Advancements in Modeling of Pressurized Thermal Shock Analysis in Reactor Pressure Vessels

Pressurised thermal shock is a complex postulated phenomena that may occur in pressurized vessels. During an overcooling event, the temperature in the reactor pressure vessel drops rapidly generating significant thermal gradients. These thermal gradients induce stress states thought the reactor pressure vessel, RPV. Fabrication flaws present in the wall structure, may start expanding under the effect of the generated thermal stresses and the already present pressure inside the vessel. An important factor that must be taken into consideration is the effect of the neutron flux present in RPVs. Radiation embrittlement is induced by the neutrons and weaken the strength of the RPV wall materials. The complexity of the phenomena occurring in a PTS scenario makes the analysis of large 3D deterministic models time-consuming and computationally demanding. They are therefore not particularly suitable for performing probabilistic calculations. PTS Evaluation Tool (PETO) is a one-dimensional probabilistic code developed in Python language, with the aim of analysing the PTS scenario with reliable results comparable to 3D deterministic models. PETO implements various mathematical models and approximations. The first version of the code, capable of postulating a crack geometry and orientation, is able to determine the probability that the selected crack will initiate in cleavage fracture. This paper focuses on presenting the first version of PETO code. More specifically, the first part is intended for the description of the code structure logic and the models implemented. The second part instead, with testing purposes only, contains a brief demonstration case where the various results coming from the code modules are shown.