Enhancing the energy deposition model in STREAM with photon transport module

Abstract

The conventional analysis of nuclear reactors often neglected the consideration of photon transport, aiming to simplify computational complexity. Photon’s energy was either simplified as locally deposited, incorporated into Kappa values, or smeared throughout the system. However, the advent of advanced reactor designs, characterized by strong gamma emitters and intricate material distributions in radial and axial directions, has exposed the shortcomings of such approaches due to significant photon flux gradients that can arise. High-fidelity reactor analysis necessitates accurate photon calculations to obtain precise photon heating distribution. This thesis introduces the development of a photon module within STREAM (Steady-state and Transient REactor Analysis code with Method of Characteristics). The module encompasses a multigroup photon library, a photon fixed source solver, and an energy deposition model integrating explicit neutron and photon heating. Furthermore, this module also includes the calculation of secondary photons from atomic relaxation and bremsstrahlung processes. The validity of the developed module was established through verification against Monte Carlo codes across a spectrum of Light Water Reactor (LWR) scenarios. Additionally, validation against decay heat data from discharged fuel assemblies in LWRs underscored the module's capability to compute photon heating.