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AEC PROPOSED REGULATIONS

U.S. ATOMIC ENERGY COMMISSION,

Washington, D.C., November 29, 1971.

AEC PROPOSING STANDARD GUIDELINES FOR EVALUATING
ENVIRONMENTAL IMPACT OF REACTOR ACCIDENTS

The Atomic Energy Commission is considering an amendment to its regulations to provide guidelines for evaluating possible environmental impact of a series of postulated accidents in nuclear power plants. This would be done in environmental reports prepared by applicants for construction permits and operating licenses.

The proposed guide would be added as an annex to Appendix D of Part 50, "Implementation of the National Environmental Policy Act (NEPA)." It would provide standardized assumptions to be used in preparing the "accidents section" of environmental reports required by the AEC in its implementation of NEPA.

The proposed amendment, which the Commission expects will be useful as interim guidance until further action is taken, places a spectrum of possible accidents, from the most minor to severe, into nine classifications, some with subclasses.

Accidents in classes two to eight are representative of the types of accidents that should be analyzed and the assumptions which must be used in the analysis. Because of the very minor consequences involved, it would not be necessary for applicants to analyze class one accidents. Class nine and some class eight accidents would not have to be evaluated because the probability of such an accident occurring is so small that the environmental risk is quite low.

Other accident assumptions which may be more suitable for individual cases could be substituted or added if they can be justified. In licensing nuclear plants, the AEC has always considered the safety features provided both to prevent accidents and to limit their consequences. The AEC pointed out that the principal line of defense to prevent accidents is through correct design, manufacture, and operation of the reactor and through a quality assurance program which provides and maintains the necessary high integrity of the reactor system. Deviations that may occur in plant operation are handled by protective systems to place and hold the plant in a safe condition. However, the conservative assumption is made that serious accidents might occur, in spite of the fact that they are extremely unlikely and engineered safety features are installed to mitigate their consequences. In considering the environmental risks associated with the postulated accidents, the probabilities of their occurrence and their consequences both must be taken into account. The assumptions provided by the

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proposed amendment are intended to be as realistic as the present state of knowledge will permit.

The public is invited to make written comments or suggestions on the proposed amendment and on the probabilities of occurrence for the various types of postulated accidents.

Interested persons may submit comments or suggestions to the Secretary of the Commission, Atomic Energy Commission, Washington, D.C. 20545, Attention: Chief, Public Proceedings Branch. Comments and suggestions must be received within 30 days of publication of the proposed amendment in the Federal Register. [From the Federal Register, Vol. 36, No. 231-Wed., Dec. 1, 1971] PROPOSED RULE MAKING

[10 CFR Part 50]

LICENSING OF PRODUCTION AND UTILIZATION FACILITIES

Consideration of Accidents in Implementation of the
National Environmental Policy Act of 1969

The Atomic Energy Commission has under consideration amendments to Appendix D of its regulation 10 CFR Part 50, Licensing of Production and Utilization Facilities, an "Interim Statement of General Policy and Procedure: Implementation of the National Environmental Policy Act of 1969 (Public Law 91-190)." The proposed amendments would, by the addition of an annex to Appendix D, specify certain standardized accident assumptions to be used in Environmental Reports submitted by applicants for construction permits or operating licenses for nuclear power reactors pursuant to Appendix D.' The accident assumptions and other provisions of the proposed amendments would also be applicable to AEC draft and final Detailed Statements.

The Commission invites written comments or suggestions from all interested persons on the proposed amendments set forth below as well as on the treatment of the probabilities of the accidents.

The Commission expects that the provisions of the proposed amendments will be useful as interim guidance until such time as the Commission takes further action on them.

Pursuant to the Atomic Energy Act of 1954, as amended, and section 553 of title 5 of the United States Code, notice is hereby given that adoption of the following amendments to 10 CFR Part 50 is contemplated. All interested persons who desire to submit written comments or suggestions for consideration in connection with the proposed amendments should send them to the Secretary of the Commission, U.S. Atomic Energy Commission, Washington, D.C. 20545, Attention: Chief, Public Proceedings Branch, within 30 days after publication of this notice in the FEDERAL REGISTER. Copies of com

1 In conjunction with the revision of Appendix D on Sept. 9, 1971 (36 F.R. 18071), there was transmitted to applicants for licenses to construct or operate nuclear power plants, and made available to the public, a document dated Sept. 1, 1971, entitled “Scope of Applicant's Environmental Reports with Respect to Transportation, Transmission Lines and Accidents.' This document was a supplement to the guldance provided to license applicants in the "Draft AEC Guide to the Preparation of Environmental Reports for Nuclear Power Plants,' dated Feb. 19, 1971, also made available to the public.

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ments received may be examined in the Commission's Public Document Room, 1717 H Street NW., Washington, D.C.

1. A sentence is added at the end of paragraph 4, of section A of Appendix D to read as follows:

APPENDIX D-INTERIM STATEMENT OF GENERAL POLICY AND PROCEDURE: IMPLEMENTATION OF THE NATIONAL ENVIRONMENTAL POLICY ACT OF 1969 (PUBLIC LAW 91-190)

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4. *** The Environmental Report required by paragraph 1 shall also include a discussion of accidents, based on the assumptions set forth in the annex to this appendix.

