JPS5953517B2 - Reactor coolant sampling device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nuclear reactor coolant sampling device, and more particularly to a nuclear reactor coolant sampling device suitable for reducing adhesion of radioactive ions.

Metal impurities are leached from the structural materials of the primary cooling system of a nuclear reactor, for example a boiling water reactor.

This metal impurity is carried into the reactor pressure vessel and becomes radioactive corrosion products.

Radioactive corrosion products include components dissolved in cooling water (hereinafter referred to as
There are ions (referred to as ions) and insoluble solid components (mainly iron oxide, hereinafter referred to as cladding).

Crud is mainly generated by oxidation of ions in the reactor pressure vessel.

In this way, long-half-life radioactive corrosion products such as 60CO1''Mn are deposited on the inner surfaces of recirculation system piping, furnace purification system piping, etc., resulting in an increase in the surface dose rate of these piping.

In order to predict the degree of increase in the surface dose rate of such piping, etc., the radioactive concentration and chemical concentration of radioactive corrosion products in cooling water are measured.

The radioactivity concentration and chemical concentration of impurities in the cooling water of a boiling water reactor are determined by collecting a portion of the cooling water as a sample water through a sampling pipe and conducting radioactivity and chemical analysis of the sample water.

Depending on the sampling location, sampling piping is typically over 50 meters long.

Therefore, radioactive corrosion products adhere to the pipe wall of the sampling pipe, and even if the radioactive concentration and chemical concentration in the sample water are determined, the error becomes large.

An object of the present invention is to improve the accuracy of analyzing radioactive materials in nuclear reactor coolant.

A feature of the present invention is to supply a pH-lowering substance to the sampled coolant of a nuclear reactor, and to adjust the pH of the sampled coolant to a predetermined value or less.

The inventors discovered through experiments using 58CO, a radioactive isotope of 60CO, that the adhesion coefficient of radioactive ions to sampling piping (stainless steel piping) varies greatly depending on the pH of sample water flowing inside the sampling piping.

Here, the adhesion coefficient δ of 58CO to the sampling pipe is
(cm/h) is approximately expressed by the following formula.

Here, P is the amount of 58CO attached per unit area (μCi
/cm”), t is time (hr), R is 58C in the sample water
O concentration (7zCi/ml).

FIG. 1 shows the results of investigating the pH dependence of the adhesion coefficient of 58CO under the condition of a sample water temperature of 280°C.

The adhesion coefficient of 58CO when the sample water pH is 7 is 1.0.
In this case, the values were 0.49 when the pH was 6.3, 0.03 when the pH was 5.0, and 0.02 when the pH was 3.5.

Therefore, if the pH of the sample water is lowered to below 5.0,
It was revealed that the amount of 8CO attached to the sampling pipe could be reduced to about 1730 compared to normal cooling water conditions (pH = 6 to 7).

FIG. 2 is a system diagram of the experimental apparatus used in the above experiment.

An example of an experiment conducted using this experimental device will be explained in detail.

Reference numeral 11 denotes a reactor simulation tank, which is equipped with a heater around its outer periphery so that the temperature and pressure of the simulated cooling water can be adjusted to the conditions of an actual boiling water reactor, 285° C. and 70 atm.

After adjusting the 58co radioactivity concentration and CO chemical concentration in the simulated cooling water and the pH of the simulated cooling water to predetermined values in the simulated cooling water tank 20, the valve 23 is opened and the booster pump 2
1, the simulated cooling water is injected into the reactor simulated tank 11.

After injection of the simulated cooling water into the reactor simulated tank 11 is completed, the valve 23 is closed.

The pH of the simulated cooling water at this time is 7,"C.The radioactivity concentration is I
X 10 = cci/ml and CO chemical concentration is 0
．． It is 4 ppb.

While the circulation pump 12 is operated and the simulated cooling water is circulated within the circulation loop 22, the temperature and pressure are increased by the outer peripheral heater of the reactor simulation tank 11.

When the temperature reaches 285°C and 70 atm, the temperature and pressure increase is stopped, and then the valve 24 is opened to maintain a constant flow rate (l l /
A portion of the simulated cooling water is introduced into the sampling loop 14 as sample water.

In the acidic solution tank 15, 0.001 mo
Pour in nitric acid (HNO3) solution and set aside.

Activating the injection pump 16 at the same time as opening the valve 25,
The nitric acid solution in the acidic solution tank 15 is supplied into the sampling loop 14 at a rate of 10 ml/min.

By this operation, the pH of the sample water flowing within the sampling loop 14 is adjusted to about 5.

Piping adhesion test section 1 provided in the sampling loop 14
A sample pipe (stainless steel pipe) 17 is placed in 3.

A part of 58CO in the sample water adheres to this sample pipe 17.

