JP6776426B2 - Decontamination method and decontamination equipment - Google Patents

Description

An embodiment of the present invention relates to a technique for carrying out decontamination before dismantling a nuclear reactor at the time of decommissioning a boiling water reactor.

In the decommissioning of the reactor, after the reactor operation is stopped, fuel is taken out from the reactor, and then decontamination before dismantling the primary reactor system is carried out.
Such decontamination is carried out for the purpose of reducing the exposure of workers during the reactor demolition work and reducing the radioactivity level of the demolition waste.

Reactor primary systems include Reactor Presser Vessel (RPV), Primary Loop Recirculation (PLR) system, Reactor Water Clean-Up (CUW) system, and residual heat removal. (RHR; Residual Heat Removal) strain is included.
If chemically decontaminate system including a RPV, system capacity to meet the decontamination liquid extends to several hundred m ^3.

For this reason, conventionally, for chemical decontamination inside the RPV, a method of circulating the decontamination liquid with a PLR pump, which is a device mainly installed in the primary reactor system, has been adopted.
The PLR pump can secure a huge circulation flow rate and can obtain a large linear flow velocity.

Japanese Unexamined Patent Publication No. 2000-69589

However, the above-mentioned technique using the conventional PLR pump has a problem that the work is complicated and a huge cost is required.

For example, in the case of decontamination before dismantling, it may be carried out several years after the shutdown of the reactor, and it takes enormous cost and labor to restore the PLR pump.
In terms of operation, the amount of liquid being decontaminated increases due to the pump seal water due to the operation of the PLR pump, so it is necessary to monitor and adjust the chemical concentration to prevent overflow.
Further, in order to prevent this overflow, it is necessary to lower the initial decontamination liquid level, and the decontamination effect of the upper part of the inner wall of the RPV is lowered.

The present invention has been made in consideration of such circumstances, and decontamination before dismantling the reactor is performed to decontaminate the RPV and the system including at least one of the PLR systems containing the RPV without using the PLR pump. It is an object of the present invention to provide a method and a decontamination implementation device.

The decontamination method according to the present embodiment includes a step of extracting the decontamination liquid inside the reactor recirculation system to the temporary circulation system connected to the reactor recirculation system, and the decontamination liquid extracted by the temporary circulation system. Is purified by the purification system connected to the temporary circulation system, and the decontamination liquid extracted into the reactor recirculation system is refluxed by bypassing the PLR pump provided in the reactor recirculation system. It includes steps.

The decontamination implementation device according to the present embodiment has two branch points provided on opposite sides of the PLR pump inside the reactor recirculation system, one end connected to the one branch point and the other end. A temporary circulation system connected to the branch point in a ring shape and a decontamination liquid provided in the temporary circulation system and inside the reactor recirculation system are allowed to flow into the temporary circulation system from the branch point to drive the PLR pump. It includes a temporary pump that bypasses and returns to the inside of the reactor recirculation system, and a purification system that is provided in the temporary circulation system and purifies the decontamination liquid that flows through the temporary circulation system.

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INDUSTRIAL APPLICABILITY The present invention provides a method for carrying out decontamination before dismantling a nuclear reactor and a device for carrying out decontamination thereof, which decontaminates an RPV and a system including at least one of the PLR systems containing the RPV without using a PLR pump.

The schematic block diagram of the nuclear power plant which the decontamination implementation method which concerns on 1st Embodiment makes decontamination target. The explanatory view of the decontamination execution method which concerns on 1st Embodiment. The flowchart which shows the decontamination execution method which concerns on 1st Embodiment. The explanatory view of the decontamination execution method which concerns on 2nd Embodiment. The explanatory view of the decontamination execution method which concerns on 3rd Embodiment. An explanatory view showing a state in which the decontamination liquid is regurgitated and circulated according to the decontamination method according to the third embodiment. The explanatory view of the decontamination execution method which concerns on 4th Embodiment. The explanatory view which shows the state which the decontamination liquid was regurgitated by the decontamination execution method which concerns on 4th Embodiment. The explanatory view of the decontamination execution method which concerns on 5th Embodiment. The explanatory view of the decontamination execution method which concerns on 6th Embodiment. The explanatory view of the decontamination execution method which concerns on 7th Embodiment. The explanatory view of the decontamination execution method which concerns on 8th Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

(First Embodiment)
FIG. 1 is a schematic configuration diagram of a nuclear power plant targeted for decontamination by the decontamination implementation method according to the first embodiment.

1. 1. Reactor Recirculation System 200 (PLR System; Primary Loop Recirculation System)
First, the basic structure of the reactor pressure vessel 13 (RPV; Reactor Presser Vessel), the PLR system 200, and its surroundings will be described.
In the boiling water reactor plant 100, a sleeve-shaped downcomer 14 is formed between the core shroud 11 surrounding the core 10 and the RPV 13 surrounding the core shroud 11. For example, 16 or 20 jet pumps 16 are arranged in an annular shape on the downcomer 14.

A shroud head 17 covering the upper plenum of the core is provided above the core 10. Then, a steam separator 18 is provided above the shroud head 17. Further, a steam dryer 19 is provided above the steam separator 18.
An RHR head spray tube 26 for spraying a liquid such as a primary coolant in the RPV 13 is provided on the crown of the RPV 13.

