ML19259B903
| ML19259B903 | |
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|---|---|
| Issue date: | 02/26/1979 |
| From: | Hendrie J NRC COMMISSION (OCM) |
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| NUDOCS 7905150010 | |
| Download: ML19259B903 (26) | |
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N THIS DOCUMEttT CONTAINS
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TESTIMONY OF CHAIRMAll JOSEPH M. HENDRIE
.k U.S. NUCLEAR REGULATORY COMMISSION g:
BEFORE THE v.-
SUBCOMMITTEE ON EllERGY AND THE ENVIRONMENT FIOUSE COMi1ITTEE ON INTERIOR AND INSULAR AFFAIRS FEBRUARY 26, 1979 hr si E.4-h 1
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a Good corning Mr. Chairman and members of the Comittee.
My fellow
.f Cornissioners are with me today to join in the discussion.
I hope that we will be able to answer your questions about reactor 3
safety, about the use of risk assessment in the licensing process, j#:
e and about the significance of the Commission's recent policy
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statement on the Reactor Safety Study, WASH-1400.
Comissioner Kennedy,
sends his regrets at being unable to be with us today.. He is opening
}!!5 a symposium today iri Tucson on waste management, a responsibilit;y he C~.
had accepted long before this hearing was scheduled.
We agreed that waste management is a very important subject and that he should be
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there today.
j-I should note that although I speak here this morr.ing as the Chairman of the NRC, the press of business and the recent weather problems 3_
have not allowed the Comission any real chance to review these remarks and present them as a fully collegial statement.
I hope my colleagues will be able to join me in most or all of what I I
have to say, but you will want to hear from each of them.
Commissioner a:
Kennedy will send you a letter so that his views can also be part of your record.
I will turn now to the first topic in your letter announcing these hearings, Mr. Chairman: What is the basis for the Comission's assessment of reactor safety? The best answer to that is car regulatory system, which depends upon having nuclear plants
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sited, designed, constructed, and operated on the basis of conservative fj.
application of sound and accepted engineering principles, on require-b_
cents for cultiple and redundant safety systems, and on a set of hh EF regulatory requirements that are updated to reflect operating experience.
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The designers, builders, and operators of these plants are required to k-Fr have quality assurance programs and their work is subjected to a continuing licensing and inspection process by the NRC.
The
- j results of the licensing and inspection process are,'in turn, subject D_
to independent review by the Advisory Committee on Reactor Safeguards and often to examination in public hearings.
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- b We believe this regulatory system has served us well.
It is a 5
E rigorous system, and appropriately so in view of the technology
{j we regulate.
It is our job as regulators to make sure that there is no il; undue risk from licensed facilities and, while one must acknowledge strongly
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held views to the contrary, over 400 reactor-years of experience to date give us some reason to believe we are on the right track.
I am going to outline the essential elements of the regulatory system
---i which gives us our assurance of reactor safety and I will be emphasizing
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the strong points of that system.
In doing so, I do not want to leave the impression that everything is just fine and that there are no h-)
problem areas. Like cost hunan institutions, our regulatory system is an evolving one and it is certainly not perfect.
As you know, there
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n are a number of safety issues, some of which we touched on at your f.
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hearing last Thursday, that are in various stages of resolution and that may require changes in plant designs.
Steam generator tube
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Si integrity in pressurized water reactors, hydraulic phenomena in the
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in containments of boiling water reactors, stress-assisted corrosion f.ff in reactor primary coolant system piping, enviro.nmental qualification of safety-related electrical equipment -- these are same of the E.
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safety issues listed in the report to Congress on such matters. We gg
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believe we have sufficient understanding of these issues and have
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taken appropriate steps in the short term to provide adequate protection
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of the public safety, but full resolution of them is still to come.
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In other areas, we are examining many of our regulations with a view 37 it to improving and upgrading them.
Part 100, our siting regulation, g;
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Like our regulations, our licensing, inspection, and
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safety research programs could be improved.
So could the quality assurance programs of our applicants and licensees, which occasionally are found deficient in one aspect or another; and our process of 5:
reviewing and inspecting industry quality assurance programs for
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compliance with our regulations could be improved. However, I think 3E all these programs are on balance, very good and, judged against past
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8 efforts by society to control new technologies, are outstanding.
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But again, they are not perfect; they can and should be improved; and we are working to do just that.
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. Basis of Safety The underpinning for our safety assurances is our. licensing process.
It
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provides for the issuance of construction and operating licenses only
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a af ter a mulci-level review that includes public g
w participation and input at its key stages.
The licenses issued in E
-x accordance with this process specify the framework and necessary details "I
of actions that designers, builders and operators of muclear power plants a#
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must follow in order to provide assurance that there will be no undue
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risk to the public health and safety. Compliance wit:h the license
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conditions is enforced by HRC inspectors during plant construction and a
in operation. This system has been strengthened further with the assignment g
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'of resident inspectors at operating reactors, reactors under construction, g
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and fuel facilities.
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Licenses are issued for those nuclear power plants wirich, based on
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careful and independent reviews by the NRC staff, the Advisory Com-mittee on Reactor Safeguards, a Licensing Board, and if necessary, an f
Appeal Board or the Commission itself, are found to aseet the q
safety criteria and standards required by our regulations.
