Demonstration of the calorimetric assay of large mass, high burn-up PuO2 samples

A joint U.S./Euratom/IAEA evaluation of the calorimetric assay of large mass, high burn-up PuO2 was conducted at CEN/SCK, Mol, Belgium, under the U.S. DOE/Euratom agreement for cooperation in safeguards R and D. Mound provided a large, twin-bridge calorimeter for this demonstration. PuO2 material from COGEMA France (Pu-239 approx. = 58 wt %) was prepared by Belgonucleaire. The demonstration was conducted in two phases. The first phase was to evaluate the homogeneity of two batches of PuO2 which had been blended and characterized at Belgonucleaire in 1980. Watts/gram tests were made on twelve approximately 70g samples from each batch. For the batch selected, the watts/gram test showed an RSD of 0.25%, in good agreement with an RSD of 0.21% in chemical assay values obtained in 1980. Thus, suitable Pu elemental homogeneity with little or no isotopic nonhomogeneity was demonstrated. For the second phase, PuO2 from the selected batch was packaged into four containers with the PuO2 content varying from approximately 1 kg to 3 kg; the thermal powers of the four samples varied from 14.5 to 35.8 W. The accuracy of the calorimetric assay of the Pu content of these four containers, compared to chemistry, was 0.3% with measurement times ranging from 4 to 8 hr. These well characterized samples are being used by Euratom and the IAEA for additional NDA evaluation