JP2009109253A - Method and device for chemical decontamination - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for chemical decontamination which allow decontamination efficiency to be improved in the chemical decontamination of piping. <P>SOLUTION: A chemical decontamination method for chemically decontaminating oxides on the inner surface of the piping with a decontamination liquid is characterized in that a region to be decontaminated is chemically decontaminated while being heated. Moreover, a chemical decontamination device which chemically decontaminates the oxides on the inner surface of the piping with the decontamination liquid is characterized in that the device includes a supply system to supply the decontamination liquid to the piping, a discharge system to discharge the decontamination liquid from the piping and a heating device to heat the region to be decontaminated. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a chemical decontamination method and an apparatus therefor.

  For chemical decontamination in the reactor coolant recirculation system piping (hereinafter referred to as “PLR piping”), the vertical piping for supplying coolant to the horizontal piping section of the PLR piping (hereinafter referred to as “ring header”) and the reactor. Decontamination of the piping section (hereinafter referred to as “riser pipe”).

  The coolant supplied to the nuclear power plant reactor pressure vessel (hereinafter referred to as “pressure vessel”) is circulated by the reactor coolant recirculation pump (hereinafter referred to as “PLR pump”) via the PLR pipe, The coolant in the container is circulated to absorb the heat generated by the nuclear fission of the fuel to form steam, and after the moisture is separated and dried, the steam is sent to the turbine for power generation.

  The PLR pipe is used to pressurize and circulate the coolant supplied from the pressure vessel by the PLR pump. However, in order to distribute the flow rate into the pressure vessel, the PLR pipe outlet part passes through the pump outlet vertical part and enters the furnace. A horizontal pipe ring header that retains the coolant over the semicircular part of the riser pipe is a riser pipe that is 4 to 5 vertical pipes for flow rate distribution for evenly injecting the flow rate into the furnace on the downstream side It has a piping configuration unique to nuclear power plants where is installed.

  On the other hand, nuclear power plants have been trying to improve reliability by appropriately applying the preventive maintenance technology developed as technology advances. As part of preventive maintenance, in order to confirm the soundness of PLR pipe welds and the like, the pipes are regularly inspected.

  An oxide (oxide film) is attached to the inner surface of the PLR pipe, and a radioactive substance is contained in the oxide film. Therefore, removing radioactive material by removing the oxide film prior to inspection or maintenance work of PLR piping is effective in reducing exposure during the work, and as a method there is oxidation attached to the inner surface of the piping. A chemical decontamination method is used in which the film is dissolved with chemicals.

  As a technique related to chemical decontamination, for example, the contents disclosed in Patent Document 1 as a first prior art are shown in FIG.

  FIG. 10 illustrates the operation of returning the decontamination liquid in the decontamination tank to the storage tank for the decontamination object in the decontamination tank, or starting or stopping the pump, or supplying the decontamination liquid supply line and the circulation line. The decontamination concentration is prevented from being lowered by switching or repeating every predetermined time such as supply and stop of air, nitrogen and inert gas. FIG. 10 shows a dissolution rate by repeatedly performing a solid-liquid separation operation for separating a chemical decontamination target 31 provided with a decontamination tank 32 and a storage tank 33 for storing a chemical decontamination liquid, and a solid-liquid contact operation for contact. The radioactivity level can be reduced in a short time.

  As another technique related to chemical decontamination, for example, as a second prior art, there is a case where PLR piping is chemically decontaminated in the operation flow shown in FIG. 9 with the decontamination configuration shown in FIG. A conventional PLR pipe decontamination method will be described with reference to FIGS.

  In this configuration, the PLR pipe 22 which is a decontamination object is connected to the bonnet portion of the coupling valve 25a on the discharge side of the A circulation pump 4 and the bonnet portion of the coupling valve 25b on the suction side of the B circulation pump 5. Closure plates 26a and 26b are installed in each valve body so that the decontamination liquid does not flow in the direction opposite to the PLR pipe 22 in both the coupling valves 25a and 25b.

  As shown in FIG. 9, the system configuration of the circulation path including the surge tank 1, the A circulation pump 4, the PLR pipe 22, the B circulation pump 5, and the surge tank 1 is performed as STEP 1, and the operation of the A circulation pump 4 and the B circulation pump 5 is performed as STEP 2. The liquid in the surge tank 1 is supplied to the PLR pipe 22 by the A circulation pump 4, and the liquid in the PLR pipe 22 is returned to the surge tank 1 by the B circulation pump 5 to perform the circulation operation.

  Thereafter, in order to perform decontamination of the ring header 23 and the riser pipe 24 of the PLR pipe 22 located above the A joint portion 27 flowing into the PLR pipe 22, the flow rate of the A circulation pump 4 is changed to the B circulation pump as STEP3. The liquid level is raised to a predetermined position by increasing the flow rate of 5 and increasing the supply amount from the surge tank 1 to the PLR pipe 22. When reaching a predetermined position, the liquid levels are kept constant by making the flow rates of the A circulating pump 4 and the B circulating pump 5 the same. Thereafter, the power supply of the heater 2 built in the surge tank 1 is turned on as STEP 4 to start heating the decontamination solution.

