MEGAPIE: The World’s First High-Power Liquid Metal Spallation Neutron Source

Abstract

A key experiment in the accelerator-driven systems (ADS) roadmap, the MEGAwatt PIlot Experiment (MEGAPIE) (1 MW) was initiated in 1999 in order to design and build a liquid lead–bismuth spallation target, then to operate it at the Swiss spallation neutron facility, SINQ, at the Paul Scherrer Institute (PSI). The target has been designed, manufactured at ATEA (France), then set-up, fitted with all the ancillary systems, on an integral test stand at PSI for off-beam tests dedicated to thermo-hydraulic and operability tests, carried out during the last months of 2005. The system was then placed with its ancillary system in the SINQ facility, for final operation under irradiation, which was carried out from August 14th to December 21st, 2006. The irradiation allowed very important results to be obtained, including those showing the very good operational behavior of the target. Moreover, a lot of results in the thermal hydraulic and neutronics fields, and gas analysis contributed to validating the design studies and the assumed theoretical models. Decommissioning of the target has been carried out and PSI teams have prepared samples (760) for post-irradiation examination (PIE). The samples have been distributed to the following partner laboratories: Commissariat à l’énergie atomique et aux énergies alternatives (CEA), Karlsruhe Institute of Technology (KIT), Paul Scherrer Institute (PSI), SCK·CEN, and the US Los Alamos National Laboratory (LANL). The Centre national de la recherche scientifique (CNRS) and ENEA will also contribute to the PIE to be carried out in the SCK-Mol and PSI hot laboratories, respectively. The goal is to study the changes to the structural material properties caused by the harsh environment of high temperatures, contact with flowing liquid metal (lead–bismuth eutectic, LBE), and proton irradiation. After presenting an overview of the project history, we describe the target decommissioning, PIE sample preparation and distribution, and highlight the first results that have been obtained. The successful behavior of the target and the coming results about irradiated materials will provide to ADS community with unique operational feedback, paving the way to develop high-power spallation targets as neutron sources and for future ADS-based options for the transmutation of nuclear wastes.