Simulation of the Winfrith SGHWR X-trip blowdown experiment using RELAP-UK Mk IV and RETRAN-UK. Final report

The paper describes calculations with the thermal hydraulics codes RELAP-UK Mk IV and RETRAN to model the behavior of the Winfrith Steam Generating Heavy Water Reactor (WSGHWR) during a controlled depressurization experiment. The results of the simulations are compared with each other and with the experimental data. In the X-trip experiment a reactor trip was initiated from a steady operating condition of 90% of full power and the reactor allowed to depressurize via steam dump lines from the steam drums. During the transient data from a variety of instruments measuring coolant parameters, such as pressures, flows and temperatures, and plant state such as valve positions, were recorded. The version of RETRAN employed in the calculations was a development version of RETRAN-UK with the addition of a number of features from RELAP-UK, including Bryce slip and the Holmes drift flux model. The first 100 seconds of the X-trip transient in one of the two reactor loops has been simulated, during which time the system pressure falls from 940 to 170 psia