• The overall PLiM programme is known as the Life Cycle Management Plan for the Bruce Station

• Detailed ageing assessments for high importance, long life items (steam generators, fuel channels, feeders) have been performed. These are usually called life cycle management plans, and they are regularly updated and fed into station asset management and business plans.

• Condition assessments have been prepared for many systems, structures, and components. These are used to update the station life cycle management plan.

• Condition assessments are being used to update the system performance monitoring plans.

• For replaceable and short life components, a preventive maintenance review was performed and is implemented by the station, with effort on continual improvement in the maintenance process and equipment reliability.

• Bruce U3 and U4 were restarted in 2003/4; U1 and U2 are shutdown and undergoing a major refurbishment.

New Brunswick Power (Point Lepreau)

• Performed life assessments on the most important critical components and structures

• Carried out plant-wide condition assessment, involving major systems, components, structures and commodity groups

• The SSC ageing assessments have provided important inputs into business decisions for the investment in life extension

• Carried out systematic assessment of maintenance studies covering 30 key systems. Currently conducting functional failure & criticality analysis of system components in support of system health plans. Recommendations from earlier PLiM studies were dispositioned as part of the condition assessment & system health plans.

• Started a major plant refurbishment programme, as part of the plan for extended service operation. This involves an 18-month outage to allow an additional 25-30 years operation. This outage is planned to start April 2008, with the principle activity being replacement of all Fuel Channels, Calandria Tubes and portions of the feeders. It is also planned to take advantage of this outage to perform other modifications in support of safe and reliable operation.

• Ongoing programme on maintenance tasks evaluation and to improve life cycle management plans on feeders, steam generators and fuel channels.

Condition assessment (CA) of systems addresses the system perspective as it applies to understanding the current condition and provides indications about future behaviour. A standard has not been identified for system CA, but the process follows logic similar in many ways to that for SMP assessment. The assessment includes screening of components captured within the boundary, and can address all components types. The screening provides a means of identifying those components requiring a greater focus for the balance of the assessment. The specific ageing assessment sections of the process consider components or groups of components, following the processes identified in the component CA discussed further below. In many cases, SCCs will be assessed under individual component CAs or LAs depending upon their criticality. The system CA brings the overall results together from a system perspective.

The system CA focus impacts on the level of effort and the content. For PLiM programme CAs, there is interest in reviewing the ongoing programme to address ageing elements, together with understanding the current condition of the components. The screening typically performed reflects the impact of component failure on safety and production. The report provides a technical basis for improvements to the maintenance strategy, identifies short term requirements to confirm the prognosis, reviews potential obsolescence issues, and provides a prognosis for the service life period under consideration. The technical basis is developed through consideration of susceptibility to ageing related degradation mechanisms (ARDMs), review of the current status with regard to the ARDMs of interest, and a review of existing programmes to identify and mitigate these ARDMs.

For CAs focused on a specific need, such as defining elements of refurbishment, those items handled by normal maintenance would require less scrutiny. Typically the overall assessment ensures there are no issues associated with the maintenance trends and obsolescence, and gives a prognosis whether the component should be replaced during the refurbishment outage. The assessment relies on the review of ARDMs as discussed above.

The detailed steam generator life assessment work is expected to lay the foundation for the plant inspection, maintenance (cleaning) and operations (chemistry) programme enhancements that will ensure extended life of this critical equipment. Following completion of the Phase 1 assessment work, implementation of the inspection, monitoring and maintenance programme recommendations that result from this (and other assessments) should begin.

However, it is recognized that programmes that simply increase the plant total inspection, maintenance and monitoring effort will not be compatible with plant performance goals. Hence, the programmes must be “optimized” for ageing management effectiveness, to preserve the life extension option. This optimization should make use of a proactive ageing management approach for steam generators, involving use of advanced diagnostic and inspection techniques. These techniques can be used to focus the plant programmes on those areas-at-risk of potential significant ageing in the steam generators during the operational period ahead. A structured and managed approach to this part of the implementation process has been developed for implementation prior to life extension.

The reactors with loose fit design of garter spring spacers require their relocation to improve the service life of the coolant channels. Systems have been developed for extending service life of coolant channels by carrying out the task of repositioning of garter springs in new as well as operating reactors.

