In order to improve the reliability of the accident management technique “low-pressure injection by intentional depressurization of steam generator secondary side” in small-break loss-of-coolant accidents (SBLOCAs) with high-pressure injection failure, a statistical safety evaluation method is applied to the thermal-hydraulic analysis of this event. In a past study, the Phenomena Identification and Ranking Table (PIRT) was made and important phenomena were extracted. Then, sensitivity analyses with the important phenomena were carried out, and the influence on peak cladding temperature (PCT) was checked. As a result, one of the parameters whose influence on PCT was especially great was identified as “uncovered core heat transfer”. In this study, the uncertainty of the uncovered core heat transfer model was quantified using separate effect test data. As the separate effect test, uncovered-bundle heat transfer tests done with the Thermal Hydraulic Test Facility (THTF) of Oak Ridge National Laboratory (ORNL) were used. The THTF is a high-pressure bundle thermal-hydraulics loop, and was designed to produce a thermal-hydraulic environment similar to that expected in a SBLOCA.

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