METHOD FOR RECYCLING PLUTONIUM FROM SPENT RADIOACTIVE FUEL

Abstract

The present invention relates to a method for recovering plutonium from spent radioactive fuel. In one embodiment, the method comprises steps of extracting tetravalent plutonium from an aqueous solution of the spent radioactive fuel using a first organic solvent comprising tributyl phosphate; reducing tetravalent plutonium to trivalent plutonium by adding to an organic phase a second organic solvent comprising dimethylhydroxylamine; and stripping plutonium into the aqueous phase for recycling by adding an aqueous dilute acid solution into an organic phase. The method can significantly improve the efficiency of recovering plutonium from spent radioactive fuel compared with HAN stripping, and at the same time, can avoid the problems resulting from U(IV) reduction and extraction.

Claims

1. A method for recovering plutonium from spent radioactive fuel, comprising the following steps: (i) extracting tetravalent plutonium from an aqueous solution of the spent radioactive fuel using a first organic solvent comprising tributyl phosphate; (ii) reducing tetravalent plutonium to trivalent plutonium by adding to an organic phase a second organic solvent comprising dimethylhydroxylamine; and (iii) stripping plutonium into the aqueous phase for recycling by adding an aqueous dilute acid solution into an organic phase.

2. A method according to claim 1, wherein the first organic solvent comprising tributyl phosphate is a mixture of tributyl phosphate and alkanes.

3. A method according to claim 1, wherein the second organic solvent comprising dimethylhydroxylamine is a mixture of dimethylhydroxylamine and organic solvent comprising tributyl phosphate.

4. A method according to claim 1, wherein in step (ii), a volume ratio of the organic phase and the second organic solvent comprising dimethylhydroxylamine is 1:10-10:1.

5. A method according to claim 1, wherein in step (ii), a reaction time of the reduction of plutonium is 0.1-10 minutes.

6. A method according to claim 1, wherein the dilute acid aqueous solution is dilute nitric acid aqueous solution.

7. A method according to claim 6, wherein the dilute nitric acid aqueous solution comprises methyl hydrazine (MMH) or hydrazine.

8. A method according to claim 7, wherein the dilute nitric acid aqueous solution comprises 0.1-1.0 mol/L nitric acid and 0.05-0.3 mol/L methyl hydrazine or hydrazine.

9. A method according to claim 1, wherein in step (iii), a volume ratio of the organic phase to the dilute acid aqueous solution is 1:10-10:1.

10. A method according to claim 1, wherein a stripping time for step (iii) is 0.1-10 minutes.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0027] FIG. 1 shows the absorption spectrum of Pu before and after reaction with DMHAN in organic phase.

[0028] FIG. 2 is an illustrative flowchart of a method for complementary Pu stripping from organic phase.

DETAILED DESCRIPTION OF THE INVENTION

[0029] The specific embodiments of the present invention are further described in combination with the embodiments and the attached drawings, and the concentrations herein are all percentage by volume unless otherwise specified.

Example 1: Effects of Organic Phase Containing DMHAN on Reduction of Pu(IV)

[0030] A solution of 30% TBP/n-dodecane which contained 1.02 g/L Pu was exposed to radiation, receiving an irradiation dose of 1.4 Wh/L, which produced about 100 mg/L HDBP. Absorption peaks in the region of 720 nm and 740 nm appeared, which were characteristics of the Pu(IV)-HDBP complex. Above-mentioned Pu-containing organic phase was thoroughly mixed with the same volume of a 30% TBP solution containing 0.31 mol/L DMHAN, in less than five seconds of mixing, brown Pu(IV) in solution was reduced to blue Pu(III), and after 1 minute of mixing, absorption peaks in the region of 570 and 605 nm appeared, which were the characteristics of Pu(III), and absorption peaks in the region of 720 nm and 740 nm disappeared, which were characteristics of Pu(IV), as shown in FIG. 1. The absorption spectrum results showed that reduction of Pu(IV) by DMHAN in organic solution was complete, even in the presence of HDBP.

[0031] For the above TBP organic phase containing HDBP, if Pu was stripped with 0.50 mol/L HNO.sub.3 containing HAN, the absorption peaks of Pu (IV)-HDBP complex in the region of 720 nm and 740 nm were almost unchanged, indicating that HAN could not strip Pu(IV)-HDBP complex.

Example 2: Complementary Stripping Test of Pu in Organic Phase

[0032] A complementary stripping test of plutonium in organic phase was designed. The flow chart is shown in FIG. 2.

