Review and modification of existing plant programmes

As stated in Section 2.6, the existing plant programmes described next are considered preconditions for LTO. The preconditions identified below were specifically selected by WG1 because these plant programmes impact all areas of plant operation identified in the scope of Working Groups 2, 3 and 4.

In addition to programmes described below, Appendices II-IV provide a more detailed description of the candidate programmes within their focus area and provide recommendations for a number of additional plant programmes useful for LTO (e.g. applied diagnostic systems including load monitoring, nondestructive material properties testing, chemical regimes monitoring, destructive tests and material research carried out during NPP operation).

Any existing plant programme intended to be used to support long term operation and manage the ageing effects identified for LTO should be reviewed to determine whether it meets the respective requirements set forth by the nine attributes defined in Section 3.2. The outcome of the review should provide the technical basis to clarify whether the ageing effects relevant to maintaining intended safety functions will be detected and characterized, or modifications and/or new programmes are necessary.

3.1.1. In-service inspection

The basic in-service inspection (ISI) methods are visual checks, destructive and non-destructive tests and continuous monitoring by permanently built-in systems. The range, periods, methods, evaluation, technology, etc. of ISI are mostly defined using deterministic methods; complementary risk informed (RI-ISI) approach which use contribution to core damage (risk), consequence of failure and an assessment of degradation to define the scope and periods of ISI (mainly piping) is increasingly adopted and developed.

The ISI programmes are usually tailor-made, taking into account the specific features of the plant design, material selection, and construction practices.

ISIs include inspections of structures and components set by national regulations and implemented through quality assurance documentation, equipment checks, diagnostic inspections and measurements etc. ISI of passive components and structures is a critical part

of the operation and maintenance of nuclear power plants. ISI programmes provide part of the technical basis for ensuring that the structural integrity of systems, structures and components is adequate for operation.

The methodology, equipment and personnel, which are part of the ISI process, should be qualified according national standard, regulatory requirements, and IAEA recommendations. The qualification process should include requirements that provide a quantitative measure of effectiveness (e.g. UT detection capability and UT flaw characterization error) through blind trials on test block.

Operating organization should develop a review process for evaluating current ISI practices for effectiveness in detecting and characterizing the ageing mechanisms for each structure and component. The review process should provide a technical basis that justifies that the ageing phenomena will be adequately detected with the proposed inspection or monitoring activities.

Operating organizations should consider developing a living database that documents the effectiveness of ISI in detecting and characterizing degradation mechanisms. The database should provide technical references to support findings and conclusions.

If RI-ISI programmes are to be used during the period of LTO, consideration should be given to 1) developing comprehensive regulatory requirements for implementation of RI-ISI and 2) the effectiveness of RI-ISI should be evaluated as recommended under attribute 7 in Section 3.2, because RI-ISI programmes have limited operational experience.

The ISI result should be correctly documented so that a comparative analysis of the inspection results obtained during inspection can be done, especially when the inspections are performed in separate areas and at different periods of time.

3.1.2. Maintenance

Similar to in-service inspection, maintenance for active components include: testing activities for components set by national regulations and implemented through quality assurance documentation, equipment checks, diagnostic monitoring and measurements, repair, replacement etc. Testing of active components is a critical part of the operation and maintenance of nuclear power plants. The programmes to maintain the active components are typically country specific. The objective of the periodic maintenance activities is to ensure that active components are capable for performing its designed function.

Maintenance programmes for LTO should clearly identify the type of maintenance (preventive, predictive and corrective), the links with ageing management programmes, the frequency and tasks, the records, their evaluation and storage for optimization.

Operating organizations should evaluate current maintenance programmes for effectiveness in detecting and characterizing the ageing mechanisms for each structure and component. The evaluation should provide a technical basis to justify that the ageing phenomena will be adequately detected with the proposed inspection or monitoring activities.

The attributes of such a programme should be made clear in terms of target performance goal, identification of the functional failure, feedback on operational experience.

Operating organizations should consider developing a systematic approach to the maintenance with respect to long term operation, addressing inadequacy of current programmes and technical development such as application of risk informed technology.

Operating organizations should consider developing a living database that documents the effectiveness of maintenance in detecting and characterizing degradation mechanisms.

The database should provide technical references to support findings and conclusions.

Operating organizations should consider developing and maintaining databases (similar to RPV surveillance specimens) for I&C materials.

Operating organizations should consider applying destructive testing methods using specimens of electrical cables that were exposed actual environmental conditions during operation to monitor material degradation of during LTO.

The maintenance programme for the structures in the scope of the LTO based on standard preventive maintenance is not suitable to support an LTO programme. The maintenance programme should be focused to the monitoring of its effectiveness and therefore to be of the “condition based” type.

