JP2017227446A - Chemical decontamination method for pressurized water type nuclear power plants - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chemical decontamination method for pressurized water type nuclear power plants by which nuclear reactor cooling systems contaminated with radioactive substance can be efficiently decontaminated according to a reactor decommissioning plan.SOLUTION: By a chemical decontamination method for pressurized water type nuclear power plants in which a primary cooling system 51, a residual heat removing system 52 and a chemical volume control system 53 are connected to one another via plural boundary valves 10, 20 and 30, all the boundary valves 10 and 20 connected to the primary cooling system 51 are set at least to closure, and decontaminating agent is caused to circulate in the primary cooling system 51.SELECTED DRAWING: Figure 3

Description

  Embodiments of the present invention relate to a method for chemically decontaminating radioactive materials attached to a reactor cooling system of a pressurized water nuclear power plant.

  In recent years, the number of nuclear power plants that have reached the end of their useful lives has increased, and in the future, the number of nuclear power plants that will be decommissioned is expected to increase. In the decommissioning, the nuclear power plant is finally demolished, but as the first step, chemical decontamination of the cooling system is carried out for the purpose of reducing the exposure of decommissioning workers and reducing the dose of waste generated by the demolition.

JP-A-4-276596

  In nuclear power plant decommissioning plans, chemical decontamination of cooling systems may be planned to be performed by dividing the cooling system into multiple sections. For example, in a decommissioning plan, it may be planned to leave a high-dose section for a certain period of time and then dismantle and remove it after the dose has dropped. In this case, chemical decontamination is not performed in the cooling system at the same time so that the period of chemical decontamination and dismantling is too long and impurities do not re-accumulate during the standing period. Chemical decontamination of each section is planned.

  Further, for example, depending on the contamination status of the cooling system, there may be a concern that the low-dose site is contaminated at the time of chemical decontamination by collectively decontaminating the high-dose site and the low-dose site.

  In this way, decommissioning plans for nuclear power plants require decontamination of specific sections at specific times, so chemical decontamination that can only chemically decontaminate only the necessary parts of the reactor cooling system. If there is a way, decommissioning plans can be promoted efficiently.

  Embodiments of the present invention have been made in view of such circumstances, and provide a chemical decontamination method for a pressurized water nuclear power plant capable of chemically decontaminating only necessary portions of a reactor cooling system. The purpose is to do.

  A chemical decontamination method for a pressurized water nuclear power plant according to an embodiment includes a reactor melter, a pump, a pressurizer, and a steam generator, and a primary that circulates a coolant heated in the reactor vessel to the steam generator. A cooling system, a residual heat removal system that lowers the coolant to a predetermined temperature after heating in the reactor vessel is stopped, and a chemical volume control system that is responsible for adjusting the boric acid concentration and holding amount of the coolant. A chemical decontamination method for pressurized water nuclear power plants that are connected to each other via a plurality of boundary valves, in which all boundary valves connected to the primary cooling system are set to at least closed, and decontamination is performed in the primary cooling system. The agent shall be circulated.

  According to an embodiment of the present invention, a chemical decontamination method for a pressurized water nuclear power plant is provided that can efficiently decontaminate a reactor cooling system to which a radioactive substance is attached in accordance with a plan of a decommissioning plan.

The block diagram which shows the structure of the reactor cooling system of a pressurized water nuclear power plant. (A) is a table | surface which shows the decontamination classification and decontamination range prescribed | regulated in the decontamination method of the pressurized water nuclear power plant which concerns on embodiment of this invention, (B) is pressurized water nuclear power generation which concerns on embodiment of this invention. The table | surface which shows the decontamination pattern of each apparatus contained in each decontamination range in the decontamination method of a plant. The figure which shows the decontamination range 1 of the reactor cooling system to which the decontamination method of the pressurized water nuclear power plant which concerns on embodiment is applied. The figure which shows the decontamination range 2 of the reactor cooling system to which the decontamination method of the pressurized water nuclear power plant which concerns on embodiment is applied. The figure which shows the decontamination range 3 of the reactor cooling system to which the decontamination method of the pressurized water nuclear power plant which concerns on embodiment is applied. The figure which shows the decontamination range 4 of the reactor cooling system to which the decontamination method of the pressurized water nuclear power plant which concerns on embodiment is applied. The figure which shows the decontamination range 5, 6, 7 of the reactor cooling system to which the decontamination method of the pressurized water nuclear power plant which concerns on embodiment is applied. (A) is the elements on larger scale of the apparatus which piping connects, (B) is explanatory drawing of the method of isolating equipment from piping, (C) is explanatory drawing of the method of bypassing piping after isolating equipment.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
Prior to the description of the chemical decontamination method for a pressurized water nuclear power plant according to an embodiment of the present invention, the reactor cooling system of the pressurized water nuclear power plant will be described.
As shown in FIG. 1, the reactor cooling system 60 of the pressurized water nuclear power plant includes a system such as a primary cooling system 51, a residual heat removal system 52, and a chemical volume control system 53.

  The primary cooling system 51 and the residual heat removal system 52 are connected to each other via the first boundary valve 10 (10A, 10B, 10C), and the primary cooling system 51 and the chemical volume control system 53 are connected to each other. The residual heat removal system 52 and the chemical volume control system 53 are connected to each other via the third boundary valve 30. The boundary heat 20 and the chemical volume control system 53 are connected to each other via the boundary valve 20 (20 </ b> A, 20 </ b> B, 20 </ b> C).

The primary cooling system 51 includes pipes 2A and 2B that circulate the coolant (light water) heated in the reactor vessel 1 to the steam generators 3A and 3B, and a pump 4A that applies power for circulating the coolant. 4B.
In addition, although the primary cooling system 51 of FIG. 1 has illustrated the case of 2 systems of A and B, it may be comprised from a single system or 3 systems or more.

