US vs International LTO

According to the IAEA’s SSG-48, aging management for NPPs is implemented to ensure that the effects of aging will not prevent structures, systems and components (SSCs) from being able to fulfil their intended safety functions throughout the lifetime of the plant.

IAEA guidance considers the changes that occur with time and use, addressing the effects of the physical aging of SSCs, as well as the non-physical aging of SSCs, commonly referred to as obsolescence. In the case of physical aging, IAEA guidance refers to both passive and active components. These components are addressed through aging management programs, which must be consistent with the nine generic attributes of an effective AMP.

The regulatory body of each country may impose, in greater or lesser extent, requirements on NPPs regarding the management of passive and active components and their obsolescence, as well as establish which management or monitoring program to be applied or, on the contrary, allow the NPPs to define the one they consider best.

Based on the description of active or passive components provided in the IAEA Nuclear Safety and Security Glossary or NEI 95-10 and their assessment of aging effects, there are different AMPs for the establishment of their aging management.

The management of passive components can be carried out through NUREG-1801 (GALL report), NUREG-2191 (SLR GALL), IGALL, or another program based on manufacturers' recommendations and internal and external operating experiences.

For active components, the aging of these components may be monitored by the Maintenance Rule (MR) requirements established in 10 CFR 50.65 by the U.S. NRC, or those established in the Equipment Reliability Process described in INPO reference AP-913(WANO reference GL 2018-02). Alternatively, the active components may be managed as indicated in the case of passive components, by another program based on manufacturers' recommendations and internal and external operating experiences.

It is known that there are differences in the management of components between the US and the International approaches. The U.S. NRC approach is that the licensee’s existing regulated processes and the Maintenance Rule (MR) adequately manage the aging of active components, and these do not require specific aging management as part of the license renewal process. It should be added that active components are monitored during normal operation or are periodically tested to determine pump capacity, that valves stroke properly, and that the system initiation logic functions properly. All of this could be supported by the Equipment Reliability Process.

Note, there may be differences in the scope criteria of each tool depending on the main purpose of the tool. For example, the Maintenance Rule (MR) analyzes the number of failures and hours of non-availability of the components to monitor the effectiveness of the maintenance of the components. However, the Equipment Reliability Process aims to achieve reliability targets as high as possible, in order to "eliminate critical component failures" and "maintain acceptable levels of reliability for noncritical components".

While it may seem that active and passive components are managed differently between US and international approach, both methodologies ensure efficient management and integration of active components.

The following table provides examples of different approaches to aging management of active or passive components.

	Components Management Tool
Country	Passive	Active
USA	GALL	Operational Testing Maintenance Rule
Czech Republic	IGALL	IGALL Equipment Reliability
Spain	GALL	Maintenance Rule Equipment Reliability

Finally, there are also different options for managing equipment obsolescence. An obsolescence program can be developed as a stand-alone program or incorporated into existing plant processes. Other programs to manage obsolescence could be IAEA's TOP401 “Technological Obsolescence Programme”, EPRI's 1019161 “Plan Support Engineering: Proactive Obsolescence Management” or other applications developed for this purpose.

Active vs Passive Component Management

Maintenance Rule

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The Maintenance Rule (10 CFR 50.65) applies to a broader range of systems and components than the SSCs that are in scope for license renewal. The Maintenance Rule is a performance-based rule that focuses on the effectiveness of the maintenance of plant equipment so that the plant equipment within the scope of MR is capable of performing its intended function. The Maintenance Rule includes:

1. Safety-related SSCs,
2. Nonsafety-related SSCs that mitigate accidents or transients,
3. Nonsafety-related SSCs that are used in emergency operating procedures,
4. Nonsafety-related SSCs whose failure prevents safety-related SSCs from fulfilling their safety-related function, and
5. Nonsafety-related SSCs whose failure causes a reactor scram or actuates a safety system.

When a plant implements the Maintenance Rule, after identifying the SSCs that are in the scope of the Maintenance Rule, the plant establishes plant specific risk significant and performance criteria for the SSCs in scope of the Maintenance Rule. The plant then, as an ongoing activity, monitors the performance of these SSCs against the performance criteria. If the performance criteria are not met, corrective action is taken and if the cause determination concludes that the current maintenance strategy is not effective, the plant must establish goals to bring about the necessary improvements in performance. The plant then monitors the performance of the SSCs until it is determined that the goals have been achieved. Once achieved, the plant can then return to appropriate preventive maintenance and performance monitoring activities to meet established performance criteria.

Resources:

• NUMARC 93-01, “Industry Guideline for Monitoring the Effectiveness of Maintenance at Nuclear Power Plants”
• EPRI Maintenance Rule Users Group (MRUG) Wiki

Technical Specifications

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A plant’s technical specifications (e.g. 10 CFR 50.36) requires testing of plant safety systems that are used to respond to or mitigate a plant shutdown or transient on a periodic basis to demonstrate that the systems are capable of performing their intended functions. Testing can include tests for proper pump capacity, valves stroke capability, and system initiation logic.

