuclear fuel and the temperature of cooling water, for example.

  Therefore, according to the decay heat removal apparatus for a reactor according to the present invention, the reactor is stably stopped or scrammed, and the temperature of the cooling water inside the reactor pressure vessel is determined in advance by the decay heat. When the above is reached, the water supply on-off valve is automatically opened to supply the other cooling water stored in the gravity-type cooling water injection water tank to the inside of the reactor pressure vessel by its head pressure (ie, gravity). be able to. As a result, the cooling water can flow in the reactor pressure vessel and the decay heat can be effectively removed. In other words, since the cooling water in the reactor pressure vessel can be cooled by the sensible heat of the other cooling water stored in the gravity-type cooling water injection water tank, the nuclear fuel can be cooled. Furthermore, as described above, the decay heat removal apparatus for a reactor according to the present invention is a so-called passive apparatus that does not require power equipment or a power source for operating the reactor. Moreover, even if the existing main cooling device or the cooling device such as ECCS does not operate or the power source for operating them is lost, the decay heat can be removed.

  In addition, the decay heat removal apparatus according to the present invention includes a loop heat pipe that dissipates decay heat to the atmosphere, and the loop heat pipe is predetermined after the water supply opening / closing valve is opened. After the passage of time or as described above, the cooling water inside the reactor pressure vessel is generated by the sensible heat by supplying other cooling water from the gravity-type cooling water injection water tank to the inside of the reactor pressure vessel. It is configured to operate when the temperature of the temperature becomes equal to or lower than another predetermined temperature. Therefore, after the decay heat immediately after the reactor shutdown is removed to some extent by the sensible heat of other cooling water supplied from the gravity cooling water injection tank, the loop heat pipe automatically operates to remove the remaining decay heat to the atmosphere. It is configured to dissipate heat. From the above, according to the decay heat removal apparatus for a reactor according to the present invention, decay heat can be removed sufficiently and continuously without the need for power equipment or a power source.

  FIG. 4 schematically shows an example of the configuration of a nuclear reactor to which the present invention can be applied. The nuclear reactor shown here is a boiling water reactor 1 as an example, and an assembly of nuclear fuel 2 that absorbs neutrons and undergoes fission and emits two to three neutrons along with the fission (that is, the core) is a cylinder. It is supported by the shape shroud 3 and is accommodated inside the reactor pressure vessel 4. Each nuclear fuel 2 is supported inside a shroud 3 by a core support plate (not shown) that supports the lower portion of the nuclear fuel 2 and an upper lattice plate 5 that supports the upper portion of the nuclear fuel 2. Control rods 6 are provided between the nuclear fuels 2 in the core so as to be able to be taken in and out. The control rod 6 is configured so that the number of neutrons in the core can be adjusted by absorbing neutrons. Therefore, the control rod 6 is adjusted to adjust the number of neutrons in the core by taking the control rod 6 in and out of the core. It is configured to be able to control a typical fission reaction.

  The core is immersed in cooling water, and water is generally used as the cooling water. The water is boiled by the heat accompanying the fission reaction, and becomes a mixed fluid of water and steam. The mixed fluid is introduced into a steam separator 7 provided above the reactor core, and is separated into steam and water by passing through the steam separator 7. The separated steam is introduced into a steam dryer 8 to further remove droplets, and thereafter supplied to a steam turbine 9 described later. The droplets separated by the steam separator 7 and the steam dryer 8 are returned to the core.

  A water supply sparger 10 is provided above the upper grid plate 5. The water supply sparger 10 is a part of a plurality of cooling devices constituting the ECCS, and is configured to operate in the event of a loss of coolant accident (LOCA) and supply cooling water to the reactor core. A jet pump 11 is provided between the shroud 3 and the inner wall surface of the reactor pressure vessel 4. The jet pump 11 is supplied with low-temperature cooling water sent from the recirculation pump 12 via a riser pipe (not shown), and the low-temperature cooling water is ejected at a high pressure to thereby change the reactor pressure. The cooling water filled in the container 4 is made to flow, and the cooling water is supplied to the reactor core.

