Safety Studies for European Space Nuclear Power Systems

Radioisotope power systems (RPS) have been employed in space since the dawn of spaceflight. They generate heat and electricity for long periods of time thanks to the radioactive decay of the fuel, independently of the solar flux; therefore, they are the most viable energy source for deep space missions and the exploration of planetary surfaces with long day/night cycles.

The European Space Agency (ESA) started its own RPS programme in 2009, aiming towards European capability and independence for RPS design and manufacturing; the selected fuel is americium-241, due to its availability and relatively cost-effective production in Europe. The University of Leicester is developing two RPS technologies: radioisotope thermoelectric generators and heater units.

An important aspect of any RPS programme is safety: the RPS must meet stringent design requirements to minimise the release of radioactive material into the environment in case of accident. Fundamental is the generation of data from experiments and models involving the fuel containment systems, in order to construct a safety case for their launch.

The activities here presented started in 2018 as a collaboration, supported by ESA, between the University of Leicester and ArianeGroup. The objectives were to perform the first-ever impact tests for the European heat sources, and to start developing models to simulate their behaviour in different impact accident scenarios. Metallographic analyses were then performed on the tested samples: the fuel inner containment layers had remained sealed, and they had successfully survived impacts at speeds three times higher than their final velocities. Their design could therefore be considered successful, although some minor improvements might still be required.

Since Europe and ESA currently do not have an operational nuclear launch safety framework, this project was also a key step in starting the definition of a launch safety and authorization process for European missions with RPS.