ML17329A124
| ML17329A124 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 08/09/1991 |
| From: | Colburn T Office of Nuclear Reactor Regulation |
| To: | Fitzpatrick G AMERICAN ELECTRIC POWER CO., INC., INDIANA MICHIGAN POWER CO. (FORMERLY INDIANA & MICHIG |
| References | |
| IEB-88-002, IEB-88-2, TAC-67301, NUDOCS 9108190109 | |
| Download: ML17329A124 (9) | |
Text
Docket No. 50-315 August 9, 1991 0 Mr. Gene Fitzpatrick, Vice President Indiana Michigan Power Company c/o American Electric Power Service Corporation 1 Riverside Plaza
- Columbus, Ohio 43216
Dear Mr. Fitzpatrick:
SUBJECT:
D. C.'OOK NUCLEAR PLANT, UNIT NO.
1 -
RESPONSE
TO NRC BULLETIN 88-02, "RAPIDLY,PROPAGATING FATIGUE CRACKS IN STEAM GENERATOR TUBES" (TAC NO. 67301)
On February 5, 1988, the staff issued NRC Bulletin 88-02, "Rapidly Propagating Cracks in Steam Generator Tubes."
You responded to that bulletin by letter dated March 31, 1988, AEP:NRC:1056.
In your response, you concluded that D.
C.
Cook Unit 1 showed evidence of service-induced tube denting and provided, as required by Bulletin Action Item c, your program for minimizing the probability of tube rupture.
On September 29, 1988, the staff transmitted a request for additional information (RAI) concerning your implementation of Bulletin 88-02.
You responded by letter dated January 26, 1990, AEP: NRC: 1056A revising your position that service-induced denting was present in the D.
C.
Cook Unit 1 steam generators.
By letter dated May 9, 1990, the staft transmitted to you a second RAI concerning your revised response.
You responded to our request by letter dated June 5, 1990, AEP:NRC: 1056B.
The staff and its contractor, Oak Ridge National Laboratory (ORNL), have reviewed your June 5, 1990, response.
As described in the enclosed letter trom ORNL to the staff, there are concerns with the threshold detection level of magnetite and the amount of magnetite needed for pinning among others.
We request that you review the enclosed report and be prepared to discuss the report in a conference call with the staff and ORNL in the near future.
I will contact you to arrange a date and time for the conference call.
If you have any questions, please contact me at (301) 492-1341.
Sincerely, Original signed by Timothy G. Colburn, Senior Project Manager Project Directorate III-1 Division of Reactor Projects III, IV, V Office of Nuclear Reactor Regulation
Enclosure:
ORNL Report cc w/enclosure:
See next page DISTRIBUTION See attached page OFC
- LA:PDIII-1:db
- PM:PDIII-1 D'PD II:1 NAME
- PShut eworth
- TColburn
- TMarsh DATE:08 +/91: 08/(/91: 08
/91 OFFICIAL RECOR COPY g," g)digh&t Name:
BULLETIN 8802
RESPONSE
Vi08i9'Oi09 9i0809 PDR ADQCK 05000315 8,
Mr.
Gene Fitzpatrick Indiana Michigan Power Company Donald C.
Cook Nuclear Plant CC:
Regional Administrator, Region III U. S. Nuclear Regulatory Commission 799 Roosevelt Road Glen El lyn, Illinois 60137 Attorney General Department of Attorney General 525 West Ottawa Street Lansing, Michigan 48913 Township Supervisor Lake Township Hall Post Office Box 818 Br idgman, Michi gan 49106 Al Blind, Plant Manager Donald C.
Cook Nuclear Plant Post Office Box 458
- Bridgman, Michi gan 49106 U.S.
Nuclear Regulatory Commission Resident Inspectors Office 7700 Red Arrow Highway Stevensvi 1 1 e, Michi gan 49127 Gerald Charnoff, Esquire
- Shaw, Pittman, Potts and Trowbridge 2300 N Street, N.W.
Washington, DC 20037 Mayor, City of Bridgman Post Office Box 366
- Bridgman, Michigan 49106 Special Assistant to the Governor Room 1 - State Capitol
- Lansing, Michigan 48909 Nuclear Facilities and Environmental Monitoring Section Office Division of Radiological Health Department of Public Health 3500 N.
Logan Street Post Office Box 30035
- Lansing, Michigan 48909 Mr. S.
Brewer American Electric Power Service Corporation 1 Riverside Plaza
- Columbus, Ohio 43216
OAK RlDGE NATIONALLABORATORY Oe%AATSCI SY MARROW MA%ETTAENERGY SYKKQS. NC POST OFFiCE BOX 2008 OAK RIDGE, TENNESSEE 3783141SS (d15) 57~
July 2, 1991 Mr. Emmett L Murphy OKce of Reactor Regulation Materials Engineering Branch U.S, Nuclear Regulatory Commission MS %FN-9H15 Washington, DC 20555
Dear Emmett:
At your request I have reviewed the document submitted for D. C. Cook and suggested course of action to demonstrate the measurement of magnetite at the tube supports.
