PERFORMANCE AND RELIABILITY COVERED

Reliability refers to whether the system would function; performance refers to how well it would function. Performance was the subject of the hearing; reliability is covered by the design criteria included in part 50 of title 10 of the Code of Federal Regulations. Thus, no questions relative to safety are ignored. They have either been considered here, if relevant; or they fit naturally in the context of other inquiries.

We, therefore, indicate in our opinion that matters beyond the scope of this or other rules may be considered on a case-by-case basis in individual licensing proceedings.

REGULATORY RESPONSIBLE FOR IMPLEMENTATION

The Regulatory staff, which took no part in the preparation of the Commission decision, will now have responsibility for implementation of the new rule.

Mr. Edson Case, Deputy Director of Licensing, is here this morning to elaborate on the technical details of the rule and accompanying decision, and to provide information on the way in which the Regulatory staff proposes to implement the rule.

Before we turn to Mr. Case, I would like to provide an introductory overview of the new rule.

INTRODUCTORY OVERVIEW

The Interim Policy Statement included four criteria to be used to review calculated performance of emergency core cooling systems of water reactors. The purpose of this hearing was to gather scientific evidence on the adequacy of these criteria, and to modify or refine them where appropriate. Because of our confidence in the Interim Acceptance Criteria, they have remained in effect throughout the hearing and will continue in effect until the new rule is implemented. This new rule will provide a more objective basis for safety analysis. This is possible because the proceedings have improved our focus on the technical basis for a rule. As Mr. Case will tell you, we have made a numerical change in one criterion, and we have added a fifth criterion.

IMPROVEMENTS POSSIBLE IN MODELS

The evidence presented during the hearing has shown that a number of improvements could be made in the models used to evaluate the ECCS. We have, therefore, added a considerable amount of detail to the list of features required of the calculational models that are used to determine whether designs of emergency core cooling systems meet the criteria.

We believe that the new rule and the new required features of the evaluation models will continue to protect the public health and safety, and, in fact, enhance it. To that end, a number of conservative features have been incorporated where data are not yet firm enough. These deal principally with the temperature of the fuel and

cladding and the rate of core cooling. These conservatisms are discussed on pages 27 and 28 of the opinion.

The first conservative feature is the almost certain overestimation of the initial temperature of the fuel for the time the improbable accident is supposed to occur. This means that damage to the cladding would be less than current calculations indicate.

CORE COOLING RATE DURING BLOWDOWN

Second, the assumed rate of cooling of the reactor core during the blowdown phase is probably underestimated. Considerable evidence exists that the cooling rate would be much better than we assume, and such core damage as might occur should be much less than will be calculated using the rule.

Third, the rate of heating of the core is overestimated, again leading to less damage than is calculated.

Fourth, and finally, the limitation of the peak calculated temperature of the cladding and the stipulation that this limit be applied to the hottest region of the hottest fuel rod provide a substantial margin of safety. They insure that the core would suffer very little damage.

Most of these conservative assumptions also have been attached to the use of the interim acceptance criteria.

We have instructed our Director of Reactor Safety Research to institute the research necessary to sharpen our understanding of some of the information on which our rule rests. We expect that in some areas research will provide data that will allow relaxation of some of the more conservative features of the evaluation models. Again, we believe that these conservatisms provide more than is necessary to protect the public health and safety.

The Commission's opinion states several principles which it applied in arriving at the implementation schedule. The schedule for implementing the rule should insure that the incremental increase in safety is effectuated at the earliest practicable time. At the same time, it must allow for thorough development of the required complex evaluation models. This implementation should be accomplished without unwarranted disruption in the Nation's production of electric energy.

IMPLEMENTATION SCHEDULE

The regulatory staff proposed an implementation schedule in its concluding statement. That schedule called for implementation of the rule within 4 months after its publication. We reviewed the need for development of analytical methods to take into account the additional phenomena that must be considered in the evaluation models. We also noted that many new calculations will have to be done for each reactor plant.

In our judgment, 4 months' time is not adequate to accomplish these tasks, particularly in light of the fact that the rule adopted by the Commission differs in several respects from that proposed by the staff. Therefore, we have called for calculations to be completed

within 6 months after the effective date of the rule. That date will be February 4, 1974, 30 days after publication in the Federal Register. There may be exceptions to the implementation schedule.

First, we have defined circumstances under which extension of the 6-month period can be requested and granted by the Director of Regulation.

And, second, we have indicated that exemptions from the operating requirements associated with the rule may be granted by the Commission where good cause has been shown. Any requests for such exemptions must show, with appropriate affidavits and technical submissions, that it would be in the public interest to allow the licensee an additional period of time within which to alter the operation of the facility. This request must include a discussion of the alternatives available for complying with the rule.

In our discussion of the schedule for implementation of the new rule, we observed:

A requirement of immediate compliance would be tantamount to an order shutting down or substantially derating all reactors until requisite calculations were complete. We would not hesitate to take that action if circumstances so warranted. But the record shows, and we find, that the Interim Acceptance Criteria will provide reasonable assurance of protection for the public health and safety during the relatively brief transitional period which will culminate in compliance with the new rule.

COMMISSIONER ANDERS OBSERVATIONS

Commissioner Anders, in his concurring opinion, remarked on the lack of an adequate basis in the record for the balancing of benefits and penalties of compliance with the operational requirements of the rule. His concurrence is based on the potential which the implementation procedure offers for the development of information which is now lacking. He points out that.

