ML25196A366
| ML25196A366 | |
| Person / Time | |
|---|---|
| Issue date: | 04/12/1976 |
| From: | Moeller D Advisory Committee on Reactor Safeguards |
| To: | Murphy G US Congress |
| References | |
| Download: ML25196A366 (1) | |
Text
ADVISORY COMMITTEE ON REACTOR SAFEGUARDS NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 Apri 1 12, 1976 Mr. George F. Murphy, Jr.
Executive Director Joint Committee on Atomic Energy Congress of the United States Washington, DC 20510
Dear Mr. Murphy:
The information attached is provided in response to your request of March 15, 1976, regarding the t~stimony of the ACRS during t~e JCAE hearings on the safety of the commercial nuclear power program.
Attachment:
Response to Questions Regarding ACRS Testimony Before the Joint Conmittee on Atomic Energy 2560 Sincerely, BakVM~
Dade W. Moeller Chairman
RESPONSE TO QUESTIONS REGARDING ACRS TESTIMONY BEFORE THE JOINT COMMITTEE ON ATOMIC ENERGY
- 1.
Q.
ls there any 1 imit on the number or type of unresolved safety issues that should be permitted to remain unresolved at any one time before nuclear power plant operation should be curtailed?
A.
The important word in the preceding question is~ rather than number.
Most unresolved safety issues may be classi-fied 1nto the following categories of increasing significance beginning with those of low consequence; (1) Conditions with potential for degrading system safety but for which it is judged that further theoretical and/or experimental evaluation will demonstrate no safety significance; (2) Conditions of minor safety significance resulting from marginal engineering practice; (3) Conditions having known safety significance but which have a low probability of occurrence and marginally acceptable consequences (approaching but less than 10 CFR 100 limits);
(4) Conditions that could lead to low probability accidents of serious consequences whose correction would require extensive evaluation or possibly substantial plant modifications, but where the delay in implementing cor-rection can be justified on grounds of improbability for a limited period of delay; (5) Conditions leading to events having a high probability of occurrence and possibly serious consequences whose correction should occur prior to plant operation but where consequences can be acceptably mitigated by a decrease in power or other operational restrictions until corrective modifications are completed or where the occurrence likelihood is reduced by other means.
Instances of conditions falling into the first three categories can be numerous without creating significant jeopardy to public safety.
Only a few items in Category 4 would be tolerable at any one time because the cumulative effect would be unacceptable.
2561 A limited number of items in Category 5 might be tolerable for varying periods of time depen~ing upon the degree to which (a) operational restrictions can effect a reduction in the event probability to a tolerable level or (b) sur-veillance can provide an acceptable means of mitigating risk.
A fully quantitative basis for making judgments regarding the type and number of unresolved safety issues which are acceptable is difficult to develop but should be pursued.
In the current approach, major dependence is placed upon reaching a conclusion through engineering judgment that the overall risk from the plant \-1ould not be significantly increased by the existence of the unresolved safety issues in question.
- 2.
Q.
On Page 1 of the testimony, it was indicated that the safety issues raised by the four engineers are, "for the !T'ost part",
not new to the ACRS.
Why was this statement so qualified?
Which of the issues raised, if any, are new to the ACRS?
A.
This statement was qualified because certain of the issues raised had not previously been brought to the attention of or considered by the ACRS.
The issues in this category are listed below:
(1) Reactor pedestal acceleration; (2) Thermal shock of the concrete reactor pedestal; (3) Potential for criticality of new fuel in storage during fir~ fighting; (4)
Need for updating of training simulators; (5) Standardization of control rooms; (6) Recent experiments on core spray distribution.
The first four of these items had been considered by the NRC Staff, had been found not to be a problem, and, therefore, had neither been called to the attention of the ACRS nor included in the NRC Staff's Safety Evaluation Reports.
There have undoubtedly been other similar questions relating to details of analysis or design that have not been brought to our attention.
The ACRS believes that the NRC Staff has at-tempted to alert the Committee to all significant unresolved questions.
2562 The fifth item was new to the ACRS only in the special context in which it was raised.
Matters relating to the arrange~ent of control rooms have been considered by the ACRS in numerous license reviews, but the question of com-plete standardization as a means of reducing or eliminating human error had not been considered specifically.
The sixth item which refers to a European core spray test was new to the ACRS as were recent tests by GE on core spray distribution. A check of the ACRS records revealed that the September 24, 1974 minutes of a prior discussion between the Regulatory Staff and GE had not been received.
Review of this matter by the NRC Staff indicates that the new core spray effects do not introduce significant safety concerns although some additional study is in progress by GE for the very early reactors.
- 3.
Q.
Is the ACRS aware of any instances where NRC Staff, in its presentations or written reports to the Committee, has toned down the significance of unresolved safety issues, or any other matter relating to safety?
A.
To the knowledge of the ACRS, the NRC Staff has generally presented safety matters to the ACRS in an identifiable and timely manner.
