JPH07198894A - Method for treating radioactive waste liquid - Google Patents

Abstract

PURPOSE:To reduce the concentration of each element included in waste liquid to below an exhaust water monitoring standard by removing such alpha and/of betadecay species as uranium, UD (radioactive decay species of uranium), FP (nuclear fission products), TRU (transuranium elements) and fluorine out of radioactive waste liquid. CONSTITUTION:Calcium compound and iron chloride are added to alkaline radioactive waste liquid including uranium, UD, FP, and TRU and besides fluorine and stirred, and the precipitation agglomerated by the stirring is filtered and removed from the stirred liquid. This filtrate is controlled to have pH of 3 or less by adding nitric acid and to this pH-controlled liquid, selected one or two kinds of compound out of the group consisting of lathanoid compound, titanium compound, zirconium compound and hafnium compound are added to dissolve or mix the compound. After controlling the pH to 9 or more by adding alkaline solution to this solution or mixture liquid, the precipitate agglomerated by the pH-control is filtered and removed from the pH-controlled liquid.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to uranium which is an α and / or β decay nuclide, a radioactive decay nuclide of uranium (hereinafter referred to as UD) and a fission product (hereinafter referred to as FP).
And uranium, UD, FP from alkaline radioactive waste liquid containing transuranium element (hereinafter referred to as TRU) and fluorine
And TRU and fluorine are removed to remove uranium and U in the waste liquid.
The present invention relates to a treatment method for reducing the contents of D, FP, TRU and fluorine, respectively.

[0002]

BACKGROUND OF THE INVENTION Cylinders containing uranium hexafluoride used to produce UO ₂ pellets are cleaned after being used and before being filled with new uranium hexafluoride. In addition to fluorine and uranium, this cleaning solution contains β decay nuclides such as thorium which is a daughter nuclide of uranium. Discharging this cleaning liquid as it is from the plant is a problem in terms of environmental protection. For this reason, wastewater management standards are set for each contained element, and radioactive waste liquid, which is a cleaning liquid, is treated so that it falls below each wastewater management standard before being discharged from the plant. Conventionally, as shown in FIG. 3, an aqueous solution of an alkaline compound such as NaOH is added to a uranium-containing solution that is a cylinder cleaning solution and stirred, and the stirring solution is filtered to remove the aggregated uranium precipitate by stirring. Done.
The radioactive liquid waste obtained by the stirring step 1 and the preliminary filtration step 2 was treated by the following method. That is, this treatment method is a step 3 in which slaked lime and iron chloride are added to the radioactive waste liquid that is the filtrate of the filtration step 2 and stirred, and a calcium and iron fluoride aggregated by the filtration of this stirred solution by stirring. It consisted of a filtration step 4 for removal and an ion exchange step 5 for removing the residual uranium and β-decay nuclide such as thorium which is a daughter nuclide of uranium by passing the filtrate through an ion exchange column.

[0003]

This conventional coagulation-sedimentation treatment method requires not only an expensive ion-exchange resin but also a solid waste containing a used ion-exchange resin which is not easily treated. There was such a problem. Moreover, this treatment method was effective as a waste liquid treatment method for the washing liquid of natural concentrated uranium, but a small amount of FP and TRU
However, it has a drawback that it cannot be applied to the case of the recovered uranium-enriched uranium mixed with. That is, although fluorine can be treated at a concentration lower than the wastewater management standard value of 15 ppm, for α decay nuclides, the wastewater management standard value of α waste liquid is: 1
× 10 ^-2 Bq / cm ³ and β for β decay nuclides
The wastewater management standard value of the waste liquid was 3 × 10 ⁻¹ Bq / cm ³ and there was a drawback that it could not be treated to a radioactivity concentration below both.

The object of the present invention is to remove uranium, UD, FP, TRU and fluorine from radioactive waste liquid containing uranium, UD, FP and TRU and fluorine, and to remove each element contained in the waste liquid as a wastewater management standard. It is to provide a method for treating radioactive waste liquids, each of which reduces the radioactivity concentration below the specified value.

