Comparison of semi-heavy water and H2O as coolant for a conceptual research reactor from the view point of neutronic parameters

Abstract

Although semi-heavy water for nuclear reactors has not been industrialized, however due to its interesting characteristics, many research studies have been carried out. A previously high neutron flux research reactor with H2O as coolant and D2O as moderator, with low plutonium production and LEU (3.7%) fuel, is used as our basis design to compare the neutronic parameters of a reactor cooled with either semi-heavy or light water. Neutronic and thermal hydraulic calculations for three core designs: 1) core with H2O/D2O as coolant/moderator and lattice pitch equal to 105 mm as the basis design, 2) core with HDO/D2O as coolant/moderator and core lattice pitch of 105 mm as the first design and 3) core with HDO/D2O as coolant/moderator and core lattice pitch of 120 mm as the second design, have been performed and results are compared. The results show that by substituting HDO for H2O, thermal neutron flux is raised from 1.0811 × 1014 n/cm2-s to 1.146542 × 1014 n/cm2-s at the Beginning of Cycle (BOC) and reactor cycle length is reduced from 158 to 95 days. To compensate the cycle length reduction, core lattice pitch is raised from 105 mm to 120 mm. The new design has achieved thermal neutron flux of 1.160774 × 1014 n/cm2-s as well as improved power distribution and acceptable cycle length (154 days). Based on the presented results, HDO can be used as coolant instead of H2O to increase thermal neutron flux and improve axial and radial Power Peaking Factor (PPF) which improves safety in D2O moderated research reactor.