ML20237J818
| ML20237J818 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 01/19/1987 |
| From: | Lippold W BALTIMORE GAS & ELECTRIC CO. |
| To: | Strosnider J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| NUDOCS 8708260329 | |
| Download: ML20237J818 (3) | |
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GAS AND ELECTRIC CHARLES CENTER P.O. BOX 1475 BALTIMORE, MARY $AND 21203 W. JAMES LIPPoLo MANAGER NUCLE AR (NGINEERING $ERVICES DEPARNENT j
I 3anuary 19,1987 U. S. Nuclear Regulatory Commission Docket Nos.
50-317 l
Region 1 50-318 631 Park Avenue License Nos.
DPR-53 King of Prussia, PA 19406 DPR-69 ATTENTION:
Mr. Jack R. Strosnider, Acting Chief
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Materials and Processes Section
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Division of Reactor Safety
SUBJECT:
Review and Evaluation of Reactor Coolant Pump Shaf t Axial Cracking j
REFERENCES:
(a)
Teleconference between Messrs. 3. R. Strosnider and H. I. Gregg (NRC), and members of our staff (BG&E), on January 7,1987 (b)
Letter from Mr. A. R. Thornton (BG&E), to Mr. 3. R..Strosnider (NRC), dated January 8,1987, same subject Gentlemen:
This letter is in response to a request made by you during Reference (a). During this meeting you expressed concern about the shaf t on No.12A Reactor Coolant Pump (RCP),
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and our decisions leading up to the Unit I startup. This letter explains the inspections and evaluations performed at Calvert Cliffs.
In Spring of 1986, we noticed unusual vibrations on No.12A RCP. The vibration data were investigated and the cause could not be determined because of insufficient information. An analysis was performed justifying continued operation and was reviewed by our Plant Operations and Safety Review Committee. As a result of these vibration
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Indications, problems in the industry involving RCPs, and consultation with the pump l
manufacturer, we decided to inspect No.12A RCP during the Fall 1986 refueling outage.
With the assistance of Byron-Jackson, the pump manufacturer, and Babcock and Wilcox, the pump was overhauled during the outage. The rotating assembly was removed and replaced.
The inspections of the pump case and cover revealed no dimensional Inaccuracies or indications of a problem. All of the pump bolting and drive pins were inspected, and a few bolts on the hydrostatic bearing were found to be less than their G,,i."
initial torque values.
The pump impeller was inspected and found to be in the "as-manufactured" condition.
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The pump shaii was checked as part of the RCP inspection. The shaf t was examined both visually and with liquid dye-penetrant (PT). The PT revealed thin axial cracks at the top of the ACME threads. This was in the thermal barrier region of the pump cover.
Southwest Research Institute (SwRI) was contracted to use an eddy current testing technique for determining crack depth.
SwRI found that 95Vo of the 120 indications were less than.050" in cepth, approximately 59u were in the.0$0
.060" range and one mdication was about.090" in depth. The SwRI eddy current test results were provided in Reference (b).
We also provided the eddy current cata to the pump manufacturer for determination of crack initiation and propagation mechanisms. Byron-Jackson, with Babcock and Wilcox as a consultant, performed thermal stress and fracture mechanics analyses.
The preliminary results concluded that catastrophic shaf t cracking was not credible and that the cause of the cracking wa: not due to the vibrations or vice versa. The report provided by Byron-Jackson stated that the cracks would arrest at a depth of.24". This report was also provided as an attachment in Reference (b).
The draf t written report was recently received, and has been given a cursory review. We are in the process of conducting a more c' tailed in-house review. However, based on Byron-Jackson's conclusions and recommendations and our review to date, we have concluded that the remaining RCPs are safe to operate. In the unlikely event the conclusions are wrong and a RCP shaf t should fail, the event would be bounded by the existing safety analyses contained in our UFSAR.
Our decision not to inspect additional RCPs prior to the restart of Unit I was based on several factors. First, the nature of the cracks on No.12A RCP indicates that the thermal boundary condition in the shaft / cover annular region imposed stresses on the threaded area of the shaf t.
These stresses were relieved in the form of shallow axial cracks. The thermal stress and fracture mechanics analyses performed concluded that
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the cracks will arrest and remain benign. Second, the pump manufacturer stated that l
based on the physical examination of the shaft and their analyses, returning the three
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remaining pumps to service for the next fuel cycle is a low risk. Finally, as stated j
earlier, any single failure of a RCP shaft is bounded by the accident analyses in our j
UFSAR. The failure mode is not expected to be a common mode failure. The RCPs are physically independent of each other.
I We will schedule a meeting with Byron-Jackson (now Borg-Warner) to review their report 1
in detail. We will discuss the advisability of future RCP inspections at this meeting.
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Additionally, we have conttacted the University of Virginia to determine the operating
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characteristics of the RLP and motor, including the shaf t mode shapes, shaf t loading and effects of vibration. This type of data is currently unavailable for vertical rotating machines with three bearings.
Future analyws, inspections, and overhauls will be I
performed if warranted.
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Should you have futher questions regarding this' matter, we would be pleased to discuss -
thern with.you.
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Very truly yours,
-WJL/SRC/ dim cc:
D. A. Brune, Esquire-
- 3. E..Silberg, Esquire i
A. C. Thadani, NRC S. A. McNeil, NRC-T. E. Murley, NRC
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