JP2012013555A - Method for chemical decontamination of nuclear power plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for chemical decontamination capable of shortening the time required for chemical decontamination work.SOLUTION: In a chemical decontamination system, a surge tank 1 provided with a heater 2, circulation pumps 4, 5, a mixed bed resin tower 7, a cation resin tower 8, and a reducing agent decomposition device 9 are provided along a circulation pipe line 30. One end part of the circulation pipe line 30 is fixed to a mounting jig 25 with a plurality of through holes formed thereon. The mounting jig 25 is inserted in an upper end of a vertical part 24c of a riser pipe 24. No sealing is provided between the vertical part 24c and the mounting jig 25. Decontamination liquid boosted by the circulation pump 4 is supplied by the circulation pipe line 30 to the inside of the vertical part 24c where the mounting jig 25 is inserted, flows through the riser pipe 24, a ring header 23, and a recirculation pipe 22, and returns to the circulation pipe line 30, which allows inside surfaces of the pipes to be decontaminated. A free liquid level of the decontamination liquid is formed in the vertical part 24c.

Description

  The present invention relates to a chemical decontamination method for a nuclear power plant, and more particularly to a chemical decontamination method for a nuclear power plant suitable for application to decontamination of a recirculation system piping of a boiling water nuclear power plant.

  Cooling water in the reactor pressure vessel of the boiling water nuclear power plant (hereinafter referred to as reactor water) is pressurized by the recirculation pump, passes through the recirculation system piping, and is formed outside the reactor core in the reactor pressure vessel. It is supplied to a nozzle of a jet pump arranged in an annular downcomer. When the pressurized reactor water is injected into the bell mouth of the jet pump from this nozzle, the reactor water in the downcomer around the nozzle is sucked into the bell mouth, and the reactor water discharged from the jet pump is supplied to the core. Is done.

  The reactor water supplied into the core is heated by the heat generated by the nuclear fission of the nuclear fuel material contained in the fuel assembly loaded in the reactor core, and a part of the reactor water becomes steam. The steam is supplied to a turbine connected to a generator after moisture is removed by a steam separator and a steam dryer in the reactor pressure vessel. The turbine is rotated by steam to generate electricity.

  A plurality of jet pumps are disposed in the downcomer surrounding the core. These jet pumps are supplied with reactor water from the recirculation piping. In order to distribute the reactor water from the recirculation system pipe to each jet pump, the recirculation system pipe is connected to a semicircular ring header to which a riser pipe connected to each nozzle of each jet pump is connected. Yes. The ring header is a horizontal pipe and is disposed outside the reactor pressure vessel. Each riser pipe is a vertical pipe and penetrates the reactor pressure vessel, and a part thereof is disposed in the reactor pressure vessel.

  On the other hand, the boiling water nuclear power plant is trying to improve the reliability by applying the preventive maintenance technology developed along with the advancement of technology. As part of preventive maintenance, recirculation piping is regularly inspected to confirm the soundness of welds and the like of the recirculation piping.

  An oxide film containing a radioactive substance adheres to the inner surface of the recirculation piping. For this reason, removing the radioactive material by removing this oxide film prior to the inspection or repair work of the recirculation system piping is effective in reducing the exposure during the check or repair work. In order to remove the oxide film, a chemical decontamination method is used in which the oxide film is dissolved using a chemical.

  Examples of chemical decontamination of recirculation piping in a boiling water nuclear power plant are described in Japanese Patent Application Laid-Open No. 2005-164344, Japanese Patent Application Laid-Open No. 2009-109253, and Japanese Patent Application Laid-Open No. 11-109094.

  The chemical decontamination described in JP-A-2005-164344 and JP-A-2009-109253 uses a chemical decontamination apparatus to supply an oxidative decontamination solution into the recirculation system pipe and to supply the recirculation system pipe. The inner surface is oxidatively decontaminated, and then the inner surface of the recirculation piping is reductively decontaminated with a reducing decontamination solution. In these chemical decontamination methods, the free liquid level of the decontamination liquid is formed in the recirculation piping while chemical decontamination is performed.

  The chemical decontamination apparatus includes a circulation line, a heater, a surge tank, two circulation pumps, a cation resin tower, a mixed bed resin tower, and a reducing agent decomposition apparatus. A heater is provided in the surge tank. A surge tank, a circulation pump, a cation resin tower, a mixed bed resin tower, and a reducing agent decomposition apparatus are provided in the circulation line. A chemical inlet for introducing a decontamination agent is provided in a pipe line connecting the circulation pipe and the surge tank.

  When chemical decontamination is performed on the recirculation pipe, one end of the circulation pipe is connected to the recirculation pipe upstream of the recirculation pump provided in the recirculation pipe, and the other end of the circulation pipe is Connected to the recirculation piping downstream of the recirculation pump. The surge tank and the circulation line are filled with water. One circulation pump (referred to as the first circulation pump) is installed in the circulation line downstream of the surge tank, and supplies water or decontamination liquid (oxidation decontamination liquid and reductive decontamination liquid) to the recirculation system piping. . Another circulation pump (referred to as a second circulation pump) is installed in the circulation line upstream of the surge tank, and returns water or decontamination liquid in the recirculation system pipe to the surge tank.

  Before decontaminating the recirculation system piping by introducing the decontamination agent from the chemical inlet, the first and second circulation pumps are driven, and the water in the surge tank is formed by the recirculation system piping and the circulation pipeline. Circulate in a closed loop. The number of water supplied from the first circulation pump to the recirculation system pipe is increased by the number of rotations of the first circulation pump higher than that of the second circulation pump, and the amount of water sucked from the recirculation system pipe by the second circulation pump More than the amount. As a result, the liquid level in the riser pipe rises, and when the liquid level reaches a predetermined liquid level, the increase in the number of rotations of the first circulation pump is stopped, and the predetermined liquid level is maintained in the riser pipe. Each of the first circulation pump and the second circulation pump is operated at a constant rotational speed.

