JPH05100081A - Suppressing/reducing method for all organic carbon of feed/condense water - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce or suppress the total organic carbon concentration before the reactor is started to reduce the TOC brought into the reactor at the time of reactor startup, and to suppress or mitigate the deterioration of the water quality of the reactor water. [Constitution] A condenser 7 for condensing steam from a turbine 6,
Condensate filter 9 and condensate demineralization tower 10 connected to this condenser 7
And a water supply line 17 connected to the condensate purification line 5, and the condensate filter 9 alone purifies the condensate before starting the reactor 1. Further, the in-service of the condensate demineralization tower 10 is performed after the vacuum degree of the condenser 7 is raised immediately before the reactor 1 is started.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the control of total organic carbon in feed / condensate water before starting a reactor in a boiling water nuclear power plant.
Regarding a reduction method.

[0002]

2. Description of the Related Art In a nuclear power plant, in order to maintain a high-purity water quality environment affecting primary reactor structural materials, fuels, etc., all organic matter (hereinafter referred to as TO
It is necessary to reduce / suppress C).

In addition, when the reactor is started, the water conductivity of the reactor may transiently rise and the water quality may deteriorate. This is because the TOC component contained in the condensate water before start-up is brought into the reactor by the water supply accompanying the start-up of the reactor and is thermally decomposed and radiolyzed to generate ionic impurities. Before the reactor is started up, the recirculation purification operation of the feed / condensation system is carried out in advance. The main purpose of this is to remove the corrosion products, so-called clad, in the conventional feed / condensate, and at the same time remove the ionic impurities in the feed / condensate. To do.

Therefore, during the supply / condensate recirculation purification operation before the reactor is started, the condensate purification system such as the condensate demineralization tower is in-service by using the feedwater recirculation line returning from the front of the reactor to the condenser. However, circulation purification may be performed for about one month. By in-service and operating the condensate demineralization tower during the supply / condensate purification operation before the reactor is started, the TOC component eluted from the condensate demineralizer resin will be accumulated in the condensate water. TOC is generally difficult to detect by conductivity monitoring, and TOC eluted from the condensate demineralization tower resin is difficult to remove by the condensate demineralization tower itself. The amount will increase further.

[0005]

Conventionally, in order to reduce / suppress TOC in feed / condensation water before reactor startup, the TOC that has been eluted and accumulated in the tower before the condensate demineralization tower in-service is restored. In some cases, so-called bottom drain is implemented to remove it outside the water system.

However, the TOC concentration of the feed / condensate in the feed / condensate system is increased by the recirculation / purification operation of the feed / condensate system before starting for a long time, and the TOC concentration is brought into the reactor by the start of the feed water accompanying the start-up of the reactor and is pyrolyzed or radioactively decomposed. However, there is a problem that ionic impurities are generated by this and the water quality of the reactor is deteriorated.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a TOC reduction / suppression method for feed / condensation water before the reactor is started.

[0008]

The present invention is directed to a condensate purification line having a condenser for condensing steam from a turbine, a condensate filter connected to the condenser, and a condensate demineralization tower, and the above-mentioned condensate purification line. In a method for suppressing / reducing total organic carbon of feedwater / condensation water of a boiling water nuclear power plant equipped with a feedwater line for feeding condensed water having passed through a condensate demineralization tower to a reactor, the reactor is provided with only the condensate filter. Condensate purification before start-up is performed, and in-service of the condensate demineralization tower is performed after the degree of vacuum of the condenser is increased immediately before the reactor is started up.

[0009]

[Operation] Reduction of TOC concentration in the water supply / condensation water before reactor startup
In order to suppress it, the in-service period of the condensate demineralization tower should be shortened as much as possible, and the dissolved oxygen concentration of the condensate water in the condensate water should be low, and the in-service condenser should be able to suppress TOC elution from the condensate desalination tower. It is effective to make it after the degree of vacuum is increased.

Further, in order to remove TOC existing in the feed / condensation system before the reactor is started, it is effective to promote the decomposition by the γ-rays emitted from the irradiated fuel at the time of pre-start purification. It can be said to be one of the removal methods.

