United States Nuclear Regulatory Commission - Protecting People and the Environment

Speech-97-26: Chairman Shirley Ann Jackson Keynote Address to the Plant Life Management and Plant Life Extension International Conference and Exhibition


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No. S-97-26

 

Regulation of Aging Power Plants:

Ensuring Safety in a Changing Environment

by

Dr. Shirley Ann Jackson, Chairman

U.S. Nuclear Regulatory Commission

Keynote Address to the

Plant Life Management and Plant Life Extension

International Conference and Exhibition

December 8, 1997

I. Introduction

Good morning. I am very pleased to be addressing this conference on Plant Life Management and Plant Life Extension--an excellent forum for discussing and sharing insights on the technical, commercial, and strategic issues of nuclear plant life management. This lovely city of Prague, with its mixture of well-preserved history, renovation, renewal, and state-of-the-art technology, offers a near-perfect setting for discussing these important subjects. The current state of the nuclear power industry in the United States in some ways is a similar mixture, a combination of first-generation operating reactors, considerations for license renewal, and an industry seeking to use technological advances to improve operational efficiency and to reduce operating and maintenance costs without compromising public health and safety.

I would like to focus your attention today on four areas with direct bearing on plant life management and plant life extension: (1) the development and application of safety margins; (2) aging mechanisms and the use of inspection and testing methods; (3) the U.S. license renewal process; and (4) risk-informed, performance-based regulation.

II. Development and Application of Safety Margins

The initial designs of U.S. commercial nuclear power plants included significant margins of safety for a variety of vital parameters. Explicit margins were established and required by the various design codes and regulations. These explicit margins are well-known and documented, and have evolved somewhat over time as operational experience has accumulated and design analysis methods have improved.

Another set of safety margins also were included in these plant designs, which I will call "implicit" margins. These implicit margins resulted from the conservative assumptions and materials data that were incorporated into design, procurement, construction, and operational guidance. Individual margins were introduced to address specific uncertainties, by applying conservative judgments in the development of design and operating codes, as well as in promulgating regulations. However, in many cases, the implicit margins from one aspect of a design intersected with or were combined with the implicit margins from another aspect, sometimes yielding a much different margin than anticipated. These compounding effects sometimes were increased further in areas where implicit safety margins intersected with explicit margins.

For some plants, aging effects can complicate the picture both from a technical and financial point of view. The emergence of aging considerations may affect the ability of a plant to satisfy these margins. Examples of requirements that include both implicit and explicit margins include: (1) slow heatup and cooldown rates, set to ensure protection of the reactor pressure vessel; and (2) criteria for evaluating the flaw indications detected during in-service inspections. In certain key areas, such as the effect of radiation embrittlement on reactor pressure vessel integrity, conservatism makes sense if definitive data to the contrary is lacking.

Attempting to satisfy these combined margins can have significant technical and financial impact on plant operators, who are monitoring carefully and balancing plant performance and its capital, operation, and maintenance costs.

License renewal (extension of a nuclear power plant 40-year operating license for an additional 20 years) is explicitly allowed in NRC regulations in 10 CFR Part 54. For a utility considering license renewal, these technical and financial aspects are important considerations to be weighed against the benefits to be derived from the license renewal itself. I will return to the subject of license renewal for U.S. commercial nuclear power plants, but first let me speak briefly to issues surrounding inspection and testing methods for the evaluation of age-related degradation of key systems, structures, and components.

III. Aging Considerations and the Use of Inspection and Testing Methods

The key aging degradation mechanisms are well-known--irradiation damage, fatigue, environmentally assisted cracking, erosion, various corrosion mechanisms, and so on. Some of these mechanisms have resulted in forced plant shutdowns, such as the shutdown of several boiling water reactors due to concerns over intergranular stress corrosion cracking in piping systems. Others, such as irradiation embrittlement of the reactor pressure vessel and steam generator tube degradation, have brought about the permanent closure of some plants. Still other effects, such as the flow accelerated corrosion in feedwater and steam piping, have resulted in property damage and loss of life.

