The APAL project aims to advance safety assessment methods for nuclear power plants (NPP) with the goal of improving their safety across Europe. In particular, APAL will develop an advanced probabilistic and deterministic pressurised thermal shock (PTS) assessment method, quantify safety margins for long-term operation (LTO) improvements and establish best practice guidance. The planned work is divided into five technical objectives:

1. Extensive literature review and collection of experience: APAL aims to identify the state-of-the-art of LTO improvements (NPP hardware and software) that may have an either beneficial or adverse impact on the results of PTS analysis. This includes the identification of technology gaps and the definition of possible improvements. Furthermore, the human factor relevant during a PTS event will be identified (and quantified) based on available operator experience and expert judgement. Moreover, state-of-the-art reports on selected parts PTS assessment, like treatment of residual stresses, application of warm prestress approach, thermal hydraulic analyses and probabilistic PTS assessment, will be issued.

2. Broad thermal hydraulic (TH) assessment: As one of the most important steps in the entire PTS analysis, APAL aims to quantify the impact of LTO improvements and human factor on the results of TH analysis. Moreover, this impact will be assessed by subsequent structural and fracture mechanics benchmarks while considering uncertainties in TH analysis (due to plant data, used computer codes and human factor) and addressing their impact on the entire PTS analysis.

3. Deterministic structural and fracture mechanics analyses: APAL aims to quantify the safety margins related to LTO improvements and uncertainties in TH analysis through assessments which will be carried out based on a common deterministic benchmark. This common benchmark will be defined based on the extensive benchmark provided by the NUGENIA+ project DEFI-PROSAFE, for which a solid validation and verification basis is available.

4. Probabilistic margin assessment based on probabilistic fracture mechanics analysis: As the quantification of safety margins grows in importance and deterministic assessments are reaching their limits, APAL aims to establish an appropriate benchmark for the probabilistic fracture mechanics analysis. This will be defined in accordance with the benchmark performed for deterministic margin assessment. An advanced probabilistic PTS assessment will be performed by considering the TH uncertainties in the subsequent structural mechanics and probabilistic fracture mechanics analyses. In addition, a link between deterministic and probabilistic margin assessment will be established.

5. Recommendations and definition of best-practices: APAL will analyse the performed work to define best-practices for an advanced PTS analysis for LTO in close cooperation with the Advisory Board (AB), regulatory bodies and end users and disseminate these results through dedicated workshops, training events and additional communication channels targeting the scientific community.