A Scheme on Sump Boundary Condition in Shallow Water Equation Solver for OPR1000

Two-dimensional (2-D) Shallow Water Equation (SWE) has been used to predict the transient flow field on containment floor following a loss-of-coolant accident (LOCA) in pressurized water reactor (PWR), encouraged by its fast-running capability and a reasonable predictability. Finite Volume Method (FVM) is frequently used to solve the SWE with unstructured grid system representing the containment floor. However, the limitation from 2-D has been a problem. One of the problems was a difficulty in modeling of the recirculation sump which is a steppeddown region over the containment floor. Discontinuity in bed elevation between the floor and the sump cannot be directly modeled by the SWE, which always requires a complicated approximation during solution procedure. Special boundary condition scheme suitable to simulate the falling flow into the sump pit can be applied, instead of the special technique. To apply the SWE solver to the Optimized Power Reactor (OPR) 1000, three types of phases related to the sump boundary condition should be considered: (1) water falling to the sump, (2) floor filling-up phase after sump filled, and (3) recirculation. Among the three phases, the boundary condition for the recirculation can be easily deduced. The present paper has its aim to discuss a scheme of determine the boundary condition suitable to the phases (1) and (2)