But these are the higher profile cases. Aging degradation affects, or may affect, a broad range of plant systems, structures, and components. Aging must be addressed in areas as diverse as the degradation of electrical cable insulation, degradation of concrete structures, degradation of service water piping, and the degradation and cracking of reactor internals. We also are looking the into possible effects of aging on the torque required to ensure operation of motor operated valves under design basis conditions after they have been exposed to operating environments for several years.

For active components, such as pumps and valves, periodic in-service testing can provide confidence that the component will work as designed. Current testing programs are quite comprehensive but also quite costly, and a number of U.S. initiatives are underway to optimize those testing programs.

For passive structures and components, monitoring and periodic inspection are needed to ensure that aging degradation is not challenging the safety function. However, some of these structures and components may have been inspected only once over the life of the plant. In addition, this sampling approach does not emphasize those locations that are experiencing degradation. For example, in-service inspection programs for piping systems have missed fatigue cracking in some cases, resulting in service leaks and forced shutdowns. In addition, some inspection techniques simply are not as effective as one might expect. The experience with eddy current inspection of steam generator tubes over the last few years certainly has shown improvement, but even today we cannot size cracks accurately in certain steam generator tube locations.

An increased emphasis and reliance on in-service testing has resulted in certain improvements. When it was discovered that ultrasonic testing, in certain cases, had missed leaking cracks, and had failed to detect other cracks that subsequently led to piping leaks, both the U.S. Nuclear Regulatory Commission (NRC) and the U.S. nuclear power industry came to the realization that a mechanism was needed that would require industry inspectors to demonstrate not only their personal knowledge of the inspection or testing process, but also the capabilities of the inspector and the inspection equipment and procedures. This has become known as performance demonstration. The American Society of Mechanical Engineers (ASME) has codified this concept into specific requirements in Section XI of the ASME Boiler and Pressure Vessel Code. The U.S. nuclear power industry subsequently initiated a large program to provide a framework for inspectors to satisfy the Code requirements. The U.S. NRC has reviewed this industry initiative, and has found it to be an acceptable way for inspectors to demonstrate their capabilities, and to satisfy the Code. We believe this has been an important step forward in improving confidence in the results of in-service inspections. Currently, the NRC has an initiative underway to evaluate applying a similar approach to steam generator tube integrity.

I also should note that there is a large effort underway here in Europe to provide performance demonstration for qualifying non-destructive examination (NDE) techniques. While we may have some differences in approach, we believe that an appropriate emphasis is being placed on demonstrating the capabilities of those inspectors and inspection procedures that are used to ensure the integrity of safety-significant passive components.

Before leaving the subject of in-service inspection and testing, let me mention the challenge I gave to the U.S. nuclear power industry and the international nuclear technical community shortly after becoming Chairman of the U.S. NRC. I challenged the industry to draw on advanced technology to devise a method for directly measuring material properties on a more microscopic level, and to use it to develop better microscopic and predictive models for radiation-induced aging effects. I believed then, and I continue to believe, that more direct, nondestructive measures of material properties and associated model development are possible. My focus was on embrittlement of the reactor pressure vessel, but there are other applications in which direct measures of material properties would facilitate greatly decisions on the performance of critical components--for example, the degradation of electric cable insulation. While some activity has occurred in this area, I actually had anticipated a more robust response. So I will renew my challenge to you, and to the scientific community at large. I believe this is an area in which we can make substantial progress, and in which that progress would help to build confidence for the continued safe operation of nuclear power plants. I also believe it may have important cost-saving implications in the future, if used to validate extended plant life.

IV. License Renewal Process

Let me turn now to the subject of license renewal, a topic of considerable interest in the U.S. By way of background: about 10 percent of the remaining U.S. nuclear plant licenses will expire by the end of 2010 (with the first to expire in 2006), and more than 40 percent will expire by 2015. The timely renewal of licenses for an additional 20 years, where appropriate, may be important to the economic viability of a utility, due to the additional time over which capital investments can be amortized. It may be important to ensuring an adequate energy supply mix for the U.S. during the first half of the 21st century. It also could play into the debate over the mitigation of global warming.

