Structural Integrity Evaluation of Reactor Pressure Vessel Bottom Head without Penetration Nozzles in Core Melting Accident

Abstract

In this paper, structural integrity evaluation of reactor pressure vessel bottom head without penetration nozzles in core melting accident has been performed. Considering the analysis results of thermal load, weight of molten core debris and internal pressure, thermal load is the most significant factor in reactor vessel bottom head. The failure probability was evaluated according to the established failure criteria and the evaluation showed that the equivalent plastic strain results are lower than critical strain failure criteria. Thermal-structural coupled analyses show that the existence of elastic zone with a lower stress than yield strength is in the middle of bottom head thickness. As a result of analysis, the elastic zone became narrow and moved to the internal wall as the internal pressure increases, and it is evaluated that the structural integrity of reactor vessel is maintained under core melting accident.

Investigation of Nozzle Shape, Number of Nozzles and Nozzle Inclination Angle and Its Optimization

“…They came to the conclusion that high stresses at junctions are produced by discontinuity shear stresses and moments that exist to keep the junction compatible. Lee et al [11] performed evaluation of structural integrity of reactor pressure vessel (RPV) bottom head without penetrating nozzles. They found that thermal load was most significant factor in failure of RPV.…”