Evaluation of Isotopics and Assay of Pu Solution prepared from MOX as the Base Material of LSD Spikes

The preparation technique for Pu reference materials and associated Large Size Dried (LSD) spikes from a uranium and plutonium mixed oxide, MOX, has been studied by the joint study between JAEA and NBL. All accountancy analyses at Plutonium Fuel Development Center (PFDC) of JAEA are performed by means of isotope dilution mass spectrometry (IDMS) with well-characterized standard materials preparing from Pu and U reference materials at PFDC. The Pu reference materials have been obtained from foreign suppliers because there has been no facility with the capability for preparation and supply of the Pu reference materials in Japan, and, importing those Pu reference materials is gradually becoming more difficult. Thus, it is important to establish the capability and expertise for the preparation of Pu reference materials and associated LSD spikes in Japan. In order to obtain a small quantity of plutonium material with suitable purity and composition, the MOX was dissolved and subjected to a series of purification steps to remove uranium as much as possible. The isotopics and concentration of uranium and plutonium in the sampled purified plutonium solution were analyzed by means of the IDMS, Finnigan MAT 262, using the total evaporation method. This paper describes the evaluated results of measurement data by IDMS at PFDC from a viewpoint of precision, and also summarizes the results of the detailed uncertainty analyses on these measurement data conducted by NBL. These uncertainty analyses are performed based on the Guide to the expression of Uncertainty in Measurement, GUM.