ML19257D679
| ML19257D679 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 01/10/1980 |
| From: | Weeks J BROOKHAVEN NATIONAL LABORATORY |
| To: | Atomic Safety and Licensing Board Panel |
| Shared Package | |
| ML19257D675 | List: |
| References | |
| NUDOCS 8002050397 | |
| Download: ML19257D679 (5) | |
Text
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UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION BEFORE THE ATOMIC SAFETY AND LICENSING BOARD In the Matter of
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Docket Nos. 50-295
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50-304 COMMONWEALTH EDISON CO.
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Proposed Amendment to
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Facility Operating License No. OPR-39 (Zion Station, Units 1 and 2
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and DPR-48 to permit storage pool modifi-cation SUPPLEMENTAL AFFIDAVIT OF JOHN R. WEEKS I, John R. Weeks, being duly sworn, do state as follows:
I am employed by the Brookhaven National Laboratory, Department of Nuclear Energy, as Leader of the Cor-resion Science Group.
The statement of my professional qualifications has been pre-viously filed in this matter.
This affidavit addresses the second question of the Atomic Safety and Licensing Board as expressed in their memorandum and Order of January 8,1980, whether the water inside the proposed vented fuel storage tubes would be a " stagnant oxygenated borated water system", and if so, what would be the effect on the fuel storage tubes and racks.
The environment inside the proposeo vented fuel storage tubes would be a
" stagnant, oxygenated borated water system" in my opinion.
Nevertheless, I do not anticipate significant stress corrosion cracking to develop in this area.
The ISE Bulletin 79-17 described stress corrosion that has occurred on piping in stagnated borated water systems at several PWR's.
The most recent example of this cracking is that which occurred at Three Mile Island Unit 1 in the spent fuel pool piping in a line that only occasionally saw flowing water.
The exact cause of this cracking is yet to be fully understood.
Examination of samples of the failed pipe are underway at a number of laboratories.
BNL expects to receive a sample of this piping in the near future for examination here.
As I understand it at the present time, this attack occurred in heavily sensitized stainless steel piping in the vicinity of welds where a combination of sensitization from welding and residual 1872 347 s o n e o 0 0 37 7
stresses from welding caused conditions promoting SCC to develop.
The affidavit of W.L. Clarke clearly showed that the portion of the piping in which the cracks devel-oped was heavily sensitized compared to adjacent piping on the other side of t..a same weld where cracking did not develop.
Attempts to duplicate this phenomenon in our laboratory using boric acid solutions at room temperature and chloride concentrations up to 100 ppm have failed to produce intergranular stress corrosion cracking (IGSCC) under conditions at which the same material will crack in neutral pure water.
Ce r-tain of the older Babcock and Wilcox designed PWR's used sodium thiosulfate solutions as part of their emergency cooling as a scavenger for iodine.
It is possible at Three Mile Island that traces of sodium thiosulfate may at one time have entered this pipe.
Sone sulphur was obst.rved during the examinatior.., at Battelle Northwest, and in our laboratory, we have routinely been able to crack the test material that we are investigating in the presence of boric acid when small amounts of thiosulf ate were also present.
It would, however, be premature to conclude that thiosulfate contami-nation wa, +he cause of the problem at Three Mile Island at this time.
In any event, I do not anticipate that SCC of the type that developed in the stagnant line at Three Mile Island or at Arkansas Nuclear Unit 1, which also had thiosulf ate, is likely to develop in the spent fuel racks at Zion, for the reasons described below.
SCC requires a combination of an aggressive environment, a se.'sitized or sus-ceptible material, and high stresses generally equal to or greater than the yield stress.
From the evidence submitted in this case, I think it is unlikely that these particular requirements are all met in the creviced areas in the spent fuel storage racks at Zion for the following reasons:
1.
A sensitized material.
As Professor Staehle pointed out in his Appendix 1, the degree of sensitization of stainless steel in general increases with the carbon concentration in the steel.
The affidavit of Roger Staehle on page 6 points out that carbon content of the Type 304SS in the Zion spent fuel rack tubes is low, ranging from.03 to.04% by weight.
This is subetantially lower in carbon than the heat of material that failed at Three Mile Island which had.07 to.08 weight % carbon.
The lowest carbon level at which IGSCC has developed in sensitized stainless steels at Icw temperatures to my knowledge is.06% and even at much higher temperatures in BWR's, it has been almost exclusively confined to stainless steels containing more than.05%
Further, the tests performed by W.L. Clarke (described in his affidavit) show that the P values, (which are a measure of the amount of a
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sensitization present in the heat affected zones of the welds in the Zion spent fuel racks) were small, ranging from less than 1 to a maximum of 3.1.
