ML19320C167
| ML19320C167 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 06/11/1980 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Counsil W NORTHEAST NUCLEAR ENERGY CO. |
| References | |
| NUDOCS 8007160357 | |
| Download: ML19320C167 (1) | |
Text
UNITE 3 STATES f@
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NUCLEAR REGULATORY COMMISSION
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REGION I U
j 631 PARK AVENUE KING OF PRUS$1 A PENNSYt.VANI A 19406 Docket No. 50-336 June 11, 1980 50-423 Northeast Nuclear Energy Company ATTN:
Mr. W. G. Couns11 Senior Vice President - Nuclear Engineering and Operations P. O. Box 270 Hartford, Connecticut 06101 Gentlemen:
The enclosed IE Information Notice No. 80-27, " Degradation of Reactor Coolant Pump Studs", is forwarded to you for information.
No written response is required.
If you desire additional information regarding this matter, please contact this office.
Sincerely, Y.
oyce H. Grier Director
Enclosures:
1.
IE Information Notice No. 80-27 2.
List of Recently Issued IE Information Notices CONTACT:
L. E. Tripp (215-337-5282) cc w/encls:
J. F. Opeka, System Superintendent Nuclear Operations 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 8007160359 Q
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ENCLOSURE 1 i
SSINS No.:
6835 Accession No.:
UNITED ~ STATES-8005050068-t NUCLEAR REGULATORY COMISSION
,gy "f4 0FFICE OF INSPECTION AND ENFORCEMENT f TPp i
WASHINGTON, D.C.
20555 h
g gg IE Information Notice No. 80-27 Date: June 11, 1980 4
Page 1 of 2 DEGRADATION OF REACTOR COOLANT PUMP STUDS
' Description of Circumstances:
On May'17, 1980, the NRC staff was informed by Omaha Public Power District (0 PPD) that severe corrosion. damage was-found on a number of closure studs in two of the four Byron Jackson reactor coolant pumps at Fort Calhoun Unit 1 (PWR).
At the time, the reactor coolant system was undergoing a routine low pressure leak test (180 psig) and visual inspection prior to plant restart after a four-month outage-for refueling, pipe support modifications and scheduled inservice inspection.
During the visual inspection, saturated and dripping insulation was observed at one of the Byron Jackson reactor coolant pump flange regions.
Upon removal of the. insulation, evidence of coolant leakage was found emanating from the seating surfaces between the pump casing and the pump cover.
Further investigation of the three remaining pumps indicated similar coolant leakage past botn.nner and outer flange, gaskets on two of the three pumps.
After complete removal of the nonmetallic insulation, further visual observations revealed three studs located side-by-side on one pump and three studs similarly located on the other. pump had significant corrosion wastage in the shank area next to the' lower thread section in the lump casing flange. Wastageofapproximately50%ofthe l
original diameter of tie stud giving them an " hour glass' type appearance was observed.
The corroded' studs were located in the vicinity of a component cooling l
water line on both affected pumps but no direct correlation of this fact has been established.
Although not confirmed by metallurgical analysis, the cause'of the stud wastage is thought to be corrosive attack by hot boric acid from the primary coolant.
The~ pump cover and casing for these pumps are constructed of ASTM A-351, Grade
-CF8M stainless steel.
Sealing between the cover and casing is achieved by two concentric 304 stainless steel flexitallic gaskets.
A leak-off line installed
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between the gaskets on each pump was plugged and not instrumented.
The leak-off line was not-in use and therefore, no ladication of RCS leakage from the inner i
' seal was available.
Each pump has 16 closure studs, consisting of ASTM A-193 Grade B7 low alloy steel, which ire chrome plated in the thread area and.
phosphate' coated in-the shank area..The studs are approximately 3-1/2 inches 21n diameter and about 29 inches.long.
No maintenance requiring removal of the pump casing studs had been perf: med on
- the reactor _ coolant pumps since initial construction.
The studs were covered
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IE Information Notice No. 80-27 June 11, 1980 Page 2 of 2 with block type insulation since construction thereby limiting them from view.
The studs on two pumps were ultrasonically inspected in place in accordance with the applicable ASME Section XI code rules.
These ultrasonic examinations were intended to locate cracks in bolting and were not effective in revealing wastage of the studs.
The three affected pumps will be disassembled for further cleaning and inspection of the studs and mating surfaces.
Prior to reassembly, all studs exhibiting significant corrosion will be replaced.
All new, or acceptable used studs, will be subjected to ultrasonic, visual and magnetic particle examinations.
Installation of instrumentation for actively monitoring the leak-off lines between the flexitallic gaskets is being performed.
Future inservice inspec-tions, presently limited to ultrasonic examination, will be supplemented with visual examination of the studs installed in the reactor coolant pumps.
Replace-ment insulation will be in the form of a removable blanket to facilitate visual examination.
The condition of the studs discovered at Ft. Calhoun raises concerns that such severe corrosion, if undetected, could lead to stud failures which could result in loss of integrity of the reactor coolant pressure boundary.
The lack of effectiveness of current ultrasonic examinations in revealing wastage emphasizes the need for supplemental visual inspections and use of instrumented leak detec-tion systems to preclude unacceptable stud degradation going undetected.
Licensees should cbnsider that the potential for undetected wastage of carbon steel bolting by a similar mechanism could exist in other components such as valves.
This IE Information Notice is provided as an early notification of a signi-ficant matter that is still under review by the NRC staff.
It is expected that recipients will review the information for possible applicability to their facilities.
No specific action or written response to this IE Information Notice is required.
If NRC evaluations so indicate, further licensee actions may be required.
IE Information Notice No. 80-27 June 11, 1980 RECENTLY ISSUED IE INFORMATION NOTICES Information Subject Date Issued To Notice No.
Issued n
80-26 Evaluation of Contractor 6/10/80 All Part 50 Licensees QA Programs 80-25
-Transportation of 5/30/80 Material Licensee in Pyrophoric Uranium Priority / Categories II-A, II-D, III-I and IV-DI; Agreement State Licensees in equivalent categories 80-24 Low Level Radioactive 5/30/80 All NRC and Agreement Waste Burial Criteria State Licensees 80-23 Loss of Suction to 5/29/80 All power reactor to Emergency Feedwater facilities with an Pumps OL or CP 80-22 Breakdown In Contamination 5/28/80 All power reactor Control Programs OLs and near term cps 80-21 Anchorage and Support of 5/16/80 All power reactor Safety-Related Electrical facilities with an Equipment OL or CP 80-20 Loss of Decay Heat Removal 5/8/80 All light water reactor Capability at Davis-Besse facilities holding Unit 1 Whi.le in a Refueling power reactor OLs or cps Mode 80-19 NIOSH Recall of Recircu-5/6/80 All holders of a power lating-Mode (Closed-Circuit) reactor OL, Research Self-Contained Breathin Reactor License, Fuel Apparatus (Rebreathers)g Cycle Facility License and Priority I Material License 80-18 Possible Weapons Smuggling 5/5/80 All power reactor Pouch facilities with an OL, fuel fabrication and processing facilities o iority I and Materials r
licensees (processors and distributors) i