Simulation of critical heat flux experiments in Neptune-CFD code

This paper presents a CFD simulation of selected 'Large Water Loop' critical heat flux experiments. Calculations were performed by NEPTUNE-CFD code. The Large Water Loop (LWL) is non-active pressurised-water equipment with technological and thermal parameters corresponding to those of PWR. The CHF experimental facility (a part of the Large Water Loop) has been designed for research into CHF in water flow through a bundle of electrically heated vertical rods. The critical conditions were determined under constant pressure, inlet water temperature and mass flux and for quasi steady-state - by gradually increasing the heat input. The rods are modelled by hollow tubes with direct heating of the wall. Thirteen CHF tests were calculated with NEPTUNE. In all calculated tests, a sudden rise of the wall temperature was observed. Simulations of cases with a higher mass flux were successful. Simulation of cases with a low mass flux indicates that the modelling approach might not be suitable for lower mass fluxes. The results show that NEPTUNE has some potential for predicting boiling flow up to CHF in the geometry of reactor fuel assembly. The presented work was carried out as part of the NURESIM project. NEPTUNE-CFD code is implemented in the NURESIM platform. (authors)