Two PLR systems 200 are provided on the outside of the RPV 13. The primary coolant that has flowed into the PLR system 200 from the downcomer 14 below the RPV 13 is boosted by the PLR pump 21 provided in the PLR system 200. The flow rate of the primary coolant flowing into the PLR pump 21 is adjusted by the PLR suction valve 22 provided at the suction port and the PLR discharge valve 23 provided at the discharge port of the PLR pump 21, respectively.

This primary cooling material is guided to the jet pump 16 via the recirculating water inlet nozzle 24, is ejected from the nozzle of the jet pump 16 as a jet drive fluid, and sucks the primary cooling material in the annular portion above the downcomer 14 into a jet flow. Become.

The primary coolant ejected from the jet pump 16 is heated while passing through the core 10, and becomes a gas-liquid mixed two-phase flow. The gas-liquid mixed flow sent into the gas-water separator 18 is separated into steam and water, and the steam is further removed by the steam dryer 19 and then flows out from the steam outlet nozzle 27 on the upper part of the RPV 13. ..

Further, the water separated by the steam separator 18 and the steam dryer 19 flows down between the core shroud 11 and the wall surface of the RPV 13 and is sucked into the jet pump 16 to repeat the circulation in the furnace.

In such a circulation loop of the primary coolant, the corrosion products activated by the passage of the core 10 adhere to and accumulate on the above-mentioned various devices including the constituent devices (21 to 24) of the PLR system 200 and emit radiation. Become a source. Therefore, it is necessary to apply chemical decontamination or the like to contaminated pipes and equipment in order to reduce the exposure dose of workers at the time of decommissioning.

The decontamination method according to each embodiment mainly targets such RPV13 or PLR system 200 containing the RPV13 for chemical decontamination.

In each embodiment, the above-mentioned RHR head spray tube 26 and PLR system 200 are the main systems. In each figure, these main systems are indicated by thick broken lines.
Further, for the sake of simplification of the description, other main systems connected to the RPV 13 are omitted. Further, in the figure, the configurations provided on the left and right sides of the paper surface with high symmetry centered on RPV13 are distinguished left and right, and the words "left side PLR system 200L" and the like are appropriately added. Call.

2. Temporary circulation system 300A
Next, a temporary circulation system 300A for carrying out the decontamination implementation method according to the first embodiment will be described.
The temporary circulation system 300A is a system that mainly connects the lower part and the upper part of the RPV 13 and circulates the decontamination liquid from the lower part to the upper part or from the upper part to the lower part by the temporary circulation pump 25.

Hereinafter, a specific example of the temporary circulation system 300A will be described.
On the lower side of the RPV 13, the temporary circulation system 300A is connected to, for example, the control rod drive housing 29 and the RPV bottom drain line 31 of the furnace bottom 28. Hereinafter, this pipe is referred to as a furnace bottom pipe 32.

Further, in the temporary circulation system 300A, pipes are connected to the left and right PLR systems 200 at two locations so as to sandwich the PLR discharge valve 23, for example. Of these two pipes, the pipe connected between the PLR pump 21 and the PLR discharge valve 23 is called a PLR bottom pipe 33. The other pipe is called a PLR middle pipe 34.

The right side PLR middle pipe 34R is branched and connected to the left side PLR middle pipe 34L via the left and right connecting pipes 34C. The decontamination liquid flowing through the right side PLR middle pipe 34R can be supplied to the left side PLR middle pipe 34L. The pipe that branches and is connected to the left side PLR middle pipe 34L is hereinafter referred to as a left and right connecting pipe 34C. It should be noted that the two circles A described on the left and right connecting pipes 34C in the figure indicate that they are continuous with each other.

The left and right connecting pipes 34C are provided with left and right connecting valves 37. Further, in the right side PLR middle pipe 34R, a PLR middle valve 38 is provided between the branch point of the left and right connecting pipe 34C and the connection point of the PLR system 200.

The right PLR middle pipe 34R is connected to the steam nozzle connecting pipe 39 connected to the steam outlet nozzle 27 in a T shape. The steam nozzle connecting pipe 39 is provided with a temporary circulation pump 25 for circulating the decontamination liquid.

The right PLR middle pipe 34R is connected between the temporary circulation pump 25 and the steam outlet nozzle 27 in the steam nozzle connection pipe 39. Further, a first backflow pipe 41 for reversing the circulation of the decontamination liquid is connected to the steam nozzle connection pipe 39 in an annular shape so as to sandwich the temporary circulation pump 25. The first backflow pipe 41 is provided with a first backflow valve 42 that is closed during forward circulation.

Further, the head spray pipe connecting pipe 44 connected to the RHR head spray pipe 26 branches from the steam nozzle connecting pipe 39. The head spray pipe connecting pipe 44 is provided with a head spray pipe connecting valve 46. Further, in the steam nozzle connection pipe 39, a steam nozzle valve 47 is provided between the connection point of the right side PLR middle pipe 34R and the connection point of the head spray pipe connection pipe 44.

On the other hand, the above-mentioned furnace bottom pipe 32 and PLR bottom pipe 33 (33L, 33R) are both connected to the decontamination liquid recovery pipe 48. The decontamination liquid recovery pipe 48 extends above the RPV 13 and is connected to the steam nozzle connection pipe 39 on the upstream side of the temporary circulation pump 25.

