PERFORMING ACCURATE MEASUREMENTS OF FISSIONABLE MATERIAL FOR SAFEGUARD PURPOSES IN REPROCESSING PLANTS IN EUROPE,

This paper describes the results obtained over a period of about five years, of a procedure which allows accurate certification of fissile nuclide and/or element concentrations at time and place of Safeguard Inspection at a reprocessing plant, although the actual measurements are performed some weelcs later in a. distant Safeguards measurement laboratory. In the procedure the Safeguards Inspector at plant site adds a known amount (\"\"spike\") or supervises the addition of isotopically different U and Pu to the unknown (hot) input/output solutions. Isotope Dilution Mass Spectrometry (IDMS) is used for the measurements of isotopic composition and fissionable isotope/element concentration at the measurement laboratory. By performing the procedure twice, with different amounts of spike added, it has been possible to confirm the expectation that, if an error occurs, it is detected in time and will prevent Safeguards Authorities to draw unjustified conclusions. At present, the attained accuracy is 0.3% for U or U-concentration and there is potential for achieving the same for Pu. It is believed that this accuracy can still further be improved.