NUREG-1070, 07-18-84 ACRS Report on NUREG-1070, NRC Policy on Future Reactor Designs - Decisions on Severe Accident Issues

07-18-84 ACRS Report on NUREG-1070, NRC Policy on Future Reactor Designs - Decisions on Severe Accident Issues

ML25167A193
Person / Time
Issue date:	07/18/1984
From:	Ebersole J Advisory Committee on Reactor Safeguards
To:	Palladino N NRC/Chairman
References
Download: ML25167A193 (1)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION ADVISORY COMMITTEE ON REACTOR SAFEGUARDS WASHINGTON, D. C. 20555 July 18, 1984 The Honorable Nunzio J. Palladino Chairman U.S. Nuclear Regulatory Commission Washington, DC 20555

SUBJECT:

ACRS REPORT ON NUREG-1070, "NRC POLICY ON FUTURE REACTOR DESIGNS:

DECISIONS ON SEVERE ACCIDENT ISSUES IN NUCLEAR POWER PLANT REGULATION" During its 291st meeting, July 12-14, 1984, the Advisory Committee on Reactor Safeguards continued its discussion with the NRC Staff of the development of a Severe Accident Policy for nuclear power plants.

The ciiscussion focused on the description of the policy contained in the draft NUREG-1070 dated April 18, 1984.

The report was discussed in Subcommittee meetings held on April 27 and May 31, 1984 and in the Com-mittee's June 14-16, 1984 meeting.

The draft policy statement enunciates a policy that may be described for existing plants as follows:

The risk from accidents more serious than the analyzed design basis accidents for nuclear power plants now in operation or nearing completion is acceptable subject to the resolution of Unresolved Safety Issues, to a decision on whether and how Safety Goals will be applied, and to the results of a source term rulemaking.

Although some changes in equipment or procedures may be required after these programs are concluded, it is anticipated that these will not be major changes.

This conclusion is reached in light of:

a) the operating experience that hes been accumulated; b) the changes in required equipment, operating procedures and personnel requirements that have occurred as a result of the accident at TMI-2; c) the results and insights gained from a significant number of PRAs for existing plants; d) the results of studies such as the Severe Accident Precursor Program, the Accident Sequence Evaluation Program, and the Industry Degraded Core Rulemaking Program (IDCOR).

1978

Honorable Nunzio July 18, 1984 In our various meetings with the NRC Staff we have discussed the de-sirability of formulating some systematic approach to an examination of each nuclear power plant now operating or under construction for possi-ble significant risk contributors (sometimes called "outliers") that might be plant specific and might be missed absent a systematic search.

Because previous experience indicates that systematic analysis using PRA or other methods may uncover such outliers, we believe that the policy statement should state explicitly that an appropriate approach will be aeve loped and that an analysis wi 11 be made of any pl ant that has not yet undergone an appropriate examination.

The examination should include specific attention to containment performance.

We note that rtsolution of the Unreso°lved Safety Issues will produce decisions for dealing with a number of issue5 that could have an influ-ence on the risk associated with hypothesized severe accidents.

Among these are:

a) an appropriate approach for assuring the reliability of decay heat removal systems, and b) the appropriate reliability of electrical supplies for the power plant, both AC and UC systems.

There is under way a large-scale research program that concentrates on producing better information and increased understandir1g of the release of radioactive fission products from the reactor fuel during a severe accident, their subsequent transport outside the reactor primary pres-sure boundary, their behavior in the containment, and their subsequent release from the containment.

We expect th~ results of this research to be incorporated in a rulemaking that is likely to influence the cal-culated risk from accidents involving severe core damage.

If these new calculations have a significant influence on our present perceptions of severe accident risk, we expect them to be followed by whatever changes iri regulations, plant equipment, or operational and emergency procedures are indicated.

There are a number of significant efforts on the part of the nuclear industry. Activities such as the IDCOR Program, and the organization of INPO and NSAC are industry initiatives which should lead to a decrease in the risk of severe accidents.

We support the consideration of cost-effectiveness as one of the import-ant determinants iri formulating an approach to risk management in existing plants.

There will, however, always be substantial uncer-tainties in the calculation of risks, costs, and benefits, so that both prudence and sophistication will be required.

We believe that, taking into account the results of programs now in progress, ana assuming a systematic examination of each plant, the proposed policy provides an acceptable basis for dealing with the severe accident issue tor plants now in operation or under construction.