A plurality of devices for maintaining the optimum state of the decontamination liquid are connected to the decontamination liquid recovery pipe 48.
Specifically, for example, as shown in FIG. 1, a heat exchanger 49, a drug preparation unit 50, an ozone generator 51, a decontamination agent decomposition unit 52, a filter 53, and an ion exchange unit 54 are provided.

Of these devices (49 to 54), the purification mechanism 57 composed of the decontamination agent decomposition unit 52, the filter 53, and the ion exchange unit 54 need only operate when it is necessary to purify the decontamination liquid. .. Therefore, as shown in FIG. 1, it is preferable to connect the purification mechanism 57 and the purification system 58 having the purification valve 59 to the decontamination liquid recovery pipe 48 in an annular shape. Then, the purification valve 59 is opened only when necessary, and the purification pump 55 on the purification system 58 is activated to guide the decontamination liquid into the purification system 58.

Further, the right PLR middle pipe 34R and the decontamination liquid recovery pipe 48 are connected so that the second backflow pipe 62 having the second backflow valve 61 is parallel to the temporary circulation pump 25.
Further, in the decontamination liquid recovery pipe 48, a third backflow valve 63 is provided between the connection point of the second backflow pipe 62 and the connection point of the steam nozzle connection pipe 39.

Further, the RPV 13 is connected to an exhaust gas treatment system 64 which is provided with a gas treatment mechanism 65 and discharges the gas accumulated in the RPV 13. When gas is generated in the RPV 13 by using ozone gas or the like for decontamination, the gas is discharged from the exhaust gas treatment system 64.

The temporary circulation system 300A described above does not necessarily have to include all the configurations. Among the above configurations, it is sufficient as the configuration if the configuration that enables the decontamination implementation method according to each embodiment described below is included.

Further, the description of the above configuration does not limit the number and position of installation of each component device such as a valve and a pump arranged in the temporary circulation system 300A, and piping. That is, a valve or the like may be added to the above configuration as appropriate.

3. 3. Decontamination Implementation Method Next, the decontamination implementation method according to the first embodiment will be described with reference to FIGS. 2 and 3.
FIG. 2 is an explanatory diagram of a decontamination implementation method according to the first embodiment.
Further, FIG. 3 is a flowchart showing a decontamination implementation method according to the first embodiment.

In the decontamination implementation method according to the first embodiment, first, a decontamination route is constructed so that the RPV 13 becomes a flow path of the decontamination liquid (S11).
In the first embodiment, as shown in FIG. 2, an example will be described in which the furnace bottom pipe 32 is included in the distribution path of the decontamination liquid and the PLR system 200 is not included in the decontamination path.

Specifically, for example, the third check valve 63, the steam nozzle valve 47, the head spray pipe connecting valve 46, and the bottom valve 69 provided in the bottom pipe 32 are opened. On the other hand, the PLR intake valve 22, the PLR discharge valve 23, the left and right connecting valve 37, the PLR middle valve 38, the first check valve 42, the second check valve 61, and the purification valve 59 are closed.
The black-painted valve represents the closed state, and the white-painted valve represents the open state.

The core fuel is carried out from the RPV 13 after the reactor is shut down. On the other hand, in-core equipment such as the jet pump 16, the core shroud 11, the steam separator 18, and the steam dryer 19 may be built-in.
However, the steam separator 18 and the steam dryer 19 may have already been carried out at the time of decontamination. The presence or absence of the steam separator 18 and the steam dryer 19 does not significantly affect the effect of the decontamination method according to the first embodiment.

Next, the inside of the RPV 13 is immersed in the decontamination liquid (S12).
The decontamination liquid into which the drug is charged from the drug preparation unit 50 is supplied into the RPV 13 from the RHR head spray pipe 26 or the left steam outlet nozzle 27L and stored in the RPV 13.

Next, the bottom valve 69 is opened, and the decontamination liquid stored in the RPV 13 is pulled out to the bottom pipe 32 (S13).
Sludge, which is an insoluble component, is often deposited on the bottom 28 of the furnace.
This sludge obstructs the flow of the decontamination liquid at the bottom 28, which originally tends to slow the linear flow velocity, and in addition to insufficient the linear flow velocity, also inhibits the contact of the decontamination liquid with the bottom 28. ..

Therefore, the decontamination liquid recovery pipe 48 in the decontamination range is set to the furnace bottom portion 28, which is the connection point of the furnace bottom pipe 32, and the accumulated sludge is directly collected.
By recovering sludge from the bottom 28, in addition to adding a linear flow velocity to the decontamination liquid at the bottom 28, the decontamination liquid can be brought into contact with the bottom 28 to improve the decontamination efficiency.

The decontamination liquid extracted from the furnace bottom pipe 32 is collected in the decontamination liquid recovery pipe 48 (S14).
The recovered decontamination liquid is heated or cooled by the heat exchanger 49 to adjust the temperature by the time it reaches the steam nozzle connecting pipe 39. At the same time, the content of the reducing agent and other chemicals prepared by the drug preparation unit 50 in the decontamination liquid is adjusted by the preparation pump 45.
When the oxidizing agent is ozone, ozone is mixed from the ozone generator 51 via the gas mixer 75.

