Alkali Metal Thermal-to-Electric Converter cells for long lived radioisotope power systems require durable, compatible seals between the beta-alumina solid electrolyte and the Niobium one percent Zirconium components of the cell. While strict hermeticity is not required, seal leakage must be kept small and stable for lifetimes of at least 12 years in a sodium vapor environment and operating temperatures up to 900oC. Seals meeting these criteria have been difficult to fabricate and a new approach appears to be required. Several new concepts for seals meeting the leak rate and durability criteria are being proposed for initial experimental evaluation in the Phase I program and the most promising will be selected for finished development in a Phase II program. These include strictly mechanical seals using specialized configurations that take advantage of the good coefficient of thermal expansion match between the Nb-1Zr and the beta-alumina and matching of the facing seal surfaces with high temperature sealants, compatible with sodium. Bsed on development risk and projected benefits, a review and an initial selection of promising concepts has been made. Those selected will be followed through with seal configuration designs tailored to each concept. Seals will be fabricated according to the designs and experimental leak rates will be measured at full Alkali Metal Thermal-to-Electric Converter operating temperatures in both vacuum and sodium environments. The candidate seals will be operated in working Alkali Metal Thermal-to-Electric Converter cells and cell performance measured against established standards to determine whether seal processing adversely affects any other cell components, and particularly the electrode and current collection subsystems.
Commercial Applications and Other Benefits as described by the awardee: These advanced sealing methods will allow the design of small, durable, long lived Alkali Metal Thermal-to-Electric Converter systems that will have applications in silent, efficient, portable power systems for both military and commercial markets. With successful implementation of anticipated manufacturing cost reductions, Alkali Metal Thermal-to-Electric Converter modules at the 500 W level will find applications in mobile power, residential cogeneration and remote power stations. Widespread use of the combined electric generation and high temperature heat rejection of Alkali Metal Thermal-to-Electric Converter systems can provide very substantial net energy savings nationally.
