Modelling of graphite properties for GT MHR loaded with Pu fuel

Ageing of materials under neutron irradiation conditions is one of the most important issues of high temperature reactors. The modelling of the gas turbine modular helium cooled reactor (GT MHR) is performed in order to evaluate the neutron induced displacement damage in the graphite core and reflectors in case of using the Pu fuel from military applications. The MCNPX modelling is performed to obtain the neutron fluxes in reflectors and core zone during the fuel cycle of GT MHR. Neutron induced displacement damage per atom (DPA) in each zone is evaluated based on binary collision approximation (BCA) formalism using several codes: SPECTER, SRIM2013 and GEANT4. The highest DPA intensity occurs in the hexagons near fuel channels, while the lowest DPA intensity is observed in the outer graphite reflector. It is concluded, that no significant microstructural changes would occur in the reflectors of GT MHR, so they could be used for all operating lifetime without the need to change them. (author)