JP2009216577A - Chemical decontamination method and chemical decontamination device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a chemical decontamination method for shortening furthermore a decontamination time. <P>SOLUTION: Chemical decontamination is performed for a recirculation system A (A-system) and a recirculation system B (B-system) of a boiling water reactor nuclear power plant. Water is filled into the A-system and circulated to raise a temperature of the A-system. Then, the water in the A-system is transferred into the B-system and circulated to raise a temperature of the B-system. After the temperature rise, while transferring the water in the B-system into the A-system, oxidization decontamination liquid containing an oxidization decontamination agent is injected into the water. Oxidization decontamination of the A-system and oxidization decontamination of the B-system are executed successively by circulating the oxidization decontamination liquid. Reduction decontamination liquid containing a reduction decontamination agent is injected to decompose the oxidization decontamination agent, and then reduction decontamination of the A-system and the B-system by the reduction decontamination liquid is executed alternately. After finish of the reduction decontamination, the reduction decontamination agent is decomposed, while transferring the reduction decontamination liquid reciprocally between the B-system and the A-system. After finish of decomposition of the reduction decontamination agent, a purification process is executed, while transferring the water between the A-system and the B-system. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a chemical decontamination method and a chemical decontamination apparatus, and more particularly to a chemical decontamination method and a chemical decontamination apparatus suitable for application to a water-cooled nuclear power plant.

  Examples of conventional techniques related to chemical decontamination are described in JP-A-2000-105295, JP-A-2004-205245, and US Pat. No. 6,466,636. The chemical decontamination methods described in JP-A Nos. 2000-105295 and 2004-205245 use an aqueous solution of potassium permanganate (oxidative decontamination agent) as an oxidative decontamination solution, and hydrazine as a reduction decontamination solution. An aqueous solution of oxalic acid (reductive decontamination reagent) containing is used. Structural members of water-cooled nuclear power plants (for example, recirculation piping for boiling water nuclear power plants) by oxidative decontamination using potassium permanganate aqueous solution and reductive decontamination using oxalic acid aqueous solution containing hydrazine ) Chemical decontamination of the surface in contact with the cooling water. Furthermore, oxalic acid and hydrazine contained in the reductive decontamination solution are decomposed into carbon dioxide, nitrogen and water by the catalyst and hydrogen peroxide. For this reason, it is suppressed that secondary waste increases.

  In addition, US Pat. No. 6,466,636 describes a chemical decontamination method for two recirculation pipes of a boiling water nuclear power plant. Each nozzle of the reactor pressure vessel to which each recirculation system pipe is connected is sealed with a plug, and provided at the upper end of each riser pipe (installed in the reactor pressure vessel) to which each recirculation system pipe is connected Each pipe bend is sealed with a plug. A decontamination unit having a heater and an ion exchanger is connected to the recirculation system pipe A and the recirculation system pipe B at one location via a switching valve. By switching the switching valve, the decontamination liquid in the recirculation system pipe A is supplied into the recirculation system pipe B, and the decontamination liquid in the recirculation system pipe B is supplied into the recirculation system pipe A. Supply is performed alternately. That is, the fill-and-drain of the decontamination liquid is repeatedly performed on one system recirculation piping. US Pat. No. 6,466,636 further describes the removal of the drug in the decontamination solution with an ion exchanger.

JP 2000-105295 A JP 2004-205245 A US Pat. No. 6,466,636

  In the chemical decontamination method described in Japanese Patent Application Laid-Open No. 2000-105295, a decontamination liquid is supplied to one decontamination target site (for example, piping of a reactor plant). When this chemical decontamination is carried out with two recirculation pipes, for example, it may be possible to chemically decontaminate another recirculation pipe after the completion of chemical decontamination of one recirculation pipe. It is done. In this case, twice the time required for chemical decontamination of one recirculation piping is required. Furthermore, it is also conceivable that two recirculation pipes are connected in series or in parallel by temporary pipes and constructed as a single process using one chemical decontamination apparatus. In this case, since the necessary amount of the decontamination liquid circulating in the two recirculation system pipes increases, the time required for the decomposition of the decontamination agent contained in the decontamination liquid and the purification in the system increases. Since the number of free liquid levels increases, it becomes difficult to perform the circulating operation stably.

  In the chemical decontamination method described in US Pat. No. 6,466,636, the fill and drain of the decontamination solution is repeatedly performed by using one chemical decontamination apparatus for the two recirculation pipes to be decontaminated. Is called. This chemical decontamination alternates between each recirculation system piping, leaving enough decontamination liquid to maintain a level of water head that does not generate cavitation due to negative pressure on the suction side of the pump. Since it is transferred, the volume of the necessary decontamination solution is about 1.5 times the volume necessary for chemical decontamination of one recirculation pipe. In addition, the chemical decontamination method can shorten the decontamination time as compared with the case of chemical decontamination of another recirculation system pipe after one system recirculation system pipe.

  However, in the chemical decontamination method described in US Pat. No. 6,466,636, the fill and drain of the decontamination liquid is repeated for each recirculation system pipe, so that the temperature of the decontamination liquid may decrease. There is. This drop in temperature is caused by the fact that, since fill and drain are performed, regions where no decontamination solution exists are alternately formed in the two recirculation system pipes. The decrease in the temperature of the decontamination liquid increases the risk that the decontamination performance of the recirculation system pipe will decrease.

  In chemical decontamination methods, it is desired to shorten the time required for chemical decontamination. When performing chemical decontamination of a plurality of systems of decontamination objects, the inventors require a decontamination process for chemical decontamination, particularly a decontamination process for reducing decontamination, in order to shorten the time. I found that it was to shorten the time. Note that US Pat. No. 6,466,636 does not mention any decontamination process.

  The objective of this invention is providing the chemical decontamination method and chemical decontamination apparatus which can shorten decontamination time more.

  The feature of the present invention that achieves the above-described object is that decontamination of the inner surface of the piping system is performed by supplying a decontamination solution containing a decontamination agent into a plurality of piping systems provided in the plant, and the decontamination is completed. When transferring the decontamination liquid in one piping system to another piping system after decontamination, the decontamination agent contained in the transferred decontamination liquid is decomposed.

  When transferring the decontamination liquid in one piping system after decontamination to another piping system after decontamination, the decontamination agent contained in the decontamination liquid is decomposed. Therefore, it is possible to prevent the decontamination liquid in which the concentration of the decontamination agent is lowered and the decontamination solution before the concentration of the decontamination agent is reduced. For this reason, the decomposition efficiency of a decontaminating agent improves and decontamination time can be shortened in the chemical decontamination for several piping systems.

  According to the present invention, the decontamination time can be shortened in chemical decontamination for a plurality of piping systems.

  The inventors have made various studies in order to find a chemical decontamination method that can shorten the decontamination time when performing chemical decontamination on a plurality of lines. The decontamination time is not the time required when decontaminating a member to be decontaminated directly using decontamination agents (oxidative decontamination agent and reductive decontamination agent). This is the time required for carrying out a series of steps of chemical decontamination including a decontamination step and a purification step of the reductive decontamination agent. The inventors particularly examined measures that can reduce the time required for the decontamination process. The inventors were able to find a new chemical decontamination method by this study. The concept of an example of the obtained new chemical decontamination method will be described with reference to FIG.

  The new chemical decontamination method shown in FIG. 1 has two systems, that is, a system A provided in the plant (for example, a recirculation system A of a boiling water nuclear power plant) and a system B (for example, boiling water nuclear power generation). It is an example which performs chemical decontamination for the recirculation system B) of a plant.

