JPH0531482A - Condensed water demineralizing method - Google Patents

Abstract

PURPOSE:To prevent the stress corrosion cracking of reactor constituting materials by previously subjecting the primary cooling water of a BWR type atomic power plant to chemical passage regeneration or lowering the dissolved oxygen concn. in the treated water or lowering a water passage line flow velocity, thereby lowering the concn. of org. impurities. CONSTITUTION:Condensate is introduced from a condensate tank 1 by a pump 3 into a resin column 2 consisting of a mixed bed composed of granular cation exchange resins and anion exchange resins and is circulated through a pipe 6 to the condensate tank 1. The dissolved oxygen concn. in the condensate is lowered to <=100ppb by executing a deaeration operation (a) at the time of treating the condensate with the mixed bed as the purifying operation before starting following the shutdown of the plant by a periodic inspection. The drawn water is charged to many demineralizers to lower the water flow line-flow velocity (b). The cation exchange resins and anion exchange resins are previously subjected to the chemical passage regeneration (c). The mixed bed before the water passage is subjected to the recirculating operation by the deaerated water for a long time as far as possible (d). A plurality of the methods (a) to (d) are combined and executed (e).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a condensate desalination method for treating primary cooling water of a BWR nuclear power plant, and more particularly, to improving the purity of the primary cooling water at the time of purification operation before starting the plant, Condensed water desalination method for achieving furnace cleaning.

[0002]

2. Description of the Related Art In a BWR nuclear power plant, the inside of the reactor must be kept clean at all times. Therefore, the condensate flowing into the reactor from the condenser is purified by a condensate demineralization tower. After being highly purified, it is used as cooling water into the furnace. This condensate demineralization tower was filled with a mixture of granular cation exchange resin and anion exchange resin,
This is a so-called mixed bed desalting tower, which removes and purifies impurities in the condensate. Conventionally, before the start-up after the periodical inspection of the plant, before the primary cooling water is supplied into the reactor, the purification operation using the condensate circulation line is performed to check the ionic impurities brought into the system during the periodic inspection. In order to send the condensate to the reactor after removing the iron oxides generated in the pipes, etc., the condensate is treated by the condensate demineralizer, but in this case, no pretreatment is required. In addition, the number of desalting towers to collect water was set to the minimum necessary.

[0003]

Recently, in order to prolong the life of the plant, it has become necessary to maintain the quality of the primary cooling water in the nuclear reactor at a high purity, which is the case in the above-mentioned purification method. As a result, although it was possible to remove ionic impurities, it was found that the ability to remove organic impurities (hereinafter referred to as TOC) was not sufficient, and it was not possible to meet the requirement for high purification of the apparatus. That is, the above-mentioned organic impurities that are difficult to remove include those that are brought in from outside the system and those that are eluted from the ion exchange resin itself, and are usually non-conductive, but when they enter the reactor, they are irradiated with neutrons. By heating or by heating, it changes to ionic impurities and increases the conductivity of the reactor water as shown in FIG. 5, which adversely affects the reactor. It is an object of the present invention to provide a condensate desalination method capable of performing a purifying operation so that a condensate having a sufficiently small amount of organic impurities can be obtained when performing a condensate purifying operation before starting a plant.

[0004]

In order to solve the above-mentioned problems, according to the present invention, in the treatment of primary cooling water of a BWR type nuclear power plant, condensate is mixed with a granular cation exchange resin and an anion exchange resin. In a condensate desalination method that treats with a water type desalination device, (a) deaeration process is performed to purify the condensate before the start-up after plant shutdown and the dissolved oxygen concentration in the condensate is 100 ppb or less. To reduce the flow rate of condensate flowing through the desalination device to a lower level than in normal operation to reduce the water flow velocity to perform the purification operation. A method in which the cation exchange resin and the anion exchange resin of the salt device are regenerated through a recycle, and (d) the recirculation operation of the condensate demineralization tower before water passage is performed as long as possible compared to normal times. A method of performing a purifying operation after the operation, (a) to (d) The method is a condensate demineralization method characterized by reducing organic impurities flowing into condensate by performing a purification operation using one or more of the above methods.

That is, the present invention provides a condensate desalination method in which condensate is treated with a mixed bed of granular cation exchange resin and anion exchange resin in the treatment of primary cooling water of a BWR type nuclear power plant, In carrying out the cleaning operation before the start after the plant is stopped by the periodic inspection, the following (a) ~
This is a condensate demineralization method for increasing the purity of the primary cooling water of the BWR type nuclear power plant by operating the method of (d), and especially for cleaning the reactor. (A) When the condensate is treated in a mixed bed, a degassing operation is performed so that the dissolved oxygen concentration in the condensate is 100 ppb or less, preferably 5
The first method is to reduce the amount to less than 0 ppb to suppress the oxidative deterioration of the ion exchange resin and reduce the amount of TOC to be eluted. (B) When treating condensate in a mixed bed, by introducing many desalting towers to reduce the flow rate per tower and reduce the water flow velocity, The second method of improving the TOC removal performance and reducing the amount of TOC flowing out.

