ML18214A292

Acrs' Enduring Legacy Contributing to Reactor Safety - Proceedings of the 2018 26th International Conference on Nuclear Engineering

ML18214A292
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Issue date:	07/22/2018
From:	Hossein Nourbakhsh Advisory Committee on Reactor Safeguards
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Proceedings of the 2018 26th International Conference on Nuclear Engineering ICONE26 July 22-26, 2018, London, England ICONE26-82275 ACRS' ENDURING LEGACY CONTRIBUTING TO REACTOR SAFETY Hossein Nourbakhsh Senior Technical Advisor for Reactor Safety Office of Advisory Committee on Reactor Safeguards (ACRS)

U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Hossein.Nourbakhsh@nrc.gov ABSTRACT 1 In 1950, the AEC established a second advisory committee, Industrial Committee on Reactor Location For over 60 years the Advisory Committee on Problems, charged with the responsibility of advising Reactor Safeguards (ACRS) has had a continuing on what we would today consider siting issues, statutory responsibility for providing independent including seismic and hydrological characteristics of reviews of, and advising on, the safety of proposed or proposed sites. In 1953, the Reactor Safeguards existing reactor facilities and the adequacy of Committee and the Industrial Committee on Reactor proposed reactor safety standards in the United Location Problems were combined by the AEC and States. This paper discusses the role of the Committee the ACRS was formally born.

as it has evolved during its more than 60 years of history, noting some of its significant contributions to The 1957 amendment to the Atomic Energy Act reactor safety. of 1954 established the ACRS as a statutory committee advising the AEC. According to Section 29

1. INTRODUCTION of the Act the Committee shall review safety studies and facility license applications referred to it and The history of ACRS goes back to 1947 when the shall make reports thereon, shall advise the U.S. Atomic Energy Commission (AEC) recognized Commission with regard to the hazards of proposed the need for an independent technical group to review or existing reactor facilities and the adequacy of and provide advice on reactor safety matters and thus proposed reactor safety standards and shall perform a Reactor Safeguards Committee, chaired by Dr. other such duties as the Commission may request.

Edward Teller was established. Dr. Teller has been quoted to recall that Reactor Safeguards Committee With the enactment of the Energy Reorganization was about as popular - and as necessary - as a Act of 1974, the AEC was reorganized into two traffic cop [1]. As stated by former NRC Chairman, separate entities, the Nuclear Regulatory Commission Richard Meserve, the Reactor Safeguards Committee (NRC) and the Energy Research and Development clearly established an enduring characteristic of the Administration (now the Department of Energy). The ACRS - a willingness to provide candid views on ACRS was assigned to the newly established NRC reactor safety issues, even at the risk of taking with its statutory requirements intact.

unpopular positions [2].

This paper discusses the role of ACRS as it has evolved during its more than 60 years of history, noting some of its significant contributions to reactor 1

The views expressed in this paper are solely those of the author safety.

and do not necessarily represent those of either the ACRS or NRC.

1 Copyright © 2018 by ASME

2. ROLE OF ACRS OVER ITS HISTORY risk-informed and performance-based regulatory system and has taken a leading role in considering The role of ACRS has evolved over its 60 years some of the challenging issues that have arisen in this of history. Figure 1 depicts the number of effort.

reports/letters issued by the Committee on various topics over its history. The passage of the 1954 Throughout its history, an essential activity of the Atomic Energy Act made it possible for private ACRS has also been reviewing the research companies to build and operate nuclear reactors under sponsored by the agency. This includes evaluation of license. This Act also assigned to the AEC the technical and programmatic aspects of the overall responsibility of protecting the health and safety of reactor safety research program as well as episodic the public through licensing process. Most of todays review of particularly important ongoing research.

U.S. nuclear power plants were licensed during the 1960s and 1970s, when both the technology and its In 1988, the Commission established the governing regulations were in the formative stages. Advisory Committee on Nuclear Waste (ACNW) to The ACRS review has always been an important advise the Commission on high-level waste and low-element of the reactor licensing process. level waste issues. Previously, the ACRS and its Waste Management Subcommittee performed this After 1975, not only the orders for new function. In 2007, ACNW was renamed to Advisory reactors plummeted, but there were also many Committee on Nuclear Waste and Materials cancellations of existing orders. Following the March (ACNW&M). In 2008 the ACNW&M merged into 28, 1979 accident at Three Mile Island Unit 2 (TMI- the ACRS. The decision to merge ACNW&M into 2), power reactor licensing was suspended for a year. ACRS was based on the changing workload and As the ACRS moved into the 1980s, the Committee technical challenges facing the agency and the shifted much of its attention from plant design and anticipated increased need for expertise in health construction to improvements in both the operation physics, waste management, and earth sciences in the and regulation of nuclear power plants. The ACRS agency's licensing reviews.

