Ageing, Life Limiting Factors Presented by: Tibor Szikszai Ri-man - - PowerPoint PPT Presentation

International Atomic Energy Agency

Ageing, Life Limiting Factors

Presented by: Tibor Szikszai Ri-man Consulting, Hungary t.szikszai@riman.hu

Joint ICTP-IAEA Essential Knowledge Workshop on Deterministic Safety Analysis and Engineering Aspects Important to Safety, Trieste, Italy 12 – 23 October 2015 (week 1)

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! Introduction ! Design lifetime considerations

! Cycle management

! Ageing mechanisms ! Ageing evaluation tasks ! Ageing management ! Management of obsolescence

Contents of the presentation

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Introduction

81% of

• perational

reactors have more than 20 years of

• peration

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Introduction " The time related or time dependent changes affecting the safety of the NPP shall be followed and evaluated, and the necessary follow-up actions shall be taken to keep the safety on an acceptable level. " Structures, systems, and components (SSCs) of a nuclear power plant experience two kinds of time- dependent changes: ! physical ageing and wear of SSCs causing degradation of their performance characteristics over time or with use ! obsolescence, where SSCs become out of date in comparison with current knowledge, technology, standards, and regulations

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Introduction " Ageing management is the engineering, operational, inspection, and maintenance actions that control, within acceptable limits, the effects of physical ageing and

• bsolescence of SSCs occurring over time or with use.

" An ageing management program (AMP) is a set of policies, processes, procedures, arrangements, and activities for managing the ageing of the SSCs for an NPP.

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Design lifetime considerations " The design lifetime of the plant is dependent on the non-replaceable plant component with the shortest designed lifetime " The designed progress of the ageing effects of the non- replaceable components predetermines the lifetime of the plant " Also the allowed by the design maximum number of the cycle of specific events may be a lifetime limiting factor It is essential to observe and follow the development of the limiting factors, and demonstrate the safety during the residual lifetime.

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Design lifetime considerations " The design should specify the number of allowed load cycles of different types: ! Number of specific operational events, like power changes in different ranges ! Number of reactor scrams ! Number of other initiating events with equipment damages

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Cycle management " Control of the cycles: ! The occurring operational events and incidents should be analyzed in order to determine, if they “consume” from one or more allowed cycles, and the residual allowed number of cycles should be kept in

• perational records and likely in licensing

documentation ! If the number of events of a kind reaches the maximum allowed cycles, the plant operator should implement special technical measures to allow continued operation, otherwise this would mean the end of the lifetime of the plant... ! Difficulty is the interpretation of the maximum number, if it is 1.

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Ageing effects

" “Ageing effects are net changes in the characteristics of an SSC that

• ccur with time or use and which

are due to ageing mechanisms.“

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Ageing effects " Ageing effects may be positive or negative. ! Examples of positive effects are increase in concrete strength from curing and reduced vibration from wear-in of rotating machinery. ! Examples of negative effects are reduction in diameter from wear of a rotating shaft, cracking, thinning or loss in material strength from fatigue or thermal ageing, and loss of dielectric strength or cracking of cable insulation.

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Ageing mechanisms " An ageing mechanism represents an increased likelihood of failure / degradation of the SSCs. The following elements should be evaluated to identify and characterize an ageing mechanism: ! Type of ageing mechanism and its impact on the reliability parameters in time; ! Stressors and environment; ! Maintenance programs; ! Inspection programs (detection of degradation); ! Replaceable components, etc.

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Ageing mechanisms " An ageing mechanism also can map into one of the three categories: ! It induces an initiator (typically: fails or degrades an

• perating system or its boundary);

! It fails or degrades mitigation system, but does not induce an initiator (e.g. fails or degrades a standby safety system); ! It, at the same time, induces an initiator and fails or degrades a mitigation system.

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Ageing evaluation tasks " Screening of SSCs and related ageing mechanisms for incorporation into the an AMP ! Divide the SSCs of each generic type (e.g. motor driven pumps, motor operated valves, piping, !) into sub-groups by considering selected attributes including:

" System / function; " Safety class " Location and environment; " Operating stressors " Applicable ageing mechanisms, etc.