A few exceptions can be recalled where the ACRS believes specific matters could have been identified more clearly at an earlier time in the review of individual projects. At times, the ACRS has advised the NRC Staff that certain informa.tion of a generic nature would better have been called to the attention of the ACRS earlier.
The ACRS recognizes that the desire on the part of some members of the NRC Staff to be able to present the near-resolution of a new safety question at the time it is identified as of potential safety concern may influence the NRC Staff deci-sions concerning the timing of safety issue reports.
- 4.
Q.
Why is it necessary for the ACRS to conduct any of its meetings in closed sessions? Wouldn't the public have greater faith in your decisions if they were reached com-pletely in the open?
A.
During closed executive sessions, preliminary observations and opinions are exchanged among the members.
Alternate conclusions and recommendations are also discussed.
These preliminary views and alternate conclusions in open session could be misunderstood, misinterpreted and even misused by persons or groups outside the ACRS.
Members of the ACRS frequently test their own tentative views and philosophies as well as those of their fellow members using "devil's advocate" techniques for reaching a decision.
The give and take involved in such exchanges would be inhibited 2563 if conducted in open session, and the quality of the decision making process would be impaired.
During its regular meetings, the ACRS must, from time to time, have closed portions to discuss national security information, industrial security, trade secrets and proprietary information in evaluating proposed projects.
The ACRS also has a need for reactor safety information possessed by foreign governments.
Such information is often supplied only after assurances that the information \'till be treated confidentially.
Information is also discussed in closed session regarding proposed new consultants, and new members which would represent an un~ue invasion of privacy if discussed in open session.
The results of ACRS deliberations in executive session are embodied in written reports that are made public.
In order to keep the public informed of substantive differences of opinion on safety issues, members not in agreement with the majority are free to include their conclusions as added com-ments to the ACRS report.
- 5.
Q.
What do you view as the functions and responsibilities of the ACRS vis-a-vis the NRC Staff, the Safety Licensing Board, and the Appeals Panel:
A.
The ACRS believes its role is defined in Section 29 and Section 182b of the Atomic Energy Act of 1954, as arrended in 1957, quoted below:
From Section 29 11 *** The Committe-e shall review safety studies and facility license applications referred to it and shall make reports thereon, shall advise the Commission '1.'ith regard to the hazards of proposed or existing reactor facilities and the adequacy of proposed reactor safety standards, and shall perform such other duties as the Commission may request".
Section 182b "b. The Advisory Committee on Reactor Safeguards shall review each application under Section 103 or Section 104 b.
for a construction permit or an operating license for a facility, any application under Section 104 c. for a con-struction permit or an operating license for a testing facility, any application under Section 104 a. or c. spe-cifically referred to it by the Commission, and any appli-cation for an amendrrcnt to a construction permit or an amendment to an operating 1 i cense under Section 103 or 104 a., b., or c. specifically referrod to it by the Commission, and shall submit a report thereon".
2564 This requires the ACRS to assess the technological safety basis used in licensing nuclear pm*1er reactors and the related fuel cycle.
To this purpose the ACRS is obliga-ted to assess safety engineering premises used in design, construction and operation; supporting scientific and technological data; safety philosophy; the potential for safety enhancement through plant modifications; research.
and developnent; and operational performance verification.
The NRC Staff has an obligation to develop and implement the safety evaluation basis for licensing nuclear instal-lations using similar information.
The ultimate licensing basis is usually developed from an interactive relationship between the NRC Staff and the ACRS, the latter often acting as a sounding board to test the Staff position and as a monitor on the adequacy of NRC safety evaluation bases.
The ACRS report is provtded to both the Atomic Safety and Licensing Board and the Atomic Safety and Licensing Appeal Panel as par: of the record considered in the licensing of a nuclear plant.
The reviews conducted by the ACRS are independent technical evaluations.
The ACRS concentrates on the safety aspects of proposed nuclear installations and brings to bear its opinion and experience as an independent group of specialists knowledgeable in nuclear safety matters. Although the ACRS takes into accqunt NRC regulations and guides, the ACRS is free to, and frequently does, recommend additional safety features, tests, or other requirements considered necessary to adequately protect the public health and safety.
In addition to the review of proposed ~uclear facilities, the ACRS provides advice and recommendations related to generic safety matters and to proposed criteria and stan-dards.
The ACRS also reviews the reactor safety research program sponsored by the NRC, ERDA, and the nuclear industry.
- 6.
Q.
Please comment on the safety margins in the assumptions with regard to design basis accidents.
Can a double-ended pipe rupture actually occur in an instantaneous manner?
If it were not instantanerus, how would this affect the resulting consequences?
A.
The ACRS believes that the double-ended break of a large pipe is very improbable, and that its abrupt, sudden com-plete rupture (in several milliseconds) is still less probable.
The full spectrum of break sizes up to and including the sudd~n, double-ended pipe break, nevertheless, is used in establishing the acceptability of emergency core cooling systems.
2565 If the pipe-break were not sudden (or nearly instantaneous) some questions concerniny blowdo\'m forces on structures would be less important.
- 7.
Q.
