ML20032D441
| ML20032D441 | |
| Person / Time | |
|---|---|
| Issue date: | 08/06/1981 |
| From: | Harold Denton Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| NUDOCS 8111160501 | |
| Download: ML20032D441 (19) | |
Text
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A Paper Presented at the ANS/ ENS Topical Meeting AJdd CStorc tt August 2-6, 1981 at Sun Valley, Idaho hCNstak C
Of kSS/S }ano thff LICENSING C0tCERNS AND FUEL BEHAVIOR W
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Harold R. Denton, Director g~ RL*i khg Office of Nuclear Reactor Regulation
/t U. S. Nuclear Regulatory Commission s
IV0V12198;w T' 3
Washington, D.C.
20555 USA s.a.g 9
ABSTRACT The licensing of nuclear fuel assemblies is governed by a well defined set of requirements which have evolved over a period of years. Accumulated operational experience and fuel safety research provide substantial insight into the behavior of nuclear fuel under normal and transient operation.
Because of the relative maturity of our understanding of fuel behavior and of the similarities of core design features within a product line, licensing reviews for new plants should be facilitated.
However, competitive pressure to reduce operation margins, increasing interest by new vendors and utilities in doing their own reload analysis and the results of some research programs result in a continuing evaluation of licensing requirements.
This talk will outline the agency's response to these pressures and their effect on fuel assembly licensing actions.
INTRODUCTION I will discuss the aspects of reactor safety indicated in Figure 1.
i First, I will present the number of reactors that we project to be in l
operation in the U.S. based on ti;e number of applications before the l
NRC today.
I will describe a new licensing framework -- how to integrate all the knowledge we've learned since TMI from all areas -- and some i
. specific elements in that framework.
Then I will turn to fuel behavior and how work in that area relates to the total picture.
l PROJECTIONS OF THi. fiUl1BER OF REACTORS Uhere are we in the U.S. today in tems of numbers of reactors?
l There has been talk of a licensing freeze or licensing moratorium.
l There was a pause n our licensing efforts following TMI but since that time we've licensec five reactors for full power operation; one other l
plant, Sequoyah 2, has a license for low power operation.
The Ti1I-1 restart hearing is finally over and we are awaiting a decision from the l
Board.
These numbers show that today there are' about 75 reactors in i
the U.S. licensed for full power operation.
If we add to this the number of applications before the Commission today, we get a total of Q1g501810806~
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163 plants, as indicated in Figure 2.
About 150 plants actually have been issued construction pemits.
The number of reactors where concrete has actually been poured is about 140.
Figure 3 shows the magnitude of the current licensing review effort.
Listed are the plants that are expected to be completed in the U.S. in the 1981-1982 framework.
Plants being built during the TMI i'
pause are now being finished, and the OL workload for itRR is larger than ever.
If all the plants are constructed as scheduled and our i
~
safety reviews are complated on time, we will issue 15 to 18 licenses in 1982.
The f1RC has never done that in the past and it will be a challenge to do it in the future.
For each plant, we have indicated whether or not we have finished the draft environmental impact statement, whether we've issued the safety evaluation report, whether the ACRS meetings have been held, and whether we have issued the final supplement.
Also indicated are the
[
dates when the applicants expect construction of the plants to be r
completed.
He provide this infomation to Congress once a month. We are committed to meet the dates for issuing our safety evaluation i
reports.
Howevar, recent history would indicate that their plants will'
?
not be completed on the date shown.
In fact over the past few months there have beer a number of unanticipated delays in nearly conpleted plants.
The problems are mainly in the conventional engineering parts of the plant.
For example, ficGuire has loaded fuel, but has not gone i
critical because of leakage of valves that are in interconnecting piping between high pressure and low pressure systens.
fiorth Anna 2 has had four transfomer failures.
Sequoyah 2 has a galled bolt in the reactor vessel flange.
La Salle has buckled their reactor building roof during a ventilation test.
Figure 4 shows the major factors affecting the probability of new plant orders.
The total electrical generating capacity today is around 600,000 megawatts. We have a large rescrve margin, but this is not true for some specific regions of the country.