has been very supportive of the evolution toward a Figure 1. The number of reports/letters issued by the ACRS on various topics (1957-2017) 2 Copyright © 2018 by ASME

3. LICENSING REVIEWS The proposed Malibu reactor was never built. An The ACRS has played an important role in intervener group successfully contested the licensing reviews of reactors [3]. The ACRS early construction of the proposed Malibu plant. The reviews also led to evolution of many new safety adequacy of seismic design was one of the main requirements dealing with a wide range of technical points of contention [5].

issues. Following are some examples of the issues raised by the ACRS during its early licensing reviews.

• Effectiveness of ECCS Design: By the mid-1960s, as proposed plants increased significantly

• Control Rod Ejection Accidents: The ACRS in power level, the ACRS became concerned that report on licensing review of the Connecticut a core meltdown accident, particularly one in Yankee plant [4] was the first to call out the which the plants emergency core cooling system requirements for study of the control rod ejection (ECCS) might fail to operate as designed, could accident. This led to design changes in large lead to a breach of containment. The ACRS LWRs, either to limit the reactivity worth of emphasized the need for improved emergency control rods or to add an additional mechanical core-cooling systems (ECCS). By August 1966, restraint to control rod ejection (an approach General Electric responded in support of the taken in BWRs) [5]. Dresden 3 plant by proposing a redundant core-flooding system and an automatic

• Design Considerations for a Tsunami Following a depressurization system, which would reduce the Major Earthquake: The ACRS report on the primary system pressure sufficiently to maximize proposed 1473 MWt Malibu Nuclear Plant Unit the effectiveness of the low-pressure core spray 1 for construction at Corral Canyon (twenty-nine or core-flooding system. Later that year miles west of Los Angles) was the first to raise Westinghouse introduced accumulators.

the issue of the adequate protection against a tsunami following a major seismic event. The

• Anticipated Transients without Scram (ATWS):

following paragraph from the July 15, 1964 The issue of ATWS was first raised by E. P.

ACRS report on the proposed Malibu Plant is Epler, an ACRS consultant, in a January 21, 1969 particularly noteworthy. letter to the ACRS executive secretary [5]. Few months later, the ACRS decided to identify the The ability of the plant to withstand the issue in its letter reports on Hatch unit 1 [6] and effects of a tsunami following a major on the application for the construction earthquake has been discussed with the authorization for the Brunswick Units 1 and 2 applicant. There has not been agreement among [7]. In each report the Committee recommended consultants about the height of water to be a study be made by the applicant of further expected should a tsunami occur in this area. means of preventing common failure modes from The Committee is not prepared to resolve the negating scram action and of design features to conflicting opinions, and suggests that intensive make tolerable the consequences of failure to efforts be made to establish rational and scram during anticipated transients.

consistent parameters for this phenomenon. The applicant has stated that the containment In the early 1980s, the U.S. nuclear utility structure will not be impaired by inundation to a industry in cooperation with DOE, and with support height of fifty feet above mean sea level. The from the Electric Power Research Institute (EPRI),

integrity of emergency in-house power supplies initiated the Advanced Light Water Reactor (ALWR) should also be assured by location at a suitable program to ensure a viable nuclear power generation height and by using water-proof techniques for option for the 1990s and beyond. The ACRS followed the vital power system. The emergency power the development of the ALWR program from its system should be sized to allow simultaneous inception and offered suggestions regarding safety operation of the containment building spray improvements on several occasions [9].

system and the recirculation and cooling system.

Ability to remove shutdown core heat under In 1989, the NRC established alternative conditions of total loss of normal electrical licensing processes to improve regulatory efficiency supply should be assured. If these provisions are and add greater predictability to the licensing process.

made, the Committee believes that the plant will The ACRS has played an important role in new be adequately protected [6]. reactor licensing reviews including the design 3 Copyright © 2018 by ASME

certification process. According to NRC regulation emergency planning. In 1966, the Committee (10 CFR 52.53), the design certification application is noted that many applicants and licensees would referred to the ACRS for a review and report. The rely heavily on local authorities to carry out ACRS has identified many technical issues during its evacuation, if it should become necessary. There design certification reviews which were resolved were also no guidelines for judging when an before the Committee provided its final evacuation would be advisable. The ACRS recommendations for approvals [10-11]. decided that it should alert the AEC to a problem area where little efforts being exerted The License Renewal Rule (10 CFR Part 54), [13]. Pressed by the ACRS, the AEC undertook a first issued in 1991, establishes the technical and study of emergency plans and procedures that procedural requirements for renewing power reactor eventually led to adding a new Appendix E to 10 operating licenses. According to 10 CFR 54.25 each CFR Part 50, Emergency Planning and license renewal application shall be referred to the Preparedness for Production and Utilization ACRS for a review and report. To date, the ACRS has Facilities.