Then, the decontamination liquid is returned to the RPV 13 from the steam nozzle connecting pipe 39 and the RHR head spray pipe 26 (S15).
The return point to the RPV 13 is not particularly limited to the steam nozzle connecting pipe 39 or the RHR head spray pipe 26 as long as it is above the RPV 13.

By the way, when the decontamination liquid is circulated, it is preferable to adjust the water flow time of the decontamination liquid according to the flow rate of the decontamination liquid at the target site of chemical decontamination.
Normally, systematic decontamination of a plant in service affects the subsequent inspection work process, so decontamination in the shortest possible time is required. However, in the case of decommissioning, there are few time constraints, so it is possible to take a long water flow time in the part where the linear flow velocity of the decontamination liquid is slow. Therefore, in consideration of the output of the temporary circulation pump 25, the water flow time is lengthened when the flow velocity is slow, and conversely, the water flow time is shortened when the flow velocity is high.

Further, it is desirable to use an oxidizing agent and a reducing agent as the decontamination liquid, and to perform chemical decontamination while alternately switching between the oxidizing step and the reducing step. As the oxidizing agent, for example, ozone or permanganate is used.

As the reducing agent, it is desirable to use at least one of oxalic acid, formic acid, virbic acid, glyoxylic acid, malonic acid, maleic acid, and citric acid as the organic acid.
In the decontamination implementation method according to each embodiment for decommissioning before decommissioning, it is less necessary to consider the influence on the constituent materials with which the decommissioning liquid comes into contact. Therefore, the chemical to be added to the decontamination liquid may be selected mainly in consideration of the decontamination effect or ease of handling.

Usually, in chemical decontamination including a reduction step, oxalic acid is preferably used as a reducing agent. This is because oxalic acid is a strong acid having a small acid dissociation constant (pKa) among the decomposable organic acids, so that a decontamination effect can be obtained by using it at a relatively low concentration.

However, oxalic acid may not be suitable for strains with a large amount of iron elution due to the low solubility of iron oxalate. In addition, since oxalic acid has a slow dissolution rate in water, it is difficult to dissolve oxalic acid at a high concentration. Therefore, for example, when it is difficult to use oxalic acid, it is desirable to use an organic acid that is soluble in water or is in a liquid state in the temperature range from room temperature to the decontamination condition temperature.

Organic acids having such properties as pKa of about 3 or less include, for example, formic acid, pyruvate, glyoxylic acid for monocarboxylic acid, malonic acid, tartaric acid, maleic acid for dicarboxylic acid, and citric acid for tricarboxylic acid. There are acids and so on. In order to obtain a higher decontamination effect, a plurality of these organic acids may be used as appropriate.

The description of the flowchart of FIG. 3 will be continued.
When purifying the decontamination liquid (YES in S16), the purification valve 59 is opened and the purification pump 55 is started to guide the decontamination liquid to the purification system 58 (S17).

The decontamination agent decomposition unit 52 is, for example, an ultraviolet irradiation device that decomposes the decontamination agent with ultraviolet rays. The filter 53 removes insoluble components in the decontamination solution. The ion exchange unit 54 removes the dissolved component. The ion exchange unit 54 uses, for example, two types of resin towers, a cation exchange resin tower and a mixed bed resin tower in which a cation exchange resin and an anion exchange resin are mixed.
The purified decontamination liquid is returned to the RPV 13 from the steam nozzle connecting pipe 39, the PLR middle pipe 34, and the RHR head spray pipe 26 (returning to S15).

When purification of the decontamination liquid is not required (NO in S16), circulation of the decontamination liquid is continued until the decontamination is sufficient (NO in S18) (to S13).
When sufficient decontamination is performed, the decontamination implementation method according to the first embodiment ends (END if YES in S18).

As described above, according to the decontamination method according to the first embodiment, it is possible to decontaminate the PLR system 200 including the RPV 13 or the system including the RPV 13 without using the PLR pump 21.
Further, according to the decontamination method according to the first embodiment, by extracting the decontamination liquid in the RPV 13 directly from the furnace bottom pipe 32, the sludge accumulated on the furnace bottom 28 can be recovered and largely moved. ..

(Second Embodiment)
FIG. 4 is an explanatory diagram of a decontamination implementation method according to the second embodiment.

In the decontamination embodiment according to the second embodiment, as shown in FIG. 4, in the same configuration of the temporary circulation system 300A as in the first embodiment, the circulation of the decontamination liquid inside the RPV 13 is substantially reversed.

In the second embodiment, the first check valve 42 and the second check valve 61, which were closed in the first embodiment, are opened in order to reverse the circulation. On the other hand, the head spray pipe connecting valve 46, the steam nozzle valve 47, and the third check valve 63 that were opened in the first embodiment are closed.

Depending on the open / closed state of the valve, the decontamination liquid flows through the first backflow pipe 41 and the second backflow pipe 62 to perform backflow circulation as shown in FIG.
That is, the decontamination liquid rises in the RPV 13 and forms a circulation discharged from the vapor outlet nozzle 27. In this operation, by circulating the decontamination liquid through the first backflow pipe 41 and the second backflow pipe 62, the temporary circulation pump 25 can be used for forming the backflow circulation without changing the direction of the pumping water.