Since projected rate of growth of electrical consumption in this country over the next few years is probably no more than 3 or 4 percent, the number of coal plants and of nuclear plants that are currently being built will fully satisfy the need for additional capacity in this country over the next
.five years or so.
In effect, if they are put into operation on reasonable schedul.es, the reserve margin in the U.S. with no new starts of power plants of either type will be about 27 percent in 1985.
Ilone of the utilities have indicated any interest in starting new plants except for those few like Boston Edison which are obtaining construction pemits.
I would expect these few to go forward, but no new utilities to submit applications in the near future. !!any of the utilities in this country have some financial difficulties.
Other aspects are the uncertainty in the regulatory policies, and our failure to address waste storage '
issues.
Considering all factors, I do not think it likely that any new applications will be submitted before about 1985... During the next few years, therefore, we have a unique opportunity to relook at safety requirements. We can take advantage of this period so that to integrate all the design, construction, and operational lessons learned.
DEVELOPING A NEW LICENSING FRAMEWORK Ue are looking at what is needed to establish a new licensing framewcrk, as indicated in Figure 5.
Of the rule-skings that are going on, the big ones like emergency planning and the interim hydrogen rule may have an impact on fuel design.
Degraded core cooling is probably the largest single rulemaking that may influence fuel design in the futu re. We need to digest all the lessons that have come out of various studies of TMI.
Internally, there has been an effort by all our technical branches to rewrite the Standard Review Plan which is the guide by which we review applications.
This is almost finished now and the Standard Review Plan should be available by September.
ELEMENTS OF A FUTURE LICENSING FRAMEWORK Specifics for a new licensing framework are given in Figure 6.
The first element is a new siting policy, or at least resolution of those siting issues that have been so difficult in the past. We have always encouraged the banking of sites, or site designation, and standard plants, so the two can be meshed when the demand warrants.
Siting is a major problem because the perceived distribution of the benefits and the risks by the national, state, ar.d local interests involved.
With regard to improvirag the safety of the plant itself, I have a number of concepts I waat to mention.
Fuel is not on this list.
I think you designers of fuel should take a great deal of pride in what you have accomplished in achieving reliable fuel perfomance.
One concept is to improve containment capabilities. Large, strong containments have a lot to offer in tems of providing increased protec-tion for the public.
Not only is design strength important, but also issues such as the adequacy of residual heat removal systems.
Even a large containment can fail if the heat is not eventually removed.
We need diverse ways to remove heat from the reactor core other than through steam generators and the low pressure residual heat removal systems.
A high pressure residual heat removal system, for exampTe, would be advantageous.
Other concepts that could be applied to PWRs are already done in BWRs, such as primary system depressurization.
.Similarily, containment sprays could be used in BWRs.
A lot is being done with instrumentation: better control rooms, more automation, providing the operator more time, making the plant more forgiving, and more tolerant of operator errors.
One lesson from TMI is that we are all too concerned with hardware.
It is very easy to get involved in hardware design and forget the person in the control room.
Risk studies show that fully half of all the risks come from what I'd call the human factors areas.
I'm not talking about just the operators, but about maintenance people, control and instrumentation technicians, plant nanagement, and corporate staff, the whole gauntlet of people issues which we engineers sometime neglect.
Another possibility is steam generators with high thermal-inertia.
You nay remember that Shippingport can stand a loss of feedwater for
i l
hours.
There has been a tendency to design smaller steam generators which nakes the primary system more sensitive to losses of secondary heat renoval.
I want to mention standardization because there is a trend happening in fuel design that parallels what's happening in the reactor area. We have four vendors in this country and twelve architect engineers, as indicated in Figure 7.
If we could achieve a few standard designs, we could do a better job of reviewing those plants from the standpoint of
- safety, i
Among other improvements are those in the area of licensee management 1
capability as indicated in Figure 8.
Every power company needs to have someone at about the Vice President level who is sclely in charge of 1
nuclear activities.
This person should haYe a background in nuclear power and understand operational 3afety.
In the past some companies have organizationly placed reactor operations under an officer who was mainly experienced in fossil plant operation. We are also finding that some utilities in the U.S. are understaffed.
It takes 40 to 60 technical support people per two-unit station to provide the kind of staffing j
that we think desirable. Overall it takes about 400 people to operate a modern two-unit station.
