Standard-less IM-NAA for compositional analysis of nuclear reactor materials: Flux characterization and uncertainty evaluation

Abstract

The standard-less IM-NAA approach using research reactors requires characterization of the different irradiation sites with respect to neutron flux parameters, specifically the sub-cadmium to epithermal flux ratio (f) and the epithermal neutron flux shape factor (α). The flux characterization was performed at two research reactor facilities at BARC, Mumbai: the outer core irradiation position (H7) of the Apsara-U reactor and the Pneumatic Carrier Facility (PCF) of the Dhruva reactor. The accuracy and robustness of the developed methodology was validated using certified reference materials (CRMs). The optimized IM-NAA methodology was subsequently employed for the comprehensive chemical characterization of different steel samples relevant to advanced reactor technology. The uncertainty associated with IM-NAA measurements was rigorously evaluated, accounting for nuclear data parameters (e.g., Q₀, k₀, $\overline{E_r}$) reactor flux parameters (f, α), and other contributors often neglected in conventional analysis. The work successfully demonstrated that IM-NAA, when implemented with properly characterized flux parameters, provides a reliable, standard-less methodology for the accurate and precise compositional analysis of complex alloys, thereby strengthening quality control and material verification protocols for advanced nuclear technologies.