Doel 3 - Tihange 2 / German RSK Evaluation & Reply

examined here, but not the conservatism of the method. From the point of view of the RSK, the validation does not cover all loading conditions – in particular not the multiaxial loads to be postulated – and the complex interaction between closely spaced cracks in a crack field. In addition, only a small number of experiments were performed to validate the calculation model. Against this background, the RSK welcomes the fact that experiments are being carried out by the Belgian side in cooperation with the French CEA in France under multiaxial loads on comparable, flawed material. The RSK also welcomes the readiness of the Belgian side to get involved in German research projects. This contributes to further improving the validation of the computational models. • The Belgian side investigated the influence of potential residual tensile stresses on the inner surface of the RPV. For the RSK, the results are comprehensible, which show that such residual tensile stresses have only a minor influence on the stresses on flakes. • The thermal shock analyses in case of a loss-of-coolant accident is based on generic analysis for French and American plants with a rotationally symmetric temperature distribution in the RPV. According to the results of international research projects, this represents the enveloping load case for plants of the Westinghouse design.

• From the point of view of the RSK, the requirements of the ASME code for demonstrating a safety factor of 1.5 with regard to the plastic collapse load are met for the RPVs of the two plants.

Overall, most of the open questions of the RSK could be clarified in exchange with the Belgian side. However, there remains the question of adequate experimental validation of the calculation methods for crack fields. The research projects initiated in Germany and Belgium in cooperation with the French CEA can contribute to further improving the validation of the calculation methods.

RSK/ESK Secretariat at the Federal Office for the Safety of Nuclear Waste Management

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