ML20134N724
| ML20134N724 | |
| Person / Time | |
|---|---|
| Issue date: | 11/18/1996 |
| From: | Kress T Advisory Committee on Reactor Safeguards |
| To: | Shirley Ann Jackson, The Chairman NRC COMMISSION (OCM) |
| References | |
| ACRS-R-1666, FACA, NUDOCS 9611270089 | |
| Download: ML20134N724 (3) | |
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November 18. 1996 The Honorable Shirley Ann Jackson Chairman U.S. Nuclear Regulatory Commission Washington. D.C.
20555-0001
Dear Chairman Jackson:
SUBJECT:
PLANT-SPECIFIC APPLICATION OF SAFETY G0ALS During the 436th meeting of the Advisory Committee on Reactor Safeguards.
November 7-9. 1996, we discussed the application of Safety Goals on a plant-specific basis.
This subject was also discussed at meetings of our Joint Subcommittees on Probabilistic Risk Assessment and Plant Operations on July 17-18, 1996, and of our Subcommittee on Probabilistic Risk Assessment on August 7, 1996. We also had the benefit of the documents referenced.
In a Staff Requirements Memorandum dated June 11. 1996, we were requested to 3rovide recommendations on how the Commission's Safety Goals and Safety Goal
)olicy should be revised to make them acceptable for use on a plant-specific basis.
The Safety Goal Policy Statement made it clear that the Quantitative Health Objectives (OH0s) and the subsidiary Core Damage Frequency (CDF) goal were to provide standards for the NRC staff to judge the overall effectiveness of the i
regulatory system. That is, if the risk posed by the population of plants on the average proved to be less than the Safety Goals, then the staff (and presumably i
the public) would deem that the regulatory system had functioned appropriately to protect the health and. safety of the public.
j The Safety Goals quantified "how safe is safe enough" for the population of U.
S. plants.
For an individual plant, however, the acceptable level of risk is determined by the concept of " adequate protection." which in the final analysis means compliance with the body of regulations.
Risk-informed analyses would provide a more rational basis for making regulatory decisions regarding plant-specific requests for exemptions from the rules or for changes to the licensing basis, and the acceptability of new regulations.
In our August 15, 1996 report, we stated: "the safety goals and subsidiary objectives can and should be used to derive guidelines for plant-specific applications.
It is. however.
im to rely exclusively on the Quantitative Health Objectives (OH0s) practical L
for routine use on an individual plant basis.
Criteria based on core damage frequency (CDF) and large. early release frequency (LERF) focus more sharply on safety issues and can provide assurance i
that the OH0s are met."
In developing plant-specific criteria, it is important to consider the regulatory l
needs in the near future and to ensur' " 't the process will be evolutionary
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rather than so revolutionary that it might discourage the licensees from using l
this approach.
It appears that most of the anticipated licensee requests for l
changes to their current licensing basis will deal with Level 1 probabilistic l
risk assessment (PRA) issues, e.g., inservice inspection, extension of allowed outage times.
Furthermore most licensees have only recently familiarized l
themselves with Level 1 PRA methodology for the narrow regime of power l
operations. They are just beginning to integrate findings of such Level 1 risk assessments with the safe operation of their plants. Even the NRC staff is still coming to grips with the implications of Level 1 risk assessment results for regulation of nuclear plants.
Many licensees do not have access to the l
technologies for facile conduct of full-scope Level 2 or Level 3 PRAs that treat l
Jower operations, low power / shutdown operations, as well as accidents initiated Jy external events.
Commonly accepted standards for such extensive, in-depth analyses do not exist.
An evolutionary and pragmatic approach for using Safety Goals on a plant-specific basis would be to use the CDF as the primary criterion for evaluating pro)osed changes along with a qualitative or quantitative evaluation of the possible _evel 2 and Level 3 PRA issues raised by these changes. For a quantitative analysis, the following two options are offered:
1)
Full-scope Level 2 PRA (with fission product transport capability).
To use this option, a conservative value for a LERF criterion must be determined.
This value, along with the CDF criterion, will provide an acceptable basis for decisionmaking. We note that both the NRC staff and the Electric Power Research Institute, in its "PSA Application Guide," are proposing the use of LERF as an acceptance criterion.
2)
Full-scope Level 2 PRA (without fission product transport capability).
To use this option, conservative values for early containment failure frequency criteria for different reactor designs must be determined. These values, along with the CDF criterion, will provide an acceptable basis for decisionmaking.
In the longer term, we believe the agency should move beyond the evaluation of risk associated with proposed changes to individual plant licenses and apply the Safety Goals to assess the acceptability of plant-specific risk. This could be done in terms of the CH0s, along with the CDF or in terms of the CDF and LERF.
