Applicability of LEFM to the analysis of PWR vessels under LOCA-ECC thermal shock conditions

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Abstract
The LOCA-ECC Thermal Shock Program was established to investigate the potential for flaw propagation in pressurized-water reactor (PWR) vessels during injection of emergency core coolant following a loss-of-coolant accident (LOCA). Following preliminary scoping studies involving a PWR reference calculational model, the program was oriented toward determining the validity of linear-elastic fracture mechanics (LEFM) for shallow cracks under LOCA-emergency core coolant (ECC) thermal shock conditions. Four thermal shock experiments were conducted with 0.53-m-OD by 0.15-m-wall (21-in. by 6-in.) modified-PWR-steel cylindrical test specimens. The results of these experiments indicated that LEFM is applicable to the analysis of the thermal shock problem in that agreement with predictions was good and there were no anomalies. Following the four thermal shock experiments, the LEFM methods of analysis were applied to a PWR LOCA-ECC sensitivity analysis in which several primary parameters were varied over anticipated real-life ranges. The results indicated that for the PWR reference calculational model considered, crack initiation could be expected in high-copper vessels, but penetration would be limited to approximately 50% of the wall thickness, if warm prestressing were effective. If warm prestressing were not effective, a long axial flaw would penetrate deeper than 80%. Low-copper vessels may experience crack propagation in the absence of warm prestressing, but penetration would be limited to approximately 50%.

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