Year
2014
Abstract
Over a period of five years the Atomic Weapons Establishment (AWE) has performed a variety of measurements using two identical calorimeters. The instruments used were novel, fluid-free, ANTECH model CHF400 series large volume, twin cell, heat-flow calorimeters. Each calorimeter comprises of 53 litre cells, one of which is the measurement chamber and the other acts as a reference. Both calorimeters perform in a consistent manner and achieve a thermal detection level in the order of 500 microwatts (5.50×1011Bq tritium equivalent assuming 3.244×10-1 W g-1, 3.57×1014 Bq g-1). The analysed measurement data and conclusions represent a comprehensive study of the performance of this calorimeter design. The work includes both the measurement of electric calibration samples and radioactive items containing tritium with a range of masses and thermal power outputs. The studies reported in the paper indicate the performance of the algorithms for predicting end-point and thermal equilibrium compared with the operator-determined result. The analysis further examines the effects of baseline power stability, environmental influences, sample self- heating, instrument recovery time and sample packaging masses. Measurement accuracy and precision data are presented covering a range of sample thermal powers and characteristics. The data generated over five years of operations demonstrate the environmental and sample characteristics have a negligible effect on the instrument performance. The calorimeters have exceeded the minimum performance set out in the design requirements. As a result of their ease of use, sample capacity, baseline stability, significant improvements in safety and efficiency have been made.