Study on the performance of pebble bed HTR initial core with plutonium oxide fuel

The most promising design concept of Generation IV nuclear reactor is high temperature reactor (HTR) with pebble bed type because of its inherent safety characteristics and high coolant temperature. Pebble bed reactor design has tens or even hundreds thousands of fuel pebbles with a graphite moderator and coolant helium. In this study, the reactor core has 8⅓-33⅓ m³ volume and power density of 3 MW/m³ which generate 25-100 MW thermal power. Some stages were carried out, starting from the modeling of fuel and reactor core, optimization of pebble bed HTR initial core as a function of height per diameter ratio (H/D) until optimization of pebble bed HTR initial core as a function of heavy metal loading. The whole calculation was done by utilizing the Monte Carlo transport code MCNPX and continuous energy nuclear data library ENDF/B-VII. Results of the analysis conclude that low H/D ratio and high Pu mass/pebble is the most ideal option in HTR pebble bed core from the viewpoint of neutron economy. (author)