JPS6247593A - Method of reducing radioactivity of nuclear reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a primary cooling system of a nuclear power plant, and more particularly to a method for reducing radioactivity for reducing radiation exposure of workers during periodic inspections and the like.

[Background of the invention]

Japanese Patent Application Laid-Open No. 56-1480 describes a method for reducing radioactivity in nuclear reactors.
As shown in Japanese Patent No. 99, there is a method of adding ammonia to cooling water. This method uses ammonia to capture Co ions, which account for most of the surface dose of pipes, to prevent them from adhering to pipes, etc., but it does not take into account radioactive metals that have already become oxides.

[Purpose of the invention]

An object of the present invention is to add β-diketone to the primary cooling water of a nuclear reactor, thereby preventing an increase in the radiation dose rate of piping and reducing the exposure dose of workers during periodic inspections and the like.

[Summary of the invention]

The cause of the increase in radiation dose rate in the piping of the reactor secondary cooling system is
This is the adhesion of cladding mainly composed of iron oxide to piping.

In the present invention, by adding β-diketone to cooling water, metal oxides are dissolved and metal ions are captured, thereby preventing an increase in the radiation dose rate of piping.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a schematic diagram of a boiling water nuclear power plant using the present invention. A boiling water nuclear power plant is a nuclear reactor.1. Turbine 2. Condenser 3. Condensate purification bag @4. It is composed of a reactor coolant purification device 5 and the like. According to the present invention, it is the reactor coolant recirculation system piping 6 and the reactor coolant purification system piping 7 that are intended to prevent an increase in radiation dose rate. When β-diketone is added to the reactor cooling water, the β-diketone dissolves and traps metal ions and iron oxides, which are the main components of the cladding, in the reactor 1 and piping 6.7 through the following reaction.

Fes++3HacaenFs(acac)s+3H+
Co”+ + 2Hacac→Co(a, cac)x+
2H÷FszOa + 6Hacac-+ 2Fa(a
cac) a + 3HzOFeaOa + 8) 1a
cac→2Fa(acac)s+Fe(acac)z+
4Hz.

However, Hacac represents acetylacetone, which is a type of β-diketone. Although the metal β-diketone complex produced by the above reaction is a neutral molecule that is slightly soluble in water, the total amount of metal in the reactor cooling water is 10 ppb or less. It is completely soluble in water. This prevents the clad from adhering to the piping and prevents the radiation dose rate of the piping from increasing. When carrying out the present invention, a certain amount of β-diketone is injected from the chemical tank 8 between the condensate purification device 4 and the nuclear reactor 1. The amount of β-diketone injected is an amount corresponding to the radiolysis of β-diketone in the 1M slave reactor, and the β-diketone concentration in the reactor cooling water is kept constant. The β-diketone added in this manner undergoes the reaction described above within the reactor 1 and piping. In boiling water, β-diketone complexes of metals undergo repeated decomposition and formation through the following reaction, as β-diketones evaporate together with water.

Fast 2Fe (acac) a + 6Hx0 6
Hacac + 2Fe (OR) 5Fezes +
3HtO+ 6Hacac However, the reaction of iron hydroxide produced by decomposition to become iron oxide is slow, and the β-
Since the diketone complex formation reaction is fast, the removal of the zero-order metal β-diketone complex will be explained so that the cladding will not adhere to the piping or the like again. Because the complex is a neutral molecule, it cannot be removed by ion exchange resins commonly used for atomic couplant water treatment. Therefore, it is necessary to use a reverse osmosis membrane or the like in the reactor coolant purification device 5.

Note that, except for special types, β-diketones are composed of carbon, hydrogen, and oxygen, so that what is produced by radiolysis is carbon dioxide, oxygen, hydrogen, water, etc., and there is no problem.

〔Effect of the invention〕

An experiment to demonstrate the effects of the present invention will be described.

A dissolution experiment of iron(II) oxide (m) in an aqueous solution of acetylacetone, which is a type of β-diketone, was conducted.

An example of the results is shown in Figure 2. Figure 2 shows the elapsed time and dissolved iron when iron oxide (n) (m) sintered to a size of φ20xt5I was added to an acetylacetone 0.01 mo 12/Q aqueous solution. It shows the relationship between quantities.

It turns out that beta-diketones effectively dissolve iron oxide. Therefore, according to the present invention, it is possible to prevent the crud in the reactor cooling water from adhering to the piping, and it is possible to prevent an increase in the radiation dose rate of the piping and, in turn, to reduce the exposure dose of workers.

[Brief explanation of the drawing]

FIG. 1 is a schematic system diagram of a boiling water nuclear power plant using the present invention, and FIG. 2 is a diagram showing experimental results demonstrating the present invention. 1... Nuclear reactor, 2... Turbine, 3... Condenser,
4... Condensate purification device, 5... Reactor coolant purification device, 6... Reactor coolant recirculation system piping, 7... Reactor coolant purification system piping, 7... Drug tank.

Claims (1)

[Claims] 1. A method for reducing radioactivity in a nuclear reactor, which comprises adding β-diketone to the reactor primary cooling water.