Do you have any comments on the effectiveness of the regulatory program for nuclear power reactors? For example, what confi-dence level do you believe that the Arrerican Public can -have in the quality of the review conducted by the Regulatory Staff?
A.
The ACRS believes that the techni.cal depth and effectiveness of the review conducted by the NRC Staff have increased through the years and that the. Arr.erican public can have confi-dence in the dedication of the Staff to public health and safety and to the quality of their review.
The NRC Staff, including many seasoned engineers having a wide range of ex-perience, supported by the extensive technical assistance programs at the ERDA National Laboratories and similar insti-tutions, and by the broad use of consultants, provides a safety review which is corr.prehensive and on a sound technical footing.
The ACRS expects that improverr.ents wi 11 continue as regulatory experience is gained.
In large part because of the philosophy of multiple, concurrent approaches to safety, the health and safety of the public has been well protected, despite the occurrence of specific errors or anomalous events.
The ACRS notes that extensive efforts have been made to include large safety margins and diverse and/or red1.mdant safety fea-tures so that in the long-term, it may develop that the levels of safety in reactors have been rrore conservative than neces-sary when compared to risks accepted for comparable technologi-cal systems.
Nevertheless, because safety improverr.ents can be achieved in nuclear power plants, and because the public per-ception of risk from nuclear power has been particularly vivid as compared to their perception of other risks in society or even risks from alternate sources of energy, the ACRS believes that improvements in reactor safety should continue to be sought.
- 8.
Q.
Has the ACRS experienced a satisfactory relationship with the Nuclear Regulatory Commission since January 19, 1975? What changes \*10uld you suggest in this relationship or in methods of operation? Are any changes requiring legislative action necessary to improve the effectiveness of ACRS operations?
A.
The relationship of the ACRS with the Nuclear Regulatory Co~nission and the NRC Staff has been satisfactory.
2566 The ACRS believes that it is still appropriate to implement the proposed nonmandatory review pro visions of Section 29 of the Atomic Energy Act as noted in previous correspondence and testimony before the Joint Committee on Atomic Energy (Ref. - Letter to the Honorable John Pastore from Dr. C. P.
Siess dated April 14, 1972).
In addition, it is suggested that Section 201 (g) (1) of the Energy Reorganization Act of 1974 (P.L.93-438) be amended to read as follows:
"Section 201 ( g)
(1) The Advisory Committee on Reactor Safeguards (2) The functions ~f the Atomic Safety and Licensing....
11 This change would correct the oversight in P.L.93-438 noted by Senator Ribicoff (Congressional Recor~ S. 19016 dated October 11, 1974).
- 9.
Q.
In hearings before this Committee on March 2, 1976, Commissioner Gilinsky stated the need for an explicit, quantitative safety s tan da rd.
Pl ease comment on whether the achievement of such a standard is a practical goal.
What is a satisfactory alternative safety goal until a quantified standard is developed?
A.
The ACRS believes that efforts should continue toward defining safety standards quantitatively.
It is doubtful that in the immediate future it* will be possible to make these standards entirely quantitative.
The ACRS believes that among other considerations, those representatives of the public formulating such standards must consider risks both to individuals living near nuclear installations and to society in terms of statistical predictions of effects on public health and safety. Allowances should be included within standards for uncertainties in estimation. Account should also be taken of the benefits of the proposed plant and the risks and costs associated with alternate methods of producing power.
In addition, standards should be es-tablished in the light of other societal risks and the level of safety that society can achieve without intro-ducing other undesirable effects on the national well being.
The ACRS believes it will be difficult to establish such safety standards and that it will be impossible to apply them without considerable reliance on engineering and scientific judgment.
The ACRS has endorsed the develop-ment of a simple probabilistic risk standard as a reasonable 2567
- 10.
- starting point with full recognition that there are various degrees of seriousness in postulated accidents and that, for the long term, a relation between acceptable probability and consequence nmy be needed.
Also, there does not currently exist a well-defined means for factoring uncertainties per-taining to the estimation of low probability events into deci-cisions using a quantitative probabilistic safety standard.
The ACRS believes that, for reactors to be constructed in the next sever~l years a probability of less than one in a million per reactor year for an accident having serious con-sequences to the public health and safety is suitable as an interim objective.
Q.
At the hearing on this matter on February 24, 1976, the subject of comments of a Subcommittee of the ACRS in 1970 on the protection of electrical systems in Indian Point 2 was discussed.
Dr. Moeller stated that the minutes of the ACRS meeting in question would have to be checked to deter-mine the accuracy of certain statements.
Does the ACRS now wish to supolement their testiroony of February 24, 1976, with regard to the attitude of the Committee on this matter?
A. A detailed review of ACRS meeting minutes reporting the review of Indian Point Unit 2 does not indicate that either the ACRS Subcommittee or the full ACRS used the term 11 appalled 11 to characterize their attitude with respect to the Indian Point Plant. Although the Subcommittee and full ACRS were not satis-fied with the design and physical arrangement of the electrical and control systems at Indian Point 2, several changes were subsequently incorporated by the applicant to provide an ac-ceptable arrangement.
2568