Evaluation and results of loft steady state departure from nucleate boiling tests

Steady state departure from nucleate boiling (DNB) tests have been performed on electrically heated rod bundles simulating the central region of the Loss-of-Fluid Test (LOFT) nuclear reactor core. Objectives of the tests were to determine the effects on DNB due to thermocouples mounted externally on the LOFT fuel rod cladding under steady state operating conditions, and to obtain a data base for the development of a DNB correlation for LOFT Core-1. Tests were conducted on 25-rod bundles with and without rod external thermocouple simulators. The test data indicated that the DNB heat fluxes in the rod bundles with external thermocouple simulators were 5 percent to 28 percent lower than those in the rod bundle without rod external thermocouple simulators over the pressure range of 2000 psia (1.38 x 104 kPa) to 2400 psia (1.65 x 104 kPa). A LOFT DNB correlation has been developed to predict thermal safety margins in the LOFT reactor for steady state and plant transient (non-blowdown) operation. The LOFT correlation predicts the 455 data points from the bundles with rod external thermocouple simulators with a mean value of 0.9998 and a standard deviation of 0.0645, and provides a 95 percent probability at a 95 percent confidence level of not experiencing DNB on a rod at a minimum departure from nucleate boiling ratio of 1.13