  The recirculation pump 12 supplies the cooling water in the reactor pressure vessel 4 to the jet pump 11 and forcibly supplies the cooling water to the core via the jet pump 11 to remove heat generated in the core, It is configured to control the thermal output of the nuclear reactor by changing the amount of cooling water supplied to the core. The reactor pressure vessel 4 and the recirculation pump 12 are confined in the reactor containment vessel 13. Therefore, the jet pump 11 and the recirculation pump are configured to function as a so-called main cooling device that cools the core during normal operation of the reactor.

  A vent 14 is provided above the reactor containment vessel 13 to release the pressure to the outside when the internal pressure rises. A pressure suppression pool 15 is provided below the reactor pressure vessel 4. The pressure suppression pool 15 condenses the steam released from the reactor pressure vessel 4 as the internal pressure of the reactor pressure vessel 4 rises, and stores the supplementary cooling water in the reactor pressure vessel 4. Or, when the nuclear reactor is scrammed and the ECCS operates, it is configured to function as a cooling water source.

  When the reactor is scrammed and the ECCS operates, the cooling water stored in the pressure suppression pool 15 is supplied into the reactor containment vessel 13 via the containment pump 16, and The high pressure core pump 17 and the low pressure core pump 18 are supplied to the inside of the reactor pressure vessel 4. The reactor containment vessel 13 and the pressure suppression pool 15 described above are confined in the reactor building 19. That is, the containment pump 16, the high pressure core pump 17, the low pressure core pump 18, and the like are also configured to function as ECCS.

  The steam turbine 9 described above is provided in the turbine building 20, and the steam turbine 9 includes a turbine blade 9a and a shaft portion 9b that rotatably supports the turbine blade 9a. When the high-temperature and high-pressure steam supplied from the reactor pressure vessel 4 hits the turbine blade 9a, the shaft portion 9b of the turbine blade 9a is rotated by the steam energy. That is, the steam turbine 9 is configured to convert steam energy into rotational force. The above-described shaft portion 9 b is connected to the generator 22 via the power transmission shaft 21. The generator 22 converts rotational force into electric power, and the electric power generated by the generator 22 is converted into a predetermined voltage by a transformer (not shown) and transmitted. .

  The steam obtained by rotating the turbine blade 9 a is supplied to the condenser 23. In the example shown here, the condenser 23 is provided below the steam turbine 9 and includes a plurality of cooling pipes 24. As an example, when the nuclear reactor according to the present invention is constructed at the seaside, the seawater taken in using the circulating water pump 25 is supplied to the inside of each cooling pipe 24. . Therefore, the steam that rotates the turbine blade 9 a is configured to exchange heat with seawater through the cooling pipes 24. The cooling water cooled and condensed by heat exchange is supplied again into the reactor pressure vessel 4 by the feed water pump 26.

  FIG. 1 schematically shows an example of a configuration in the case where the decay heat removal apparatus according to the present invention is applied to the boiling water reactor. A gravity-type cooling water injection water tank 27 is provided outside the reactor building 19, that is, exposed to the atmosphere. As described above, the gravity-type cooling water injection water tank 27 is an airtight tank in which a predetermined amount of cooling water is stored. The amount is an amount that can reduce the relatively high decay heat after the reactor shutdown to a temperature that is assumed in advance. Therefore, the amount can be obtained in advance by experiments or simulations. In addition, the bottom of the gravity-type cooling water injection water tank 27 is disposed above the level of the cooling water in the reactor pressure vessel 4 during the normal operation of the reactor described above. The gravity-type cooling water injection water tank 27 is communicated with the reactor pressure vessel 4 through a water supply pipe 28. More specifically, one end of the water supply pipe 28 is connected to the bottom of the gravity-type cooling water injection water tank 27 and the other end is connected to the lower part of the core through the reactor pressure vessel 4. Has been. In the example shown in FIG. 1, the other end is branched into a plurality of pipes, for example, via a header, and the plurality of pipes are arranged substantially vertically inside the reactor pressure vessel 4. Therefore, the other end and the nuclear fuel 2 are parallel to each other. In the example shown in FIG. 1, the cooling water supplied from the other end is supplied from below to above inside the reactor pressure vessel 4.