  First, the temperature of system A is increased while water is circulated by circulating water in system A. After completion of the temperature increase in the A system, the water in the A system is transferred into the B system, and the temperature of the B system is increased while circulating this water. An oxidative decontamination agent (for example, potassium permanganate) is injected into the transferred water while transferring the water in the B system into the A system after completion of the temperature increase in the B system. Thereafter, oxidative decontamination of the A line and oxidative decontamination of the B line are sequentially performed by an oxidative decontamination liquid (for example, potassium permanganate aqueous solution) containing the oxidative decontamination agent. When oxidative decontamination is performed in each system, the oxidative decontamination solution is circulated through each system. After the oxidative decontamination is completed, water is transferred from the B system to the A system while decomposing the oxidative decontamination reagent. The decomposition of the oxidative decontamination reagent is performed by injecting a reductive decontamination reagent (for example, oxalic acid) into the oxidative decontamination liquid. The injection of this reductive decontaminant produces not only the amount of reductive decontaminant required for the decomposition of the oxidative decontaminant, but also the reductive decontaminant used for the next reductive decontamination (eg, oxalic acid aqueous solution) The amount of reductive decontamination agent necessary for the injection is also injected. Therefore, the reductive decontamination solution in which the oxidative decontamination agent is decomposed and the reductive decontamination agent is dissolved is led into the A line, and the reductive decontamination of the A line is started. During reductive decontamination, reductive decontamination liquid is circulated through the A line. In many cases, the reductive decontamination process takes a long time exceeding 10 hours. Therefore, in order to prevent the temperature of the B system in which the reductive decontamination liquid is not circulated, the reductive decontamination of the A line is performed in FIG. Stopped once in half of the reductive decontamination time required. The reductive decontamination solution in the A system is transferred to the B system, and the reductive decontamination of the B system is performed while circulating the reductive decontamination solution through the B system. The reductive decontamination of the B line is temporarily stopped in half of the required reductive decontamination time. After that, reductive decontamination for the remaining reductive decontamination time is sequentially performed on the A line and the B line. After the reduction decontamination of the B system is completed, the reductive decontamination agent contained in the reduction decontamination liquid is decomposed while reciprocating the reduction decontamination liquid between the B system and the A system. After the decomposition of the reductive decontamination agent, the purification process is carried out while transferring water between the systems. This completes the first cycle of chemical decontamination. In the chemical decontamination method shown in FIG. 1, a second cycle having the same steps is performed after the first cycle.

  In contrast to this new chemical decontamination method, an example of a conventional chemical decontamination method includes the steps shown in FIG. The example shown in FIG. 2 is a process of a chemical decontamination method performed for one system of a plant (for example, one recirculation system of a boiling water nuclear power plant). This chemical decontamination method includes steps of temperature increase, oxidant injection, oxidation, oxidant decomposition, reduction, reductant decomposition, intermediate purification, oxidant injection, oxidation, oxidant decomposition, reduction, reductant decomposition and final purification. Is included. When the chemical decontamination method shown in FIG. 2 is applied to two systems of the plant, each of the above steps is separately repeated twice. When chemical decontamination is separately performed for the two systems, a decontamination time twice as long as the decontamination time shown in FIG. 2, and an oxidative decontamination solution and a reduction decontamination solution twice are required.

  From the above examination, the new chemical decontamination method shown in FIG. 1 can shorten the decontamination time compared to the case where the conventional chemical decontamination method shown in FIG. It was revealed that the amount of decontamination liquid (oxidative decontamination liquid and reductive decontamination liquid) required also decreased.

  Examples of the present invention reflecting the above-described examination results will be described below.

  A chemical decontamination method which is a preferred embodiment of the present invention will be described below with reference to FIGS. This chemical decontamination method is an example applied to two recirculation piping of a boiling water nuclear power plant (hereinafter referred to as a BWR plant). The chemical decontamination method in the present embodiment is performed in a periodic inspection period after the operation of the BWR plant is stopped.

  The BWR plant 1 has a reactor pressure vessel (hereinafter referred to as RPV) 2 and two recirculation systems A and B constituting the reactor. As described in US Pat. No. 6,466,636, a core (not shown) loaded with a plurality of fuel assemblies, a core shroud (not shown) surrounding the core, and between the core shroud and the RPV 2 A plurality of jet pumps (not shown) arranged in the formed annular downcomer are arranged in the RPV 2. The recirculation system A has a recirculation pump 4 disposed outside the RPV 2 and a recirculation system pipe 2 provided with the recirculation pump 4. Isolation valves 6 and 7 are installed in the recirculation system pipe 2 upstream and downstream of the recirculation pump 4. The recirculation system B has a recirculation pump 5 disposed outside the RPV 2 and a recirculation system pipe 3 provided with the recirculation pump 5. Isolation valves 8 and 9 are installed in the recirculation system pipe 3 upstream and downstream of the recirculation pump 5. The upstream ends of the recirculation pipes 2 and 3 are connected to two nozzles 52 and 53 formed in the RPV 2 and communicated with the downcomer, respectively. The respective downstream end portions 54 and 55 of the recirculation pipes 2 and 3 reach the inside of the RPV 2 and are respectively connected to nozzles (not shown) of the corresponding jet pumps.

  A detailed configuration of the chemical decontamination apparatus 11 will be described with reference to FIG. The chemical decontamination apparatus 11 includes a surge tank 12, pumps 13 and 14, a circulation pipe (decontamination liquid pipe) 16, a filter 26, a heater 27, a cation exchange resin tower 29, a decomposition apparatus 31, an oxidant tank 32, and a connection pipe. 17, 19, 21, 23. From upstream, a valve 34, a pump 13, a heater 27, valves 35, 36, and 37, a surge tank 12, a pump 14, and a valve 38 are provided in the circulation pipe 16 in this order from the upstream. A pipe 39 that bypasses the valve 34 is connected to the circulation pipe 16. The filter 26 is provided in the pipe 39, and valves 40 and 41 arranged upstream and downstream of the filter 26 are installed in the pipe 39. A pipe 42 that bypasses the heater 27 and the valve 35 is connected to the circulation pipe 16. A cooler 28 and a valve 43 are installed in the pipe 42. A cation exchange resin tower 29 and a valve 45 are installed in a pipe 44 having both ends connected to the circulation pipe 16 and bypassing the valve 36. The mixed bed resin tower 30 and the valve 47 are installed in a pipe 46 that is connected to the pipe 44 at both ends and bypasses the cation exchange resin tower 29 and the valve 45. A pipe 48 that bypasses the valve 37 and is provided with a decomposition device (for example, a catalyst tower) 31 and a valve 49 is connected to the circulation pipe 16 and the surge tank 12, respectively. The decomposition apparatus 31 is filled with, for example, an activated carbon catalyst in which 0.5% of ruthenium is impregnated on the surface of the activated carbon. A pipe 52 connected to the circulation pipe 16 between the pump 14 and the valve 38 is connected to the surge tank 12. A hopper 25 and a valve 53 are installed in the pipe 52. Although not shown, potassium permanganate (oxidative decontamination agent) for oxidizing and dissolving contaminants on the inner surfaces of the recirculation pipes 2 and 3 to be subjected to chemical decontamination, and contaminants in those pipes. Each tank (not shown) for supplying oxalic acid (reduction decontamination agent) for reducing and dissolving and hydrazine as a pH adjusting agent is connected to the hopper 25. The oxidant tank 32 is connected to the pipe 48 upstream of the decomposition apparatus 31 by the pipe 50. An injection pump 33 and a valve 51 are installed in the pipe 50.