1979

Honorable Nunzio July 18, 1984 For new plants we interpret the policy statement to say that:

New plants must meet existing regulations.

They will be required to deal v1ith the resolution of all the Unresolved Safety Issues.

They

\\'t'i 11 be subject to any new regulations that result from the source tern rulemaking.

The severe accident risk from new plants is ex-pected to be dealt with in the foreseeable future through rulemaking for standard plants.

One of the requirements of the rulemaking process will be a full scope PRA for the proposed plant.

Severe accident risk will be dealt with primarily through consideration of the results and insights gained from the PRA.

We have several recommendations concerning the proposed po 1 icy for dealing with new plants. These recommendations follow:

There shoulrl be a statement that the policy is expected to lead to rew plants producing less risk than the older ones.

The policy statement indicates that heavy reliance is to be placed on the results of the required PRA in deciding whether or not the severe accident risk associated with a proposed design is acceptable.

Guidance on the required scope of the PRA and the way it is to be used are probably not appropriate to a policy statement.

However, the policy statement should say that such guidance will be developed.

We approve of the general approach of using a combination of deter-ministic and probabilistic considerations to provide the information on which a decision is to be based.

The policy statement should speak to some balance between prevention and mitigation of risk.

As a minimum, some clarification of contain-ment performance expectations should be given.

If the NRC Staff has concluded that performance criteria cannot be formulated at this time, the statement should say that such criteria or some appropriate description of expected performance will be formulated.

The effectiveness of human performance, including that of management, has a substantial influence on risk.

For this reason, we recommend that attention be given to these matters for both new and existing plants to assure that inadequate human performance at individual plants will not result in unacceptable risk.

In particular, methods of analysis and associated data bases need to be developed which can rroperly account for both positive and negative human performance contributions.

. Although we recognize the uncertainty in dea 1 i ng with sabotage, we believe the policy statement should indicate that the issue of both insider and outside threats will be carefully examined, and, to the extent feasible, taken into account in the design and in the opera-tional procedures that are developed for new plants.

1980

Honorable Nunzio July 18, 1984 lt.e conclude that in its present form that part of the policy statement that deals with new plants needs strengthening iri the areas that we have indicated.

Additional comments by ACRS Members Robert C. Axtmann, Harold W. Lewis and uavid Okrent are presented below.

~ncerely,

~f:- ~~

Jesse C. Ebersole Chairman Additional Comments by ACRS Member kobert C. Axtmann Absent an urgent domestic need or a public appetite for new nuclear power plants of !!!l design, the policy statemt::11t 1s emphasis on regu-latory attention to future plants could be a misallocation of resources.

Wh.ile there may be an international market for advanced reactors, it is not clear why the U.S. public should unaerwrite creatior1 of a regulatory framework that may not have domestic application for fifteen years or more.

Should that schedule be fureshortened, I am confident that we can pick up where I propose we leave off in 1984.

Additional Comments by ACRS Member Harold W. Lewis As I interpret the proposed policy statement it is that the Commission will not seek to further decrease the risk from existing reactors, unless programs now in being lead to the conclusion that it is necessary to do so.

There is also a statement about new reactors, in a similar vein.

I am not persuaded of the need to issue such a statement at this time, although I share in a widespread recognition of the need to do something to relieve the apparent open-eudedness of the regulatory process.

I simply doubt that it is appropriate to formulate a policy on severe accidents without some sort of clarification of the overall objectives of NRC regulation of the nuclear enterprise.

That the function of the Conmission is to protect the health and safety of the public need not be repeated, but that in itself is hardly a guide to an appropriate level or direction of regulation.

In the absence of guidance on this point, regulation has often become the objective iri itself, imperfectly linked to its purpose.

The Commission has struck a glancing blow at this problem by promulgat-ing a safety goal, for evaluatior,, test, and corrment, but there remain open questions about the underlying rationale for the specific criteria chosen.

1981

Honorable Nunzio J. Palladino

- 5..,

July 18, 1984 It would be far healthier to bring these scattershot efforts together into a coherent statement of Con1nission policy on an appropriate level of safety, and on NRC's perception of its role in achieving and/or maintaining that level.

We said this in our letter of September 14, 1982.

I believe that, however painful, an unhurried effort to generate an agency philosophy would make it far easier to deal with severe accidents and related questions in a coherent way.

In the corporate world this is known as a long-range plan.