This indicates substartially less sensitization of this material than was present in the heat af fected zone of the weld where the crack developed at Three Mile Island Unit 1 which gave a Pa value of the order of 20 or greater.
While obvicusly not all welds were tested, the combination of the low values on the welds that were tested and the low carbon level of the material used in fabricating these tubes indicates to me that severely sensitized stainless steel is not present in the Zion spent fuel racks.
2.
An aggressive environment.
Pure water containing oxygen is a sufficiently aggressive environcent to cause localized IGSCC of heavily stressed heavily sensitized stainless steel, even at room temperature, as has been demon-strated in the laboratury. Our recent experiments at Brookhaven, however, suggest that the addition of boric acid into this water has a beneficial effect and reduces its aggressiveness. However, even if we accept the f act that in these deep crevices an environment at least as aggressive as that which developed in the stagnant lines at Three Mile Island 1 could develop, i.
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we have in these crevices the additional beneficial factor that there is boral with an aluminum cladding on it present in electrical contact with the stainless steel.
The pitting studies performed by Exxon and Battelle which ware discussed at the hearing last Spring in this natter have shown conclusively that it is the aluminum that pits rather than the stainless steel in this galvanic couple.
This pitting of the aluminum, shculd it occur in these crevices, would provide additional insurance that a. e ivironment corrosive to the stainless steel would be unlikely to develop in these crevices.
3.
Stresses greater than the yield stress.
In our tests on heavily sensitized stainless steel in room temperature water containing oxygen, it was necessary to stress the stainless steel specimens to a level equal to approximately 150% of their design yield strength in order to initiate IGSCC.
Maintenance of stresses of this magnitude or the 1mi strain rates associated with these stresses (10-7 nches/ inch-sec.) over a long enough period of tine to initi-i ate and propagate an intergranular stress corrosion crack would in my opinion be quite unlikely in a low stressed component such as the fuel storage racks at Zion.
Should the material be temporarily stressed as high as this, the material would give and the stresses would be reduced by natural relaxation processes in the stainless steel.
For these reasons, I do not anticipate that the combinat.on of a sensitized material, an aggressive environment, and high stresses is likely to develop in the creviced areas in the spent fuel racks in the Zion pool.
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The above statements are true and accurate to the best of my knowiedge.
A Jo n R. Weeks
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Subscribed and sworn to before me this 10thday of January,1980 f
V
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a k
Notar'y Public
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My Cemission expires: July 1, 1932
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1872 350 4
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UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION BEFORE THE ATOMIC SAFETY AND LICENSING BOARD In the Matter of
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COMMONWEALTH EDIS0N COMPANY
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Docket Nos. 50-295
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50-304 (Zion Station, Units 1 and2)
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CERTIFICATE OF SERVICE I hereby certify that copies of "NRC STAFF'S RESPONSE TO LICENSING BOARD'S MEMORAt:DUM AND ORDER OF JANUARY 8,1980 R2GARDING STAGNANT B0 RATED WATER IN ZION STATION SPENT FUEL POOL" in the above-captioned proceeding have been served on the followino by deposit in t'ie United States mail, first class or, as indicated by an asterisk, throut,h deposit in the Nuclear Regulatory Comission's internal mail system, this 24th day of January,1930.
Atomic Safety and Licensing Board John F. Wolf, Esq., Chairman Panel 3409 Shepherd Street U.S. Nuclear Regulatory Comission Chevy Chase, Maryland 20015 Washington, D. C.
20555 Dr. Linda W. Little Atomic Safety and Licensing Appeal 5000 Hermitage Drive Board Panel Raleigh, North Carolina 27612 U.S. Nuclear Regulatory Commission Washington, D. C.
20555 Dr. Forrest J. Remick Docketing and Service Section 305 E. Hamilton Avenue U.S. Nuclear Regulatory Commission State College, Pennsylvania 16801 Washington, D. C.
20555 j
1 Philip P. Steptoe, Esq.
Mr. Gregory Minor Isham, Lincoln and Beale MHB Associates One First National Plaza 1723 Hamilton Avenue Chicago, Illinois 60603 San Jose, California 95125 Susan N. Sekuler, Esq.
Assistant Attorney General
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Environmental Control Division 188 West Randolph Street, Suite 2315 gA Chicago, Illinois 60601
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Richp'rd M Goddard Cou(selforNRCStaff Mr. Rick Konter 617 Piper Lane Lake Villa, Illinois 60046 1872 351
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