Thermal Release of 3He from Tritium Aged LaNi4.25Al0.75 Hydride

Abstract

Recently, the demand for He-3 has increased dramatically due to widespread use in nuclear nonproliferation, cryogenic, and medical applications. Essentially all of the world's supply of He-3 is created by the radiolytic decay of tritium. The Savannah River Site Tritium Facilities (SRS-TF) utilizes LANA.75 in the tritium process to store hydrogen isotopes. The vast majority of He-3 "born" from tritium stored in LANA.75 is trapped in the hydride metal matrix. The SRS-TF has multiple LANA.75 tritium storage beds that have been retired from service with significant quantities of He-3 trapped in the metal. To support He-3 recovery, the Savannah River National Laboratory (SRNL) conducted thermogravimetric analysis coupled with mass spectrometry (TGA-MS) on a tritium aged LANA.75 sample. TGA-MS testing was performed in an argon environment. Prior to testing, the sample was isotopically exchanged with deuterium to reduce residual tritium and passivated with air to alleviate pyrophoric concerns associated with handling the material outside of an inert glovebox. Analyses indicated that gas release from this sample was bimodal, with peaks near 220 and 490°C. The first peak consisted of both He-3 and residual hydrogen isotopes, the second was primarily He-3. The bulk of the gas was released by 600°C.

Performance Restoration of a Tritium-Aged LaNi4.25Al0.75 Sample

“…4 and in Table I, regeneration at 600°C shows marked improvements over regeneration at 450°C. These improvements are likely due to removal of the bulk of the remaining 3 He trapped in the metal. Regeneration at 750°C showed slight additional improvements over regen-175 eration at 600°C, but the plateau pressure remained approxi-mately~33.3 kPa greater than that measured for the virgin LANA.75 sample.…”

“…Regeneration at 750°C showed slight additional improvements over regen-175 eration at 600°C, but the plateau pressure remained approxi-mately~33.3 kPa greater than that measured for the virgin LANA.75 sample. These changes may be due to stress releif within the metal matrix beyond those obtained by simply releasing the 3 He. 180 While regeneration testing produced extremely promising results, observation of a plateau pressure higher than that for a virgin LANA.75 sample was unexpected and is not well understood.…”

“…As part of an effort to recover 3 He from retired LANA beds at Savannah River Tritium Enterprise (SRTE), previous testing was performed to determine 40 the thermal release characteristics of 3 He from tritiumaged LaNi 4.25 Al 0.75 (LANA.75) (Ref. 3).…”

“…Gases 45 evolved from the sample were quantified with a mass spectrometer (MS), and test data showed two primary peaks. The first peak consisted of both hydrogen isotopes and 3 He. The second peak was primarily 3 He.…”

“…Performance restoration would likely include 70 a reduction in the amount of unusable tritium trapped in the metal. An additional benefit of regeneration includes recovery of significant quantities of 3 He from the tritiumaged LANA.75. Helium-3 is a valuable by-product used predominantly in neutron detectors, ultra-low-75 temperature cryogenics, and medical imaging.…”