  A connection pipe (first decontamination liquid supply pipe) 17 and a connection pipe (second decontamination liquid supply pipe) 22 are connected to one end of the circulation pipe 16. An on-off valve 18 is provided in the connection pipe 17, and an on-off valve 22 is provided in the connection pipe 21. A connection pipe (first decontamination liquid return pipe) 19 and a connection pipe (second decontamination liquid return pipe) 23 are connected to the other end of the circulation pipe 16. The on-off valve 20 is provided in the connection pipe 19, and the on-off valve 24 is provided in the connection pipe 23. The on-off valves 18 and 22 are first switching devices that switch the supply of a liquid such as a decontamination liquid to one connection pipe selected from the connection pipes 17 and 21. The on-off valves 20 and 24 are second switching devices that switch the supply of liquid such as decontamination liquid from one connection pipe selected from the connection pipes 19 and 23 to the circulation pipe 16.

  After the operation of the BWR plant 1 is stopped, the chemical decontamination of the recirculation pipes 2 and 3 is performed. In carrying out this chemical decontamination, the temporary chemical decontamination apparatus 11 must be connected to the recirculation pipes 2 and 3. The connection pipes 17 and 19 of the chemical decontamination apparatus 11 are connected to the recirculation system pipe 2, and the connection pipes 21 and 23 are connected to the recirculation system pipe 3. That is, the valve 12 provided in the return pipe 56 of the residual heat removal system connected to the recirculation system pipe 2 is opened, and the valve 13 provided in the return pipe 57 of the residual heat removal system connected to the recirculation system pipe 3. Is released. A connection pipe 17 is connected to the flange of the opened bonnet of the valve 12. The side of the opened valve 12 opposite to the recirculation pipe 2 is sealed with a plug. The connection pipe 21 is connected to the flange of the opened hood of the valve 13. The side of the opened valve 13 opposite to the recirculation pipe 2 is sealed with a plug. The connection pipe 19 is connected to a drain pipe (not shown) connected to the recirculation system pipe 2. The connection pipe 23 is connected to a drain pipe (not shown) connected to the recirculation system pipe 3. At this time, the downstream end portions 54 and 55 are open to the atmosphere.

  By connecting the connection pipes 17 and 19 to the recirculation system pipe 2 and connecting the connection pipes 21 and 23 to the recirculation system pipe 3 as described above, the recirculation system pipe is used using the temporary chemical decontamination apparatus 11. The inner surfaces of the recirculation pipes 2 and 3 can be decontaminated while the decontamination liquid is circulated in each of 2 and 3.

  The chemical decontamination method in this example will be specifically described based on the steps shown in FIG. 1 and FIGS. 4 to 14, the white valve indicates the open state, the black valve indicates the closed state, and the hatched valve indicates the intermediate opening state.

  First, the temperature of the A-system recirculation piping 2 is increased. This temperature raising step will be described with reference to FIG. The on-off valves 18 and 20 and the valves 34 to 38 are opened, and the on-off valves 22 and 24 and the valves 40, 41, 43, 45, 47, 49, 51, and 53 are closed. The pumps 13 and 14 are driven, and the water in the surge tank 12 is supplied into the recirculation system pipe 2 through the circulation pipe 16 and the connection pipe 17. The water passes through the recirculation system pipe 2, returns to the circulation pipe 16 through the connection pipe 19, and is heated by the heater 27. The water supplied to the recirculation system pipe 2 is heated to 85 ° C. or higher, for example, 92 ° C. by the heater 27. When the temperature of the water returned from the connection pipe 19 to the circulation pipe 16 reaches 90 ° C., the temperature raising process of the recirculation pipe 2 is completed.

  In order to increase the temperature of the recirculation system pipe 3 of the B system, an operation of transferring water from the recirculation system pipe 2 to the recirculation system pipe 3 is performed. This transfer operation will be described with reference to FIG. Several valves of the chemical decontamination apparatus 11 are operated. The on-off valve 22 and the valves 40 and 41 are opened, and the on-off valve 18 and the valve 34 are closed. The 90 ° C. water circulating in the recirculation pipe 2 and the circulation pipe 16 is supplied from the circulation pipe 16 through the connection pipe 21 into the recirculation pipe 3. At this time, the water returned from the recirculation system pipe 2 through the connection pipe 19 is guided to the filter 26 so that the chemical decontamination apparatus 11 is not contaminated by radioactive substances, and is peeled off from the inner surface of the recirculation system pipe 2. Then, the clad contained in the water is removed by the filter 26. The water heated to 90 ° C. by the heater 27 through the filter 26 is transferred into the recirculation system pipe 3 through the connection pipe 21. As the pump 13, it is desirable to use a diaphragm pump that does not generate cavitation. By using the diaphragm pump, as much water as possible in the recirculation pipe 2 can be transferred into the recirculation pipe 3. The completion of the water transfer can be known from the change in the sound of the pump 13. When a diaphragm pump completes the transfer of water and air is entrained on the inlet side, the noise of the pump clearly changes. It can be known that the transfer of water is completed by the change of the noise. Similarly, the completion of transfer from a recirculation system pipe having an oxidative decontamination liquid and a reduction decontamination liquid, which will be described later, to another recirculation system pipe can be known from the change in the noise of the pump. The completion of the water transfer can also be known by installing a pressure sensor for measuring the head in the recirculation system piping and monitoring the water level in the recirculation system piping based on the measurement value of the pressure sensor. That is, the transfer completion can be known by confirming that the water level on the liquid level is lower than the lower surface of the horizontal piping of the recirculation piping. Furthermore, the liquid level can be confirmed at the position of the manometer indicating the liquid level in the recirculation system pipe, and the completion of the transfer can be known.

  After the transfer of water from the recirculation system pipe 2 to the recirculation system pipe 3 is completed, the temperature of the B system recirculation system pipe 3 is increased. The temperature rise of the recirculation pipe 3 will be described with reference to FIG. The on-off valve 24 and the valve 34 are opened, and the on-off valve 20 and the valves 40 and 41 are closed. The water heated by the heater 27 is circulated in the circulation pipe 16, the connection pipe 21, the recirculation system pipe 3 and the connection pipe 23 by driving the pumps 13 and 14. When the temperature of the water returned to the circulation pipe 16 through the connection pipe 23 reaches 85 ° C. or higher, for example, 90 ° C., the temperature raising process of the recirculation system pipe 3 is completed. When the flow rate of the circulated water varies depending on the presence or absence of water flow to the filter 26, the rotation speed of the pump 14 is adjusted as appropriate while monitoring the water level of the surge tank 12, and the water discharged from the pump 14 is monitored. Adjust the flow rate.

