Advancing structural integrity safety issues in the nuclear industry

Structural integrity is paramount in nuclear safety issues. Following the Fukushima accident (March 2011), questions about the resurgence in nuclear energy and worries about operational safety have once again come to the forefront of the news. It is obvious that dealing with safety as well as public relations are both very important topics in the nuclear industry, as the political, social and a ‘nervously-oriented’ media scrutiny always influence the governmental decision-makers who have the duty to balance public concerns with the need to guarantee energy production.

The UK, being one of the early pioneers of civil nuclear build, chose the Advanced Gas Cooled Reactor design. This operates at high temperatures and where aggressive environments such as creep, oxidation and corrosion drastically reduce components’ safe lives. Resulting from this, during the early years of operation under the-then Central Electricity Generating Board (CEGB) and later British Energy, the UK nuclear industry embarked on a pragmatic approach to develop advanced safety codes. This approach aimed to make as certain as possible that these plants would run safely under an extended lifetime without endangering public safety. As a result, the UK now leads the world through its advanced hands-on approach in day-to-day safety of the plants.

Since the 1970s, Imperial College has been a major contributor in the field – supported by CEGB, British Energy and now EDF Energy (UK). At present, Imperial is an international leader in the research and development of novel fracture mechanics concepts and safety methodologies using a multidisciplinary micro/meso/macro approach for predicting remaining life.

In 2008, Imperial College – in collaboration with EDF Energy – officially established a ‘High Temperature Centre’ in the Mechanical Engineering Department. The facility has state-of-the-art and advanced equipment in a new laboratory area at the South Kensington Campus, London. The research identifies case-specific testing analyses that are carried out in the laboratories and that help develop structural integrity models using detailed material properties. The results are validated with data from actual components in order to increase confidence in using the methodologies.

The research areas are shown schematically in the diagram below, highlighting the testing, modelling and validation methods that are used in the structural integrity approach carried out by the group. Based on fracture mechanics methods, the modelling uses models ranging from sub-grain size to macro simulations, continuum damage mechanics, numerical multi-scaling, virtual testing and probabilistic life prediction methodologies to improve methodologies for establishing the safe life of critical components.


Structural Integrity for Design and Life Assessment

The results are implemented in international codes and standards that the industry uses for safe operations. The Versailles Project on Advanced Material and Standards (VAMAS) – a pre-standardisation committee – takes this information from members and makes early recommendations to improve the codes. These codes include the relevant fracture mechanics documents which have and are being developed in ISO, ASTM, ASME, BSI, EDF Energy’s R5/R6 and many other focused codes of practices.

The work is being developed by an expert team of academics, supported by students, who are all a part of a wider Imperial College Nuclear Grouping. The fundamental research carried out at Imperial filters through to new design and international safety codes, which are continually being developed, improved and validated at a national and international level. This centre, in collaboration with EDF Energy (UK) and supported by the Royal Academy of Engineering, leads the field internationally in extending the boundaries for predicting safe life in the nuclear industry.


 

For further information please contact K. Nikbin, Mechanical Engineering Department, Imperial College, London SW7 2AZ,(E-mail: k.nikbin@imperial.ac.uk; or visit: http://www3.imperial.ac.uk/
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