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Final Report Summary - STYLE (Structural integrity for lifetime management – non-RPV components)

The overall objective of the STYLE project has been to assess, optimise and develop the use of advanced tools for the structural integrity assessment of reactor coolant pressure boundary components relevant to ageing and life time management. The range of assessment tools considered has included those for assessment of component failure by advanced fracture mechanics analyses, validated on small and large scale experiments, quantification of weld residual stresses by numerical analysis and by measurements, stress corrosion crack initiation/growth effects, and assessment of RCPB components under dynamic and seismic loading.

Several technical issues have been addressed in STYLE. These include:

• Dissimilar metal weld integrity,
• Effect of weld residual stress on fracture and damage modelling,
• Weld residual stress simulation and measurement with and without weld repairs,
• Transferability of material properties,
• Stress corrosion cracking,
• Thermal fatigue through turbulent mixing,
• Dynamic impact testing and FE analysis,
• Benchmarking of engineering assessment methods and leak-before-break approaches.

The STYLE project has been largely centred on structural mock-ups and supporting experiments from small to large scale. The overall aim of the project was to establish enhanced tools and methodologies to be applied in lifetime assessments of pipes and associated components. Highly sophisticated experimental and computational methods and advanced tools have been developed, in order to realistically describe the complex physical mechanisms leading to ageing and failure of the reactor coolant system piping and components. Various European Leak-before-break (LBB) and engineering assessment (EAM) methods to predict the integrity of welds and weld repair issues, including manufacturing procedures, qualification of inspection techniques and mitigation measures have been compared within the project and validated against the mock-up experiments. The STYLE project has made significant achievements, but there is still further work required in order to enhance the structural integrity understanding and best practice guidance for nuclear piping systems and associated components. This work includes:

• Properly quantifying and understanding the levels of conservatism in current integrity assessment methods with a view to revising guidance and procedures using data which have been produced during the STYLE project
• Consolidating results in the form of best practice guidelines for harmonization of procedures for fracture toughness assessment (testing and integrity) of dissimilar metal welds
• Further developing advanced tools for structural integrity assessment and plant lifetime management
• Benchmarking safety assessment methodologies including comparison of outputs from deterministic versus probabilistic methods and integration into the safety assessment
• Completing the knowledge of material properties and their testing techniques for relevant materials.

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