In the case of backflow circulation, the circulation in the RPV 13 can be effectively strengthened by injecting the entire amount of the decontamination liquid from the bottom 28 of the furnace. Further, by injecting the decontamination liquid from the furnace bottom 28 by backflow circulation, the sludge accumulated on the furnace bottom 28 can be agitated from the bottom to promote the movement of the sludge.

Further, it is desirable to inject the gas 43 and bubbling the furnace bottom 28 in conjunction with the injection of the decontamination liquid from the furnace bottom 28. This is because bubbling can enhance the agitation of the decontamination liquid at the bottom 28 of the furnace to promote the movement of accumulated sludge.

It is desirable that the gas 43 to be supplied is ozone gas that also functions as an oxidizing agent in the oxidation step. This is because ozone gas exerts an effect as an oxidizing agent at the same time as promoting stirring of the decontamination liquid.

On the other hand, in the decontamination reduction step, it is desirable that the gas 43 has poor reactivity such as nitrogen. This is because during the reduction step, the redox potential in the decontamination liquid may be controlled in order to control the decontamination effect.
When the redox potential is not particularly controlled, the gas 43 may be air.

Further, as described above, since the decontamination method according to each embodiment is carried out at the time of decommissioning before decommissioning, it is not necessary to consider the required time. Therefore, in the decontamination at this time, the time constraint is small, and the switching operation of the forward circulation and the reverse circulation can be repeated.
In particular, when bubbling is involved, the stirring action is enhanced by the reversal operation of the circulation at regular intervals, so that a high decontamination effect can be obtained.

Since the second embodiment is structurally and operationally the same as the first embodiment except for the backflow circulation and bubbling, a duplicate description will be omitted.

As described above, according to the decontamination method according to the second embodiment, in addition to the effect of the first embodiment, the decontamination liquid is injected into the RPV 13 from the furnace bottom pipe 32 to sufficiently stir the inside of the RPV 13. At the same time, the accumulated sludge can be greatly moved.

Further, according to the decontamination method according to the second embodiment, since the circulation of the decontamination liquid of RPV13 can be substantially reversed, it is possible to decontaminate a portion where the linear flow velocity is not sufficient in the forward circulation. Further, by bubbling at the same time as injecting the decontamination liquid, stirring in the RPV 13 can be promoted.

(Third Embodiment)
FIG. 5 is an explanatory diagram of a decontamination implementation method according to the third embodiment.
In the decontamination implementation method according to the third embodiment, as shown in FIG. 5, at least a part of the PLR system 200 is included in the decontamination route.
For example, the PLR system 200 can be included in the decontamination path by opening the PLR suction valve 22, the left / right connecting valve 37, and the PLR middle valve 38 that have been closed in the first embodiment.

By the way, in a nuclear reactor plant scheduled to be decommissioned, the PLR pump 21 is shut down when the reactor is shut down, and is usually in a state of being shut down for a long period of time thereafter. In the opened / closed state of the valve described above, substantially the entire area of the PLR system 200 including the PLR pump 21 serves as a distribution path for the decontamination liquid.
At this time, in order to obtain the flow of the decontamination liquid in the RPV 13, it is desirable to circulate the decontamination liquid in the PLR system 200.

However, when the PLR pump 21 is stopped, it is usually blocked by the PLR pump 21 and it is difficult to circulate the decontamination liquid in the PLR system piping. Therefore, the electric motor and the rotating body in the PLR pump 21 are removed, the opening is temporarily closed with a pressure resistant cap or the like, and the inside of the PLR pump 21 is used as a flow path for the decontamination liquid.

The decontamination liquid that has passed through the PLR pump 21 is drawn from the decontamination seat on the PLR system 200 or the closing cap portion of the PLR pump 21 to the PLR bottom pipe 33.

Further, the decontamination liquid branched from the steam nozzle connecting pipe 39 into the PLR middle pipe 34 flows into the PLR system 200 and then flows into the jet pump 16 to circulate the RPV 13. That is, in the third embodiment, most of the PLR system 200 is decontaminated, and the flow of the decontamination liquid in the furnace is promoted by utilizing the power of the jet pump 16.

Further, FIG. 6 is an explanatory diagram showing a state in which the decontamination liquid is reflux-circulated by the decontamination implementation method according to the third embodiment.
In the backflow circulation in the third embodiment, in order to circulate the decontamination liquid in the PLR system 200, the PLR suction valve 22 or the PLR discharge valve 23 is further opened (in the open / closed state of the valve of the second embodiment (FIG. 4)). In FIG. 6, only the PLR discharge valve 23 is opened). Further, as in the case of forward circulation in the third embodiment, the left and right connecting valves 37 and the PLR middle valve 38 are opened (in FIG. 6, since the PLR discharge valve 23 is opened, only the left and right connecting valves 37 are opened). The decontamination liquid is distributed to most of the PLR system 200.

At this time, the decontamination liquid flows into the PLR system 200 from the PLR bottom pipe 33. Therefore, when the jet pump 16 is used to generate circulation in the RPV 13 as in the forward circulation, the PLR suction valve 22 is closed and the PLR discharge valve 23 is opened.

In addition, except that the PLR system 200 is included in the decontamination route, the third embodiment is structurally and operationally the same as that of the first embodiment or the second embodiment, and thus the overlapping description will be omitted. ..