These ll) safety standards include requirements for considerable margins between 5.5 design and operating conditions and for redundancy in primary and
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backup equipment, in order to compensate for the fact that no body of f:.
knowledge can ever be complete enough to reduce uncertainties and
. risks to zero.
Thus, although the operation of nuclear power plants is not risk-free, the safety objective of the fiRC, as implemented through this licensing process, is to require plant builders and operators to take all those actions considered necessary to assure that the risk to public healtn and safaty is, and continues tc be acceptably small.
One of the primary tools in achieving this safety objective is the use of the defense-in-depth concept for protecting public health and safety.
In its more general application, this concept calls for the incorpora-tion of three levels of safety in nuclear plants.
The first level requires that measures be taken to design, build and operate a nuclear power plant so it will, with a high degree of as-surance, operate without failures that could lead to accidents.
The plant is designed to conservative standards so that it will be safe in all phases of operation and have a substantial tolerance for errors,
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off-normal operation and component malfunction.
Despite the care that is taken in design, construction and operation to avoid equipment failures or operating errors that could lead to safety problems, su 2 failures or errors must be expected to occur during the service life of a nuclear power plant.
The second level of safety requires the provision of measures to cope with them.
Protection for the reactor operating staff and the public is provided by protection devices and systems designed so that expected occurrences and off-normal conditions will be detected and either arrested or
. accomodated safely.
The requirements for these protection systems are based on consideration of a spectrum of events that could lead to off-normal operations which the plant design must accom-g modsta.
In adaition, tes-ing programs are required to verify that P
the protection systems will function as designed.
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The third level of safety supplements the first two by requiring design 7
features and equipment to protect the public, even in the event of the occurrence of very Onlikely accidents.
The additional safety margins
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provided by these features are assessed primarily by evaluating the response of the plant to a number of assumed accidents, involvir.g in
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most instances the assumption of an independent failure of an element of
,w the protective systems simultaneously with the occurrence of the accident a
31' they are intended to control.
From analyses of these postulated accidents, f
a number of sequences called " design basis accidents" are selected as a basis for the design of the additional plant features and equipment that are provided to further protect public health and safety.
One of the third-level requirements for all nuclear plants is the emergency,
j core cooling systems that are designed to cool the core in the event of a major instantaneous rupture of the normal plant cooling systems.
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Application of the defense-in-depth concept also results in the provision of multiple physical barriers between the radioactivity contained in the reactor fuel and the environment outside the plant.
The fuel is contained
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in a sealed metal cladding; the clad fuel is contained in a -heavy steel
5 primary coolant system; and the primary coolant system is enclosed in 7,
a sealable containment building.
The defense-in-depth concept is also applied widely in the design and review of many of the individual
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systa.ns of the plan, leading to requirements for racundant and inde-pendent subsystems and backup systems. These requirements are embodied 3
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in hRC regulations, standards and regulatory guides that are based on M.i t-35.
sound engineering practices established over the past twenty years,
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and that undergo continued review and improvement as operating experience
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accrues.
Our comprehensive research program provides the technical E-(tl bases for.the confirmation of NRC's safety decisions and for needed E:,
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improvements.
i-E The NRC Standard Review Plan, first published in 1975 after years of im W
development, provides documented guidance for the staff and applicants E
t as to current staff positions on acceptable ways to implement the 5
regulations.
It consists of over 1400 pages of detailed criteria and b
zcz methods used for safety reviews and evaluations.
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These comprehensive safety reviews are performed by the NRC staff during h,
plant design, construction, and operations.
Independent safety reviews h)
.e are also conducted by the Comnission's Advisory Cocaittee on Reactor j
b Safeguards, and the results of these reviews are discussed in the
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public hearings conducted by the Commission's Atomic Safety and Licensing i;
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Boards. The reviews are designed to assure the proper and conservative application of the Comission's regulations which implement the defense-in-depth concept. The puroose, scope and effect of these reviews si in minimizing public risk can best be shown by relating them to the f
3 siting, design, construction, and operation phases of nuclear power plants.
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- Siting E
The principal fiRC requirements for the siting of nuclear power plants are found in our regulations in 10 CFR Part 100 and its Appendix A, a
Geologic and Seismic Siting Criteria for fluclear Power Plants. The 1-_
siting reviews carried out by the staff in implementing this regula-tien play an important role in assuring that the likelihood of severe
--l reactor accidents due to siting considerations is very low.
For example, f_
the requirements of this regulation, supported by the independent evaluations f:~
of seismic and geologic conditions at and near a reactor site by the fRC i--
i staff and its consultants, provide the basis for establishing the p,.7 p
seismic design parameters for a plant.
The seismic design parameters El
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are required to be conservative enough so that the likelihood of an bb W
earthquake more severe than the design basis earthquake is very low, hi-and the possibility of a severe accident resulting from such an
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earthquake is even lower.
Similarly, fiRC regulations require that other environmental considerations that have the potential to cause
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-9 SS a severe reactor accident, such as ficoding, tornadoes, industrial accidents at nearby facilities, and overflying aircraft, be evaluated and designed against.
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[5 Design
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There are nany URC regulations that require the implementation of the defense-in-depth concept in the design of nuclear power plants.
