ML20132E840
| ML20132E840 | |
| Person / Time | |
|---|---|
| Issue date: | 07/13/1977 |
| From: | Check P Office of Nuclear Reactor Regulation |
| To: | Ross D Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20132A685 | List:
|
| References | |
| FOIA-83-619, RTR-NUREG-0999, RTR-NUREG-999 NUDOCS 8507180173 | |
| Download: ML20132E840 (12) | |
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p- 4* NUCLEAR REOULATORY COMMIS$10N j [
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'i JUL 1 3 EFF !
i MEMORANDUM FOR: D. F. Ross, Jr.,' Assistant Director for !
/ Reactor Safety, DSS FRON: F. S. Check, Chief, Core Performance Branch, [
SUBJECT:
MsgTINGS WITH UKAEA & UKNII REGARDING FUEL CLAD BALLOONING As part of the UK's effort to select a reactor type for future {
installations in Britain the Nuclear Installations Inspectorate ;
j (NII) has performed a review of FWR safety. In May, NII pre- !
seated NRC with a draft version of its report.
l In the portion of the report which deals with the fuel the 1 behavior of the fuel during a LOCA is discussed and reference _ l is made to tests performed at UKAEA Reactor Fuels Laboratory 1 (RFL) in Springfields. These tests were designed to study ,
ballooning of Eircaloy fuel cladding. This phenomenon has -
been and continues to be the object of extunsive experimental -
work in the US and Germany. Unlike the results from Us and .
German programs, however, the British tests, which were markedly l untypical of in-reactor conditions in that the cladding was '
directly heated, exhibited axially-extended balloons. The '
bulk of world data on the other hand shows that swelling is i highly localised both axially and circumferentially because of [
.the strong dependence of strain rate on temperature in combi- i nation with the expected local variation in cladding temperature. .i The British tests have now been reported in UKAEA report ND-R-6(3). -i i
The NII draft report was our introduction to this work and we !
set about immediately to reemanine our understanding of the !
cladding swelling phenomenon to determine whether the observed :
" sausage" balloons could actually occur at some point in a FWR l during a LOCA. Although we found there are many arguments why ;
it is highly improbable that sausages would develop (all of which are some variant of the unlikelihood that sufficiently unifera cladding temperatures could be maintained), we could not demon-strate that it is impossible that they would form.
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- t D.F. Ross, Jr. JUL 13 B77 Given the questions about the British experimental method and the importance of the conclusions regarding the extent of fuel rod ballooning during a LOCA, meetings were arranged with the British researchers and regulators. The first meeting was held on 28 June 77 at RFL in Springfields with E. Hindle, the prin-cipal UKAEA investigator, and his associates. This meeting, which is summarized in Enclosure 1 dealt mainly with the features of the experiment that are unrepresentative of in-reactor con-ditions. The second meeting, held at the NII offices in London on 29 June 77, discussed what conclusions might appropriately be drawn from the Springfields tests. This meeting is summarized in Enclosure 2. Researchers and regulators from Germany, as well, attended this meeting owing to'their strong interest in PWR safety and their extensive experience with cladding ballooning experiments.
It was concluded by all parties that further work is required to establish whether the results from the recent UK tests have role-vance to the PWR LOCA situation. The US and German research representatives state that the British tests are net representa-tive of actual reactor conditions. We have carefully reviewed this phenomenon and also believe the conditions were not repre-sentative. Accordingly, and in view of the large amount of world data that indicates localized swelling, we conclude that no immediate licensing action is required. ( Additional discussion of the unrepresentativeness of the tests and the unlikelihood that uniform cladding temperatures will exist during a LOCA is given in Enclosure 1.) Nevertheless, since further tests can be performed that will resolve the question of relevance of the British work, we plan to propose that such tests be included in the RES programs.
An ad hoc fuel behavior group was formed to guide and coordinate future work in this area. For the US, M.L. Picklesimor (NRC) assisted by R.O. Heyer (NRC) will servet for the UK, T.N. Rutherford (NII): and for FRG, H. Schnurer was designated. Tentative meetings .
have been planned for November 1977 in Washington (in connection with the WRS meeting) and June 1976 in Stratford-on-Avon (in connection with the ASTM international conference on Zircaloy).
The NII report will be published Inter this summer.