In order to relocate the GS in irradiated coolant channel, an alternative system called the INtegrated Garter spring REpositioning System (INGRES) had been developed indigenously. This system can perform following functions:

(a) Eddy current based Garter Spring Detection Probe (GSDP).

(b) Eddy current based Concentricity Detection Probe (CDP) for ensuring PT-CT concentricity.

(c) Hydraulically operated PT Flexing Tool (PTFT), for un-pinching the target GS.

(d) Linear induction motor principle based Garter Spring Relocation Device (GSRD) for relocating the garter springs.

During the design of the original HWR stations, potential mechanisms for ageing of the plant were considered, and inspection and maintenance programmes were developed. These programmes were based on the best information available from the nuclear power industry at that time. Since then, the HWR industry have been using the experience gained through the operation of these reactors, and throughout the industry in general, to develop systematic and comprehensive PLiM programmes to assure the on-going safe and economic operation of the reactors.

As stated previously, the objective of a PLiM programme is to effectively integrate ageing management programmes and economic planning to maintain a high level of safety, optimize the operation, maintenance and service life of SSCs, maintain an acceptable level of performance, maximize return on investment over the service life of the NPP; and provide NPP utilities/owners with the optimum pre-conditions for PLiM. The following are typical specific objectives of a systematic PLiM programme for HWRs:

• To perform a comprehensive assessment of the critical SSCs;

• To develop or enhance the plant maintenance, surveillance/monitoring, inspection and testing, and rehabilitation programmes to effectively manage the effects of ageing degradation;

• Strengthening the role of proactive ageing management;

• Implementing a systematic ageing management process;

• For in-service plants, ensure continuing safe, reliable, and cost effective operation during the plant design life in accordance with the following goals:

• Maintain public risk well within the regulatory requirements;

• Maintain high lifetime capacity factors, contributing to providing electricity at a competitive cost;

• Be able to anticipate new and emerging ageing issues and therefore minimize “unexpected” problems; and

• Preserve the option for long term operation of NPP.

For new HWR plants, additional objectives may be to:

• Assure plant owner/operators that HWR can meet and exceed its target design life; and

• Provide an optimized cost effective maintenance programme (using ageing assessment experience to provide this assurance).

The starting point should be the definition of the desired operational life. The programmes and measures for ensuring the required safety and performance levels, also the investments needed, depend on the target time of operation. A reasonable time-target should be selected for the economic investments in order to achieve the profit expected.

In recent years, Canadian utilities have completed several refurbishment projects, notably restarts of reactors following a long term shutdown. The scope of these projects depended both on the age of the plant, and on the projected operating life following refurbishment. The projects to date have been carried out within the existing Canadian nuclear regulatory framework and the operating licenses issued by the Commission for each facility.

Key regulatory goals for LTO projects are obtaining assurance of the adequacy of the scope of life extension and safety upgrades proposed by the licensee and verifying the proper execution of that work by the licensee, prior to return of the unit to service.

In order to meet these goals, the CNSC specifies requirements for the LTO scope of work that is prepared by the licensee, assesses the proposed work scope, evaluates the licensee programmes for the control of all activities and evaluate engineering submissions, procurement, construction and commissioning carried out. The following steps will be required of licensees in establishing the scope of work:

• Perform an environmental assessment (EA) pursuant to the Canadian Environmental Assessment Act, which involves:

• An assessment of the environmental effects of the project, including the environmental effects of malfunctions or accidents that may occur in connection with the project and any cumulative environmental effects that are likely to result from the project in combination with other projects or activities that have been or will be carried out;

• The significance of these effects;

• Comments from the public;

• Measures that are technically and economically feasible and that would mitigate any significant adverse environmental effects of the project; and

• Any other matter that the CNSC requires to be considered.

• Carry out PSR activities, which is considered an effective way to obtain an overall view of actual plant safety, in order to determine reasonable and practical modifications that should be made in order to maintain a high level of safety and to improve the safety of older nuclear power plants to a level approaching that of modern plants.