He need to find sone way to modify the design and review process.
I often feel that the NRC is the only quality check on the designs that are offered by the industry, that utilities accept designs rather uncritically, whether they are fuel designs or plant designs, and then expect the NRC review to discover any defects. We are trying to find methods whereby the industry would adopt NASA-type practices -- strong internal design audits, independent reviews by peer panels. He are a weak reed for utilities to depend upon. He only do an audit review.
We find that the designs fron even the same vendor vary considerably depending on the individuals that actually do the design on a particular plant.
Systems much as auxiliary feedwater systens vary by about two I
orders of magnitude in reliability, all depending on the specific details.
We alte need to stabilize the staff review process.
I think it is widely rece;11 zed that rapidly changing regulatory requirements creates l
turmoil wher done in a manner which doesn't allow changes to be phased in.
l Finally, some institutional changes nay be needed. We have been i
talking to the Public Utility Commission representatives for example, to be re that the costs associated with safety are recognized and consic red.
Some members of Congress have proposed that there be a l
national reacto ocaining center. This would be a major step toward l
making a profes.fon of reactor operation.
FUEL BEHAVIO?.
Let me turn now to fuel performance and discuss the itens given in Figere 9.
! think fuel performance in normal operation can be only
classified as outstanding.
Figure 10 lists the fuel failure rates or the percent leakers over the past few years for the different vendors.
Several million fuel rods were exposed during this time period and it is interesting how low these failure rates are.
In the early seventies some vendors were.having trouble achieving a 1 percent leaker perfomance.
Recent leakers seem to ha somewhat' episodic.
For example, I think the B&W numbers all come from. just 2 plants - Crystal River and Arkansas-1.
The most recent entry in the fuel market, Exxon, is having the best experience.
Perhaps they have gained from the lessons of the other vendors or have been lucky so far, but overall it would be very hard to complain about fuel perfomance at this level.
I think it shows a remarkable advance in the fuel design process.
I should mention one other fact about this chart. As you know, man */ vendors are supplying fuel to reactors other than the ones which they originally designed.
For example, Westinghouse designs fuel for CE reactors. Westinghouse is trying to get into the boiling water fuel market.
Exxon supplies fuel for a number of reactors.
The current issues in fuel design from the NRC perspective are given in Figure 11.
All the issues involve fuel behavior under accident conditions.
I don't think we have any major issues with industry with regard to nomal operations.
All of these current issues, to the extent that they are issues, are minor ones.
The first four are areas where we are still trying to achieve improvements, the last two are amas that we think are satisfied and don't really have concerns with.
The first one, clad swelling, came up about a year ago and probably produced considerable controversy.
Agreement has been reached recently with Westinghouse on how to treat that issue, and I would expect that we would soon reach agraement with the other fuel designers. We hope to resolve that issue.by the end of the year with all fuel suppliers.
We are interested in fission gas release because there is very little empirical data for fuel irradiated to 40,000 MWD /T or more.
There is a tendency toward longer burnups so we're itill perhaps a little more conservative than some of you would like us to be in that area.
Pre-LOCA power history is really an analytical issue -- modeling codes are being fine tuned to reflect operating experience and to' adjust themal margins. The fourth, pellet cladding interaction, is mainly an operational problem; we and industry still don't quite agree
.on that one.
None of these four could be classified as najor issues.
As to enthalpy limits, we require reactivity excursion accident limits of less than 280 calories per gram.
Improved three dimensional analysis done in the physics area in the past few years has shown that reactivity excursions are much smaller than we used to expect.
I dun't think item five will remain an issue. He have been evaluating the mechanical response of fuel assenblies to seismic events for the past year, but I think now we have convinced ourselves that it is not a problem.
There are some licensing trends, apart from the technical issues themselves, that may require attention. Three of--them are given in Figure 12.
Fuel manufacturet s are marketing fuel for their competitors.
It causes some difficulties such as proliferating the number of computer codes and the number of fuel designs that we have to keep track of.
Vendors are continuing to improve their analytical models, so valuable
staff effort is expended just to keep up with the detailed changes in c
the codes themselves.
Finally, another trend, which I think should be encouraged, is that the utilities are developing their own reload capability. There are at least five that are talking to the NRC about plans to do their own reload analysis.