Initial values and maintenance results for mechanical, electrical, and physical/chemical properties of the cables should be properly documented.

3.1.3. Equipment qualification

Equipment qualification (EQ) establishes, through quality assurance processes and testing, that equipment within the scope of LTO is capable of performing an intended function during the period of LTO or that the equipment will be replaced / repaired in order that its intended function will not compromise safe operation during LTO. The EQ programmes are part of long term programmes and strategies.

Environmental and seismic qualification should be required for equipment important to safety and or equipment whose failure could jeopardize any safety function performance.

It should be demonstrated that equipment qualification remains valid over the expected period of LTO. The demonstration should support technical justification that the ageing effects on mechanical equipment will be managed effectively for LTO.

Equipment qualification status should be validated mainly through surveillance, maintenance, modifications and replacement control, environment and equipment condition monitoring and configuration management.

Environmental conditions should be assessed, taking into account natural phenomena, different accidents and also electromagnetic compatibility.

Equipment designed according to earlier standards should be requalified under a comprehensive programme that is focused to ensure that the equipment can perform its design function under current design basis accident conditions.

The operating organization should consider timely replacement of environmentally qualified mechanical and electrical equipment that is not qualified for the period of LTO, or have its qualification extended prior to reaching the ageing limits. A specific programme for replacement of environmentally qualified and non-environmentally qualified mechanical and electrical equipment should be developed.

Non-environmentally qualified mechanical and electrical equipment in the scope of LTO should be evaluated to determine if it can perform its function during the period of LTO.

Equipment reclassified as part of an LTO engineering evaluation should have an appropriate testing schedule or replacement programme including corrective measures to ensure the functionality during the period of LTO.

Qualification documentation should be stored in auditable form during the entire installed life of equipment including LTO.

Mechanical and electrical equipment in mild environment within the scope of LTO should be evaluated to determine if it can perform its function during the period of LTO.

3.1.4. In-service testing

Component in-service testing is a part of the normal operation or maintenance programme of operating power plants and serves to verify that the SSCs are capable of performing their design function. In addition to verifying the functional capability of equipment, these tests are often combined with a trending scheme to reveal potential problems, before the problems could lead to failure of the SSCs.

Start up functional tests are performed to check functionality of individual equipment as well as the entire system(s) following maintenance on the system or extended shutdown of the system. These tests involve calibration checks to ensure the accuracy of required metrological settings. Procedures should be detailed and well referenced ensuring that the uncertainty in the measurements is known and corresponds to the required accuracy of the measurement.

The power range tests are executed according to a schedule that is in compliance with the corresponding prescriptions of the operating limits and conditions (technical specifications).

A separate set of tests are generally conducted prior to unit shutdown to justify that the conditions of SSC required for the cool down of the reactor coolant system and its subsequent depressurization comply with the corresponding requirements.

In-service testing should be clearly tied with the operational requirements for the component. In general, component in-service tests are based on the operational limits and conditions specified and include:

− Acceptance criteria are established based on the safety analysis report and regulatory requirements;

− Check of the initial conditions prior to the tests;

− Start-up of the active equipment and monitoring of the basic parameters to be in the range of the allowable values;

− Check of the control and performance of the electrically and pneumatically driven valves, check of the full or partial stroke depending on the purpose and requirements of the performed tests;

− Check of correctness of any automated functions;

− Monitoring of the parameters during the tests.

The minimum requirements for component in-service tests should address the following topics 1) scope and scheduling, 2) acceptance criteria, and 3) criteria for monitoring and trending the results.

3.1.5. Surveillance and monitoring programmes

Surveillance and monitoring programmes monitor and trend the material properties or performance of structures and components important to safety. The results provide data that may be used to validate the forecasted material properties or component performance, based upon the available knowledge and well in advance of potential problems. Their scope (materials, type number of specimens or specific components), their pertinence (dosimeter sets, lead factors, and means for irradiation temperature control) as well as the completeness and the quality of the valuation of the results differ among Member States depending upon specific regulatory requirements.

Surveillance programmes using representative material samples addressing time limiting mechanisms should be extended or supplemented for LTO, if necessary.

Operating organizations should consider implementing controlled ageing programmes namely for electrical cables at their NPPs. Initial values and surveillance and monitoring results for mechanical, electrical, and physical/chemical properties of the cables should be properly documented. Periodic monitoring of the changes during the NPP lifetime is presumed, and the evaluation of their lifetime based on the experimental results and monitoring of the environment should be performed.

Operating organizations should consider conducting experiments on verifying the influence of the current effect of gamma radiation, increased temperature and electric load of the cables with the aim to create a relevant mathematical model.