For nuclear power plant licensees, license renewal can be a two-edged sword. The benefits of gaining 20 years on the existing investment must be weighed against the uncertainties associated with the cost of renewal, based on a consideration of economic, political, regulatory, and environmental factors. As I earlier indicated, uncertainties may exist associated with future operation and maintenance costs. The timing of major replacements, such as steam generators--or major maintenance operations such as thermal annealing--are major factors to be considered.

In the U.S., the decision on whether to seek license renewal rests with a licensee. The NRC task is to establish a reasonable process and clear safety standards, so that licensees can make timely decisions about whether to seek license renewal.

For our part, the NRC has created the regulatory structure to support license renewal. The Commission published the original license renewal rule, 10 CFR Part 54, in December 1991. However, several provisions of that rule, related to implementation issues, raised significant concerns in the nuclear power industry. After reviewing public comments, conducting stakeholder workshops, and considering carefully the various issues raised, the Commission published an amended license renewal rule in May 1995, revising the requirements that an applicant must meet to obtain a renewed operating license.

The amended rule is based on two key principles. The first principle is that the current regulatory process, continued into the extended period of operation, is considered adequate to ensure that the current licensing basis provides the foundation for, and will help to maintain, an acceptable level of safety, with the possible exception of detrimental aging effects for certain systems, structures, and components. The second key principle is that the licensing basis for each plant must be maintained during the renewal term. In other words, the foundation of license renewal hinges on the determination that currently operating plants will continue to maintain adequate levels of safety, and that maintenance of the licensing basis has helped and must continue to help to sustain these safety levels over the life of the plant. This assumes appropriate adjustments to address aging effects identified during license renewal review, and to address relevant operating experience.

In support of license renewal efforts, the NRC staff issued a Generic Environmental Impact Statement (GEIS) that reviewed over 90 possible environmental impacts of license renewal. Out of this group, more than 60 issues were ranked as Category 1 and analyzed generically, based on meeting three criteria: (1) the issue was generic in scope to all licensees; (2) the potential impact, whether high, medium, or low, was the same for all licensees; and (3) no sufficiently beneficial mitigation measures covered in the GEIS, license renewal applicants need not perform a site-specific analysis, but simply can adopt the analysis given in the GEIS. For the remaining issues, ranked as Category 2, applicants will need to present plant-specific impact analyses in their environmental reports.

One issue that has caused some potential applicants concern relates to the environmental impact of transporting high-level waste (HLW) to the proposed U.S. geologic repository at Yucca Mountain. At the time the GEIS was produced, given the uncertain status of the U.S. Department of Energy (DOE) activities at Yucca Mountain, this issue was designated as Category 2, requiring plant-specific environmental impact review. In June 1997, the Commission asked the staff to revisit this issue, and to prepare a set of options, both near-term and long-term, for treating environmental impact analyses related to HLW transportation and disposal for license renewal applications. The staff recently completed this effort, and the options developed are currently under Commission review.

The current U.S. nuclear power industry approach to license renewal is to submit for NRC approval plant-specific and Owners' Group technical reports on specific topics, prior to submitting complete license renewal applications. This approach is intended to establish a foundation of technical information that a licensee can use to evaluate the feasibility of a license renewal application, and to reference that information later in the application itself. The NRC is reviewing plant-specific technical reports prepared by the Baltimore Gas and Electric Company addressing the Calvert Cliffs units, and by the Duke Power Company addressing the Oconee units. We also are reviewing generic reports prepared by owners groups, including the Babcock & Wilcox (B&W) Owners' Group on behalf of five operating B&W plants, the Boiling Water Reactor Owners' Group, and the Westinghouse Owners' Group, which has submitted reports on several structures and components. This level of activity on the part of the U.S. nuclear power industry clearly reflects a serious interest in license renewal.

