Study on Temperature Coefficient of Reactivity for Pebble Bed Reactor with Thorium Fuel

The pebble bed reactor has a flexibility to utilize a wide range of different fuel cycles without significantly modifying the reactor core geometry. These fuel cycles can be comprised of various fissile and fertile fuel isotopes. The purpose of this paper is to study the temperature coefficient of reactivity for pebble bed reactor fuelled by thorium. The HTR-Modul was chosen as the reactor model. A series of calculations was performed by the use of the Monte Carlo transport code MCNP6 with the continuous energy nuclear data library ENDF/B-VII. The k∞ calculation results show that the fuel load with a mass of 2g Th/pebble, 5g Th/pebble and 20g Th/pebble can achieve a critical core with discharge burnup of 65,644; 101,500; and 114,215MWd/t, respectively. The calculation results of temperature coefficient conclude that specific mass of thorium per pebble might have a positive temperature coefficient of reactivity at a certain temperature. Further investigation needs to be conducted to analyze the behavior of these temperature reactivity coefficients in more detai