ML19338F974
| ML19338F974 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 10/10/1980 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Counsil W NORTHEAST NUCLEAR ENERGY CO. |
| References | |
| NUDOCS 8010280173 | |
| Download: ML19338F974 (1) | |
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UNITED STATES 3 -l" g(f'.::[g y })
NUCLEAR REGULATORY COMMISSION d
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Docket Nos. 50-245 October 10, 1980 50-336 50-423 Northeast Nuclear Energy Company ATTN:
Mr. W. G. Counsil Senior Vice President - Nuclear Engineering and Operations P. O. Box 270 Hartford, Connecticut 06101 Gentlemen:
The enclosed IE Information Notice No. 80-36, " Failure of Steam Generator Support Bolting," is forwarded to you for information.
No written resporise is required.
If you desire additional information regarding this matter, please contact this office.
Sincerely, cc Boy e H. Grier Director i
Enclosures:
1.
IE Information Notice No. 80-36 2.
List of Recently Issued IE Information Notices CONTACT:
E. G. Greenman (215-337-5267) cc w/encis:
E. J. Mroczka, Station Superintendent D. G. Diedrick, Manager of Quality Assurance J. R. Himmelwright, Licensing Safeguards Engineer K. W. Gray, Supervisor of Construction Quality Assurance H. R. Nims, Director of Nuclear Projects 8010280/73-C
SSINS Ns.:
6835 Acesssicn No.:
8006190085 IN 80-36 UNITED STATES NUCLEAR REGULATORY COMMISSION s.,.
OFFICE OF INSPECTION AND ENFORCEMENT D
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WASHINGTON, D.C.
20555 WJJ October 10, 1980 IE Information Notice No. 80-36:
FAILURE OF STEAM GENERATOR SUPPORT BOLTING Description of Circumstances:
On September 4, 1980, the NRC staff was informed by the Northern States Power Company that extensive cracking of the bolting for the supports attached to bottom of the steam generators on Prairie Island Unit I had occurred.
The licensee initially discovered the bolting problem when two bolts failed during detensioning.
The licensee was attempting to remove the pre-load on the bolting (specified at 1400 ft-lbs) to minimize the potential for stress corrosion cracking of the high strength 1-1/2 in.
dia.
250 ksi maraging steel bolting (Vascomax 250).
Ultrasonic examination of the support bolting revealed cracks or breaks in 47 of 48 support bolts for the two steam generators at the Prairie Island Unit 1 facility.
The licensee subsequently shut down the Prairie Island Unit 2 facility and performed ultrasonic examinations of the same steam generator support bolting, that failed on Unit 1.
The results of the UT examinations revealed cracks in three of the 48 steam generator support bolts.
The licensee attempted to remove the cracked bolts from the steam generator supports.
Two i
cracked bolts were successfully removed while the third failed during removal.
1 Two bolts that were judged as defect free by the ultrasonic examination were also removed.
Magnetic particle examinations confirmed the results of the ultrasonic examinations on the bolts which were removed.
As part of the short term corrective actions taken, the licensee has unloaded and retensioned the bolting at approximately 50 to 100 ft.-lbs.
Inservice ultrasonic examination of the affected bolting had been performed previously.
In the case of Unit 1 a significant number of the bolts were examined at the last refueling outage 14 months ago.
No cracks were found at that time.
The susceptibility for stress corrosion cracking was identified in NUREG-0577 (for comment).
The NUREG identifies those facilities which have utilized maraging steels for reactor coolant pump and steam generator support bolting.
Further the NUREG recommends augmented inspections for the facilities included in Group I.
Licensees are encouraged to review the bolting materials used at their respective facilities and consider inspection of maraging steel bolting that are either pre-loaded or significantly loaded during operation.
This Information Notice is provided as an early notification of a possibly significant matter that is still under review by the NRC staff.
It is expected that recipients will review the information for possible applicability to their facility.
No specific action or response is requested at this time.
If you have any questions regarding this matter, please contact the Director of the appropriate NRC Regional Office.
e IE Information Notice No. 80-36 October 10, 1980 RECENTLY ISSUED IE INFORMATION NOTICES Information Subject Date Issued to Notice No.
Issued 80-35 Leaking and Dislodged 10/10/80 All holders of a Iodine-125 Implant Category G or G1 Seeds Medical License 80-34 Boron Dilution of 9/26/80 All holders of a Reactor Coolant During PWR Power Reactor OL Steam Generator Decontamin. tion 80-33 Determination of 9/15/80 All holders of Teletherapy Timer a teletherapy Accuracy license 80-32 Clarification of 9/12/80 All holders of Certain Requirements an NRC or Agreement for Exclusive-use State License Shipments of Radioactive Materials 80-31 Maloperation of Gould-8/27/80 All holders of Brown Boveri 480V-Type a power reactor K-600S and K-Don 600S OL or CP Circuit Breakers 80-30 Potential for Unaccept-8/27/80 All holders of able Interaction a BWR power reactor Between the Control OL or CP Rod Drive Scram Function and Non-essential Control Air at Certain BWR Facilities 80-29 Broken Studs on 8/7/80 All holders of Terry Turbine a power reactor Steam Inlet Flange OL or CP Supplement Notification of 7/29/80 All holders of a to 80-06 Significant Events power reactor OL at Operating Power and near term OL Reactor Facilities applicants 80-28 Prompt Reporting 6/13/80 All applicants of Required Information for and holders To NRC of a power reactor construction permit