Advancing structural integrity safety issues in the

www.innovationandresearchfocus.org.ukInnovation & Research Focus Issue 98 AUGUST 20146

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 fi eld 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: [email protected]) or visit http://www3.imperial.ac.uk/mestructuralintegrity).

CARBON & CLIMATE CHANGE, ENERGY, RESEARCH & INNOVATION, SAFETY

Advancing structural integrity safety issues in the nuclear industryStructural integrity is paramount in nuclear safety issues. Following the Fukushima accident (March 2011), questi ons about the resurgence in nuclear energy and worries about operati onal safety have once again come to the forefront of the news. It is obvious that dealing with safety as well as public relati ons are both very important topics in the nuclear industry, as the politi cal, social and a ‘nervously-oriented’ media scruti ny always infl uence the governmental decision-makers who have the duty to balance public concerns with the need to guarantee energy producti on.

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 fi eld – supported by CEGB, British Energy and

High Temperature Structural Integrity Centre

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T-buttPipe on plateTubular TTubular YPipe ButtCold Bent tubeRepair (pipe girth)

Crack Detection NDE: Crack/Damage

Measurement/Models Condition monitoring

Structural Integrity for design and Life Assessment

Modelling Numerical/Analytical Multi-scale Validation

FM Parameters Linear/Nonlinear Geometry/Size Constraint Load history Residual stress

Fracture Toughness Dynamic/Impact

Fatigue da/dN, LCF, HCF Crack initiation

Corrosion Damage/ Cracking Environment-Assisted Time dependent

Creep- da/dt Damage/Cracking TMF, Creep/Fatigue Time Dependence

Materials Props. Low alloy steels Advanced steels DS/ Single crystals Coatings - TBC Composites, FGM Weldments

Virtual testing Predictive modelling

Failure assessment

Remaining life

Component check

DECISION Operate – Inspect Replace - Repair Cost/Safety Implications Risk Management Expert Advice

STURCTURAL

Safety requirements Certification

Design Life extension

VALIDATION

CODES


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Failure assessment

Remaining life

Component check


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Failure assessment

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Structural Integrity for Design and Life Assessment:

Creep- da/dtDamage/Cracking

TMF, Creep/FatigueTime Dependence

Fatigueda/dN, LCF, HCFCrack initiation

FractureToughness

Dynamic/Impact

CorrosionDamage/Cracking

Environment-AssistedTime Dependent

STRUCTURALSafety requirements

Certi� cationDesign

Life Extension

Crack DetectionNDE: Crack/DamageMeasurement/ModelsCondition Monitoring

Virtual TestingPredictiveModelling

Failure assessmentRemaining life

VALIDATION

DECISIONOperate – InspectReplace – Repair

Cost/SafetyImplications

Risk ManagementExpert Advice

CODES

Component check

ModellingNumerical/Analytical

Multi-scaleValidation

FM ParametersLinear/Non-linearGeometry/Size

ConstraintLoad History

Residual Stress

Materials Props.Low Alloy SteelsAdvanced Steels

DS/Single CrystalsCoatings – TBC

Composites, FGMWeldments

Materials Props.Low Alloy SteelsAdvanced Steels

DECISION

NDE: Crack/DamageMeasurement/ModelsMeasurement/Models

Linear/Non-linearGeometry/Size

Constraint

NDE: Crack/DamageMeasurement/ModelsMeasurement/Models

da/dN, LCF, HCFCrack initiation

Dynamic/Impact

Environment-Assisted

DECISION

NDE: Crack/Damage

Load HistoryResidual Stress

Toughness

DECISION


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Failure assessment

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VALIDATION

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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 –offi cially 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 identifi es case-specifi c 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 confi dence in using the methodologies.

The research areas are shown schematically in the diagram opposite, 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.

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 fi lters through to new design and international safety codes, which are continually being developed, improved and

Documents

Advancing structural integrity safety issues in the