Some examples are:

• Demonstration of proper system operation, if needed during a transient or emergency event, of the High-Pressure Coolant Injection system and the Core Spray system in a BWR.
• Tests that ensure the plant shutdown and emergency cooling system logic operates properly.
• Routine calibration of plant instrumentation

In addition to testing required by the technical specifications, normal plant operation demonstrates control systems that are used for both normal operation and in emergency and transient situations are operating properly.

Equipment Reliability Process

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The IAEA Safety Standard SSG-48 states that all systems, structures, and components (SSCs) within the scope of the aging management (AM) should be managed. This includes components with active and/or passive functions.

The components with active functions historically have been the most challenging and, therefore, nuclear power plants (NPPs) carry out a wide scope of activities aimed at assessing the condition of their active components. These activities may be based on the maintenance rule, surveillance and testing, preventive and/or predictive maintenance of systems and equipment, reliability or lifecycle of components, or various combinations thereof. INPO AP-913(WANO GL 2018-02) "Equipment Reliability Process"] was created to bring all these activities together into a process that identifies, organizes, and integrates them to maximize their efficiency and effectiveness.

The integration and coordination of all the above-mentioned activities ensures a high level of reliability of plant equipment, whether in operation or newly installed. To achieve this goal, the Equipment Reliability (ER) process was established allowing plant personnel to assess the condition of plant equipment, develop and implement long-term maintenance plans, monitor individual equipment or system performance, and make ongoing adjustments to predictive and preventive maintenance tasks and frequencies based on operating experience more easily.

The Equipment Reliability Working Group (ERWG) and International Equipment Reliability Working Group (IERWG) are industry stakeholder groups chartered to advance industry efforts in advancing ER processes and are supported by EPRI as listed on Plant Reliability and Resilience (PRR) - Equipment Reliability (ER) and Related Processes Wiki.

Based on the information presented in the objectives as well as the methodology of the ER process, the following image summarizes the objectives, benefits, and impact of implementing an Equipment Reliability process in a new or existing plant.

Objectives, Benefits and Impact of an Equipment Reliability Process

Objectives

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The ER process is based on the implementation and development of an Equipment and System Reliability Monitoring and Improvement Plan for the entire NPP. It integrates several existing monitoring activities into a common objective: to achieve reliability targets as high as practical, in order to "eliminate critical component failures" and "maintain acceptable levels of reliability for noncritical components".

The main objectives of an ER process could be summarized as follows:

1. Maintain high capacity factors and eliminate or minimize the causes of unscheduled shutdowns and load reductions.
2. Adequate maintenance scopes and frequencies to minimize equipment unavailability due to preventive maintenance and unexpected failures.
3. Define, recognize, and understand the degradation mechanisms that affect equipment.
4. Establish necessary measures to identify degraded equipment or underperforming systems and adopt the appropriate corrective actions, as well as verify their effectiveness before they are incapable of performing their intended function.

To achieve these objectives, NPPs need to identify the scope of important components or functions of the plant systems, and design and implement a maintenance program, based on surveillance and monitoring activities. A procedure or guide is needed to establish periodic monitoring and review of the performance of in-scope components. Health reports will be maintained to evaluate the condition of the plant equipment/systems and corrective action will be taken if necessary.

Equipment Reliability takes into account various existing activities related to other programs, including In-Service Inspection, Maintenance Rule, Obsolescence, internal and external Operating Experience, as well as WANO Indicators when developing maintenance strategies for plant components/systems.

Methodology

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INPO's AP-913 and WANO's GL 2018-02 contain an overview of the methodology used in the implementation of an ER process which is summarized by the figure below:

Equipment Reliability Key Point Diagram

The activities necessary to achieve the Equipment Reliability process objectives are summarized in the following points:

1. Scope and reliability analysis: Where the identification and selection of critical systems and equipment are assessed for inclusion in the scope of the process. Criticality is based on SSC’s importance for maintaining safety, reliability, and energy generation.

To carry out this point, it is convenient to consider those components which are single point vulnerabilities (SPVs). Just one failure of an SPV can cause weeks of lost generation and challenge safety system performance as it is described in the Single Point Vulnerability Process Guide.

The steps to perform the analysis are the following:

1. Identification of important functions
2. Determination of critical component or noncritical SSCs
3. Controls for component classification changes
4. Determination of run to maintenance
5. Document SSCs classification.