That is, the TO that is eluted from the ion exchange resin in the condensate demineralization tower at the time of cleansing the condensate recirculation before starting the reactor
In order to avoid an increase in the TOC concentration of the condensate water due to C, in a plant equipped with a condensate filter and a condensate demineralization tower in the condensate purification system, the condensate purification system filter alone should be used to purify the condensate before startup. To do. The in-service of the condensate demineralization tower will be performed after the condenser vacuum level is raised before the reactor is started, and if TOC is mixed into the feed / condensate system due to the in-service of the condensate demineralization tower, the removal will be efficient. In order to do so, it is effective to backwash and regenerate the condensate purification system filter immediately before in-service of the condensate demineralization tower.

On the other hand, in the case where the condensate purification system is a plant having only a condensate demineralization tower, the condensate demineralization tower must be in-service for the supply / condensate purification operation before the reactor is started. In this case, bypass the condensate demineralization tower and perform a feed / condensate system recirculation operation to sufficiently remove the clad that adheres to the inner surface of the feed / condensate piping.
It is effective to shorten the in-service period of the condensate demineralization tower for removing the clad as much as possible and to make the in-service period after the condenser vacuum degree is raised.

Further, it is very effective to decompose and remove the TOC existing in the condensate water at the time of recirculation of the condensate water in advance in order to suppress deterioration of the water quality of the reactor water at the time of starting the reactor. TOC is decomposed by heat radiation, ultraviolet rays and the like to become carbon dioxide gas, but at the same time, nitrogen and sulfur compounds contained in TOC become ions such as ammonia, nitric acid, nitrous acid and sulfuric acid. When these ionic impurities are present under low temperature conditions, it is generally said that they contribute little to the corrosion of stainless steel, which is the primary material for nuclear reactors. Can be said to be small enough.

Therefore, as one of the methods for decomposing and removing the condensate water TOC before and after the start-up, a part of the condensate water is continuously transferred to a reactor or a fuel pool in which irradiated fuel exists. , It is effective to decompose and remove by γ-ray emitted from the irradiated fuel. In a plant equipped with a condensate filter using powdered ion-exchange resin, in order to mitigate the TOC concentration increase in the condensate in the condensate in the condensate demineralization tower, the Before injecting water, it is necessary to backwash and regenerate the condensate filter before in-service.
It is effective in removing C.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method for suppressing / reducing TOC of supplied / condensed water according to the present invention will be described with reference to FIGS. FIG. 1 is a system diagram showing a feed / condensation system and a reactor recirculation system applied to a boiling water nuclear power plant for explaining the method of the present embodiment.

In FIG. 1, reference numeral 1 denotes a boiling water reactor, which is provided with a reactor recirculation system 20 having a recirculation pump 2 and which is connected to the suction side of the recirculation pump 2. It is branched and the reactor coolant purification system 3 is connected. The outlet side of this reactor coolant purification system 3 is connected to a water supply line 17,
The water supply line 17 is connected to the reactor 1. The condenser blowdown line 4 is branched from the outlet side of the reactor coolant purification system 3, and the purification line 5 is connected to the inlet side of the water supply line 17. The condenser blowdown line 4 and the purification line 5 are connected to the turbine 6.

A condenser 7 is connected to the turbine 6, and a condenser pump 8 is connected to the condenser 7. A condensate filter 9 and a condensate demineralizer 10 are sequentially connected to the discharge side of the condensate pump 8, and an outlet side of the condensate demineralizer 10 is connected to the purification line 5. The condensate filter 9 and the condensate demineralization tower 10 are provided with bypass lines 11 and 12, respectively. One end of the spillover line 13 is branched from the purification line 5, and the other end of the spillover line 13 is connected to the CRD cooling water line 16.

One end of the CRD cooling water line 16 is connected to the bottom of the nuclear reactor 1, and the other end is connected to the fuel storage pool 14. This fuel storage pool 14 is a fuel pool purification system.
The outlet side line of this fuel pool purification system 15 connected to 15.
18 is connected to the condenser blowdown line 4. One end of a return line 19 is branched from the outlet side line 18 of the fuel pool purification system 15, and the other end of the return line 19 is connected to the fuel storage pool 14.

As shown in Table 1, the ion exchange resin used in the condensate demineralization tower 10 undergoes oxidative deterioration and Hofmann
TOC is eluted by decomposition, amine elimination reaction, etc.

