Evaluation of the Deterministic and Probabilistic Benchmark for the Advanced Pressurized Thermal Shock Analysis for Long Term Operation (APAL) Project

Abstract The APAL project (Advanced PTS analyses for long term operation), launched in October 2020 under the EU’s HORIZON 2020 program, aims to develop advanced probabilistic methods for assessing pressurized thermal shock (PTS), quantify the impact of long-term operation (LTO) improvements and thermal-hydraulic (TH) uncertainties on safety margins, and create best-practice guidelines for PTS analysis. This paper summarizes findings from the deterministic benchmark (WP3) and the probabilistic benchmark (WP4). Various crack types, locations, fracture toughness concepts, and factors like LTO improvements and TH uncertainties were analyzed. The deterministic benchmark involved structural and fracture mechanics assessments of the reactor pressure vessel (RPV) under PTS to harmonize results across different tools and quantify safety margins. The probabilistic benchmark (WP4) assessed the same cases, focusing on calculating the conditional probability of crack initiation (CPI) and failure (CPF). A key objective was comparing probabilistic and deterministic safety margins, particularly regarding maximum allowable adjusted reference temperature (ART), RPV lifetime, and reliability index. This paper presents comparisons and key insights from both benchmark studies.