Abstract
This article simulates the multiphysics coolant thermohydraulic conditions and fuel performance of a pressurized water reactor (PWR) during a loss-of-coolant accident (LOCA). In the coolant channel of a PWR, the coolant undergoes a series of different boiling regimes along the axial direction. At the inlet of the coolant channel, heat exchange between the cladding wall and coolant is based on single-phase forced convection. As the coolant flow distance increases, the boiling regime gradually converts to nucleate boiling. When a LOCA occurs, on the one hand, the coolant flux and coolant pressure decrease sharply; on the other hand, the heat flux at the cladding wall decreases relatively slowly. They both contribute to a swift increase in coolant temperature. As a consequence, a boiling crisis may occur as critical heat flux (CHF) decreases. In this article, the void fraction along the length of coolant channel in a reactor and mechanical performance of Zr cladding enwrapping UO2 fuel are investigated by establishing a fully coupled multiphysics model based on the CAMPUS code. Physical models of coolant boiling regimes are implemented into the CAMPUS code by adopting different heat transfer models and void fraction models. Physical properties of the coolant are implemented into the CAMPUS code using curve-fitting results. All physical models and parameters related to solid heat transfer are implemented into the CAMPUS code with a 2D axisymmetric geometry. The modeling results help enhance our understanding of void fraction along the length of the coolant channel and mechanical performance of Zr cladding enwrapping UO2 fuel under different coolant pressure and mass flux conditions during a LOCA.
Highlights
Developing a computational code fully coupling multi-physical fields in the pressurized water reactor (PWR) is of great interest
We investigated the void fraction of the coolant and the mechanical properties of fuel cladding before the flow boiling reaches critical heat flux (CHF) in this article, fully coupling key fuel performance phenomena, and cladding-coolant heat transfer
The experiments were carried out for a 5 × 5 fuel rod bundles, and they covered typical PWR-type conditions: coolant pressure ranges from 100 to 155 bar, mass flux ranges from 3,000 kg/m2/s to 4,600 kg/m2/s, and heat flux varies from 570 kW/m2 to 1,400 kW/m2
Summary
Developing a computational code fully coupling multi-physical fields in the pressurized water reactor (PWR) is of great interest. The modeling results of a previous work were adopted and combined with different heat transfer models and void fraction models to predict the void fraction along the length of the coolant channel in a reactor and mechanical performance of Zr cladding enwrapping UO2 fuel under normal operating conditions and conditions with a drop of pressure and coolant mass flux. Our understanding is toward void fraction along the length of coolant channel and mechanical performance of Zr cladding enwrapping UO2 fuel cladding under different coolant pressures and mass fluxes through fully coupled modeling including a LOCA. This is useful for the prediction of CHF and the safety of cladding material
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