Benchmark-based neutronic and thermal-hydraulic evaluation of a modified beryllium reflector for enhanced irradiation capability in an MTR-10 MW reactor

A benchmark-based neutronic and steady-state thermal-hydraulic assessment was performed to evaluate beryllium reflector configurations for enhancing irradiation capability in the MTR-10 MW research reactor. The reference one-trap core was modified to a symmetric four-trap layout, and a constrained sequence of graphite and beryllium reflector substitutions was assessed with MCNP4C2/MTRMC. The four-trap configuration reduced the initial excess reactivity from 141.71 to 82.85 mk. The selected 22-block beryllium reflector recovered the excess reactivity to 139.38 mk, corresponding to 96.04% recovery of the reactivity loss relative to the shifted four-trap base case. The four-site average thermal neutron flux increased from the reference central-trap mean of 1.055 × 10 14 to 1.319 × 10 14 n·cm -2 ·s -1 , an average gain of 25.0%, while the maximum site reached 1.904 × 10 14 n·cm -2 ·s -1 . After applying a comparable active neutron-history basis, OpenMC reproduced the same recovery trend, giving 96.94% recovered reactivity. The steady-state thermal-hydraulic assessment used CAUDVAP/TERMIC-1H at 550 m 3 /h, giving a total mass flow rate of 151.607 kg/s and a mean pressure drop of 5.372 kPa. The maximum plate power in the hottest fuel element was 28.93 kW, giving a hot-plate peaking factor of 1.24 and a hot-plate heat-flux input of 49.4 W/cm 2 . The TERMIC-B2 case at 50 W/cm 2 therefore represents the rounded-up hot-plate condition for the final configuration, with redistribution and DNB ratios above unity over the assessed hot-channel velocity interval.