JPH0331799A - Method for demineralizing condensate - Google Patents

Abstract

PURPOSE:To prevent the generation of stress corrosion cracking (SCC) in the constitutional materials of a reactor by discharging water from a mixed floor type demineralizing tower to the outside of the system at the time of restarting water supply to the tower and then supplying water to the tower. CONSTITUTION:The condensate demineralizing tower 1 is filled with pure water and its run is stopped. Under that state, an air compressor 2 is started and a feeding air main valve 3, a waste liquid outlet valve 4, a feeding air inlet valve 5 are opened to discharge water stored in the tower 1. After finishing the water discharge, the valves 3 to 5 are closed. Then an air vent valve 4 and a spray water valve 7 are opened, a reproducing water pump 8 is started, the tower 1 is filled with water, and after filling the tower 1 with water, the pump 8 is stopped and the valves 6, 7 are closed. A series of operation of water discharge and filling is repeated 3 times to remove impurities eluted from resin to the outside of the system. Consequently, the generation of SCC in the materials constituting the reactor can be prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a condensate desalination method used to treat the primary cooling water of a boiling water (BWR) nuclear power plant, and in particular, to This invention relates to a condensate desalination method for increasing the purity of desalinated water.

[Conventional technology]

At the BWR Nuclear Power Plant, the inside of the reactor must always be maintained in a clean state, so the condensate that flows into the reactor from the condenser is purified by a condensate desalination tower to a high degree of purification. It is used as cooling water for the after-furnace. This condensate demineralization tower is a so-called hot bed demineralization tower filled with a mixture of granular cation exchange resin and anion exchange resin, and is used to remove and purify impurities in condensate. .

This mixed-bed demineralization tower, which uses cation exchange resin and anion exchange resin, uses pure water inside the demineralization tower to prevent deterioration of the ion exchange resin when condensate is not being treated, such as during regular plant inspections. When starting condensate treatment, perform recirculation operation in advance and confirm that the conductivity of water at the outlet of the demineralization tower is below the specified value (IIL1μ8/m) before discharging the condensate. A method has been used to maintain water quality downstream of the condensate purification system by supplying desalinated water to the reactor.

[Problem to be solved by the invention]

Recently, in order to extend the life of a plant, it has become necessary to maintain the quality of the primary cooling water in the reactor at a high level of purity. Although the purification method can remove ionic components eluted from the ion-exchange resin during storage full of water, it was found that the ability to remove organic impurities was insufficient and could not meet the demands for more sophisticated equipment.

In the present invention, when restarting the water flow to the mixed bed type desalination tower which has been stored in a full water state for a long period of time after stopping the water flow, the present invention provides a method for reducing ionic content and organic impurities from the desalination tower to a sufficiently low level. The purpose is to perform K so that demineralized water can be obtained.

[Means to solve the problem]

The present invention is a condensate desalination method in which condensate is passed through a mixed bed consisting of a granular cation exchange resin and an anion exchange resin when treating the primary cooling water of a boiling water nuclear power plant, and the water flow is stopped. And keep it full of water for a long time! ! iK When restarting water flow to a certain mixed-bed desalination tower, a condensate desalination method is used, which is characterized in that the water in the demineralization tower is discharged from the system and then water is passed through it.

In order to concretely discharge the water in the desalination tower to the outside of the system, it is necessary to not only discharge the water contained in the demineralization tower out of the system from the desalination tower which is stored at full capacity. It is preferable to repeat the operation of filling the system with water again and draining the water out of the system. This is because the purpose of using the above-mentioned water discharge means is to remove ions and organic impurities in the demineralization tower, so when simply discharging the water, the demineralizer is used to prevent air from entering the resin layer. Since the water in the salt tower cannot be reduced below the surface of the resin layer, the water stored in the desalination tower remains unchanged, so water should not be filled and drained until all of this stored water is removed. Need to repeat. This draining and filling operation is usually repeated several times (preferably 5 to 5 times).

