Characterisation of highly enriched uranium samples seized in the Czech Republic

In the framework of the PECO project between Joint Research Centre, EC Institute for Transuranium Elements and Nuclear Research Institute Rez, plc (NRI), Czech Republic, the analyses of four HEU samples (named A, B, C, and D) seized in the Czech Republic during 1994 - 1995 were performed. Complex analytical procedures were used for the characterisation of seized nuclear material. The techniques include mass spectrometry (TIMS, ICP-MS, SIMS), electron microscopy (SEM, TEM, optical microscopy) and various radiometric techniques (gamma and alpha spectrometry). The main results can be summarised as following: uranium content in the samples is around 85 %, which corresponds to a non-stoichiometric UO2; isotopic abundance of 235U is 87.78 wt. %; no difference in the 235U abundance between the small and big particles are seen; total content of metallic impurities was very low being between 200-300 ppm; uranium is contaminated by a small amount of plutonium (26 ppb); particle size varies from 0.2 to 10 μm and particles create big conglomerates; particles are quite soft and they do not show expansion structure on the surface, thus they are, most-likely, not calcinated at high temperature; determined age points to a production period of 1976-1977. The analysed material could be characterised as a laboratory product or laboratory side-product, which could be - considering the high abundance of 235U - used for research reactors or military applications