Some members of the U.S. nuclear power industry also have expressed concerns related to the efficiency of NRC license renewal processes, and in particular the possibility of unnecessarily lengthy hearings. As you may be aware, the Commission always has the authority to exercise its inherent supervisory authority over the conduct of adjudicatory proceedings, and has done so in the past, both to provide guidance to its Atomic Safety Licensing Board (which conducts adjudicatory licensing proceedings) on novel issues and to direct the use of expedited schedules. When the Commission adjudicatory review process was revamped several years ago to make the Commission the sole appellate body, it gave the Commission greater opportunity and flexibility to exercise oversight of its adjudicatory processes. In addition, we may be able to modify certain internal NRC procedures in a way that would increase the efficiency of reviews, safety evaluations, or other aspects of the license renewal process. I should mention, however, that in an era of fiscal restraint, the level of NRC staff resources applied to this area must remain commensurate with the degree of foreseen activity and the existing initiatives by potential license renewal applicants. We remain confident that we can address current and future challenges, and craft a clear and stable regulatory process for license renewal in the United States.

V. Risk-Informed, Performance-Based Regulation

One of my early initiatives as the NRC Chairman was to push for greater use of risk information and, where appropriate, a performance-based approach in our regulatory activities--in other words, risk-informed, performance-based regulation. I believed then, and continue to believe, that a risk-informed, performance-based approach to regulation benefits the agency, the industries we regulate, and the public--through better decision-making, more judicious use of resources, and the reduction of unnecessary burdens.

In developing a proposed strategy for the reassessment of regulatory requirements, and for moving to risk-informed, performance-based regulation, our fundamental objective is to incorporate more risk-informed thinking into NRC rulemaking, licensing, inspection, and enforcement, so that NRC regulations and the prioritization of NRC activities are consistent with the actual risk importance of the issues involved. The most demanding requirements and the highest resource commitments should be directed at the highest risk contributors. Less demanding requirements and lesser resource commitments should be directed at less important contributors.

In order to accomplish this, it is important for us to have a common understanding on the meaning of the term "risk-informed, performance-based regulation." A "risk-informed" approach means that, in the decision-making process, quantitatively derived risk information is considered along with other factors such as the need for defense-in-depth, good engineering practice, and operating experience. Risk information does not become the sole basis for a decision (that is, the decision is not "risk-based"), but rather provides a systematic way of identifying and comparing what is important and where uncertainties exist.

Recently, increased attention has been focused on "performance-based" regulation. Performance-based regulation is, by definition, results focused--that is, focused on meeting certain performance objectives, whether selected for and applied to human operational performance, to the efficacy of licensee corrective actions, to equipment, or to some other measure of licensee behavior. Performance-based initiatives should be selected where objective performance criteria can be established and reliably measured for performance monitoring, and where failure to meet the performance criteria results in tolerable conditions for which appropriate corrective action will be taken in a timely manner. Of course, if failure to meet performance criteria could result in intolerable conditions, we will continue to pursue a more prescriptive approach.

An essential component of a performance-based approach is the feedback of actual operating experience into subsequent evaluations. For example, for equipment, as data from performance monitoring of structures, systems, and components are accumulated, the NRC expects licensees to incorporate that performance data by re-evaluating previous assumptions and making any needed adjustments--not only to reduce testing or other requirements, but also, where appropriate, to increase test frequency, to incorporate additional performance monitoring, or to perform additional or more frequent maintenance. In fact, this is what the new NRC Maintenance Rule requires. When the results focus or performance basis is linked to risk analysis and ranking, the result is risk-informed, performance-based regulation.

The Commission intends to incorporate risk analysis into all relevant regulatory matters, to the extent supported by the law and by the state of the art in risk analysis methods and data. This philosophy was articulated in the 1995 Commission Policy Statement on the use of probabilistic risk assessment (PRA) methods, and is being implemented across the full range of NRC functions. The Commission has devoted considerable focus to ensuring the development and application of effective guidance--both for the NRC staff and for licensees--for incorporating risk insights into decision-making. As one example, for nuclear power plant operators, the NRC staff currently is developing criteria to evaluate the risk contributions of proposed licensee changes to their plants, procedures, or their licenses themselves. These criteria may reference various elements of the Commission Safety Goals or their subsidiary numerical objectives, and thus become, in effect, plant-specific applications of the goals and subsidiary objectives.

