Numerical analysis of thermally stratified flow in the pressurizer surge line

Thermal stratification in the pressurizer surge line of pressurized water reactor has been known to cause considerable local thermal stress and global bending stress in the surge line piping, which may consequently threat the integrity of the piping. Thus the assessment of the potential for piping damage due to the thermal stratification-induced stresses has become one of the major safety issues. To obtain reliable results of stress evaluation, it is necessary to determine as accurately and realistically as possible the transient temperature distribution in the wall of the piping in which thermally stratified flow occurs. This paper presents an effective numerical method for simulating the transient behavior of thermally stratified flow and temperature distributions in the pressurizer surge line piping using the finite volume. The method presented in this paper employs a body-fitted, non-orthogonal grid system to accommodate the piping wall of circular geometry and the interface of the two fluids at different temperatures, of which the level is variable. As an illustration, the present method was applied to calculate the thermally stratified flow and temperature distribution in the piping of a typical pressurizer surge line. For verifying the effectiveness of the method, the result was compared with available analytical steady-state solution. In addition, this study investigates the effects of level of the interface between two thermally stratified fluids on the transient temperature distribution in the piping