  When the pure water rises to a predetermined temperature, an oxidizing agent is introduced from the chemical introduction port 3 as STEP 5 to make the pure water in the chemical decontamination apparatus into an oxidative decontamination solution. The oxidative decontamination liquid increases the flow rate of the A circulation pump 4 from the flow rate of the B circulation pump 5, increases the supply amount from the surge tank 1 to the PLR pipe 22, and the predetermined liquid in the ring header 23 and the riser pipe 24. Raise to the top. When reaching a predetermined position, the liquid levels are kept constant by making the flow rates of the A circulating pump 4 and the B circulating pump 5 the same. By maintaining this state for several hours, chromium oxide and the like taken into the oxide film adhering to the inner surfaces of the PLR pipe 22, ring header and riser pipe are dissolved.

  Several hours later, in order to decompose the oxidative decontamination liquid, the flow rate of the B circulation pump 5 is made larger than the flow rate of the A circulation pump 4, the supply amount from the PLR pipe 22 to the surge tank 1 is increased, and the ring header and riser The predetermined liquid level of the pipe is lowered to the lower part of the vertical pipe 28.

  When the predetermined oxidative decontamination is completed, a reducing agent is introduced into the oxidative decontamination liquid from the chemical inlet 3 as STEP 6 to decompose the oxidative decontamination liquid.

  When the decomposition of the oxidizing agent is completed, as STEP 7, a reducing agent is additionally charged from the chemical charging port 3, and the liquid in the chemical decontamination apparatus is made into a reducing decontamination liquid. The reductive decontamination liquid increases the flow rate of the A circulation pump 4 from the flow rate of the B circulation pump 5 and increases the supply amount from the surge tank 1 to the PLR pipe 22, and the predetermined liquid in the ring header 23 and the riser pipe 24. Raise to the top. When reaching a predetermined position, the liquid levels are kept constant by making the flow rates of the A circulating pump 4 and the B circulating pump 5 the same. By holding this state for about 10 hours or more, iron oxide or the like, which is the main component of the oxide film of the PLR pipe 22, the ring header 23, and the riser pipe 24, is dissolved. At this time, the reducing decontamination solution is passed through the cation resin tower 7 to remove the metal ions dissolved by the reduction decontamination solution and the metal ions generated by the decomposition of the oxidative decontamination solution.

  After 10 hours, in order to decompose the reductive decontamination liquid, the flow rate of the B circulation pump 5 is made larger than the flow rate of the A circulation pump 4, the supply amount from the PLR pipe 22 to the surge tank 1 is increased, and the ring header 23 And the predetermined liquid level of the riser pipe 24 is lowered to the lower part of the vertical pipe 28.

  Thereafter, as STEP 8, water is passed through the reducing agent decomposing apparatus 9 to decompose the reducing decontamination solution. The reducing agent is decomposed while the reducing decontamination liquid in the vertical pipe 28 is replaced with the liquid in the circulation path.

  When the decomposition of the reductive decontamination liquid is completed, the liquid is passed through the cooler 6 and the cation resin tower 7 as STEP 9. Also here, the flow rate of the A circulation pump 4 is made larger than the flow rate of the B circulation pump 5, the amount of pure water supplied from the surge tank 1 to the PLR pipe 22 is increased, and the predetermined liquid levels in the ring header 23 and the riser pipe 24 are obtained. Raise to. When the predetermined position is reached, the flow rates of the A circulating pump 4 and the B circulating pump 5 are made the same, the liquid level is kept constant, and the inner surfaces of the PLR pipe 22, ring header 23 and riser pipe 24 Wash. After completion of the cleaning, the flow rate of the B circulation pump 5 is increased from the flow rate of the A circulation pump 4, the supply amount from the PLR pipe 22 to the surge tank 1 is increased, and the predetermined liquid levels of the ring header 23 and the riser pipe 24 are set. Reduce to the bottom of the vertical pipe 28.

  The above-mentioned chemical decontamination operation is set as one cycle, and the operation from STEP5 to STEP9 is repeated about 2 to several cycles depending on the degree of contamination of the PLR pipe 22, the ring header 23 and the riser pipe 24, and the chemical decontamination is finished. .

Japanese Patent Laid-Open No. 7-25396

  In the first prior art, it is shown that the decontamination liquid level in the decontamination tank is changed, and solid-liquid separation and solid-liquid contact are repeated with respect to the decontamination object. An operation method in the case of chemically decontaminating an object to be decontaminated by separately using two types of decontamination liquids of the reduction decontamination liquid is not shown. Further, even after the chemical decontamination of the decontamination target is completed, the cleaning method is not shown although the decontamination liquid remains attached to the decontamination target. Furthermore, although the used decontamination liquid needs to be treated by a method such as decomposition, a decontamination liquid treatment method is not shown.

  In the second prior art, the decontamination liquid is a PLR pipe, a ring header, and a riser pipe that are decontamination objects, and the A circulation pump that supplies the decontamination liquid from the surge tank to the PLR pipe and the PLR pipe to the surge tank The decontamination liquid is supplied to the PLR pipe, the ring header, and the riser pipe by making a difference in the flow rate of the B circulation pump that supplies the decontamination liquid. In the boiling water reactor, the ring header and riser pipe are installed at the outlet of the recirculation pump, and the piping that supplies coolant into the reactor increases the amount of water and space capacity. Therefore, several hours are required for the difference in flow rate between the A circulation pump and the B circulation pump used in the chemical decontamination apparatus. In addition, the decontamination liquid supplied to the ring header and riser pipe raises the horizontal piping section and the vertical piping section and cannot be replaced with the decontamination liquid in the circulation path. As a result, the temperature of the decontamination solution is lowered and the decontamination efficiency is very poor.

