Session: MF-05-01 Fitness-For-Service and Failure Assessment-1

Paper Number: 123271

123271 - Review of Secondary Stress Treatment in the R6 Fracture Assessment Procedure 

This paper is looking to review ongoing developments related to the treatment of secondary stresses in fracture such that best practice and pertinent information are identified.  This will then allow a more informed position such that the best practice can be implemented, as well as being able to focus future research to areas of most benefit.

In recent years there has been considerable activity on work associated with understanding the impact of secondary stresses on fracture.  Here, secondary stresses are defined as displacement controlled stresses such as thermal and weld residual stresses that do not contribute to plastic collapse.  The consideration of such secondary stresses is crucial to the ongoing justification of nuclear power plant.  The range of work internationally that has focussed on the treatment of secondary stresses includes work performed by Jacobs and others as part of the R6 development programme, work within other UK national programmes into fracture and work published internationally in the open literature.  Given the wide range of activities and potential developments elsewhere, it is considered timely to provide a review of the recent work to understand the areas of progress, relative strengths and weaknesses, potential gaps in understanding, and how this may lead to developments in the associated guidance (such as within R6). 

Secondary stresses are often seen to produce the dominant contribution to the overall crack driving force in fracture assessments of steam raising plant components.  There are known cases where small limiting defect sizes have been evaluated based on extant methods in the procedures but that more recent developments can allow mitigation to these assessments (i.e. removing inherent conservatism, providing larger limiting defect sizes).  More realistic methods for the treatment of secondary stress thus inevitably lead to improved margins that better reflect reality, potentially avoiding or decreasing the need to deploy in-service inspection or allowing less onerous inspections during manufacture offering cost and programme benefits.  Improved methods for treatment of secondary stresses will also usefully contribute to the development of best-estimate probabilistic fracture models that include less inherent conservatism.

The review has identified a number of forward recommendations for further work, which has resulted in an outline for the future work scope at Jacobs.

Presenting Author: Peter James Jacobs

Presenting Author Biography: TBC

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