P. S. Check, Chief Core Performance Branch Division of Systems Safety Enclosures An stated
r D.F. Ross, Jr. ' '
DISTRIBUTION .
1 E. Case S. Hanauer R. Mattson ,
W. Dirks J. Lafleur S. Levine L. Tong V. Stello D. Eisenhut R. Beer -
F. Coffaan ;
R. Meyer N. Lauben ACRS W. Johnston .
M. Picklesiser Z. Rosatoczy Fuels Section ,
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ENCLOSURE I SUt9%RY OF DISCUSSIONS AT SPRINGFIELD NUCLEAR POWER DEVELOPMENT LABORATORIES, 28 JUNE,1977 On June 28, 1977. P.S. Check (CPB/ DSS),R.O.Meyer(CP8/ DSS)andM.L.
Picklesimer (FBRB/RSR) met with E. D. Hindle (RFL), R. A. Shaw (RFL), K. T.
Tregonning (NII), and T. N. Rutherford (NII) at the Springfields Nuclear Power Development Laboratories, Preston, England to discuss the work conducted by Hindle on the ballooning and burst testing of Zircaloy fuel element clad-ding. Sir John Harper, Head SNPDL, attended the early part of the meeting.
Of particular concern was the work Hindle reported in NO-R-6(S), "Zircaloy Fuel Clad Ballooning Tests at 900-1070K in Steam" which was used by N!! as the reference test and data for preliminary evaluation of LOCA in PWR's.
Hindle's work has shown that " extended" axial ballooning with up to 70%
circumferential elongation can be produced in internally pressurized PWR type Zircaloy fuel element cladding when self-resistance heated specimens are held at temperatures between about 650 and 800'C (1200 and 1475*F) for extended times before bursting. " Sausage" balloons up to 13 inches long in an 18 inch long specimens can be produced if (a times to burst are more than about 40 seconds at constant temperature (b)) severe axial restraint is provided by an internal stack of aluminum oxide pellets), (c) there is a steam atmo:phere, (d) isothermal conditions exist in the cladding (e) the void volume for gas in the specimen is small, and (f) " cold" surroundings are available for rapid loss of temperature by radiation 9n the " locally bulging" region of the specimen (provided by the metal bell jar wall at '
less than 100'C). NI! has used the results of these tests to propose that .
coplanar flow blockage may be possible in a PWR LOCA by the overlap of such
" extended" balloons in neighboring rods.
The meeting was opened by Shaw, who outlined the organization of the
$ringfields Laboratory and stated that it was project oriented with project leaders working through research groups. Shaw is Group Leader, Reactor Fuels Group, and has under him a total of 40 professional people in seven .
sections, the largest of which is the Water Reactor Fuel Section headed by K. M. Rose and the section to which E. D. Hindle is assigned. Most of the work in the recent past has been conducted on SGHWR fuel elements, but Hindle has conducted work on PWR fuel cladding under an assignment wherein UKAEA furnishes the experimental data used by N!! in fulfilling their responsibility in appraising PWR's for possible use in the UK.
Shaw then outlined their seven point program on PWR cladding and the status of each program as follows:
- 1. ballooning: Iaboratory studies well advanced (Hindle)
- 2. pin / pin interactions one bundle test has been conducted W t not yet examined, bulge interactions visible without disassen61y
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work completed, no' problem exists pin / spring eutectic femation:
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- 4. can sections irradiated for testing: delayed, done at Windscale !
i 5. pins irradiated for testing: delayed, done at Windscale USA, GfK-Karlsruhe, others, on continuous '
- 6. International liaison: basis ;
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- 7. liaison with N!!: on a continuous basis !
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i In reply to Shaw's question as to the need for the ,[ vis l so that better understanding and modeling could Check be obtaine t the datatest results.and any other work being done on Zircaloy cladding.
obtained, i
then explained that he and Meyer had accompanied P 1 tests and the personnel involved, and to ask a set of specific questions formulated in the past week during the NRC examination of the Hindle data l !
on extended axial ballooning t l
Meyer briefly outlined the questions infor the discussion and the meetiner pA0 PAT
- 1a6 oratory, >
l to allow a ofscheduled demonstration
- and tours the test loop SWEL, theof81owdown balloonin R g,"and the Multimd Test l i
l facility. One specimen was ballooned at 680'C in cold" steam with lt t initial pressure being 1260 psia. ;
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being observed through the viewing ports of the vel While it was being removed from the test rig and replaced with 1
of length. t i
a second specimen, we toured SWEL and the Blowdown Rig.
