JPS592360B2 - How to dispose of radioactive waste liquid - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for treating radioactive waste liquid.

More specifically, the present invention relates to a method for removing radioactive substances from radioactive waste liquid, which is difficult to treat by conventional waste liquid treatment methods because the concentration of radioactive substances contained therein is extremely low.

Conventional methods for treating radioactive waste liquid include (b) Evaporation treatment (b) Ion exchange treatment (c) Coagulation sedimentation treatment ) Dehydration filtration treatment (e) Freeze-re-thaw treatment and (f) Foam separation treatment etc. have been adopted.

In the case of these conventional treatment methods, the decontamination coefficient (Note 1) is generally low, on the order of one to two digits.

Further, in the case of evaporation treatment, a decontamination coefficient of 103 to 105 or more can be expected, but it has the drawback of high cost.

(Decontamination Factor: D
F) Conventional technology has a low decontamination coefficient of 1 to 2 digits,
Although it can be applied to general industrial wastewater where the concentration range of harmful elements is about ppm,
It cannot be expected to be effective against radioactive waste liquids, which are required by law to be decontaminated to a level of pm before being disposed of.

In other words, even if the concentration of radioactive substances contained in radioactive waste liquid is sufficiently low, it may be extremely dangerous to biological systems in terms of radioactivity concentration [amount of radioactivity per unit volume (μCi/crt)]. This is because this is a characteristic of radioactive waste liquid.

For example, in the case of 58Co, the content in the liquid is 110-6pp.
Even at such a low concentration, the radioactivity concentration is 0.03μCi.
It is a dangerous (medium level) waste liquid called 〆琥.

(According to Science and Technology Agency Notification No. 22, the permissible concentration in water is 9xlO.
'μCi is employed.

Notification No. 22 Attached Table 1) Normal industrial wastewater treatment technology reduces the concentration of harmful substances contained in wastewater from several ppm to 110-3p.
It is aimed at the case of p, and is 10-4 to 110
The technical idea is essentially different from the radioactive waste liquid treatment technology whose purpose is to remove extremely small amounts of radioactive substances of 10 pp.

In general, in extremely low concentration solutions, even if the substances contained are of the same type, they exhibit complex behavior that differs from macroscopic amounts.

Therefore, in many cases, conventional general industrial wastewater treatment techniques cannot be applied at all in principle.

Therefore, conventionally in the field of nuclear power production, centered on nuclear power plants, a method has been adopted in which the radioactive waste liquid is completely evaporated, the condensed water is released into the general environment, and the radioactive elements are concentrated in the slurry that evaporates and remains. was.

As mentioned above, this treatment technology has a high decontamination coefficient and is capable of stable operation for a wide variety of radioactive waste liquids, but it also has the disadvantage of high costs, and in fact, it reduces fuel costs and other costs. The current situation is that they are adopted without considering economic efficiency.

As a result of extensive research, the present inventors have found that by subjecting radioactive waste to direct current electrolysis using aluminum or aluminum alloy as an anode, aluminum dissolves at the anode and reacts with water to precipitate aluminum hydroxide, as shown in the following equation. is generated and hydrogen gas is generated at the cathode.

Anode Cathode AZ+3 H20-+At(OH) 3. ! ,+3H
2 The aluminum hydroxide produced is highly active and can adsorb and remove extremely low concentrations of harmful nuclides in waste liquid.

This anodic reaction proceeds even with a single-element aluminum anode, but if electrolysis continues for a long time, passivation may occur, so alloys with indium, gallium, sodium, lithium, etc. are used as the anode. It is more preferable.

When used as an alloy, its composition is 0.1 to 1% by weight in the case of indium or gallium, and 0.1% by weight in the case of sodium.
The content can be increased by 0.01 to 0.1% by weight.

Therefore, an object of the present invention is to provide a new method for efficiently and economically removing harmful radionuclides from a radioactive waste liquid containing extremely low concentrations of 10 to 10 ppm.

Radionuclides that can be efficiently separated and removed by the method according to the present invention include (A) heavy metal elements such as 51Cr, 58Co, and 60Co;
(B> ) Lantide elements such as 4°La, 3Ce,
(C) Actinide elements such as 23"P u + ""9Np, etc.

Among them, heavy metal radionuclides such as chromium and cobalt are 102
With a decontamination coefficient of ~104, it can be separated and removed extremely efficiently.

