As a CANDU6 reactor has a high pressure primary cooling system and an independently cooled moderator system, the moderator in the calandria would act as a supplementary heat sink during a loss of coolant accident (LOCA) if the primary cooling and emergency coolant injection systems fail to remove the decay heat from the fuel. For the safety concern it is required to predict the 3-dimensional velocity and temperature distribution of moderator fluid to confirm the effectiveness of moderator heat sink.
Korea Atomic Energy Research Institute (KAERI) is carrying out a scaled-down moderator test program to simulate the CANDU6 moderator circulation phenomena during steady state operation and accident conditions. This research program includes the construction of the Moderator Circulation Test (MCT) facility, production of the validation data for self-reliant CFD tools, and development of optical measurement system using the Particle Image Velocimetry (PIV). In the present work the PIV technique is used to measure the velocity distributions in the scaled moderator tank of MCT under iso-thermal test conditions. The preliminary PIV measurement data are obtained and compared with CFX code predictions.