Megapie - irradiation experience of the first megawatt liquid metal spallation target

A key experiment in the road-map for accelerator-driven systems is the demonstration of the feasibility, licensibility and reliable operation of a high-power spallation target. The Megawatt Pilot Experiment (MEGAPIE) 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 Paul Scherrer Institute (PSI). The project is supported by an international group research institutions. After completion of the manufacturing in mid-2005, the target and the ancillary systems were first integrated into a test bench to verify the proper functioning and design predictions and to train the handling operations like filling and draining. The test bench was able to deliver about 200 kW heating power, which allowed to simulate the principal thermal-hydraulic processes. The results confirmed the proper functioning and readiness for beam. The target system was integrated and tested in the SINQ facility at the beginning of 2006. This process, as well as the upgrading of some of its supporting systems, took several months. The license, for active operation was obtained in August. First protons were delivered on 14 August 2006 on the target. During a short start-up procedure of about a week, the proton beam was ramped up in steps to full power and the response of the target and its safety systems was verified. With all systems working satisfactorily and according to predictions, standard (24 hour) operation delivering neutrons for the regular users of the facility was started, first in manned operation, then unmanned. Until its scheduled stop on 21 December 2006 an accumulated proton current of 2.8 Ah has been achieved and more than 6 000 beam trips have been experienced. (authors)