  A water supply opening / closing valve 29 is provided in the water supply pipe 28. As an example, the water supply opening / closing valve 29 can be configured by a so-called normal open type electromagnetically controlled opening / closing valve configured to be closed by being energized and to be opened by cutting off the energization. The on-off valve 29 for water supply may be configured to open when, for example, the power supply fails or is lost, or the temperature of the cooling water in the reactor pressure vessel 4 is higher than a predetermined temperature. In such a case, the energization may be cut off and opened.

  An upper space portion in the gravity-type cooling water injection water tank 27 is connected to the reactor pressure vessel 4 side with respect to the water supply opening / closing valve 29 in the water supply pipe 28 by a pressure equalizing pipe 30. The pressure equalizing pipe 30 is supplied with the internal pressure of the reactor pressure vessel 4 via the water supply pipe 28, and therefore, the space of the gravity-type cooling water injection water tank 27 communicated via the pressure equalizing pipe 30. The partial pressure and the internal pressure of the reactor pressure vessel 4 are substantially equal. As a result, only the head pressure of the cooling water stored in the gravity-type cooling water injection water tank 27 acts on the on-off valve 29 for water supply, and therefore the bottom of the gravity-type cooling water injection water tank 27 from the above-described liquid level. The flow rate and flow rate of the cooling water supplied from the gravity-type cooling water injection water tank 27 to the inside of the reactor pressure vessel 4 can be appropriately set by appropriately setting the height of the water supply pipe 28 and the inner diameter of the water supply pipe 28. it can.

  Further, when the temperature of the cooling water in the reactor pressure vessel 4 exceeds a predetermined temperature because the reactor is scrammed and the ECCS is not activated, the decay heat is radiated to the atmosphere. A loop heat pipe 31 is provided. The loop heat pipe 31 basically uses, as a working fluid, a fluid that evaporates and condenses in a target temperature range such as water or alcohol, and the working fluid is evaporated by receiving heat from the outside, and the vapor Is configured to transport heat by dissipating heat and condensing after flowing toward a location where the pressure is low. The part where the working fluid evaporates is the evaporation unit 32, and the part where the working fluid vapor dissipates heat and condenses is the condensation unit 33, and the loop heat pipe 31 uses the working fluid vaporized in the evaporation unit 32. A steam pipe 34 that flows toward the condensing unit 33 and a liquid return pipe 35 that recirculates the working fluid that has been radiated and condensed toward the evaporating unit 32 are connected in a loop.

  In the example shown in FIG. 1, the evaporation section 32 of the loop heat pipe 31 is provided so as to be able to transfer heat to the reactor pressure vessel 4. The evaporation section 32 includes a plurality of evaporation pipes 32 a, a first header 32 b that communicates one end of the pipes 32 a with the steam pipe 34, and a second header 32 c that communicates the other end with the liquid return pipe 35. ing. FIG. 2 is a cross-sectional view taken along the line II-II 'shown in FIG. As shown in FIG. 2, the plurality of pipes 32 a are, for example, arranged between the jet pump 11 and the inner wall surface of the reactor containment vessel 13 in parallel with each other and vertically or substantially vertically, and the shroud 3. It can be arranged in a circular shape so as to surround. The first header 32b is disposed above the second header 32c and communicates with one end of each pipe 32a. On the contrary, the second header 32c is disposed below the first header 32b. The other end of each pipe 32a is communicated.

  FIG. 3 shows a three-dimensional example of the configuration of the evaporation unit 32 described above. As described above, when the steam pipe 32a is arranged in a circular shape so as to surround the shroud 3, as shown in FIG. 3, each header 32b, 32c is formed in a circular shape, and one end of the steam pipe 32a is formed. Is communicated by the first header 32b, and the other end is communicated by the second header 32c.