As described above, according to the decontamination method according to the third embodiment, the PLR system 200 can be included in the decontamination target.
Further, by circulating the decontamination liquid in the PLR system 200 toward the recirculating water inlet nozzle 24, the circulation function of the jet pump 16 can be utilized to promote stirring in the RPV 13.

(Fourth Embodiment)
FIG. 7 is an explanatory diagram of a decontamination implementation method according to the fourth embodiment.
In the decontamination implementation method according to the fourth embodiment, as shown in FIG. 7, the temporary circulation pump 25 is moved to the upstream side of the purification system 58 on the decontamination liquid recovery pipe 48 and operated.

In the temporary circulation system 300B of the fourth embodiment, the relative arrangement relationship between the first check valve 42, the second check valve 61, and the temporary circulation pump 25 is maintained the same as that of the temporary circulation system 300A of the fourth embodiment. ing.

For example, it may not be preferable to install the temporary circulation pump 25 on the steam nozzle connecting pipe 39 in relation to other components (not shown). In such a case, the worker can move the temporary circulation pump 25 to the upstream side of the purification system 58 while maintaining the circulation direction within the decontamination range as in the fourth embodiment. ..

Further, FIG. 8 is an explanatory diagram showing a state in which the decontamination liquid is reflux-circulated by the decontamination implementation method according to the fourth embodiment.
The opened / closed state of the valve is the same as the opened / closed state of the first embodiment, as shown in FIG. Further, as a result, the circulation state within the decontamination range is the same as the backflow circulation shown in the second embodiment.

The fourth embodiment is structurally and operationally the same as the first or second embodiment, except that the position of the temporary circulation pump 25 is moved to the upstream side of the purification system 58. , Omit duplicate description.

As described above, according to the decontamination implementation method according to the fourth embodiment, the position of the temporary circulation pump 25 can be changed while maintaining the effect of the first embodiment or the second embodiment.

(Fifth Embodiment)
FIG. 9 is an explanatory diagram of a decontamination implementation method according to the fifth embodiment.

In the decontamination implementation method according to the fifth embodiment, as shown in FIG. 9, the PLR pump 21 installed in the PLR system 200 is bypassed and operated. That is, in the fifth embodiment, the temporary circulation system 300C includes a bypass line 81 for bypassing the PLR pump 21.
Then, the PLR bottom pipe 33 is connected to the bypass line 81, and the decontamination liquid bypassing the PLR pump 21 is extracted from the bypass line 81.

In the third embodiment, in order to generate circulation in the PLR system 200 without operating the PLR pump 21, it is necessary to temporarily close the PLR pump 21. However, depending on the disassembly status of the PLR pump 21, the electric motor or the like may not have been removed yet and may not be temporarily closed.

Therefore, in the fifth embodiment, by bypassing the PLR pump 21, chemical decontamination is carried out regardless of the dismantling status of the PLR pump 21 after the reactor shutdown. Further, by this bypass, chemical decontamination can be performed without taking any special measures for the PLR pump 21.

As shown in FIG. 9, this sluice valve may be a PLR suction valve 22 modified into a three-way valve.

Since the fifth embodiment is structurally and operationally the same as the fourth embodiment except that the PLR pump 21 is bypassed, a duplicate description will be omitted.

As described above, according to the decontamination method according to the fifth embodiment, in addition to the effect of the fourth embodiment, chemistry is performed regardless of the disassembly status of the PLR pump 21 and without any special treatment for the PLR pump 21. Decontamination can be carried out.

(Sixth Embodiment)
FIG. 10 is an explanatory diagram of a decontamination implementation method according to the sixth embodiment.

In the decontamination implementation method according to the sixth embodiment, as shown in FIG. 10, the assistive pump 83 is used to increase the linear flow velocity of the left PLR system 200L for decontamination.
Further, in order to carry out this decontamination method, the temporary circulation system 300D includes an assist path 84 for connecting the left steam outlet nozzle 27L and the left PLR system 200L, and an assist valve 86 provided on the left PLR bottom pipe 33L. , Equipped with. The assisting pump 83 is provided in the assisting path 84.

Since the capacity of the RPV 13 is very large, when decontamination including the RPV 13 is performed, a temporary circulation pump 25 installed at one place may not obtain a sufficient flow velocity. In particular, the left PLR system 200L, which is separated from the temporary circulation pump 25 and flows only through the left and right connecting pipes 34C, cannot obtain a sufficient flow velocity.

Therefore, in the sixth embodiment, the circulation of the left PLR system 200L, which tends to have an insufficient linear flow velocity, is directly pumped by the assisting pump 83. It is preferable to close the assist valve 86 so that all the decontamination liquid flowing through the left PLR system 200L is guided into the RPV 13 from the left steam outlet nozzle 27L.

At this time, since the circulation of the left PLR system 200L is mainly controlled by the assisting pump 83, the left and right connecting pipes 34C and the PLR middle pipes 34 shown in the sixth embodiment and the like are not shown in FIG. .. However, the circulation by the left and right connecting pipes 34C and the PLR middle pipes 34 (34A, 34B) may be appropriately maintained.

The sixth embodiment is structurally and operationally the same as the first embodiment, except that the assisting pump 83 assists the circulation of the decontaminated portion where the flow velocity tends to be small. The explanation to be performed is omitted.

