Year
2010
Abstract
At the Rokkasho Reprocessing Plant (RRP), interim inventory verification (IIV) has been implemented based on the operator’s Near Real Time Accountancy (NRTA) for verification timeliness. RRP handles a large amount of Pu in continuous operation. In order to carry out the analysis for NRTA, the declaration data for the IIV is required to be available promptly and to be as accurate as possible. However, accurate destructive analysis (DA) requires about a week for analysis including sample treatment. In order to make a quick and accurate analysis of samples for an effective NRTA evaluation, JNFL and LANL jointly have studied the applicability of an Epithermal Neutron Multiplicity Counter (ENMC) for material accounting for NRTA. An ENMC has been developed at LANL for the accurate measurement of Pu and MOX samples. It was specially designed to measure Pu nitrate solutions and MOX powder samples based on the high efficiency and short dieaway time characteristics of the ENMC. Concurrent High Resolution Gamma Ray Spectroscopy (HRGS) measurement is used to verify the plutonium isotopic composition. The NRTA area at RRP is composed of solution handling and powder handling processes, and so the ENMC is required to measure Pu solution samples from 10g-Pu/L to 250g-Pu/L (without fission products) and MOX powder samples, and the target measurement uncertainty is about ±0.2-0.5% on the 240Pueffective for the ENMC. JNFL performed applicability tests of the ENMC for material accountancy analysis with LANL cooperation. This paper describes the system calibration and validation results using well characterized MOX powder and Pu nitrate solution samples with tag mass values established by Isotopic Dilution Mass-Spectrometry (IDMS).