Design optimization studies for 238Pu production

With the dawn of a new space exploration era, some challenges must be faced. One of the most important ones is finding a reliable way to provide energy and heat for the different space missions that humanity intends to carry out in the coming years. Historically, solar power and its combination with batteries have been used for low orbital satellites, but there are circumstances in which they cannot be relied upon due to their lack of availability. This is the case of deep space exploration or permanence in the dark side of planets and satellites. One of the main alternatives that has been traditionally used are Radioisotope Thermoelectric Generators (RTGs) and Radioisotope Heating Units (RHUs). These devices take advantage of the heat generated by the radioactive decay of a radioisotope, such as 238Pu or 241Am, as a reliable energy source. This was the case for some important missions that took place in the past, like the Voyager Program. Although 238Pu is an ideal candidate for powering RTGs, its production is very complex and has never been done in Europe for space applications. In the framework of a European Space Agency funded assessment of the European capabilities for 238Pu based radioisotope power systems (Pu4Space project), the Belgian Nuclear Research Centre studied the feasibility of producing this isotope in the Belgian Reactor 2 (BR2). This project determined that it is possible to produce sizable amounts of this isotope with the required quality for its use as fuel for RTGs. Validation of the initial assessments remains to be done. In particular, the isotopic composition of the Pu-vector varies significantly with the chosen irradiation positions in the BR2 reactor and the target geometries. Consequently, in the framework of the EC Horizon Europe PULSAR project, optimization studies are being performed. In the PULSAR project, the implementation of a subrogated irradiation model in Python that has as input the initial composition of the target and the characteristics of the spectrum in different irradiation channels inside the reactor, leading to the optimization of the production based on a nonlinear optimization model through different variables like the position of the target, the irradiation time and the cooling time, is presented. This will allow maximizing the production of 238Pu, while minimizing the contaminants in the irradiated target, such as 238Pu, other actinides or fission products, and establishing a feasible irradiation route with the aim of achieving an actual demonstration with an irradiation of a target in BR2.