Without attempting to prejudge the outcome of any particular exemption request, the advantage of a further reduction in an already "negligible” risk must be weighed critically against potential adverse impacts of rapid implementation.

Commissioner Anders also recognizes in his opinion a need to protect proprietary information so as to preserve for industry the benefits of its own research. He states that this need must be weighed against the public need for disclosure where data provide the underpinning of a particular safety requirement applicable to an entire industry.

The Commission opinion discusses the ultimate treatment of the proprietary data that were relied upon or incorporated in the decision. We determined to make public certain information of this kind, because it forms part of the basis for the rule.

PUBLIC COMMENT SOLICITED

The Commission is considering the position to be taken in the future regarding proprietary information submitted in support of licensing actions. Currently, we are soliciting public comment with a view to fixing future Commission policy.

Finally, I might note that it is not possible to state with precision at this time what effect, if any, the new rule will have on the power output of currently operating reactors. Only after the required calculations have been completed will we have accurate data.

The difficulties of predicting the effects on reactor power level are compounded by the fact that options, such as altering the control rod pattern within the core, are available and may well limit the amount of derating, if any, required to comply with the rule.

I should now like to turn to Mr. Case for a review of the technical aspects of the rule.

Chairman PRICE. Mr. Case?

STATEMENT OF EDSON G. CASE, DEPUTY DIRECTOR, DIRECTORATE OF LICENSING, ATOMIC ENERGY COMMISSION

Mr. CASE. Thank you, Dr. Ray.

Mr. Chairman and members of the committee, I am pleased to be here with you today to discuss the more important technical considerations involved in the acceptance criteria for emergency core cooling systems for light water-cooled nuclear power reactors recently issued by the Commission, and the ongoing AEC program for developing new calculational techniques for complying with these criteria.

Before discussing these matters in more detail, it is important that the purpose and importance to safety of emergency core cooling systems for these reactors be placed in their proper context.

EMERGENCY CORE COOLING SYSTEM FUNCTIONS

In the Commission's interim policy statement of June 1971, which established the interim acceptance criteria for emergency core cooling systems ECCS-the Commission noted that the protection provided by these systems against a highly unlikely loss-of-coolant accident has long been an essential part of the defense-in-depth concept used by the nuclear power industry and the AEC to assure the safety of nuclear powerplants.

In this concept, the primary assurance of safety is accident prevention, by correctly designing, constructing, and operating the reactor. To achieve this primary assurance of safety, extensive and systematic quality assurance practices are required and applied. Nevertheless, deviations from expected behavior are postulated to occur and protective systems are installed to take correction action as required in such events.

Notwithstanding all this, the occurrence of serious accidents is also postulated, in spite of the fact that they are highly unlikely, and engineered safety features are installed to mitigate their consequences.

Emergency core cooling systems are one of the engineered safety features required by AEC regulations for all water-cooled nuclear powerplants. It should be emphasized that these systems are not needed in normal plant operation but would be called upon to func

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tion if there were a sudden and unexpected rupture of the reactor cooling system.

Such ruptures, even small ones, are very unlikely during the service life of an individual nuclear plant because of the extensive measures the AEC insists upon to assure the quality and integrity of these systems. Those sudden major ruptures that would place the highest demands on the ECCS are not expected to occur at all during the lifetime of a plant.

Nevertheless, in keeping with the defense-in-depth concept of reactor safety, the AEC requires extremely high standards in the design, fabrication, and testing not only of the reactor cooling systems, but also the emergency core cooling systems for nuclear plants, as well as in the reliability and performance of these systems.

The purpose of the new acceptance criteria for emergency core cooling systems for light water-cooled nuclear powerplants is to assure that ECCS performance requirements are satisfied.

MAJOR FEATURES OF ECCS ACCEPTANCE CRITERIA

The new acceptance criteria include four major features: (1) overall ECCS requirements applicable to light water reactors; (2) requirements for analyzing ECCS performance; (3) requirements for acceptable evaluation models; and (4) provisions for application to various classes of reactors by specified dates.

OVERALL ECCS REQUIREMENTS

1. Overall ECCS requirements: with regard to overall ECCS design, performance, and operating requirements, the criteria require in a new section 50.46 of 10 CFR part 50 that each boiling and pressurized light water nuclear power reactor be provided with an ECCS.

This statement parallels existing requirements for the provision and design of ECCS for reactors of this type specified by criterion 35 of the general design criteria for nuclear power plants-appendix A to part 50.

Paragraphs (b)(1) through (b) (5) of this same new section specify the performance requirements of these systems in the event of a postulated LOCA, including maximum calculated fuel cladding temperature, maximum calculated cladding oxidation, maximum calculated hydrogen generation, maintenance of a coolable geometry and long-term cooling.

These ECCS performance criteria implement the more general requirements now given in general design criterion 35, and have been somewhat modified from the previous criteria specified in the interim acceptance criteria of June 1971. The bases for these changes will be covered later in this testimony.

Operating requirements for existing and new reactors are also contained in new section 50.46 in that it provides that compliance with the new performance criteria may require restrictions to be imposed on reactor operations.

Finally, the new acceptance criteria add additional overall requirements to section 50.34 concerning the technical content of con