Design analysis of CAMOLYP reactor core model with Th-UN fuel blanket

The design of the reactor critical assembly for Molly-99 production (CAMOLYP) based on mixed fuel thorium-uranium (Th-UN) is being studied. The CAMOLYP reactor core is spherical in shape with uranium nitrate (UN) as fuel surrounded by Th-UN as a blanket, with a fuel concentration of 300 g/L respectively. The first design model is the core with a single layer reflector and the second is the core provided with a double layer reflector. Both designs will be varied in fuel radius, with 20 cm thick graphite reflector for the first model, and 10 cm thick each for the second model. The MCNPX computer code was used for this calculation of modelling. The result shows that the reactor core with a double layer reflector gives a higher value of neutron multiplication factor (k_eff) than a single layer reflector model. This happens because, in the double layer reflector, neutrons from the exiting UN will be reflected directly to the UN, so that fission reactions occur more. In a single layer reflector, neutrons from the UN that come out will be absorbed by Th-UN so that the neutron population will decrease. The analysis result show that no significant changes in the k_eff value for the increment of blanket thickness for the reactor with a UN fuel radius above 20 cm.