  After the temperature raising process of the recirculation system pipe 3 is completed, an oxidative decontamination liquid containing an oxidative decontamination liquid is injected into the circulating water in order to perform oxidative decontamination of the recirculation system pipe 2 (oxidative decontamination agent). Injection process). The injection process of this oxidative decontamination agent will be described with reference to FIG. The on-off valve 18 and the valves 39, 40, 53 are opened, and the on-off valve 22 and the valve 44 are closed. In this injection process, the water in the recirculation system pipe 3 is transferred into the recirculation system pipe 2 by the pumps 13 and 14 driving the filter 26 and passes through the filter 26, so that the clad contained in the transferred water is filtered. 26. Potassium permanganate (oxidative decontamination agent) is injected from the hopper 25 into the water flowing in the pipe 52. The injected potassium permanganate flows into the surge tank 12 through the pipe 52, flows through the circulation pipe 16, and is mixed into the water heated by the heater 27. The temperature of this water is 90 ° C. Mainly, potassium permanganate is dissolved in water in the surge tank 12, and an oxidative decontamination solution (potassium permanganate aqueous solution) is generated. The concentration of potassium permanganate contained in the water transferred to the recirculation piping 2 is charged from the hopper 25 to the piping 52 so that the concentration is set to the decontamination target system, for example, 200 to 300 ppm. Adjust the amount of oxidative decontamination solution. The on-off valve 18 is opened at the start of injection of the oxidative decontamination agent from the hopper 25. After opening the on-off valve 18, the on-off valve 22 is immediately closed. The oxidative decontamination solution supplied to the circulation pipe 16 is guided into the recirculation system pipe 2 by the connection pipe 17. While transferring water from the recirculation system pipe 3 to the recirculation system pipe 2, the oxidative decontamination agent to the hopper 25 is supplied so that all necessary amount of the oxidative decontamination agent is supplied from the hopper 25 to the surge tank 12. The injection volume is adjusted.

  After the transfer of water from the recirculation system pipe 3 to the recirculation system pipe 2 is completed in the oxidative decontamination agent injection process, the recirculation system pipe 2 is subjected to oxidative decontamination (oxidation decontamination process). In this oxidative decontamination step, as shown in FIG. 4, the on-off valve 20 and the valve 34 are opened, and the on-off valve 24 and the valves 40 and 41 are closed. An oxidative decontamination solution containing potassium permanganate circulates in the closed loop formed by the circulation pipe 16, the connection pipe 17, the recirculation system pipe 2 and the connection pipe 19. In the oxidative decontamination process, the reason why the oxidative decontamination solution is not supplied to the filter 26 is that (1) the viscosity of manganese dioxide produced by the reaction in the oxidative decontamination is high, and the differential pressure of the filter 26 is likely to increase. It is difficult to operate the pumps 13 and 14 for circulating the dye solution, and (2) to prevent unnecessary decomposition of permanganate ions in the vicinity of the filter 26. During the oxidative decontamination, the oxidative decontamination liquid supplied to the recirculation system pipe 2 is heated to 90 ° C. by the heater 27. The oxidative decontamination on the inner surface of the recirculation pipe 2 is completed after a predetermined time (for example, 6 hours). After the oxidative decontamination of the recirculation system pipe 2 is completed, the oxidative decontamination of the recirculation system pipe 3 is performed. In the oxidative decontamination process of the recirculation system pipe 3, as shown in FIG. 6, the on-off valves 22 and 24 are opened and the on-off valves 18 and 20 are closed. The oxidative decontamination liquid heated to 90 ° C. by the heater 27 is supplied into the recirculation system pipe 3 through the connection pipe 21. In the oxidative decontamination step of the recirculation system pipe 3, the oxidative decontamination liquid circulates in a closed loop formed by the circulation pipe 16, the connection pipe 21, the recirculation system pipe 3 and the connection pipe 23. The oxidative decontamination on the inner surface of the recirculation pipe 3 is also completed after a predetermined time (for example, 6 hours).

  After the oxidative decontamination process of the recirculation system pipe 3 is completed, the oxidative decontamination agent contained in the oxidative decontamination liquid is decomposed (oxidative decontamination reagent decomposition process). The open / close state of each valve of the chemical decontamination apparatus 11 in the oxidative decontamination agent decomposition step is the same as the open / close state of the valves in the oxidative decontamination agent injection step shown in FIG. The oxidative decontamination solution in the recirculation pipe 3, that is, water in which potassium permanganate is dissolved is transferred from the recirculation pipe 3 to the circulation pipe 16 through the connection pipe 23. Oxalic acid (reductive decontamination agent) is injected into the pipe 52 from the hopper 25. The injected oxalic acid is guided into the surge tank 12 and is dissolved by the water of the oxidative decontamination solution. Permanganate ions contained in the oxidative decontamination solution present in the surge tank 12 are decomposed by oxalic acid. Manganese peroxide contained in the oxidative decontamination liquid in the recirculation system pipe 3 in which the oxidative decontamination liquid in the recirculation system pipe 3 is returned to the circulation pipe 16 by supplying oxalic acid into the surge tank 12. Ions are decomposed by oxalic acid in the surge tank 12. In this way, manganese peroxide ions contained in the oxidative decontamination solution are completely decomposed by oxalic acid. The amount of oxalic acid injected from the hopper 25 is necessary for the production of an aqueous oxalic acid solution (reducing decontamination solution) used for the reductive decontamination in the next step together with the amount necessary for the decomposition of the remaining permanganate ions. This is the total amount. When the permanganate ions are decomposed, the aqueous potassium permanganate solution becomes an oxalic acid aqueous solution. As a result, the aqueous oxalic acid solution is transferred into the recirculation system pipe 2 through the connection pipe 17. The concentration of oxalic acid contained in the oxalic acid aqueous solution injected from the hopper 25 so that the concentration of oxalic acid contained in the reductive decontamination liquid transferred into the recirculation system pipe 2 becomes a predetermined concentration (for example, about 2000 ppm). Is adjusted.

  After the transfer of the reductive decontamination solution into the recirculation system pipe 2 is completed in the oxidative decontamination process, the recirculation system pipe 2 is subjected to reductive decontamination (reduction decontamination process). In this reductive decontamination step, as shown in FIG. 8, the on-off valve 20 and the valves 34 and 45 are opened, the valve 36 is set to an adjusted opening (intermediate opening), and the on-off valve 24 and the valves 40 and 41 are closed. . The reductive decontamination liquid heated to 90 ° C. by the heater 27 circulates in the closed loop formed by the circulation pipe 16, the connection pipe 17, the recirculation system pipe 2 and the connection pipe 19. In this way, reductive decontamination is performed on the inner surface of the recirculation pipe 2. In the reductive decontamination, since the valve 45 is open, a predetermined flow rate that is a part of the reductive decontamination liquid returned to the circulation pipe 16 is guided to the cation exchange resin tower 29. The remaining reductive decontamination liquid passes through the valve 36 having an adjusted opening degree. The cation exchange resin tower 29 reduces cation components such as iron ions, manganese ions, nickel ions, and cobalt ions that are generated in the recirculation piping 2 by reductive decontamination and contained in the reductive decontamination solution together with radionuclides. Remove from decontamination solution.

  At the time of reductive decontamination for the recirculation system pipe 2, the pH of the reductive decontamination solution is adjusted to, for example, about 2.5 by adding hydrazine as a pH adjusting agent to the reductive decontamination solution. By adjusting the pH with hydrazine, corrosion of the structural member (for example, the recirculation pipes 2 and 3) to be subjected to chemical decontamination is suppressed. The above-described addition of hydrazine to the reductive decontamination solution is performed by injection from the hopper 25, and is continuously performed throughout the reductive decontamination period. By adding hydrazine, the pH of the reducing decontamination solution is always controlled to about 2.5. However, after hydrazine breaks from the cation exchange resin tower 29, injection of hydrazine from the hopper 25 is stopped.