Here, the suffix “A” added to the reference sign means that the coolant sent from the A system of the primary cooling system 51 to the other system is a member that passes therethrough.
The subscript “B” added to the reference sign means that the coolant sent from the B system of the primary cooling system 51 to the other system passes.
Further, the suffix “C” added to the reference sign means that the coolant returning from one of the other systems to either the A system or the B system of the primary cooling system 51 passes.
The suffix “D” added to the reference sign means that the coolant sent from the residual heat removal system 52 to the chemical volume control system 53 passes therethrough.

From both the pipes 2A and 2B, pipes 6A and 6B from the downstream sides of the pumps 4A and 4B to the pressurizer 5 are branched in both systems A and B.
The branch pipes 6A and 6B are joined together after passing through the on-off valves 7A and 7B, respectively, and connected to the pressurizer 5.

The pressurizer 5 is connected between the reactor vessel 1 and the steam generator 3A only for the piping 2A of the A system after passing through the on-off valve 7C.
The pressurizer 5 installed in this way maintains the coolant circulating through the pipes 2A and 2B and the reactor vessel 1 in a high temperature and high pressure state so as not to boil.

  The primary cooling system 51 configured as described above transmits reaction heat caused by nuclear fission in the core in the reactor vessel 1 to the steam generators 3A and 3B by circulation of the coolant. During the plant operation, the primary cooling system 51 is always in an environment where it is exposed to a high-temperature and high-pressure coolant. Therefore, it is considered that the primary cooling system 51 has the most radioactive metal corrosion products attached to the piping and the inner surface of the equipment in contact with the coolant as compared with the residual heat removal system 52 and the chemical volume control system 53.

  The residual heat removal system 52 starts with pipes 9A and 9B branched from the pipes 2A and 2B sandwiched between the reactor vessel 1 and the steam generators 3A and 3B. The branch pipes 9A and 9B are merged with each other after passing through the first boundary valves 10A and 10B, the pumps 11A and 11B, and the heat exchangers 12A and 12B. It is returned downstream of the 2B pump 4B. In addition, front and rear valves 14A, 14B, 15A, and 15B are arranged on the pipes connected before and after the heat exchangers 12A and 12B.

The residual heat removal system 52 configured as described above has a function of removing decay heat and sensible heat generated even after the nuclear fission reaction of the reactor vessel 1 is stopped.
The residual heat removal system 52 has a function of lowering the temperature of the coolant circulating in the primary cooling system 51 to a predetermined temperature within a predetermined time after stopping the operation of the plant.
The place where the coolant is extracted from the pipes 2A and 2B to the residual heat removal system 52 is located between the reactor vessel 1 and the steam generators 3A and 3B and is at a high temperature.
For this reason, it is considered that a relatively large amount of radioactive metal corrosion products adhere to the residual heat removal system 52, although not as much as the primary cooling system 51.

  The chemical volume control system 53 starts with a pipe 16A branched from the A system of the primary cooling system 51, a pipe 16B branched from the B system of the primary cooling system 51, and a pipe 16D branched from the A system of the residual heat removal system 52. Finally, the chemical volume control system 53 ends with the piping 16C returning to the downstream of the pump 4B of the piping 2B of the B system of the primary cooling system 51.

The branch pipe 16A has a starting end connected to the path of the pipe 2A sandwiched between the steam generator 3A and the pump 4A.
The branch pipe 16B has a starting end connected to the path of the pipe 2B sandwiched between the steam generator 3B and the pump 4B.
The branch pipe 16D has a start end connected to the path of the branch pipe 9A sandwiched between the heat exchanger 12A of the residual heat removal system 52 and the front and rear valves 15A downstream thereof.

The branch pipe 16A reaches the volume control tank 17 via the second boundary valve 20A, the pipe side of the regenerative heat exchanger 19, the on-off valve 25, and the non-regenerative heat exchanger 21.
The branch pipe 16 </ b> B reaches the volume control tank 17 via the second boundary valve 20 </ b> B, the excess extraction water heat exchanger 22, and the sealed water heat exchanger 23.
The branch pipe 16 </ b> D joins the branch pipe 16 </ b> A on the upstream side of the non-regenerative heat exchanger 21 via the third boundary valve 30 and reaches the volume control tank 17.

From the volume control tank 17, a return pipe 16C passing through the filling pump 24 and the trunk side of the regenerative heat exchanger 19 is connected to the downstream side of the pump 4B of the B system pipe 2B.
In the return pipe 16C, an on-off valve 26 is provided upstream of the regenerative heat exchanger 19 body side, and a second boundary valve 20C is further provided downstream thereof.

The chemical volume control system 53 configured as described above is for purification of coolant (removal of impurities, fission products, metal corrosion products, etc.), filling of the coolant to the primary cooling system 51, and reactivity control. It performs functions such as adjusting the boric acid concentration of the coolant and adjusting and maintaining the amount of coolant retained.
The place where the coolant is extracted from the pipes 2A and 2B to the chemical volume control system 53 is located between the steam generators 3A and 3B and the pumps 4A and 4B and is at a low temperature.
However, since the inflow / outflow of the coolant is frequently repeated between the primary cooling system 51 and the chemical volume control system 53 during the plant operation, the chemical volume control system 53 is not as radioactive as the primary cooling system 51, but is radioactive. It is thought that a relatively large amount of metal corrosion products adhere.

Next, a decontamination section and a decontamination range of the reactor cooling system 60 (see FIG. 1 as appropriate) of the pressurized water nuclear power plant to which the chemical decontamination method according to the embodiment is applied will be described based on FIG.
The decontamination section of the reactor cooling system 60 includes a primary cooling system 51, a residual heat removal system 52, and a chemical volume control system 53 partitioned by the first boundary valve 10, the second boundary valve 20, and the third boundary valve 30. In FIG. 2, a large section is set, and a small section is set by further subdividing the large section.
2 is set for each device arranged on the pipe, there may be a case where only a certain range of pipes or a certain range of pipes including valves is set.