These include the majority of the present 64 General Design Criteria, z.T-other Appendices of *10 CFR Part 50, and Section 50.55a, Codes and
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Standards for Nuclear Power Plants. A large amount of the effort c"
involved in NRC design reviews is for the purpose of determining whether these requirements are being properly and conservatively imple-mented, and we rely heavily on these detailed design reviews for our
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}E assurance that we are achieving our safety objective.
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In addition to the design reviews performed by the NRC staff, our regulations require license applicants to perform analyses of various postulated
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equipment, system, and personnel failures.
Independent evaluations of these events on a selective basis are then performed by the NRC to assure that equipment and personnel performance under the assumed
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conditions are properly described and the accident consequences conser-
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vatively calculated. These independent accident analyses provide further assurances of the design adequacy of licensed nuclear power E.'
plants.
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- n and Osera: ion Ap;er. dix B to 10 CFR Part 50 of the NRC regulations establishes mandatory
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quelity assuranca criteria for all phases of nuclear power plant design, fg-r consti uction, and operation. These criteria are icolemented by field rey!e.vs ar.d inspection by the hRC staff.
Each license for operation of a nuclear reactor contains Technical Specifications, which set forth the particular safety and environmental protection measures to be imposed upon the plant, and the operating conditions that are to be met in order to assure protection of
..I the health and safety of the public and of the surrounding environment.
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EE The riRC's Office of Inspection and Enforcement continues its inspections ja during the operating life of the plant to ensure that the requirements of NRC's licenses are enforced, that problems arising in operation are well handled, and that valuable feedback from operating experience g
is made available to other licensees and incorporated into the safety r:
reviews of other plants.
Furthermore, NRC licenses require utilities bk E
to test important safety systems periodically and to report failures of all safety-related equipment to the NRC.
I should note that we have some steps underway to improve this process of getting operating experience and testing information out to other licensees.
The results of NRC inspections and reports of equipment failures are routinely
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nade public.
.- 13 Tne continuing revien-cf operating experience by lic,ensees and by the URC staff provides another important contribution to the assurance of' nuclear power plant safety. Design improvements, based on this experience, can be incorporated into new plants, and any mistakes in 2
design and construction of operating plants can be corrected.
Even after nuclear plants begin cornercial operation, they are not insulated from safety improvements.
There has been a continuing NRC program of improveme'nts in existing nuclear power plants, based on operating experience, new criteria, and better understanding of
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safety issues through research, testing and analysis.
As the number of operating nuclear power plants has increased over the years, there f-has been a. corresponding increase in the allocation of NRC staff
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resources to the inspection program and to the technical safety
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evaluation efforts necessary to provide continued assurance of safe operation of licensed reactors.
One of the many examples of the feedback of operating experience l"
to upgrading of safety requirements involves fire protection.
After the Browns Ferry fire in March 1975, an NRC Special Review
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Group was established to identify the lessons learned from this c,ent and to make recornendations for the future. As a result,
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the Commission's Office of Inspection and Enforcement issued bulletins to licensees and initiated special fire protection inspections.
In response, licensees instituted a nu=Ser of iv.madiate i.mprovements in fire protection at their picnts.
A generic task activity was initiated by the staff to develop upgraded guidelines for fire protection in nuclear power plants.
The generic task culminated in mid-1976 with the issuance of a revised Standard Review Plan section on fire protection. At that time we started a re-evaluation of each operating reactor against the new guidelines and we are requiring appropriate plant modi-fications to upgrade fire protection. The new guidelines have been used as a basis for fire protection review for all operating license and construction permit applications under review since mi d-1976.
In summary, the fiRC recognizes that the operation of nuclear power plants presents sr.e element of risk.
Bu*. we believe that our process, which involves a well-developed safety approach, tha specification of safety design requirements to implement that wroach, and an extensive safety review, licensing and inspection process, gives reasonable assurance that that risk is comparatively very small.
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The saftty record so far achieved in.ae operation of nuclear power piants givas suppo.-t to the validity of the 2C aopecach.
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at this point, approxirately 440 reactor-years of ope: tion of licensed y.}
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comnercial nuclear plants in the United States without an accident having significant effect on the health and safety of the public. While this experience is, of course, much less than that needed to prove our belief that large reactor sccidents have a low probability of occurrence, it is an encouraging record and an outstanding one for a major industrial activity.
!!RC's regulatory process has relied and will continue to rely on the PTh
.iudgment of highly skilled engineers and scientists as the source for
[5 its safety decisions. Based on the aforementioned considerations, and without prejudice to any conclusion we might reach in any indivi. dual licensing proceeding, we believe that nuclear power plants designed, constructed, licensed to operate, and operated in accordance with our regulations and requirements present no undue risk to the public.
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It would be nice to be able to say that there are absolutely nct problems with respect to the safety of nuclear power plants, that perfection has e
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While we believe that nuclear power plants are adequately safe, in the ordinary sense of the word, and that the risk to the public health and safety from their operation is very small, the Commission's
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intsntion is to assure that this risk remains very s sali so that nuclear h
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power can continue to represent a suitable and safe alternative for satisfying a portion of the nation's electrical energy needs.
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The Reactor Safety htudy (WASH-1400)
The question of risk from reactor accidents is not a new one, and I I
should like now to talk about how the Reactor Safety Study (WASH-1400)
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and the subsequent Risk Assessment Review Group came about.
