Se debe distinguir entre:

The Member States that follow the PSR process to periodically take stock of the safety condition of the plant will find the task of justifying LTO easier if they have implemented a systematic approach to plant ageing management. A good AMP conducted from day one in the service life of a plant is an assurance that the plant will be in its best possible condition and will require a minimum number of changes at the time of its PSR submission for longer term operation, which usually requires more demanding justifications for continuing operation than regular PSRs. The plan of action shown in Fig. 12 illustrates a systematic phased approach developed by the Swedish Radiation Safety Authority for its operators to adequately justify continuing operation for a period longer than first postulated in the original design. This methodology has proven successful in the preparation of the PSR submission for longer term operation.

The blocks at the top of Fig. 12 represent the preparatory phase prior to the LTO safety review submission.

The middle blocks denote the LTO assessment phase. In this phase, nuclear power plant operators are required to verify that their AMP is adequate. They conduct this verification through an ageing management review in which

they ensure that the original component design that has operating time limitations is verified for the new intended time of operation (e.g. 60 years). This verification is referred to as TLAA.

In keeping with IAEA Safety Guide publication on Ageing Management for Nuclear Power Plants (NS-G-2.12) [1], paragraph 2.5, and Safety Reports Series No. 57 [15], section 5.3, the regulator in Sweden requires that plant ageing be managed proactively, by coordinating existing programmes such as maintenance, ISI, surveillance, operation programmes, technical support programmes (including analysis of ageing mechanisms) and R&D. Ageing management should be a cross-cutting programme that provides a methodological process to detect and mitigate material degradation. This process should be used as part of the justification for safe LTO.

The blue block at the centre of Fig. 12 represents the proactive review effort of the AMPs of all passive SSCs, singled out by the screening process and grouped by major systems and engineering disciplines. All existing maintenance and surveillance programmes are checked for LTO acceptability, as represented by the yellow box on the left. The blocks to the right of the central blue box represent the typical major LTO projects being assessed for LTO and for which TLAAs are produced to qualify components, subcomponents and subsystems requiring it in each of the major LTO projects. Out of this assessment phase, a number of changes and upgrades are recommended and eventually committed.

The lower blocks in Fig. 12 represent the implementation phase of the committed changes. The figure shows how Sweden’s nuclear regulatory framework integrates IAEA recommendations within the PSR process [12].

It should be noted that during the plant wide scoping and screening process, all relevant SSCs are considered.

However, during the review of the plant AMP in the following stage of the process, only the long lived or hardly replaceable passive structures and components are considered.

Another model, shown in Fig. 13, was developed in the context of the Chinese licensing framework and national standard that requires a safety review submission for operation beyond the period first postulated in the original design.

Figure 13 represents a systematic ageing management model, provided by Qinshan phase 1 nuclear power plant in Zhejiang Province, China. The model includes an overall AMP and a series of topical and equipment specific AMPs. The overall AMP model deals with general aspects of ageing management at the plant level, such

LTO demonstration

Phase prior to LTO assessment

(SRS 57, fig1)

Documentation of basis for LTO

Civil / structural Feasibility

Verification of preconditions

Scoping Screening

IAEA SafetyReport Nr 57 safe long term operation of nuclear power plants

IAEA IGALL International Generic Ageing

Lessons Learned

IAEA

guidelines Regulatory framework

IAEA-SRS-57 Active

Check of existing maintenance and surveillance

programmes

Electrical and I&C Mechanical

Primary system

AMR passive SCs

Regulatory oversight Phase LTO

approval &

implementation (SRS 57, fig1)

Implementation of plan commitments

for LTO RPV Fatigue LBB Underclad

cracks CASS

TLAAs

RPV internal vibration Fatigue crane

cranes Flywheel HCFsteam generatur tubes

EQ Containment

tendons Concrete creep

Thermal ag martensitic

PSR

Phase LTO assessment (SRS 57, fig1)

FIG. 12. Plan of approach for LTO projects (Swedish Radiation Safety Authority). AMR — ageing management review; CASS — cast austenitic stainless steel; EQ — equipment qualification; LBB — leak before break; SC — structure and component.

as plant policies, organizational structure, division of responsibilities, resource allocation, screening of ageing management equipment and identification of significant ageing mechanisms, among others. The equipment specific AMPs cover ageing management procedures for structures or components selected in the screening process.

The AMPs define the ageing issues, the plan and the work scope, including the ageing mechanism analysis, the inspection programme, data collection, the ageing assessment, corrective actions for ageing mitigation and record keeping, among others. The topical AMPs focus on ageing issues across the plant by topic, such as FAC, SCC and obsolescence, among others. The systematic AMP model also includes the development of an ageing management database to be merged with the general plant information system. PSRs can be used to improve, as well as to evaluate, the plant AMP system. In the PSR cycles, the AMP system is reassessed based on the PSR guidelines, potential weaknesses are identified and recommendations are made for further improvements.

When a design upgrade is deemed necessary to enhance safety or performance for an LTO submission, there is a process to assess the project (see Fig. 14). From right to left, first a screening or clustering step is undertaken to review all issues, namely the native LTO issues, the pre-existing proposed improvement projects, which may or may not have LTO implications, and the non-LTO issues. A selection of the issues to be addressed in an LTO submission is undertaken based on a safety impact assessment and expert judgement supported by probabilistic insights (if available). The list of possible changes is consolidated and a short list of LTO issues is included in

Overall AMP Previous PSR

AMP organization and responsibilities

Equipment specific AMPs Equipment screening

­ Degradation mechanisms

­ Ageing detection

­ Ageing mitigation

­ Ageing assessment

­ Amp procedures

­ Degradation mechanisms

­ Ageing detection

­ Ageing mitigation

­ Ageing assessment

­ Amp procedures

­ Degradation mechanisms

­ Ageing detection

­ Ageing mitigation

­ Ageing assessment

­ Amp procedures

New PSR Life extension

Topic for FAC 

­ Investigation

­ Detection

­ Mitigation

­ Assessment

­ AMP procedures

Review of existing programs and procedures

Topical AMPs

Topic for SCC 

­ Investigation

­ Detection

­ Mitigation

­ Assessment

­ AMP procedures

Topic of obsolescence

AMP for T1

AMP for T2

AMP for Tn

AMP for RPV

AMP for  steam generator

AMP for En

FIG. 13. Systematic ageing management model for Qinshan-1, China. En — engineering; SG — steam generator; T — topic 1; T —

the PSR submission to the regulatory body for an LTO permit. A cost–benefit analysis is also conducted on all consolidated issues and is to include the proposed improvements in a feasibility study, which requires an estimate of the safety benefits. All inputs are then collected and an integrated assessment is conducted. The process eventually leads to an improvement plan, which includes both the short listed LTO drivers and the work plan containing the approved design upgrades.