To use the QH0s directly, it would be necessary to have full-scope Level 3 PRAs.
We believe that the use of Level 3 PRAs in the future should be encouraged.
Sincerely,
/s/
l T. S. Kress l
Chairman ACRS l
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References:
1.
Staff Requirements Memorandum dated June 11, 1996, from John Hoyle.
Secretary, NRC, to John T. Larkins Executive Director, ACRS.
Subject:
Meeting with ACRS, Friday, May 24, 1996 2.
ACRS report dated August 15, 1996, from T. S. Kress, Chairman, ACRS, to Shirley Ann Jackson, Chairman, NRC,
Subject:
Risk-Informed Performance-Based Regulation and Related Matters 3.
Electric Power Research Institute Report TR-105396. "PSA Application Guide " prepared by ERIN Engineering and Research Inc., August 1995 l
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November 19, 1996 The Honorable Shirley Ann Jackson Chairman U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Dear Chairman Jackson:
SUBJECT:
POSITION ON DIRECTION SETTING ISSUE 22 -- FUTURE ROLE OF NRC RESEARCH During the 435th and 436th meetings of the Advisory Committee on Reactor Safeguards. October 9-12 and November 7-9, 1996, respectively, we reviewed Direction Setting Issue (DSI) 22. At the 435th meeting, we discussed this issue with the NRC staff.
We also had the benefit of the documents referenced.
Direction Setting Issue 22 raises the question of what role the Office of Nuclear Regulatory Research (RES) will have in the future. A range of possible roles is defined in the discussion. These vary from elimination of a research capability at NRC to continuation of the research at its current, dimir.ished level on a broad range of topics.
The 3reliminary thinking is to select the continuing
" business as usual" role for RES.
We contend that, first, changes are occurring within both the nuclear industry and the regulatory community that make it essential for NRC to have a research function. Second, we contend that a " business as usual" approach to NRC research 4
is too timid.
There is an urgency for the NRC to have researr.h information to
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meet its obligations to protect the public health and safety in a changing environment.
Finally, we contend that the planning for future research should be directed toward areas of focused need.
In particular, research is needed to support NRC's transition to risk-informed and performance-based regulation.
i The research arm of NRC has occupied a central role in the development of the body of regulations needed to ensure public health and safety in the commercial use of nuclear power.
Since the division of the Atomic Energy Commission into the NRC and what eventually became the Department of Energy. RES has overseen the work needed to develop the design-basis analysis of nuclear power plants. This has included ensuring through a combination of experimental and analytical research that the analyses done for Appendix K to 10 CFR Part 50 are on a sound i
technical foundation.
RES has also undertaken a vast effort to understand the residual risk posed by the use of nuclear power through the studies of severe accidents and the associated radionuclide source terms. RES has, in fact, been responsible for the evolution in the analysis of reactor safety from the bounding l
and the qualitative to the use of quantitative risk analysis.
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From the pinnacle following the accident at Three Mile Island. RES has suffered a continuing scale-back of the activities it can afford to undertake.
As with many institutions facing budgetary pressures the longer term benefits of research activities have been sacrificed to ensure that there is the necessary financial backing for day-to-day activities that are the responsibility of NRC.
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6 NRC's research budget has then, suffered disproportionately when funding cutbacks have been inflicted on NRC as a whole Today, the available funding for research is, indeed, small enough that it is a legitimate question whether a viable research program can be maintained.
At the time these cutbacks in research funding have been taking place. changes have also been taking place in the way society deals with safety regulation.
Most directly obvious has been the effort supported by both the Executive Branch i
and by Congress to base regulation on actual r'isk rather than bounding conservatism.
The Vice President heads a Government-wide effort to base regulation, including regulation of nuclear power, on risk.
Relative to most other regulatory agencies. NRC is well on the way to developing a risk-informed and performance-based regulatory system. NRC may well set an exam)le for other i
regulatory agencies in this regard.
It is, then, important that t11s be a good example.
A second societal development that will have safety implications is the economic deregulation of electrical power generation.
This development has yet to be t
l fully realized, but already efforts are being undertaken by the nuclear utilities i
to achieve greater economic competitiveness.
Increases in reactor operating l
power and the extension of fuel life are just two immediate steps the industry l
l is taking that have obvious safety implications.
It is widely forecast that draconian measures will be necessary in the future to maintain nuclear power as l
l a viable option for the generation of electrical energy. There are, of course i
other changes taking place in the industry that fall in the domain of NRC such l
as )lant aging: plant decommissioning: development of new. passive plant designs:
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anc disposal of nuclear waste.
