Research on Consistency Control of Thermal Neutron Sensitivity of Rhodium Self-Powered Neutron Detectors

The rhodium self-powered neutron detector (SPND) serves as the in-core neutron detector for the Hua-long Pressurized Reactor 1000 (HPR1000) nuclear reactor. Effective control over the consistency of its neutron sensitivity is of great significance for improving the reconstruction accuracy of the reactor’s three-dimensional power distribution.To conduct a quantitative analysis of the consistency of the thermal neutron sensitivity of the rhodium SPNDs, this study first established a model of the rhodium SPND based on Geant4, investigating the correlation between the thermal neutron sensitivity of the rhodium SPND and the dimensions of the detector’s key components.Then, an iterative method was adopted to derive the functional expressions that describe the relationship between the thermal neutron sensitivity of the rhodium SPND and two critical structural parameters: the emitter radius and the insulation layer thickness. Finally, based on these expressions, rapid calculation of the thermal neutron sensitivity of the rhodium SPNDs with arbitrary dimensions within a specified range, as well as an analysis of sensitivity consistency, could be achieved.To verify the feasibility of this method, eight rhodium SPNDs were fabricated. The consistency of their sensitivity was analyzed using the fitted formulas, followed by validation tests via in-reactor experiments. The results showed that the relative errors between the calculated and measured thermal neutron sensitivity values of all eight rhodium SPNDs were less than ±1%, which demonstrated that the method proposed in this paper can effectively analyze the sensitivity consistency of rhodium SPNDs.To achieve a sensitivity consistency deviation within a%, it was necessary to control the dimensional error of the detector relative to its standard dimensions. The permissible dimensional error can be determined by the exhaustive method, in which the fitted formula is adopted to calculate and screen all dimensions satisfying the range: (1−0.01a)S0<S<(1+0.01a)S0.