CATHENA simulation of the WOLSUNG D20 spill incident of 1984 November 25

The CATHENA (formerly ATHENA) has been used to simulate the thermalhydraulic behaviour of the WOLSUNG-1 CANDU-600 reactor during the D20 spill incident of 1984 November 25. A 4-inch (nominal) Liquid Relief Valve inadvertently opened in the reactor auxiliary system during normal reactor operation, resulting in a discharge of heavy water from the primary heat transport system. The valve remained open for approximately 29 minutes. CATHENA is an advanced thermalhydraulic computer code for analysis of postulated loss-of-coolant accidents (LOCA) and transient faults in CANDU nuclear reactors. A full two-fluid (six-equation) representation of the two-phase flow is used. Component models are used to represent pumps, valves, critical discharge, etc., which are necessary to describe the behaviour of the CANDU system under upset conditions. Heat transfer between the fluid and piping walls (or fuel) is modelled using applicable correlations for boiling, condensation and convective heat transfer. The two, figure-of-eight, primary heat transport (PHT) loops of the reactor were modelled with CATHENA using initial conditions and relevant boundary conditions derived from actual plant data. The CATHENA simulation of the event showed excellent agreement with available plant data