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Afterwards, in the Multired Test facility, we examine 11sts inside :
j a muffle furnace for external heating, solid aluminum oxide ly spaced SGWR l the pins. for axial restraint, and an outside "freme" of clo !
tubes to act as a rostraint to the expansion ofHowever, the outer PW l I
support for the test bundle. test at about 760*C (1400'F) conducted withj a valve on the pressurizing line failed to seal cospletely throughout the ,
from the pressurising system into the test ins continuous I i
test. The pressure 'n the pins did drop d ing the test, but not as much as I
! it should have for the increase in volume that occurred expanded.
balleens extending 3 to 4 inchesSince along the pin, and all such balloons!
the bundle had not been dis-i near one grid at one end of the bundle.
l assembled, no other information was available. '
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- PROPAT = Programed Pressure. And Temperature
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l On returning to the PROPAT laboratory, we observed the ballooning of the -
second specimen at 700'C in steam, with an initial pressure of 1260 psia, and a burst time of 98 seconds. Later examination of this specimen showed it to have a maximum circumferential elongation away from the ruptum of i about 50% with several " necks" having only 33% elongations. It also showed
" extended" axial ballooning with ' knots," and was not as unifonnly expanded as the first specimen demonstrated. The meeting was adjourned for lunch l imediately after this demonstration.
On runnyening, the list of nine prepared questions was presented to Hindle and Shaw. These questions concerned the applicability of the test method and data to the behavior expected of a nuclear md during a PWR LOCA. Also presented were the answers we had stipulated for four of the questions as a result of our detailed examination of the problem. The remaining questions were discussed in considerable detail. The nine questions are presented below with the stipulated answers and the discussions.
Questions:
P
- 1. Are " flat-topped" temperature transients possible in a LOCA7 Yes.
- 2. Is sufficient gas available in a PWR rod to pmduce extended balloons? ,
Yes.
- 3. Are pressure histories in the RFL tests reasonable? Yes.
- 4. Does direct heating of the cladding affect the test? This question was discussed by Meyer, with the essence of the discussion sumarized as follows:
Test Method of Heatino Method sel f-resistance Internal Heater Nuclear Te e mpej Iclad > Tp ,3j,g Tpellet> Tclad Tpellet>Tclad heat flow.100w/ft heat flow 100 w/ft heat flow from from clad to pellet from pellet to clad pellet to clad Steady-State T T pellet Tp ,jj,g> Tclad Tpellet > Tclad (flat-topped clad no heat flow heat flow from heat flow from transient) pellet to clad Pellet to clad 200w/ft 150 s af ter initiation The development of temperature gradie'nts around or along the fuel cladding (which would prevent extended axial ballooning) requires
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both a non-unifonn gap conductance and a heat flux, Both of these exist in nuclear rods and those heated by an internal conduction heater, and neither exists in the stea@-state test of a specimen .
heated by self-resistance. Therefore, the test conditions used by Hindle do not approximate those thought to exist in a nuclear fuel rod during a LOCA. .
- 5. Can isothennal rod conditions exist in a reactor? Meyer stated "no."
Picklesimer discussed the calculations reported by Wil11 ford and Hann (to be published as BNWL-2285 " Effects of Fill Gas Composition and Pellet Eccentricity") from analyses of experimental gap conductance measurements made at Halden. They calculated as much as 17% greater thermal conductivity for off-center pellets compared to eccentric, l and increase of 1% or mon in volumetric average fuel temperature for the eccentric pellet, a variation in surface temperature of the eccentric pellet from 578 to 1107't(coldest to hottest positions and zero to*.naximum gap, respectively) and cladding temperatures from 289 to 271*C on the ID(respectively) and 255 to 250'C on the 00 (ms-pectively). These tagerature gradients existed during nonnel operation -
at 200 w/cm in a xenon filled rod. He also discussed the chlculations presented by A. L. Lowe, Babcock & Wilcox, to the October 10, 1975, meeting the minutes of of thethat NRC meeting Zircaloy) showing Cladding Review differences in theGroup average (and reported in surface tegeratums of neighboring pellets at their midslanes at an instant of time during the " flat-topped" portion of tie time-temperature history of a PWR LOCA. The calculations were based entirely on the statistical variations within permissible (and observed) manufacturing and enrichmenttolerances and their effects of fuelon pellets as to heat the stored diameter, in a consnerc densityIa1 PWR fuel rod in nonnal operation. The maximum calculated between neighboring pellets was 42'F, and the average was 14'F. I
- 6. Does Joule (self-resistance) heating result in unusual effects in the vicinity of the bulge? No.
