Large Volume Calorimeter Comparison Measurement Results Collected at the Los Alamos National Laboratory Plutonium Facility

A calorimeter capable of measuring the power output from special nuclear material in 208- liter (55-gal) shipping or storage containers was designed and fabricated at Los Alamos National Laboratory (LANL). This high-sensitivity, large-volume calorimeter (LVC) provides a reliable NDA method to measure many difficult-to-assay forms of plutonium and tritium more accurately. The entire calorimeter is 104 cm wide x 157 cm deep x 196 cm high in the closed position. The LVC also requires space for a standard electronics rack. A standard 208-l drum with a 60- cm-diameter retaining ring with bolt will fit into the LVC measurement chamber. With careful positioning, cylindrical items up to 66 cm in diameter and 100 cm tall can be assayed in the LVC. The LVC was used to measure numerous plutonium-bearing items in 208-l drums at the Los Alamos Plutonium Facility. Measurement results from real waste drums that were previously assayed using multiple NDA systems1 are compared with the LVC results. The calorimeter previously performed well under laboratory conditions using Pu-238 heat standards2. The inplant instrument performance is compared with the laboratory performance. Assay times, precision, measurement threshold, and operability of the LVC are also presented.