A coupled neutronics/thermal–hydraulics tool for calculating fluctuations in Pressurized Water Reactors

This paper describes a tool for estimating fluctuations in neutron flux, fuel temperature, moderator density and flow velocity in Pressurized Water Reactors by coupling a dynamic thermal–hydraulic module and a dynamic neutron kinetic module. The code calculates the static solution first, giving the profile of the static fuel temperature, moderator density, velocity and neutron flux. The fluctuations (called noise in this work) are the differences between the actual time-dependent values and the corresponding mean values. The fluctuations are in general induced by perturbations in the thermal–hydraulic parameters, e.g. moderator temperature or density, at the inlet of the core. There is also a possibility to directly define the perturbations in the macroscopic cross-sections and to supply them to the neutronic part of the model. The model was validated against two separate calculations using two different commercial tools.

► Numerical fluctuation calculations for a commercial PWR. ► Fluctuations in neutron flux, fuel and moderator temperature and coolant velocity. ► Coupled models for neutronics and thermal–hydraulics. ► Validated against FLUENT and RELAP5/PARCS.