completed the review of 56 license renewal applications and the associated NRC staff safety

• Quantitative Safety Goals: In 1979, The ACRS evaluation reports involving 90 nuclear power units. recommended that consideration be given to the The ACRS has contributed significantly to the establishment of quantitative safety goals for success of the license renewal program by nuclear power reactors. In its May 16, 1979 establishing expectations on the quality of the letter on quantitative safety goals [14], the ACRS submittals and of the license renewal programs recognized the difficulties and uncertainties in committed to by licensees. the quantification of risk and acknowledged that in many situations engineering judgment would Utilities have been using power uprates since the be the only or the primary basis for a decision.

1970s as a way to increase the power output of their Nevertheless, the Committee believed that the nuclear plants. Power uprates are submitted to NRC existence of quantitative safety goals and criteria as license amendment requests. ACRS reviews the could provide important yardsticks for such power uprates that are amounting to power increase judgment [14].

greater than 5 percent above originally licensed value.

Since 1998, The Committee has reviewed 26 The ACRS was at the forefront of the applications for power uprates. ACRS has development of quantitative safety goals. The contributed significantly to the success of the power first set of trial goals (NUREG-0739) [15] was uprate program by establishing expectations on the developed by the ACRS in 1980. These safety quality of the power uprate license amendment goals were the basis for the later NRC work on requests and supporting documentations. The the development of an NRC Safety Goal Policy Committee was instrumental in the staff development in 1983 [16].

of a review standard for extended power uprates [12].

• PRA Policy Statement: In the early 1990s, the

4. REGULATORY POLICIES AND ACRS became concerned about the inconsistent PRACTICES use of PRA in NRC. In a July 19, 1991 letter on the consistent use of PRA [17], the ACRS The ACRS has played a significant role in the acknowledged, PRA can be a valuable tool for review and resolution of key technical issues judging the quality of regulation, and for helping associated with regulation of nuclear power plants. to ensure the optimal use of regulatory and The Committee has a history of recommending industry resources. The Committee also stated innovative approaches to regulatory problems. that it would have liked to see a deeper and Following are some examples of the roles ACRS has more deliberate integration of the methodology played in shaping the regulatory policies and into the NRC activities. The ACRS also pointed practices of the agency: to issues such as the inconsistent use of conservatism and the lack of the treatment of

• Emergency Planning: As the size of proposed uncertainties. In response to the ACRS, NRC nuclear power plants increased and containment chartered a PRA Working Group and a could no longer be regarded as an Regulatory Review Group to review processes, unchallengeable barrier to the escape of programs, and practices to identify the feasibility radioactivity, ACRS paid more attention to of substituting performance-based requirements 4 Copyright © 2018 by ASME

and guidance founded on risk insights in place of fabrication, installation testing, and operating prescriptive requirements [18]. These efforts led history of important plant components and this the Commission to issue a policy statement on information should be adequate for the the use of PRA so that the many potential comprehensive reviews by the regulatory staff. [22].

applications of PRA can be implemented in a consistent and predictable manner that would ACRS has made valuable contributions over a wide promote regulatory stability and efficiency [19]. range of issues at operating plants including the following:

• Risk-Informed Regulations and Practices: ACRS has been very supportive of the evolution toward

• Generic Safety Issues (GSIs): Starting in 1972, a risk-informed and performance-based the ACRS developed a list of generic items regulatory system [20] and had technical related to construction or operation of light-water oversight of this transformation. The Committee reactors [23]. This grew into a list which was last has followed closely the development of reported in an ACRS letter dated March 21, 1979 regulatory guidance for the implementation of [24]. The work of the NRC staff to resolve these risk-informed programs and processes, and of items, as well as the generic items identified by PRAs standards that have been used to support them, became steadily more formal, stemming these programs and processes. The ACRS has from the requirement of Section 210 of the also taken a leading role in considering some of Energy Reorganization Act of 1974 which the challenging issues that have arisen in this required the NRC to develop a plan providing effort, such as the application of defense-in-depth for the specification and analysis of unresolved in a risk-informed context. In its May 19, 1999 safety issues relating to nuclear reactors and letter on the Role of Defense in Depth in a Risk- take such action as may be necessary to Informed Regulatory System [21], ACRS implement corrective measures with respect to forwarded a paper, prepared by several of its such issues.

