| Thermal fatigue estimation due to thermal stratification in the RCS branch line using one-way FSI scheme Kwang-Chu Kim
The Journal of Mechanical Science and Technology, vol. 22, no. 11, pp.2218-2227, 2008
Abstract : The scheme and procedure for thermal fatigue estimation of a thermally stratified branch line were developed. Oneway
FSI (fluid and structure interaction) scheme was applied to evaluate the thermal stratification piping. Thermal flow
analysis, stress analysis and fatigue estimation were performed in serial order. Finally, detailed monitoring locations
and mitigation scheme for the integrity maintenance of piping were recommended. All wall mesh and transient temperature
distribution data obtained from the CFD (computational fluid dynamics) analysis were directly imported into
the input data of stress analysis model without any calculation for heat transfer coefficients. Cumulated usage factors
for fatigue effect review with nodes were calculated. A modified method that combines ASME Section III, NB-3600
with NB-3200 was used because the previous method cannot consider the thermal stratification stress intensity. As the
results of evaluation, the SCS (shutdown cooling system) line, branch piping of the RCS (reactor coolant system) line,
shows that the CUF (cumulative usage factor) value exceeds 1.0, ASME Code limit, in case thermal stratification load
is included. The HPSI (high pressure safety injection) line, re-branch piping, shows that temperature difference between
top and bottom of piping exceeds the criterion temperature, 28℃, and that the CUF value exceeds 1.0. Therefore,
these branch pipings require a detailed review, monitoring or analysis. In particular, it is recommended that the HPSI
piping should be shifted backward to decrease the influence of turbulent penetration intensity from the RCS piping.
Keyword :
Thermal stratification; Thermal fatigue estimation; RCS branch line; FSI scheme
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