  The region of the reactor cooling system 60 of the pressurized water nuclear power plant corresponding to the decontamination range 1, 2, 3, 4, 5, 6, 7 set in FIG. Expressed in

  In addition, chemical decontamination is implemented by the method of performing an oxidation reaction and a reduction reaction alternately, for example. The chemicals used for chemical decontamination are reducing agents and oxidizing agents. Representative examples of the reducing agent include dicarboxylic acids, particularly oxalic acid. Representative examples of the oxidizing agent include permanganic acid, potassium permanganate, hydrogen peroxide, ozone and the like.

  Since the reactor cooling system of nuclear power plants has different doses for each system and site, when the reactor cooling system is subjected to chemical decontamination in a batch, the low-dose site is contaminated by chemical decontamination of the high-dose site. There is. Therefore, in order to reduce each system and each part to a desired dose, it may be necessary to decontaminate all systems multiple times.

  On the other hand, in this embodiment, chemical decontamination can be performed for each system or site. Since recontamination due to chemical decontamination can be prevented, it is not necessary to decontaminate all systems multiple times, and chemical decontamination can be performed efficiently according to the decommissioning plan.

  Also, depending on the system or part, it may be more efficient to leave it for a while and reduce the dose than to reduce the dose by chemical decontamination. For this reason, decontamination plans may require chemical decontamination only for specific areas. In this embodiment, chemical decontamination can be performed for each system or part. Therefore, chemical decontamination can be performed efficiently according to the decommissioning plan.

  For example, in the decommissioning, since the steam generator provided in the primary cooling system has a particularly high dose, it is required that the decommissioning and chemical decontamination be performed after the dose is reduced after being left for a while. In that case, by separating the steam generator from the primary system and chemically decontaminating the primary system other than the steam generator, the efficiency of the steam generator can be improved without delaying the entire primary cooling system and thus the entire decommissioning process. Chemical decontamination and decommissioning.

(First embodiment)
A first embodiment of the chemical decontamination method will be described based on the decontamination range 1 (see FIGS. 2A and 2B) set in the reactor cooling system shown in FIG. First, all the boundary valves connected to the primary cooling system 51 (the first boundary valve 10 and the second boundary valve 20) are set to be closed. Further, the on-off valves 7A, 7B and 7C for the pressurizer 5 are closed, and the openings of the pipes 2A and 2B are connected by the bypass jig 28 inside the reactor vessel 1. Thereby, the piping 2A, 2B of the primary cooling system 51, the pumps 4A, 4B and the steam generators 3A, 3B are set as the decontamination range 1, and these are decontaminated collectively by circulating the decontamination agent. The This corresponds to the decontamination pattern (A) in FIG. Here, the decontamination method in which each device and each part included in the decontamination range is decontaminated without being isolated within the decontamination range is referred to as “in-range collective decontamination X”.

The pressurizer 5, its front and rear pipes 6 </ b> A, 6 </ b> B, 6 </ b> C and the reactor vessel 1 are isolated from the decontamination range by the functions of the above-described on-off valves 7 </ b> A, 7 </ b> B, 7 </ b> C and the bypass jig 28. Similarly, the residual heat removal system 52 and the chemical volume control system 53 are also isolated from the decontamination range.
In addition, the method of isolating from the decontamination range is not limited to the closing setting of the boundary valve, and can be implemented by using an isolating jig or cutting a pipe.

  The pumps 4A and 4B and the steam generators 3A and 3B are particularly high dose locations in the nuclear power plant. In a decommissioning plan, it may be desirable to decontaminate the pumps 4A, 4B and steam generators 3A, 3B in a limited manner to minimize the risk of recontamination of the low contamination level. The decontamination pattern (A) can be chemically cleaned by separating the pipes 2A and 2B, the pumps 4A and 4B, and the steam generators 3A and 3B of the primary cooling system 51 from other portions. Therefore, it is possible to reduce the chance of decontamination again for the recontaminated part, and it is possible to efficiently proceed with the decommissioning of the nuclear power plant according to the plan.

(Second Embodiment)
A second embodiment of the chemical decontamination method will be described based on the decontamination range 1 (see FIG. 2) set in the reactor cooling system shown in FIG.
In the second embodiment, after the decontamination described in the first embodiment is performed, the steam generators 3A and 3B are isolated from the pipes 2A and 2B of the primary cooling system 51, and the steam generators 3A and 3B are independently used. Decontaminate. This corresponds to the decontamination pattern (b) in FIG. Hereinafter, after performing batch decontamination X within the decontamination range, each decontamination method and parts of each part are isolated and further decontamination is performed separately after batch decontamination. This is referred to as dye Y. In single decontamination Y after collective decontamination, the first decontamination (corresponding to in-range collective decontamination X) is carried out for the first decontamination, followed by the first decontamination for some devices and parts The dyeing is called second decontamination.

Based on FIG. 8, the procedure of 2nd decontamination is demonstrated. 8A and 8B, the device 31 is a device to be decontaminated solely by the second decontamination, and here, it is assumed to be the steam generators 2A and 2B.
FIG. 8A shows a state before the second decontamination, in which the pipes 2 and 2 are connected to the inlet 32 and the outlet 33 of the device 31 through the adapter pipes 35 and 35, respectively. ing. FIG. 8B shows a state where a circulation path 40 for single decontamination is attached to the device 31. This circulation path 40 connects the coolant inlet 32 side and the outlet 33 side of the device 31 to be isolated in a closed loop, and circulates the cleaning agent.

