Three dimensional numerical simulation of a full scale CANDU reactor moderator to study temperature fluctuations

• 3D model of a Candu reactor is modeled to investigate flow distribution.
• The results show the temperature distribution is not symmetrical.
• Temperature contours show the hot regions at the top left-hand side of the tank.
• Interactions of momentum flows and buoyancy flows create circulation zones.
• The results indicate that the moderator tank operates in the buoyancy driven mode.

Three dimensional numerical simulations are conducted on a full scale CANDU Moderator and transient variations of the temperature and velocity distributions inside the tank are determined. The results show that the flow and temperature distributions inside the moderator tank are three dimensional and no symmetry plane can be identified.Competition between the upward moving buoyancy driven flows and the downward moving momentum driven flows in the center region of the tank, results in the formation of circulation zones. The moderator tank operates in the buoyancy driven mode and any small disturbances in the flow or temperature makes the system unstable and asymmetric.Different types of temperature fluctuations are noted inside the tank: (i) large amplitude are at the boundaries between the hot and cold; (ii) low amplitude are in the core of the tank; (iii) high frequency fluctuations are in the regions with high velocities and (iv) low frequency fluctuations are in the regions with lower velocities.