  Therefore, even if the ring header and the riser pipe are subjected to chemical decontamination to remove radioactive substances and the decontamination liquid level is raised to the ring header and the riser pipe, the decontamination efficiency is poor. A chemical decontamination technique is desired that increases the decontamination efficiency by reheating the decontamination solution supplied to the ring header and the riser pipe unit above the temperature in the circulation path at the ring header unit.

  An object of the present invention is to provide a chemical decontamination method and apparatus for improving decontamination efficiency in chemical decontamination of piping.

  A chemical decontamination method for chemically decontaminating oxide on the inner surface of a pipe with a decontamination liquid, characterized in that chemical decontamination is performed while heating a decontamination site.

An object of the present invention is to provide a chemical decontamination method and apparatus for improving decontamination efficiency in chemical decontamination of piping.

  As a result of various studies to solve the above problems, the solubility of iron oxide, which is the main component of the oxide film on the inner surface of the PLR pipe, tends to increase as the temperature increases (see FIG. 6).

  That is, oxidative decontamination or reductive decontamination agent is introduced into the vertical piping section of the PLR pipe to obtain a uniform decontamination liquid, and then the liquid level is raised to remove the ring header and riser pipe. Supply the dye liquor. Decontamination efficiency by reheating the decontamination liquid heated in the surge tank to a more soluble temperature while heating the ring header and riser tube part in advance to prevent the decontamination liquid temperature from decreasing Chemical decontamination method that raises Specific means are as follows.

  In the chemical decontamination method in the reactor coolant recirculation system piping, the horizontal piping part of the PLR piping and the vertical piping part that supplies the coolant into the reactor by changing the liquid level in the piping especially during the decontamination The decontamination method and its method are carried out by raising the temperature of the decontamination solution to 90 ° C. to 100 ° C. by reheating the ring header and the riser tube part by decontamination.

  The chemical decontamination equipment consists of a surge tank with a built-in heater, an A circulation pump that supplies decontamination liquid to the PLR pipe (first circulation pump), and a B circulation pump that returns decontamination liquid from the PLR pipe to the surge tank (second circulation). Pump), cationic resin tower for removing dissolved oxide, mixed bed resin tower for purifying decontamination liquid, decontamination apparatus for decomposing reduction decontamination liquid, cooler for cooling decontamination liquid, decontamination agent PLR pipes including ring headers and riser pipes that are decontamination objects are the discharge side of the A circulation pump and the bonnet part of the coupling valve. And the suction side of the B circulation pump and the bonnet portion of the coupling valve. The valves used for these connections are provided with a closing plate in each valve body so that the decontamination liquid does not flow in the direction opposite to the PLR pipe.

  In the circulation path consisting of the surge tank, A circulation pump, PLR piping, and B circulation pump, the pure water in the surge tank is supplied to the PLR piping by the A circulation pump, and the pure water in the PLR piping is supplied to the surge tank by the B circulation pump. Perform circulating operation to return. Thereafter, the flow rate of the A circulation pump is made larger than the flow rate of the B circulation pump, the supply amount from the surge tank to the PLR pipe is increased, and the level is raised to a predetermined liquid level. When the predetermined liquid level is reached, the liquid levels are kept constant by making the flow rates of the A circulating pump and the B circulating pump the same. Thereafter, the power source of the heater built in the surge tank is turned on to raise the temperature of the pure water to a predetermined temperature.

  When pure water reaches a predetermined temperature (˜90 ° C.), an oxidant is introduced from a chemical inlet to make a uniform oxidative decontamination solution. Thereafter, the flow rate of the A circulation pump is made larger than the flow rate of the B circulation pump, the decontamination liquid supply amount to the PLR pipe is increased, the liquid level is increased to the ring header and the riser pipe, and the oxidative decontamination liquid is supplied. . When the liquid level reaches a predetermined level, the flow rates of the A circulating pump and the B circulating pump are controlled so that the liquid level is kept constant, and the chromium oxide is dissolved by maintaining this state for several hours. At this time, the temperature of the oxidative decontamination liquid of the ring header and the riser pipe is increased in the PLR pipe due to the rise of the liquid level of the decontamination liquid to the ring header and the riser pipe, and the heat radiation and the temperature rise of the pipe within the holding time. Lower than the temperature heated in the circulation path. In order to prevent the oxidative decontamination effect from decreasing due to a decrease in the temperature of the decontamination liquid, the ring header and the riser from the start of the decontamination liquid level increase with the electric heater installed in the ring header turned on When the decontamination liquid level rises while preheating the pipe, the decontamination liquid is reheated and maintained at a temperature in the circulation path or higher, thereby promoting the oxidative decontamination effect (promoting dissolution of chromium oxide) Effect).

