ML20212H741

Review & Evaluation of NRC Safety Research Program for FY88, Rept to Congress

ML20212H741
Person / Time
Issue date:	02/28/1987
From:	Advisory Committee on Reactor Safeguards
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ML20212H746	List: ML20212H741 ML20212R292
References
ACRS-R-1239, NUDOCS 8703060209
Download: ML20212H741 (7)

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A,..;g, REVIEW AND EVALUATION OF THE NUCLEAR REGULATORY'COMISSION SAFETY RESEARCH PROGRAM FOR FISCAL YEAR 1988 A REPORT TO THE CONGRESS OF THE UNITED STATES OF AMERICA BY THE ADVISORY COMMITTEE ON REACTOR SAFEGUARDS

.U.S. NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C.,20555 FEBRUARY 1987 l 70 Bob 209 f ..'

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1 INTRODUCTION-Our coments. be. low relate to the proposed program-support funding of

$103.6 mi.llion - for the FY 1988 NRC Safety Research Program. These coments: are. limited chiefly to research 'that is not being proposed but should be, or in some cases, to research that is proposed but may not be needed.

1. REACTOR SYSTEM SAFETY 1.1 Themal-Hydraulic Transients 1.1.1 General C;oments Research planned in the thermal-hydraulic area is divided into two general parts. The first is a comprehensive program to improve the understanding of thermal-hydraulic behavior in Babcock and Wilcox (8&W) reactor. systems;.in its fullest form, this calls for substantial indus-try support. The second is a more general program of code development and experimental work that does not include direct industry. participa-tion. 'We believe that the emphasis on B&W systems is appropriate and that the. industry should provide major support-for this program, as has been proposed by the Office of Nuclear Regulatory Research (RES) Staff.

It is also important that the NRC maintain' a viable program of thermal-hydraulic research into the foreseeable . future, including integral testing, separate-effects testing, and code development.

Our corrnents on the proposed research in the thermal-hydraulic area are given below, i

1.1.2 Integral Facilities RES has developed a comprehensive research plan to address the technical issues and regulatory needs associated 'with the thermal-hydraulic perfomance of B&W plants. Central to this plan is the proposal to construct new integral test facilities. Optimum and timely results from these facilities <will depend upon financial support from the industry.

We support this plan. I 1.1.3 Separate. Effects Our February 19, 1986 report to the Congress. included the recomendation that the NRC study the complicating effects that water hamer may have on thermal-hydraulic transients. The NRC. and the industry have now initiated a cooperative effort in this regard. We support this effort and expect to monitor its progress.

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Funding levels appear adequate at this time.

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The NRC has . initiated a program to develop an information base for the '

complex thermal-hydraulic phenomena ' involved with the " bleed and feed" process used 'either to remove core : decay heat or to allow controlled depressurization. of the primary coolant of a pressurized water reactor (PWR) plant. . We believe that subs'equent- to the development of the infonnation; base: RES should allocate funding for any additional research found necessary in this area.

1.1.4 Code Development The NRC has developed a revised Emergency Core Cooling System (ECCS)

Rule (10 CFR Part 50, Appendix K - ECCS Evaluation Models) that allows the use of realistic (best estimate) evaluation models to calculate the effects. of loss-of-coolant accidents . (LOCAs). However, the acceptabil-ity cf realistic models rests on the development of satisfactory method-ology to determine the overall uncertainty' associated with these models.  ;

A related effort which addresses code applicability and scaling studies also is necessary; such work is either ongoing or planned by RES. We I strongly support these efforts. In particular, funding should be assured over the next few years sufficient to allow NRC to obtain the necessary test and analytical data, primarily through.the International Code Assessment Program and cooperative international efforts such as the 2D/3D Program.

1.2 Accident Evaluation The Accident Evaluation Research Program being proposed includes a significant e'xperimental component. We believe that the relationship of this research to the severe accident regulatory issue should be made clearer than it now is. For example, there are three major experimental programs to investigate phenomena that will be encountered (if at all) only after the reactor core has melted and'has penetrated the vessel.

