Tritium accountability of a uranium hydride bed using a calorimetry methodology

Tritium, a radioactive hydrogen isotope with a half-life of 12.32 years and emitting 0.324 W/g of heat through beta decay, is used as a nuclear fusion fuel. Thus, accurate measurement and safe storage of tritium are important technologies for nuclear fusion fuel cycles. We have developed a uranium hydride bed that can store, deliver, and measure tritium required for a tokamak-type nuclear fusion reactor fuel cycle. Calorimetry, which measures the thermal output of heat-producing substances, was chosen as the tritium accounting technique owing to its safety. The tritium amount cannot be measured directly through this technique but can be indirectly obtained by measuring the bed temperature from the calibration curve of tritium amount versus bed temperature. In this study, experiments were performed to obtain the calibration curve for the relationship between tritium amount and uranium hydride bed temperature. Additionally, characteristics including the convergence and sensitivity of the calorimetry methodology for the uranium hydride bed were determined. The relationship between the tritium amount and uranium hydride bed temperature can be expressed as a one-phase exponential decay function, and it was confirmed that the calorimetry could be applied for tritium inventory measurement with high precision under high vacuum.