History of TAGSI
Following publication of the Addendum to the Second Report the UKAEA Board, Brian Eyre (as the Board Member for Programmes) was asked to form a new group, TAGSI, and to submit new terms of reference to the board for endorsement.
Technical Advisory Group on the Structural Integrity (TAGSI) was set up in 1988 to continue studies into the integrity of nuclear power plant, following the Study Groups, chaired sequentially by Walter Marshall and Peter Hirsch, which were devoted to the integrity of the pressurised water reactor (PWR). Over the twenty-seven year period, TAGSI has been chaired by Brian Eyre, Peter Hirsch, Michael Burdekin, John Knott and Bob Ainsworth.
TAGSI sponsorship by the Nuclear Industry and MOD, and the direct involvement of regulatory observers, and the Sponsors’ right to suggest topics for the discussions ensured that the topics were of direct relevance to the Nuclear Industry. TAGSI’s method of working by setting up specialist subgroups, which reported to the main Committee, has proved to be very successful.
Achievements include the development of the TAGSI “Four Legs” methodology, as described by Michael Burdekin. In the absence of sufficient deterministic information to give confidence in a quantitative probabilistic analysis, it is possible to construct a conceptual “defence in depth”, drawing on different strands, or “legs”. These include:
- quality of build;
- any critical test, such as the proof-pressure test;
- analysis of failure mechanisms and sub-critical crack growth-rates;
- and any forewarning of failure.
As the UK prepares for the introduction of a new generation of nuclear power plants TAGSI will continue to play an important role and in a concluding section we briefly consider some of the structural integrity related challenges to be faced.
Purpose
TAGSI is an acronym for the UK Technical Advisory Group on the Structural Integrity of High Integrity Plant where the potential consequences of failure are extremely severe. The purpose of TAGSI is to address issues raised by its sponsoring organisations in discussion with eminent independent advisors. TAGSI reports to its Sponsors. TAGSI’s recommendations are made to its sponsoring organisations. Collectively, these sponsoring organisations operate, maintain and assess nuclear power producing and chemical plant.
Mode of Operation
All work done by TAGSI is to be defined by specific questions from among the sponsoring organisations and endorsed by all the Sponsors.
TAGSI will operate through ad hoc sub groups convened at the Chairman’s request to address a particular issue. A Sponsor may nominate a representative to serve on each ad hoc sub-group.
A list of potential questions will be maintained by TAGSI with choice of active questions equitably discussed at the main committee. TAGSI will endeavour to have between two and four active sub groups at one time.
Depending on the nature of a question, the Sponsor(s) introducing it may suggest a response on which TAGSI is invited to comment.
TAGSI will endeavour to ensure continuing capability of TAGSI, to support the questions from the sponsoring organisations, through continuing development and nomination of Independent Members.
Terms of Reference
On behalf of the Sponsors, TAGSI will address the following generic issues pertinent to plant structural integrity:
- Structural integrity methodologies, codes and safety case approaches;
- Acquisition and interpretation of materials data;
- Failure mechanisms;
- Inspection methods and applications;
- Probabilistic aspects of structural integrity methodology.
TAGSI will provide peer review and informed comment on the scientific principles used in structural integrity assessment methods and procedures and used to underpin the interpretation of materials behaviour in response to issues raised by the Sponsors.
TAGSI will provide advice and opinion on generic aspects of structural integrity methodology in relation to plant problems and safety issues with particular emphasis on suitably consistent standards and approaches.
The Sponsors’ use of any such information is entirely at their own risk.
TAGSI reports are not for use outside of TAGSI without the expressed permission of the Chairman and Sponsors. Where possible TAGSI outcomes will be published in the open literature.