Simulation of γ-ray spectrometry of failed TRISO fuel

Very High Temperature Reactors (VHTR) utilize the TRISO microsphere as the fundamental fuel unit in the core. To understand better its behavior under in-core conditions, the fuel is irradiated in a controlled environment that resembles anticipated operating conditions. In this work, simulated γ-ray spectra are developed for the fission product gases that are released upon fuel failure. The simulations are based on Monte Carlo calculations of spectra assuming the use of high-purity germaniun (HPGe) and high-pressure xenon (HPXe) detectors. The γ-ray source terms for the simulations are derived from ORIGEN 2.2 fuel depletion calculations. In addition, measured detector resolution information are included in the Monte Carlo simulations to produce realistically broadened spectra. The effect of fission product release processes are incorporated in the simulation by reconstructing the Monte Carlo photon source terms using a specific gas-release model. Consequently, birth and release γ-ray spectra are constructed for the Kr and Xe gaseous fission products.