In 1971, Senator Pastore, Chairman of the Joint Cocmittee on Atomic
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Energy wrote to the Chairman of the Atomic Energy Ccxamission,
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urging that a study be undertaken which would allow the AEC to. document f
in clear terms the levels of safety it deemed necessary in nuclear
.g power plants as well as the levels of safety that were actually present
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5 in current design. To quote from the appendix.to the Pastore letter.
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"One way of accomplishing this objective would be to prepare a report which, by addressing the probability of occurrence and consequences of the spectrum of accidents which could befall a nuclear power plant, i.
would represent an assessment of the risks involved in the use of nuclear plants.
Of course, it would also be necessary to compare
= "these risks with those involved in other fields of endeavor in our society in order to put them into proper perspective."
In August, 1972, the Cnairman of the Atomic Energy Commission informed the Cnairnan of the Joint Ec.nmittee on Atomic Energ/ -hat the Atomic y
Energy Commission had undertaken an in-house study "to provide a basis for submitting re:ommendations to the Congress regarding the ex; nsion or modification of the Price-Anderson Act."
The Reactor Safety Study -- WASH-1400 -- thus was sponsored by the Atomic Energy Commission to estimate the public risks that could be involved in potential accidents in commercial nuclear power plants.
It was perforced under the independent direction of Professor liorman C. Rasmussen of the flassachusetts Institute of F
Technology, and soon became known as the "Rasmussen Report." The
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study was done principally at AEC headquarters by a group of scientists and engineers drawn from the AEC, the national laboratories, and universities. The study was started in the summer of 1972 and took three years to complete. A total of 60 people, various consultants,
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70 man-years of effort, and about four million dollars were involved.
The study's objective was to make a realistic estimate of risks associated' with nuclear power plants, and to provide perspective, to compare them
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with non-nuclear risks to which our society and its individuals are already exposed.
The study used fault tree and event tree methodologies to define potential accident paths and their likelihood of occurrence.
Its focus was limited to large power reactors of the pressurized water
and boiling water types, as represented by two specific units, one
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of each type.
These two units were completed reactors, so that the
[si study could deal with the final designs and the as-built plant features.
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Thesa units were designed to the safety criteria of the 1966-72 period.
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EV Tne cassive study was released in draft forn in August of 1974, and Q
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connents were requested from environmental groups, groups critical of r
nuclear power, lawyers representing environmental groups and industry, E-government agencies, and industrial organizations representing reactor
[W manufacturers, architect-engineerina firms, and electric utilities.
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about 1800 pages.
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- E The primary focus of Criticism'of the Reactor Safety Study related to J+3 a
the numerical estimates of risk and the range of uncertainties attributed to them.
Both the probability estimates and the consequmce estimates
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were subjects of controversy.
In addition, there was considerable and 5
continuing criticism of the manner in which the peer-group review was
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handled by the study's authors. The' Executive Summary of WASH-1400 2;;?
also came in for criticism as being presented to provide a favorable picture of the risks associated with comercially-generated nuclear
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power.
The Risk Assessment Review Grouc Cognizant of these criticisms, and at the particular behest of yourself,
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Mr. Chairman, the NE organized a Risk Assessment Review Group on Julyd,1977.
It was charged with four responsibilities:
- to clarify the achievements and limitations of WASH-1400;
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-- to assess the ;;eer comments thereon, and responses to those comments ;
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-- to study the present state of such risk assessment methodology;
-- and to recomend to the Commission how (and whether) such methodology can be used in the regulatory and licensing process. -
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The Risk Assessment Review Group was chaired by Professor Harold Lewis of the University of California at Santa Barbara. and its findings have became known as the " Lewis Report." The findings we:ne published in September 1978 as NUREG/CR-0400.
As the Comittee was provided with copies of the report as soon as it was published, I will not go into extensive detail regarding the findings, which I c.m sur? are familiar to all of you. The Lewis Report did come down very faard on three of the most-criticized aspects of WASH-1400 -- the risk estimates, the Executive Summary and the peer group review. To quote directly from the Findings and the Summary:
"We are unable to determine whether the absolute probabilities of accident sequences in WASH-1400 are high or low, but we believe that the error bounds on those estimates are, in
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general, greatly understated. This is true in part because there is in many cases an inadequate data base, in part because s
of an inability to quantify common cause failures, and in part
be:ause of sore questionable methodological and statistical procedures."
"Amon; cur other findings are the well-knoan one that WASH-1400 is inscrutable, and that it is very difficult
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to follow the detailed thread of any calculation through
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the report.
This has made peer review very difficult, yet peer review is the best method of assuring the
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hb technical credibility of such a complex undertaking.
In particular, we find that the Executive Summary is a poor description of the contents of the Report, should not be portrayed as such, and has lent itself to misuse in the
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r discussion of reactor risks."
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Dn the positive side. one of the important findings of the Lewis Report 55
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is that:
"Despite its shortcomings, WASH-la00 provides at this time the most con:plete single picture of accident probabilities associated with nuclear reactors.
The fault-tree / event-tree approach coupled with an adequate data base is the best
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available tool with which to quantify these probabilities."
Corrission Response After extensive deliberation, the Commission issued on January 18 a policy statenent concerning the Lewis Report, in which it accepted
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the findings of the Lewis group and re-examined its views on WASH-1400 as a result of their report.
