ML20207C279
| ML20207C279 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 12/24/1986 |
| From: | Rivenbark G Office of Nuclear Reactor Regulation |
| To: | James O'Reilly GEORGIA POWER CO. |
| References | |
| TAC-61074, NUDOCS 8612300097 | |
| Download: ML20207C279 (3) | |
Text
December 24, 1986 i
Docket No. 50-321 Mr. James P. O'Reilly Senior Vice President - Nuclear Operations Georgia Power Company P. O. Box 4545 Atlanta, Georgia, 30302
SUBJECT:
MAIN STEAM ISOLATION VALVE (MSIV) STEM FAILURES AT HATCH UNIT 1 Dear Mr. O'Reilly By letter dated January 13, 1986, Georgia Power Company (GPC) submitted a report to the NRC on the failures of the MSIV stems which took place at Hatch Unit 1 on July 24, 1985 and December 9, 1985 while the unit was operating at 100% power. We have reviewed this report to evaluate the adequacy of the GPC's analysis and to determine whether any follow-up action would be appropriate.
In the course of the review, a conference call was initiated on April 7,1986, by the staff to the GPC to obtain additional information and clarification of the subject report.
The valves in question are 24 inch "Y" Pattern Globe used in a steam environment (500-540 F) at a pressure of 1000 psi.
Information obtained through the conference call indicated that the failed stem material was 17-4 ph (precipitation hardening stainless steel) in the 1100 condition. This heat treat condition gives the steel maximum resistance to stress corrosion cracking at a modest reduction in yield and fatigue strength over other treatments which is desirable for this application. GPC stated that two independent laboratories (Battelle, Columbus and Structural Integrity, Inc.)
had reached the same conclusions as to the cause of the failure, i.e. high l
cycle fatigue due to vibrational bending moments caused by wear of the internal guide ribs on the valve body without any contribution of corrosion processes such as intergranular stress corrosion cracking (IGSCC).
- However, upon questioning, GPC indicated that some evidence of stress corrosion cracking was seen at 90 to the fracture surface, but it concluded that this was an effect of the failure rather than a cause.
Because we have further questions as to these findings and conclusions, GPC has agreed to provide us with copies of the failure analysis reports when they become available.
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GPC's immediate fix includes (1) redesigning the valve stem by increasing the diameter from 1.75 to 2.00 inches, (2) removing a relief groove where the fractures originated, and (3) reconditioning the worn guide ribs to manufacturers tolerances. These measures should help the problem in the short term even if GPCs conclusion that no corrosion /IGSCC is involved in the cause of failure is incorrect.
In audition, GPC has committed to a long term corrective action plan. We would appreciate your informing us of the schedule for the submittal of the failure analysis report, and the resolution of the long term corrective action plan. We should also like to be kept informed of the status of this corrective action plan.
The reporting and/or recordkeeping requirements contained in this letter affect fewer than ten respondents; therefore, OMB clearance is not required under P.L.96-511.
Sincerely W,pigned by George W. Rivenbark, Project Manager BWR Project Directorate #2 Division of BWR Licensing cc: See Next Page DISTRIBUTION i DocektJ11e; NRC PDR Local PDR PD#2 Plant File GRivenbark SNorris DMuller EJordan BGrimes JPartlow NThompson ACRS (10)
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Mr. J. P. O'Reilly Edwin I. Hatch Nuclear Plant, Georgia Power Company Units Nos. I and 2 cc:
Bruce W. Chruchill, Esquire Shaw, Pittman, Potts & Trowbridge 2300 N Street, N.W.
Washington, D.C.
20037 Mr. L. T. Gucwa Engineering Department Georgia Power Company Post Office Box 4545 Atlanta, Georgia 30302 Er. H. C. Nix, Jr., General Manager Edwin I. Hatch Nuclear Plant Georgia Power Company Post Office Box 442 Baxley, Georgia 31513 Mr. Louis B. Long Southern Company Services, Inc.
Post Office Box 2625 Birmingham, Alabama 35202 Resident Inspector U.S. Nuclear Regulatory Commission Route 1, Post Office Box 279 Baxley, Georgia 31513 Regional Administrator, Region II U.S. Nuclear Regulatory Commission, 101 Marietta Street, Suite 2900 Atlanta, Georgia 30303 l
Mr. Charles H. Badger Office of Planning and Budget Room 610 270 Washington Street, S.W.
Atlanta, Georgia 30334 Mr. J. Leonard Ledbetter, Commissioner Department of Natural Resources 270 Washington Street, N.W.
Atlanta, Georgia 30334 Chainnan i
Appling County Commissioners County Courthouse Baxley, Georgia 31513
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