DEVELOPMENT OF HYDROGEN GETTERS FOR USE IN TRANSURANIC WASTE SHIPMENTS

Hydrogen gas generation is a key issue in the transportation of transuranic wastes in the TRUPACT-II shipping package. U.S. Nuclear Regulatory Commission regulations require that H2 concentrations remain below the flammability limit of 5 percent by volume within all void volumes during a maximum 60-day shipping period. One of several approaches being pursued to meet this requirement for high gas generating wastes is the use of H2 getters within the transportation package. Getters are substances that absorb H2, thereby maintaining H2 concentrations below the flammability limit. The selected getter must be shown to be effective in credible scenarios expected under transportation conditions. The getter performance requirements include adequate H2 absorption rate and capacity, ability to function over a temperature range of -20°F to +160°F and pressures up to 50 psig, and performance in the presence of radiation. In addition, it must be demonstrated that the getters will adequately perform in the presence of gases such as CO, hydrocarbon vapors (such as methanol and toluene) and chlorinated solvent vapors (such as carbon tetrachloride and trichloroethene). These gases, referred to as getter “poisons”, may be present in some waste shipments, and are known to degrade the performance of some types of H2 getters. Several types of getters have been considered for use in TRUPACT-II containers. Metal hydride (ZrCo and LaNi4Al alloys) getters reversibly store H2 within the alloy structure and the H2 can be released upon heating so that the getters can be recycled. Organic polymers (DEB [1,4-bis(phenylethynyl)benzene] and a proprietary formulation developed by Sandia National Laboratories) contain double and triple carbon-carbon bonds that irreversibly hydrogenate upon exposure to H2. Operating in the presence of poisons is the most challenging requirement for these getters, and is the main thrust of the development and testing program. Required getter performance specifications are provided, along with an update on the status of the getter testing effort.