Determinations of plutonium and curium in the insoluble materials of spent fuel dissolver solutions at the Tokai Reprocessing Plant

摘要

Plutonium and curium in the insoluble materials of spent fuel dissolver solutions were determined by alpha spectrometry after sulfate fusion of insoluble materials and purification of plutonium and curium in the fused solution. A small amount of plutonium exists in insoluble materials such as sludge and chips of cladding tube, which are generated during dissolution of spent fuel and are removed from the dissolver solution by a pulse filter at clarification process. The filtered insoluble materials are removed by washing with water from the reverse direction and the washed filter is transferred to a waste storage area, but it is supposed that fine particles of the insoluble materials slightly remain in the pulse filter. For the measurement of plutonium in the spent pulse filter by non-destructive analysis, High Level Neutron Coincidence Counter (HLNCC) based on passive neutron measurement has been studied for safeguards under the cooperation between JAEA and the Los Alamos National Laboratory (LANL). In the HLNCC measurements, detections of neutron emission from the sample are dominated by curium-244. It is therefore difficult to detect the neutron emitted by plutonium. However, if the ratios of plutonium to curium-244 for insoluble materials in spent fuel dissolver solution were known, the amount of plutonium in the pulse filter can be calculated from a passive neutron measurement. The measurement data of plutonium and curium-244 in the insoluble materials of dissolver solution has not been reported in the case of engineering scale facilities. In this work, three kinds of insoluble materials were filtrated from spent PWR fuel dissolver solutions and were completely fused with ammonium hydrogen sulfate. Plutonium in the sample was selectively extracted with TEVA resin. Curium was also purified from plutonium and other fission products with di (2-ethylhexl) phosphoric acid (HDEHP). Each sample was electrodeposited onto stainless steel discs, and plutonium and curium were determined by alpha spectrometry, respectively. The amounts of plutonium and curium-244 in insoluble materials were in the range from 3.7 mg g-1 to 17 mg g-1 and in the range 0.058 g g-1 to 0.24 g g-1. They are valuable data for evaluation of the ratios of plutonium to curium-244.