This paper presents fracture mechanics analysis for highly loaded reactor pressure vessel (RPV) of the WWER-440/213 unit during in-vessel core melt retention (IVMR) scenario. In-Vessel Core Melt Retention strategy via external vessel cooling is widely applied for reactors of relatively low power like WWER-440. During the IVRM a reactor pressure vessel is affected by huge thermal loading from molted core (a source of heat generation), also internal pressure may be present. To resist these loadings RPV is cooled from the outer surface by the flooding of the reactor cavity. This may lead to thermal shock conditions, as we obtain a huge temperature gradient through the RPV wall, with relative cold water on the outer surface.

The calculations were performed using global 2D RPV model and local 3D sub-model with crack embedded into mesh for J-integral evaluations. First 2D RPV model was used to calculate the global stress-strain state of the RPV. During the calculation plasticity and creep material behavior was considered, as well as melt of the fuel elements during calculation, which were ‘killed’ (excluded) when their temperature was above the melting line. Then a 3D sub-model with crack was calculated, with boundary conditions taken from the 2D axisymmetric analysis. Finally, a J-integral was evaluated according several procedures. Different crack positions are considered, as well as different crack axis ratio. Conclusions were drawn about applications of J-integral procedures for such a highly loaded scenario.

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