• Develop an integrated implementation plan for safety improvements, which involves the development of an integrated implementation plan for the necessary corrective actions, safety upgrades and compensatory measures to ensure the plant will not pose an unreasonable risk to health, safety, security and the environment and will conform to Canada’s international obligations over the proposed life. All generic action items and station specific actions items will be reviewed and each will be resolved to the extent practicable.

In assessing the adequacy of the proposed LTO workscope, CNSC staff reviews the Environmental Assessment Study Report and the Periodic Safety Review report, and takes into consideration information gathered through its own regulatory oversight activities. The CNSC notifies the licensee of its assessment of the proposed workscope, either accepting it or requiring changes. Subsequently the licensee proceeds with execution of LTO activities.

Once LTO activities are underway, the licensee is required to have acceptable programmes for the control of all LTO activities. Regulatory verification of project execution includes assessment of engineering change submissions, and inspections of licensee procurement, construction, and commissioning activities. Engineering change, procurement, construction and commissioning are to be performed in accordance with CNSC requirements and appropriate industry standards.

During the refurbishment phase the licensee submits updated safety analysis that demonstrates the acceptability of the refurbished plant. The analysis must be submitted in time to allow for CNSC staff review prior to making recommendations on restart to the Commission.

The CNSC expects that the licensee carries out a thorough commissioning plan for a LTO project. The scope and depth of this plan need not be as extensive as it would for a new facility, however, the baseline and confirmatory data must exist. If relevant system baseline data is available from past commissioning, then it can be referenced. However, if commissioning baseline data is no longer available, it will have to be reconstituted.

The PLiM and LTO considerations for shared facilities or common areas could bring in some specific requirements. Some typical examples are covered in the following:

1.9.1. CONTAINMENT

The IAEA TECDOC on Concrete Containment Buildings [I.4] includes a section on design features of containment for multi-unit CANDUs. The main components of the containment for these NPPs are a common vacuum building (VB) and pressure relief duct (PRD). Up to 8 reactor buildings are connected to the PRD. During normal operation the VB and PRD are isolated from the reactor buildings. An increase in pressure in a reactor building due to an accident will rupture panels so hot gases and steam will flow through the PRD to the vacuum building, and be condensed by a dousing system. There are 2 basic designs of RB at multi­unit CANDUs: 1) domed cylindrical structures with unlined single exterior walls and 2) thick — walled cube shaped structures with steel liner and post tensioned roof beams. The VB and PRD at multi-unit NPPs are reinforced concrete. ARDMs are similar to those discussed in section 3.6.4 for single-unit HWRs.

1.9.2. CONTROL ROOM, CONTROL EQUIPMENT ROOMS, FUELLING MACHINES, etc.

Common areas have been used for control room, cable spreading or control equipment rooms in some multi unit stations. Similarly certain refuelling facilities like fuelling machines, fuel transfer to storage bay could have shared features. This may necessitate taking up related PLiM for life attainment or for long term operation with appropriate management and logistics control such that safety and availability is assured for all units in the process.

REFERENCES TO APPENDIX I

[1.1] INTERNATIONAL ATOMIC ENERGY AGENCY, Assessment and Management of Ageing of Major Nuclear Power Plant Components Important to Safety: CANDU Pressure Tubes, IAEA-TECDOC-1037, IAEA, Vienna (1998).

[1.2] INTERNATIONAL ATOMIC ENERGY AGENCY, Assessment and Management of Ageing of Major Nuclear Power Plant Components Important to Safety: Steam Generators, IAEA-TECDOC-981, IAEA, Vienna (1997).

[1.3] INTERNATIONAL ATOMIC ENERGY AGENCY, Assessment and Management of Ageing of Major Nuclear Power Plant Components Important to Safety: Primary Piping in PWRs, IAEA-TECDOC-1361, IAEA, Vienna (2003)

[1.4] INTERNATIONAL ATOMIC ENERGY AGENCY, Assessment and Management of Ageing of Major Nuclear Power Plant Components Important to Safety: Concrete Containment Buildings, IAEA-TECDOC-1025, IAEA, Vienna (1998).

[1.5] INTERNATIONAL ATOMIC ENERGY AGENCY, Assessment and Management of Ageing of Major Nuclear Power Plant Components Important to Safety: CANDU reactor assemblies, IAEA-TECDOC-1197, IAEA, Vienna (2001).