[0005]

In order to achieve the above object, as shown in FIG. 1, the treatment method of the present invention comprises uranium, which is an α and / or β decay nuclide, radioactive decay nuclide of uranium, and fission production, respectively. Of Ca (OH) ₂ , CaO, and C in alkaline radioactive waste liquid containing substances and transuranic elements and fluorine
a step 13 in which a calcium compound such as aCO ₃ and iron chloride are added and stirred, and a first filtration step 14 in which a precipitate aggregated by the stirring in the step 13 is removed by filtering from the stirring liquid in the step 13. A first pH adjusting step 15 of adjusting the pH to 3 or less by adding nitric acid or nitric acid and iron chloride to the filtrate of the step 14, and a lanthanoid compound, a titanium compound, a zirconium compound and a hafnium compound in the pH adjusting solution. Step 16 of adding one or more compounds selected from the group consisting of to dissolve or mix the compounds, and N in the solution or mixture of Step 16.
A second pH adjusting step 17 in which an alkaline solution such as H ₄ OH solution or NaOH solution is added to adjust the pH to 9 or more, and a precipitate aggregated by the pH adjusting in the step 17 is filtered from the pH adjusting solution in the step 17. Second to remove by separating
This is a method including a filtration step 19.

The radioactive waste liquid stirred in the stirring step 13 is adjusted to pH 1 by adding an alkali solution to a uranium-containing solution, which is a cylinder cleaning solution, and stirring the solution as shown in FIG.
After the stirring step 11 of 0 or more, the uranium precipitate aggregated by the stirring is preliminarily filtered out from the stirring solution to be removed by the preliminary filtration step 12.

[0007]

After adding the calcium compound and iron chloride to the radioactive waste liquid of the present invention in the stirring step 13, fluorine is mainly removed as a fluoride in the first filtering step 14. Further step 1
After adjusting the filtrate to an acidic side having a pH of 3 or less in step 5, dissolving or mixing the lanthanoid compound, titanium compound, zirconium compound or hafnium compound in step 16, and bringing the pH to the alkaline side of 9 or more again in step 17, Two
In the filtration step 19, the α and / or β decay nuclides are removed as aggregate precipitates of lanthanoid compound, titanium compound, zirconium compound or hafnium compound. Particularly, a feature of the present invention is that the lanthanoid compound in step 16,
It is to add a titanium compound, a zirconium compound or a hafnium compound, and to coagulate and precipitate these compounds in step 19 to simultaneously remove α and / or β decay nuclides. As the lanthanoid compound, LaCl ₃ , CeCl ₃
And the like, and TiCl ₄ is exemplified as the titanium compound. The zirconium compound is exemplified by ZrCl ₄ , and the hafnium compound is exemplified by HfCl ₄ .

[0008]

EXAMPLES Next, examples of the present invention will be described in order to show specific embodiments of the present invention. The examples described below do not limit the technical scope of the present invention.

<Example 1> Fluorine concentration 340 ppm, α
(Uranium) Concentration = 6.96 × 10 ³ Bq / cm ³ and β Concentration = 5.72 × 10 ³ Bq / cm ³ 0.5 liter of cylinder cleaning liquid containing 15 N NH ₄ OH solution 20 c
m ^{3 was} added and stirred for 30 minutes. The precipitate which was aggregated by this stirring was filtered off, and Ca (OH) ₂ was added to the obtained filtrate in an amount of 0.
Add 95 g and 1 cm ³ of FeCl ₃ with a concentration of 37%,
Stir for minutes. The precipitates aggregated by this stirring were separated by filtration, and 15 cm ³ of nitric acid having a concentration of 6 N and 1 cm ³ of FeCl ₃ having a concentration of 37% were added to the obtained filtrate to adjust the pH to 2-3. To this pH adjusting solution, 50 mg of commercially available CeCl ₃ .7H ₂ O was added and dissolved. 25% Na in this solution
The pH was adjusted to 9 to 10 by adding 10 cm ^{3 of the} OH solution. The aggregated precipitate was filtered off by this pH adjustment, and the fluorine, α concentration and β concentration contained in the obtained filtrate were measured. The results are shown in Table 1 and FIG.

