Report on ECCS Cladding Models, NUREG-0630 (Generic Letter 80-106)
GL80106
UNITED STATES
NUCLEAR REGULATORY COMMISSION
WASHINGTON, D.C. 20555
November 28, 1979
TO ALL PENDING OPERATING LICENSEES AND CONSTRUCTION PERMIT APPLICANTS TO ALL
LICENSEES OF PLANTS UNDER CONSTRUCTION
SUBJECT: REPORT ON ECCS CLADDING MODELS
On November 1, 1979, we met with reactor fuel vendors, some plant licensees,
and other interested parties to discuss recently developed staff views on
cladding rupture, swelling, and coolant blockage that could result from
reactor accidents. Based on a preliminary evaluation of the correlations
being developed, the NRC staff determined that parts of the ECCS models
might be non-conservative in this area and therefore might not be in
compliance with Appendix K of 10 CFR 50. We understand from the discussions
at the meeting, confirmed by vendor letters of November 2, 1979, that
differences between the present models and our preliminary correlations are
either small within the limited range of applicability or that these
differences do not produce large changes in peak cladding temperature. In
either case we now understand that such differences should not, affect
compliance with the temperature limit specified in 10 CFR 50.46 for licensed
operating reactors. On this basis it might be expected that the effect on
plants under review would also be small, but that effect has not yet been
determined.
We are transmitting herewith our draft report on cladding rupture
temperature, strain, and resulting assembly flow blockage; this report
provides a full discussion of the information we presented at the November
1, 1979 meeting. Should you desire to comment on this draft report,
"Cladding Swelling and Rupture Models for LOCA Analysis," please provide us
with written comments by December 10, 1979. Because we are requesting a
critique that will help ensure the technical quality of the final report, we
request that the focus of your comments be technical in nature. You may also
wish to address the topics for discussion that we have sent to the fuel
vendors and which are set forth in the enclosure to this letter. We also
welcome comments and suggestions on clarity so that the final report can be
made complete and explicit on correlation derivation and use.
Sincerely,
D. B. Vassallo, Acting Director
Division of Project Management
Office of Nuclear Reactor Regulation
Enclosures:
1. Draft Report of NUREG-0630
2. Topics for Discussion
ccs: Service Lists
.
ENCLOSURE 2
Topics for Discussion
1. Confirm that the Zircaloy cladding models displayed in Section 4.0 and
which are referenced in Section 5.0 are the models that are used in
your licensing LOCA analyses. Confirm that your models have been
displayed accurately (i.e., to within + - 5%). If you are unable to
respond affirmatively to the above requests, provide the appropriate
references and describe the discrepancies.
2. The location, magnitude, and shapes of superplastic strain peaks and
low-ductility valleys cannot be determined precisely from prototypical
rod burst tests because there are too few such experiments with enough
controlled variables. Do you have any information that could suggest
altering the shapes and magnitudes of the strain and blockage
correlation curves?
3. Most of the recent (since 1974) prototypical data were supported by
public funds and are publically available. It therefore appears
practical and beneficial to develop standardized rupture temperature,
strain, and blockage curves. The curves in the report (or modifications
that we might make) could serve as an interim licensing standard, and
an industry standards committee could develop revised curves based on
present and future research results.
4. It may be appropriate to require that approved vendor cladding models
be revised to conform with the correlations that will appear in the
final version of the report. If your present models are in agreement
with, or conservatively overpredict, the NRC correlations over the
range of temperature and stress of interest, and if you wish not to
change your present curves, your ECCS model revision could simply
consist of explicit limits on the range of applicability of your
correlations.
5. The alpha-plus-beta strain and blockage "valleys" portray a real
phenomenon, but the exact location of the very steep sides of the
valley may be unknowable for real LOCA conditions. Sensitivity analyses
could be done to account for uncertainties in the location of the
curves and in prediction of the rupture temperature and stress, but
this would have the effect of narrowing the allowable calculated valley
and creating a pseudo singularity in the analysis. It might be better
for the licensing analysis to be insensitive to this feature.
6. The on-going NRC research program has produced data over a wide range
of conditions. Based on discussions with those performing licensing
LOCA analyses, it appears that the actual range of interest may be
quite narrow, and that the future program could be beneficially focused
on a narrower range.
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PLANTS UNDER CONSTRUCTION
1. Palo Verde 1/2/3 50-528, 50-529, 50-530
2. Perry 1/2 50-440, 50-441
3. Cherokee 1/2/3 50-491, 50-492, 50-493
4. Beaver Valley 2 50-412
5. St. Lucie 50-389
6. Vogtle 1/2 50-424, 50-425
7. River Bend 50-458, 50-459
8. Clinton 1/2 50-461, 50-462
9. Forked River 50-363
10. Wolf Creek 1 50-482
11. Jamesport 1/2 50-516, 50-517
12. Nine Mile Point 2 50-410
13. Millstone 3 50-423
14. Bailly 1 50-367
15. Limerick 1/2 50-352, 50-353
16. Hope Creek 50-354, 50-355
17. Marble Hill 1/2 50-546, 50-547
18. Seabrook 1/2 50-443, 50-444
19. Sterling 50-485
20. Hartsville 1/2/3/4 50-518, 50-519, 50-520, 50-521
21. Phipps Bend 1/2 50-553, 50-554
22. Yellow Creek 1/2 50-566, 50-567
23. North Anna 3/4 50-404, 50-405
24. WPPSS 1/3/4/5 50-460, 50-508, 50-513, 50-509
25. Callaway 1/2 50-483, 50-486
26. Harris 1/2/3/4 50-400, 50-401, 50-402, 50-403
.
PLANTS UNDER CP REVIEW
1. Pilgrim 2 50-471
2. Greenwood 2/3 50-452, 50-453
3. Perkins 1/2/3 50-488, 50-489, 50-490
4. Allens Creek 1 50-466
5. New England 1/2 50-568, 50-569
6. Montague 1/2 50-496, 50-497
7. New Haven 1/2 50-596, 50-597
8. Erie 1/2 50-580, 50-581
9. Pebble Springs 1/2 50-514, 50-515
10. Clinch River 50-537
11. Black Fox 1/2 50-556, 50-557
12. Skagit 1/2 50-522, 50-523
13. Davis Besse 2/3 50-500, 50-501
14. Haven 50-502
15. Greene County 1 50-549
16. FNP 50-437
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PLANTS UNDER OL REVIEW
1. Farley 2 50-364
2. Byron/Braidwood 50-454, 455, 456, 457
3. LaSalle 1/2 50-373, 374
4. Zion 1/2 50-295, 304
5. Midland 1/2 50-329/330
6. Catawba 50-413, 414
7. McGuire 50-369, 370
8. So. Texas 1/2 50-498, 499
9. Shoreham 50-322
10. Waterford 50-382
11. Grand Gulf 1/2 50-416, 417
12. Diablo Canyon 1/2 50-275, 323
13. Susquehana 1/2 50-387, 388
14. Salem 2 50-311
15. Summer 1 50-395
16. San Onofre 2/3 50-361, 362
17. Bellefonte 1/2 50-438, 439
18. Watts Bar 1/2 50-390, 391
19. Sequoyah 1/2 50-327, 328
20. Comanche Peak 1/2 50-445, 446
21. North Anna 2 50-339
22. WPPSS-2 50-397
23. Fermi 2 50-341
24. Zimmer 1 50-358
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