[Effect]

The condensate demineralization tower allows the cation exchange resin and anion exchange resin in the condensate to adsorb ionic components, cutluad components, and organic impurities by passing condensate through it. When the water flow is stopped for a long period of time, as mentioned above, when the desalination tower is kept in a full water storage state, due to the use of pure water to fill the desalination tower, the ion exchange resin is removed from the ion exchange resin due to the ion exchange equilibrium. Ionic components are eluted, and organic impurities are released due to hydrostatic conditions. Figure 2 shows the total organic carbon (ROE) concentration of the stored water on the horizontal axis and the number of storage days when the cation exchange resin and anion exchange resin are stored in a demineralization tower full of water. According to this K, it can be seen that the longer the storage period, the higher the Too concentration. For this reason, when water is resumed through the desalination tower when the blunt is restarted, the aforementioned ions and organic impurities enter the primary cooling water of the nuclear reactor.

Because of this problem, conventionally, recirculation operation was performed before restarting condensate treatment, but at that time, the ionic components in the stored water were once again transferred to the cation exchange resin and anion. Organic impurities are difficult to be completely re-adsorbed by these ion exchange resins and require a certain amount of recirculation time.

In the present invention, since stored water containing eluted ionic components, organic impurities, etc. is discharged from the system, secondary cooling water can be maintained at a high purity.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples.

However, the present invention is not limited to this example.

Embodiment FIG. 1 shows a condensate demineralization tower 1 and a group of pipes attached thereto. The condensate desalination tower 1 is filled with pure water and its operation is stopped. At this time, the air compressor 2 is started, the transfer air source valve 3, the waste liquid outlet valve 4, and the transfer air inlet valve 5 are opened, and the stored water in the demineralization tower 1 is discharged. At this time, the amount of water discharged is limited to the surface of the resin layer in order to prevent air from entering the resin layer. This is because if air enters the resin layer, the resin particles to which the air is attached will float up during the next water filling process and the resin layer will be disturbed. After draining, close valves 3 and 4.5. Next, the air vent valve 6 and the spray water valve 7 were opened, the regeneration water bonder 8 was started, and the desalination tower 1 was filled with water to perform water filling. After completion, the regeneration water pump 8 is stopped and the valve 6.7 is closed.

Repeat this series of draining and filling operations three times,
Impurities eluted from the resin are removed from the system.

In contrast, a comparative test was conducted in which water was passed through a desalination tower using a conventional method.

The water quality of the primary cooling water at the time of startup of the BWR atomic couplet when the water stored in the desalination tower is removed from the system according to the present invention and then passed to the desalination tower, and when the water is passed through the desalination tower using the conventional method. The measurement results are shown in Table 1.

According to Table 1, the condensate desalination method of the present invention maintains the quality of the reactor sub-cooling water at a higher purity, and can be said to be an extremely effective method in practice.

Table 1 [Effects of the Invention] According to the present invention, in a method for desalinating condensate performed in the treatment of primary cooling water of a BWRWL child reactor power plant, it is possible to increase the purity of desalinated water when the water flow is resumed. This makes it possible to increase the purity of the primary cooling water supplied to the reactor when restarting operations. Thereby, stress corrosion cracking (Saa) of the reactor constituent materials can be prevented and the life of the defund can be extended.

[Brief explanation of drawings]

Figure 1 shows the condensate demineralization tower and the piping group attached to it, and Figure 2 shows the total organic carbon of the stored water when the demineralization tower is filled with cation exchange resin and anion exchange resin. A diagram showing the relationship between concentration and storage days is shown. 1... Condensate desalination tower 2... Pneumatic compressor 3...
・Air source valve for transfer 4...Waste liquid outlet valve 5...Air population valve for transfer 6...Air vent valve 7...Spray water valve 8...Regeneration water pump Figure 1 (and 3 others)

Claims (1)

[Claims] When treating the primary cooling water of a boiling water nuclear power plant, in a condensate desalination method in which condensate is passed through a mixed bed consisting of granular cation exchange resin and anion exchange resin, water flow is stopped for a long period of time. A condensate desalination method characterized in that when water is restarted to flow into a mixed-bed desalination tower that has been kept full of water for over a period of time, the water in the desalination tower is drained out of the system and then water is flown through the tower. .