Heat transfer during a small-break loss-of-coolant accident in a pressurized water reactor - a parametric study for a 4 in. lower-plenum break

A major safety concern in pressurized-water-reactor (PWR) design is the loss-of-coolant accident (LOCA), in which a break in the primary coolant circuit leads to depressurization, boiling of the coolant, consequent reduced cooling of the reactor core, and, unless remedial measures are taken, overheating of the fuel rods. This concern has led to the development of several computer models for safety analysis, the validity of which can be assessed only after their accuracy and sensitivity has been subjected to parametric studies, such as: nodalization studies to ensure grid-independency of the results; investigation of alternative empirical input, such as heat-transfer representations, choice of flow regimes, etc., and the representation of stratified two-phase flow in the horizontal pipes. This paper presents such parametric studies for a postulated PWR accident. The results are presented and discussed. It is concluded that the predictions are significantly affected by the number of grid nodes used, by the chosen heat-transfer and interphase friction correlations and by the modelling of stratified two-phase flow in horizontal pipes. Such sensitivities may, it is suggested, be exhibited by other LOCA simulations. (author)