I think this is a healthy trend because it goes along with ny view that we need to enhance the technical j
capability of the utilities, but it does add to the number of methods and codes that we have to look at.
CONCLUSIONS My conclusions with regard to fuel are indicated in Figure 13.
Even though there are no major issues and I think the fuel industry should be praised for its accomplishments in keeping fuel out of the area of major safety implications, an increased number of designs by suppliers doe ~s divert staff to keeping the codes updated.
I would prefer to spend such staff effort in other areas, such as human factors, because they are far more important from a safety standpoint.
The other negative trend is that every fuel design that comes in tends to cut the margins a little closer.
I think there is a widespread feeling among many in the fuel industry that fuel is over-designed and i
therefore some of the margin can be taken out.
That must be done selectively, since there is a potential that fuel performance will deteriorate. There is no problem with these margins at present, but i
care must be taken to make sure that gains in reactor safety are net lost.
l Overall, reactor safety problems at present do not lie in the fuel i
area. They lie in the areas highlighted earlier.
In conclusion, if all of these areas of reactor design had had the same anount of research, analysis, and effort as has gone into fuel, we would all be a lot more-comfortable with the level of reactor safety today.
i l
me
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OUTLINE s
1.
PROJECTIONS OF THE NUMBER OF REACTORS l
II.
DEVELOPING A NEW LICENSING FRAMEWORK
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l III.
ELEMENTS IN THE FRAMEWORK IV.
FUEL 8EHAVIOR 2
Figure 1 4
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t ESTIM ATES OF REACTORS IN COMMERCIAL OPER ATION DATA AS OF DECEMBER 31,1980 Number of Reactors No.of Reactors 7tM) 1 81) 163 til
,g 152 121 l4:1
- - - - 139 D1 120 100 80 c,o 40 20 1
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I
ELECTRICAL INDUSTRY PROJECTIONS OF NUCLEAR PLANT ORDERS (ELECTRICAL WORLD SEPT. 1980)
IN 1981 - 600,000 MWE PEAK CAPACITY IN 1981, 32% MARGIN IN PEAK CAPACITY ilATIONNIDE PROJECTING 4.4% ANNUAL GROWTH IN PEAK DEMAND DVER THE NEXT 4 YEARS ADDING 22,000 MWE/ YEAR AVERAGE 1981-86 (11,000 MWE/ YEAR NUCLEAR AVERAGE)
IN 1986, PROJECTED MARGIN IN PEAK CAPACITY IS 27%
PROBLEMS FACING THE ELECTRICAL INDUSTRY NIGH INTEREST RATES LONG-RANGE INFLATION FINANCIAL DECLINE OF UTILITIES SLACKENED GROWTH RATd 0F DEMAND UNCLEAR ADMINISTRATION NUCLEAR POLICIES UNSTABLE REGULATORY CLIMATE NO NEW llVCLEAR PLANT ORDERS BEFORE.1985-86 Figure 4 e
9
STEPS IN DEVELOPING Tile LICEllSillG FRAMEWORK A.
COMPLETE THE RULEMAKINGS EMERGENCY PLANNING j
OL RULE CP RULE INTERIM llYDROGEN RULE SITING MINIMUM ENGINEERED S F$TY FEATURES DEGRADED CORE COOLING B.
DIGEST ALL THE LESSONS REG GulDES BRANCH IECHNICAL POSITIONS C.
UPDATE THE STANDARD REVIEW PLAN Figure 5 i
t ELEME!!TS OF A FUTURE LICEf!SlilG FRAMEWORK A.
SITING POLICY SITIllG INDEPEl4 DENT OF SPECIFIC DESIGN FEATURES
' ENCOURAGE STATES TO ESTABLISH SITE BAtlKS B.
