JPS5852599A - Treatment of radioactive waste liquid - 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 The present invention relates to an improvement in a method for treating radioactive waste liquid for reuse by removing turbid or dissolved substances.

The low-level radioactive waste liquid that is generated in the waste treatment facilities of nuclear power plants is evaporated and concentrated, the concentrated waste liquid is solidified, and the evaporated water is condensed and treated with ion exchange resin for reuse. are doing.

Incidentally, anion exchange resins are generally not very stable against heat or radiation, and partially decompose to produce amines (eg, trimethylamine) and alcohols (eg, methanol). These organic compounds inherently have low boiling points and easily volatilize, and other non-volatile organic compounds are also thermally decomposed during evaporation and concentration to produce volatile components, which are sent to the condenser along with water vapor.
Some of the organic compounds contained in the condensed water (mostly dissolved at °C) are adsorbed by the ion exchange resin, but some remain unadsorbed and circulate in the treated water. The adsorbed substances are also released when the ion exchange tree is regenerated, and since the regenerated waste liquid is treated together with the above-mentioned waste liquid treatment, it is eventually transferred to the treated water.

In this way, organic compounds tend to gradually accumulate in the recycled recycled water and must be removed.

Methods for removing organic compounds from water include adsorption using activated carbon, air stripping, and oxidative decomposition using ultraviolet rays plus chlorine, but there are issues with adsorption efficiency, secondary waste treatment, and equipment corrosion. Both methods are unsuitable for treating radioactive waste fluids due to their associated problems.

This time, the present inventors have discovered a method for removing organic compounds in waste liquid without the above-mentioned problems by oxidative decomposition using an oxidizing agent, particularly ozone or hydrogen peroxide, under irradiation with ultraviolet light.
We have established a method for treating radioactive waste liquid that incorporates this, and we would like to propose it here.

The radioactive waste liquid treatment method of the present invention is a treatment method in which the radioactive waste liquid is evaporated and concentrated, and the generated water vapor is condensed and recovered and reused. Our mission is to obtain recovered water that does not contain organic compounds by oxidizing and decomposing organic compounds contained in waste liquid or condensate by applying an oxidizing agent while irradiating ultraviolet rays. The concentrated waste liquid generated by evaporation concentration may be sent to a solidification system for treatment.

As the oxidizing agent, ozone or hydrogen peroxide is used as described above, and ozone is particularly useful as an electrophilic reagent such as an amine. These oxidizing agents have little risk of corroding equipment, and furthermore, after use, they decompose into harmless 02, I-1, and O, and do not accumulate.
There is no problem of secondary waste.

In the present invention, when performing oxidative decomposition of organic compounds using an oxidizing agent under ultraviolet irradiation prior to evaporative concentration, that is, when performing oxidative decomposition of the waste liquid to be evaporated and concentrated, an apparatus having the flow shown in Fig. 1 is used.・It will happen.

That is, the radioactive waste liquid Rw to be treated is first irradiated with ultraviolet rays in the oxidation treatment tank 1 and an oxidizing agent Ox is applied thereto to oxidize the organic compounds therein, and the effluent is sent to the evaporation concentration device 2. When ozone is blown in together with air as an oxidizing agent, the exhaust gas is passed through the mist catcher 3 and passed through a suitable exhaust gas treatment device 4 for treatment before being discharged. The concentrated waste liquid from the evaporative concentrator 2 is received in the concentrated waste liquid tank 5 and sent to the solidification process. The volatile components are condensed in a condenser 6, treated in an ion exchange resin tower 7, stored in a recovered water tank 8, and recycled for reuse.

On the other hand, when oxidative decomposition is performed after evaporative concentration, that is, when performing oxidative decomposition on condensate obtained by evaporative concentration, an apparatus having the flow shown in FIG. 2 is used. The steps in this case do not need to be explained again because only a part of the order is changed from that described above.

In general, the former mode, that is, the embodiment shown in Figure 1, is suitable to be carried out on waste liquids that are foamy or contain volatile organic substances during evaporative concentration, and the latter, that is, the embodiment shown in Figure 2, is suitable for evaporative concentration. Carry-y:g-bars are advantageous when waste liquids containing volatile organic compounds are to be treated.

Needless to say, the treatment method of the present invention can be carried out either batchwise or continuously. The conditions for oxidation treatment, such as the residence time in the tank, the intensity of ultraviolet rays, and the amount of oxidizing agent supplied, vary depending on the type and concentration of organic compounds contained in the waste liquid to be treated, but those skilled in the art will be able to use the examples given below. For reference, appropriate conditions can be easily found by performing some additional experiments if necessary.

According to the treatment method of the present invention, recovered water containing not only radioactive substances and salts but also organic compounds can be obtained from radioactive waste liquid, and can be suitably reused.

In this way, according to the invention, a closed system is realized for the treatment of radioactive waste liquid in the waste treatment facility of a nuclear power plant.

EXAMPLE Using an apparatus having the configuration shown in FIG. 1, it was found that the amount of condensate generated in the drying process of ion exchange resin was 5 tons/hour (7).

It was treated at a rate of This waste liquid contains I as an organic compound.
・Remethylamine 300ppm and methanol 1
．． Contains 5Orlr1m.

The oxidation treatment tank has a volume of 100 W and has an aeration tube at the bottom, through which air containing ozone is supplied at a rate of 0.5 f/min, and a mercury lamp with an output of 00 W is supplied. irradiated with ultraviolet light from

The decomposition rates of trimethylamine and methanol in the effluent from the tank were both about 99%.

The organic compounds in the condensate obtained by evaporation and concentration were within the detection limit. Hereinafter, the treated water was treated with an ion exchange resin according to a conventional method, and there was no problem in terms of reuse.

In order to understand the practical operating conditions or the limits of the equipment's capacity, we treated a waste liquid containing 170 ppm of methanol and shortened the residence time of the liquid in the oxidation treatment tank. The decomposition rate was obtained. From this graph, it can be seen that in the device used, 80
Almost complete oxidative decomposition can be achieved by giving a liquid residence time of about 1 minute (8)

[Brief explanation of drawings]

1 and 2 are flowcharts for explaining the radioactive waste liquid treatment method of the present invention. FIG. 2 shows a mode in which the oxidative decomposition of an organic compound is carried out on condensate obtained by an evaporative concentration operation. FIG. 3 is a graph showing the effects of the embodiment of the present invention. 1... Oxidation treatment tank 2... Evaporation concentration device 6... Condenser 7... Ion exchange resin column patent applicant JGC Corporation

Claims (5)

[Claims] (1) In a treatment method in which the water vapor generated by evaporating and concentrating radioactive waste liquid is condensed and recovered for reuse, the waste liquid undergoing evaporative concentration or the condensate obtained after evaporative concentration is oxidized while being irradiated with ultraviolet rays. 1. A method for treating radioactive waste liquid, which comprises oxidizing and decomposing organic compounds contained in the waste liquid or condensate by applying an agent to obtain recovered water. (2) The treatment method according to claim 1, wherein ozone or hydrogen peroxide is used as the oxidizing agent. (3) A two-step method in which organic compounds contained in waste liquid or condensate are first treated with an oxidizing agent to oxidize and decompose a portion of them, and then irradiated with ultraviolet rays and treated with an oxidizing agent to decompose the remainder. The processing method according to claim 1. (4) The treatment method according to claim 1, wherein the radioactive waste liquid containing an organic compound is a radioactive waste liquid obtained by condensing vapor generated by drying a radioactive ion exchange resin. (5) The treatment method according to claim 1, which includes a step of sending the concentrated waste liquid generated in the evaporation concentration step to a solidification system for treatment.