  The circulation path 40 includes a decontamination tank 41, a pump 42 for sending the decontamination agent from the tank 41 to the delivery path 43, and the tip of the delivery path 43 is fixed to seal the opening on the inlet 32 side of the device. The first sealing plate 44 that stops and feeds the decontamination agent to the device 31 and the decontamination agent that has passed through the device 31 after sealing the opening on the outlet 33 side of the device are returned to the tank 41 via the return path 46. And a second sealing plate 45 to be made.

  When the device 31 is decontaminated alone, the adapter pipes 35 and 35 are removed, and the first sealing plate 44 and the second sealing plate 45 are respectively attached to the opening on the inlet 32 side and the opening on the outlet 33 side of the device. Attach. Note that sealing plates 36 and 36 are also provided at the opening of the pipe 2 to prevent leakage.

  As described above, after the circulation path 40 for single decontamination is attached to the device 31 to be second decontaminated, the pump 42 is activated and the decontamination agent is circulated between the tank 41 and the device 31. Note that the method of isolating the device 31 is not limited to the method illustrated in FIG. 8B, and a method of using a valve disposed immediately upstream and downstream of the device 31, connection And a method of cutting the piping to be performed.

  Since the devices of the steam generators 3A and 3B have a complicated shape, the decontamination efficiency may be lower in the collective cleaning with the pipes 2A and 2B than the simple-shaped pipe. Further, the steam generators 3A and 3B use nickel-based alloy material as a part of the material, and may exhibit a decontamination behavior different from the stainless steel used in most other places. Therefore, in the decommissioning plan, the pipes 2A and 2B of the primary cooling system 51, the pumps 4A and 4B, and the steam generators 3A and 3B should be decontaminated at once, and then the steam generators 3A and 3B should be decontaminated alone. May be desired.

  In the decontamination pattern (b), the pipes 2A and 2B of the primary cooling system 51, the pumps 4A and 4B, and the steam generators 3A and 3B are decontaminated at once, and then the steam generators 3A and 3B are decontaminated independently. Can do. Therefore, the decontamination range 1 can be chemically decontaminated, the decontamination conditions of the steam generator can be optimized, and the decommissioning of the nuclear power plant can proceed efficiently according to the plan. is there.

(Third embodiment)
A third embodiment of the chemical decontamination method will be described based on the decontamination range 1 (see FIGS. 2A and 2B) set in the reactor cooling system shown in FIG.
In the third embodiment, as in the first embodiment, all of the boundary valves connected to the primary cooling system 51 (the first boundary valve 10 and the second boundary valve 20) are set to be closed. Further, the on-off valves 7A, 7B and 7C for the pressurizer 5 are closed, and the openings of the pipes 2A and 2B are connected by the bypass jig 28 inside the reactor vessel 1.
In the third embodiment, before the decontamination agent is circulated, each of the steam generators 3A and 3B is subsequently isolated like the device 31 of FIG. 8B. Further, as shown in FIG. 8C, the openings of the two pipes 2 and 2 separated after isolating the steam generators 3A and 3B are connected to both ends of the bypass pipe 48, and both are connected.

Then, a decontaminating agent is introduced into the primary cooling system 51 that isolates the steam generators 3A and 3B and is connected by the bypass pipe 48, starts the pumps 4A and 4B, circulates them, and the pipes 2A and 2B and Pumps 4A and 4B are decontaminated.
After the pipes 2A and 2B and the pumps 4A and 4B are decontaminated, the isolated steam generators 3A and 3B are decontaminated (see FIG. 8B). This corresponds to the decontamination pattern (c) in FIG. Here, the decontamination method of isolating each device and each part included in the decontamination range and decontaminating each of them independently is the single decontamination Z within the range (the second decontamination of single decontamination Y after collective decontamination) Corresponding). The order of decontamination may be reversed, and the pipes 2A and 2B and the pumps 4A and 4B may be decontaminated after the steam generators 3A and 3B are decontaminated.

  The steam generators 3A and 3B are portions having a particularly high dose in the cooling system, are complicated in shape, and have different constituent materials from other portions. Therefore, it is abolished to prevent the pipes 2A and 2B and the pumps 4A and 4B from being contaminated by the steam generators 3A and 3B at the time of chemical decontamination, and to optimize the decontamination conditions of the steam generators 3A and 3B. In the planning of measures, it may be desired to decontaminate the pipes 2A and 2B of the primary cooling system 51 and the pumps 4A and 4B and the steam generators 3A and 3B, respectively.

  In the decontamination pattern (C), the pipes 2A and 2B and the pumps 4A and 4B and the steam generators 3A and 3B of the next cooling system 51 can be decontaminated independently. Therefore, it is possible to prevent the pipes 2A and 2B and the pumps 4A and 4B from being contaminated by the steam generators 3A and 3B, and to optimize the decontamination conditions of the steam generators 3A and 3B. It is possible to proceed efficiently according to the plan.

So far, the embodiment applied to the decontamination range 1 shown in FIG. 3 has been described.
In-range collective decontamination X, single collective decontamination Y after collective decontamination, and in-range single decontamination Z described in the first to third embodiments are the decontamination range 2 shown in FIG. 4 (FIG. 2A). (See also). In-range collective decontamination X in decontamination range 2, single decontamination Y after collective decontamination, and in-range single decontamination Z are decontamination patterns (d), (e), (f) in FIG. It corresponds to.

  The decontamination range 2 is set as follows. As shown in FIG. 4, all of the boundary valves connected to the primary cooling system 51 (the first boundary valve 10 and the second boundary valve 20) are set to be closed. Further, the openings of the pipes 2 </ b> A and 2 </ b> B are connected by the bypass jig 28 in the reactor vessel 1. The on-off valves 7A, 7B and 7C for the pressurizer 5 are opened. As a result, the pressurizer 5 is set as the decontamination range 2 in addition to the pipes 2A and 2B of the primary cooling system 51, the pumps 4A and 4B, and the steam generators 3A and 3B.