The sample water is cooled to a temperature of around 50° C. by the cooler 18 and then passed through the ion exchange resin tower 19 .

Here, 002+ ions and NO3- ions are collected,
Pure water is returned into the reactor simulating tank 11 by the boost pump 21.

After passing water for a certain period of time, the sample pipe 17 is taken out.

Radioactivity in the sample pipe 17 was measured with a Ge (Li) semiconductor detector, and the amount of 58CO attached to the sample pipe 17 was determined.

Furthermore, the radioactivity concentration of 58CO in the ion exchange resin tower 19 was also measured.

As a result, the amount of 58CO attached to the sample pipe 17 was 1
It decreases to 720 or less.

Furthermore, it was found from the radioactivity concentration in the ion exchange resin column 19 that the loss due to adhesion in the piping of the sampling loop 14 was only 1%, whereas it would be more than 20% if the pH was not adjusted.

A preferred embodiment of the present invention based on such experimental results will be described below with reference to FIG.

Steam generated in a reactor pressure vessel 31 of a boiling water reactor passes through a main steam pipe 32, is supplied to a turbine 33, and rotates the turbine 33.

Steam exhausted from the turbine 33 is condensed in the condenser 34 and returned to cooling water.

Thereafter, the cooling water is returned to the reactor pressure vessel 31 through the demineralizer 35 and the feedwater heater 36.

On the other hand, the cooling water in the reactor pressure vessel 1 is transferred to the recirculation system piping 3.
7 and a part of it is cooled in a heat exchanger 38, and then radioactive ions and the like are removed in a demineralizer 39.

48 is a furnace purification system piping.

The sampling pipe 40 is connected to a furnace purification system pipe 48 that connects the heat exchanger 38 and the demineralizer 39.

An acidic solution tank 41 is installed on the upstream side of the sampling pipe 40.
．． An acidic solution injection system 46 consisting of an injection pump 42 and a regulating valve 43 is provided.

A pH meter 44 is provided downstream of the acid solution injection system 46 of the sampling tube 40 .

By opening the valve 47 provided in the sampling pipe 40, a portion of the cooling water flowing in the furnace purification system pipe 48 flows into the sampling pipe 40.

The pH of this cooling water is measured by a pH meter 44.

The pH meter 44 transmits the pH signal of the sample water to the adjustment valve 43.

Since the pH of the sample water is in the range of 6 to 7, the adjustment valve 4
3 opens, and the 0. OO1mol
The nitric acid solution (iii) is supplied into the sampling pipe 40.

As a result, the pH of the sample water flowing through the sampling pipe 40 is adjusted to a predetermined value of 5.5 or less.

However, if the pH of the sample water falls into the acidic range, there is a risk that substances originally attached to the sampling pipe 40 will be eluted, so the pH of the sample water should be 4.5 to 5.
It is desirable to set it in the range of 5.

60CO, which is a radioactive ion in the sample water, is collected by a collector 45 made of cation paper or ion exchange resin.

Although the length of the sampling pipe 40 is nearly 50 m, the amount of 60CO in the sample water adhering to the inner surface of the sampling pipe 40 is small, and most of the 60CO flowing into the sampling pipe 40 is collected by the collector 45.

The sample water that has passed through the collector 45 is processed in an equipment drain processing device that is a liquid waste processing system.

After passing the sample water through the collector 45 for a predetermined time,
The radioactivity of No. 5 is measured using a Ge (Li) semiconductor detector.

By lowering the pH of the sample water in this way, the radioactivity of the reactor cooling water and the chemical concentration of metal ions can be determined with high accuracy.

The pH of the sample water can also be lowered by injecting carbon dioxide gas into the sample water instead of an acidic solution.

The present invention can be applied to pressurized water reactors other than boiling water reactors and new converter reactors.

According to the present invention, the amount of radioactive substances adhering to the inner surface of the sampling pipe is significantly reduced, and the amount of radioactive substances in the coolant of a nuclear reactor can be measured with high accuracy.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing the relationship between the pH of sample water and the adhesion coefficient of 58CO, Figure 2 is a system diagram of the experimental equipment that confirmed the effects of the present invention, and Figure 3 is a preferred embodiment of the present invention. 1 is a system diagram of a boiling water reactor to which a reactor coolant sampling device is applied. 31... Reactor pressure vessel, 40... Sampling piping, 41... Acidic solution tank, 4
3...Adjustment valve, 44...pH meter, 45...Collector, 46...Acidic solution injection system.

Claims (1)

[Claims] 1. A pipe for sampling coolant of a nuclear reactor, means for measuring the pH of the sampled coolant flowing within the pipe, means for supplying a substance that lowers the pH of the coolant into the pipe, and A reactor coolant sampling device comprising means for controlling an amount of a substance that lowers the pH to be supplied into the piping so that the pH value measured by the pH measuring means is equal to or less than a predetermined value.