THIEF Model Evaluation for Cables used in Nuclear Plants in Japan

Many nuclear power plants in the U.S. and elsewhere are transitioning from a prescriptive to a risk-informed performance-based fire protection program. The acceptance of a proposed performance-based fire protection program is partly based on the results of a probabilistic risk assessment (PRA), which quantifies the likelihood of core damage and harmful radiological release in the event of a fire. The fire PRA relies on engineering analyses to determine the effect of fires on safety-related equipment and components, such as electrical cables critical for safe plant shutdown. The report of the CAROLFIRE research program published in 2008 provides thermal and electrical performance data for a broad range of cable types used in U.S. nuclear power plants. The report also describes the thermally-induced electrical failure (THIEF) model, which estimates the temperature response of a cable for a specified thermal exposure. The purpose of the research described in this paper was to obtain thermal and electrical performance data and to evaluate the predictive capability of the THIEF model for some cables that are used in nuclear plants in Japan. Two types of cables were tested, designated as CCV and PSHV. The average fire-induced electrical failure temperature under the jacket of the CCV cable was approximately 400 °C. The average failure temperature of the PSHV cable was approximately 370 °C. Both Japanese cables therefore performed like the thermoset cables in the CAROLFIRE tests. The THIEF model predictions are in remarkably good agreement with the measured cable temperatures for the tests in which electrical failure was observed. However, the model overestimates the cable temperature at the end of the tests in which failure was not observed.