  When the decontamination time for the recirculation system pipe 2 in the recirculation system A reaches half of the reductive decontamination time required for the recirculation system pipe 2 after the start of the reduction decontamination, the recirculation system pipe 2 Reductive decontamination of is temporarily stopped. Then, the reductive decontamination liquid in the recirculation system pipe 2 is transferred into the recirculation system pipe 3 of the recirculation system B. The reductive decontamination liquid is transferred with the on-off valves and the open / closed states of the valves shown in FIG. That is, the on-off valve 22 and the valves 40 and 41 are opened, and the on-off valve 18 and the valve 34 are closed.

  After the transfer of the reductive decontamination liquid into the recirculation system pipe 3 is completed, a reductive decontamination step for the recirculation system pipe 3 is performed. At this time, as shown in FIG. 10, the on-off valve 24 and the valve 34 are opened, and the on-off valve 20 and the valves 40 and 41 are closed. The reductive decontamination liquid heated to 90 ° C. by the heater 27 circulates in the closed loop formed by the circulation pipe 16, the connection pipe 21, the recirculation system pipe 3 and the connection pipe 23, and the inner surface of the recirculation system pipe 3. Reductive decontamination is performed. The pH of the reductive decontamination solution is maintained at about 2.5 by hydrazine injection as described above. The cation exchange resin tower 29 removes the above-described cation component generated in the recirculation system pipe 3 by reductive decontamination and contained in the reductive decontamination liquid together with the radionuclide from the reductive decontamination liquid. When the recirculation decontamination time for the recirculation system pipe 3 reaches half of the reductive decontamination time required for the recirculation system pipe 3 after the start of the reduction decontamination of the recirculation system pipe 3, the recirculation system pipe The reductive decontamination of 3 is once stopped. The open / close state of each valve is changed to the state shown in FIG. 11, and the reducing decontamination liquid in the recirculation system pipe 3 is transferred into the recirculation system pipe 2.

  When the transfer of the reductive decontamination liquid into the recirculation pipe 2 is completed, the open / close state of each valve in the chemical decontamination apparatus 11 becomes the state shown in FIG. In the remaining half of the reductive decontamination period necessary for the recirculation system pipe 2, reductive decontamination for the recirculation system pipe 2 is performed again as described above. When this reductive decontamination for the recirculation system pipe 2 is completed, the open / close state of each valve is changed to the state shown in FIG. 9, and the reductive decontamination liquid in the recirculation system pipe 2 is transferred into the recirculation system pipe 3. Is done. When the transfer of the reductive decontamination liquid is completed, the open / close state of each valve is changed to the state shown in FIG. In the remaining half of the reductive decontamination period required for the recirculation system pipe 3, reductive decontamination for the recirculation system pipe 3 is performed again as described above.

  After the reduction decontamination process described above is completed, a reduction decontamination process is performed. The reductive decontamination liquid contained in the reductive decontamination liquid is decomposed by transferring the reductive decontamination liquid from the recirculation pipe 3 to the recirculation pipe 2 and recirculating the reductive decontamination liquid from the recirculation pipe 2. It is executed using the decomposition device 31 while alternately transferring to the circulation system pipe 3.

  First, decomposition of oxalic acid and hydrazine contained in the reductive decontamination liquid when the reductive decontamination liquid is transferred from the recirculation system pipe 3 to the recirculation system pipe 2 will be described. After the reduction decontamination, as shown in FIG. 12, the valve 53 is closed, and the flow rate of the reduction decontamination liquid discharged from the pump 13 is adjusted to an appropriate value when the reduction decontamination agent is decomposed. In accordance with this, the flow rate of the reductive decontamination liquid discharged from the pump 14 is also adjusted to maintain the water level in the surge tank 12 at a predetermined set water level. The adjustment of the discharge flow rate from the pump 13 and the adjustment of the water level in the surge tank 12 are performed in a state where the on-off valves 22 and 24 are open and the on-off valves 18 and 20 are closed. Thereafter, as shown in FIG. 12, the valve 36 is closed, the valve 49 is opened, and the valve 37 is closed. The reductive decontamination liquid is heated to 90 ° C. by the heater 27, supplied to the decomposition apparatus 31, and guided to the surge tank 12. After the decomposition device 31 is warmed, the valve 51 is opened and the infusion pump 33 is driven. Hydrogen peroxide present in the oxidant tank 32 is supplied into the decomposition apparatus 31 via the pipes 50 and 48. Oxalic acid and hydrazine contained in the reductive decontamination solution supplied from the circulation pipe 16 to the decomposition device 31 are decomposed in the decomposition device 31 by the action of a catalyst in the presence of hydrogen peroxide. The amount of hydrogen peroxide supplied to the decomposition apparatus 31 is about 1.2 times the number of moles required for decomposition of oxalic acid and hydrazine. By injecting this amount of hydrogen peroxide, the decomposition device 31 simultaneously decomposes oxalic acid and hydrazine.

  After confirming that the conductivity of the reductive decontamination solution measured by a conductivity meter (not shown) installed in the circulation pipe 16 downstream of the pump 14 is greatly reduced by decomposition of oxalic acid, etc. The valve 18 is opened and the on-off valve 22 is closed. By this opening / closing valve operation, the reductive decontamination liquid in the recirculation system pipe 3 is supplied to the decomposing device 31, and the reductive decontamination liquid whose oxalic acid and hydrazine are decomposed to reduce their respective concentrations becomes the surge tank 12 and the circulation pipe. 16 flows into the connection pipe 17 via 16. The reductive decontamination liquid having reduced concentrations of oxalic acid and hydrazine is transferred into the recirculation system pipe 2 through the connection pipe 17.

  The reason why the on-off valve 18 is opened and the on-off valve 22 is closed after the conductivity downstream of the pump 14 is greatly reduced is as follows. If the on-off valve 18 is opened before the electrical conductivity decreases, that is, if the on-off valve 18 is opened too early, the reductive decontamination liquid remaining in the surge tank 12 and having a high concentration of oxalic acid and hydrazine. Will flow into the recirculation piping 2. This is because the reductive decontamination liquid in which the concentrations of oxalic acid and hydrazine are reduced by the action of the decomposition apparatus 31 is mixed with the reductive decontamination liquid containing the above high concentrations of oxalic acid and hydrazine in the recirculation system pipe 2. The concentration of oxalic acid and hydrazine in the former reductive decontamination solution is increased. Therefore, the time required for the decomposition of oxalic acid and hydrazine is increased. In this embodiment, since the on-off valve 18 is opened after the electrical conductivity downstream of the pump 14 is greatly reduced, the time required for the decomposition of oxalic acid and hydrazine can be shortened.

  The initial concentration of oxalic acid contained in the reductive decontamination solution supplied to the decomposition apparatus 31 is about 2000 ppm. When the decomposition rate of oxalic acid by the catalyst in the decomposition apparatus 31 is 90%, the concentration of oxalic acid contained in the reducing decontamination liquid discharged from the decomposition apparatus 31 is about 200 ppm. The concentration of oxalic acid contained in the reductive decontamination liquid guided to the recirculation system pipe 2 by the connecting pipe 17 becomes the concentration (about 200 ppm) of the reductive decontamination liquid discharged from the decomposition apparatus 31. The decomposition process of the reductive decontaminating agent is performed until the concentration of the reductive decontaminating agent (oxalic acid) contained in the reductive decontamination liquid becomes 10 ppm or less.

