PTS Benchmark Performed Within IAEA Coordinated Research Project 9

During the period 2005 – 2008, the Coordinated Research Project 9 (CRP 9) “Review and Benchmark of Calculation Methods for Structural Integrity Assessment of RPVs During PTS” was organised by the IAEA. The overall objective of this Coordinated Research Project was to perform benchmark deterministic calculations of a typical pressurised thermal shock (PTS) regime and finally to recommend the best practice for PTS assessment. The benchmark concerns the assessment of the reactor pressure vessel (RPV) resistance against fast fracture for events in the NPP leading to PTS. This assessment is based on the stress intensity factors K_I for a postulated crack. The aim of the benchmark was to compare the results obtained by individual participants for well-defined task, to compare the results obtained when applying national codes requirements, and to assess the influence of individual parameters entering the analysis when performing a large set of sensitivity studies. Further aim of this benchmark was to create data which can be used for training of young specialists and for validation of their approach. The benchmark phase of CRP 9 comprised: • Definition of two separate benchmarks for generic WWER-440/213 and PWR-900 (3 Loop) designs, considering the Participants’ own experience and the results of previous international studies. • Basic case analysis of the benchmark problems and application of national code approaches. • Sensitivity studies to assess the impact of individual parameters on the assessment results. The basic (mandatory) case was defined uniquely (all input parameters precisely defined) to enable comparison of the results. Only effect of different models, methods of solving the problems or user effect can be source of the differences in the results, but not the difference in the input data (e.g. material properties, crack geometry, safety margins etc.). The extent and format of output data to be used for comparison were also well-specified. This paper describes the definition of the PTS benchmarks and some examples of the comparative results, like: • variation of temperature through the RPV wall thickness, • variation of stress through the RPV wall thickness, • K_I and K_IC in dependence on temperature, • variation of K_I along crack front, • resulting maximum allowable transition temperature. Finally, it was concluded that the differences among the results were reasonably low and that the methods and models used by the participants can be used for integrity assessment of real RPVs.