A Summary of Tritium In-Bed Accountability for 1500 Liter LaNi_4.25Al_0.75 Storage Beds

In-bed accountability (IBA), a steady-state, flowing gas calorimetric method, has been implemented for production measurement of tritium inventories in metal hydride storage beds utilizing a LaNi_4.25Al_0.25 metal hydride alloy. Six-point calibration curves have been completed for six, nominal 390 gram, and two nominal 1310 gram tritium metal hydride storage beds. The equations used to calculate inventory errors are derived and presented in the Appendix. Beds with the same amount of insulation gave similar IBA calibration curves and bed temperature versus tritium inventory results. Tritium IBA inventory measurement errors varied slightly with bed inventory and maximum values at the 95% confidence level ranged from 4 to 9 grams for the 390 gram beds (1.1 to 2.6%) and from 8 to 13 grams for the 1310 gram beds (0.7 to 1.2%). Comparison of other methods for determining inventories on the same beds (hydride pressure, hydride bed temperature, and hydride bed temperature rise above the glove box temperature) showed the IBA method gave the highest accuracy tritium measurements. These other inventory methods also showed greater variability in measurement error over the range of tritium inventories, van't Hoff plots of hydride bed pressure under steady-state IBA conditions revealed a reduction in hydride pressure after several months of tritium service compared to other beds without tritium exposure.