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Three asymmetric cracks were postulated at the circumferential horizontal weld H7 of a boiling water reactor type 5 core shroud after 25 years of operation. They were arranged in an irregular distribution with different depths. Unstable crack propagation can be induced when an earthquake and a loss of coolant accident take place. In this paper, a ductile failure analysis has been reported. It has been done following an elastoplastic analysis and a plastic limit load analysis. The crack conditions after 30 and 60 years of operation were evaluated. The results show that the core shroud will keep its structural integrity during sixty years under normal conditions of operation. On the other hand, its operational life is reduced five years under failure conditions. In general terms, the methodology, which has been developed, can be applied for any number of circumferential cracks located in the same cross section. Fast and reliable outputs can be obtained. It can be applied in any moment of the life of the plant, to support the decision on “Use as is”, “Mandatory Repair”, or “Estimation of the remaining life.”

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Flow-induced vibrations occur in some of the internal components of a nuclear reactor. When specific conditions are present, these vibrations may result in excessive deformations or fatigue that can generate mechanical damage. Several boiling water reactor (BWR) of nuclear power plants (NPP) have experienced failures in the jet pump assembly due to flow-induced vibration (FIV) which could be caused by acoustic pulsations derived from recirculation pumps, vibration induced by turbulence and vibration induced by leakage at the slip joint. The purpose of this paper is to establish a viable numerical methodology to evaluate the fluid-structural interaction at the slip joint of a jet pump. In this analysis, the fluid-structural interaction was evaluated with the finite element method and finite volume method with ANSYS® code in the case of two steel plates with a divergent gap. Results show that a critical velocity could cause fluidelastic instability, if only one flow in a two-way fluid-structural interaction was considered. This is one of the phenomena that could take place at the slip joint of a jet pump assembly.

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