Hydride Bed Helium-3 Recovery and Partial Regeneration

Abstract

Savannah River Tritium Enterprise has used LaNi_4.25Al_0.75 (LANA75) hydride beds to store hydrogen isotopes for over two decades. A benefit of using LANA75 is that the ³He generated from tritium decay is retained in the hydride material, allowing the hydride beds to deliver high-purity product gas. A disadvantage is that the ³He accumulates in the LANA75 material over time, which forms a heel that cannot be removed under normal operating conditions. The heel traps hydrogen in the bed, slowly reducing the operational capacity of the bed as the heel grows. Eventually, the ³He begins to release from the material, preventing the delivery of high-purity product. The hydride beds are replaced when (1) operational capacity is reduced such that it is impactive to routine operations, and/or (2) product purity is not maintained due to ³He release.

Several beds were operated beyond their design life. One of these beds was selected to undergo heating beyond its normal operating temperature to evaluate the possibility of removing a portion of the hydrogen and helium heel to improve bed function until a replacement could take place. This bake-out removed a portion of the hydrogen and helium heel, and preliminary data indicate that bake-outs may partially regenerate the beds. The bed’s performance will continue to be monitored, and additional bake-outs will likely be performed. Performing bake-outs results in increasing the recovery of ³He, more efficient end-of-life activities (such as isotopic exchange), and extension of the useful service life of the bed.

Keywords:

• Hydride
• regeneration
• helium
• tritium

Acknowledgments

The authors would like to thank Tritium Operations and Savannah River National Laboratory for their support of this work. This paper was prepared in connection with work done under contract number DE-AC09-08SR22470 with the U.S. Department of Energy.