  When the oxidative decontamination is complete, turn off the heater power, increase the flow rate of the B circulation pump from the flow rate of the A circulation pump, increase the amount of decontamination liquid returned to the surge tank, and increase the liquid level of the ring header and riser pipe. In order to maintain the liquid level constant when the liquid level reaches the predetermined liquid level in the PLR pipe, the reducing agent is supplied from the chemical inlet while controlling the flow rates of the A circulation pump and the B circulation pump. Input and decompose the oxidative decontamination solution.

  When the oxidative decontamination liquid is decomposed, water is passed through the cation resin tower, and a reducing agent is additionally added from the chemical inlet to make a reductive decontamination liquid. Thereafter, the flow rate of the A circulation pump is increased from the flow rate of the B circulation pump, the decontamination liquid supply amount to the PLR pipe is increased, the liquid level is increased to the ring header and the riser pipe, and the reduced decontamination liquid is supplied. . The flow rate of the A circulating pump and the B circulating pump is controlled so that the liquid level is kept constant when the predetermined liquid level is reached, and the iron oxide is dissolved by maintaining this state for more than 10 hours. Adsorbed in the resin tower. Also at this time, the temperature of the decontamination liquid in the ring header and the riser pipe, the temperature of the decontamination liquid in the ring header and the riser pipe by the heat release and the temperature rise of the pipe within the holding time, the PLR pipe It is lower than the temperature heated in the internal circulation path. In order to suppress the reduction of the decontamination effect due to a decrease in the temperature of the decontamination solution, the ring header and riser pipe are turned on before the start of the decontamination solution level increase with the electric heater installed in the ring header part turned on. And preheating the decontamination liquid at a predetermined liquid level, and the temperature in the circulation path in the PLR pipe or higher (90 ° C or higher, preferably 90 ° C to 100 ° C) ), The reduction decontamination effect (iron oxide dissolution promoting effect) is increased. At this time, the temperature of the ring header part and the liquid temperature of the uppermost part of the riser pipe, which is a vertical pipe, decrease due to heat dissipation, in parallel with the fact that the temperature can be increased by reheating the electric heater and controlled to a constant temperature. A temperature difference of over ten degrees occurs. Therefore, the natural convection due to the buoyancy of the decontamination liquid becomes forced convection by setting the temperature to 90 ° C to 100 ° C, and the oxide film on the inner surface of the pipe is dissolved by circulating in the vertical pipe of the riser pipe portion. At the same time, the decontamination effect is further increased by providing a synergistic effect that promotes removal of the film.

  Also, the iron oxide in the riser pipe part may be removed and deposited on the ring header part, and if the apparent decontamination effect of the ring header part is stagnant, Increase the flow rate from the flow rate of the A circulation pump, increase the decontamination liquid return amount to the surge tank, lower it from the liquid level of the ring header and riser pipe, and liquid when the liquid level reaches the predetermined liquid level of the PLR pipe So that the flow rate of the A circulation pump and the B circulation pump is controlled so that the position is kept constant, the flow rate of the A circulation pump is increased again than the flow rate of the B circulation pump, and the decontamination liquid to the PLR pipe Increase the supply amount, raise the liquid level to the ring header and riser pipe, and supply reductive decontamination liquid. When the liquid level reaches a predetermined level, the flow rates of the A circulation pump and the B circulation pump are controlled so that the liquid level is kept constant.

  When the reduction decontamination is completed within a predetermined time, the electric heater is turned off, the flow rate of the circulation pump B is made larger than the flow rate of the circulation pump A, the decontamination liquid return amount to the surge tank is increased, the ring header and Decontaminating agent while controlling the flow rate of the A circulation pump and the B circulation pump so that the liquid level is kept constant when the liquid level is lowered from the liquid level of the riser pipe and the liquid level reaches the predetermined liquid level of the PLR pipe Water is passed through the decomposition device to decompose the reductive decontamination solution.

  When the decomposition of the reducing decontamination liquid is completed, the cation resin tower is bypassed, and the decontamination liquid is passed through the cooler and the mixed bed resin tower for purification. Thereafter, the flow rate of the A circulation pump is increased from the flow rate of the B circulation pump, the decontamination liquid supply amount to the PLR pipe is increased, the liquid level is increased to the ring header and the riser pipe, and the purification liquid is supplied. When the predetermined liquid level is reached, the flow rates of the A circulating pump and the B circulating pump are controlled so that the liquid level is kept constant, and the reducing decontaminant adhering to the inner surface of the ring header and the riser pipe is removed. After that, the flow rate of the circulation pump B is made larger than the flow rate of the circulation pump A, the decontamination liquid return amount to the surge tank is increased, and the liquid level is lowered from the liquid level of the ring header and riser pipe. When the liquid level is reached, the flow rates of the A circulation pump and the B circulation pump are controlled so that the liquid level is kept constant. The reductive decontaminant adhering to the inner surface of the ring header and the riser pipe is removed by repeating such rise and fall of the cleaning liquid.

  The chemical decontamination operation as described above is set as one cycle, and the chemical decontamination is completed by repeating about two to several cycles depending on the degree of contamination of the PLR pipe.