Furthermore, the treatment method according to the present invention varies from a high level to a low level depending on the pH of the radioactive waste liquid, that is, the radioactivity concentration is 106μ.
It can be applied to radioactive waste liquids ranging from CiΔml to 10-6μCi.

That is, when applying the present invention, the pH of the radioactive waste liquid is
It is necessary to adjust the concentration to about 9, and this cannot be expected for strongly acidic and strongly alkaline radioactive waste liquids.

In addition, although it cannot be expected to be effective against radionuclides of alkali metals such as lithium, sodium, and potassium, and alkaline earth metals such as magnesium and calcium, it is effective against strontium among alkaline earth metals. .

Hereinafter, the structure and effects of the present invention will be specifically explained with reference to Examples.

It should be noted that the Examples list the modes in which the effects of the present invention are most prominently exhibited, and the present invention is not limited to these Examples.

In addition, in the examples, the radioactivity concentration is μCi, and the lagoon content is pp.
Represented by m.

Example I UO21TIIi was irradiated in a nuclear reactor, dissolved in HNO3, dried and dissolved in 100 yd of water, and the pH was adjusted to 7 with NaOH.The solution was used as a radioactive waste liquid to be treated.

This radioactive waste liquid was electrolyzed using an aluminum alloy containing 0.5 weight of indium as an anode and a stainless steel plate as a cathode at a direct current concentration of 0.5 people/l and an electrolysis time of 90 minutes.

The radioactive concentration (tt Ci/7') El content (ppm) of the precipitate suspended in the waste liquid after electrolytic treatment was separated by furnace using Toyo Filter Paper A5C, and the decontamination factor (DF) was compared with the value before electrolysis. )
I asked for

The results are shown in Table-1.

Example 2 Stainless steel 17711! was irradiated in a nuclear reactor, dissolved in aqua regia, evaporated to dryness, dissolved in 100-g water, and purified with NaOH.
The liquid with H adjusted to 7 is fi as the radioactive waste liquid to be treated.
However, the same method as in Example 1 was repeated except that an aluminum alloy containing 0.05% by weight of lithium was used as the anode.

The results of the experiment are shown in Table-2.

Example 3 1 ml of nickel sheet was irradiated in a nuclear reactor, dissolved with HNO3, 58Co was separated with an ion exchange resin, and NaOH
The method of Example 1 was repeated except that the solution whose pH was adjusted to 7 was used as the radioactive waste solution to be treated, and a single-element aluminum anode was used.

The results of the experiment are shown in Table 3. Table 3 Example 4 Pu waste liquid from spent nuclear fuel reprocessing facility of Japan Atomic Energy Research Institute (
The procedure of Example 1 was repeated, except that the effluent was diluted approximately 60 times with ~4NHNO3) and used as the radioactive waste fluid to be treated.

The results are shown in Table 4.

Table 4 As is clear from the results of Examples 1 to 4, many radionuclides can be removed from radioactive waste liquid according to the present invention.

For example, for 239Np, the content is 1.7 x 1
Even if the concentration is as low as 00-7pp, the radioactivity concentration is 41. As a result of treating radioactive waste liquid, which is quite dangerous with an OX of 10-2μC1, by the method of the present invention, 239 Np was removed with a high decontamination coefficient of over 600.

Also, for 140LaK, the content is 3.4X10-9pp
As a result of treating a radioactive waste liquid with a radioactivity concentration of 1.9×10 −3 μC1 by the method of the present invention, 140 La was removed with a high decontamination coefficient of 160 or more.

For 58Co, the content is 3.15X10-6p p
rn, a radioactive waste liquid with a radioactivity concentration of 0.1 μCi Al11 was treated with the method of the present invention, resulting in a high decontamination coefficient of 230 and 58c.

has been removed.

In addition, 239, which is considered to be particularly harmful, has become a problem.
As for Pu, 239Pu was removed with a high decontamination coefficient of 200 when a radioactive waste liquid with a content of 4.9xlO-3ppm1 and a radioactivity concentration of 3.6x10-'μCi/Tll was treated by the method of the present invention.

211-

Claims (1)

[Claims] 1. A waste liquid containing radioactive nuclides is subjected to electrolysis using aluminum or an aluminum alloy as an anode, and the radioactive nuclides in the waste liquid are adsorbed and removed by the highly active aluminum hydroxide produced thereby. Processing method.