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Characterization of a fast to thermal neutron spectrum converter on PROSPERO reactor

The PROSPERO reactor is located at CEA Valduc Center in France. The reactor is composed of an internal core made of High Enriched Uranium metal alloy surrounded by a reflector of depleted uranium. The size of the assembled core is 352 mm length and 314 mm in diameter. The reactor is used as a fast neutron spectrum source and is operated in delayed critical state with a continuous and steady power for several hours, which can vary from 3 mW to 3 kW, which is the nominal power. The core of the PROSPERO reactor is made critical by driving depleted uranium control rods through the length of the reflector. The PROSPERO reactor is operated in a cell 10 m × 8 m × 6 m high, with 1.4-meter-thick concrete walls. This large cell offers a wide range of irradiation sites from the reflector surface to 6 meter away from the reactor central axis. The flux at nominal power varies from 5.10+10 n.cm-2/s at the reflector surface to 10+7 n.cm-2/s at 5 meters from reactor axis. Due to scattering events in the assembly, the mean energy of the leakage neutron spectrum is 0.8 MeV. This experimental tool is devoted to mixed neutron and gamma fluxes production. The neutron over gamma fluences ratio near the reflector surface is approximately equal to 10.