NRC is making great efforts to respond to the challenges posed by societal and industrial changes that are now taking place. The information available to the agency to meet these challenges is, however, proving to be limiting. By way of l
examples, consider the following:
o NRC is attempting to develo) a risk-informed and performance-based regulatory system to improve t1e safety of nuclear plants and to relieve the industry of unnecessary burden. But. NRC is trying to do this without any detailed knowledge of shutdown risk because RES is unable to fund studies comparable to the NUREG-1150 studies performed to understand risk during power operations.
NRC development of probabilistic methods has not kept pace with its needs.
e Methods to treat human errors of commission or the impacts of organizational factors and management practices on risk are not available.
Experience shows that human errors, organization, and management are l
responsible for or contributing to many accidents and "near misses."
e NRC wants to regulate in light of risk, but there is now only the techaical capability for routine, noncontroversial evaluation of core-damage frequency.
The capacity to extend estimates of core-damage frequency to evaluate risk has not been made widely available.
There is a
not even consensus on how accurately analyses of risk, given that core l
7 damage has occurred. must be done nor how comprehensive such analyses must be.
The introduction of digital instrumentation and control (I&C) systems in e
nuclear power plant safety related systems requires NRC to have the capability to regulate high-reliability software-based systems.
NRC's understanding is limited to current software engineering methods which employ highly disciplined development process to design and 3roduce high-reliability software.
A consequence of this approach is ~ ack of well-developed methods for evaluating the product of the process.
NRC is limited to regulating the process of design and development of digital I&C systems because no accepted tools are available for evaluating the product.
Financial constraints forced NRC to allow its codes for predicting fuel e
behavior to atrophy so they are no longer up to the state of the art.
These codes cannot adequately predict fuel and clad behavior at burnups now Ning used by licensees.
Recovery actions by RES have been conetrained by resource limitations to narrow topical areas.
NRC has not yet been able to formulate a risk-informed and performance-e based fire protection rule to replace Appendix R to 10 CFR Part 50 which has been the source of so many exemptions and other controversies.
NRC's opportunities to leverage its research budget by participating in e
intern 3tional research consortia are becoming limited as NRC has less to contribute to the consortia efforts.
e NRC finds it must evaluate new, passive plant designs using tools developed for older plant designs because it cannot afford to develop analytical tools better suited for the simulation of the physics of these new designs.
NRC must "make do" with computational tools that are now over a decade old and don't even begin to take advantage of all the more recent advances in computer technology.
NRC is unable to predict or detect newly discovered modes of degradation e
of the primary pressure boundaries of pressurized water reactors.
It has been forced to use rules designed to deal with wastage and corrosion of steam generator tubes to protect against a variety of forms of stress corrosion cracking.
There is clearly a need for a more aggressive NRC research program to confront the many challenges that the agency continues to face. We can be confident that the agency will meet its obligation to protect the public health and safety.
But, without up-to-date tools produced by a forward thinking research l
organization, the agency will have to msort to methods that do not contribute to either regulatory efficiency or economit efficiency of the nuclear industry.
The financial resources now available to the agency for performing research are indeed limited. It has been necessary to make hard choices on what is to be done and what must be abandoned. A significant factor in the thinking on what is to i
8 be supported and what is to be abandoned has teen a desire to preserve technical capability.
This effort to preserve technical capability appears to have:
led to an emphasis on the things that the agency knows best such as the e
thermal hydraulics of existing reactors, and diluted the efforts in many areas to preserve the current organizational e
units of RES.
The preliminary decision for DSI 22, which is to continue conducting research as it has been done in recent years, appears to enforce this emphasis on what is known well and to preserve the existing organizational structure of RES.
It is our position that more aggressive options need to be developed in response to DSI 22.
One of these options is to focus the research in areas to meet the agency needs as it embarks on its experiment with risk-informed and performance-based regulation.
The goal of research, then, ought to be, first, to provide risk information that is far more comprehensive than that now available, and then, to identify the performance indicators that do indeed reflect the risk.
Furthermore, efforts are needed to use plant data and event reports to assess the adequacy of current probabilistic risk assessment methods.
RES also needs to anticipate safety implications that licensees will make in response to economic pressures.
RES should be in a position to provide tools suitable for the safety evaluation of these changes. To do this, the split of work by RES between user requests and self-directed work may have to be reevaluated.
Sincerely.
/s/
T. S. Kress Chairman, ACRS
References:
1.
United States Nuclear Regulatory Commission. " Strategic Assessment and Rebaselining Initiative. Stakeholder Involvement Process Paper." dated September 16, 1996 2.
United States Nuclear Regulatory Commission.
" Strategic Planning Framework." dated September 16, 1996 3.
United States Nuclear Regulatory Commission. " Strategic Assessment Issue Paper." dated September 16, 1996 l