Copies of this policy statement and of the Cortission's instructior.s to the staff as to actions to be taken
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regarding the Review Group Report have been provided to the Comittee, p-and are also appended to this statement.
I will not repeat the policy statement here.
Rather, I would like to make a comment on the J
relation of WASH-1400 and the Lewis Report to our regulatory process.
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- 2 A primary goal of the Reactor Safety Study was to obtain "a quantitative evaluation of the risk from the operation of a nuclear plant." Th0 Safety Study was, in effect, a " measurement," made by analyzing two f,.
. typical plant designs, of the results of our system of nuclear regulation.
i; m-What the Lewis group has told us is that the " measurement" of these
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results of our regulatory system, as reflected in the overall risk b.
estimates of the Reactor Safety Study, is much less precise than had been asserted. The Lewis group did not conclude that the overall risk estimates were higher or lower than reported in WASH-1400, although they speculated on possible factors in both directions, but only that they thought the error bounds on those estimates were substantially larger than had been reported.
On that account, they recommended to us that the overall risk estimates of WASH-1400 should be used with great caution - "should not be used uncritically were their words -- in
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the regulatory process or for public policy ourposes.
We have accented and are implementing with vigor that recomendation, as well as the other findings and re:omendatior.s of the Lewis group.
EL I should like to emphasize that our regulatory system, much of which evolved long before the Reactor Safety Study was carried out, does not depend on the ability to make precise quantitative estimates of overall bU f.f risk.
That abilit3 wculd be highly useful, and should be developed. but it is not essential to our regulatory system.
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Instructions to the Staff
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The Conmission bolstered its January 18 policy statement with instructions I
to the staff that I can paraphrase as follows:
-- review the extent to which past and pending licensing or other s.
regulatory actions have relied on the risk assessment g
models and estimates of the Reactor Safety Study; y
-- give special attention to those activities identified by the
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r Review Grcup as being especially amenable to risk assessment, such as generic safety issues or new regulatory requirements, assessing and revalidating existing regulatory requirements, n
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evaluating new designs, and formulating reactor safety research and inspection priorities; l;
-- prepare and submit by June 30, 1979 detailed procedures to
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ensure the proper and ' effective use of risk assessment theory, methods, data development, and statistical analyses
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by the staff; I
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-- prepare a review of current NRC practices and procedures in two areas of particular concern to the Review Group:
the pcar revie.: process for risk assessment "evelopments, and the coordinction.among the research and probabilistic analysis staff and the licensing and regulatory staff. in order to promote the effective use of these techniques;.
-- follow Cocmission-defined procedures in the use of risk assessment techniques during the licensing process; such use is encouraged with full cognizance of the comments of the Lewis Report; and
-- send copies of the Risk Assessment Review Group Report
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and Commission policy statement to all known recipients of the Reactor Safety Study.
The Commission stated that it would make whatever changes are necessary
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to assure that effective peer review and interoffice coordination are integral features of NRC's risk assessment program.
Finally, the Conmission directed the staff to examine the significance of the technical issues raised by the Review Group and the appropriate courses of action for dealing with them.
The Com. mission noted that it will address changes that should be proposed in the approved i...
FY 1979 and FY 1980 research program to improve the data base.
including that on human behavior.
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Staff Actions co Date The staff has begun the Cccmission-directed review of the extent to wnich past and pending licensing or other regulaccry accions have relied on risk assessment models and estimate 3 of the Reaccor Safety Study.
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preliminary survey, completed in December, identified many instances where the Reactor Safety Study was mentioned or discussed, but only a few where the staff considered that the RSS played a substantial role in the licensing process.
In general, the survey revealed no general disposition toward primary reliance on the RSS, with only three items identified as warranting reconsideration:
sote aspects of the Clinch River application, a staff report on anticipated transients..without scram (ATWS), and d.c. power supply reliability.
The survey also II r-revealed a wide range of opinion on the RSS within f!RC.
Some staff members were very critical of the RSS, while others found the benefits of the RSS greatly to outweich its flaws.
Because of the subjective factors involved in staff ur.c of the RSS, the review was more carefully refined.
The Director of Nuclear Reactor Regulation and his Division Directors met with individuals responsible.
for those documents which appeared to involve at least s
partial reliance on the RSS in justifying either the status quo or a relaxation of recuirements.
Approximately 40 cases were reviewed. The discussiens focused cn the role that the RSS actually played in the anayisis, whether its use was a determinative factor in tne decision, and whether a different conclusion would nave been reached today.
Once again, the survey team found no pattern indicating significant dependence on the RSS for licensing decisions.
Four additional instances were identified where the staff's use of the RSS would not now be in con-formance with the Co.nmission's recent guidance, although primary reliance was not placed on WASH-1403.
Future actions on these matters will 7,eflect the new guidelines.
Reviews of correspondence did reveal numerous references to WASH-1400 estimates of failure rates, principally the probability of a pipe break or a large loss of coolant accident. The written record generally does not contain a discussion of the uncertainties associated with those t-estimates, but discussions with the responsible individuals indicate h
S that these uncertainties were considered by the staff and were an element fE of the decision-making process, albeit an implicit one.
The Director of Nuclear Reactor Regulation will provide specific guidelines to assure the explicit treatment of uncertainties in the future.
