PU-238-coupLed dynamic power system for SpAce exploRation and beyond

Project Information

PULSAR

Grant agreement ID: 101061251

Project closed

EC signature date 9 June 2022

Start date 1 September 2022

End date 31 October 2024

Funded under

• Euratom Research and Training Programme (EURATOM)

Total cost

€ 2 294 710,00

EU contribution

€ 1 821 166,00

Coordinated by

TRACTEBEL ENGINEERING S.A.
Belgium

Periodic Reporting for period 2 - PULSAR (PU-238-coupLed dynamic power system for SpAce exploRation and beyond)

Reporting period: 2023-09-01 to 2024-10-31

Summary of the context and overall objectives of the project

Powering space exploration in regions where the sunlight is absent or insufficient requires the use of nuclear technologies. Today, Europe has a dependency on US, Russia and other external players to achieve its space exploration ambitions.

Launched in the frame of HORIZON-EURATOM 2021 program, PULSAR project has two overarching goals :
- to develop in Europe, the building blocks to establish the complete end-to-end capability to produce Plutonium-238 isotopes, and fabricate PuO2 fuel pellets. This is the best fuel for powering space exploration missions with the Radioisotope Thermoelectric Generators (RTG) and Radioisotope Heater Units (RHUs) technologies. The development of these building blocks addresses the critical and non-dependencies technology needs.
- At the same time, to increase the thermo-electrical conversion efficiency for space applications with the development of a dynamic Radioisotope Power Systems (RPS) making use of advanced Stirling engines. The conversion through the Stirling technology has a large performance advantage over thermoelectric materials, reducing the need for the fuel production for a given mission. Knowing that the production of sufficient quantities of isotopes for fueling the missions takes several years, improving the conversion efficiency is key to make the technology more widely accessible. It can also open the door to other markets looking for very reliable power systems over long periods in remote environments (like monitoring in deep sea or mine environments).

The project will develop the proof-of-concept for this first European dynamic RPS. The ambition for PULSAR is to pave the way for the production of a European dynamic radioisotope power system by 2030.
PULSAR supports the application of nuclear technologies beyond their traditional areas of implementation (energy, medical).

The project is organized around the following activities :
- Performing first designs and studies for selecting targets for Pu-238 generation, examining fabrication constraints and separation options,
- Characterization of PuO2 pellets microstructure properties achieved through the fabrication process, and designing a new welding methodology for iridium encapsulation by laser welding and produce a prototype capsule,
- Addressing the regulatory and safety framework for Pu-238 launched in space from a European territory,
- Designing and evaluating the adequacy of the radioisotope heat source
- Designing a robust Stirling convertor for use as an RPS
- Integrating the heat source, and Stirling converters in the RPS assembly, and validating that the design meets the specifications (thermal, structural and shielding requirements).
- Performing an analysis of the market potential for the RPS technology building blocks.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Pu-238 production and processing (WP1) has started with the Pu isotopic vector objective definition and the methodology of resolution to resolve the irradiation model development and validation. The following actions were accomplished the frame of WP1:
- Optimization analyses approach was led focusing on the production at the BR2 Material test reactor at SCK CEN (Belgium).
- A state-of-the-art review paper about neptunium target fabrication and processing of irradiated Np-targets was prepared.
- The preferred Pu/Np separation technique is solvent extraction process.
- The synthesis procedure based on the GPHS PuO2 pellet production was successfully tested byJRC.

The review of the state of the art of energy conversion systems, with potential for space applications, comparing the different converters by means of performance indicators, such as efficiency, Technology Readiness Levels (TRL), specific energy, and assessing the status of European R&D for the different technologies. The study concludes that the Stirling engine is the best fit for space RPS applications. It is characterized by its high efficiency, long demonstrated lifetime potential and modularity, what motivates the extensive international R&D effort of this technology.

A comprehensive review on the state of the art of free piston Stirling Engine for aerospace application was accomplished by UFC, indicating the free-piston Stirling engine (based on type beta structure) as being a good candidate due to its reliability, with an architecture that minimizes detrimental vibrations.

Preparation of a CAO model for the radioisotope Heat Source. The study made by the CEA on this model helped identifying missing dimensional parameters and calculate thermal fields and fluxes. These exploratory calculations show that the model need to be consolidated, but it provides already strong indications that it goes in the right direction.

A first RPS 3D preliminary design was proposed within Work Package 3, integrating the general RPS architecture choices, orientation and sizing of the radiators, material properties and housing structure thickness, coupling principles. The thermal analysis performed on this 3D design by Tractebel provides information on the maximum temperature (in penalizing conditions on the Moon surface) at the Stirling cold source.

Pu-238 availability study (WP4) shows that Europe could have all what is needed to produce Pu-238, taking advantage of existing facilities in Europe (with some adaptation or complementary facilities). This development path is encouraged by the recent investment in space sector developing programs funded by the European Space Agency.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

A Radioisotope Power System offers a unique combination of advantages for space exploration, such as high energy density, long lifespan, independence from sun exposure, high robustness, and combined heat and power. As such, the RPS is a
key enabling technology for exploratory space missions, which go beyond the orbit of Jupiter or, more generally, into regions where sunlight is not sufficient. Pu-238, on the other hand, is considered to be the isotope with the best properties
for for this application, in term of specific power (in W/kg), half life, low shielding requirements (practically inexistent for the Pu-238) and demonstrated positive return of experience from the NASA past missions.

The development of a Pu-238 RPS technology in European would guarantee both sovereignty and leading position for deep space probes. In addition, integrating successfully the Stirling conversion technology would provide further improve the system efficiency (reducing to a minimum the amount of Pu-238 to be produced for a specific mission).
PULSAR paves the way to independent exploratory space missions for Europe, and contribute to the strengthening of the European space industry.

Moreover, the development of the Stirling technology can have other applications linked waste heat recovery.
And RPS can potentially also play an important role for a growing market of unmanned submarine for continuous deep-sea exploration or inspection of undersea cables. The robustness of the technology can essentially eliminate the need for resurfacing and greatly reducing servicing.