New U/Pu metallic spikes for safeguards accountancy measurements at reprocessing plants

A new generation of metallic uranium/plutonium spikes has been developed for U and Pu determinations in undiluted input solutions of reprocessing plants. The Pu spike is in the form of a Gd-6% Pu-0.16% Nd (mass%) alloy disc prepared by levitation melting. The Gd provides a ductile matrix in which the Pu is present in solid solution. The alloy has good oxidation resistance, but is readily soluble in the nitric acid medium of the input solution. The Nd addition is to permit a determination of input tank volume via the measurement of 142/143Nd ratios. The U spike is a metal disc with a 235U enrichment of 19.9 amount%. A γ-counting method of plutonium homogeneity control was developed using a Monte-Carlo simulation to correct for γ-ray self-absorption. The spikes were certified for uranium and plutonium mass fractions and amount ratios as isotopic reference material spike IRMM-1030. (orig.)