  Then, the power supply of the heater installed in the surge tank is turned on to heat the water in the surge tank, and the temperature of the water supplied to the circulation pipe is increased to the set temperature. Then, an oxidizing agent (for example, potassium permanganate) is supplied from the chemical inlet and supplied to the surge tank, and the oxidizing agent is dissolved in water in the surge tank to generate an oxidative decontamination solution. This oxidative decontamination liquid is supplied into the recirculation system pipe through the circulation line by the driven first circulation pump. The oxidative decontamination liquid is also supplied into the vertical riser pipe by natural convection. The oxidative decontamination liquid in the recirculation system pipe is returned to the surge tank through the circulation line by the driven second circulation pump. By maintaining this state for several hours, the oxidative decontamination solution performs oxidative decontamination, and dissolves chromium oxide and the like taken into the oxide film adhering to the inner surface of the recirculation piping.

  When the oxidative decontamination on the inner surface of the recirculation piping is completed, a reducing agent (for example, oxalic acid) is supplied from the chemical inlet and supplied to the surge tank. By supplying the reducing agent in an amount more than necessary for decomposing the oxidizing agent contained in the oxidizing decontamination solution, the reducing decontamination solution is generated in the surge tank. The reductive decontamination liquid is also supplied into the recirculation pipe by the first circulation pump. The reductive decontamination solution is also supplied into the vertical riser pipe by natural convection. The reductive decontamination liquid in the recirculation system pipe is returned to the surge tank through the circulation line by the second circulation pump. By holding this state for about 10 hours, the reductive decontamination solution performs reductive decontamination, and dissolves iron oxide, which is the main component of the oxide film attached to the inner surface of the recirculation piping. The reducing decontamination liquid returned to the circulation line is supplied to the cationic resin tower, and the metal ions dissolved by the reducing decontamination liquid and the metal ions generated by the decomposition of the oxidative decontamination liquid are removed by the cationic resin tower. After the reduction decontamination is completed, the reducing agent contained in the reduction decontamination solution is decomposed by the decontamination agent decomposing apparatus. Thus, chemical decontamination is completed.

  In JP 2005-164344 A, in the above chemical decontamination, the liquid level is raised to the ring header, and the inner surface of the ring header is also subjected to chemical decontamination by the decontamination liquid (oxidation decontamination liquid and reduction decontamination liquid). Is going. In this chemical decontamination, the decontamination liquid supplied to the ring header and the riser pipe rises in the ring header and the riser pipe. And the temperature of the decontamination liquid in the riser pipe falls. For this reason, the decontamination efficiency of the inner surface of a ring header and a riser pipe will fall.

  In the chemical decontamination described in JP 2009-109253 A, in order to solve this problem, an electric heater is installed at a decontamination site such as a ring header, and a decontamination solution at the decontamination site such as a ring header. Prevents temperature drop. However, due to the problem of the circulation pump capacity, it takes time to raise the liquid level in the riser pipe, and decontamination cannot be performed in the process of raising the liquid level, and the work time for chemical decontamination becomes longer as a whole. Further, since the electric heater needs to be attached before chemical decontamination, the amount of exposure of the worker increases when the electric heater is attached to the ring header or the like.

  The chemical decontamination method described in FIG. 11 of JP-A-11-109094 supplies decontamination liquid from the reactor pressure vessel to the recirculation system piping. In this chemical decontamination method, the inlet mixer including the nozzle and throat of the jet pump and the bent pipe part connecting the nozzle and the riser pipe is removed from the diffuser and riser pipe of the jet pump, the upper end of the riser pipe, and the recirculation The other end of the system pipe (the end connected to the riser pipe and different from the end of the recirculation system pipe) is sealed with a closing plug. A decontamination solution supply hose attached to one end of the circulation pipe of the chemical decontamination equipment placed on the operation floor in the reactor building is attached to the pipe provided through the closure plug attached to the riser pipe. ing. Another decontamination liquid return hose attached to the other end of the circulation line of the chemical decontamination equipment is attached to the pipe provided through the other closing plug attached to the other end of the recirculation system pipe. It has been. The decontamination liquid supplied from the chemical decontamination device to the riser pipe through the decontamination liquid supply hose flows through the riser pipe and the recirculation system pipe, and is returned to the chemical decontamination apparatus by the decontamination liquid return hose. By circulating the decontamination solution in this way, the inner surfaces of the riser pipe and the recirculation system pipe are decontaminated.

  In the chemical decontamination method described in JP-A-11-109094, the decontamination liquid heated by the chemical decontamination apparatus is forcibly circulated in the riser pipe and the recirculation system pipe. It does not decrease, and there is no need to install an electric heater at a decontamination site such as a ring header as in the chemical decontamination method described in JP-A-2009-109253. Moreover, in the chemical decontamination method described in Japanese Patent Application Laid-Open No. 11-109094, it is not necessary to drain high-dose reactor water in the reactor pressure vessel.

JP 2005-164344 A JP 2009-109253 A Japanese Patent Laid-Open No. 11-109094

  In a boiling water nuclear power plant, a plurality of jet pumps (for example, 10 jet pumps) are installed in a downcomer. In the chemical decontamination method described in JP-A-11-109094, the decontamination liquid heated in the chemical decontamination apparatus is forced to circulate in the riser pipe and the recirculation system pipe. All the riser pipes other than the riser pipe sealed with the closed plug to which the connected decontamination liquid supply hose is attached need to be sealed with the closed plug not provided with the pipe to which the hose is attached. When decontaminating the inner surfaces of all riser tubes, each inlet plug with multiple decontamination solution supply hoses (for example, 10 hoses) connected to the chemical decontamination equipment is connected to the inlet mixer. It must be attached to the upper end of the removed riser tube.

