Simplification in 3-D Neutronics Analysis: Implication for Fusion Diagnostic Systems

Accurate Monte Carlo (MC) simulations are essential for predicting system performance, optimizing design, and ensuring reliable operation. One of the aspects of achieving high-fidelity simulations is the level of detail present in the CAD geometry, especially for diagnostics. This study investigates how varying levels of geometric details, ranging from simplified to more detailed models, affect the neutron and photon flux distributions on the JT-60SA tokamak model. In particular, it focuses on the effect of backscattering from surrounding components on diagnostic and actuator systems such as the Thomson scattering system (TSS) and pellet launching system (PLS). After a brief explanation of the simplification procedure, this work highlights an increase of up to 20% in terms of neutron flux in some diagnostic locations due to the implementation of the ex-cryostat components (e.g., common stage) while decreasing at larger distances from the tokamak.