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This report summarizes the results of the NURESIM project for the work package 2.1 “Pressurized Thermal Shock (PTS)”. It includes summaries of the single tasks done by the partners involved in this work package. In the Introduction chapter some more general information on the PTS issue is given, which should help to clarify the integration of the single activities. Since the PTS scenario involves different flow situations, for which also different modelling approaches are necessary, the tasks are sorted according to these flow situations. The relation of the work done to the general aim of the NURESIM project, which is to establish a new code platform, is indicated by assigning the activities to 6 different types. The results achieved in the PTS work package are in agreement with the expectations to the NURESIM project. The conclusion drawn from the single investigations and recommendations for future work are discussed in a separate chapter. It was shown, that for further improvement of the CFD-code capabilities for the two-phase PTS case new well-instrumented experimental data are needed especially for condensation at the surface of a sub-cooled liquid jet in a steam environment as well as on free surfaces, turbulence production and bubble entrainment below the jet and mixing in a stratified flow. Integral experiments, which reflect the PTS flow situations, are important to test the interplay between all the sub-models. Some of the local flow situations can be already captured quite well by presently available CFD codes, for other still many open questions exist. In general more flexible models are required which allow switching between different approaches within one flow domain but for the different local flow situations. Examples for such model approaches are the Large Scale Simulation (LSS) which should allow the application of a two-fluid model for dispersed flows and Interface Tracking Methods for large surfaces and the Scale Adaptive Simulations (SAS) which allow the simulation of large eddies while modelling the turbulence at the unresolved scales. The work done leads to a clear improvement of the simulation capabilities regarding a two-phase PTS situation, but caused by the complexity of the issue it will still be a long way to enable predictive simulations for all the different phenomena that occur in this application. In the near term, one may envisage a simplified treatment of two-phase PTS transients by neglecting some effects which are not yet controlled.

This report identifies PTS-scenarios for the French 900 MW CPY PWR, the German 1300 MW Kon-voi reactor, the Loviisa 400 MW VVER, the Russian VVER-1000 and the Czech VVER-100. Accord-ing to the resulting basic flow conditions relevant physical phenomena for the simulation of the scenes during Emergency Core Cooling (ECC) injection into the cold leg are identified. The main focus is on two-phase flow phenomena. The state of the art of modelling these phenomena and needs for models improvement are discussed. Thus the report is a suitable basis for the specification of the main topics to be provided in Task T2.1.4 of the NURESIM project.