  Each closing plug is attached to each riser pipe by supplying compressed air into each closing plug to inflate the closing plug to contact the inner surface of the riser pipe. The gap between the closing plug and the riser pipe is sealed by the expansion of the closing plug. A closing plug having a decontamination liquid return hose attached to the other end of the recirculation system pipe is also attached to the other end of the recirculation system pipe in the same manner as the upper end of the riser pipe. The gap between the closing plug and the recirculation pipe is also sealed by the expansion of the closing plug.

  If the decontamination liquid leaks from the upper end of the riser pipe and the other end of the recirculation system pipe and enters the reactor water in the reactor pressure vessel, all the reactor water is discharged from the reactor pressure vessel. Therefore, it is necessary to clean the inside of the reactor pressure vessel.

  According to such Japanese Patent Laid-Open No. 11-109094, it takes time to perform sealing work to prevent the leakage of the decontaminating agent, which is performed on the upper end of each riser pipe and the other end of the recirculation system pipe. Become. As a result, the decontamination work takes a long time.

  The objective of this invention is providing the chemical decontamination method of a nuclear power plant which can shorten the time which chemical decontamination work requires.

  A feature of the present invention that achieves the above-described object is that a reactor vessel, a recirculation system pipe disposed at the outside of the reactor vessel and having one end connected to the reactor vessel and provided with a recirculation pump, a recirculation system pipe A plurality of riser pipes connected to the outer pipe part connected to the reactor vessel nozzle and the recirculation pipe, and the vertical pipe part connected to the nozzle and existing in the reactor vessel. In a chemical decontamination method for a nuclear power plant, a mounting jig to which a decontamination liquid supply end of a decontamination liquid pipe provided in a chemical decontamination apparatus is attached is inserted into a vertical pipe having an open top. The recirculation system pipe between the end of the recirculation system pipe connected to the recirculation pump and the reactor vessel. To the first space above the liquid level of water formed in the reactor vessel In the state where the second space formed in the vertical pipe portion below the mounting jig and above the free liquid surface formed in the vertical pipe portion is in communication, the decontamination liquid is introduced into the vertical pipe portion through the decontamination liquid conduit. It is to supply.

  When the mounting jig to which the decontamination liquid supply end of the decontamination liquid pipeline is attached is placed in the vertical pipe section with the upper end open, it is above the water level formed in the reactor vessel. Since the first space in the vertical pipe and the second space formed in the vertical pipe below the mounting jig and above the free liquid surface are in communication with each other, no seal is required. Less time is required for placing the jig in the vertical tube. For this reason, the time required for chemical decontamination including the preparation stage can be shortened.

  According to the present invention, the time required for the chemical decontamination work can be shortened.

It is a block diagram of the chemical decontamination apparatus used for the chemical decontamination method of the nuclear power plant of Example 1 which is one suitable Example of this invention. It is explanatory drawing which shows the process of the chemical decontamination method of Example 1 using the chemical decontamination apparatus shown in FIG. It is explanatory drawing which shows the mounting state of the decontamination liquid supply line to the riser pipe upper end part in the nuclear reactor pressure vessel shown in FIG. It is an expansion perspective view of the mounting part of the decontamination liquid supply pipeline shown in FIG. It is the characteristic view which showed the relationship between the dissolution rate of the iron oxide in a decontamination liquid, and the temperature of a decontamination liquid.

  Examples of the present invention will be described below.

  A nuclear plant chemical decontamination method applied to a boiling water nuclear plant, which is a preferred embodiment of the present invention, will be described with reference to FIGS.

  First, the chemical decontamination apparatus used for the chemical decontamination method of the nuclear power plant of a present Example is demonstrated based on FIG. As shown in FIG. 1, the chemical decontamination apparatus includes a circulation line (for example, a high-pressure hose) 30, a surge tank 1 provided with a heater 2, circulation pumps 4 and 5, a mixed bed resin tower 7, and a cation resin tower 8. And a reducing agent decomposition apparatus 9. In the circulation line 30, a valve V5, a circulation pump 5, valves V6, V7, V10, V13, V16, a surge tank 1, a circulation pump 4, a valve V1, and a valve V3 are installed in this order from the upstream side. . The circulation pump 4 supplies the decontamination liquid (or water) in the surge tank 1 to the recirculation piping 22 that is a decontamination target. The circulation pump 5 returns the decontamination liquid from the recirculation system pipe 22 to the surge tank 1. The mixed bed resin tower 7 purifies the decontamination liquid, and the cation resin tower 8 removes cations (for example, iron ions) dissolved in the decontamination liquid. The decontamination agent decomposing apparatus 9 decomposes the reducing decontamination agent contained in the decontamination liquid.

  Both ends of the pipeline 34 that bypasses the valve V7 are connected to the circulation pipeline 30 respectively. The cooler 6 is provided in the pipe line 34, and valves V 8 and V 9 disposed upstream and downstream of the cooler 6 are provided in the pipe line 34. A pipe 35 in which the valve V11, the mixed bed resin tower 7 and the valve V12 are provided in this order from the upstream side is provided to bypass the valve V10, and both ends of the pipe 35 are connected to the circulation pipe 30 respectively. A pipe line 36 in which the valve V14, the cation resin tower 8 and the valve V15 are provided in this order from the upstream side is provided to bypass the valve V13, and both ends of the pipe line 36 are connected to the circulation pipe line 30, respectively. Both ends of a pipe line 33 provided with the decontamination agent disassembling apparatus 9 and bypassing the valve V16 are connected to the circulation pipe line 30. A valve V17 located upstream of the decontamination agent decomposing apparatus 9 and a valve V18 located downstream of the decontamination agent decomposing apparatus 9 are provided in the pipe line 33, respectively. A line 32 connected to the circulation line 30 downstream of the valve V1 is connected to the surge tank 1. A valve V2 and a chemical inlet 3 are provided in the conduit 32. One end of the bypass pipe 31 provided with the valve V4 is connected to the circulation pipe 30 between the valve V5 and the circulation pump 5, and the other end of the bypass pipe 31 is connected to the connection point between the pipe 32 and the circulation pipe 30 and the valve. Connected to the circulation line 30 between V3.

