RELAP4 pre-test predictions for the LOFT transient (blowdown) DNB tests in the Columbia University test loop

Rod bundles simulating the LOFT Core-1, both with and without rod external thermocouple simulators, will be tested to determine the effect of rod external thermocouples on time-to-DNB under blowdown conditions similar to those in LOFT. Pre-test predictions have been made using the RELAP4 computer code. The purposes of this analysis were (1) to predict blowdown orifice sizes which result in the closest simulation of coolant pressure, quality, and flow rate between the test section and the LOFT core for a LOFT 200 percent simulated cold leg break at a peak linear heat generation rate of 19 kw/ft, (2) to determine ranges for instrumentation, and (3) to estimate the time-to-DNB in the rod bundles. An exact simulation of the LOFT blowdown conditions, however, can not be obtained in the test section because the rod bundles have a uniform axial power profile and the Columbia test loop is not scaled to the LOFT configuration