Neutronic design of a very high temperature reactor core with low graphite content

A relevant issue concerning the deployment of the very high temperature reactors is the accumulation of radioactive graphite and its final disposal. One way to reduce the amount of graphite in this type of reactors is to replace the reflector with other material. In this study the Gas Turbine Modular Helium Reactor was investigated, and most of the reflector was replaced with Ferritic-Martensitic steel. The Monte Carlo particle transport code MCNPX 2.6 was used. A fully detailed three dimensional core model was set up in order to evaluate the neutronic response of the modified core design. Results show that the proposed core performs well in terms of the neutron multiplication factor and reactivity coefficients. Considering a reactor life time of 60 years, and taking into account 6 years period for the replacement of the removable reflector, more than one thousand cubic meters of irradiated graphite are saved, which represents estimated economic saving of USD $237,541,000 and 7.73 x 10(15) Bq in radioactivity. (c) 2012 Elsevier Ltd. All rights reserved.