SAFETY DESIGN GUIDELINES IMPROVED CONTAINMENT (LARGER VOLUME, GREATER PRESSURE,}l EAT REMOVAL, PRESSURE RELIEF, IlYDROGEN CONTROL, MOLTEN FUEL RETENTION, MISSILE SHIELDS)
DIVERSE DECAY llEAT Rm0 VAL SYSTEM PWR PRIMARY SYSTEM DE~ PRESSURIZATION BWR CONTAINMENT SPRAY l
MORE INSTRUMENTATION BETTER CONTROL ROOMS MORE AUTOMATION
(
IMPROVED SHUTDOWN SYSTEMS (ATWS FIXES)
PWR STEAM GENERATORS OFIGli IHERMAL INERTIA C. STANDARDIZATION i INITIATIVE MUST COME FROM INDUSTRY NRC CAN IMPROVE INCENTIVES Figure 6
ELEMENTS OF A FUTURE LICENSING FRAMEWORK (CONTINUED) s D. LICENSEE ACCREDITATION MANAGEMENT'0RGANIZATION OPERATIONS ORGANIZATION DESIGN AND SAFETY SUPPORT STAFFS E. GUIDELINES FOR THE DESIGN PROCESS CONFIGURATION MANAGEMENT INTEGRATE RELIABILITY }NTO DESIGN PROCESS INDEPENDENT DESIGN REVIEWS F. STABILIZE NRC STAFF REVIEW PROCESS MAINTAIN SRP AS A REQUIREMENT CONTROL DOCUMENT TRACKING SYSTEM FOR OPERATING REACTOR REQUIREMENTS PRIORITIZESAFETYISIVES MAKE USE OF PRA METHODS IN DEdISION-MAKING G. INSTITUT'IONAL CHANGES (SPECULATIVE) WORK WITH PUCS TO REMOVE. FINANCIAL DISINCENTIVES TO SAFETY NATIONAL REACTOR OPERATING ORGANIZATION i e . Figure 7 A
q .1 4 I -NSSSIAE Combination of Ught Water Reactors Under Constrbetion or On Order Combustion Westinghouse Generst Electne Engineeneg Eabcoct & Wilcox 6 10 6 5 Se:Ptet........ Burns & Poe..... 1 1 2 Stack 1 Vesten..... Brown & Root........ 2 E asco.. 4 1 4 Giiberticemmonwealtn. 1 2 Giees & Hsil.......... 2 Gittert Assoc:stes..... 7 6 Utility Cweer.... Auct Power Services.... 8 7 Sargent & Luncy. Stone & Weester....... 5 6 2 2 2 Uritec Er gineers.. 2 Tee.aessee Valley Autienty.... 3 6 2 2 s0.a L 3*ce os ?ec3%ogy assessmeas. Figure 8 1 l i k
i l FUEL BEHAVIOR i i i i A. RECEN FUEL PERFORMANCE 8. CURRENT ISSUES C. RESEARCH RESULTS j D. HISTORICAL IMPROVEMENTS 1 l E. FUTURE DESIGNS F. LICENSING IRENDS Fioure 9 m a f 1 l
c FilEL PERFORMANCE 1978 - 1980 PERCENT 1 SilPPLIER LEAKERS B&W 0,04 CE 0.01 EXXON 0.004 GE 0,015 W 0,013 i Ocure 10 a I k I i f
w I CURRENT ISSUES 1 h, f [ o CLADDING SWELLING ann RUPTURE IIURING LOCA 1 o FISSION GAS RELEASE FROM FUEL AT HIGH BURNUP 1 } o PRE-LOCA POWER HISTORIES l o PELLET / CLADDING INTERACTION (PCI) } o ENTHALPY LIMITS FOR REACTIv!TY INITIATED ACCIDENTS (RIAS) 1 o MECHANICAL RESPONSE To EXTERNAL LOADS l g Figure 11 4 i ( j-
LICENSING TRENDS O REACTOR MANUFACTURES ARE MARKETING FUEL FOR COMPETITOR'S REACTORS. O ALL VENDORS CONTINUE TO' IMPROVE ANALYTICAL TECHNIQUES TO MAINTAIN SAFETY MARGINS. 1 O UTILITIES ARE DEVELOPING THEIR OWN RELOAD ANALYSIS CAPABILITY. Figure 12 e N e S .m.
CONCLUSIONS 0 INCREASED NUMBER bF DESIGNS AND SUPPLIERS IS A DRAIN ON SCARCE NRC RESOURCES. f l O DRIVE TO REDUCE MARGIN HAS POTENTIAL TO REVERSE STEADILY IMPROVING FUEL PERFORMANCE. Figure 13 i { 1 t c}}