LOFT transient (blowdown) critical heat flux tests

Transient (blowdown) Critical Heat Flux (CHF) tests have been performed on two electrically heated 25-rod bundles simulating a portion of the central assembly of the LOFT nuclear reactor core-1. The bundles were identical except that one bundle incorporated simulated rod surface thermocouples similar to the cladding surface thermocouples attached to some of the LOFT fuel rods. The purpose of these tests was to determine the effect of rod surface thermocouples on time-to-CHF under blowdown conditions similar to those in LOFT. A comparison between bundles showed that differences in time-to-CHF were less than 0.45 sec at any location in the bundles and most of the differences were less than 0.20 sec. An analysis of a LOFT hot fuel rod for a L2-4 blowdown test indicated that a difference in time-to-CHF of 0.5 sec would result in only a 170C difference in peak cladding temperature. Thus, it is inferred that cladding surface thermocouples will not affect time-to-CHF or peak cladding temperature for the nuclear rods in the LOFT core under loss-of-coolant conditions