As described above, according to the decontamination implementation method according to the sixth embodiment, in addition to the effect of the first embodiment, the flow velocity of the decontaminated portion having an insufficient flow velocity is assisted to support the decontamination portion having an insufficient flow velocity. Occurrence can be prevented.
Further, according to the decontamination method according to the sixth embodiment, the overall flow velocity can be increased, so that the decontamination time can be shortened.

(7th Embodiment)
FIG. 11 is an explanatory diagram of a decontamination implementation method according to the seventh embodiment.

In the decontamination method according to the seventh embodiment, as shown in FIG. 11, the backflow pump 87 provided in the second backflow pipe 62 is used to generate the backflow circulation.

In the first embodiment, the decontamination liquid was circulated through the first backflow pipe 41 (FIG. 1 and the like) and the second backflow pipe 62 to generate backflow circulation.
However, depending on the arrangement of other devices, the first backflow pipe 41 may not be connected to the steam nozzle connection pipe 39.

Therefore, in the temporary circulation system 300E of the seventh embodiment, the backflow pump 87 is provided in the second backflow pipe 62, and the backflow pump 87 generates the same backflow circulation in the RPV 13 as in the second embodiment.

A fourth check valve 88 is provided in the PLR middle pipe 34 in order to guide all the decontamination liquid flowing into the PLR middle pipe 34 to the second backflow pipe 62.
A circulation pump closing valve 78 is provided on the steam nozzle connecting pipe 39 on the downstream side of the temporary circulation pump 25 and is closed during backflow circulation.

Since the seventh embodiment is structurally and operationally the same as the second embodiment except that the backflow pump 87 is used for backflow, redundant description will be omitted.

As described above, according to the decontamination implementation method according to the seventh embodiment, by using the backflow pump 87, the same operation as in the second embodiment is performed in the same manner as in the second embodiment without using the first backflow pipe 41. Can exert the effect of.

(8th Embodiment)
FIG. 12 is an explanatory diagram of a decontamination implementation method according to the eighth embodiment.

The decontamination method according to the eighth embodiment includes the RPV13 and the PLR system 200 as targets for chemical decontamination, as well as peripheral systems (not shown).
The peripheral system is a peripheral system capable of forming a small circulation system including at least one of a reactor coolant purification (CUW) system and a residual heat removal (RHR) system. Is.

Then, in the eighth embodiment, the RPV13, the PLR system 200, and the peripheral systems are separated from each other to form individual water flow areas to form a small circulation path. Then, among these isolated water flow areas, decontamination is carried out sequentially from the water flow areas having a low amount of contaminated radioactivity and a small decontamination capacity.

It is desirable to configure a platform 89 on the temporary circulation system 300F in order to purify the decontamination liquid and manage the state of the decontamination liquid collectively.
The platform 89 includes a heat exchanger 49, a drug preparation unit 50, an ozone generator 51, a purification system 58, and a temporary circulation pump 25, and is directly or indirectly connected to all water flow areas.

For example, the platform 89 is configured as a closed circulation path by connecting the steam nozzle connecting pipe 39 and the decontamination liquid recovery pipe 48 by the platform pipe 91. In order to form this closed circulation path, a closed circulation constituent valve 92 and a closed circulation open valve 93 are provided at the branch portion between the platform 89 and the decontamination liquid recovery pipe 48, respectively.

The platform 89 is provided with a decontamination liquid supply header 94a and a decontamination liquid return header 94b. Branch pipes connected to each water flow area are connected to these headers 94 (94a, 94b). Each of the branch pipes is provided with a selection valve 98 (98a to 98f) for adjusting the water flow of each branch pipe and selecting a water flow area to be decontaminated.

The decontamination liquid is supplied to a water flow area selected from the decontamination liquid supply header 94a to decontaminate the water flow area. When the decontamination liquid is supplied from the decontamination liquid supply header 94a to the water flow area, the supply valve 97 provided between the decontamination liquid supply header 94a and the decontamination liquid return header 94b is closed. By closing the supply valve 97, the decontamination liquid flowing through the platform pipe 91 is blocked, and all of the flowing decontamination liquid flows into the decontamination liquid supply header 94a.

The decontamination liquid circulated in the water flow area and decontaminated is returned to the platform 89 from the decontamination liquid return header 94b. By switching the selection valve 98 one after another, each water flow area can be decontaminated in order.

By the way, in the case of sequential decontamination in this way, the platform 89 is contaminated to a high level when a high dose rate water flow area such as RPV13 is initially decontaminated. Further, in this case, a liquid having a high radioactivity concentration may accumulate in a flow stagnant portion in a water flow area having a low dose rate. Therefore, for example, decontamination of the water flow region having the next lowest dose rate, such as the RHR system, may spread the contamination accumulated in the decontamination target range. Therefore, it is preferable to decontaminate each water flow region in order from the portion having the low level of contaminated radioactivity to the portion having the high level of contaminated radioactivity.

In addition, the required water flow rate of RPV 13 is orders of magnitude larger than the capacity of other water flow areas. Therefore, when decontaminating other target areas after decontaminating RPV13 at the initial stage, it is necessary to drain a large amount of decontamination liquid. Since this wastewater requires decomposition treatment and purification treatment of the decontamination agent, these treatments and drainage work take time.