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r-In sumary, a preliminary view of the use of WASH-1400 in licensing actions indicates that its principal application has been to supplement or confirm the main stream of analyses and judgments reached by the staff.
past ar.d present regulatory decisions depended on traditional y
engir.eering analyses rather thsn any assuced finality of the RSS.
When ii the final report on these reviews is prepared and documented and the
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Commission has reviewed it, we will forward it to you.
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Where Do We Go Fro:a Here?
The Risk Assessment Review Group raised a series of technical issues
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that will have to be examined and deal'. with by the staff.
These issues include questions about statistical methods, the availability J
G and quality of data bases, consequence modeling, her;an factor consid-erations, earthquakes, fires, and common cause failures. Work is i
v.-
already underway on all of these matters as part of our confirmatory f
=
research program, and we will soon be considering what additional efforts an e needed in order to address all of the areas requiring 3
improvement in WASH-1400.
Because there is a substantial amount of work to be done in improving the data and the methods, I _ do not believe it would be desirable to i
launch another full-blown Reactor Safety Study at this poant.
Those
.(
improvements need to be in hand and agreed to before we will be in
good shape to reduce significantly the uncertainties in the predicted values of overall risk. I believe that this effort will take three or four years to acco.:plish.
However, there are sor.e useful parts of the effort that can be dpne in shorter time.
For example, we have
[$
s bean naking studies of the consequence model to determine the sensitivity
~ -
of its predictions to various meteorological factors such as rain, plume rise, and wind shear, to the correlation between wind direction and population, and to evacuation modeling assumptions. We would be able,
~
within the coming year, to produce an updated risk curve that would 1
indicate the impacts of these sensitivity explorations with the
.I i
consequence model.
~
Beyond that, we will be examining the possibility, and also considering the usefullness and the resources required, of a program of periodic updating of the RSS overall risk curves to indicate the effects of various ~ additional modeling improvements that we will be making. This type of effort would c
help to answer various criticisms that have been made of the RSS and put us in better posture to be ready for a more complete update of the RSS after several years.
By taking this step-by-step route, we could gradually reduce the uncertainties in RSS-type risk predictions.
In conclusion, I think it is important to keep in cind what the Commission did and did not do in response to the Lewis Report.
It did reevaluate its reliance on, and relationship to, the Reactor Safety Study.
But it did not thereby take a new view of reactor safety..I continue to
,+.
'believe that our licensing proceedings, standards, and requirements are such that each licensed nuclear power plant is constructed and o, care:ed se as to pr vide adequate grotection to the health and
.2
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safety of the public.
Thank you Mr. Chairman.
I think you may want to hear from my colleagues now.
~
e.
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Z.
R e
ATTACHi4Elli 1 Janua ry 18, 1979 fiRC STATEMEliT Ori RISr, ASSESSMEriT AtiD THE REACTOR SAFETY STUDY REPORT (WASH-1400)
Ill LIGHT OF THE RISrs ASSESSMEtiT REVIEW GROUP REPORT The Risk Assessnent Review Group, chartered by the f4RC in July,1977
~'
to " provide advice and inforcMion to the Comissian on the final report of the Reactor Safety Study, WASH-1400," and related matters,1/
submitted its report to the Comission on September 7,1978.
The Review Group, chaired bi Professor Harold Lewis of the University of California at Santa Barbara, 2/ was formed in response to letters from Congressman Udall, Chairman of the House Comittee on Interior and Insular Affairs.
expressing misgivings about the Reactor Safety Study (MASH-1400), and in particular about the " Executive Sumary" published with the Main Report.
It was expected that the Review Group's report would " assist the Comission in establishing policy, regarding the use of risk assessment in the regulatory process" and that it would " clarify the achievements and limitations of the Reactor Safety Study."
In August,1972, the Chairman of the Atomic Energy Cornission informed the Chaiman of the Joint Committee on Atomic Energy that the Atomic Energy Comission had undertaken an in-house study "to provide a basis for submitting recomendations to the Congress regarding the m.
extension or modification of the Price-Anderson Act."
A draft version of the study report was circulated for comment in Aprill,1974.
On October 30, 1975, the Nuclear Regulatory Commission 3/ announced that the final report had been completed.
Criticism of the document following release centered on the method of treating peer connents on the draft report as well as on the substance of the report.
The NRC phss. release accompanying publication of WASH-1400 praised the report, describing it as a " realistic assessment.... providing an objective and meaningful estimte of the present risks associated with the operation of present E
day light water reactors in the United States," gave several com;iarisons to show that the risk from nuclear power was much less than from other
=
man-made activities, and included a statement that "the final report is a soundl'y based and impressive work....
Its overall conclusion is that the risk attached to the operation of nuclear power plants is very low
-\\
compared with other natural and man-made risks." 4/
In view of the importance attached to the Reactor Safety Study, within and outside the Co= mission, both prospectively and after it was made public, the Comission has reexamined it's views regarding the Study,in light of the Review Group's critique.
O
Knile praising the study's general methodology and recognizing its conttjbution to assessing the risks of nuclear power, the Review Group was critical of the Executive Summary, the procedure followed in producing tne final report and the calculaticas in the body of the. report.
Among the major failings of the study, the Review Group cited:
The ' Executive 3emmary:
The Review Group concluded that "the Executive 3c: mary of the ?.35 is a poor cescriptien cf the c' ;
content's of the report, should not be portrayed as such, and 1:
has lent itszlf t.o misuse in the discussion of reactor risks."
