Gas production in the MEGAPIE spallation target

The MEGAwatt PIlot Experiment (MEGAPIE) project was started in 2000 to design, build and operate a liquid Lead-Bismuth Eutectic (LBE) spallation neutron target at the power level of 1 MW. The target was irradiated for four months in 2006 at the Paul Scherrer Institute in Switzerland. Gas samples were extracted in various phases of operation and analyzed by γ spectroscopy leading to the determination of the main radioactive isotopes released from the LBE. Comparison with calculations performed using several validated codes (MCNPX2.5.0/CINDER'90, FLUKA/ORIHET and SNT) yields the ratio between simulated in-target isotope production rates and experimental amount released at any given time. This work underlines the weak points of spallation models for some released isotopes. Also, results provide relevant information for safety and radioprotection in an Accelerator Driven System (ADS) and more particularly for the gas management in a spallation target dedicated to neutron production facilities.