members and an ACRS Senior Fellow, in which two (Structuralist and Rationalist) views of The ACRS has made significant contribution defense-in-depth were discussed along with a toward resolution of many generic safety issues preliminary proposal regarding its role in a risk- (GSIs). One recent example is the Committees informed regulatory system. The ACRS role in the resolution of GSI-191, Assessment of motivation for this had arisen because of Debris Accumulation on PWR Sump instances in which seemingly arbitrary appeals to Performance. ACRS was first to express defense in depth had been used to avoid making concerns about the effects of chemical reaction changes in regulations or regulatory practices products and particle/fiber mats that could form that seemed appropriate in the light of results of on screens. The Committee was also the first to quantitative risk analyses. alarm that increasing screen area, though it could reduce head loss, might result in more

5. OPERATING REACTORS SAFETY fiber debris passing through the screens and OVERSIGHT increase downstream effects [25].

The ACRS has always been attentive to safety

• Safety Culture: The concept of safety culture improvements in operation of nuclear power plants. received much attention in the aftermath of the In fact, ACRS was the first to recommend periodic 1979 accident at TMI-2 which underscored the comprehensive (ten year) review of operating power importance of management and organizational reactors. In a June 14, 1966 letter on the subject, the factors to the safe operation of nuclear power Committee recommended that the AEC institute a plants. The 2002 incident at the Davis-Besse program of periodic comprehensive review of nuclear power plant renewed the interest in safety operating licensed power reactors [22]. The culture and provided an impetus to the Committee also recommended that the reports, to be deliberations of the ACRS regarding the role and submitted by reactor operators for these effectiveness of the NRC Reactor Oversight comprehensive reviews, contain summaries of Process (ROP) in monitoring organizational operating history with special emphasis on performance. ACRS organized a workshop on significant problems [22]. The ACRS believed that safety culture on June 12, 2003 [26] and issued a each reactor operator should be responsible for the report to the Commission on July 16, 2003 [27].

maintenance of appropriate records of the design, 5 Copyright © 2018 by ASME

6. SAFETY RESEARCH REVIEWS improvement of means for evaluating the factors that may affect the nil ductility transition Throughout its history, ACRS has made temperature and the propagation of flaws during significant contribution to safety research conducted the vessel life [30].

by the agency. From the very beginning of its establishment, the Committee recognized the need for

• Early Concerns about Core Meltdown Accidents:

a safety research program. In a November 16, 1959 In 1966, at the prodding of ACRS, the AEC letter on proposed study of the reactor hazard and established a special task force to look into the criteria problem, the Committee acknowledged the problem of core meltdown [31]. The task force, increasing difficulties which it foresaw in the chaired by William K. Ergen, a former ACRS adequate evaluation of the hazards of reactor facilities member, issued its report in October 1967 [32].

due to the absence of a critical evaluation of the The report offered assurances about the existing data relating to reactor safety and the reliability of ECCS designs and improbability of absence of written and agreed upon criteria for a core meltdown, but it also acknowledged that a judging the adequacy of the proposed design, loss-of-coolant accident (LOCA) could cause a construction and operation of the various parts of a breach of containment if the ECCS failed to reactor [28]. The ACRS believed that the problem perform. In an ACRS letter on the task force required a study of the available information on report, dated February 26, 1968, the Committee reactor safety, arranging it so it is readily available strongly recommended that a positive approach and deriving from it logical conclusions pertinent to be adopted toward studying the workability of answering the questions: protective measures to cope with core meltdown A) Is the available knowledge sufficient to set [33]. The Committee also recommended, as it did criteria? in its 1966 report on safety research, that a B) Is more research needed and of what kind? vigorous program be aimed at gaining better C) Is this the sort of problem that is not understanding of the phenomena and susceptible to solution by planned research and mechanisms important to the course of large-therefore, must primary reliance be placed upon scale core meltdown. The task force report and judgment and experience?[28]. ACRS recommendations formed the basis of some of the most important research initiatives During its early licensing reviews, the ACRS and regulatory decisions by the AEC and the identified many technical safety issues for further NRC, including the AECs decision to undertake research. Following are some examples of technical a study to estimate the probability of a severe issues raised by ACRS for further study: accident which resulted in the publication of the landmark Reactor Safety Study (WASH-1400)