The Review Group indicated the Executive Summary does not adequately indicate the full extent of the consequences of
~
reactor accidents and does not sufficiently emphasize the uncertainties involved in the calculations of their probability.
As a result, the reader may be left with a misplaced confidence in the validity of the risk estirates and a more favorable impression of reactor risks in comparison with other risks than warranted by the study. 5/
The Peer Review Process:
The Review Group Report criticized the RSS staff response, pointing out that in some cases cogent
~
comments from critics either were not acknowledged or were evaded and that, in general, the record of response to valid criticism was weaker than it should ha.e been.
The Report points out -
that the lack of clarity of WASH-1400 itself led.to major diffi-
=
culty in tra'cing a line of thought through the study and crippled many efforts to accomplish responsible peer reviews.
l-Accident Probabilities:
The Review Group was unable to deter-I mine whether the absolute probabilities of accident sequences in WASH-1400 are high. or low, but believes that the error bounds on those esticates are, in general, greatly understated.
This, the Report said, is true in part because there is in many cases an inadequate data base, in part because of an inability
~
to quantify common cause failures, and in part because of sone questionable methodological and statistical procedures.
The Review Group also criticized, in some cases severely, various of the calculational techniques in the Study as well.as its lack of clarity.
The Review Group cited the following as major achieverents of the study:
" WASH-1400 was a substantial advance over previous attempts to estirete the risks of the nuclear option.
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9
7
" WASH-1400 was largely su:cessful in at least three ways; in making the study of reactor safety more rational, in r
establishing the topology of many accident sequences, and in delineating procedures through which quantitative estimates r-iEi
- of the risk can be derived for those sequences for which a data base exists.
h.
c "Despite its shortcomings, WASH-1400 provides at this time it-
=
the most complete single picture of accident probabilities associated with nuclear reactors.
The fault-tree / event-tree
[E approach coupled with an adequate data base is the best available
_2=
tool with which to quantify these probabilities.
" WASH-1400 made clear the importance to reactor safety <fis-cussions of accident consequences other than early fatalities."
E The Comission accepts these findings and takes the following
.[
ctions:
Executive Sumary: The Comission withdraws any explicit or i=f implicit past endorsement of the Executive Sumary.
,5 um-The Peer Review Process: The Comission agrees that the az peer review process followed in publishing WASH-1400 was inadequate and that proper peer review is fundamental to 5
making sound, t,echnical decisions.
The Comission will take
=
whatever corrective action is necessary to assure that c.7 effective peer review is an integral feature of the NRC's e
risk assessment program.
Accident Probabilities: The Comission accepts the Review Group Report's conclusion that absolute values of the risks
~
presented by WASH-1400 should not be used uncritically either I
M in the regulatory process or for public policy purposes and has taken and will continue to take steps to assure that any such use in the past will be corrected as appropriate.
In C
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particular, in light of the Review Group conclusions on accident G
.l.~
probabilities, the Comission does not regard as reliable the Reactor Safety Study's numerical estimate of the overall risk
-[
of reactor accident.
Comunication with the Congress and the Public:
Comission Z
correspondence and statements invciving k' ASH-1400 are being re' viewed and corrective action as necessary will be taken.
6
.y_
With rescett to the cer.:Oner.t parts of the Study, the C0=ission expects the staff to make use of them as appropriate, that is, where the data basi-is adepuate and ar.aiytical techniques per.it.
Taking due account cf tr.e reservatiens expressed in the Review Group Re, cort and in its presentation to the Comission, the Comission supports the extended use of probabilistic risk assessment in regulatory decisionmaking.
The Cc=ission has provided additional detailed instructions to the NRC s.af C;.'cerning c:nti. -ad usa Of risk assessr.er.: te:hni:ues and results e
ir. response to specific criticisms raised by the Risk Assessment Review Group.
s e
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g
NOTES
))
Its charter reads:
The Revie,( Group will provide advice and
,information to the Comission regarding the final report of the Reactor Safety Study, WASH-1400, and the peer corrents on the Study, advice and reco.:nendations on developments in the field of risk assessc-ent methodology and on future courses of
. action which should be taken to improve this methodology and its application.
This advice and information will assist the Comis-ion in establishing policy regarding the use of risk assessment in the regulatory process, in impreving the base for the use of such assesscents.
It will also clarify the achieve-i rents and limitations of,the Reactor Safety Study."
2f The other tambers were Dr. Robert J. Budnitz (Lawrence Berkeley
~
Laboratory, University of California), Dr. Herbert J. C. Kouts (Brookhaven National Laboratory), Dr. Walter Loewenstein (Electric Power Research Institute)
Dr. William Rowe (Environ-mental Protection Agency), Dr. Frank von Hippel (Princeton University) and Dr. 'Fredrik Zachariasen (California Institute of Technology).
Dr. Budnitz is presently on leave from the University of California and is serving (since August 1978) as Deputy Director of the NRC's Office of Huclear Regulatory Research.
-3/
The Nuclear Regulatory Co:: mission was established on January 19 1975 to carry out the regulatory functions of the Atomic Energy J
Cornission., which was abolished on that date.
4f The press release at the time of publication said that the report
- ~
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is "the culmination of the most comprehensive risk assessment of nuclear power plants made to date. The objectives of the study were to make a realistic assessment.... The overall conclusion...is that the risks attached to the operation of present day nuclear power plants are very low compared to other natural and man-madc risks....
