Launch Safety Analysis for Radioisotope Power Systems

Radioisotope power systems (RPS) are essential for the exploration of the outer solar system and other destinations where solar power is insufficient. The alpha decay of plutonium-238 fuel in the form of plutonium dioxide (PuO2) provides the thermal and electrical power for these missions. Because of the radioactive nature of the fuel, launch of an RPS requires an extensive safety analysis, an independent review, and approval by the U. S. Executive Branch, per Presidential Directive / National Security Council Memorandum 25. This paper summarizes the launch approval process, the safety and containment features of RPSs, the potential launch accident scenarios, the relevant phenomena that must be considered, and the software used in the safety analyses. Launch accident scenarios and accident environments that can affect potential release and dispersal of radioactive materials include blast waves, impact of the RPS onto hard surfaces, impact of debris onto the RPS, rocket propellant fires, high-speed reentry from sub-orbit or orbit, lofting of radioactive aerosols, atmospheric dispersal and settling of those aerosols, inhalation and ingestion of released material, and subsequent health effects and land contamination. All of these phenomena are assessed and modeled by a suite of computer codes with extensive verification, validation, and quality assurance. A probabilistic risk assessment is performed to determine the range of possible release amounts and consequences, along with their estimated probability of occurrence. This information becomes the basis for the launch approval decision.