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)
Contents of the presentation ! Introduction ! Design lifetime considerations ! Cycle management ! Ageing mechanisms ! Ageing evaluation tasks ! Ageing management ! Management of obsolescence International Atomic Energy Agency 2
Introduction 81% of operational reactors have more than 20 years of operation International Atomic Energy Agency 3
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 obsolescence , where SSCs become out of date in comparison with current knowledge, technology, standards, and regulations International Atomic Energy Agency 4
Introduction " Ageing management is the engineering, operational, inspection, and maintenance actions that control, within acceptable limits, the effects of physical ageing and obsolescence 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. International Atomic Energy Agency 5
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. International Atomic Energy Agency 6
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 International Atomic Energy Agency 7
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 operational 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. International Atomic Energy Agency 8
Ageing effects " “Ageing effects are net changes in the characteristics of an SSC that occur with time or use and which !"#"$%&'()*$%)&+,&-,. are due to ageing mechanisms.“ H;B)MB;F?EFCGK)M?;MA?)=G@)F<?)?GNCB;G>?GF "/(0+/$1&+&/(2(+)$'3-$ 4567(&-$839(-$87&+). %&'()*$<50,( 43:$4%;<;=:>= International Atomic Energy Agency 9
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. International Atomic Energy Agency 10
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. International Atomic Energy Agency 11
Ageing mechanisms " An ageing mechanism also can map into one of the three categories: ! It induces an initiator (typically: fails or degrades an operating 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. International Atomic Energy Agency 12
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. International Atomic Energy Agency 13
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 of: " Increased likelihood of failure, and " Consequences of failure Increased Likelihood of Failure Low High Risk Category: Risk Category: Low Low Medium Consequences of Failure Risk Category: Risk Category: High Medium High International Atomic Energy Agency 14
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. International Atomic Energy Agency 15
Ageing managament Concept of ageing PLAN 2. Development and optimization of activities for ageing management of a management structure/component Preparing, coordinating, maintaining and improving activities for ageing management: " PLAN • Document regulatory requirements and safety criteria • Document relevant activities • Describe coordination mechanisms • Improve effectiveness of ageing " DO management based on current Improve effectiveness understanding, self-assessment and Minimize of ageing management peer review expected programmes degradation " CHECK 1. Understanding ageing of a structure/component " ACT Key to effective ageing management based DO on the following information: ACT 3. Operation/use of a • Materials and material properties, 5. Maintenance of a structure/component fabrication methods structure/component Managing ageing mechanisms: • Stressors and operating conditions Managing ageing effects: • Ageing mechanisms • Operation according to • Preventive maintenance • Sites of degradation procedures and technical • Corrective maintenance • Consequence of ageing degradation specifications • Spare parts management and failures • Chemistry control • Replacement • R&D results • Environmental control • Maintenance history • Operational experience • Operating history, including • Inspection/monitoring/maintenance history transient records • Mitigation methods • Current status, condition indicators Check CHECK Mitigate for degradation degradation 4. Inspection, monitoring and assessment of a structure/component 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 International Atomic Energy Agency 16
Ageing managament " Understanding the 1. Understanding ageing of a ageing of a structure structure/component or component is the Key to effective ageing management based key to its effective on the following information: ageing management. • 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 International Atomic Energy Agency 17
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