Guidelines on pressurized thermal shock analysis for WWER nuclear power plants. A publication of the extrabudgetary programme on the safety of WWER and RBMK nuclear power plants

These guidelines deal with the reactor pressure vessel (RPV) pressurized thermal shock (PTS) analysis required to justify RPV integrity for nuclear power plants with WWER type reactors. The guidelines provide advice on individual elements of the PTS analysis, such as acceptance criteria, selection and categorization of initiating events to be considered, thermal hydraulic analysis, structural analysis including fracture mechanics assessment, evaluation of material properties and neutron field calculations. The objective of the guidelines is to establish a set of recommendations to guide the RPV PTS analysis. The purpose of the PTS analysis is to provide a reasonably bounding plant specific demonstration of the RPV integrity by using realistic modelling methods for the individual elements of the analysis with conservative assumptions, initial and boundary conditions and appropriate safety factors in the assessment of the results. Deterministic approach is used in the guidelines. The demonstration of the RPV integrity is performed in terms of the safety margin between maximum allowable value of critical brittle fracture temperature and its actual RPV material specific values. The recommendations for computer codes used in the PTS analysis are provided as well as requirements on quality assurance for the whole assessment. The guidelines are complemented with a series of Appendices, containing lists of initiating events used for PTS analysis of WWER plants and other plants as well as examples of some national practices. Example of PTS evaluation performed for Loviisa plant is also provided. 26 refs, 13 figs, 7 tabs