In addition, as some of you are aware, we have been conducting a series of pilot applications with the U.S. nuclear power industry in the areas of Technical Specifications (TSs), Graded Quality Assurance (QA), In-Service Inspection, and In-Service Testing, using the draft probabilistic risk assessment (PRA) Standard Review Plans and draft PRA Regulatory Guides which the NRC published and released for public comment earlier this year. The NRC staff has received license amendment applications in each of these four topical areas, and we are well into the process of reviewing and issuing the associated Safety Evaluation Reports. As one example, the staff has been working with the Combustion Engineering Owners Group (CEOG) on a joint application that would modify existing CE TSs to allow a degree of risk-informed operating flexibility. This TS change would allow licensees to employ a Configuration Risk Management Program to make decisions on whether or not to enter an extended Allowed Outage Time on specific plant structures, systems, and components, based on incorporating probabilistic risk assessment (PRA) insights into the analysis of the existing or intended plant configuration. A similar TS change was issued for the South Texas plant last year. In May, the Commission reviewed this program and did not object to the issuance of safety evaluations using this rationale. This program is illustrative of the types of enhancements that are being achieved through a risk-informed approach to regulation.

A risk-informed, performance-based approach also must be taken in the evaluation of research needs. First, as operating experience or the results of other research identifies new issues, each such issue must be evaluated in terms of its relative importance. Risk analysis provides a consistent, systematic framework for this evaluation, since it provides an integrated look at plant systems and potential accidents. Secondly, in planning research on a specific issue, the systematic use of risk information can help to identify what is needed to answer the focal question or to reduce uncertainties associated with it. For example, nuclear reactor shutdown operations involve a wide range of activities. Which of these pose the greatest risk? What is the level of risk? What could and should be done to reduce this risk? Risk assessment is a useful tool in answering such questions--and, in fact, the NRC staff has conducted limited-scope shutdown risk assessments, and is proposing to initiate an additional study to improve agency understanding of shutdown safety issues. Thirdly, risk assessment work itself can identify areas in which additional research is needed to reduce uncertainties and to improve the quality of data or analysis methods. Finally, risk assessment can be useful in prioritizing research programs. As resources and issues change, difficult choices must be made regarding which programs to continue, and which to reduce or terminate. On a very practical note, recent U.S. Congressional action on the NRC Fiscal Year 1998 budget may affect some of our research programs, and if any such changes are necessary, we will endeavor to make them in a risk-informed fashion.

VI. Conclusion

As we approach the 21st century, the nuclear power industry faces an array of challenges and opportunities. The economic constraints already facing some nuclear power plants are significant. Controlling operating and maintenance costs, dealing with increased competition, and recovering stranded costs are considerations that have suggested that some plants may not be financially viable. In the U.S., we have seen five nuclear plants close, and several others have announced plans that could lead to early closure. All is not, and need not be, doom and gloom, however. Nuclear power is and can be economic, if properly managed for reliability and safety. Because of this, as I have discussed, there is considerable interest in license renewal in the U.S. nuclear power industry.

As we move into the future, we will need effective programs for monitoring, inspecting, and testing systems, structures, and components to ensure that aging degradation is detected, characterized, mitigated, and managed over the operating life of the plants. In this context, effectiveness must be measured by early and reliable detection, accurate characterization, and low implementation costs. The risk-informed performance-based approach offers the potential for both cost and worker dose savings. Performance demonstration can help to provide confidence in inspection capabilities, and research programs can provide insights into the types and nature of the degradations for which we need to inspect, and how to model them and their progression over time.

In closing, let me again reiterate that the primary interest of the U.S. Nuclear Regulatory Commission remains ensuring the adequate protection of public health and safety. To that end, operational safety remains paramount. In addition, we who regulate must continue to examine our effectiveness as regulators, and we must position ourselves for change. We will continue to work with the nuclear power industry to improve the effectiveness of inspection and test programs. We also believe that advances in our analytical tools and material property characterizations can provide a basis for examining and potentially changing some of the inherent margins in our regulatory analyses, while ensuring safe performance of the affected systems, structures, and components. These improvements, in turn, may lead to reductions in costs and worker exposures as well as to improvements in safety. These are important considerations today, and they will continue to be important in the future, not just for the U.S. nuclear power industry, but for the international nuclear community as well. Thank you.


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