Knowing the predicted overpressure rate under anticipated operational occurrences (AOOs) is very important when evaluating the integrity of a BWR reactor pressure vessel. One of the factors that influence the overpressure rate is the wall condensing performance. Many condensing studies have been done under low-pressure conditions without vapor flow, but few condensing test results under BWR conditions have been reported. Therefore, the purposes of this study were to extend the vapor condensing data base for high-pressure, high-temperature conditions, to improve the heat transfer correlation and to evaluate the condensing effect on the overpressure rate. Condensation heat transfer tests have been performed with the pressure range from 0.5 to 8 MPa under upward and downward vapor flow. The test section consisted of a condensing tube and a water-cooling jacket. The condensing tube was a circular tube. The test results showed that the condensation heat transfer coefficient increased with the velocity of vapor flow due to enhancement of heat transfer caused by turbulence of the liquid film. We obtained a new correlation for condensation heat transfer that considered vapor shear force and condensate film Reynolds number. This new correlation agreed well with experimental data over a wide range of pressure. New correlation was incorporated into TRACG02modT1 code. When the condensation heat transfer tests were analyzed using this modified TRACG02modT1 code, the calculated condensation heat transfer coefficients were found to be in considerable agreement with the measured data. Furthermore, when the main steam isolation valve AOO (safety relief valve capacity design) of the BWR plant was evaluated by this modified TRACG02modT1 code, we found that the vapor condensation effect appeared under relatively high-pressure conditions and the pressure with improved condensation model was lower than that without vapor condensation. In summary, the condensation heat transfer model of TRACG02modT1 code has been improved based on high-pressure, high-temperature condensation test data with vapor flow. The vapor condensation effect was found to be strong, especially in the pressure increase AOO of the actual plant.

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