The structural integrity of the RPV is an essential issue for the plant safety. At the design stage, the demonstration is required with material properties at end of life, to ensure the adequacy of the design with the expected operating transients in all conditions. During operation, the integrity assessment is updated every ten years with new existing knowledge and feedback of operating experience, in particular in service aged material data coming from Irradiation Surveillance Program ISP, fluence evaluations taking into account the effective in service core arrangements in each vessel, in service detected flaws plus a postulated subclad crack whose detection cannot be guaranteed by the qualified ISI program. The final assessment showed that the regulatory criteria are met until the fourth decennial outage for 900 MW RPV. The analysis is performed in accordance with French regulations (use of safety coefficients) and follows a deterministic approach in which the input parameters and uncertainties are taken into account conservatively. For the future demonstration beyond 40 years, a multidisciplinary effort is committed to improving knowledge in order to reduce uncertainties in data and in methods. This extensive program involves in particular: - Thermohydraulic analysis and description of transients: temperatures and heat exchange coefficients; - Mechanical analysis: warm pre-stress effect and crack arrest. In addition, a complementary study using a probabilistic approach to rationalize the level of conservatism of input data is launched. In this report, the French deterministic approach and the main results for 40 years duration are presented and the new developments for the future.
The Reactor Pressure Vessel (RPV) assessment and lifetime evaluation of the nuclear plants leads EDF and AREVA to use CFD tools for the demonstration of the Reactor Pressure Vessel (RPV) integrity. French PWR plants have been studied for a long time and so a large number of computations have been performed in three steps: System — CFD — Mechanical Analysis. This paper focuses on the CFD aspects and especially on the two different CFD tools imposed by the physical phenomena of the transient scenarii. Indeed, the results of the system code analysis (CATHARE computations) of the PTS transient induce two kinds of scenarii: single phase and two-phase flows in the cold leg. According to the approach considered, it was interesting to carry out a global benchmark with the different thermalhydraulic tools. In this frame, Code_Saturne and Star CD CFD tools used for single phase flow scenario configuration and NEPTUNE_CFD used for two phase flow configuration were confronted with UPTF (Upper Plenum Test Facility) experiment results in a single phase scenario. The choice to perform this benchmark on UPTF test case was retained because this integral test was very representative of the main physical phenomenon that is well suited for the validation of the CFD tools used to study the Pressurised Thermal Shock for the RPV integrity.
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