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Ageing evaluation tasks " Screening of SSCs and related ageing mechanisms for incorporation into an AMP ! Each SSC group / ageing mechanism from the Preliminary List is first classified into one of the several risk categories, based on the consideration

• f:

" Increased likelihood of failure, and " Consequences of failure

Increased Likelihood of Failure Low High Consequences

• f Failure

Low Risk Category: Low Risk Category: Medium High Risk Category: Medium Risk Category: High

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Ageing evaluation tasks " Screening of SSCs and related ageing mechanisms for incorporation into an AMP ! Evaluate each sub-group from the perspective of increased failure likelihood due to ageing by considering attributes such as:

" Type of applicable ageing mechanism and associated time dependent reliability model; " Testing and maintenance programs; " Replacing / renewing; " In-service inspection programs; " Ageing management strategies, etc.

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Ageing managament Concept of ageing management " PLAN " DO " CHECK " ACT

PLAN CHECK DO ACT Detecting and assessing ageing effects:

• Testing and calibration
• Pre-service and in-service inspection
• Surveillance
• Leak detection, vibration monitoring, etc.
• Assessment of functional capability/fitness

for service

• Record keeping
• 4. Inspection, monitoring and

assessment of a structure/component Key to effective ageing management based

• n the following information:
• Materials and material properties,

fabrication methods

• Stressors and operating conditions
• Ageing mechanisms
• Sites of degradation
• Consequence of ageing degradation

and failures

• R&D results
• Operational experience
• Inspection/monitoring/maintenance history
• Mitigation methods
• Current status, condition indicators
• 1. Understanding ageing of a

structure/component

• 2. Development and optimization of

activities for ageing management of a structure/component Preparing, coordinating, maintaining and improving activities for ageing management:

• Document regulatory requirements and

safety criteria

• Document relevant activities
• Describe coordination mechanisms
• Improve effectiveness of ageing

management based on current understanding, self-assessment and peer review Minimize expected degradation Improve effectiveness

• f ageing management

programmes Mitigate degradation Check for degradation

• 5. Maintenance of a

structure/component Managing ageing effects:

• Preventive maintenance
• Corrective maintenance
• Spare parts management
• Replacement
• Maintenance history
• 3. Operation/use of a

structure/component Managing ageing mechanisms:

• Operation according to

procedures and technical specifications

• Chemistry control
• Environmental control
• Operating history, including

transient records

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Ageing managament " Understanding the ageing of a structure

• r component is the

key to its effective ageing management.

Key to effective ageing management based

• n the following information:
• Materials and material properties,

fabrication methods

• Stressors and operating conditions
• Ageing mechanisms
• Sites of degradation
• Consequence of ageing degradation

and failures

• R&D results
• Operational experience
• Inspection/monitoring/maintenance history
• Mitigation methods
• Current status, condition indicators
• 1. Understanding ageing of a

structure/component

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Ageing managament The PLAN activity means coordinating, integrating and modifying existing programmes and activities that relate to managing the ageing of a structure or component and developing new programmes, if necessary.

• 2. Development and optimization of

activities for ageing management of a structure/component Preparing, coordinating, maintaining and improving activities for ageing management:

• Document regulatory requirements and

safety criteria

• Document relevant activities
• Describe coordination mechanisms
• Improve effectiveness of ageing

management based on current understanding, self-assessment and peer review

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Ageing managament The DO activity means minimizing expected degradation of a structure

• r component through its

‘careful’ operation or use in accordance with operating procedures and technical specifications.

DO

• 3. Operation/use of a

structure/component Managing ageing mechanisms:

• Operation according to

procedures and technical specifications

• Chemistry control
• Environmental control
• Operating history, including

transient records

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Ageing managament The CHECK activity means the timely detection and characterization of significant degradation through inspection and monitoring of a structure or component, and the assessment of observed degradation to determine the type and timing of any corrective actions required.

