Deep space missions currently rely on radioisotope power systems (RPS) to generate power up to 5?kWe over long periods. In particular, the mission under study in PULSAR would require 100-500 We. These systems use the heat released from the spontaneous decay of radioisotopes, such as Plutonium-238 (Pu-238), to produce electricity. However, Europe does not currently produce Pu-238.
Work Package 1 of the PULSAR project, titled “Pu-238 production and processing,” addressed key challenges in establishing European production of Pu-238. The project progressed from a feasibility study, confirming the realistic potential for Pu-238 production in Europe, towards proof of concept developed:
- Optimization studies on target geometry and irradiation conditions have identified trends in Pu-238 yield and Pu vector quality. Two irradiation scenarios using channels at BR2 reactor in SCK CEN, Belgium have been proposed by SCK CEN, with estimated production rates of 378 and 418 g of Pu-238 per year if enough neptunium-237 is available.
- At
SCK CEN
, the conventional oxalate conversion route has been reproduced at the laboratory scale, with modifications and advanced methods like external gelation to produce NpO2 kernels. These processes achieved production yields between 84 and 91 wt.%, resulting in free?flowing materials suitable for pelletization.
- Solvent extraction in a continuous process has been identified as the preferred method for separating neptunium and plutonium from fission products and each other. Distribution ratios for various solvents and nitric acid concentrations were determined by SCK CEN.
- The synthesis and characterization of PuO2 pellets with representative microstructure were explored. The process at the European Commissio's Joint Research Centre (JRC) facilities successfully produced PuO2 from reactor-grade plutonium with tailored microstructure and density, closely mimicking results from US studies.
- The feasibility of using laser welding techniques for the iridium encapsulation was studied and tested at JRC laboratories. Due to material shortages, the limited welding tests were inconclusive. Additionally, the composition of the iridium tested differed from DOP26, potentially affecting weld quality.
Additionally, the work package focused on the safety aspects of handling Pu-238, including processing it in gram quantities in a nuclear laboratory addressed by JRC, and identifying the necessary framework for conducting safety assessments, licensing, and regulation of the PULSAR heat source addressed by Tractebel.
