PTS thermal hydraulic testing in the OSU APEX facility

The APEX Test Facility at Oregon State University has been modified to simulate a typical 2 x 4 loop Combustion Engineering nuclear plant. The new configuration, APEX-CE, will be used to perform a series of separate effects and integral systems overcooling tests that examine the conditions that lead to primary loop stagnation and cold leg thermal stratification. RELAP5 calculations will be compared to the test data to assess its ability to predict the onset of loop stagnation. A computational fluid dynamics (CFD) code will be assessed against the APEX-CE cold leg and downcomer fluid mixing data. This work is part of the US nuclear regulatory commission's (USNRC) effort to review its existing pressurized thermal shock (PTS) guidance.