Reactivity cost for different top reflector materials in miniature neutron source reactors

The cost of reactivity of the top reflector in MNSRs was investigated based on the market prices. A 3-D model for the reactor components was used. Three reflectors were compared, namely: graphite, beryllium and heavy water. The average cost of reactivity revealed to be minimum for graphite (maximum value of 3.92 US$/mk), while the second cheapest reflector resulted to be beryllium up to the price of 650 US$/kg. Heavy water can compete with beryllium only for higher prices of beryllium. The best reflector for MNSRs results to be graphite from the economy and safety points of view.