  The mounting jig 25 having a plurality of through holes 37 is attached to the downstream end (decontamination liquid supply end) of the circulation conduit 30 (see FIG. 4). The circulation line 30 is attached to the mounting jig 25 through the center of the mounting jig 25. A plurality of through holes 37 are arranged so as to surround the circulation conduit 30. Instead of the plurality of through holes, a plurality of grooves that penetrate the mounting jig 25 may be formed on the side surface of the mounting jig 25.

  In this embodiment, a schematic configuration of a boiling water nuclear power plant to be subjected to chemical decontamination will be described with reference to FIG. The boiling water nuclear power plant has a reactor pressure vessel 20 containing a core (not shown) loaded with a plurality of fuel assemblies (not shown), and a recirculation system. The recirculation system includes a recirculation system pipe 22 provided with a recirculation pump 41, a ring header 23, and a plurality of riser pipes 24. A cylindrical core shroud (not shown) is installed in the reactor pressure vessel 20 and surrounds the core. A downcomer (not shown), which is an annular region, is formed between the core shroud and the reactor pressure vessel 20. A plurality of jet pumps (not shown) for supplying reactor water to the reactor core are disposed in the downcomer surrounding the reactor core. Although not shown, the jet pump includes a nozzle, a bell mouth, a throat, and a fuser. The bell mouth is fixed to the upper end of the throat, and the lower end of the throat is removably attached to the upper end of the diffuser. The nozzle is disposed above the bell mouth and is fixed to the bell mouth by a plurality of support plates.

  One end of a recirculation system pipe 22 arranged outside the reactor pressure vessel 20 is connected to a nozzle provided in the reactor pressure vessel 20 and communicated with a downcomer. The other end of the recirculation pipe 2 is disposed outside the reactor pressure vessel 20 and connected to a semicircular ring header 23. A plurality of riser tubes 24 are connected to the ring header 23. The number of riser tubes 24 is equal to the number of jet pumps installed in the reactor pressure vessel 20. Each riser tube 24 has a vertical tube portion 24 a and a horizontal tube portion 24 b disposed outside the reactor pressure vessel 20, and a vertical tube portion 24 c disposed inside the reactor pressure vessel 20. The vertical tube portion 24a and the horizontal tube portion 24b are referred to as external tube portions. The horizontal pipe portion 24b is connected to a nozzle (N2 nozzle) 21 provided in the reactor pressure vessel 20 (see FIG. 3). The lower end portion of the vertical pipe portion 24c is also connected to the nozzle 21 (see FIG. 3). One end of the bent pipe (not shown) is detachably attached to the upper end of the vertical pipe portion 24 c of the riser pipe 24. The other end of the bent pipe is connected to the nozzle of the jet pump. A joint portion (for example, a branch pipe) 27b provided with the coupling valve 29b is connected to the vertical pipe portion 28b of the recirculation system pipe 22 located upstream of the recirculation pump 41. A closing plate 26b is attached to the lower end of the joint portion 27b and seals the joint portion 27b. A junction (for example, a branch pipe) 27 a is connected to a vertical pipe part 28 a of the recirculation system pipe 22 located upstream of the recirculation pump 41. A closing plate 26a is attached to the lower end of the joint portion 27a and seals the joint portion 27a.

  At the time of operation of the boiling water nuclear power plant, the recirculation pump 41 is driven, and the reactor water in the downcomer is sucked into the recirculation system pipe 22 by the recirculation pump 41 to be pressurized and led to the ring header 23. . Reactor water that has reached the ring header 23 is distributed into the plurality of riser pipes 24, rises in the riser pipes 24, and is supplied to the nozzles of the respective jet pumps. Reactor water is injected into the bell mouth from the nozzle, and the reactor water present in the downcomer around the nozzle is sucked and flows into the bell mouth by the jet flow of the reactor water. The injected reactor water and the sucked reactor water are discharged from the jet pump through the throat and the diffuser and supplied to the core. Reactor water supplied to the core is heated by heat generated by fission of nuclear fuel material contained in the fuel assembly, and a part of the reactor water becomes steam. The steam is supplied to the turbine after moisture is removed by a steam separator and a steam dryer in the reactor pressure vessel.

  When the operation of the boiling water nuclear power plant in one operation cycle is completed, the boiling water nuclear power plant is stopped and a periodic inspection of the boiling water nuclear power plant is performed. Before the periodic inspection of the recirculation system pipe 22 and the like is started, chemical decontamination of the recirculation system pipe 22 is performed. The chemical decontamination method of this example will be specifically described with reference to FIGS.

  After shutting down the boiling water nuclear power plant, the upper lid 39 (see FIG. 3) of the reactor pressure vessel 20 is removed, and a steam dryer (not shown) and a steam / water separator installed in the reactor pressure vessel 20 (Not shown) is removed and carried out of the reactor pressure vessel 20. The bent tube and jet pump nozzle, bell mouth and throat are integrated to form an inlet mixer. This inlet mixer can be removed by releasing the connection relationship between the bent pipe and the vertical portion 24c and releasing the connection relationship between the throat and the diffuser. Before performing chemical decontamination of the recirculation system pipe 22, an inlet mixer for one jet pump among a plurality of jet pumps installed in the reactor pressure vessel 20 is removed and moved out of the reactor pressure vessel 20. Take it out.