On the other hand, if decontamination is carried out sequentially from a system with a small volume and a low pollution level, it is sufficient to remove some radioactivity and eluted metal by passing water through a cation exchange resin in the reduction step of the final cycle. .. In other words, by decontaminating from a system with a small volume and a low contamination level, water and chemicals are added to reduce the reduction step in the first cycle of the next target range without performing decontamination agent decomposition and final purification. Can be migrated to.

Therefore, in the eighth embodiment, it is desirable to carry out decontamination in order from a system having a small volume and a low contamination level.
It is desirable that the platform pipe 91 is provided with a buffer tank 99 for maintaining a liquid level and a liquid amount sufficient for decontaminating the target water passage section. The buffer tank 99 is provided with a buffer valve 96 for buffering only when necessary.

The platform 89 is not limited to the arrangement relationship of the above example as long as it has a configuration that exhibits the same function. For example, the connection position of the platform pipe 91, the header 94, and the position of the buffer tank 99 can be appropriately changed in consideration of the arrangement with other devices.

The eighth embodiment also operates in terms of configuration with the third embodiment, except that the decontamination liquid supply / purification platform 89 is constructed and the decontamination range is divided and decontaminated sequentially according to a predetermined rule. The same applies to the above, so duplicate explanations will be omitted.

As described above, according to the decontamination implementation method according to the eighth embodiment, in addition to the effect of the first embodiment, the decontamination range is divided and reduced, so that even if the capacity of the temporary circulation pump 25 is small, The linear flow velocity of the decontamination liquid can be increased to improve the decontamination effect.

Further, according to the decontamination method according to the eighth embodiment, the decontamination of the next water flow area can be performed without decomposing the decontaminating agent and final purification, so that the decontamination can be performed efficiently. Can be done.

According to the decontamination method of at least one embodiment described above, the decontamination liquid is circulated using the temporary circulation system 300A, so that the RPV 13 and the PLR system 200 including the RPV 13 are included without using the PLR pump 21. It is possible to decontaminate a strain containing at least one of the above.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention.
These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention as well as the invention described in the claims and the equivalent scope thereof.

100 ... boiling water type reactor plant, 200 (200L) ... reactor recirculation system (PLR system), 300 (300A-300F) ... temporary circulation system, 10 ... core, 11 ... core shroud, 13 ... reactor pressure vessel , 14 ... Down Kama, 16 ... Jet pump, 17 ... Shroud head, 18 ... Gas-water separator, 19 ... Steam dryer, 21 ... PLR pump, 22 ... PLR suction valve, 23 ... PLR discharge valve, 24 ... Recirculating water Inlet nozzle, 25 ... Temporary circulation pump, 26 ... RHR head spray pipe, 27 (27L, 27R) ... Steam outlet nozzle, 28 ... Furnace bottom, 29 ... Control rod drive housing, 31 ... RPV bottom drain line, 32 ... Furnace Bottom piping, 33 (33L) ... PLR bottom piping (left side PLR bottom piping), 34 (34L, 34R) ... PLR middle piping, 34C (34) ... left and right connecting piping, 37 ... left and right connecting valve, 38 ... PLR middle valve, 39 ... Steam nozzle connection pipe, 41 ... First backflow pipe, 42 ... First backflow valve, 43 ... Gas, 44 ... Head spray pipe connection pipe, 45 ... Preparation pump, 46 ... Head spray pipe connection valve, 47 ... Steam nozzle Valve, 48 ... Decontamination liquid recovery pipe, 49 ... Heat exchanger, 50 ... Chemical preparation section, 51 ... Ozone generator, 52 ... Decontamination agent decomposition section, 53 ... Filter, 54 ... Ion exchange section, 55 ... Purification pump , 57 ... Purification mechanism, 58 ... Purification system, 59 ... Purification valve, 61 ... Second backflow valve, 62 ... Second backflow piping, 63 ... Third check valve, 64 ... Exhaust gas treatment system, 65 ... Gas treatment mechanism, 69 ... Furnace bottom valve, 75 ... Gas mixer, 78 ... Circulation pump shutoff valve, 81 ... Bypass line, 83 ... Assistance pump, 84 ... Assistance path, 86 ... Assistance valve, 87 ... Backflow pump, 88 ... 4th check valve, 89 ... Platform, 91 ... Platform piping, 92 ... Closed circulation configuration valve, 93 ... Closed circulation open valve, 94 (94a, 94b) ... Header (decontamination liquid supply header, decontamination liquid return header), 96 ... Buffer valve, 97 ... Supply valve, 98 ... selection valve, 99 ... buffer tank.

Claims (2)

The step of extracting the decontamination liquid inside the reactor recirculation system to the temporary circulation system connected to the reactor recirculation system, and
A step of purifying the decontamination liquid extracted by the temporary circulation system with a purification system connected to the temporary circulation system, and
A step of bypassing the PLR pump provided in the reactor recirculation system and refluxing the decontamination liquid extracted into the reactor recirculation system.
The step of extracting the decontamination liquid inside the reactor pressure vessel to the temporary circulation system connected to the steam outlet nozzle, and
A step of purifying the decontamination liquid drawn from the steam outlet nozzle by the purification system, and
A method for carrying out decontamination, wherein the decontamination liquid purified by the purification system is allowed to flow into the reactor pressure vessel from the bottom of the reactor pressure vessel . The decontamination method according to claim 1, wherein the bypass flow direction of the decontamination liquid is reversed.

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