Pressurization of Sealed Pu-238 Bearing Containers in Design Basis Accidents: Analysis and Risk Reduction

Plutonium-238 has been used since the 1960’s as the fuel in various Radioisotope Thermoelectric Generator (RTGs) systems to power numerous NASA space systems. Most recently, Los Alamos manufactured Plutonium-238 heat sources to power the Cassini-Huygens mission to Saturn, the Pluto New Horizons mission and the Mars Science Laboratory Rover. Plutonium-238 is an ideal material for space power applications due to its high curie content, which is proportional to the decay heat of the material. When Plutonium-238 decays, an energetic, ionized helium atom is also released. Helium gas generation and subsequent pressure build-up in sealed containers is a primary area of concern at the Plutonium Facility due to the high specific activity of Plutonium-238 (17 Ci/g for Pu-238 compared to 0.062 Ci/g for Pu-239). Therefore, many of the bounding design basis accidents at the Plutonium Facility in Los Alamos involve the potential release of Plutonium-238 oxides. As part of an overall effort to improve the safety posture of the nuclear facility, we developed a container capable of maintaining confinement of Plutonium-238 oxides for long times during normal storage and handling conditions and when exposed to facility design basis accidents. The storage container was designed and tested to meet facility design basis accident performance criteria and the requirements of the DOE M441.1-1 Nuclear Material Packaging Manual (hereafter referred to only as the “Packaging Manual”. The analysis techniques and methodology for the development of the storage container is presented along with testing performed to demonstrate Packaging Manual compliance. In addition, techniques developed for rapid assessment of the over-pressurization hazard of legacy Plutonium-238 bearing containers, where design basis information is incomplete or unavailable, are presented.