  After the transfer of the reductive decontamination solution from the recirculation system pipe 3 to the recirculation system pipe 2 is completed in the decomposition process of the reductive decontamination agent, as shown in FIG. close. At this time, as shown in FIG. 12, the on-off valve 18 is open and the on-off valve 22 is closed. The reductive decontamination liquid in the recirculation pipe 2 is returned to the circulation pipe 16 and supplied to the decomposition apparatus 31 to which hydrogen peroxide is introduced. In the decomposition apparatus 31, oxalic acid and hydrazine contained in the reductive decontamination solution are decomposed. At this time, the concentration of oxalic acid contained in the reductive decontamination liquid discharged from the decomposition apparatus 31 is about 20 ppm. After confirming that the conductivity of the reductive decontamination liquid discharged from the surge tank 12 to the circulation pipe 16 has further decreased at the position where the conductivity meter is installed downstream of the pump 14, as shown in FIG. 22 is opened and the on-off valve 18 is closed. The reductive decontamination liquid whose oxalic acid concentration has been reduced to about 20 ppm is transferred into the recirculation system pipe 3 through the connection pipe 21.

  After the transfer of the reductive decontamination liquid from the recirculation system pipe 2 to the recirculation system pipe 3 is completed in the decomposition process of the reductive decontamination agent, as described above, the reductive decontamination liquid in the recirculation system pipe 3 is removed. It is again transferred to the recirculation piping 2. Also during this transfer, oxalic acid contained in the reductive decontamination liquid in the recirculation pipe 3 is decomposed by the decomposition device 31. By this decomposition, water containing about 2 ppm of oxalic acid is discharged from the decomposition device 31. The water containing about 2 ppm of oxalic acid is transferred into the recirculation system pipe 2 through the connection pipe 17. Since the oxalic acid concentration has been reduced to about 2 ppm, which is 10 ppm or less, due to the decomposition of the reducing decontaminating agent by the third transfer in the reducing decontaminating step, the reducing decontaminating step is completed.

In the decontamination process of the reductive decontamination described above, the amount of reductive decontamination liquid present in the recirculation system pipe is 10 m ³ , and the flow rate during reductive decontamination is 1 In the case of 4 m ³ / h at the time of transfer and 12 m ³ / h at the second and subsequent transfers, the decomposition time of the reductive decontaminant (oxalic acid) is 4 hours and 10 minutes. In the conventional method of decomposing reductive decontaminant (oxalic acid) while circulating reductive decontamination liquid in the recirculation system piping, even if the decontamination rate of reductive decontaminant is the same, reductive decontaminant Since the decomposition efficiency deteriorates due to the dilution, the decomposition time is assumed to be about 7 hours and 40 minutes. That is, when the reductive decontamination solution is decomposed while being reciprocated between the recirculation system pipe 2 and the recirculation system pipe 3 as in this embodiment, In comparison, shortening of the decomposition time of about 3 and a half hours can be expected.

  After the decomposition process of the reductive decontamination agent is completed, an intermediate purification process that is a purification process is performed. At the start of the intermediate purification process, as shown in FIG. 14, the on-off valve 20 is opened and the on-off valve 24 is closed. At this time, as shown in FIG. 12, the on-off valve 18 is open and the on-off valve 22 is closed. Further, the valve 37 is opened, the injection pump 33 is stopped, and the valves 49 and 51 are closed. After the heating by the heater 27 is stopped and cooling water is passed through the cooler 28, the valve 43 is opened and the valve 35 is closed. Since the pumps 13 and 14 are driven, water containing about 2 ppm of oxalic acid in the recirculation system pipe 2 is returned to the circulation pipe 16 by the connection pipe 19 and supplied to the cooler 28. When the temperature of the water is lowered to 60 ° C. or lower that can be supplied to the mixed bed resin tower 30, the valve 47 is opened and the valve 45 is closed, and the water cooled by the cooler 28 is supplied to the mixed bed resin tower 30. In this way, intermediate purification is started. In the intermediate purification process, the eluate resulting from the chemical decontamination remaining without being removed by the cation exchange resin tower 29 in the decomposition process of the reductive decontamination and the remaining decontamination reagent are removed by the mixed bed resin tower 30. The The mixed bed resin tower 30 is filled with a cation exchange resin and an anion exchange resin. When the conductivity measured by the above-described conductivity meter installed downstream of the pump 14 is lowered to a level sufficient for the start of the next oxidative decontamination step, the on-off valve 22 is opened and the on-off valve 18 is closed. . By the operation of this on-off valve, the low conductivity water discharged from the mixed bed resin tower 30 is transferred into the recirculation system pipe 3 by the connection pipe 21. When the transfer of the low conductivity water into the recirculation pipe 3 is completed, the intermediate purification process is completed.

  With the completion of the intermediate purification process, the first cycle of chemical decontamination from the temperature raising process to the intermediate purification process shown in FIG. 1 is completed. After the end of the first cycle, the second cycle shown in FIG. 1 is performed in the same manner as the first cycle.

  When the intermediate purification process of the first cycle is completed, the valve 35 is opened and heating by the heater 27 is resumed. The valve 43 is closed and the supply of cooling water to the cooler 28 is stopped. Further, the valve 34 is opened and the valves 39 and 40 are closed. Thereafter, operations from the temperature raising step to the final purification step in the second cycle are performed in the same manner as those in the first cycle shown in FIG. The final purification process of the second cycle is basically performed in the same manner as the intermediate purification process, but it is necessary to perform flushing of vent pipes and drain pipes connected to each recirculation system pipe. For this reason, in a final purification process, transfer of water etc. is repeated several times between two recirculation system piping.

  In this embodiment, in the oxidative decontamination process and the reduction decontamination process, the closed loop formed by the circulation pipe 16, the connection pipe 17, the recirculation system pipe 2 and the connection pipe 19 is re-reused with respect to the recirculation system pipe 2. A closed loop formed by the circulation pipe 16, the connection pipe 21, the recirculation system pipe 3, and the connection pipe 23 is formed for the circulation system pipe 3. Since the oxidative decontamination liquid heated to 90 ° C. by the heater 27 circulates in each closed loop during the oxidative decontamination process, the temperature of the recirculation pipes 2 and 3 is maintained at a predetermined temperature and circulated. The temperature of the oxidative decontamination solution does not decrease. For this reason, the present embodiment improves the oxidative decontamination performance for each of the recirculation pipes 2 and 3.

  In the reductive decontamination process of the present embodiment, the reductive decontamination liquid heated to 90 ° C. by the heater 27 circulates in the respective closed loops, so that the temperature of the recirculation system pipes 2 and 3 is a predetermined temperature. The temperature of the reductive decontamination liquid held and circulated does not decrease. For this reason, the present embodiment improves the reductive decontamination performance for each of the recirculation pipes 2 and 3. Therefore, the decontamination performance in the chemical decontamination of this example is improved.

  In this embodiment, the oxidative decontaminant is not decomposed while circulating the oxidative decontamination solution in each of the above closed loops, but one recirculation piping (for example, the recirculation piping 3) is recirculated to the other. Since the oxidative decontamination reagent is decomposed when the oxidative decontamination liquid is transferred to the circulation system pipe (for example, the recirculation system pipe 2), the decomposition efficiency of the oxidative decontamination agent is increased and the time required for the decomposition is increased. Can be shortened. That is, when the oxidative decontamination agent is decomposed while circulating the oxidative decontamination solution in a closed loop, the liquid after the oxidative decontamination agent is decomposed and the oxidative decontamination solution in which the oxidative decontamination agent is not decomposed As a result, the decomposition efficiency of the subsequent oxidative decontamination agent decreases. In this embodiment, since the liquid after the oxidative decontamination is decomposed and the oxidative decontamination liquid that is not decomposed are not mixed, the decomposition efficiency of the oxidative decontamination improves.