The in-range collective decontamination X in the decontamination range 2 is decontaminated in a lump without isolating the pipes 2A and 2B, the pumps 4A and 4B, the steam generators 3A and 3B, and the pressurizer 5 of the primary cooling system 51. It is carried out by doing.
The reactor vessel has a particularly large capacity among nuclear power plants, and a large amount of cleaning liquid is required for chemical decontamination. Therefore, in the decommissioning plan, when the primary cooling system is chemically decontaminated, in order to reduce the amount of the decontamination solution, the components other than the reactor vessel 1 in the primary cooling system may be decontaminated in a batch. May be desired.

The decontamination pattern (d) can decontaminate components other than the primary reactor vessel 1 in the primary cooling system. Therefore, the amount of decontamination solution necessary for chemical decontamination of the primary cooling system can be reduced, and the decommissioning of the nuclear power plant can be advanced efficiently according to the plan.
The single decontamination Y after the collective decontamination in the decontamination range 2 decontaminates only the steam generators 3A and 3B as the second decontamination after the decontamination range 2 in the range as a first decontamination X. It is carried out. The second decontamination is performed in the same manner as in FIGS. 8A and 8B, and the steam generators 3A and 3B are each decontaminated after being isolated from other devices.

  In the decommissioning plan, when the primary cooling system is chemically decontaminated, it may be desired to decontaminate all components other than the primary cooling system reactor vessel 1 in order to reduce the amount of decontamination solution. is there. In addition, in order to optimize the decontamination conditions of the steam generators 3A and 3B with complicated shapes and special constituent materials, it is desired to decontaminate the steam generators 3A and 3B alone in the decommissioning plan. There is.

  In the decontamination pattern (e), the pipes 2A and 2B of the primary cooling system 51, the pumps 4A and 4B, and the steam generators 3A and 3B are decontaminated at once, and then the steam generators 3A and 3B are decontaminated independently. Can do. Therefore, it is possible to decontaminate the components other than the primary cooling system reactor vessel 1 in a batch and optimize the decontamination conditions of the steam generator. Along the way.

  In the in-range single decontamination Z in the decontamination range 2, the pumps 4A and 4B, the steam generators 3A and 3B, and the pressurizer 5 are first isolated from each other as described with reference to FIG. Then, as shown to FIG. 8 (C), the upstream piping and downstream piping of steam generator 3A, 3B are connected by bypass piping. Similarly, the upstream side pipe and the downstream side pipe of the pressurizer 5 are connected by a bypass pipe. Then, decontamination is performed by introducing the decontamination liquid into the circulation path constituted by the pipes 2A and 2B of the primary cooling system 51 and the pumps 4A and 4B and the bypass pipe. Thereafter, circulation pumps are connected to the steam generators 3A and 3B and the pressurizer 5, respectively, and single decontamination is sequentially performed. The order of performing the decontamination of the pipes 2A and 2B and the pumps 4A and 4B of the primary cooling system 51, the decontamination of the steam generators 3A and 3B, and the decontamination of the pressurizer 5 is arbitrary. After decontamination of the steam generators 3A and 3B, the pipes 2A and 2B of the primary cooling system 51 and the pumps 4A and 4B may be decontaminated, and finally the depressurizer 5 may be decontaminated.

  The reactor vessel has a particularly large capacity in the primary cooling system. In addition, the steam generators 3A and 3B and the pressurizer are particularly high dose portions in the cooling system. Moreover, the shape is complicated like the steam generator of the pressurizer 5. Therefore, the circulation amount of the decontamination liquid is reduced, and the pipes 2A and 2B and the pumps 4A and 4B are prevented from being contaminated by the steam generators 3A and 3B and the pressurizer at the time of chemical decontamination, and the steam generator In order to optimize the decontamination conditions of 3A and 3B and the pressurizer 5, the reactor vessel is excluded from the decontamination range in the decommissioning plan, and the piping 2A and 2B of the primary cooling system 51 and the pumps 4A and 4B In some cases, it may be desirable to decontaminate the steam generators 3A, 3B and the pressurizer 5 independently.

  In the decontamination pattern (f), the pipes 2A and 2B of the next cooling system 51 and the pumps 4A and 4B, the steam generators 3A and 3B, and the pressurizer 5 can be decontaminated independently. Therefore, the piping 2A, 2B and the pumps 4A, 4B are prevented from being contaminated by the steam generators 3A, 3B and the pressurizer, and the decontamination conditions of the steam generators 3A, 3B and the pressurizer 5 are optimized. It is possible to proceed with decommissioning of nuclear power plants efficiently according to the plan.

  The in-range collective decontamination X and the single decontamination Y after collective decontamination described in the first and second embodiments are also applied to the decontamination range 3 shown in FIG. 5 (see FIG. 2A). be able to. The in-range collective decontamination X in the decontamination range 3 and the single decontamination Y after the collective decontamination correspond to the decontamination patterns (G) and (H) in FIG.

  The decontamination range 3 is set as follows. As shown in FIG. 5, all of the boundary valves (first boundary valve 10 and second boundary valve 20) connected to the primary cooling system 51 are set to be closed, and the on-off valves 7A, 7B, and 7C for the pressurizer 5 are set. Close. Note that the openings of the pipes 2A and 2B are not connected inside the reactor vessel 1 (the bypass jig 28 is not used). Thereby, in addition to the piping 2A, 2B of the primary cooling system 51, the pumps 4A, 4B, and the steam generators 3A, 3B, the reactor vessel 1 is set as the decontamination range 3.