  The chemical decontamination apparatus shown in FIG. 1 is installed outside the reactor containment vessel (not shown) in the reactor building. The circulation line 30 is arranged in the reactor containment vessel, and the end of the circulation line 30 to which the mounting jig 25 is attached is connected to the reactor pressure vessel from the operation floor (not shown) of the reactor building. 20 is lowered. An operator on a refueling machine (not shown) moving on the operation floor uses the tongue to insert the mounting jig 25 into the vertical pipe portion 24c of the riser pipe 24 from which the inlet mixer has been removed. It arrange | positions at the upper end part of the pipe part 24c (refer FIG. 3). Thereafter, a plurality of spacer members 40 are arranged on the upper flange of the reactor pressure vessel 20, and the upper lid 39 is placed on these spacer members 39. In the present embodiment, when performing chemical decontamination in the recirculation system piping 22 or the like, the coolant water level 41 (see FIG. 3) in the reactor pressure vessel 20 exists in the reactor pressure vessel 20. The riser is lowered below the upper end of the vertical pipe portion 24c of the riser pipe. By placing the upper lid 39 on the flange on the upper part of the reactor pressure vessel 20 through the plurality of spacer members 40, radiation emitted from the reactor pressure vessel 20 toward the operation floor is shielded by the upper lid 39. be able to.

  The diameter of the mounting jig 25 is substantially the same as the inner diameter of the vertical tube portion 24c. The connection jig 25 has a role of preventing vibration of the circulation line 30 when the decontamination liquid is injected from the circulation line 30 into the riser pipe 24. The other end of the circulation conduit 30 is attached to a joint valve 29b provided at the joint 27b. By placing the mounting jig 25 of the circulation pipe 30 in the upper end of the vertical pipe 24c and connecting the other end (contamination liquid receiving end) of the circulation pipe 30 to the joint valve 29b, the circulation pipe 30, the closed loop which connects the riser pipe | tube 24, the recirculation system piping 22, and the junction part 27b is formed.

  Before placing the mounting jig 25 in the upper end of the vertical pipe portion 24c, the reactor water in the reactor pressure vessel 20 is discharged from a drain pipe (not shown) connected to the bottom of the reactor pressure vessel 20. Thus, the liquid level of the reactor water in the reactor pressure vessel 20 is lowered below the upper end of the vertical pipe portion 24c.

  After the communication to the recirculation system pipe 22 of the circulation line 30 of the chemical decontamination apparatus is completed, the steps S1 to S9 shown in FIG. 2 are performed. First, a valve is opened and closed to configure a system (step S1). Among the valves provided in the chemical decontamination apparatus, the valves V1, V4, V6, V7, V10, V13, and V16 are set to “open”, and the other valves are set to “closed”. In this state, pure water is filled in the chemical decontamination equipment such as the surge tank 1 and the circulation pipe 30. The operation of the chemical decontamination apparatus is started (step S2). By starting the circulation pumps 4 and 5, the pure water in the surge tank 1 is circulated in the closed loop formed by the circulation pipe 30 and the bypass pipe 31. At this time, since the valves V3 and V5 are closed, pure water is not supplied into the recirculation pipe 22. Thereafter, pure water is filled into the chemical decontamination object (step S3). The valves V3 and V5 are “opened”, the valve V4 is “closed”, and pure water in the surge tank 1 is supplied to the recirculation system pipe 22 through the circulation line 30 by the circulation pump 4. The pure water supplied into the recirculation pipe 22 is returned to the surge tank 1 through the circulation pipe 30 by the circulation pump 5. The pure water whose pressure has been increased by the circulation pump 4 is supplied by the circulation pipe 30 to the vertical pipe portion 24 c of the riser pipe 24 in which the mounting jig 25 is inserted. Thereafter, the pure water flows through the horizontal pipe portion 24 b and the vertical pipe portion 24 a of the riser pipe 24, the ring header 23 and the recirculation system pipe 22, and is discharged from the joint portion 27 b to the circulation pipe line 30. As described above, the pure water circulates in the closed loop formed by the circulation pipe 30, the riser pipe 24, the recirculation system pipe 22, and the joint portion 27 b.

  The number of rotations of the circulation pump 5 is controlled, and the inside of the vertical pipe part 28b is below the end of the recirculation system pipe 22 on the vertical pipe part 28b side and above the junction of the recirculation system pipe 22 and the joint part 27b. The amount of pure water that the circulation pump 5 sucks from the recirculation system pipe 22 is adjusted so that a free liquid level is formed. Further, the rotational speed of the circulation pump 4 is controlled to be larger than the rotational speed of the circulation pump 5, and the flow rate of pure water supplied to the recirculation system pipe 22 by the circulation pump 4 is recirculated by the circulation pump 5. The free water level 38 of pure water is formed in the vertical pipe portion 24 c of the riser pipe 24 by increasing the flow rate of pure water sucked from the pipe 22. The free liquid level 38 exists at a position higher than the free liquid level formed in the vertical pipe portion 28b. A free liquid level 38 is formed not only in the riser pipe 24 in which the mounting jig 25 is inserted, but also in each vertical pipe portion 24c of all the remaining riser pipes 24 in which the mounting jig 25 is not inserted. The In this state, a space (second space) formed below the mounting jig 25 and above the free liquid surface 38 in the vertical pipe portion 24c is passed through the through hole 37 formed in the mounting jig 25. The reactor pressure vessel 20 communicates with a space (first space) formed above the liquid level of the reactor water.

  In this embodiment, pure water is supplied into the recirculation pipe 22 in step S3 after step S2. However, the process in step S2 is omitted, and the process in step S3 is performed after step S1. Also good.