[0010] were treated <Example _2> CeCl ₃ · 7H 2 O cylinder washes were repeated, except that a commercially available LaCl ₃ · 7H ₂ O was added 50mg of Example 1 in place of. The fluorine, α concentration and β concentration contained in the finally obtained filtrate were measured. The results are shown in Table 1 and FIG.

Example 3 Example 1 except that 50 mg of commercially available TiCl ₄ was added instead of CeCl ₃ .7H ₂ O.
The cylinder cleaning liquid was treated in the same manner as in. The fluorine, α concentration and β concentration contained in the finally obtained filtrate were measured. The results are shown in Table 1 and FIG.

Example 4 Example 1 except that 50 mg of commercially available ZrCl ₄ was added instead of CeCl ₃ .7H ₂ O.
The cylinder cleaning liquid was treated in the same manner as in. The fluorine, α concentration and β concentration contained in the finally obtained filtrate were measured. The results are shown in Table 1 and FIG.

[0013]

[Table 1]

As is clear from Table 1, the concentrations after the treatments of Examples 1 to 4 can be treated to a concentration lower than 15 ppm of the wastewater management standard value for fluorine, and for α decaying nuclides such as uranium. α Wastewater drainage control standard value:
Treated to a concentration of 1 × 10 ^-2 Bq / cm ³ or less, and for β-decay nuclides such as uranium radioactive decay nuclides to a drainage management standard value of β waste liquid: 3 × 10 ^-1 Bq / cm ³ or less. We were able to.

[0015]

As described above, in comparison with the conventional treatment method, in the treatment method of the present invention, the decontamination coefficient of the waste liquid is 2 in α-activity.
The radioactivity increases by about one digit in terms of β and β activity, and fluorine, uranium, and α and / or β decay nuclides other than uranium can be treated at concentrations below the drainage control standard value. Further, instead of using an expensive ion exchange resin, lanthanoid compounds, titanium compounds, zirconium compounds and hafnium compounds, which are easily available and can be used in small amounts, are used.
Since there is no generation of used ion exchange resin or the like that is not easy to process, there is an advantage that the processing cost is lower than in the past as a result.

[Brief description of drawings]

FIG. 1 is a process diagram of a method for treating radioactive waste liquid according to the present invention.

FIG. 2 is a graph showing decontamination coefficients of α-activity and β-activity for each additive of the examples of the present invention.

FIG. 3 is a process diagram of a conventional radioactive waste liquid treatment method.

Claims (4)

[Claims] 1. An alkaline radioactive liquid waste containing fluorine and one or more of uranium, a radioactive decay nuclide of uranium, a fission product, and a transuranium element, which are α and / or β decay nuclides, respectively. A step (13) of adding a calcium compound and iron chloride and stirring, and a precipitate aggregated by the stirring of the step (13) in the step (1).
The first filtration step (14) of removing the agitated liquid of 3) by filtering, and the first pH adjusting step (15) of adjusting the pH to 3 or less by adding nitric acid to the filtrate of the step (14). A lanthanoid compound, a titanium compound,
A step (16) of dissolving or mixing the compound by adding one or more compounds selected from the group consisting of a zirconium compound and a hafnium compound, and an alkaline solution in the solution or mixture of the step (16) And a second pH adjusting step (17) for adjusting the pH to 9 or more, and a precipitate aggregated by the pH adjusting in the step (17) is removed from the pH adjusting solution in the step (17) by filtration. A method of treating radioactive waste liquid, which comprises a second filtration step (19). 2. The alkaline solution added in step (17) is NH
_The method for treating radioactive waste liquid according to claim 1, which is a ₄ OH solution or a NaOH solution. 3. The method for treating radioactive waste liquid according to claim 1, wherein the calcium compound added in the step (13) is Ca (OH) ₂ , CaO or CaCO ₃ . 4. The method for treating radioactive waste liquid according to claim 1, wherein iron chloride is added to the filtrate together with nitric acid in the first pH adjusting step (15).