APPENDIX II

Nuclear PLiM programme is usually consisted of three phases. In the first phase, a feasibility of the continued operation is evaluated to support top manager’s decision making whether continuing to operate the plant. Once the policy is determined to operate the plant beyond design life on the basis of the feasibility study, the second phase programme works out to evaluate detailed lives of SSCs and to establish ageing management programmes together with field walk downs, tests, diagnosis and ageing inspections [1]. After a regulator evaluates results of PSR containing second phase life assessment and endorses, the ageing management programmes are implemented to the field. This is the PLiM third phase that replaces aged components, install new performance monitoring systems, and change designs to improve obsolescent systems in the following outages as they are scheduled.

Plant safety, which is prior to technical activities of PLiM can be affected by the status of system operating performance that could be dependent on the structural integrity and degradations of structures and components (SCs) belong to systems. To solve this issue IAEA has recommended member states to implement PSR as a tool of ensuring a high level of safety throughout plant service life. Reviewing plant safety in every 10 years, PSR can deal with the cumulative effects of the plant ageing, modification, operating experience, and technology evolutions [2].

Fig. A. II.1. Schematic diagram of a CANDU PLiMfeasibility project.

In spite that all plant SSCs has to be considered in PSR, PLiM basically focuses on the long lived passive components that are relatively hard to replace and refurbish during normal operation. Therefore it can be said that the scope of PSR ageing management is wider but depth shallower than that of PLiM life assessment, which includes engineering evaluations,
such as quantitative time limited ageing analysis (TLAA), residual life estimations, field tests and examinations, diagnosis and monitoring, and ageing management programmes.

Short lived active components excluded from PLiM programme are scoped into the ageing management of PSR, and the engineering level of life evaluation is not complicate and deep as much as that of PLiM. PSR reviews the current physical status and records of maintenance and inspection done to the components in the past. Comparing the review results with current safety standards and practical experiences on and off-shore in terms of ageing and maintenance, utility revises the technical procedures and plans how to improve the system safety and slow down the degradation of SCs for the next 10 years. So the depth of PSR engineering evaluation becomes shallower but the scope wider than that of PLiM.

The general process of ageing assessment for the critical SSCs of PLiM feasibility is shown in Figure A. II.2. The ageing assessment starts with the selection of the critical SSCs among all the plant structures and components. The selection methodology is described in detail next chapter. All possible publications about design, manufacturing, operation, inspection and maintenance should be collected and kept in database. Based on the previous CANDU PLiM experiences and publications, and technical consultations of experts, degradation and ageing mechanisms of each SCCs are identified and evaluation methodologies cleared. The ageing phenomena can be recognized through reviewing plant data and history of operation, test, inspection and maintenance. Current ageing status of the screened CSSCs is evaluated with the design criteria by document review. The next is to find the evaluation methodology for the recognized ageing phenomena and/or develop the methodology, when necessary. Finally, remaining lives of CSSCs are evaluated and PLiM cost estimation and work plan for the detailed life evaluation re established.

Fig. A. II.2. Process of ageing assessment.

An overall approach to PLiM is to consider all the issues relating to plant ageing in a fully integrated programme. Figure 6 shows an overview of a high level comprehensive approach, which determines whether the plant will continue to perform in accordance with the specified expectation or be forced to shut down, depending on several factors influencing the cost — benefit equation to restore the performance capabilities of the asset.

The physical plant assessment focuses on the continuing ability of the structure or system, component to meet the specified performance criteria over its design life. If, in spite of maintenance and or refurbishment, a critical structure or component is deemed not likely to be able to meet its performance requirements, then a timely replacement must be undertaken with due consideration to the associated cost-benefits justification. Otherwise the plant is forced to shut down by default until the issue can be resolved satisfactorily.

Similarly, if the institutional infrastructure is allowed to degrade beyond HWR owner/operator management criteria, then the plant will be forced to shutdown until the underlying issues can be resolved in a satisfactory manner. The issues related with institutional ageing are not discussed further in this report as they are primarily related to performance of the utility management.

The various key elements of a life management programme for physical plant are shown in Figure 7 as follows:

• Screening: Screening/prioritization of systems and components to understand their importance. This will allow for the application of the appropriate ageing assessment procedures.