  In particular, since it takes a considerable amount of time to decompose the reducing decontamination solution contained in the reducing decontamination solution, the reduction decontamination agent is decomposed while circulating the reduction decontamination solution in the closed loop. There is a possibility that mixing of the reduction decontamination liquid in which the concentration of the reduction decontamination agent is reduced by the decomposition and the reduction decontamination liquid before the reduction in the concentration of the reduction decontamination agent occurs for a longer period of time. For this reason, the decomposition efficiency of the reducing decontaminating agent is lowered over a long period of time, and it takes a considerable time to decompose the reducing decontaminating agent. In this embodiment, the reductive decontaminant is decomposed while reciprocating the reductive decontamination liquid between one recirculation system pipe and the other recirculation system pipe, so that the above mixing does not occur, A higher decomposition efficiency of the reductive decontamination agent can be obtained. For this reason, the time required for decomposition | disassembly of the reductive decontamination agent in a present Example can be shortened more.

  In this embodiment, the reductive decontamination liquid is passed through the cation exchange resin tower 29 during the reciprocating transfer of the reductive decontamination liquid in the decomposition process of the reductive decontamination agent. The nuclide can be removed efficiently.

  In the present embodiment, water is transferred from one recirculation system pipe to the other recirculation system pipe also in the purification step, and is passed through the mixed bed resin tower 30 at the time of the transfer. For this reason, the eluate by chemical decontamination contained in the water to be transferred and the remaining decontamination agent can be efficiently removed by the mixed bed resin tower 30. In this embodiment, the purification efficiency is improved and the time required for purification can be shortened.

  Further, in this embodiment, a diaphragm pump is used as the pump 13 provided in the circulation pipe 16. Diaphragm pumps do not require a water head on the suction side of the pump. For this reason, when liquid such as water is transferred from one recirculation system pipe to the other recirculation system pipe, most of the liquid present in the one recirculation system pipe is transferred to the other recirculation system pipe. can do. This also makes it possible to further shorten the time required for the above-described decontamination agent decomposition process and purification process.

  As described above, the present embodiment, which can shorten the decontamination time, can improve the operating rate of the BWR plant. Moreover, since the decontamination liquid (oxidation decontamination liquid and reductive decontamination liquid) to be used decreases, the generation amount of radioactive waste liquid is reduced.

  The chemical decontamination method of Example 2, which is another example of the present invention, will be described below. Example 1 is an example in which chemical decontamination was performed on two recirculation pipes of a BWR plant as two systems of decontamination objects. In the residual heat removal system described in the first embodiment, there are cases where three piping systems each provided with a pump are provided. When two piping systems out of the three piping systems of the residual heat removal system are to be decontaminated, chemical decontamination can be performed in the same manner as in the first embodiment.

  In the present embodiment, chemical decontamination is executed for each of the three piping systems. For this reason, the chemical decontamination apparatus used in the chemical decontamination method of the present embodiment is connected to one end of the circulation pipe 16 of the chemical decontamination apparatus 11 in addition to the connection pipes 17 and 21 (hereinafter referred to as “connecting pipes”). 1) and the other end of the circulation pipe 16 in addition to the connection pipes 19 and 23, another connection pipe (hereinafter referred to as a second connection pipe) is connected. On-off valves are also attached to the first and second connection pipes, respectively. Other configurations of the chemical decontamination apparatus used in the chemical decontamination method of the present embodiment are the same as those of the chemical decontamination apparatus 11. The first piping system of the residual heat removal system is called A system, the second piping system is called B system, and the third piping system is called C system. In this case, the chemical decontamination method of this example is as follows: temperature rise (A system) → temperature rise (B system) → temperature rise (C system) → oxidant injection (transfer to A system) → oxidative decontamination (A system) ) → Oxidative decontamination (B line) → Oxidative decontamination (C line) → Oxidant decomposition (transfer to A line) → Reduction decontamination (A line) → Reduction decontamination (B line) → Reduction decontamination (C line) ) → Reducing agent decomposition (transfer to system A) → Reducing agent decomposition (transfer to system B) → Reducing agent decomposition (transfer to system C) → Intermediate purification (transfer to system A) A, B, C systems Each of the decontamination liquid and the decontamination decontamination is carried out while transferring the decontamination liquid corresponding to the above, and when one process is completed, operations such as decontamination and purification are carried out while the decontamination liquid is transferred. Just do it. In the present embodiment, the decontamination work can be completed by repeating the series of steps of chemical decontamination described above for the three piping systems as in the first embodiment. Even in the case where there are three decontamination targets as in this embodiment, the number of times that the decontamination solution is decomposed and purified is smaller than when each system is performed independently. For this reason, a present Example can shorten decontamination time and can suppress the generation amount of a secondary waste. In the present embodiment, the effects produced in the first embodiment can be obtained.

  The chemical decontamination method of Example 3, which is another example of the present invention, will be described below. The chemical decontamination apparatus used in the chemical decontamination method of this example is the chemical decontamination apparatus 11 used in the chemical decontamination method of Example 1. The chemical decontamination method of this example is different from the chemical decontamination method of Example 1 only in the injection step of the oxidative decontamination agent.

  In the first embodiment, after the temperature raising process of the recirculation system pipe 3 is finished, the on-off valves 18 and 22 are switched and water is transferred from the recirculation system pipe 3 to the recirculation system pipe 2. Is called. In contrast, in this embodiment, the valve 53 is opened after the temperature raising step of the recirculation system pipe 3 is completed, that is, in the state of FIG. 6 (see FIG. 15). An oxidative decontamination solution containing potassium permanganate is injected from the hopper 25 into the water flowing in the pipe 52 and guided into the surge tank 12. This oxidative decontamination solution is supplied from the surge tank 12 to 90 ° C. water circulating in the closed loop formed by the circulation pipe 16, the connection pipe 21, the recirculation system pipe 3 and the connection pipe 23. Although the oxidative decontamination process in Example 1 is performed from the recirculation system pipe 2, in this example, the oxidative decontamination process is performed from the recirculation system pipe 3, and then to the recirculation system pipe 2. Implemented. In the present embodiment, the same temperature raising step, oxidative decontamination agent decomposition step, reductive decontamination step, reductive decontamination decomposition step and purification step are performed as in the first embodiment.

  Also in this embodiment, the effect produced in the first embodiment can be obtained. Furthermore, since the present embodiment injects the oxidative decontamination solution into the water circulating in the closed loop formed by the recirculation pipe 3 and the circulation pipe 16 after the temperature raising step, the recirculation pipe 2 and The number of times of opening and closing valves such as water flow to the filter 26 that is performed when water is transferred between the recirculation pipes 3 is reduced. For this reason, in this embodiment, the operation of the chemical decontamination apparatus becomes easy. However, this embodiment reduces the transfer of water between the recirculation system pipe 2 and the recirculation system pipe 3 after the temperature raising process is completed, so that the temperature increase process in the recirculation system pipe 2 of the recirculation system A is completed. The waiting time from the start of the oxidative decontamination process becomes longer. Thereby, the temperature of the recirculation system piping 2 at the time of an oxidative decontamination process start will become lower. In the initial slight period in the oxidative decontamination process of the recirculation system pipe 2, a slight decrease in oxidative decontamination performance is seen due to the temperature decrease, but the oxidative decontamination liquid heated to 90 ° C is circulated. The oxidative decontamination performance of the recirculation pipe 2 is improved immediately.

