Pu standard material preparation in Japan

In order to obtain reliable accountancy analysis results, the isotope dilution mass spectrometry method is applied at most of the plutonium handling nuclear facilities in Japan. Reference materials, referred to as Large Size Dried spikes (LSD spikes), were developed to allow facilities, regulatory and safeguards organizations to accurately measure and quantify a variety of nuclear materials under potentially difficult handling or measurement conditions. Because of expected difficulties in the long term supply of low burn-up plutonium reference materials, which are the main source of plutonium for LSD spike preparation, the Japan Atomic Energy Agency (JAEA) decided to evaluate the possibility of using domestically available MOX as a plutonium source material for LSD spikes. Therefore, JAEA’s Plutonium Fuel Development Center (PFDC) started to produce and certify plutonium reference materials that are suitable for use in producing LSD spikes in collaboration with the US Department of Energy’s New Brunswick Laboratory (NBL). NBL’s participation in the collaboration is sponsored by the DOE’s International Safeguards Engagement Program. At the PFDC, the plutonium contained in the MOX was separated, purified and characterized to produce plutonium standard material, referred to as MOX-Pu. For the separation and purification of plutonium from MOX, an anion exchange method was utilized after an initial separation of uranium and plutonium by preferential dissolution using the differences in solubility between them. From the MOX-Pu batch characterized in 2008, two types of LSD spikes were prepared by quantitative mixing of Pu with U nitrate solution prepared from U metal reference materials (NBL CRM-116 and CRM112A). The LSD spikes were distributed for verification measurements to the IAEA-Safeguards Analytical Laboratory, two of the IAEA’s network laboratories and Japanese laboratories. Another MOX-Pu standard was prepared in 2012 and characterization work is nearly completed. Another intercomparison for verification of this MOX-Pu has been organized and JAEA is now collecting the results. The detailed purification procedure, results of the intercomparison of LSD spikes and interim intercomparison of the MOX-Pu prepared in 2012 are presented.