  As described above, after the oxidative decontamination agent or the reductive decontamination agent is introduced in a state where the liquid level is maintained in the vertical piping portion of the PLR pipe to obtain a uniform decontamination liquid, the liquid level is increased to increase the ring header and Supply the decontamination solution to the riser tube. The supplied decontamination solution is heated by an electric heater installed in the ring header so that the temperature of the decontamination solution does not decrease, so that the decontamination effect of chemical decontamination of the conventional ring header and riser pipe is eliminated. A chemical decontamination method capable of increasing the dyeing effect can be performed.

  Next, an embodiment of the present invention will be described more specifically with reference to FIGS.

  As shown in FIG. 3, the chemical decontamination apparatus is a surge tank 1 having a heater (heater) 2 that raises the temperature of the decontamination liquid in the circulation path 1 and supplies the decontamination liquid to the PLR pipe 22. 4, B circulating pump 5 for returning the decontamination liquid from the PLR pipe 22 to the surge tank 1, 5 Cationic resin tower 7 for removing the dissolved oxide, Mixed bed resin tower 8 for purifying the decontamination liquid, Decomposing the reduction decontamination liquid A reducing agent decomposing apparatus 9 and a cooler 6 for cooling the decontamination liquid. A pipe (or hose) 30 is connected to the bonnet part of the joint valve 25a and the bonnet part of the joint valve 25b. A valve V5, a B circulation pump 5, valves V6, V7, V10, V13, V16, a surge tank 1, an A circulation pump 4, and valves V1, V3 are attached to the pipe 30 from the upstream side. A pipe (or hose) 32 having a valve V2 is connected to the pipe 30 on the downstream side of the valve V1, and further connected to the surge tank 1. A chemical inlet 3 for introducing a decontaminating agent is provided in the pipe 32.

  A pipe (or hose) 34 including valves V8 and V9 is connected to the pipe 30 so as to bypass the valve V7. The cooler 6 is installed in the pipe 34 between the valve V8 and the valve V9. A pipe (or hose) 35 including the valve V11 and the valve V12 is connected to the pipe 30 so as to bypass the valve V10. The cation resin tower 7 is installed in the pipe 35 between the valve V11 and the valve 12. A pipe (or hose) 36 provided with the valves V14 and V15 is connected to the pipe 30 so as to bypass the valve V13. The mixed bed resin tower 8 is installed in the pipe 36 between the valve V14 and the valve V15. A pipe (or hose) 33 provided with valves V17 and V18 is connected to the pipe 30 so as to bypass the valve V16. A reducing agent decomposing device 9 is installed in the pipe 33 between the valve V17 and the valve V18. A bypass pipe 31 having a valve V4 is connected to the pipe 30 on the downstream side of the valve V5 and on the upstream side of the valve V3.

  The joint valve 25a is connected to the vertical pipe 28 of the PLR pipe 22 via the A joint 27a, and the joint valve 25b is connected to the PLR pipe 22 via the B joint 27b. For this reason, the piping 30 is connected to the PLR piping 22 which is a decontamination target. The joint valves 25a and 25b are provided with closing plates 26a and 26b in the respective valve bodies so that the decontamination liquid does not flow in the direction opposite to the PLR pipe.

  By driving the A circulation pump 4 and the B circulation pump 5, the liquid in the PLR pipe 22 passes through the coupling valve 25a, the A circulation pump 4, the surge tank 1, the B circulation pump 5, and the coupling valve 25b to the PLR pipe 22. Returned.

  The chemical decontamination method of this example will be described with reference to FIG. As STEP 1, the valves V1, V4, V6, V7, V10, V13, V16 are set to “open”, and the other valves are set to “closed”. The liquid level in the PLR pipe 22 at this time is as shown in FIG.

  In STEP 2, by operating the A circulation pump 4 and the B circulation pump 5, the pure water in the surge tank 1 is circulated through the circulation path formed by the piping 30 and the bypass piping 31 of the PLR piping 22. Thereafter, the valves V3 and V5 are opened and the valve V4 is closed, and the pure water in the surge tank 1 is supplied to the PLR pipe 22 by the A circulation pump 4, and the pure water in the PLR pipe 22 is supplied to the B circulation pump. The circulation operation to return to the surge tank 1 by 5 is performed. In the above description, after passing through the bypass pipe 31 of the PLR pipe 22, the water is passed through the PLR pipe 22 and the water flow to the bypass pipe 31 is stopped. From the start of operation of the pump 4 and the B circulation pump 5, water may be passed through the PLR pipe 22.

  In STEP 3, the flow rate of pure water discharged from the A circulation pump 4 is set to be larger than the flow rate discharged from the B circulation pump 5, and the supply amount from the surge tank 1 to the PLT pipe 22 is increased. ), The pure water level in the PLR pipe 22 is raised to a predetermined water level in the vertical pipe 28. When the liquid level reaches a predetermined water level, the flow rate of pure water discharged from each of the A circulating pump 4 and the B circulating pump 5 is made the same, and the pure water level in the PLR pipe 22 is set to a predetermined level. Hold at water level.

  When the liquid level in the PLR pipe 22 is stabilized, the heater 2 built in the surge tank 1 is turned on and the temperature is raised to a predetermined temperature (STEP 4). When the pure water reaches a predetermined temperature, an oxidizing agent is introduced into the pipe 32 from the chemical inlet 3, and a uniform oxidative decontamination solution is made by circulation in the pipe 30 and the PLR pipe 22 (STEP 5).