[0020]

[Table 1]

On the other hand, the TOC elution rate from the ion exchange resin increases as the years of use increase, as shown in FIG. As shown in FIG. 3, in the air-saturated water, the TOC elution from the ion-exchange resin tends to increase as compared with the condition where the nitrogen (N ₂ ) gas is bubbled to reduce the dissolved oxygen in the solution. This indicates that under low dissolved oxygen conditions, TOC can be suppressed from being eluted from the ion exchange resin due to oxidative deterioration. Therefore, it can be said that the “water sampling” of the condensate demineralization tower 10 is effective after the degree of vacuum of the condenser 7 is increased in order to suppress the increase in the TOC concentration of the water supply / condensation system.

Further, as shown in FIG. 4, the TOC elution from the ion exchange resin has a clear dependence on the water flow rate, and the lower the water flow rate, the less the TOC elution tends to be. is there. Therefore, when system water is passed at a flow rate lower than the 100% rated flow rate, such as during the water supply / condensation system purification operation before the plant is started, all the condensate demineralization towers 10 are always used to collect water. By reducing the flow rate of sampled water for each desalting tower and lowering the water flow rate, it is possible to reduce the amount of TOC eluted from the condensate desalting tower 10 before the plant is started to accumulate in the feed / condensate system.

FIG. 5 shows an actual example of changes over time in the feedwater and reactor water TOC concentrations during the supply / condensate recirculation purification operation before the start of the plant. In FIG. 5, when the cooling water of the control rod drive device (CRD) that has been drawing water from the outlet of the condensate demineralization tower 10 is stopped, the TOC concentration of the feed water tends to increase. This is because when the CRD cooling water is supplied from the outlet of the condensate demineralization tower 10, the TOC component in the CRD cooling water brought into the reactor 1 is γ-rays or the like from the irradiation fuel in the reactor 1. However, the reactor water with a low TOC concentration was blown to the condenser 7 and had the effect of holding down the TOC concentration of the feed and condensate water to a low level. It is a phenomenon caused by the fact that decomposition in the interior is no longer promoted.

As described above, in order to reduce / suppress the TOC of the supply / condensation water before the reactor is started, the condensate demineralization tower 10 is "collected" and "collected" after the vacuum degree of the condenser is increased. It is effective to make the “water” period as short as possible and set all the “water sampling” towers to the lowest flow rate of the condensate demineralization tower 10. Further, promoting the decomposition of TOC by γ-rays from the irradiated fuel is an effective means for reducing the TOC concentration in the primary system.

That is, in FIG. 1, when the water in the condenser 7 is circulated in the supply / condensate recirculation purification line 5 by using the condenser pump 8 before the reactor is started, the degree of vacuum of the condenser 7 is set. Condensate demineralization tower until dissolved oxygen concentration of system water decreases due to rise
Water is not passed through 10 but only the condensate filter 9 is passed through, and a condensate recirculation purification operation using a condensate demineralization tower bypass line 12 is performed. Further, in order to reduce the TOC concentration of the condensate of the feed water, the spillover line 13 downstream of the condensate demineralization tower is used, and a part of the condensate is continuously supplied from the CRD cooling water line 16 to the reactor 1. The TOC decomposition is promoted by γ-rays, etc. from the irradiated fuel inside the reactor, and the reactor water with a low TOC concentration is passed through the reactor coolant purification system 3 and used as a condenser using the condenser blowdown line 4. By blowing, the TOC concentration in the water supply / condensation system can be lowered. When the irradiated fuel is stored in the fuel storage pool 14, the irradiated fuel in the fuel pool promotes effective decomposition of TOC, so spillover is always used to fuel the condensate. A method of passing water through the pool and blowing it down to the condenser via the fuel pool purification system is also an effective measure for reducing TOC concentration.