- 7. Did the md environment in the RFL tests affect the results?
Picklesimer answered " definitely." Hindle had stated in his ,
report that isothermal conditions in the specimens, specimen l temperatures between about 650 and 800'C (1200 and 1475'F), and
" cold surroundings" are required if extended axial ballooning is to occur, since the local bulge must be able to lose heat to drop its temperature below that of the neighboring regions and cause a ,
decrease in deformatten rate. Picklesimer then showed the results of a set of calculations modeling such a deformation process as a system having a " negative feedback" control. . These calculations indicate that extended axial ballooning could occur if the temper- '*
l ature of the " cold surroundings" is less than about 570'C, but ,
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l l unstable and localized bulging and rupture should occur if that
- temperature was greater than about 570'C. We can conceive of a
t md would be as much as 100*C below that of the bulge, except for the side of rods next to contml rods or water tubes. in which case there would exist a severe temperature gradient around the i' circumference of the md. In either case, t% strain should be localized, and no extended axial ballooning to larm diameters <
could occur. Our conclusion is that the test cond< tions used by !
Hindle do not apply to those existing in nuclear mds during a ;
) LOCA. Thus, the test results Hindle obtained can not be used to a j predict their behavior. -
r I 8. How were the RFL conditions selected? Hindle stated that he was 1 given no specific instructions as to test conditions, but allowed
! to choose them himself. In examining the conditions fuel cladding .,
! was expected to encounter during a LOCA in a PWR. he concluded that '
s the worst condition for flow blockage in a core would occur when '
f l the majority of the rods saw a " peak" temperature near 700-800'C for -
an extended period of time. He thought t w LOCA analysis should be i
! based on the behavior expected of them, rather than on the behavior of the hottest spot on the hottest rod. A core-wide analysis of peak ;
temperatures of rods reported in the U.S. Nuclear Reactor Safety t Hearings of 1973 showed that 805 of the fuel mds would have peak '!
temperatures below g80'C (1800*F) when the hottest rod had a peak i j temperature of 1260'C (2300*F). In studying the creep-rupture !
1 behavior of self-resistance heated mds. Hindle found that extended . t l axial ballooning with circ eferential elongations greater than 505
- i could occur for test temperatures between about 650 and 800*C when .
the propressurized rods ruptures in more than about 50 seconds after reaching test temperature. If the time to rupture was less or the (
specimen ruptured during the ramp to test temperature, the ballooning !
l was localfred and not extended axially. Two additional conditions i
! were found to be required for extended axial ballooning to occur . ;
j isothemal conditions in the specimen, and " cold surroundings." ;
I g. Is there supporting evidence for the RFL results? Hindle referenced !
recent work at 6fK Kariscruhe as supporting his findin9s, while the SfK researchers deny that their results confirm Hindle s. Picklesimer -
.' stipulated that under exactly the right set of test conditions. L creep rupture specimens could be made to undergo extended axial .:
ballooning, but did not believe that such cond tions could be l encountered by any of the fuel mds in ang kind of reactor accident, i and particularly not in a PWR LOCA. The told surroundings" could f not exist, nor could the required uniform temperature conditions !
exist at any time in the fuel rod, regardless of the amount of L ballooning. If.there was a way for one fuel red to see such dondi- I tions and so undergo extended extel ballooning, neighboring rods e i
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could not, and coplanar blockage involving several*
mds could i not occur. ,
Rutherford asked how could we be certain that extended saial ballooning would '
not be observed in the ORNL burst tests using an internal cond6ction heater if '
the specimen were held at constant temperature rather than being temperature ramped as in the present tests. Picklesimer replied that we can not be certain but are confident that it will not be observed. In any case. " steady-state" f temperature tests would be made within about one month at 0mL. and soon !