  Pure water is heated (step S4). After the inside of the recirculation system pipe 22 is filled with pure water by supplying pure water to the recirculation system pipe 22, the power supply of the heater 2 provided in the surge tank 1 is turned on. The pure water in the surge tank 1 is heated, and the temperature of the pure water rises. The heated pure water is supplied into the recirculation system pipe 22 via the vertical pipe portion 24 c by the circulation pipe 30. By the heating by the heater 2, the temperature of pure water rises to a set temperature (for example, 90 ° C.). The temperature of pure water is maintained at a set temperature, for example, 90 ° C., by turning ON / OFF the current to the heater 2. The temperature of pure water in the recirculation piping 22 will eventually reach 90 ° C. The supply of heated pure water to the recirculation system pipe 22 preheats the riser pipe 24 and the recirculation system pipe 22, and the temperature of these pipes is maintained at around 90 ° C.

  An oxidative decontamination agent is introduced (step S5). After pure water rises to the set temperature, an oxidative decontamination agent (for example, potassium permanganate) is introduced into the pipe line 32 from the chemical inlet 3. The charged oxidative decontamination agent is introduced into the surge tank 1 and dissolved in pure water to produce an oxidative decontamination solution containing potassium permanganate. The oxidative decontamination agent introduced is circulated in a closed loop formed by the circulatory line 30, the riser pipe 24, the recirculation system pipe 22 and the joint portion 27b. An oxidative decontamination solution that dissolves completely and has a uniform concentration of oxidative decontamination agent is produced. By maintaining the state in which the oxidative decontamination liquid circulates in this closed loop for several hours, chromium oxidation adhered to the inner surfaces of the recirculation system pipe 22, the ring header 23, and the riser pipe 24 by the action of the oxidative decontamination liquid. Things are dissolved. The oxidative decontamination agent reaches the vicinity of the free liquid level by diffusion also in the vertical pipe part 28b of the recirculation system pipe 22 and the vertical pipe parts 24c of all the riser pipes 24. For this reason, the inner surface below the free liquid level in the vertical pipe part 28b and the inner surfaces below the free liquid level 38 formed in each vertical pipe part 24c of all the riser pipes 24 are oxidized. It is oxidatively decontaminated with a decontamination solution (removal of chromium oxide). During the oxidative decontamination, the oxidative decontamination liquid is maintained at a set temperature (for example, 90 ° C.).

  After the oxidative decontamination of the recirculation pipe 22 and the like is completed, a reducing decontaminant is introduced (step S6). After the completion of oxidative decontamination, a reducing agent decontaminating agent (for example, oxalic acid) is introduced into the conduit 32 from the chemical inlet 3. This oxalic acid is guided into the surge tank 1 and is dissolved by the oxidative decontamination solution. Oxalic acid decomposes an oxidative decontamination agent (for example, potassium permanganate) contained in the oxidative decontamination solution. The oxidative decontamination solution becomes water by the decomposition of the oxidative decontamination agent. After the decomposition of the oxidative decontaminant is completed, the valves V14 and V15 are opened and the valve V13 is closed. By opening and closing these valves, water flowing in the circulation pipe 30 is guided to the cation resin tower 8 through the pipe 36.

  Thereafter, a reductive decontaminant is additionally charged (step S7). A reducing agent decontaminating agent is further introduced into the conduit 32 from the chemical inlet 3. This reductive decontaminant is introduced into the surge tank 1 and dissolved in pure water to produce a reductive decontamination solution containing oxalic acid. The reductive decontaminating agent introduced is circulated in a closed loop formed by the recirculation conduit 30, the riser pipe 24, the recirculation system pipe 22, and the joint portion 27b. A reductive decontamination solution that is completely dissolved and has a uniform concentration of reductive decontamination agent is produced. By maintaining the state in which the reductive decontamination liquid circulates in this closed loop for 10 or more hours, the iron adhering to the inner surfaces of the recirculation system pipe 22, the ring header 23, and the riser pipe 24 by the action of the reductive decontamination liquid. The oxide is dissolved. The reducing decontaminant reaches the vicinity of the free liquid level by diffusion also in the vertical pipe part 28b of the recirculation system pipe 22 and the vertical pipe part 24c of the riser pipe 24. Therefore, the inner surface below the free liquid level in the vertical pipe portion 28b and the inner surfaces below the free liquid surface 38 formed in each vertical pipe portion 24c of all the riser pipes 24 are reduced. Reduction decontamination is performed with the decontamination solution (removal of iron oxide). The iron oxide removed from the inner surface of the pipe by the reducing decontamination solution exists as iron ions in the reducing decontamination solution. The reductive decontamination liquid returned from the recirculation pipe 22 to the circulation pipe 30 is supplied to the cation resin tower 8. Iron ions contained in the reductive decontamination agent are removed by the cation ion exchange resin in the cation resin tower 8. During the reduction decontamination, the reduction decontamination liquid is maintained at a set temperature (for example, 90 ° C.).

  After the reduction decontamination is completed, the reduction decontamination agent contained in the reduction decontamination liquid is decomposed (step S8). When the reduction decontamination is completed, the valves V17 and V18 are opened and the valve V16 is closed. Thereby, the reductive decontamination liquid flowing in the circulation line 30 is supplied to the decontamination agent decomposing apparatus 9 through the line 33. The decontaminating agent decomposing apparatus 9 is filled with a catalyst, and when decomposing the reducing decontaminating agent contained in the reducing decontamination liquid, for example, oxalic acid, the decontaminating agent decomposing apparatus 9 is supplied with an oxidizing agent (for example , Hydrogen peroxide). The reducing decontaminating agent contained in the reducing decontamination liquid supplied to the decontaminating agent decomposing apparatus 9 is decomposed by the action of the catalyst and hydrogen peroxide.

  Water is passed through the mixed bed resin tower (step S9). After the decomposition of the reductive decontaminant is completed, the valves V8, V9, V11, V12, and V13 are each opened, and the valves V7, V10, V14, and V15 are each closed. The water returned from the recirculation pipe 22 to the circulation pipe 30 is cooled by the cooler 6 and then supplied to the mixed bed resin tower 7 to be purified.

  The chemical decontamination by each process of step S5-S9 is made into 1 cycle, and it repeats about 2 to several cycles according to the contamination degree of the recirculation system piping 22, and chemical decontamination is complete | finished.