The experiments !are related to containment- heating, to core-concrete interaction, and to containment behavior un~ der extreme overpressure.

l These areas of research all bear directly on issues relating to contain-l ment ca'pability and containment failure. modes. Each of these research i areas is ' said to be designed to reduce ; some of the uncertainties identified in NUREG-0956, " Reassessment of the Technical Bases for Estimating. Source Terms." The magnitude of these uncertainties is being estimated in the course of the preparationiof NUREG-1150, " Reactor Risk Reference Document." However, in order to plan properly additional research to reduce uncertainties, it would appear that the Office of Nuclear- Reactor Regulation (NRR), or some group, should first consider what uncertainties can be tolerated in connection with its regulatory responsibilities.- We have not seen evidence of this consideration. We, and we suppose RES as well, must, under the circumstances, try to judge the relevance ~ of the proposed research with' insufficient infonnation.

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Vith this caveat we make the coments* noted below. These comments do '

not represent a complete coverage of the Accident Evaluation Research Program. We use them as an example of our conclusion that more con-sideration needs to be given to what has been learned from the research of thenpast five' years or so, and what uncertainty can be tolerated by the regulators; or, put another way. what are the questions that regu-lators have encountered or are likely to encounter in dealing with severe .accidentss that cannot be answered ;with existing infonnation.  ;

With diminishing resources, it is increasingly important that the research be speciJfically designed to address' safety concerns. ,

' The research on containments under extreme overpressure seems well designed.and should produce results that are relevant, and that 3 will contribute to the calibration of? codes being developed for a i descr.iption of containment behavior.

• The ! work; on core-concrete interaction is probably needed, but a moreDdetailed examination of the ways in which this may affect

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containment failure, as well as the uncertainties attributable to in. complete ~ understanding of- the complex phenomena that characterize this interaction, would make it more likely that the research to be i done would answer questions that will be encountered by NRR.

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• Some risk analyses conclude that high-pressure-core-melt sequences may produce enough direct heating of the containment atmosphere to i cause early. containment failure by overpressure. The proposed j research on direct containment heating may be of considerable interest in understanding the interaction of small particles of molten metal'with containment atmospheres. However, it.is relevant to reactor safety only if sequences which could produce such small particles in PWRs have a sufficiently h.igh probability. It is our opinion that. equal effort should be , devoted to establishing the likelihood and the effect of direct heating events, since absent such work, the program may well be misdirected. We also recomend that the experimental investigation give first consideration to the

' possibility of atomizing the required amount of material as well as the effects of containment geometry, and to the presence of water 4,

in th.e subvessel cavity. ,

1 1.3 Risk and Reliability The funding for the Risk and Reliability Research Program continues to i be directed away from the development of' risk assessment methodology and toward applications. The work in the a.pplications area for the most i part consists .of software development and plant-specific risk assess-ment. However, we see some danger that with the current budget con-straints, work-on applications in support of licensing efforts will be 1

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Undertaken at the. expense of development'al work.

. It is important that

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the developmental work continue.

We recomend that the applications work be coordinated with the eventual user by a systematic process that would : encourage the user to be involved in'the' development of the work product. RES has taken steps to involve the industry and individual licensees:in this work. $le consider it appropriate that some of this applications effort should be done by the industry or ind.tvidual licensees rather than by the NRC.

In our previo~us reports to the Congress an'd to the Commission, we recomend'ed' tha t:

• The completeness of the current familyEof plant-specific probabi-listic risk assessments (PRAs) should: be examined by continued search -for possible weaknesses in: curre.nt probabilistic analyses, e.g., accident paths either not currently. evaluated or dismissed as insignificant, which may, on closer scrutiny, prove to be very important to risk.

• An improved evaluation of the entire family of containment designs

, should be perfomed.