  In STEP 6, the flow rate of the oxidative decontamination liquid discharged from the A circulation pump 4 is made larger than the flow rate discharged from the B circulation pump 5, and the supply amount of the oxidative decontamination liquid to the PLR pipe 22 is increased. As shown in (c), the liquid level in the PLR pipe 22 is raised to a predetermined liquid level in the ring header 23 and the riser pipe 24 and the oxidative decontamination liquid is supplied to the ring header 23 and the riser pipe 24. When the liquid level of the oxidative decontamination liquid reaches a predetermined liquid level, the discharge flow rates of the A circulation pump 4 and the B circulation pump 5 are controlled so that the liquid level becomes constant, and this state is maintained for several hours, The chromium oxide in the PLR pipe 22, ring header 23 and riser pipe 24 is dissolved.

  At this time, the temperature of the oxidative decontamination liquid of the ring header 23 and the riser pipe 24 is such that the heat of the decontamination liquid to the ring header 23 and the riser pipe 24 and the heat energy within the holding time and the heat energy to the piping. The temperature is lower than the temperature heated in the circulation path in the PLR pipe 22 due to the loss of the above. The oxidative decontamination effect decreases due to the decrease in the decontamination liquid temperature. In order to prevent the oxidative decontamination effect from deteriorating, preheat the ring header 23 and the riser pipe 24 before raising the level of the oxidative decontamination liquid with the electric heater 29 installed on the ring header 23 turned on. In addition, the decontamination liquid is reheated in a state where the oxidative decontamination liquid level reaches the predetermined liquid level of the ring header 23 and the riser pipe 24, and the temperature in the PLR pipe 22 circulation path or higher is reached. By holding, the oxidative decontamination effect (accelerating dissolution of chromium oxide) is increased.

  Here, as shown in FIG. 5, the electric heater 29 is directly wound around the horizontal piping portion of the ring header 23 portion, and power is supplied from the control panel 45 via the relay terminal box 44 and heated. In order to enhance the heating effect, a heat insulating material 41 is wound around the ring header 23 around which the electric heater 29 is wound to suppress heat dissipation. In addition, the temperature can be controlled to a specified temperature by the monitoring thermometer 42 and the control thermometer 43 installed in the ring header 23, and the decontamination liquid temperature can be controlled to be higher than the circulation path temperature. It is a heating device that can be controlled constant.

  When the oxidative decontamination is completed, as STEP 7, the discharge flow rate of the A circulation pump 4 is made smaller than the discharge flow rate of the B circulation pump 5, and a part of the oxidative decontamination solution in the PLR pipe 22 is collected in the surge tank 1. Thus, the oxidative decontamination liquid level is lowered to a predetermined water level in the vertical pipe 28 portion of the PLR pipe 22 lower than the ring header 23.

  When the predetermined liquid level is reached in STEP 8, the reducing agent is supplied from the chemical inlet 3 with the flow rates of the A circulating pump 4 and the B circulating pump 5 controlled so that the liquid level in the PLR pipe 22 is kept constant. To decompose the oxidative decontamination solution. After completion of the decomposition of the oxidative decontamination solution, the valves V14 and V15 are “opened” and the V13 is “closed” in STEP9, and water is passed through the cation resin tower 7 through the pipe 36. Thereafter, a reducing agent is additionally charged into the pipe 32 from the chemical inlet 3, and a uniform reductive decontamination solution is produced by circulation in the pipe 30 and the PLR pipe 22.

  In STEP 10, the flow rate of the reductive decontamination liquid discharged from the A circulation pump 4 is made larger than the flow rate discharged from the B circulation pump 5, the supply amount of the reductive decontamination liquid to the PLR pipe 22 is increased, and the surge By supplying a part of the reductive decontamination liquid in the tank 1 to the PLR pipe 22, the reductive decontamination liquid level in the PLR pipe 22 is raised to a predetermined water level in the ring header 23 and the riser pipe 24. As a result, the reducing decontamination solution is supplied to the ring header 23 that is a horizontal pipe collecting pipe and the riser pipe 24 that is a vertical pipe. When the liquid level of reductive decontamination reaches a predetermined water level, the discharge flow rates of the A circulation pump 4 and the B circulation pump 5 are controlled so that the liquid level is kept constant, and this state is maintained for 10 hours or more. To do. During this period, the iron oxide in the PLR pipe 22, the ring header 23 and the riser pipe 24 is dissolved, and the iron ions are adsorbed and removed by the cation resin in the cation resin tower 7.