  The in-range collective decontamination X in the decontamination range 3 is performed by removing the piping 2A, 2B, the pumps 4A, 4B, the steam generators 3A, 3B, and the reactor vessel 1 of the primary cooling system 51 without being isolated. It is carried out by being dyed.

  Since the pressurizer protrudes upward from other devices and pipes constituting the primary cooling system, the pressurizer is often less contaminated than other configurations. Therefore, in a plan for decommissioning, it may be desired to decontaminate components other than the pressurizer 5 at once by omitting the pressurizing step when chemically decontaminating the primary cooling system. The decontamination pattern (g) can decontaminate components other than the pressurizer 5 in the primary cooling system. Therefore, it is possible to omit processes and equipment necessary for pressurization, and it is possible to efficiently proceed with decommissioning of the nuclear power plant according to the plan.

  The single decontamination Y after collective decontamination in the decontamination range 3 decontaminates only the steam generators 3A and 3B as the second decontamination after the decontamination range 3 within the range is decontaminated X as the first decontamination. It is carried out. The second decontamination is performed in the same manner as in FIGS. 8A and 8B, and the steam generators 3A and 3B are each decontaminated after being isolated from other devices.

  In the decommissioning plan, when the primary cooling system is chemically decontaminated, it is desirable to decontaminate all components other than the primary cooling system pressurizer 5 in order to omit the steps and equipment necessary for pressurization. May be. In addition, in order to optimize the decontamination conditions of the steam generators 3A and 3B with complicated shapes and special constituent materials, it is desired to decontaminate the steam generators 3A and 3B alone in the decommissioning plan. There is.

  In the decontamination pattern (h), the pipes 2A and 2B of the primary cooling system 51, the pumps 4A and 4B, the steam generators 3A and 3B, and the reactor vessel 1 are decontaminated in a lump, and then the steam generators 3A and 3B are used alone. Can be decontaminated. As a result, the components other than the primary cooling system pressurizer 5 can be decontaminated in a batch, and the decontamination conditions of the steam generator can be optimized. It is possible to proceed efficiently.

  Further, the in-range collective decontamination X and the single decontamination Y after collective decontamination described in the first and second embodiments are for the decontamination range 4 shown in FIG. 6 (see FIG. 2A). Can also be applied. The in-range collective decontamination X in the decontamination range 4 and the single decontamination Y after collective decontamination correspond to the decontamination patterns (L) and (N) in FIG.

  The decontamination range 4 is set as follows. As shown in FIG. 6, all of the boundary valves connected to the primary cooling system 51 (the first boundary valve 10 and the second boundary valve 20) are set to be closed, and the on-off valves 7A, 7B, 7C for the pressurizer 5 are set. Is released. Further, the openings of the pipes 2A and 2B are not connected inside the reactor vessel 1 (the bypass jig 28 is not used). Thereby, the pipes 2A and 2B of the primary cooling system 51, the pumps 4A and 4B, the steam generators 3A and 3B, the pressurizer 5 and the reactor vessel 1 are set as the decontamination range 4.

  The in-range collective decontamination X in the decontamination range 4 is performed without the piping 2A, 2B, the pumps 4A, 4B, the steam generators 3A, 3B, the pressurizer 5 and the reactor vessel 1 of the primary cooling system 51 being isolated. And then decontaminated.

  The decontamination range 4 that is the entire primary cooling system is a system with a higher dose than the residual heat removal system 52 and the chemical volume control system 53. When the primary cooling system 51, the residual heat removal system 52, and the chemical volume control system 53 are chemically cleaned at once, the residual heat removal system 52 and the chemical volume control system 53 may be contaminated by the primary cooling system 51. Therefore, in the plan for decommissioning, in order to minimize the risk of contamination of the residual heat removal system 52 and the chemical volume control system 53 by the primary cooling system 51, decontamination should be limited to the primary cooling system 51. May be. The decontamination pattern (re) is composed of the piping 2A, 2B, the pumps 4A, 4B, the steam generators 3A, 3B, the pressurizer and the reactor pressure vessel 1 constituting the primary cooling system 51, the residual heat removal system 52 and the chemical volume control system Chemical cleaning can be performed separately from 53. Therefore, recontamination of the residual heat removal system 52 and the chemical volume control system 53 can be suppressed, and the decommissioning of the nuclear power plant can be efficiently advanced according to the plan.

  The single decontamination Y after collective decontamination in the decontamination range 3 is performed after the decontamination range 4 is collectively decontaminated X as the first decontamination and then the steam generators 3A and 3B and the pressurizer 5 are used as the second decontamination It is carried out by decontamination each independently. The second decontamination is performed in the same manner as in FIGS. 8A and 8B, and the steam generators 3A and 3B and the pressurizer 5 are each decontaminated after being isolated from other devices. The order in which the steam generators 3A and 3B and the pressurizer 5 are decontaminated independently is arbitrary. If it is after the 1st decontamination, you may perform independent decontamination of a pressurizer before independent decontamination of the steam generators 3A and 3B.

  Steam generators and pressurizers having relatively complex shapes have relatively complex shapes, and in order to obtain a sufficient decontamination effect, it may be necessary to optimize the respective decontamination conditions. For this reason, in the decommissioning plan, it may be desired to decontaminate the steam generators 3A and 3B and the pressurizer 5 independently after decontamination of the decontamination range 4 collectively.

  In the decontamination pattern (nu), the pipes 2A and 2B of the primary cooling system 51, the pumps 4A and 4B, the steam generators 3A and 3B, the pressurizer 5 and the reactor vessel 1 are collectively decontaminated, and then the steam generator 3A. 3B and pressurizer 5 can be decontaminated independently. Therefore, the entire primary cooling system can be quickly decontaminated, and the decontamination effect of the steam generators 3A and 3B and the pressurizer 5 can be enhanced, and the decommissioning of the nuclear power plant can be promoted efficiently according to the plan. Is possible.