A plan generated one element at a time -- safety goals, severe accidents, backfitting, etc. -- is doomed to incoherence.

The Conmittee letter, with which I have no serious disagreement, con-tains many items directed toward specifying a program plar1, but avoids the questions raised here.

I regret that we have thereby acquiesced in the current incoherent approach to safety assurance, and have thereby joined NRC in missing an opportunity for an integrated approach to resolve this matter.

Addi tior,a l Conments by ACRS Member David Okrent I generally agree with the ACRS letter.

These comments are for purpose of emphasis or are supplemental.

1. I recommend that the Conmission significantly modify the Staff's severe accident policy statement as given on the top of page 4 and again on page 15 of the April 18, 1984 ciraft of NUREG-1O7O.

In this statement, it is said:

11On the basis of currently available information, the Conmission concluaes that existing plants pose no undue risk to public safety and property and sees no present basis for prompt action on generic rulemaking or other regulatory changes for these plants because of severe accident risk. 11 I would modify this statement both for technical reasons and for reasons of public policy.

One might use something whose import was more like the following:

"The currently available information does not leaa the Conmission to conclude that existing plants pose any ur,due risk to public safety and property due to severe accidents.

However, the Corrmis-sion plans to pursue a five-year program during which systematic examination of all existing plants will be undertaken by probabi-listic risk assessment and/or other means to determine that there are no unacceptable large risk contributors and to help determine ori a plant-by-pl ant ( or generic) basis those safety improvements which it would be prudent to incorporate."

2. I believe that approval of the April 18, 1~84 draft NUREG-1O7O could easily appear to pl ace the Conmi ss ion at odds with a large segment, if not a majority, of the general public as we 11 as many members of Congress, and with many respected individuals outside of government, 1982

Honorable Nunzio July 18, 1984 all of whom want nuclear power plants to be safer.

The position of these groups seems to be supported by the several forei9n countries (Sweden, France, England,

Germany, Switzerland, etc.) who have adopted or propose to use safety requirements considerably more stringent than those of tht USNRC.

On the other hand, the proposed policy statement could be interpreted by others as an expression of satisfaction by the NRC with the status quo for existing reactors.

3. If the NRC had firm, indisputable data on the risk from each existing nuclear power plant, and it was convinced that the least safe was acceptable as is, it might be plausible for the NRC to take a posi-tion contrary to so much other opinion.

However, such data do not exist.

Only a limited number of plants have had good, "full-scope" PRAs, and their results are subject to large uncertai11ties.

The existing PkAs cannot be accepted as representative of other indi-vidual plants because of the demonstrated importance of the specific features of a plant to estimates of core melt frequency and risk.

Furthermore, several good PRAs have turned up one or more high probability core melt scenarios, so-called outliers, that required early remedy for the particular plant involved.

A much less complete set of information is available concerning the performance during severe accidents of the many variants of contain-ment design used in the U.S.

For example, the ACRS has not had the benefit of a sophisticated report evaluating containment performance for some of the concepts currently in use.

4. Thus, it seems to be premature to draw so strong a positive conclu-sion concerning the safety of existing plants as that stated on pages 4 and 15 of the draft NUREG-1O7O.

Furthermore, the proposed policy does not include a systematic examination of each plant, including its management and operation, for possible significant improvements in accident prevention ana n1itigation.

I fear the overall safety posture is further aggravated by the way benefit/cost analysis has usually been used recently, namely a ratio of median estimates of benefit and cost, lacking a prudent regard for the large uncer-tainties.

The stated intention to omit any credit for reduction in onsite losses wiil only worsen the situation, I fear, and may make few meaningful improvements in safety possible under the backfit rule.

Since all costs are eventually born by large sectors of the public, including retirees whose annuities are linkeo to utility stocks among others, I find it more meaningful and equitable to balance the cost of an improvement against all benefits, offsite and onsite.

To avoid excessive costs by being "prudent" in the inclusion of uncertainties in all benefit/cost analysis, one could include an overall limit on expenditures approved on the basis of prudence, say a few percent of the replacement cost of the plant.

1983

Honorable Nunzio July 18, 1984

5. Concerning future plants, I find the proposed criteria, in their summarized form on pages 4 and 5 of draft NUREG-1070, inadequate for the purpose.

They place no emphasis on the need for effective containment.

They do not set safer reactors as a goal for future reactors.

They appear to place a very great rtliance on the results from a PRA, despite the large uncertainties inherent in its results.

1984