Nuclear power plants are about -
10,000 times less likely to produce fatal accidents than man '
made non-nuclear activities....
Non-nuclear accidents involving comparable large dollar value damage are about 1,000 times more likely than nuclear power plant accidents....
The chance that a person living in the general vicinity of a nuclear power plant will be fatally injured in' a reactor accident is one in five billion per year....
In the event of an unlikely react'or accident with a probability of one in a million per reactor per year, latent health effects except for thyroid nodules would be such a small percentage of the normal incident rates that they would be difficult to detect...."
4 e
m e
2 The fiRC Chairman was quoted as saying, "The Comiission believes that the Reactor Safety Study Report provides an objective and meaningful esticate of the public risks associated with the operation of present di t light water reactors in the United States....
Tt e final report is a soundly based and impressive work....
Its.overall conclusion is that the risk attached to the i]
coeration of nuclear power plants is very icw compared
. ith other natural and man-made risks." The press w
. release went on to say that more than 1800 pages of
'M coments were received from a broad spectrum of people P
and all were carefuiiy considered in preparing the E
}
final report.
~T 5/
Professor Lewis, in reporting to the Comission, said that the Executive Summary was not a sur. mary of the
~ ~.-
report.
He concluded it was written as a public statement that reactors were safe compared to other
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risks to which the public is exposed and he stated it should not have been attached to the report and described as a part of it.
rr E'
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ATTACHMD1T 2 E"'
UNITED STATES J.
[r rcoq%
NUCLEAR REGULATORY COMMISSION F,,-
o Y
v;wun
=n. o. c. 2:r5ss
?.
j' ':g,, :,f }
.I
- shC-wf.4' j January 18, 1979 1
O n
3 OFFICE OF THE SECRETARY pr ic iN
?~
MEMORANDUM FOR:
Lee V. Gossick
- 3 E.v.ecutive Director for Operaticas
.' F t/J,
~ 14 FROM:
Saccel J. Chilk Secretary of the Comissio
SUBJECT:
STAFF ACTIONS REGARDING RI,K ASSESSMENT -
REVIEW GROUP REPORT Attached is a policy state:ent issued by the Conaission on January 18, 1979.
In addition, the Con:nission has provided the following instructions for the staff.
!b 1.
Send copies of the Risk Assessment Review Group Report (!WREG/CP,-
2 0400) and of the January 18, 1979 Commission policy statement to all known domestic and international recipients of the RSS.
In the future,
=
copies of the RSS Executive Summary and the complete RSS will be distri-
=
buted only when accompanied by a copy of the Review Group's report and a copy of this statement.
2.
Quantitative risk assessment techniques and results can be used in the licensing process if proper consideration is given to the results of t'~
the Review Group. The staff should use the following procedures re-
?..
garding the use of quantitative risk assessment techniques and results lii pending development of further guidance:
y k+
a.
In comparisons of risks from nuclear power plants with
. iii other risks, the overall risk assessment results of the RSS (i.e., curves or tables of the probability of occurrence of various consequences) shall not be used without an indication of the wide range of uncertainty associated with those estimates.
Any such use should note the difficulty of placing high confidence on estimates that are well below the values set by y.
experience.
[
0 e
4
E:.
.G 0
3
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b.
Quantitative risk assessment techniques may be used to
+
estimate the relative icportance of potential nuclear power P
plant accident sequences or other features where sufficient similarity exists so that the comparisons are not invalidated by lad of an adequate data base.
Sus techr.iques should not M
b2 used to euinate abschte values cf.:robEbilities of failure ti of subsystems unless an adequate data base exists, and it is
?
possible either to quantify the uncerte.inties or to support a j
=
conservative analysis.
=._
c.
The quantitative estimates of event probabilities in the p!!
RSS should not be used as the principal basis for any regu-
+
latory decision. However, these estimates saay be used for relative comparisons of alternative designs or requirements 1i provided that explicit considerations are given to the criti-Risk Assessment Review Group.
~
it cisms of those estimates as set forth in the Report of the g
d.
Th'e RSS consequence model shall not be used as the basis E
for licensing decisions regarding individual nuclear power
?
plant sites until significant refinements and sensitivity 2
tests are accomplished.
However, the consequence model may be it used for relative comparisons provided that such estimates are E
not the primary basis for such reviews and provided that E
explicit consideration is given to the criticisms of the Vi various elements of that model as set forth in the Report of is the Risk Assessment Review Group.
6
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The staff shall prepare and submit by June 30, 1979, detailed pro-
[
cedures to ensure the proper and effective use of risk assessment theory, E
methods, data development and statistical analyses by the staff.
Pending ER review by the Commission of these detailed procedures and the bases and
~
rationale supporting them, the Office Directors will obtain the advice' of the ED0's Regulatory Requirements Review Connittee should questions.
arise regarding the implementation of the above instructions.
3.
The staff shall review the extent to which past and pending li-censing or other regulatory actions, including Conmission, ACRS and li-censing board actions and statements, have relied on the risk assessment models and risk estimates of the RSS. The Comission will examine the
[
results of this review to determine whether the degree of reliance
{E identified was and continues to be justified and to decide whether.
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regulatory modifications are appropriate.
_ -...