• Radiation Damage to Reactor Pressure Vessel: In [34] and the beginning of the science of a May 20, 1961 letter on the subject of radiation probabilistic risk assessment as applied to damage to reactor pressure vessel, ACRS raised nuclear power plant safety [2].

its concern about the potential damage to reactor pressure vessel by virtue of the neutron In 1977, Section 29 of the Atomic Energy Act flux to which they are subjected during their was amended to add the following two sentences: In life. [29]. However at that time the vessel failure addition to its other duties under this section, the was not considered credible. In the mid-1960s, Committee, making use of all available sources, shall as the size of proposed reactors increased undertake a study of reactor safety research and substantially, the ACRS discussed this matter prepare and submit annually to the Congress a report extensively and in its November 24, 1965 letter containing the results of such study. The first such on the subject of reactor pressure vessels stated report shall be submitted to the Congress no later the following: than December 31, 1977." ACRS had been submitting an annual report on NRC Safety Research To reduce further the already small probability Program to Congress from 1977 until 1997. In 1998, of pressure vessel failure, the Committee Public Law 105-362 struck those two sentences in suggests that the industry and the AEC give still Section 29.

further attention to methods and details of stress analysis, to the development and implementation In 1997, the Commission transferred the research of improved methods of inspection during advisory function of the Nuclear Safety Research fabrication and vessel service life, and to the Review Committee (NSRRC) to the ACRS. In this 6 Copyright © 2018 by ASME

role, the ACRS was directed to examine the need, 2. U.S. Nuclear Regulatory Commission, The Role scope, and balance of the reactor safety research of the ACRS in Nuclear Regulation and Safety:

program [35]. The Committee was also directed to Looking Back, Looking Forward, Remarks by consider how well the Office of Research anticipates Chairman Richard A. Meserve before the ACRS research needs and how it is positioned for the Symposium on Role of Advisory Committees in changing environment [35]. Since 1998, ACRS has March 4, 2003.

been submitting reports to the Commission on review 3. Nourbakhsh, H. P. 60 Years of Contributing to and evaluation of the NRC Safety Research Program, Reactor Safety: Insights on ACRS Power Reactor initially annually and after 2004 biennially. Licensing Reviews, To be presented at the 2018 International Congress on Advances in Nuclear Since 2004, the ACRS has also been assisting the Power Plants (ICAPP 18), Charlotte, NC, April NRC Office of Nuclear Regulatory Research in an 8-11, 2018.

independent evaluation of the quality of its research 4. Advisory Committee on Reactor Safeguards, programs. An analytical/deliberative decision-making Report from Herbert Kouts, Chairman of ACRS, framework has been adopted for evaluating the to the Honorable Glenn T. Seaborg, Chairman, quality of NRC research projects. The definition of U.S. Atomic Energy Commission,

Subject:

quality research adopted by the Committee includes Report on Connecticut-Yankee Atomic Power general attributes such as soundness of technical Company, February 19, 1964.

approach and results, justification of major 5. Okrent, D., Nuclear Reactor Safety, On the assumptions, and treatment of uncertainties/ History of the Regulatory Process, the University sensitivities. of Wisconsin Press, (1981).

6. Advisory Committee on Reactor Safeguards,

7. NUCLEAR MATERIALS AND WASTE Report from Herbert Kouts, Chairman of ACRS, to the Honorable Glenn T. Seaborg, Chairman, Before the establishment of ACNW in 1988, U.S. Atomic Energy Commission,

Subject:

ACRS reviewed matters related to the long-term Report on the City of Los Angeles- Malibu management of radioactive wastes produced within Nuclear Plant-Unit No. 1, July 15 1964.

the nuclear industry. Since the merging of ACNW&M 7. Advisory Committee on Reactor Safeguards, into the ACRS in 2008, the Committee has been Report from Stephen H. Hanauer, Chairman of reviewing many aspects of nuclear waste management ACRS, to the Honorable Glenn T. Seaborg, such as handling, processing, transportation, and Chairman, U.S. Atomic Energy Commission, storage of nuclear wastes including spent fuel and

Subject:

Report on Edwin I. Hatch Nuclear Plant, nuclear wastes mixed with other hazardous May 15, 1969.

substances. 8. Advisory Committee on Reactor Safeguards, Report from Stephen H. Hanauer, Chairman of

8.

SUMMARY

AND CONCLUSION ACRS, to the Honorable Glenn T. Seaborg, Chairman, U.S. Atomic Energy Commission, Through more than 60 years of its history, the

Subject:

Report on Brunswick Steam Electric ACRS has made significant contributions to nuclear Plant Units 1 and 2, May 15, 1969.

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moved into the 1980s, the Committee shifted much of NRC,

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