Considerations on the development of large-size dried spikes

The EURATOM treaty stipulates clearly in Article 8 and annex V the need for nuclear isotopic reference material and standards. The Institute for Reference Materials and Measurements (IRMM) is producing these material standards helping the European measurement laboratories in the field of nuclear material control and accountancy to perform measurements of fissile material to the required standards. One main activity of IRMM is the development of uranium and plutonium large-sized dried (LSD) spikes for nuclear safeguards. The IRMM-1027 series of LSD spikes is produced in large batches of approximately 1200 units and contains about 50mg total uranium with an enrichment of ~ 20% 235U and about 1.8 mg of ~ 98% 239 Pu per ampoule. These amounts of U and Pu are chosen as such to enable direct measurement of the 238U and 240Pu content in spent fuel solutions. The LSD spikes are covered with a cellulose acetate butyrate (CAB) polymer as a protective stabilizer during storage and transport. The presence of Pu and other ambient factors are causing degradation of this organic layer over a period of several years, limiting the certification validity in time. Optimisation of the current procedure was done at IRMM towards improved organic coating guaranteeing the integrity of the layer for a time span of 24 months. Nevertheless for longer shelf lives research and development for alternative coating approaches are required. A particular concern is the guaranteed supply of pure 239Pu metal over the next decade and beyond. IRMM proposes therefore a different approach to decrease the amount of 239Pu used for fissile material control measurements when applying isotope dilution mass spectrometry. The IRMM proposal is based on using a 20% enriched uranium isotopic reference material in combination with measurements of plutonium carried out on a diluted sample. By this means the stability problems sometimes encountered in Pu solutions due to formation of colloids or precipitation can be dealt with in a diluted solution. This approach not only reduces the consumption of 239Pu certified reference metal but also facilitates transport of spike material to on-site laboratories and operators.JRC.D.2-Standards for Innovation and sustainable Developmen