Thermal-Hydraulic Simulation of the Moderator System of Ontario Hydro's CANDU Reactors

Abstract

The computer code SOMASS (Simulation Of Moderator And Shield Systems) is used to simulate the steady state and transient response of the moderator and shield cooling systems in Ontario Hydro's CANDU (CANadian Deuterium Uranium) reactors under normal and abnormal operating conditions.Lumped-parameter energy balance calculations are carried out for the moderator fluid and shield coolant: to determine their respective bulk temperatures. During a transient, changes in each of the components comprising the energy balance equations are calculated, and at the end of each time-step the rates of change of the moderator fluid and shield coolant temperature are determined and used to update the system temperatures.Verification of the computer code against two Sets of operating data recorded at Ontario Hydro's nuclear generating stations are presented. It is demonstrated that the code predictions are in good agreement with the station data.