The embodiment of the present invention is as follows. (1) TOC brought in from the water supply / condensation system at reactor startup
In order to prevent, suppress, or mitigate the deterioration of the water quality of the reactor water due to ionic impurities generated by thermal decomposition or radiolysis in the reactor, the TOC of the feed / condensate water before the reactor is started is reduced. As a method, the condensate demineralization tower collects water after raising the vacuum degree of the condenser. For this water sampling, the total number of water collection towers of the condensate demineralization tower should be set, and the water flow speed of the condensate demineralization tower should be slowed. (2) Condensation water In order to avoid the TOC elution from the ion exchange resin in the demineralization tower from concentrating in the condensate water, the condensate water purification before reactor startup does not collect water in the demineralization tower Do only with filters. (3) When TOC is mixed in the condensate water by condensate demineralization tower in-service, in order to remove the TOC efficiently, the condensate filter is backwashed and regenerated before the condensate demineralization tower in-service. To serve. (4) In order to efficiently remove TOC existing in the water supply / condensation water before the reactor startup before the plant is started, a part of the supply / condensation water is continuously or intermittently supplied to the reactor or the fuel pool for irradiation. TOC is decomposed by γ-rays from the spent fuel, the produced ion impurities are removed by the reactor coolant purification system and the fuel pool purification system, and the water with low TOC concentration is returned to the feed / condensation system to restore the charge before starting the reactor. To reduce the TOC concentration of water.

[0027]

According to the present invention, by shortening the in-service period of the condensate demineralization tower, it is possible to avoid an increase in the temperature of the TOC that is eluted from the condensate demineralization tower during the condensate supply. Further, the TOC elution from the condensate demineralization tower can be suppressed by in-service all the condensate demineralization towers after the degree of vacuum of the condenser is increased. Further, when the condensate demineralization tower is in-service at the time of starting the nuclear power plant, the TOC can be efficiently removed by previously rewashing all the condensate filters by backwashing.

Further, during the feed / condensate recirculation purification operation before the reactor is started, the feed / condensate is forcibly sent to the reactor or the fuel pool, and the TOC decomposition is promoted by the γ-rays emitted from the irradiated fuel to cool the reactor. It is an effective TOC removal method to remove TOC decomposition product ions by a material purification system filtration desalting tower and a fuel pool purification system filtration desalting tower. By these methods, TOC brought in from the water supply system at the time of plant startup is thermally or radiolytically decomposed in the nuclear reactor, and deterioration of the water quality of the reactor water due to ionic impurities generated can be suppressed or avoided.

[Brief description of drawings]

FIG. 1 is a system diagram showing a feed / condensation system and a nuclear reactor recirculation system of a nuclear power plant to which an embodiment of a method for suppressing / reducing total organic carbon of feed / condensation water according to the present invention is applied.

2 is a TOC of the ion exchange resin in the condensate demineralization tower of FIG.
The curve figure which shows the relationship between a dissolution rate and the years of use.

FIG. 3 is a curve diagram showing the relationship between TOC concentration and water passage time when bubbling air-saturated water and N ₂ in the condensate of FIG. 1.

FIG. 4 is a curve diagram showing the dependence of TOC elution behavior in condensate water of FIG. 1 on water flow velocity.

FIG. 5: TO in reactor water and water supply of the plant of FIG.
The curve diagram which shows the relationship between C density | concentration and elapsed time.

[Explanation of Codes] 1 ... Reactor, 2 ... Recirculation pump, 3 ... Reactor coolant purification system, 4 ... Condenser blowdown, 5 ... Condensed water recirculation purification line, 6 ... Turbine, 7 ... Condenser Water bottle, 8 ... Condensate pump, 9
… Condensate filter, 10… Condensate demineralizer, 11… Condensate filter bypass line, 12… Condensate demineralizer bypass line, 13… Spillover line, 14… Fuel storage pool, 15… Fuel pool purification system, 16 … CRD cooling water line, 17… water supply line,
18 ... Exit line, 19 ... Return line, 20 ... Reactor recirculation system.

Claims (1)

[Claims] 1. A condensate purifying line having a condenser for condensing steam from a turbine, a condensate filter connected to the condenser, and a condensate demineralizer, and a condensate demineralizer passing through the condensate purification line. In the method for suppressing / reducing total organic carbon in the feedwater / condensation water of a boiling water nuclear power plant equipped with a water supply line for supplying the condensed water to the reactor, the condensate water is purified by the condensate filter only before the reactor is started. A method for suppressing / reducing total organic carbon in feed / condensation water, which is performed while the in-service of the condensate demineralization tower is performed after the vacuum degree of the condenser is raised immediately before the reactor is started.