(C) When the condensate is treated in a mixed bed, the cation exchange resin and the anion exchange resin are passed through and regenerated in advance, the dissolved TOC is removed from the system in advance, and the surface condition is cleaned. The third method is to improve the TOC removal performance and reduce the amount of TOC that flows out when water is collected. (D) The TOC eluted from the cation exchange resin and the anion exchange resin is returned to the upstream side in advance by performing the recirculation operation using degassed water for the mixed bed before water flow as long as possible, and the desalting tower is evenly distributed. The fourth method to reduce the impact of TOC when passing water by dividing it into (E) A fifth method for reducing the TOC amount by carrying out a combination of a plurality of methods according to claims (a) to (d).

[0007]

According to the present invention, when the primary cooling water of the BWR type nuclear power plant is treated by the condensate demineralizer, the regenerator is regenerated before the water is collected, or the dissolved oxygen concentration in the treated water is reduced when the water is passed. Or lowering the water flow velocity,
It reduces the concentration of organic impurities in the treated water.

[0008]

EXAMPLES The present invention will now be specifically described with reference to examples, but the present invention is not limited to these examples. Example 1 The elution behavior of organic impurities by the mixed bed resin of this example is as follows.
The test apparatus shown in FIG. 1 was used. In FIG. 1, 1 is a condensate tank, 2 is a mixed bed resin column (30 mmφ, resin amount 1
00 ml), and the condensate is introduced from the tank 1 by the pump 3 through the pipe 5, into the resin column 2, and through the pipe 6,
It is circulated to the tank 1. The condensate tank 1 is provided with a N ₂ introduction pipe 8 and a pipe 7 connected to a vacuum device so that the oxygen concentration in the condensate can be adjusted. Reference numeral 4 is a flow meter, and 9 is a sampling pipe for sampling.

A test was conducted using the above apparatus under the following conditions. Amount of resin used: Strongly acidic gel type cation exchange resin 61.5m
1 and 38.5 ml of strongly basic anion exchange resin are used in a mixed bed Water flow velocity: 40 m / h Dissolved oxygen concentration: 20 to 8000 ppb A water passage test is conducted under the above conditions to determine the TOC concentration in the treated water. The measurement result is as shown in FIG. 2, and the TOC concentration eluted can be lowered when the dissolved oxygen concentration is lower.

Example 2 The elution behavior of organic impurities by the mixed bed resin of this example is as follows.
Using the test apparatus of FIG. 1, a test was conducted under the following conditions. Amount of resin used: Strongly acidic gel type cation exchange resin 61.5m
1 and 38.5 ml of strongly basic anion exchange resin are used in a mixed bed Water flow velocity: 40 to 80 m / h Dissolved oxygen concentration: 8 ppm A water flow test is conducted under the above conditions to determine the TOC concentration in the treated water. The measurement result is as shown in FIG. 3, and the TOC concentration to be eluted can be lowered when the water flow velocity is low.

Example 3 The elution behavior of organic impurities by the mixed bed resin of this example is as follows.
Using the test apparatus of FIG. 1, a test was conducted under the following conditions. Resins used: Cation exchange resin regenerated by acid (H ₂ SO ₄ , HCl, etc.) and alkali (NaOH, KO)
Anion exchange resin that has been regenerated by using H) and an unregenerated product. Amount of resin used: Strongly acidic gel type cation exchange resin 61.5m
1 and 38.5 ml of strongly basic anion exchange resin are used in a mixed bed Water flow velocity: 80 m / h Dissolved oxygen concentration: 8 ppm A water passage test is conducted under the above conditions to measure the TOC concentration in the treated water. The results are shown in FIG. 4, and the TOC concentration to be eluted can be lowered when the regenerant regeneration is carried out.

[0012]

According to the present invention, the TOC concentration in the condensate can be reduced in the desalination method of the condensate which is performed in the treatment of the primary cooling water of the BWR nuclear power plant. The reactor water conductivity can be lowered as shown in FIG. 5 to increase the purity. This allows
It is possible to prevent stress corrosion cracking (SCC) of the constituent material of the nuclear reactor and to extend the life of the plant.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a test apparatus used in an example of the present invention.

FIG. 2 is a graph showing the relationship between TOC concentration and dissolved oxygen concentration.

FIG. 3 is a graph showing the relationship between TOC concentration and water flow linear velocity.

FIG. 4 is a graph showing the effect of reducing the TOC concentration in the common drug regeneration process.

FIG. 5 is a graph showing the relationship between reactor water conductivity and TOC concentration.

[Explanation of symbols]

1: Condensate tank, 2: Mixed bed resin column, 3: Pump,
4: Flow meter, 5, 6: Circulation pipe, 7: Vacuum device connecting pipe,
8: N ₂ supply pipe, 9: sampling pipe

Claims (1)

Claim: What is claimed is: 1. Condensate dewatering in which a condensate is treated with a mixed bed desalination apparatus comprising granular cation exchange resin and anion exchange resin in the treatment of primary cooling water of a BWR nuclear power plant. In the salt method, when the condensate is purified by the desalination device before the start-up after the plant is stopped, (a) degassing treatment is performed to adjust the dissolved oxygen concentration in the condensate to 100 ppb.
(B) A method of performing the purification operation by reducing the flow rate of the condensate flowing in the desalination device as compared with the normal operation to reduce the water flow velocity, and (c) beforehand. A method of purifying the cation exchange resin and anion exchange resin of the desalting equipment after regenerating the same, (d) recirculation operation of the condensate demineralization tower before water passage is longer than usual. Condensate characterized by reducing the organic impurities flowing out into the condensate by performing the purifying operation using one or more of the methods (a) to (d) after performing the purifying operation after a certain period of time. Desalination method.