  As shown in FIGS. 1 and 3, the condensing unit 33 is provided above the evaporation unit 32 and outside the reactor building 19. The condensing unit 33 includes a plurality of condensing pipes 33 a, a third header 33 b that communicates one end of the pipes 33 a with the steam pipe 34, and a fourth header 33 c that communicates the other end with the liquid return pipe 35. ing. The pipes 33a are arranged in parallel with each other and vertically or substantially vertically, and each of the pipes 33a is provided with a plurality of fins 33d for improving the heat radiation efficiency. The third header 33b is disposed above the fourth header 33c and communicates with one end of each pipe 33a. On the contrary, the fourth header 33c is disposed below the third header 33b. The other end of each pipe 33a is communicated. Therefore, this condensing part can be said to be a so-called air-cooled condensing part.

  A reservoir 36 is provided above the fourth header 33c. The reservoir 36 is an airtight hollow container in which a predetermined amount of working fluid is stored. The reservoir 36 and the fourth header 33c are communicated with each other via the connection pipe 37. Therefore, the working fluid stored in the reservoir 36 is supplied to the fourth header 33c via the connection pipe 37. Has been. A main valve 38 is provided in the middle of the liquid return pipe 35. The main valve 38 is configured to be opened after a predetermined time has elapsed since the above-described water supply on-off valve 29 is opened. As an example, the main valve 38 is not particularly illustrated. However, it is possible to combine a timer that operates after the water supply opening / closing valve 29 is opened and an opening / closing valve that is linked to the timer and that is opened after a predetermined time has elapsed. it can. Therefore, the decay heat removal apparatus according to the present invention can be configured to include the gravity-type cooling water injection water tank 27 and the loop heat pipe 31 configured as described above.

  Next, the operation of the decay heat removal apparatus configured as described above will be described. For example, when the temperature of the cooling water rises above a predetermined temperature because the reactor is scrammed and the ECCS does not operate, the energization of the water supply on / off valve 29 is interrupted, whereby the water supply on / off valve 29 Is open. As described above, the internal pressure of the gravity-type cooling water injection water tank 27 is made equal to the internal pressure of the reactor pressure vessel 4 by the pressure equalizing pipe 30, and therefore, when the water supply opening / closing valve 29 is opened, the internal pressure is stored therein. The cooling water being supplied is supplied to the inside of the reactor pressure vessel 4 by its head pressure, in other words, by potential energy. As a result, the cooling water is caused to flow in the reactor pressure vessel 4 by the liquid flow when the cooling water is supplied, and the nuclear fuel 2 is effectively deprived of heat by cooling the nuclear fuel 2 generating the decay heat. it can. Moreover, since the cooling water inside the reactor pressure vessel 4 is cooled by sensible heat, the nuclear fuel 2 can also be cooled by this.

  When a predetermined time elapses after the water supply opening / closing valve 29 is opened, the main valve 38 is opened and the working fluid stored in the reservoir 36 passes through the fourth header 33c and the liquid return pipe 35. To the evaporation unit 32. In the evaporating section 32, the working fluid is vaporized by heat transfer of the decay heat in each of the steam pipes 32a and the second header 32c, and the vaporized working fluid is collected in the first header 32b and collected in the steam pipe 34. Supplied. The collected working fluid vapor flows through the vapor pipe 34 and is supplied toward the condenser 33. The working fluid vapor that has flowed through the steam pipe 34 is supplied to each condensing pipe 33a of the condensing unit 33 via the third header 33b. In each condensing pipe 33a, the heat transported by the working fluid vapor is radiated to the atmosphere via the fins 33d, and as a result, the working fluid vapor is condensed. The condensed working fluid moves below the respective condensing pipes 33a due to gravity, and is then collected by the fourth header 33c, supplied to the liquid return pipe 35, and refluxed to the evaporation section 32 through the liquid return pipe 35. . By continuing such circulation of the working fluid, the nuclear fuel 2 is cooled by gradually dissipating the decay heat inside the reactor pressure vessel 4 into the atmosphere.

