Performance Restoration of a Tritium-Aged LaNi_4.25Al_0.75 Sample

Abstract

Hydride beds containing LaNi_4.25Al_0.75 (LANA.75) are used to store significant quantities of tritium. These hydride beds have a limited service life due to radiolytic decay of tritium to ³He within the metal matrix. The crystal structure of the hydride is altered by trapped ³He, which has a very low solubility in the metal. The altered structure induces the formation of a heel of trapped hydrogen isotopes and diminishes the reversible capacity of the hydride. With sufficient tritium exposure, the bed loses the ability to deliver ³He-free tritium, and replacement is needed. Demonstration of a means to regenerate tritium-aged LANA.75 in situ would delay or even eliminate the need to replace lanthanum nickel aluminum (LANA) hydride beds. This paper presents test results obtained during regeneration testing. The efficacy of regeneration testing was evaluated by comparing tritium desorption isotherms collected on the hydride before and after exposure to regeneration conditions. Testing was performed on a bench-scale tritium-aged LANA.75 sample that was previously isotopically exchanged (from tritium to deuterium), passivated, and recovered. Once transferred to a high-temperature test cell, the deuterium heel of the sample was isotopically exchanged with tritium, and a baseline desorption isotherm was collected for comparison purposes. The sample was then heated under vacuum, and comparative isotherms were gathered between regeneration evolutions. Shifts in isotherms show progressive improvements with higher-temperature exposure over the tritium-aged baseline. The heel was significantly reduced, and the reversible capacity of the hydride was essentially restored to near virgin values. For all tested conditions, the plateau pressure remained higher than virgin LANA.75.

Keywords:

• LANA.75
• regeneration
• hydride storage
• isotherm performance

Acknowledgments

This manuscript has been authorized by Savannah River Nuclear Solutions, LLC under contract number DE-AC09-08SR22470 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting this article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States Government purposes. Financial support for this work was provided by the SRS Plant Directed Research, Development and Demonstration program. The authors gratefully acknowledge Robbie Allgood, Summer Schaufler, Paul Foster, Jared Clark, Dante Pilgrim, Dakota Hooker, and Kipp Neikirk, and several others for their assistance with this project.