Abstract:
This research presents an analysis of thermal stratification in the reactor
cold leg of the Advanced Plant Experiment-Combustion Engineering (APEX-CE).
This phenomenon may be a precursor leading to a Pressurized Thermal Shock
(PTS) event in a nuclear power plant. This work was performed in support of the
U.S. Nuclear Regulatory Commission's (USNRC) re-evaluation of its PTS
regulations.
Using the APEX-CE test facility, thermal stratification was observed for
injection flow rates ranging from 30% to 100% and natural circulation flow rates
that were generated by core decay powers ranging from 1.5% to 4%, both relative
to the scaled Palisades values.
A theoretical model was derived to estimate the hot stream entrainment that
occurs during cold leg thermal stratification. This model was applied to the
Separate Effects Transparent Loop (SETL) facility, a scaled cold leg/downcomer
configuration of the APEX-CE plant. The model predictions were in reasonable
agreement with the High Pressure Injection (HPI) fluid entrainment data from the
Purdue ½ scale facility. The same model was then used to estimate HPI
entrainment in SETL. The results proved to be very consistent.
Finally, data for the onset of loop seal spillover was obtained using SETL
and APEX-CE. A useful flow map, characterizing the onset condition, was
generated.
