Abstract
This study presents an experimental investigation on Zr separation from Zr-2.5Nb by anode potentiostatic electrorefining in LiCl-KCl-ZrCl4 0.5 wt. % at 773 K for irradiated CANDU pressure tube decontamination. By the ORIGEN-2 code calculation, radioactive characteristics were investigated to show that Nb-94 was the most significant radionuclide with an aspect of waste level reduction by electrorefining. Three electrorefining tests were performed by fixing the applied potential as −0.9 V (vs. Ag/AgCl 1 wt. %) at the anode to dissolve only Zr. A cathode basket was installed to collect detached deposits from the cathode. Electrorefining results showed Zr was deposited on the cathode with a small amount of Nb and other alloying elements. The chemical form of the cathode deposits was shown to be only Zr metal or a mixture of Zr metal and ZrCl, depending on the experimental conditions related to the surface area ratio of the cathode to the anode. It was determined that the Zr metal reduction at the cathode was attributed to the two-step reduction reaction of Zr4+/ZrCl and ZrCl/Zr.
Highlights
Zr alloy has been extensively used in nuclear fuel cladding, since Zr has corrosion resistance and a low neutron capture cross-section [1,2]
Black powdery precipitate was found at the bottom of the electrorefining cell and cathode basket in5 toefs1t0s 1 and 2, respectively, as shown in Figures 3a and 4a
For volumetric decontamination of the CANDU pressure tube, Zr separation was performed from Zr-2.5Nb alloy by anode potentiostatic electrorefining
Summary
Zr alloy has been extensively used in nuclear fuel cladding, since Zr has corrosion resistance and a low neutron capture cross-section [1,2]. The CANDU pressure tube is made of Zr-2.5Nb alloy to endure high temperature, pressure, and radioactivity during its long-term operation. The activity concentration limit of Nb-94 for the Gyeongju low- and intermediate-level waste (LILW) disposal facility is much smaller than the radioactivity caused by Nb-94 in several types of irradiated Zr-Nb components [3,4]. The irradiated CANDU pressure tube, which can be classified as intermediate-level waste (ILW), should be decontaminated by separating Zr from the alloy to reduce the final radioactive waste volume as well as its waste level
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