Measurements and visualization of velocity profiles in a scaled CANDU6 moderator tank using particle image velocimetry

The moderator tank in a CANDU reactor plays a key role in the reactor core including the fuel channels and moderator. Understanding the circulation characteristics such as the flow pattern and temperature distribution in the moderator tank is important because the cooling capability is limited inside the fuel channels in the worst accident scenarios such as large break loss of coolant accident, resulting in heat removal through the Calandria tubes contacting with the fuels via thermal expansion. Therefore, measurement of the velocity profile and temperature distribution in the moderator tank is a key factor in the safety analysis of CANDU reactors because the moderator tank provides ultimate heat sink. In the present work, the velocity profile in a scaled CANDU6 moderator tank was obtained using particle image velocimetry from the 1st and 2nd jet orifices under symmetric and asymmetric flow conditions. The scaled moderator tank was prepared with acrylic, which is transparent to allow the laser penetration to create the light sheet for illuminating tracer particles. The velocity profile in the scaled moderator tank was obtained from the inlet nozzle running to the top of the tank along and near the curved wall surface and compared to a commercial CFD code, CFX.