Abstract
The partitioning process has been developed in Japan Atomic Energy Research Institute for the removal of long-lived radionuclides from high-level waste (HLW), and was tested with actual HLW. But, the separation behavior of neptunium was not examined in the de-veloped process.
In the present study, the behavior of neptunium in the partitioning process was examined with actual HLW by means of the analysis of 237Np. At the first step of the partitioning process, 86% of neptunium was not extracted with TBP. It was suggested that most of neptunium was pentavalent in feed solution. At the following step, more than 90% of neptunium was extracted with DIDPA and was not stripped with 4 M nitric acid. It was proved in tracer experiments that most of neptunium was pentavalent before DIDPA extrac-tion and Np(V) could be extracted with DIDPA by a slow rate. Neptunium which was ex-tracted from pentavalent state was hardly stripped with nitric acid, which indicated that the extraction of Np(V) was an irreversible process. It was considered that the disproportiona-tion reaction of Np(V) was concerned in the extraction.
