Moderator temperature prediction under 35% RIH break LOCA with LOECC in CANDU-6

In CANDU-6 reactor, the fuel channel integrity depends on the coolability of the moderator as the ultimate heat sink in a transient condition such as a loss of coolant accident (LOCA) with a coincidental loss of emergency core cooling (LOECC), as well as a normal operating condition. This paper presents the assessments for real CANDU-6 of the normal operating condition and the transient condition, using a general purpose CFD code. A real Calandria vessel of CANDU-6 with 380 fuel channels was simulated and a series of calculations with optimized numerical scheme were carried out to analyze the fluid flow and temperature distributions. Under the normal operating condition, mixed type flow pattern was predicted and the three flow patterns were observed according to inlet flow rate and heat load. The transient condition of a LOCA with a coincidental LOECC was also investigated with the same calculation schemes. Detailed investigations are performed for thermal hydraulic characteristics in terms of the velocity and temperatures of moderator. (author)