[0033] Most of Pu(IV) was stripped in 2B tank by dilute nitric acid aqueous solution containing DMHAN and MMH, and the concentration of nitric acid and nitrite in organic phase was reduced to avoid adverse effects on the subsequent reaction of DMHAN with Pu(IV) inorganic phase. Due to the low concentration of plutonium in the organic phase in 2B tank, the stripping series of plutonium in 2B cell could be reduced appropriately;

[0034] The organic phase with a small amount of Pu (IV) in the 2B tank after stripping entered the organic phase reaction tank and reacted with 30% TBP containing DMHAN. The organic phase after the reaction contained Pu (III) and DMHAN and flowed into the 2BXX tank.

[0035] In the 2BXX tank, the dilute nitric acid solution containing MMH was used for multistage stripping of Pu(III) in the organic phase. Pu(III) and DMHAN entered the aqueous phase, and the effluent organic phase was recycled by alkali washing. The aqueous phase in 2BXX tank containing low concentration of Pu(III) and high concentration of DMHAN could be used as stripping agent for 2B tank after proper adjustment.

[0036] The 30% TBP/n-dodecane organic phase contained 65.4 g/LU and 16.61 g/L Pu. TBP was exposed to alpha radiation by Pu within the organic phase. After different time, the irradiation doses of TBP were 5.53 Wh/L, 11.1 Wh/L and 25.8 Wh/L, respectively. Pu was stripped by the above process. The content of Pu in the polluted solvent was less than 5 mg/L, and the content of DMHAN was less than 1*10.sup.4 mol/L.

[0037] In contrast, dilute acid containing hydroxylamine was directly used to strip the above-mentioned alpha-irradiated organic phase. The residual concentrations of Pu in the organic phase were 222 mg/L, 346 mg/L and 646 mg/L, respectively.

Example 3: Comparing Different Ways of Recovering Plutonium from Organic Phase

[0038] The plutonium-containing organic phase (29% TBP-1% HDBP-0.158 g/LPu-0.250 mol/LHNO.sub.3) was prepared and used for plutonium stripping in different ways. The operating conditions and the effects of plutonium stripping are shown in Table 1. As can be seen from Table 1, since the amount of HDBP was much larger than that of plutonium, direct use of HAN for stripping Pu in organic phase had little effect (without reduction of Pu (IV) in organic phase, so the rate of reduction of Pu (IV) in direct stripping process was very slow). Direct use of DMHAN for plutonium stripping was also limited (without reduction of Pu (IV) in organic phase, therefore, although the speed of reducing Pu(IV) in direct stripping was higher than that of direct stripping with HAN, it still can not meet the requirements). The effect of Pu stripping can be significantly improved by using DMHAN to reduce Pu (IV) in organic phase and then carrying out stripping.

[0039] Obviously, those skilled in the art can make various changes and variations to the invention without departing from the spirit and scope of the invention. In this way, if these modifications and variations of the invention fall within the scope of the claims of the invention and its equivalent technology, the invention also intends to include these modifications and variations. The above-mentioned embodiments are merely illustrations of the present invention, which can also be implemented in other specific ways or other specific forms without departing from the essence or essential features of the present invention. Therefore, the described embodiments should be considered illustrative rather than restrictive in any way. The scope of the present invention shall be explained by appended claims, and any change equivalent to the intention and scope of the claims shall also be included in the scope of the present invention.

TABLE-US-00001 TABLE 1 Comparing different methods for stripping plutonium Concentration of plutonium in organic phase Stripping methods after stripping (g/L) Specific operating conditions Direct stripping 0.155 The organic phase containing plutonium using HAN as was stripped with 0.1 mol/L stripping agent HAN-0.5 mol/L nitric acid -0.1 mol/L MMH at a volume ratio of 1:1 for 2 min. Direct stripping 0.925 The organic phase containing plutonium using DMHAN was stripped with 0.1 mol/L as stripping agent DMHAN-0.5 mol/L nitric acid-0.1 mol/L MMH at a volume ratio of 1:1 for 2 min. Stripping after 1.82 10.sup.2 After the reaction of 30% TBP-0.31 reactions in mol/L DMHAN with organic phase organic phase containing plutonium at volume ratio 1:1 for 1 min, the organic phase containing plutonium was stripped with 0.1 mol/L HAN-0.5 mol/L nitric acid-0.1 mol/L MMH at volume ratio 1:1 for 1 min.