  Also at this time, the temperature of the reductive decontamination liquid of the ring header 23 and the riser pipe 24 is reduced due to the rise time of the liquid level of the decontamination liquid to the ring header 23 and the riser pipe 24 and the heat dissipation and the heat capacity of the pipe within the holding time. The temperature is lower than the temperature heated in the circulation path of the PLR pipe 22. In order to suppress the reduction of the reduction decontamination effect due to the decrease in the temperature of the decontamination solution, the ring header 23 is started from the start of the increase in the decontamination solution level with the electric heater 29 installed in the ring header 23 being turned on. In addition, by preheating the riser pipe 24 and reheating the decontamination solution, the reductive decontamination effect (effect of promoting dissolution of iron oxide) is maintained by maintaining the temperature in the circulation path of the PLR pipe 22 or higher. Is to raise. At this time, the reheater of the electric heater 29 is higher than the temperature of the decontamination solution in the circulation path and is kept constant. Since the decontamination liquid temperature at the liquid level decreases due to heat dissipation, a temperature difference of a dozen degrees is generated. Therefore, the natural convection due to the buoyancy of the decontamination liquid becomes forced convection and circulates up and down in the vertical pipe, which increases the dissolution rate of the oxide film on the surface of the pipe due to the rise in the temperature of the decontamination liquid. This produces a synergistic effect that makes it possible to remove water and further increases the decontamination effect.

  FIG. 6 shows the relationship between the temperature of the decontamination solution in the decontamination drug and the dissolution rate of iron oxide. FIG. 6 shows that the dissolution rate of iron oxide in the decontamination drug increases in proportion to the temperature of the decontamination solution. For example, the decontamination liquid temperature of 80 ° C and the decontamination liquid of 95 ° C have a difference in dissolution rate of about twice, and the decontamination liquid temperature decreased due to heat radiation from the piping etc. By raising it above, the decontamination effect is raised.

  Further, the iron oxide in the riser pipe 24 part which is a vertical pipe may be removed and deposited on the ring header 23 part which is a horizontal pipe, and the decontamination effect of the ring header 23 appears to be stagnant. Sometimes. In this case, the flow rate of the B circulation pump 5 is made larger than the flow rate of the A circulation pump 4, the decontamination liquid return amount to the surge tank 1 is increased, and the liquid level of the ring header 23 and the riser pipe 24 is lowered. When the liquid level reaches a predetermined liquid level in the PLR pipe 22, the flow rate of the A circulating pump 4 and the B circulating pump 5 is controlled so that the liquid level is kept constant. The flow rate is made higher than the flow rate of the B circulation pump 5, the decontamination liquid supply amount to the PLR pipe 22 is increased, the liquid level is increased to the ring header 23 and the riser pipe 24, and the reduced decontamination liquid is supplied. When the liquid level reaches a predetermined level, the flow rates of the A circulation pump 4 and the B circulation pump 5 are controlled so that the liquid level is kept constant.

  In STEP 11 where the reduction decontamination is completed, the discharge flow rate of the A circulation pump 4 is made smaller than the discharge flow rate of the B circulation pump 5, and a part of the reduction decontamination solution in the PLR pipe 22 is collected in the surge tank 1. Thereby, the liquid level of the reductive decontamination liquid in the PLR pipe 22 lower than the ring header 23 is lowered.

  In STEP 12, when the liquid level of the reductive decontamination liquid drops to a predetermined water level in the PLR pipe 22, the discharge flow rates of the A circulation pump 4 and the B circulation pump 5 are controlled so as to keep the liquid level constant. Thereafter, the valves V17 and V18 are opened, the valve V16 is closed, the reducing decontamination liquid in the pipe 30 is supplied to the reducing agent decomposing apparatus 9, and the reducing decontaminating liquid is supplied to the decontaminating apparatus decomposing apparatus 9. Decompose. When decomposition of the reductive decontamination liquid is completed, the valve V13 is “open” in STEP13, the valves V14 and V15 are “closed”, the cation resin tower 7 is bypassed, and the valves V8, V9, V11, and V12 are “open”. The valves V7 and V10 are closed and the decontamination solution is passed through the cooler 6 and the mixed bed resin tower 8 for purification.

  In STEP 14, the discharge flow rate of the A circulation pump 4 is made larger than the discharge flow rate of the B circulation pump 5, the liquid supply to the PLR pipe 22 is increased, and a part of the purified water in the surge tank 1 is put into the PLR pipe 22. Supply. As a result, when the liquid level in the PLR pipe 22 reaches a predetermined water level in the ring header 23 and the riser pipe 24, the respective levels of the A circulation pump 4 and the B circulation pump 5 are maintained so as to keep the liquid level constant. The reductive decontaminant adhering to the inner surfaces of the PLR pipe 22, the ring header 23, and the riser pipe 24 is removed by controlling the flow rate discharged.

  In STEP 15, the discharge flow rate of the A circulation pump 4 is made smaller than the discharge flow rate of the B circulation pump 5, and a part of the purified water in the PLR pipe 22 is collected in the surge tank 1. As a result, the liquid level is lowered to a level lower than that of the ring header 23. The discharge flow rates of the A circulation pump 4 and the B circulation pump 5 are controlled so as to be kept constant at a predetermined water level in the PLR pipe 22.

  The reduction decontaminant adhering to the inner surface of the ring header 23 and the riser pipe 24 is removed by repeating the rising and lowering of the level of the purified water by the operation of STEP 15 and STEP 16. The chemical decontamination operation as described above is set as one cycle, and the chemical decontamination is completed by repeating about two to several cycles depending on the degree of contamination of the PLR pipe.

  FIG. 4 illustrates the state in accordance with the above-described step of FIG. In FIG. 4, it can be seen that it takes time from the circulating liquid level in the vertical pipe section to the reached liquid level in the ring header 23 and the riser pipe 24 section, and the temperature of the decontamination liquid is lowered by the heat radiation of the pipe.

