Fractional Release Behavior of Volatile and Semivolatile Fission Products During a Voloxidation and OREOX Treatment of Spent PWR Fuel

Quantitative analysis of the fission gas release characteristics during the voloxidation and oxidation and reduction of oxide fuel (OREOX) processes of spent pressurized water reactor (PWR) fuel was carried out by spent PWR fuel in a hot cell of the DUPIC Fuel Development Facility. The release characteristics of ⁸⁵Kr and ¹⁴C fission gases during voloxidation process at 500°C are closely linked to the degree of conversion efficiency of UO₂ to U₃O₈ powder, and it can be interpreted that the release from grain boundary would be dominated during this step. Volatile fission gases of ¹⁴C and ⁸⁵Kr were released to near completion during the OREOX process. Both the ¹⁴C and ⁸⁵Kr have similar release characteristics under the voloxidation and OREOX process conditions. A higher burnup spent fuel showed a higher release fraction than that of a low burnup fuel during the voloxidation step. It was also observed that the release fraction of semivolatile Cs was ~16% during a reduction at 1000°C of the oxidized powder, but over 90% during the voloxidation at 1250°C.