Year
2001
Abstract
In the Plutonium Fuel Center (PFC) of JNC, Isotope Dilution Mass Spectrometry (IDMS) has been used to determine Pu and U contents of nuclear materials since 1996. In MOX fabrication plant, many types of sample with wide variation of Pu/U ratio including aged Pu and process scrap should be analyzed for not only quality control purpose but also material accountancy. Because IDMS can eliminate influences of coexistence elements and has high accuracy, it is considered to be the best analytical method for MOX fuel plant. From analytical results of about 300 samples of MOX fuel pellets (Pu/U=1/40) with Large Size Dried (LSD) spikes (Pu/U=1/20), repeatabilities of Pu and U determinations were evaluated. These are about 0.1%, which satisfies the International Target Value (ITV). Evaluation and comparison result of IDMS accuracy are described in this paper. Three types of LSD spike with different Pu/U ratio (2/1, 1/3, 1/20) being corresponded to objective sample composition had been prepared from Pu and U metal standards and enriched UO2. The number of prepared LSD spikes is 4000 in total. 2500 of them were prepared at our laboratory and the rest was introduced from the foreign supplier. Intercomparison analysis being carried out among IAEA-SAL, NMCC-SAL, and JNC laboratories four times a year indicates no considerable bias in the determination of Pu content. The parallel analysis on the same samples by using two different kinds of LSD spikes, which were JNC spikes and commercial supplier spikes, was preformed. The result shows no significant difference. These performances are also summarized in this paper. To maintain higher quality of LSD spike is one of the significant subjects for IDMS performance. Pu metal standards are normally used for spike preparation. However it have to be transported from the outside of Japan because of no availability of Pu metal standards in Japan. It is difficult to transport it into Japan due to various constraints regarding overseas transportation. Therefore, JNC is planning to carry out R&D with regard to handling about 0.4g Pu metal standard that is possible to be transported with type A container from foreign country. In addition, JNC is also planning to prepare pure Pu solution by purification and separation after solving MOX with relatively higher 239Pu content stored in JNC MOX facility. To certify the Pu concentration and isotope composition of the solution, another scheme of intercomparison analysis is necessary to be organized. This paper also describes the plan of the preparation of LSD spike by PFC laboratory.