Voiding of ELSY Primary System During Steam Generator Leakage

Harsh coolant environment in lead-cooled fast reactors (LFRs) can cause steam generator tube leakage and/or rupture (SGTL/R). Steam from secondary side can then be entrained by the primary coolant flow into the core which has adverse effects on the reactor performance including heat transfer deterioration and reactivity feedbacks. In this paper, this issue is studied using a deterministic-probabilistic approach. Deterministic Eulerian-Lagrangian CFD model is used to simulate the primary coolant flow field of ELSY reactor and the post-SGTL transport of bubbles. Uncertainties in the relevant bubble size distribution and drag coefficient for bubbles moving in liquid metals have been studied. Probabilistic methodology to estimate the core and primary system voiding rates is proposed and demonstrated. It has been found that a correlation by Tomiyama et al. (1998) gives the best prediction of drag for steam bubbles in liquid lead. Highest probability for being entrained by the flow is for small bubbles in contaminated coolant. The lower the leak in the SG, the higher the risk of void accumulation in the primary system. Analysis also revealed that certain amount of gas can stay entrapped in the primary coolant flow. (author)