(Fourth embodiment)
A fourth embodiment of the chemical decontamination method will be described based on the decontamination range 5 (see FIG. 2A) set in the reactor cooling system shown in FIG.

  In the fourth embodiment, as in the first embodiment, all of the boundary valves connected to the primary cooling system 51 (the first boundary valve 10 and the second boundary valve 20) are set to be closed. Then, the heat exchanger 19 of the chemical volume control system 53 is isolated from the piping, and a single decontamination circuit 40 (see FIG. 8B) is attached, and the cleaning agent is circulated to decontaminate alone.

  In the heat exchanger 19 of the chemical volume control system 53, the high-temperature and high-pressure coolant flowing from the primary cooling system 51 reaches first and is rapidly cooled. For this reason, the contamination level of the heat exchanger 19 is often the highest among the devices constituting the chemical volume control system 53. Therefore, in the plan for decommissioning, it may be desired to decontaminate the heat exchanger 19 of the chemical volume control system 53 alone.

  In the fourth embodiment, the chemical volume control system heat exchanger can be decontaminated independently. For this reason, it is possible to prevent contamination of a lower-dose part during chemical decontamination of a chemical volume control system heat exchanger, and to proceed with nuclear plant decommissioning efficiently according to the plan.

(Fifth embodiment)
A fifth embodiment of the chemical decontamination method will be described based on the decontamination range 6 (see FIG. 2A) set in the reactor cooling system shown in FIG.
In the fifth embodiment, as in the first embodiment, all of the boundary valves connected to the primary cooling system 51 (the first boundary valve 10 and the second boundary valve 20) are set to be closed. Then, the heat exchanger 12B of the residual heat removal system 52 is isolated from the pipe, and the circulation path 40 for single decontamination (see FIG. 8B) is attached, and the cleaning agent is circulated for decontamination alone. Although not shown, the heat exchanger 12A can be handled in the same manner.

  In the heat exchangers 12A and 12B of the residual heat removal system 52, the high-temperature and high-pressure coolant flowing from the primary cooling system 51 is rapidly cooled. For this reason, in the apparatus which comprises the residual heat removal system 52, it is thought that the contamination level of heat exchanger 12A, 12B is high. Therefore, in the plan for decommissioning, it may be desired to decontaminate the heat exchangers 12A and 12B of the residual heat removal system 52 alone.

  In the fifth embodiment, the heat exchangers 12A and 12B of the residual heat removal system 52 can be decontaminated independently. Therefore, at the time of chemical decontamination of the heat exchangers 12A and 12B of the residual heat removal system 52, it is possible to prevent contamination of a lower-dose part and efficiently proceed with the decommissioning of the nuclear power plant according to the plan. .

(Sixth embodiment)
A sixth embodiment of the chemical decontamination method will be described based on a decontamination range 7 (see FIG. 2A) set in the reactor cooling system shown in FIG.
In the sixth embodiment, as in the first embodiment, all of the boundary valves connected to the primary cooling system 51 (the first boundary valve 10 and the second boundary valve 20) are set to be closed. Then, the pump 11A and the heat exchanger 12A of the residual heat removal system 52 are isolated from the pipe, and a single decontamination circuit 40 (see FIG. 8B) is attached, and the cleaning agent is circulated to collect the decontamination. To do. In addition, although illustration is abbreviate | omitted, it can handle similarly with respect to the pump 11B and the heat exchanger 12B.

  In the pumps 11A and 11B and the heat exchangers 12A and 12B of the residual heat removal system 52, the high-temperature and high-pressure coolant flowing from the primary cooling system 51 first reaches and is rapidly cooled. For this reason, in the apparatus which comprises the residual heat removal system 52, it is thought that the contamination level of pump 11A, 11B is high similarly to heat exchanger 12A, 12B. Therefore, in the plan for decommissioning, it may be desired to decontaminate the pumps 11A and 11B and the heat exchangers 12A and 12B of the residual heat removal system 52 individually.

  In the fifth embodiment, the pumps 11A and 11B and the heat exchangers 12A and 12B of the residual heat removal system 52 can be decontaminated independently. Therefore, at the time of chemical decontamination of the pumps 11A and 11B and the heat exchangers 12A and 12B of the residual heat removal system 52, it is possible to prevent contamination of the lower-dose part and efficiently proceed with the decommissioning of the nuclear power plant according to the plan. Is possible

In carrying out by combining the above-described embodiments, the order of decontamination work for the primary cooling system 51, the residual heat removal system 52, and the chemical volume control system 53 is not particularly limited.
However, considering that the contamination level of the primary cooling system 51 is higher than that of the other residual heat removal system 52 and the chemical volume control system 53, at least one of the chemical volume control system 53 and the residual heat removal system 52 is decontaminated first. In addition, by reusing the used decontamination solution for cleaning the primary cooling system 51, it is possible to expect an effect of reducing the amount of decontamination agent used and the amount of secondary waste generated.

By the way, even if it implements combining the embodiment mentioned above, in the reactor cooling system 60, piping, an apparatus, a valve, etc. which are not included in the decontamination range exist.
Therefore, after implementing at least one of the first to third embodiments relating to the primary cooling system 51, at least one of the first boundary valve 10 and the second boundary valve 20 is opened, Decontamination may be carried out across the two.

  According to the chemical decontamination method for a pressurized water nuclear power plant of at least one embodiment described above, the first boundary valve that connects the residual heat removal system and the primary cooling system, and the chemical volume control system and the primary cooling system. By closing all of the second boundary valves that connect to the primary cooling system and circulating the decontamination agent to the primary cooling system, the contamination level of the reactor cooling system with radioactive material attached can be reduced in accordance with the decommissioning plan. It becomes possible to reduce efficiently.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof. Moreover, the structure shown to FIG. 1, 3-7 is an example of a pressurized water nuclear power plant, and the location and place of a joint valve may differ somewhat with plants depending on a pressurized water nuclear power plant.