  Finally, an example applied to an actual plant is shown in FIG.

  FIG. 7 shows a result obtained by installing a heating device (electric heater 29) in the ring header 23 and controlling the temperature of the ring header 23 to be higher than the temperature of the decontamination solution in the circulation path. As a result of installing the electric heater 29 and performing the reheating as compared with the previous example in which the electric heater 29 was not installed and reheating was not possible, the result of the decontamination effect more than doubled in the results. It became. Therefore, it can be said that installing the electric heater 29 is effective for chemical decontamination of the ring header 23 part.

  In the first embodiment, the electric heater 29 is directly spirally wound around the ring header 23 portion, and the heat insulating material 41 is installed thereon, and the ring header 23 portion and the oxidation / reduction decontamination liquid are heated, and the PLR pipe 22 is heated. It was heated above the temperature of the decontamination solution in the circulation path. In that case, since the electric heater 29 was directly installed in a spiral shape and the heat insulating material 41 was installed before chemical decontamination, the exposure dose of workers in the preparation work was increased.

  A heating apparatus as Example 2 is shown in FIG. FIG. 8 is carried out by the same method as the above chemical decontamination method. As a heating device for the ring header 23 part, a package type heat insulating material incorporating an electric heater 29 is used as a jacket system, rationalizing preparation work and workers. This device is intended to contribute to the reduction of exposure.

It is a flowchart which shows the process step in the chemical decontamination method which is one preferable Example of this invention. Explanatory drawing which shows the state of the liquid level in PLR piping after attaching a chemical decontamination apparatus to PLR piping. Explanatory drawing which shows the state of the liquid level in PLR piping after completion | finish of oxidative decontamination and reductive decontamination. Explanatory drawing which shows the state of the liquid level in PLR piping at the time of oxidative decontamination and reductive decontamination. It is a block diagram of the chemical decontamination apparatus using the chemical decontamination method which is one suitable Example of this invention. The liquid level state diagram in each decontamination mode which is one preferred embodiment of the present invention is described with a flow. It is the figure which showed simply the installation state of the electric heater of a ring header part. It is the figure which showed the relationship of the dissolution rate of the iron oxide in a decontamination chemical | medical solution. Riser tube decontamination results. The figure which shows the decontamination result oxide of a ring header part. The example of the package type heating apparatus of a ring header part is shown. It is a flowchart of the process step in a chemical decontamination method. It is a block diagram of an example of the chemical decontamination apparatus used for the chemical decontamination method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Surge tank 2 Heater 3 Chemical inlet 4 A circulation pump 5 B circulation pump 6 Cooler 7 Cationic resin tower 8 Mixed bed resin tower 9 Reductant decomposition device 21 Reactor pressure vessel 22 PLR piping 23 Ring header 24 Riser pipe 25a , 25b Joint valve 26a, 26b Closing plate 27 Joint 28 Vertical piping 29 Electric heater

Claims (6)

  A chemical decontamination method for chemically decontaminating an oxide on the inner surface of a pipe with a decontamination liquid, wherein the decontamination site is heated and chemically decontaminated.   The first circulation pump, the surge tank to which the heater is attached, the decontamination agent decomposing apparatus, the resin tower, and the second circulation pump are connected by a hose or a pipe, and the discharge side of the first circulation pump and the suction of the second circulation pump In a chemical decontamination method using a chemical decontamination apparatus whose side is connected to a reactor coolant recirculation system pipe, the flow rate of the decontamination liquid discharged from the first circulation pump is discharged from the second circulation pump. By increasing the flow rate of the decontamination liquid, a part of the decontamination liquid generated due to the flow rate difference is supplied from the surge tank to the reactor coolant recirculation system piping, and the reactor coolant recycle is performed. The horizontal piping unit and the vertical piping unit are reheated to 90 ° C. to 100 ° C. by a chemical decontamination method that raises the decontamination liquid level in the circulation piping and supplies the decontamination solution to the horizontal piping unit and the vertical piping unit. Horizontal arrangement Parts and by increasing the dissolution rate of oxide adhering to the vertical pipe portion surface, chemical decontamination method of the feature that it is raised a decontamination effect.   In claim 2, as the reheating method, the electric heater is directly wound around the horizontal piping portion and the vertical piping portion to suppress a decrease in the decontamination liquid temperature to the horizontal piping portion and the vertical piping portion, and A chemical decontamination method comprising heating to a decontamination liquid temperature or higher (90 ° C to 100 ° C).   3. The chemical decontamination method according to claim 2, wherein the heating method includes a system capable of controlling a decontamination liquid temperature supplied to the horizontal piping portion and the vertical piping portion to a constant temperature by automatically controlling an electric heater.   3. The chemical decontamination method according to claim 2, wherein the heating device is a heat insulating jacket type package heating device equipped with a heater.   A chemical decontamination apparatus for chemically decontaminating oxide on the inner surface of a pipe with a decontamination liquid, a supply system for supplying the decontamination liquid to the pipe, a discharge system for discharging the decontamination liquid from the pipe, and a decontamination A chemical decontamination apparatus comprising a heating device for heating a part.

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