Use of a single fuel containment material during pyroprocessing tests

Abstract

The use of a single stainless steel (STS) wire mesh basket as the fuel containment material for a series of pyroprocessing steps has been studied. The use of a single basket minimizes fuel loss and was enabled by transporting and using the basket containing the fuel from one test to the next without unloading it. The series of tests consisted of electrolytic reduction, LiCl distillation, electrorefining, LiCl–KCl distillation, and finally a second electrolytic reduction and a subsequent LiCl distillation step. While the electrolytic reduction of UO2 was conducted in a LiCl–Li2O molten salt electrolyte at 650°C using the STS wire mesh basket as the cathode, the electrorefining was carried out in a LiCl–KCl–UCl3 molten salt electrolyte at 500°C, using the STS wire mesh basket as the anode. During the salt (LiCl and LiCl–KCl) distillation processes, the product of electrolytic reduction/electrorefining in the basket, which included metallic U and residual salts, was distilled at 850°C under vacuum. The electrolytic reduction, electrorefining, and salt distillation processes were successfully demonstrated with the use of a single STS wire mesh basket through the entire cycle. However, an unstable intermetallic U–Fe layer was observed between the reduction product and the STS basket, when a cross section of the basket was studied after the salt distillation steps. The influence of the U–Fe layer on the electrolysis steps needs to be studied further in order to understand and quantify the lifetime of a single STS wire mesh basket during pyroprocessing.