2. Performance Monitoring: This activity is developed on the critical components involved in the important functions of the various systems.
   1. Establish performance criteria and monitoring parameters.
   2. Monitoring and trending of each of the parameters and indicators that have been defined in the previous step. For this, EPRI’s Preventive Maintenance Basis Database (PMBD) includes a comprehensive list of failure modes in over 300 components and is essential to determine both the most common failure modes of component types, and their most effective maintenance tasks.
   3. Communicate the performance monitoring results through periodic reports.
   4. Analyze performance degradation to determine the cause and corrective action according to the corrective action program.
3. Corrective actions: This sub-process can be divided into several phases:
   1. Causal analysis: To determine failure and corrective actions required to achieve desired performance in accordance with paragraph 3.3.5 of INPO AP-913.
   2. Evaluate if failure is a Maintenance Rule Functional Failure (MRFF) in accordance with the MR Program.
   3. Prioritization of equipment issues according to their impact on plant operation, plant safety and plant availability.
   4. Aging and obsolescence considerations.
4. Continuous ER Improvement: The reliability process must be continuously reviewed and challenged looking for the best possible maintenance strategy. Continuous improvement may be carried out as follows:
   1. Evaluate the need for a change of maintenance task or frequency.
      • Assess whether monitoring criteria or parameters need to be adjusted.
      • Assess the technical basis of the current Preventive Maintenance.
      • Justify and perform Preventive Maintenance change.
   2. Analyze whether there is an applicable Preventive Maintenance template for the type of component being evaluated. There are multiple sources of preventive maintenance recommendations, such as EPRI's PMBD, EPRI's Long-Term Asset Management Basis Design Application (LAMBDA) or EPRI’s Aging Management Guides.
      • Identify whether equipment degradation can be detected.
      • Identifying monitoring parameters or predictive tasks.
      • Determine if there is a preventive maintenance task that can prevent failure.
      • Develop a new maintenance strategy specifying the preventive maintenance tasks most relevant to the reliability of the component.
      • Select preventive maintenance tasks, set frequencies and document the basis for the new maintenance strategy.
   3. Analyze if the failure or consequences of equipment failure can be controlled.
      • Initiate the design change process to eliminate the failure.
      • Apply a configuration change or other mitigation strategy to control the component failure.
5. Long-term management and planning: For each of the equipment included in the scope, an assessment is made and a strategy for its management is defined to ensure safe and reliable operation within the initial life cycle and for Long Term Operation (LTO). LAMBDA can be used for long-term management and planning for system and component health and is based on the principles of Integrated Life Cycle Management (ILCM) including:
   1. Develop and update the long-term strategy for systems and components identifying and applying the most appropriate maintenance methods for each potential failure.
   2. Review and integrate various maintenance tasks and schedules established to optimize effort by avoiding redundancy.
   3. Analyze whether the equipment problem meets the ILCM threshold criteria.
   4. Clearly define the equipment problem to be solved by the ILCM process.
   5. Define the risk of failure considering the probability and consequences of failure.
   6. Perform a detailed technical analysis to ensure that the current condition of the equipment problem is fully understood.
   7. Identify possible solutions to the problem during the detailed technical analysis.
   8. Perform cost and impact analysis of solution options using tools such as LAMBDA and select the best solution based on the result of the assessment.
   9. Generate the Life Cycle Management Plan.
   10. Obtain the approval of the Plant Health Committee (or equivalent) for the selected solution option.
   11. Obtain funding approval for the selected solution.
   12. Incorporate the selected solution in the NPP management processes, including priority, status, resources, and schedule.
   13. Implement the approved solution.
   14. Modify performance monitoring plans and monitor conditions (as required).
6. Implementation of Preventive Maintenance: The process manages the preventive maintenance activities defined in the continuous improvement process and includes the following:
   1. Organizational approach and project plan for large scale preventive maintenance project revisions to identify the optimal level of preventive maintenance tasks needed to achieve a balance between equipment performance and effective use of resources.
   2. Establish first-time performance dates for modified or created preventive maintenance programs.
   3. Develop standard post-maintenance tests.
   4. Update work management database.
   5. Develop a model preventive maintenance work order.
   6. Perform preventive maintenance tasks.
   7. Document the “as found” condition of the component. Document the degree of degradation observed, indicating whether it is worse than or less than expected so that system, component, or program engineer can adjust the task or frequency accordingly.
   8. Guide to deferring preventive maintenance. If new or updated preventive maintenance processes are not implemented within the timeframe established by the risk assessment, this may increase the probability of a significant equipment failure.

EPRI Tools for Asset Management

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• Long-term Asset Management Basis Design Application (LAMBDA)
• Equipment Condition Assessment: Cost-Benefit Guidelines
• Preventive Maintenance Basis Database (PMBD)
• NMAC Post Maintenance Testing Guide

Record of Revisions

Number	Date	Description of Changes
0	6/11/2024	Initial version

International Atomic Energy Agency

Nuclear Regulatory Commission - The US federal government agency that regulates nuclear power plants

Institute of Nuclear Power Operations

World Association of Nuclear Operators

United States of America

Generic Aging Lessons Learned - The US NRC GALL Report is NUREG-1801. The US NRC Subsequent License Renewal GALL is NUREG-2191

International Generic Ageing Lessons Learned - An IAEA's publication: SRS-82

Electric Power Research Institute

Maintenance Rule - US NRC Maintenance Rule 10 CFR 50.65

Boiling Water Reactor

Aging Management

Environmental Reports - Environmental Reports are the part of a US license renewal application that evaluates the environmental impact of operation of the plant for an additional 20 years.

International Equipment Reliability Working Group

Nuclear Power Plant

Systems, Structures, and Components

Long Term Operation

Integrated Life Cycle Management