  Therefore, with the configuration as described above, the decay heat removal apparatus according to the present invention does not operate the ECCS because the reactor is scrammed and the power source is lost, and the temperature of the cooling water in the reactor pressure vessel 4 is low. When the temperature is higher than a predetermined temperature, it automatically operates without using a power source, and the decay heat can be removed continuously and stably. That is, a so-called completely passive device can be obtained.

  DESCRIPTION OF SYMBOLS 2 ... Nuclear fuel, 4 ... Reactor pressure vessel, 6 ... Control rod, 27 ... Gravity type cooling water injection water tank, 28 ... Feed water piping, 29 ... On-off valve for water supply, 30 ... Pressure equalizing pipe.

Claims (2)

A nuclear reactor comprising a nuclear fuel that undergoes a nuclear fission reaction, a cooling water that is immersed in the nuclear fuel and that is heated and vaporized by heat accompanying the chain fission reaction, and a control rod that controls the chain fission reaction In a reactor decay heat removal apparatus comprising a pressure vessel and a core cooling device that cools the nuclear fuel by cooling the cooling water,
A gravity-type cooling water injection water tank that is provided above the water surface of the cooling water inside the reactor pressure vessel and stores other cooling water in a predetermined amount therein.
A water supply pipe communicating the gravity-type cooling water injection water tank with the reactor pressure vessel;
The nuclear fuel is provided in the middle of the water supply pipe and the nuclear fission reaction is controlled by the control rod so that the nuclear fuel generates decay heat accompanying the decay, and the operation of the core cooling device is stopped. An on-off valve for water supply that is opened when the temperature of the cooling water is equal to or higher than a predetermined temperature,
A pressure equalizing pipe for equalizing the internal pressure of the reactor pressure vessel with the pressure of the space in the gravity-type cooling water injection water tank ;
After the predetermined time has elapsed since the water supply opening / closing valve was opened, or the other cooling water stored in the gravity-type cooling water injection water tank was opened after the water supply opening / closing valve was opened. When the temperature of the cooling water inside the reactor pressure vessel falls below another predetermined temperature by being supplied to the inside of the reactor pressure vessel, the decay heat is released into the atmosphere. A heated loop heat pipe,
The loop heat pipe condenses the vaporized working fluid by dissipating heat of the vaporized working fluid, a vaporizing unit that heats and vaporizes the working fluid, and the vaporized working fluid. A condensing unit, a vapor pipe for flowing the working fluid vaporized in the evaporation unit toward the condensing unit, a liquid return pipe for flowing the working fluid condensed in the condensing unit toward the evaporating unit, A reservoir that stores the working fluid; a connection pipe that communicates the reservoir with the liquid return pipe; and a portion of the connection pipe or the liquid return pipe that is in communication with the connection pipe. And a main valve that regulates the flow of the working fluid,
The evaporation unit is disposed so as to be capable of transferring heat to the reactor pressure vessel, and the condensing unit is disposed above the reactor pressure vessel and exposed to the atmosphere,
The main valve is stored in the gravity-type cooling water injection water tank after a predetermined time has elapsed since the water supply opening / closing valve is opened or after the water supply opening / closing valve is opened. Opening operation is performed when the temperature of the cooling water in the reactor pressure vessel becomes equal to or lower than the predetermined temperature because other cooling water is supplied into the reactor pressure vessel. Configured as
Inside the reactor pressure vessel, a shroud that supports the nuclear fuel and a jet pump that flows the cooling water are provided,
The evaporating section includes a plurality of pipes arranged between the shroud or the jet pump and the reactor pressure vessel, a first header for communicating one end of the pipes with the liquid return pipe, A second header that communicates the other end of the pipe with the steam pipe, and the working fluid is configured to be vaporized by being heated by the decay heat in each header and each pipe. A reactor decay heat removal apparatus characterized by the above. The water supply pipe communicates with the lower part of the reactor pressure vessel,
The equalizing pressure tube according to claim 1, characterized in that in communication with said reactor pressure vessel side of the water supply on-off valve in the water supply pipe and the upper portion of the gravity coolant injection water tank A decay heat removal device for nuclear reactors.

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