Detecting and assessing ageing effects:

• Testing and calibration
• Pre-service and in-service inspection
• Surveillance
• Leak detection, vibration monitoring, etc.
• Assessment of functional capability/fitness

for service

• Record keeping
• 4. Inspection, monitoring and

assessment of a structure/component

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Ageing managament The ACT activity means the timely mitigation and correction of component degradation through appropriate maintenance and design modifications, including component repair and replacement of a structure or component.

ACT

• 5. Maintenance of a

structure/component Managing ageing effects:

• Preventive maintenance
• Corrective maintenance
• Spare parts management
• Replacement
• Maintenance history

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Ageing managament The closed loop indicates the continuous improvement of the ageing management programme for a particular structure or component, on the basis of ! feedback of relevant operating experience ! and results from research and development, ! and results of self-assessment and peer reviews, to help ensure that emerging ageing issues will be addressed.

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Ageing managament " Systematic approach to managing ageing in the

• peration of nuclear power plants

! Organizational arrangements; ! Data collection and record keeping; ! Screening of SSCs for the purposes of ageing management; ! Review of the management of ageing; ! Condition assessment; ! Development of ageing management programmes; ! Implementation of ageing management programmes; ! Improvement of ageing management programmes.

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Ageing managament " Systematic approach to managing ageing in the

• peration of nuclear power plants

! Organizational arrangements; ! Data collection and record keeping; ! Screening of SSCs for the purposes of ageing management; ! Review of the management of ageing; ! Condition assessment; ! Development of ageing management programmes; ! Implementation of ageing management programmes; ! Improvement of ageing management programmes.

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Proactive strategy for ageing managament " Ageing management of SSCs important to safety should be implemented proactively (with foresight and anticipation) throughout the plant’s lifetime, i.e. in design, fabrication and construction, commissioning,

• peration (including long term operation and extended

shutdown) and decommissioning. " Regulatory requirements for ageing management should be established and updated and guidance should be developed to ensure that the operating

• rganization of a nuclear power plant implements an

effective ageing management programme.

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Proactive strategy for ageing managament " The operating organization should be responsible for demonstrating that the relevant issues of ageing that are specific to the plant are clearly identified and documented in the safety analysis report throughout the plant’s lifetime. " Issues of ageing arising from other plants should be considered by the operating organization in evaluating the ageing management measures proposed by suppliers. " The ageing management activities of suppliers and the

• perating organization should be overseen by the

regulatory body throughout the plant’s lifetime.

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Managament of obsolescence " Nuclear power plant safety can be impaired if

• bsolescence of SSCs is not identified in advance and

corrective actions are not taken before associated declines occur in the reliability or availability of SSCs. " Management of obsolescence is a part of the general approach for enhancing nuclear power plant safety through ongoing improvements of both performance of SSCs and safety management.

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Managament of obsolescence " Types of obsolescence ! Knowledge

" Manifestation

• Knowledge of current standards, regulations and technology relevant

to SSCs not updated

" Consequences

• Opportunities to enhance plant safety missed; Reduced capability for

long term operation

" Management

• Continuous updating of knowledge and improvement of its application

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Managament of obsolescence " Types of obsolescence ! Standards and regulations

" Manifestation

• Deviations from current regulations and standards, both hardware and

software;

• Design weaknesses (e.g. in equipment qualification, separation,

diversity or severe accident management capabilities)

" Consequences

• Plant safety level below current standards and regulations (e.g.

weaknesses in defence in depth, or higher core damage frequency);

• Reduced capability for long term operation

" Management

• Systematic reassessment of plant against current standards (e.g.

periodic safety review) and appropriate upgrading, backfitting or modernization

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Managament of obsolescence " Types of obsolescence ! Technology

" Manifestation

• Lack of spare parts and/or technical support;
• Lack of suppliers and/or industrial capabilities

" Consequences

• Declining plant performance and safety owing to increasing failure

rates and decreasing reliability;

• Reduced capability for long term operation

" Management

• Systematic identification of useful service life and anticipated
• bsolescence of SSCs; Provision of spare parts for planned service

life and timely replacement of parts;

• Long term agreements with suppliers;
• Development of equivalent structures or components