Some considerations on the role of LSD spikes in safeguarding nuclear reprocessing plants

Large sized dried spikes (LSD) are a fundamental part of the fissile material control of irradiated nuclear fuel. They are applied to measure the uranium and plutonium content of dissolved fuel solutions from reprocessing plants using isotope dilution mass-spectrometry (IDMS). Since the first batch of LSDs was produced, the concept of directly spiking samples of the solution with dissolved irradiated nuclear fuel for later dilution and measurement of the isotopic contents of uranium and plutonium has been developed successfully. In the method employed at IRMM, very high quality isotopically enriched metals of uranium (natural and high-enriched) and plutonium are dissolved into a single large solution in nitric acid. Individual spikes are then made by aliquoting weighed amounts of the solution into penicillin vials and drying carefully. A light cellulose layer is dried on the spike material to retain the spike at the bottom of the vial during transport to where it will be used. The spikes are prepared in large batches (1000 units) under rigorous conditions. Each spike then has a certified mass of uranium (235U and 238U) and 239Pu with an associated uncertainty derived by a rigorous procedure (following the GUM) from the measured and certified parameters of all starting materials and solutions. The plutonium component is highly enriched in 239Pu and is used to measure the Pu content in the fuel. The uranium component is a mixture of two uranium source materials, natural uranium and a highly enriched uranium component. These materials are mixed to arrive at a final enrichment of just under 20% in 235U, significantly simplifying transport and handling of the spikes. A series of verification measurements are carried out during the process and the final spikes are certified from the masses of the metal starting materials, the certified assay (purity) values of uranium and plutonium in the starting materials, the mass of the solution, the mass aliquoted into each vial and the isotopic abundances of each of the starting materials.

WELLUM Roger;  VERBRUGGEN Andre;  RICHTER Stephan;  AREGBE Yetunde; 

2013-05-14

International Atomic Energy Agency (IAEA)

JRC42367

http://www-pub.iaea.org/MTCD/Meetings/1073_presentations.asp,    https://publications.jrc.ec.europa.eu/repository/handle/JRC42367,