Creep and Creep-Fatigue Crack Growth Mechanisms in Alloy 709

Predicting crack growth lives of components that are subject to long times under stress in complex operating cycles and environments is one essential element in underpinning any proposed flaw evaluation procedure for both next generation advanced nuclear reactors and for the extension of life of existing reactors (such as the UK fleet of Advanced Gas Cooled Reactors, AGRs). The proposed research will contribute to the scientific understanding of mechanisms of creep-crack growth, creep-fatigue crack growth and dwell-fatigue crack growth in a specific stainless steel alloy. Flaw evaluation procedures in future nuclear reactors can then be based with more confidence on models of materials' behaviour underpinned by increased physical understanding. In particular the study will address how results obtained from accelerated tests can be applied appropriately to predict flaw extension behaviour under envisaged operating conditions (over a design lifetime of sixty years).

This programme seeks to develop UK capability in next generation nuclear reactor technologies in close collaboration with US collaborators. Beneficiaries will include:
(i) UK industry- where the mechanistic understanding of a new generation austenitic stainless steel alloy will impact on its future use in the next generation of nuclear fission reactors. The alloy has the potential to allow improved reactor economics, increased safety margins and design flexibility. A comparison of this new alloy with existing alloys in use may contribute to the assessment of life extension methodologies for the current UK fleet of nuclear reactors;
(ii) UK society and public- the provision of safe, efficient and reliable nuclear power both now and in the future is seen as vital to UK energy policy. Improvements in design, reliable operation, increased safety margins and life extension all deliver benefits which can be appreciated readily by the general public;
(iii) UK policy makers- such joint international programmes and studies have the potential to inform and to influence important future energy policy decisions for the UK. International endorsement and appreciation of the quality of UK research contributions is critical in allowing RCUK to argue the case for continued ( and increased) investment in the UK science base for basic research which has strong technological and economic benefits.