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• Improved methods for factoring uncertainty into decision making should be developed.

The NRC Staff is currently developing methods for implementing the Severe Accident Policy and the Safety Goal Policy. We believe that difficulties are being encountered in part because of the lack of important. answers in areas such as those listed above, as well as in the treatment of external events, environmental effects, aging, management quality, and human errors. We recomend that RES initiate additional work in such areas by 'reprograming funds in the FY 1987 budget and continue to' support.this work in FY 1988. If necessary, this should be accomplished by deferring the applications work or finding other sources of support.for this. work.

6 1.4 Human Factors In its recent report to the NRC, " Revitalizing. Nuclear Safety Research,"

the National Research Council's Comittee on Nuclear Safety Research has joined the ACRS 'in ' criticizing the NRC .for not performing any research in the human- factors area. A specific study:to determine the need for and nature of. human factors research is :being' perforned by the National Research Council.'s Comittee on Human Factors. The final report of this Comitteelis.to .be provided to the NRC during~ July 1987. We anticipate that this ' report will include recomendation for a considerable program of research. effort .in the human factors area.. Plans for beginning such a program should. be factored into the budget by.RES.

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2. ENGINEERING SAFETY 2.1 Electrical Equipment Qualification No funding for electrical equipment qualification research has been proposed for FY 1988. In our February 19, 1986 report to the Congress, i

we reconnended that this research be continued; contrary to this recom-mendation, the research was terminated by the NRC at the end of FY 1986.

The objective;ofIthis research is to assess the probability of survival and perfonnance of aged electrical, equipment when subjected to hostile

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environmental conditions during and following incidents,

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including severe acc.idents, fires, hydrogen bu'rns, ' seismic events, and credible combinations. . The results obtained from this research are important to prevent should .they accident occur. 3 as well as to mitigate the consequences of accidents, We consider the continuation of this work to be vital to . the nuclear safety program. and tagain recommend that it be reinstituted and adequately funded.

Four unique test facilities, with a combined cost of over $2 million, were constructed at Sandia especially for this program. To preserve and maintain the existing test facilities and staff experience sufficient to continue. and complete the electrical equipment qualification work efficientli, it will be necessary to continue funding this work in FY 1987 Since its inception (about 1976), more than $10 million has been spent on this program. Funds needed to: continue and complete the  !

program are approxirately $1.5 mill' ion in FY 1987 and $0.9 million in FY 1988.

2.2 Effects of Earthquakes on Operating Plants In our previous reports, we urged that RES establish an integrated program in this area and coordinate- closely this work with NRR and ongoing industry ' work. We believe that. this has been accomplished effectively in the Seismic Safety Research Program. We believe that the program is well managed and will, in the near future, produce answers that will help to: resolve important issues.

2.3 Primary System Integrity Cast stainless steel components in the primary system lose ductility with time.in service. The implications of this phenomenon for long-tern primary system integrity are significant. ' Appropriate emphasis should be placed on ascertaining the likelihood of. flaws resulting from fab-rication or from. service, and on developing means of assessing con-ditions under which they could pose significant risk.

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3. WASTE MANAGEMENT '

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• 3.1 High-Level Waste

' Although we are satisfied with most aspects of the research program on hich-level wastes, we believe that more attention needs to be directed to related work under way in other countries. This extends beyond the formal. agreements for cooperative research that the NRC Staff has developed with selected foreign groups. .The Staff should also keep abreast ' of activities of the Nuclear Energy Ageng, Organization for Economic Cooperation and Development, relative to the development of guides for demonstrating, both directly and:indiret tly, the capabilities of a repository for assuring the safe retention 'of radioactive wastes.

3.2 Low-level Waste  ;;

We believe that 'more effort should b' e directed to studies that will assist the states in ranking and selecting.the most appropriate disposal systems 'for . low-l'evel wastes, based on the nature and characteristics of the sites' available and associated technological and economic consid-erations.

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