Year
1997
Abstract
A sensitive calorimeter has been combined with a small temperature-controlled water bath to compose a transportable system that is capable of measuring multikilogram quantities of highly enriched uranium (HEU). The sample chamber size, 5 in. in diameter by 10 in. high, is large enough to hold sufficient HEU metal or highgrade scrap to provide a measurable thermal signal. Calorimetric measurements performed on wellcharacterized material indicate that the thermal power generated by 93% 235U samples with 1.0% 234U can be measured with a precision of about 1% (1 sigma) for 4-kg samples. The transportable system consists of a twinbridge calorimeter installed inside a 55-gal. stainless steel drum filled with water with heating and cooling supplied by a removable thermoelectric module attached to the side. Isotopic measurements using highresolution gamma-ray measurements of the HEU samples and analysis with the FRAM code were used to determine the isotopic ratios and specific power of the samples. This information was used to transform the measured thermal power into grams of HEU. Because no physical standards are required, this system could be used for the verification of plutonium, 238Pu heat sources, or large quantities of metal or other high-grade matrix forms of HEU.