• Ageing assessment: Ageing assessments are methodologies used to assess the effect of degradation on SCCs and determine the appropriate inspection and mitigation techniques. They include:

• Condition assessment (CA): Typically for less critical systems, structures and components. The CA process may place related components in commodity groups such as instruments, and valves, where they are evaluated together. The methodology entails a general review of plant data in order to establish current condition and to evaluate ageing degradation at a component level. The CA report provides a prognosis for attainment of design life and/or long term operation with associated recommendations. Recommendations provide the technical basis for on­going ageing management of the subject structure, component or commodity and may identify a need for further assessment.

• Life assessment (LA): Performed typically for most critical structures and components that are generally passive in nature and typically designed not to be replaced as part of normal maintenance programme. This involves a rigorous assessment of all plausible ageing related degradation mechanisms. The methodology entails a detailed review of plant data in order to establish current condition and to evaluate ageing degradation at a sub-component level. Similar to a CA, the LA report provides a prognosis for attainment of design life and/or long term operation with associated recommendations. Recommendations provide the technical basis for on-going ageing management of the subject structure or component and may be used for economic planning.

•

Systematic assessment of maintenance (SAM): This form of assessment makes use of Failure Mode Effect Analysis (FMEA) methodologies and information from internal and external feedback and R&D findings. It utililizes streamlined Reliability Centred Maintenance techniques, as modified for nuclear plant applications. It is performed for critical systems with emphasis on active components (that are generally designed to be replaced as part of the normal maintenance programme), in order to preserve the defined systems functions [29].

• Integrated safety and performance assessment is an on-going activity primarily managed by the utilities with designer support in order to demonstrate continued compliance with the safety and licensing basis requirements as the plant ages.

• Technology watch programme addresses key emerging issues that may adversely impact on plant safety and reliability and may not be addressed by the assessment process described above. This programme relies on monitoring of the operating experience feedback, recent R&D activities, and new developments in regulatory requirements and industry practices. Utilities should search better methodologies to improve chemical treatment, inspection, maintenance, etc. by actively exchanging information with other plants either directly or through international organizations like IAEA, COG, WANO, INPO, or other organizations (eg. AECL).

• Obsolescence studies are performed on generic plant components that cannot be maintained or refurbished in a cost effective manner due to several factors (such as availability of spares and new developments in technology that make replacement a viable option). Obsolescence relates primarily to instrumentation and control component and computer systems.

• Feedback/Continuous Improvement: Following appropriate disposition of the

recommendations, the PLiM should remain an active programme. The technology watch programme described above provides updates to the information used during the ageing assessment process. The assumptions made and conclusions reached during the initial assessment process should be periodically reassessed to incorporate new understanding of known ageing degradation mechanisms obtained, for example, through R&D programmes and/or operational events. In addition, through surveillance programmes and, occasionally through operational events, previously unconsidered degradation mechanisms may be discovered. The SSC ageing assessments should be reviewed and revised if necessary, to ensure their continued validity.

Establishing a database of all plant information (design, manufacturing, operation, inspection, maintenance) and maintaining it throughout plant life (high degree of utilization by all plant engineers, constant updating) is one of the key factors to achieving a successful ageing management programme.

During reactor operation, the heavy water flowing through the pressure tubes reacts with their inside-surfaces forming a zirconium oxide film and releasing elemental deuterium. The loss of metal from this reaction is very small and does not limit the life of the pressure tube. However some of the released deuterium enters the pressure tube increasing the susceptibility of flaws in the pressure tube to crack initiation and growth by delayed hydride cracking (DHC) and potentially decreasing the fracture toughness if very high levels were eventually reached. Additional deuterium also enters the pressure tube end by crevice effects at the rolled joint.

Deuterium ingress in the body of the pressure tube is monitored using a tool that takes small samples from the inside surfaces of the pressure tubes in situ or by punching through-wall coupons from tubes removed from service. The resulting specimens are analysed for deuterium content. Pressure tube sampling campaigns (for hydrogen/deuterium concentration measurements) that have been completed at several reactors and results continue to show a low deuterium ingress rate relationship with time. Repeat scrapes however indicate that the ingress may be increasing with time and hence monitoring is required to confirm this trend.