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Pu-238 Production Feasibility Study

Thu, 07/28/2022 - 15:50
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Space missions operating in the inner solar system usually rely on photovoltaic solar cells as primary power source. However, these photovoltaic cells are not appropriate for all space missions, either because the solar radiation is too weak to produce sufficient power within the limitations imposed by today’s solar cell technology and spacecraft mass and volume limitations, or because the timespan to be bridged by the batteries is too long (e.g. lunar or Martian nights). Therefore, nuclear power systems have been deployed for heat (Radioisotope Heater Unit or RHU) and electrical power generation (Radioisotope Thermoelectrical Generator or RTG). Both systems do not rely on fission energy, as is common in nuclear power reactors on earth. Instead, radioactive decay is the primary energy source. In previous ESA activities, two radioisotopes have been selected for nuclear power systems in space missions: Plutonium-238 (Pu-238) and Americium-241 (Am-241). Both isotopes are mainly produced in nuclear reactors today.

The previous ESA activity assessed the costs associated with Pu-238 production to be undesirably high, while the level of investment for producing Am-241 in kilogram quantities was seen as realistic in the context of ESA programmes at that time. However, new information on the chemical separation and irradiation indicated that the previous estimates regarding cost of production may be outdated. With the aim to consolidate the options and decisions regarding the choice of radioisotopes for European RHUs and RTGs, this study will therefore investigate the feasibility and cost of the production of Pu238 in the BR2 reactor at the SCK-CEN nuclear site in Belgium, using precursor material from the French reprocessing operations at La Hague. Even though Pu-238 is being produced in nuclear fuel today, its relative concentration with respect to the other plutonium isotopes is very small (maximum a few percentages), whereas it is required by the technical specifications of the RTG and RHU to have a concentration of at least 82.5% of Pu-238. Therefore, the production of Pu-238 will proceed via neutron irradiation of Neptunium-237 (Np-237), which is created as a by-product in nuclear fission reactors and is currently located in the waste stream of the PUREX process in the La Hague fuel reprocessing facility. Bombarding Np-237 isotopes with neutrons in a nuclear reactor will produce temporarily Np-238 which will decay to Pu-238 in a few days. This Pu-238 production feasibility study was performed by Tractebel, with Orano and SCK-CEN as subcontractors, in request of ESA. It looks at the technical possibilities to produce this isotope in Europe without relying on non-European partners. The cost and lead-time for setting up a Pu-238 production chain is evaluated.

Application Domain: 
Technology Domain: 
3 - Space Systems Electrical Power
Competence Domain: 
4-Electric Architecture, Power and Energy, EMC
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