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2. An annex is added to Appendix D to read as follows:

ANNEX

DISCUSSION OF ACCIDENTS IN APPLICANTS' ENVIRONMENTAL REPORTS:

ASSUMPTIONS

This Annex requires certain assumptions to be made in discussion of accidents in Environmental Reports submitted pursuant to Appendix D by applicants for construction permits or operating licenses for nuclear power reactors.2

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Postulated accidents are discussed in another context in applicants' safety analysis reports. The principal line of defense is accident prevention through correct design, manufacture, and operation, and a quality assurance program is used to provide and maintain the necessary high integrity of the reactor system. Deviations that may occur are handled by protective systems to place and hold the plant in a safe condition. Notwithstanding all this, the conservative postulate is made that serious accidents might occur, in spite of the fact that they are extremely unlikely, and engineered safety features are installed to mitigate the consequences of these unlikely postulated

events.

In the consideration of the environmental risks associated with the postulated accidents, the probabilities of their occurrence and their consequences must both be taken into account. Since it is not practicable to consider all possible accidents, the spectrum of accidents, ranging in severity from trivial to very serious, is divided into classes. Each class can be characterized by an occurrence rate and a set of consequences.

Standardized examples of classes of accidents to be considered by applicants in preparing the section of Environmental Reports dealing with accidents are set out in tabular form below. The spectrum

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of accidents, from the most trivial to the most severe, is divided into nine classes, some of which have subclasses. The accidents stated in each of the eight classes in tabular form below are representative of the types of accidents that must be analyzed by the applicant in Environmental Reports; however, other accident assumptions may be more suitable for individual cases. Where assumptions are not specified, or where those specified are deemed unsuitable, assumptions as realistic as the state of knowledge permits shall be used, taking into account the specific design and operational characteristics of the plant under consideration.

For each class, except Classes 1 and 9, the environmental consequences shall be evaluated as indicated. Those classes of accidents, other than Classes 1 and 9, found to have significant adverse environmental effects shall be evaluated as to probability, or frequency of occurrence, to permit estimates to be made of environmental risk or cost arising from accidents of the given class.

Class 1 events need not be considered because of their trivial consequences.

Class 8 events are those considered in safety analysis reports and AEC staff safety evaluations. They are used, together with highly conservative assumptions, as the design-basis events to establish the performance requirements of engineered safety features. The highly conservative assumptions and calculations used in AEC safety evaluations are not suitable for environmental risk evaluation, because their use would result in a substantial overestimate of the environmental risk. For this reason, Class 8 events shall be evaluated realistically. Consequences predicted in this way will be far less severe than those given for the same events in safety analysis reports where more conservative evaluations are used.

The occurrences in Class 9 involve sqeuences of postluated successive failures more severe than those postulated for the design basis for protective systems and engineered safety features. Their consequences could be severe. However, the probability of their occurrence is so small that their environmental risk is extremely low. Defense in depth (multiple physical barriers), quality assurance for design manufacture, and operation, continued surveillance and testing, and conservative design are all applied to provide and maintain the required high degree of assurance that potential accidents in this class are, and will remain, sufficiently remote in probability that the environmental risk is extremely low. For these reasons, it is not necessary to discuss such events in applicants' Environmental Reports.

Furthermore, it is not necessary to take into account those Class 8 accidents for which the applicant can demonstrate that the probability has been reduced and thereby the calculated risk to the environment made equivalent to that which might be hypothesized for a Class 9

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event.

Applicants may substitute other accident class breakdowns and alternative values of radioactive material releases and analytical assumptions, if such substitution is justified in the Environmental Report.

ACCIDENT ASSUMPTIONS

TABLE OF CONTENTS

Accident

1.0 Trivial incidents.

2.0 Small releases outside containment.
3.0 Radwaste system failures.

3.1 Equipment leakage or malfunction.

3.2 Release of waste gas storage tank contents. 3.3 Release of liquid waste storage tank contents. 4.0 Fission products to primary system (BWR).

4.1 Fuel cladding defects.

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4.2 Off-design transients that induce fuel failures above those expected.

5.0 Fission products to primary and secondary systems (PWR). 5.1 Fuel cladding defects and steam generator leaks.

5.2 Off-design transients that induce fuel failure above those expected and steam generator leak.

5.3 Steam generator tube rupture.

6.0 Refueling accidents.

6.1 Fuel bundle drop.

6.2 Heavy object drop onto fuel in core.

7.0 Spent fuel handling accident.

7.1 Fuel assembly drop in fuel storage pool.

7.2 Heavy object drop onto fuel rack.

7.3 Fuel cask drop.

8.0 Accident initiation events considered in design basis evaluation in the safety analysis report.

8.1

Loss-of-coolant accidents.

8.1(a) Break in instrument line from primary system that penetrates the containment.

8.2(a) Rod ejection accident (PWR).

8.2(b) Rod drop accident (BWR).

8.3(a) Steamline breaks (PWRS outside containment).

8.3(b) Steamline breaks (BWR).

ACCIDENT ASSUMPTIONS

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ACCIDENT-1.0 TRIVIAL INCIDENTS

These incidents shall be included and evaluated under routine releases in accordance with proposed Appendix I.1

ACCIDENT 2.0 SMALL RELEASE OUTSIDE CONTAINMENT

These releases shall include such things as releases through steamline relief valves and small spills and leaks of radioactive materials outside containment. These releases shall be included and evaluated under routine releases in accordance with proposed Appendix I.

136 F.R. 11113, June 8, 1971.

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