  According to the present embodiment, the mounting jig 25 to which one end portion of the circulation pipe 30 is attached is inserted into the vertical pipe portion 24c of one riser pipe 24, and decontamination at a set temperature (for example, 90 ° C.). Since the liquid is supplied to the vertical pipe portion 24c, the temperature of the vertical pipe portion 24 is not lowered, and the efficiency of oxidative decontamination and reductive decontamination is improved. The relationship between the temperature of the decontamination solution and the decontamination effect will be described with reference to FIG. The solubility of the iron oxide that is the main component of the oxide film attached to the inner surface of the recirculation system pipe 22 increases as the temperature of the decontamination liquid (for example, reduction decontamination liquid) present in the recirculation system pipe 22 increases. Tend to. However, when the temperature of the decontamination liquid is lowered from 90 ° C. to 70 ° C., the decontamination effect is halved.

  DF (Decontamination Factor: dose equivalent rate before chemical decontamination / dose equivalent rate after chemical decontamination) is used as a coefficient representing the effect of chemical decontamination. According to the present embodiment, the DF of the horizontal pipe portion 24b and the vertical pipe portion 24c of the ring header 23 and the riser pipe 24 is higher than the ring header and the ring header in Japanese Unexamined Patent Publication No. 2009-109253. It becomes larger than each DF of the vertical pipe portion of the pipe.

  In the present embodiment, the mounting jig 25 to which the circulation pipe 30 is attached is inserted into the upper end portion of the vertical pipe portion 24 c of one riser pipe 24. At first glance, this configuration is similar to a configuration in which a closing plug to which one end of a circulation pipe of a chemical decontamination apparatus described in JP-A-11-109094 is attached is inserted into a vertical pipe of a riser pipe. Looks like. The closing plug described in Japanese Patent Application Laid-Open No. 11-109094 is a seal member that maintains airtightness between the vertical pipe portion and the closing plug. However, the mounting jig 25 used in the present embodiment is not a seal member, and it is not necessary to ensure the airtightness between the mounting jig 25 and the vertical pipe portion 24c. Is formed. For this reason, the insertion work of the mounting jig 25 in the present embodiment into the vertical pipe portion 24c of the riser pipe 24 is not required to ensure the sealing performance, and therefore the mounting work of the closing plug in JP-A-11-109094 Compared to this, the time required for the insertion work can be shortened. In Japanese Patent Application Laid-Open No. 11-109094, it is necessary to insert a closing plug at the other end of the recirculation pipe. In this embodiment, the mounting jig 25 is attached to the other end of the recirculation pipe 22. There is no need to insert. In this embodiment, the work of the preparation stage before supplying the decontamination liquid to the recirculation system pipe (the work such as the insertion of the mounting jig 25 into the riser pipe 24 is more than that of JP-A-11-109094. ) Can be shortened. As a result, the time required for chemical decontamination including the preparation stage of chemical decontamination can be shortened.

  In particular, in JP-A-11-109094, it is necessary to remove all the inlet mixers connected to all the riser pipes, but in this embodiment, only one inlet mixer has to be removed. In addition, the time required for chemical decontamination can be shortened.

  In this embodiment, the time required for the mounting jig 25 to be inserted into the vertical pipe portion 24c of the riser pipe 24 can be shortened, so that the work for engaging the mounting jig 25 into the vertical pipe portion 24c is performed. The amount of exposure of personnel can be further reduced.

  In the chemical decontamination method described in JP-A-11-109094, air is present in the circulation line of the chemical decontamination apparatus to which the closing plug is attached when the closing plug is attached to the vertical pipe portion. There is a possibility. In this conventional chemical decontamination method, since the space between the closed plug inserted into the upper end portion of the vertical pipe portion of the riser pipe and the vertical pipe portion is sealed, the air present in the circulation pipe is decontaminated. The liquid cannot be discharged to the outside from the closed loop formed by the circulation pipe and the recirculation system pipe through which the liquid flows, and circulates in the closed loop together with the decontamination liquid. For this reason, cavitation may occur in the two circulation pumps provided in the circulation pipeline. On the other hand, in the present embodiment, since the through hole 37 is formed in the mounting jig 25, air is present in the circulation conduit 30 when the mounting jig 25 is inserted into the vertical pipe portion 24c. Also, this air is discharged into a space formed in the vertical pipe portion 24 c below the mounting jig 25 and above the free liquid level 38, and through the plurality of through holes 37 formed in the mounting jig 25. It is discharged into a space formed above the liquid level of the reactor water in the reactor pressure vessel 20 that is outside the portion 24c. Therefore, in the present embodiment, the air present in the circulation pipe 30 can be easily discharged outside the closed loop formed by the circulation pipe 30 and the recirculation pipe 22 and the like. Thereby, cavitation does not occur in the circulation pumps 4 and 5.

  Moreover, since the through-hole 37 is formed in the mounting jig 25, the decomposing gas generated by the decomposition of the oxidative decontamination solution contained in the oxidative decontamination solution during the oxidative decontamination, and the reductive decontamination during the reductive decontamination. The decomposition gas generated by the decomposition of the reductive decontamination agent contained in the liquid can also be discharged through the through-hole 37 into a space formed above the liquid level of the reactor water in the reactor pressure vessel 20.

  In this embodiment, the flow rate of the decontamination liquid supplied to the recirculation system pipe 22 by the circulation pump 4 is made larger than the flow rate of the decontamination liquid sucked from the recirculation system pipe 22 by the circulation pump 5. The liquid level of the decontamination liquid can be formed in all the vertical pipe parts 24c including the vertical pipe part 24c into which the tool 25 is not inserted, and also to the inner surfaces of the vertical pipe parts 24c of all the riser pipes 24c. Chemical decontamination can be carried out.