It is my understanding that NRC is concerned with the start of corrosion of the tube support which will produce magnetite (Fe,O,).
This magnetite will grow in the gap between the tube and the support until it pins the tube and starts denting the tube.
Once the tube is pinned, it can, under certain flaw conditions, undergo fatigue cracking. I believe that eddy-current techniques can detect the initiation of this degradation, but this document does not adequately demonstrate this.
Supporting work by Steve Brown of EPRI and Westinghouse shows the potential of eddy-current techniques ta perform this test, but I still have questions about the standards used in these tests.
I do nat know if the minimum amount of corrosion to produce the amount of magnetite needed for pinning has been established, although I suspect that it has.
1.
The document does show that some sample tubes with magnetite present were detected with eddy currents, but no supporting data on the amount of magnetite for these particular tubes nor the threshold detection level of magnetite is given.
2.
The condition af the, tube support that has undergone corrosion (to produce the magnetite) will contribute ta the signaL This willdepend on the size and'shape of the corrosion and may serve to augment the test or confuse the results.
The Westinghouse tube support standard used to establish the test had a 0.020 in. grove, U4 in. long machined into the support.
While this type of grove is ideal for adding magnetite, it also will produce a large signal for a differential bobbin probe.
A more gradual and uniform corrosion would produce a
much smaller signal.
Although the corrosion of the tube support indicates that magnetite has been produced, it does not necessarily mean that it has remained in the crevice and pinning the tube.
Conversely, the lack of corrosion does not mean that magnetite formed elsewhere had not been deposited between the tube and the support.
The two effects should be separated by the eddy-current test.
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Emmeti Murphy July 2, '1991 3.
The question of dents or dings still remains.
Pro61es of the tubes should be run to show the nature of any deformation of the tube.
Neither the detection of tube support corrosion nor significant amounts of magnetite in the presence of denting (or dinging) has been demonstrated, This must be done to insure a viable test.
4.
The cited training documents, "Conam Data Analysis Manual" and the EPRI NDE Center's "Manual of ISI Training" among with any qualiQcation material should be provided.
The following action plan is the one that I would use if I were developing a test to determine this corrosion. It certainly is not the only way to solve this problem.
The steps I would take are as follows:
The typical shape of the corrosion of the tube supports should be established.
This willrequire the examination of a range of corroded support plates by metallography to determine the various shapes that different levels of corrosion take.
2.
The minimum ainount of corrosion and magnetite needed to pin the tube should be, estabhshed.
The designed test should be such that it detects a thnMold of magnetite deposit well below the threshold of critical amounts, and track the amount that has been deposited.
Although a quantitative test would be more desirable, an alternative would be to develop a test go-nogo test that would detect magnetite above a critical threshoId.
The test should be based on standards that are constructed to have properties as near as possible to what will be encountered in the Qeld.
The standard should ccnsisC af tube supports, drilled to different sizes (and shapes) to simulate the dissolution of the support due to corrosion.
Various amounts of magnetite (or a material with the same electrical and magnetic properties as magnetite) should be Axed to the inner surface of the tube supports.
The amounts of magnetite should range in thickness from "insignificant" to a completely Qlled gap.
Inconel tubes with the same dimensions as those in the plant should be used, and some of the samples should have dings, dents and cold-work to simulate conditions that are present in the plant.
When the crevice is not completely Qlled, movable standards could be constructed.
This would allow a much larger number of conditions to be simulated by a relatively small number of standards.
The standards must be carefully constructed and documented, The mechanical measurements on them should be traceable to the NITS.
r P
I'
EInmett Murphy July 2, 1991 5.
Determine at what point that the magnetite can reliably be detected under simulated Geld conditions with the different types of coils avaBable (differential bobbin, absolute bobbin, pancake array and rotating pancake),
Determine the effect of the corrosion of the tube support on the eddy-current reading for the different coil types and select the one with the best overall performance.
Investigate the shielding effects that small "dings", dents and cold working can have on the detection ofthe magnetite.
Where these properties are present, the sensitivity of the test will he reduced.
This course of action may be more than is required, but does outline the steps that I believe are necessary to provide the necessary assurance that the tubes are not pinned by magnetite.
Sincerely yours, Caius V, Dodd Nondestructive Testing Group Metals and Ceramics Division Attachment cc:
L H. Bell C, Clark L K Hetcher - DOE/ORO D. J, McGuire C.F Pugh G. M. Slaughter C. V. Dodd/File
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DISTRIBUTION
~Docket File NRC PDR Local PDR B. Boger J. Zwolinski T.
Marsh P. Shutterworth T. Colburn E.
Murphy C.
Y.
Cheng E.
P-315 PDIII-1 r/f Cook Plant File
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