A novel method of gamma ray emission estimation to assess fuel burnup in reactor systems with continuous fuel...

Accurate characterization of gamma-ray signatures from advanced reactors with mobile fuels, such as Pebble Bed Reactor (PBRs) and Molten Salt Reactor (MSRs), remains challenging due to continuously varying fuel locations, compositions, and irradiation histories. This work presents a Monte Carlo-based framework for generating high-fidelity synthetic gamma spectra corresponding to known fuel conditions and burnup states using coupled radionuclide inventory calculations and High-Purity Germanium (HPGe) detector modeling. The methodology models individual gamma-emitting radionuclides separately using characteristic emission energies and branching intensities, while accounting for self-attenuation and transport through fuel and surrounding materials. Detector responses are calculated using MCNP simulations and subsequently combined using radionuclide-specific activities and emission yields to produce composite spectra where gamma intensity is represented in counts per second. The objective of this work is not to directly determine burnup from measured spectra, but rather to establish a physics-based spectral generation capability that can support future development, calibration, and evaluation of burnup monitoring techniques for mobile-fuel reactor systems. The framework allows systematic variation of reactor, fuel, and detector parameters to evaluate spectral sensitivity to changing fuel conditions and operating states. This approach provides a foundation for safeguards, diagnostics, and future nondestructive assay methodologies in advanced reactor technologies.