Neutronics calculations and design for the medium flux test module of IFMIF

The International Fusion Material Irradiation Facility (IFMIF) is proposed as an intense neutron source to test fusion reactor materials under relevant irradiation conditions. It should provide a proper neutron spectrum with sufficiently high damage production rates to allow also accelerated tests within an appropriate volume. The primary goal of the present study was to select on the basis of neutron transport calculations a suitable design of the IFMIF medium flux test module (MFTM) for a proper irradiation response of ceramic breeder materials. On the basis of systematic screening studies of different material combinations and test module shapes, MCNP4c Monte Carlo calculations have shown that the IFMIF neutron spectrum could be largely adjusted to DEMO reactor conditions by combining tungsten plates serving as spectral shifter and carbon jackets of the test modules acting as neutron reflector. In addition, displacement damage code calculations confirmed that IFMIF provides over the entire energy range DEMO reactor specific primary knocked on atom (PKA) spectra, which governs the damage morphology and, hence, mechanical properties of many irradiated materials. For Li4SiO4 enriched with 6Li, neutron spectra, gas production and damage rates are presented and compared with those of a helium cooled pebble bed blanket of a fusion DEMO reactor.