tnereafter at G%Karlsruhe, both using internal conduction heaters. Also. 'i '
single rod tests with a heated shroud are scheduled at ORNL in the coming fiscal year, and at least one 4 x 4 multired bundle using internal heaters will be ,.;
tested by this fall. Four sin the PgF LOCA series this fall.gle-rod so thatnuclear heated both in-pile andtests will be ex-pile datamade will in be "l available within a few months. The British remained unconvinced but were willing to discuss the problem further. ,
John Hertog. Group Leader. Irradiation Projects Experiments. RFL. made 'a short presentation on their plans for testing in the High Pressure Water :
Loop in O!00 at Name11. using an instrumented fuel rod having a fuel stack i 16 inches high, with loop blowdowns before or after reactor trip. The first '1 tests are scheduled for October.197g. The present program was planned for i SGWR rods but will not be done. Instead, the programs will probably Deastudyofgbabl . fue rods.
i Narry Hughes. Reactor Gmup. RFL. briefly discussed their computer code !
CANSWEL. which used creep equations to model ballooning in Zircoloy fuel i cladding. The code predicts circumferential strains reasonably well in com- .!
parison to experimental data from several sources, but it is not capable of _l predicting extended axial ballooning, j C. A. Mann briefly discussed the analytical approach they are developing for li studying rod bowing. using the creep buckling equations for compressive stresses ,
reported by N. J. Hoff. " Creep Suckling of Rectangular Plates Jnder Unexial !
Compression." Conference on Engineerin !
(edited by J. Negman and F. A. Leckie).g Plasticity. Cedridge, March 1968Their worj results are not yet available.
t The *weting was adjourned at 4:45 pm to allow several attendees to catch the i train to London. [
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ENCLOSURE 2 pur. nary of June 29 Meeting With UK Nuclear Installations Inspectorate ,
i After introductory remarks by Gausden (NII), P. Check noted that until very recently NRC was unaware of the UK tests on ballooning but that there appeared to be important questions regarding the applicability of these tests to the PWR LOCA situation. Gast (BMI) echoed these remarks pointing out that large strains such as those observed at RFL have been known for some time. He stated that the conditions needed to produce such large strains "....certainly cannot occur in reactor," and that '
Germany did not view the RFL experiments as relevant.
Hayinger (RSK) gave a discussion about LOCA representation in general emphasizing that rod temperatures in a LOCA would be ;
even lower than those required in the RFL tests to produce the .
large balloons. While these considerations are important and may even be overriding, this subject was not the focus of the ,
group's interest and was not pursued.
The discussion then focused on what conclusions would be appropriate to draw with respect to rod ballooning based on all ,
the inforamtion available including the recent RFL tests. A conclusion that all parties thought was appropriate and will
. 'probably be incorporated in the N!! report appears below.
In order to give fuller attention to test conditions and broader needs for research in this area, and ad hoe group was l
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formed to discuss such work. M. Picklesimer will be the overall '
- coordinator and principal US contact for the effort. He will be supported by R. Meyer. The principal contact in the UK will be
( T. Rutherford (NII) and in Germany, H. Schnurer (BMI). The first meeting will be held in November 1977 in Washington in connection with the Water Reactor Safety Research Meeting. A second meeting of the ad hoc group will be in June 1978 in England in connection !
with the ASTM Zircaloy conferenc,e.
The meeting at NII was brief, lasting less than 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />, and a list of attendees is given below.
Test of the_ Conclusion of NIT Report Subject to the constraints of schedule and higher-level con-currence, the British plan to include the followies conclusion !
regarding cladding ballooning in their report on PWR safety. -
"In the event of a loss of coolant accident, the emergency ,
cooling arrangements should be able to re-establish cooling of the core. Further experimental and analytical work is required to establish whether recent UK tests concerning fuel clad deformation are representative of in-reactor conditions during a LOCA. l t
"If it is established that the tests are representative. it is reasonable to expect that following a more detailed examina- l tion of the technical issues, either the effect suggested by the l
UK experiments will be shown to be tolerable, or that by appro-priate adjustment to design or operating conditions the problem i
could be avoided." .
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Attendance at 27 June Meeting R. Causden UK NII F. Erbacher FRG GFK D. Freyer UK HII A. Fiese FRG GFK T. Rutherford UK NII H. Schulz FRG GRS K. Tregonning UK NII D. Ross US NRC F. Campbell UK NII P. Check US NRC ,
A. Edwards UK CEGB R. Meyer US NRC U. Gast FRG BMI M. Picklesimer US NRC -
F. Mayinger FRG RSK f
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