  The chemical decontamination method of each Example described above can be applied not only to the boiling water nuclear power plant system but also to the pressurized water nuclear power plant and each fuel reprocessing plant system.

It is explanatory drawing which shows the process of the chemical decontamination method of Example 1 which is one suitable Example of this invention. It is explanatory drawing which shows the schematic process of the conventional chemical decontamination method. It is explanatory drawing which shows the state which connected the chemical decontamination apparatus to 2 recirculation system piping of a boiling water nuclear power plant when implementing the chemical decontamination method shown in FIG. It is a detailed block diagram of the chemical decontamination apparatus shown in FIG. 3, and is a block diagram of the chemical decontamination apparatus showing the open / close state of the valve in the temperature raising step shown in FIG. 1 in the recirculation system piping of the recirculation system A. It is explanatory drawing which shows the open / close state of the valve | bulb of a chemical decontamination apparatus in the case of transferring water from the recirculation system piping of the recirculation system A to the recirculation system piping of the recirculation system B at the temperature rising process shown in FIG. It is explanatory drawing which shows the opening-and-closing state of the valve | bulb of the chemical decontamination apparatus in the temperature rising process shown in FIG. It is explanatory drawing which shows the open / close state of the valve | bulb of the chemical decontamination apparatus in the oxidizing agent injection | pouring process shown in FIG. It is explanatory drawing which shows the open / close state of the valve | bulb of the chemical decontamination apparatus in the reductive decontamination process shown in FIG. Explanation of the state of opening and closing of the valve of the chemical decontamination apparatus when the reducing decontamination liquid is transferred from the recirculation system pipe of the recirculation system A to the recirculation system pipe of the recirculation system B in the reduction decontamination step shown in FIG. FIG. It is explanatory drawing which shows the opening-and-closing state of the valve | bulb of the chemical decontamination apparatus in the reductive decontamination process shown in FIG. Explanation of the state of opening and closing of the valve of the chemical decontamination apparatus when the reducing decontamination liquid is transferred from the recirculation pipe of the recirculation system B to the recirculation pipe of the recirculation system A in the reductive decontamination step shown in FIG. FIG. The state of opening and closing of the valve of the chemical decontamination apparatus when the reductive decontamination liquid is transferred from the recirculation system piping of the recirculation system B to the recirculation system piping of the recirculation system A in the decomposition process of the reductive decontamination agent shown in FIG. It is explanatory drawing which shows. The state of opening and closing of the valve of the chemical decontamination apparatus when the reductive decontamination liquid is transferred from the recirculation system piping of the recirculation system A to the recirculation system piping of the recirculation system B in the decomposition process of the reductive decontamination agent shown in FIG. It is explanatory drawing which shows. It is explanatory drawing which shows the open / close state of the valve | bulb of a chemical decontamination apparatus in the case of transferring water from the recirculation system piping of the recirculation system A to the recirculation system piping of the recirculation system B in the intermediate | middle purification process shown in FIG. It is explanatory drawing which shows the open / close state of the valve | bulb of the chemical decontamination apparatus in the oxidizing agent injection | pouring process of the chemical decontamination method of Example 3 which is another Example of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Boiling water nuclear power plant, 2 ... Reactor pressure vessel, 2, 3 ... Recirculation piping, 4, 5 ... Recirculation pump, 11 ... Chemical decontamination apparatus, 12 ... Surge tank, 13, 14 ... Pump , 16 ... circulation piping, 17, 19, 21, 23 ... connection piping, 18, 20, 22, 24 ... open / close valve, 25 ... hopper, 26 ... filter, 27 ... heater, 28 ... cooler, 29 ... cation exchange Resin tower, 30 ... Mixed bed resin tower, 31 ... Decomposition unit, 32 ... Oxidant tank, A, B ... Recirculation system.

Claims (14)

  A decontamination liquid containing a decontamination agent is supplied to a plurality of piping systems provided in a plant to decontaminate the inner surface of the piping system, and the decontamination liquid in one piping system after decontamination is completed. The chemical decontamination method is characterized by decomposing the decontaminant contained in the decontamination liquid when the decontamination liquid is transferred to another piping system after decontamination.   The decontamination solution used for the decontamination is an oxidative decontamination solution containing an oxidative decontamination agent, and the decomposition of the decontamination agent is injected with a reduction decontamination solution containing a reduction decontamination agent The chemical decontamination method according to claim 1, wherein the chemical decontamination method is performed.   The decontamination solution used for the decontamination is a reduction decontamination solution containing a reduction decontamination agent, and the decomposition of the decontamination agent is to decompose the reduction decontamination solution using an oxidizing agent and a catalyst. The chemical decontamination method according to claim 1.   4. The reduction decontamination liquid transported from the one piping system to the other piping system is allowed to pass through a cation exchange resin tower filled with a cation exchange resin when the reduction decontamination liquid is decomposed. Chemical decontamination method.   5. The chemical decontamination method according to claim 3, wherein the liquid transferred from the one piping system to the other piping system is purified after the reduction decontamination agent is decomposed.   The chemical decontamination method according to claim 5, wherein the liquid to be transferred is passed through a mixed bed resin tower during purification of the liquid.   The chemical decontamination method according to any one of claims 1 to 6, wherein the transfer of the decontamination liquid from the one piping system to the other piping system is performed by a diaphragm pump.   The chemical decontamination method according to claim 1, wherein decontamination of the inner surface of the piping system is performed while circulating the decontamination solution through the piping system.   The decontamination liquid used for the decontamination is an oxidative decontamination liquid containing an oxidative decontamination agent, and decontamination of the inner surface of the piping system is performed while circulating the oxidative decontamination liquid through the piping system. The chemical decontamination method according to claim 1.   The decontamination solution used for the decontamination is a reductive decontamination solution containing a reductive decontamination agent, and decontamination of the inner surface of the piping system is performed while circulating the reducing decontamination solution through the piping system. The chemical decontamination method according to claim 1.   The chemical decontamination method according to claim 3, wherein the catalyst is ruthenium-impregnated activated carbon.   A decontamination liquid pipe provided with a pump and a decontamination liquid pipe connected to one end of the decontamination liquid pipe and flowing through the decontamination liquid pipe to one of the plurality of piping systems provided in the plant. A first decontamination liquid supply pipe that supplies the dye liquid, and a decontamination that is connected to one end of the decontamination liquid pipe and that flows in the decontamination liquid pipe to the other piping system of the plurality of piping systems A first decontamination liquid return pipe connected to the second decontamination liquid supply pipe for supplying the liquid and the other end of the decontamination liquid pipe and returning the decontamination liquid from the one pipe system to the decontamination liquid pipe. A second decontamination liquid return pipe connected to the pipe and the other end of the decontamination liquid pipe and returning the decontamination liquid from the other piping system to the decontamination liquid pipe; and the first decontamination liquid A first switching device for switching the supply of the decontamination liquid to a selected one of the supply pipe and the second decontamination liquid supply pipe; and the first decontamination A second switching device for switching supply of the decontamination liquid from one return pipe selected from the return pipe and the second decontamination liquid return pipe to the decontamination liquid pipe; Decontamination equipment.   The chemical decontamination apparatus according to claim 12, wherein the pump is a diaphragm pump.   The chemical decontamination apparatus according to claim 12 or 13, comprising a decomposition apparatus connected to the decontamination liquid pipe and filled with a catalyst, and an oxidant supply apparatus for supplying an oxidant to the decomposition apparatus.

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