Core power prediction for Nigeria research reactor-1 (NIRR-1) using measurements of dose-rate and temperature

This study presents the results of the core power prediction for Nigeria Research Reactor-1 (NIRR-1), a low power Miniature Neutron Source Reactor (MNSR) using measurements of dose-rate, temperature and neutron flux. The measurements of the dose rate, neutron flux, inlet and outlet temperatures were made for three different power levels (6.2 kW, 15.5 kW and 31 kW) at three stages: The first one was immediately after the reactor start-up (0 min). The second one was at 105 min elapsed time of the reactor operation. The final one was made at every one hour for five hours of reactor operation at 15.5 kW. The values of the dose-rate obtained at 0 min (at 6.2 kW, 15.5 kW and 31 kW power levels) were 6.1 μSv/h, 15.0 μSv/h and 34.2 μSv/h respectively and the corresponding predicted power are 6.8 kW, 15.4 kW and 33.8 kW respectively. The values of the dose-rate obtained at 105 min (at 6.2 kW, 15.5 kW and 31 kW power level) were 7.8 μSv/h, 21.5 μSv/h and 37.4 μSv/h respectively and the corresponding predicted power were 6.3 kW, 17.8 kW and 31.1 kW respectively. For temperature measurement (7.8 °C, 12.7 °C and 18.7 °C) and (7.2 °C, 12.4 °C and 18.3 °C) at 0 min and 105 min, the results obtained were (6.5 kW, 14.8 kW and 28.0 kW) and (7.2 kW, 15.0 kW and 29.0 kW) respectively. For the measured thermal neutron flux (2.07 × 1011n/cm2s, 5.53 × 1011 n/cm2s and 1.13 × 1012 n/cm2s) and (2.06 × 1011 n/cm2s, 5.70 × 1011 n/cm2s and 1.16 × 1012 n/cm2s) at 0 min and 105 min, the results obtained were: (6.21 kW, 16.60 kW and 33.90 kW) and (6.18 kW, 17.10 kW and 34.80 kW) respectively. Comparing the results obtained with the rated power by the manufacturer, it was observed that the power obtained using dose-rate is on average more accurate with deviations (9.7%, 0.6% and 9.0%) at 0 min and (1.6%, 14.8% and 0.3%) at 105 min, and is therefore recommended for all users of Miniature Neutron Source Reactor as well as for routine estimation of Nigeria Research Reactor-1 (NIRR-1) power. In the final stage, the steady state operation of Nigerian Research Reactor-1was investigated at half power.