DESCRIPTION OF SYMBOLS 1 ... Reactor vessel, 2A, 2B ... Primary cooling system piping, 3A, 3B ... Steam generator, 4A, 4B ... Primary cooling system pump, 5 ... Pressurizer, 6A, 6B, 6C ... Pressurizer piping, 7A, 7B, 7C ... open / close valve of pressurizer, 9A, 9B, 9C ... branch pipe (piping) of residual heat removal system, 10 (10A, 10B, 10C) ... first boundary valve, 11A, 11B ... residual heat removal system 12A, 12B ... residual heat removal system heat exchanger, 14A, 15A ... front and rear valves of heat exchanger, 16A, 16B, 16C, 16D ... chemical volume control system branch piping (piping), 17 ... volume control tank , 19 ... Regenerative heat exchanger (heat exchanger), 20 (20A, 20B, 20C) ... Second boundary valve, 21 ... Non-regenerative heat exchanger (heat exchanger), 22 ... Excess extraction water heat exchanger ( Heat exchanger), 23 ... Sealed water heat exchanger (heat exchanger), 24 ... Filling pump , 25, 26 ... Open / close valve, 28 ... Bypass jig, 30 ... Third boundary valve, 31 ... Equipment, 32 ... Inlet, 33 ... Outlet, 35 ... Adapter pipe, 36 ... Sealed plate, 40 ... Circulation path, DESCRIPTION OF SYMBOLS 41 ... Tank, 42 ... Pump, 43 ... Delivery path, 44 ... 1st sealing plate, 45 ... 2nd sealing plate, 46 ... Return path, 48 ... Bypass piping, 51 ... Primary cooling system, 52 ... Residual heat removal system 53 ... Chemical volume control system, 60 ... Reactor cooling system.

Claims (13)

A primary cooling system comprising a reactor melter, a pump, a pressurizer, and a steam generator, and circulating a coolant heated in the reactor vessel to the steam generator;
A residual heat removal system that reduces the coolant to a predetermined temperature after stopping heating in the reactor vessel;
A chemical volume control system responsible for boric acid concentration adjustment and holding amount adjustment of the coolant is a chemical decontamination method of a pressurized water nuclear power plant that is mutually connected through a plurality of boundary valves,
A chemical decontamination method for a pressurized water nuclear power plant, wherein all of the boundary valves connected to the primary cooling system are set to at least closed, and a decontamination agent is circulated in the primary cooling system.   2. The chemical decontamination method for a pressurized water nuclear power plant according to claim 1, wherein the decontamination agent is circulated in the primary cooling system in a state in which an on-off valve for the pressurizer is closed.   The pressurized water according to claim 2, wherein the decontamination agent is circulated in the primary cooling system after attaching a bypass jig that connects the piping of the primary cooling system that opens inside the reactor vessel. Chemical decontamination method for nuclear power plants.   The decontaminating agent is circulated in the primary cooling system with a bypass jig connected to the piping of the primary cooling system that opens in the reactor vessel, and an open / close valve for the pressurizer is opened. The chemical decontamination method for a pressurized water nuclear power plant according to claim 1.   5. The method according to claim 2, wherein after the decontamination agent is circulated through the steam generator, the steam generator is isolated from the piping of the primary cooling system and decontaminated alone. 2. A chemical decontamination method for a pressurized water nuclear power plant according to item 1. A bypass jig that connects the piping of the primary cooling system that opens inside the reactor vessel is attached, the on-off valve for the pressurizer is closed, and the steam generator is isolated from the piping of the primary cooling system. After installing the bypass piping connecting the piping,
2. The chemical decontamination method for a pressurized water nuclear power plant according to claim 1, wherein the decontamination agent is circulated in the primary cooling system, and the steam generator is decontaminated alone. After closing the on-off valve for the pressurizer and attaching the bypass pipe that connects the pipe to the steam generator in isolation from the primary cooling system pipe,
The chemical decontamination method for a pressurized water nuclear power plant according to claim 1, wherein the decontaminating agent is circulated in the primary cooling system, and the steam generator and the pressurizer are decontaminated independently.   After circulating the decontamination agent to the steam generator and the pressurizer, the on-off valve for the pressurizer is closed, the steam generator is isolated from the piping of the primary cooling system, and the steam generator and The chemical decontamination method for a pressurized water nuclear power plant according to claim 1, wherein each of the pressurizers is decontaminated independently.   The pressurized water mold according to any one of claims 1 to 8, wherein all of the boundary valves are set to at least closed, and the heat exchanger of the chemical volume control system is isolated from the piping and is decontaminated alone. Chemical decontamination method for nuclear power plants.   The pressurized water nuclear power according to any one of claims 1 to 9, wherein all of the boundary valves are set to at least closed, and the heat exchanger of the residual heat removal system is isolated from the piping and is decontaminated alone. Chemical decontamination method for power plants.   11. The device according to claim 1, wherein all of the boundary valves are set to at least closed, and the pump and heat exchanger of the residual heat removal system are separated from the pipe and collectively decontaminated. Chemical decontamination method for pressurized water nuclear power plants.   The pressurized water nuclear power according to any one of claims 4 to 11, wherein a circulating path for circulating the cleaning agent is provided by connecting a coolant inlet side and an outlet side of the target device to be isolated in a closed loop. Chemical decontamination method for power plants.   The pressurized water mold according to any one of claims 1 to 12, wherein a decontamination liquid used for decontamination of at least one of the chemical volume control system and the residual heat removal system is reused for cleaning the primary cooling system. Chemical decontamination method for nuclear power plants.

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