  A chemical decontamination method for a nuclear power plant according to embodiment 2, which is another embodiment of the present invention, will be described below. In the chemical decontamination method for a nuclear power plant according to the present embodiment, the mounting jig 25 is inserted into the vertical pipe portion 24c of one riser pipe 24 in the first embodiment, whereas a plurality of riser pipes 24 are arranged. The mounting jig 25 is separately inserted into the upper end portion of each vertical pipe portion 24c.

  The chemical decontamination apparatus used in this example has substantially the same configuration as the chemical decontamination apparatus shown in FIG. However, the number of the vertical pipe portions 24c into which the mounting jigs 25 are inserted downstream of the connection point between the circulation pipe 30 and the bypass pipe 31 because the mounting jigs 25 are separately inserted into the plurality of vertical pipe portions 24c. The circulation line 30 is branched so that the same number (for example, five) is obtained. This branched portion is also referred to as a circulation conduit 30. The end of each branched circulation pipe 30 is attached to a separate mounting jig 25. Each branched circulation line 30 is provided with a valve V3.

  There are five riser pipes 24 connected to one ring header 23, and the reactor water guided by these riser pipes 24 is supplied to the nozzles of five jet pumps as driving water. Each of the inlet mixers attached to these five jet pumps is removed when the boiling water nuclear power plant is shut down. A mounting jig 25 to which the circulation pipe 30 is attached is inserted into the upper end of the vertical pipe 24c of each riser pipe 24 from which the inlet mixer has been removed. The space between each mounting jig 25 and the inner surface of the vertical pipe portion 24c is not sealed.

  Also in the present embodiment, steps S1 to S9 performed in the first embodiment are performed. Pure water, oxidative decontamination liquid, or reductive decontamination liquid pressurized by the circulation pump 4 passes through the five circulation pipes 30 and the five vertical pipe parts 24 into which the mounting jigs 25 are inserted, that is, It is supplied into the upper ends of the five riser tubes 24. Similar to the first embodiment, a free liquid level 38 is formed in each vertical pipe portion 24c. By supplying the oxidative decontamination liquid to the recirculation pipe 22 in step S5 and supplying the reductive decontamination liquid to the recirculation system pipe 22 in step S7, each riser pipe 24, ring header is the same as in the first embodiment. 23 and the oxide adhering to the inner surface of the recirculation pipe 22 can be removed.

  In the present embodiment, the effects produced in the first embodiment can be obtained except for the time required to remove the inlet mixer from each riser tube 24. In the present embodiment, since the mounting jigs 25 are inserted into all the vertical pipe portions 24c, the temperature of all the vertical pipe portions 24c can be raised to the set temperature of the decontamination liquid. For this reason, the decontamination efficiency of the vertical pipe part 24c, the horizontal pipe part 24b, and the vertical pipe part 24a of each riser pipe | tube 24 can be improved.

  DESCRIPTION OF SYMBOLS 1 ... Surge tank, 2 ... Heater, 3 ... Chemical inlet, 4,5 ... Circulation pump, 6 ... Cooler, 7 ... Mixed bed resin tower, 8 ... Cationic resin tower, 9 ... Decontamination agent decomposition apparatus, 20 ... reactor pressure vessel, 22 ... recirculation piping, 23 ... ring header, 24 ... riser pipe, 25 ... mounting jig, 27a, 27b ... joints, 24a, 24c, 28a, 28b ... vertical pipe parts, 30 ... Circulation line, 41 ... circulation pump.

Claims (4)

A reactor vessel, a recirculation system pipe disposed at one end of the reactor vessel and connected to the reactor vessel, and provided with a recirculation pump; a plurality of riser pipes connected to the recirculation system pipe; And a riser pipe having an outer pipe connected to the nozzle of the nuclear reactor vessel and the recirculation pipe, and a vertical pipe connected to the nozzle and existing in the nuclear reactor vessel. In chemical decontamination methods,
Reducing the level of water in the reactor vessel to below the upper end of the vertical pipe section;
Open the upper end of the vertical pipe part, which leads to the jet pump installed in the reactor vessel,
A mounting jig to which a decontamination liquid supply end of a decontamination liquid pipe provided in a chemical decontamination apparatus is attached is inserted into the vertical pipe with the upper end opened and placed in the vertical pipe, A decontamination liquid receiving end of the decontamination liquid conduit is connected to the recirculation system pipe between the recirculation pump and the one end connected to the reactor vessel,
A first free liquid surface is formed in the vertical pipe portion below the mounting jig, and the recirculation pipe is connected between the decontamination liquid receiving end, the connection point of the recirculation pipe and the one end. Forming a second free liquid level inside,
A first space above the water level in the reactor vessel communicates with a second space formed below the mounting jig and above the first free liquid level in the vertical pipe portion. In this state, the decontamination liquid is supplied into the vertical pipe portion through the decontamination liquid pipe line.   The communication state between the first space and the second space is made by any one of a groove and a through hole formed in the mounting jig and open to the upper surface and the lower surface of the mounting jig, respectively. The chemical decontamination method of the described nuclear power plant.   3. The nuclear plant chemistry according to claim 1, wherein the opening of the upper end of the vertical pipe part is performed by removing an inlet mixer including a part of the jet pump and connected to the upper end of the vertical pipe part. Decontamination method.   The position of the second free liquid level in the axial direction of the reactor vessel is the rotational speed of a second pump that is provided in the decontamination liquid pipe and sucks the decontamination liquid in the recirculation system pipe. The first free liquid level is adjusted by controlling, and the position of the first free liquid level in the axial direction of the reactor vessel is provided in the decontamination liquid conduit, and the first decontamination liquid is supplied to the vertical pipe portion. The chemical decontamination method for a nuclear power plant according to any one of claims 1 to 3, wherein the rotational speed of the pump is adjusted to be larger than the rotational speed of the second pump.

Images