STRUCTURAL EVALUATION OF THERMAL STRATIFICATION FOR PWR SURGE LINE

Recent observations at operating plants and subsequent US NRC requirem ents have identified flow stratification in surge lines as a phenomeno n that must be considered in the design basis of surge lines. To addre ss these concerns, the stratified loading conditions were included in the design of YGN 3 and 4 surge line as a design basis transient and p ipe temperature and displacement measurement were taken during YGN 3 p re-core hot functional testing to determine the degree of surge line f low stratification. The measured displacements and temperatures were e xtensively reviewed and evaluated in detail: (1) to verify the validit y of the thermal hydraulic model used to predict the pipe top-to-botto m temperature differentials; (2) to analytically correlate measured su rge line temperatures and displacements; and (3) to confirm the validi ty of the stratified how analysis procedure. This paper shows that the stratified flow phenomenon is generic and therefore generic loadings can be developed and evaluated for the surge line analyses. (C) 1997 E lsevier Science S.A.