ML20247K293
| ML20247K293 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 05/14/1998 |
| From: | Cruse C BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9805220056 | |
| Download: ML20247K293 (3) | |
Text
o CurutEs 11. CRUNE Ilaltimore Gas and Electric Company Vice President Calven Cliffs Nuclear Power Plant Nuclear Energy 1650 Calven Cliffs Parkway Lusby. Maryland 20657 410 495-4455 l
May 14,1998 U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION:
Document Control Desk
SUBJECT:
Calvert Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Nos. 50-317 & 50-318 Containment Tendon Long-Term Corrective Action Plan
REFERENCES:
(a)
Letter from Mr. A. W. Dromerick (NRC) to Mr. C. II. Cruse (BGE),
dated January 23, 1998, Review of Containment Tendon Evaluation Report - Calvert Cliffs Nuclear Power Plant, Unit Nos. I and 2 (TAC Nos. M99880 and M99881)
(b)
Letter from Mr. C. II. Cruse (BGE) to NRC Document Control Desk, dated October 28,1997, Containment Tendon Engineering Evaluation By letter dated January 23,1998 (Reference a), you transmitted the results of your review of our October 28,1997, containment tendon engineering evaluation report (Reference b). In this letter, you stated that we "should have a long-term action plan with clearly defined and scheduled actions in place prior to restart from the Calvert Cliffs Unit No.1 Spring 1998 refueling outage." Please be advised that from the five options we considered in Reference (b), we have selected Option (3), the replacement option, which you characterized as "the most reassuring"in Reference (a). The details of our long-term plan and the completion schedule for major milestones are described below.
LONG-TERM PLAN By December 31,1998, Baltimore Gas and Electric Company (BGE) will complete research to determine nn effective method for removing as much of the old grease (Visconorust 2090-P) as practical from the tendon ducts. Removing the old grease and refilling the tendon ducts with new grease (Viscocorust 2090-P4) is expected to minimize future corrosion both by providing grease with superior corrosion inhibiting properties and by removing moisture entrained in the old grease. This research effort will concentrate on grease removal from tendon ducts that contain a
[9 tendon assembly under-load. Grease removal from tendon ducts that have had their assemblies removed should be relatively easy to accomplish.
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Document Control Desk May 14,1998 Page 2 By December 31,1999, BGE will re-inspect all of the vertical tendons previously identified as e
containing severely corroded wires, in an effort to monitor the potential for additional tendon l
wire degradation. His inspection will include the removal of the upper grease caps and a visual inspection of the button-headed wires to determine if additional breaks have occurred.
By December 31,2000, BGE will replace all severely corroded vertical containment tendons with e
new tendons. Currently, it is estimated that 63 of 202 vertical tendons from Unit I and 64 of 204 vertical tendons from Unit 2 will be replaced. All of the remaining vertical tendons will have their old grease removed to the maximum extent practical and replaced with new corrosion inhibiting grease that will encapsulate the wires and prevent corrosion. In addition, all vertical tendons will have a redesigned grease cap installed on the upper bearing plates to prevent water intrusion.
JUSTIFICATION FOR THE LONG-TERM PLAN In Reference (a), you stated that BGE "should not rely on the prediction of wire breakage through Weibull distribution based on the statistics of steam generator tube failures to make any lor.g-term corrective action decision." Our long-term plan does not rely on the statistical prediction of wire breakage. As we described in Reference (b), an exhaustive root cause analysis has concluded that tendon wire failures and corrosion problems resulted from a combination of water and moist air intrusion and inadequate initial grease coverage of wires in the void, which created a corrosive environment.
Baltimore Gas and Electric Company has implemented the following short-term compensatory actions, on both Units 1 and 2, to slow further degradation of the tendons and to ensure operability until long-term corrective actions are implemented.
- 1. Localized re-greasing has been performed just under the upper end tendon anchorhead. His area has been found to be the only region exhibiting excessive corrosion. He grease caps at the upper end of all the vertical tendons have been topped off with Visconorust 2090-P4 grease. In addition, the shim stacks under the upper anchorhead have been left with a slight gap between the shim halves. His gap facilitated the flow of heated, liquefied grease to any voids that may have existed under the upper anchorhead.
- 2. To reduce moisture intrusion, a sealant has been applied around the contacting surfaces and exposed threads of the grease cap hold-down bolts. nese hold-down bolts have been identified as being a potential moisture entry path.
- 3. All vertical tendons have been load tested to determine their current post-tensioned load. De results of the tendon lift-off(load) testing conducted on both units have demonstrated that the vertical tendon system retains a significant margin of strength over the minimum design requirement. For the margin to be reduced to the point where containment structural integrity would be a concern, significant localized loss of tendon wires would have to occur. Baltimore Gas and Electric Company believes that, as a result of Compensatory Actions (1) and (2), the potential for the loss of additional wires in the post-tensioning system has been greatly reduced.
Furthermore, the re-inspection planned for 1999 will enable us to re-evaluate the actual remaining load on each of the affected tendons.
Document Control Desk May 14,1998 Page 3 Our current schedule calls for the Unit I refueling outage to end on May 31, 1998. We trust the information provided in this letter meets your expectation. Should you have further questions regarding this matter, we will be pleased to discuss them with you.
Very truly yours,
),
}y,.
'%v CilC/GT/ dim cc:
R. S. Fleishman, Esquire
- 11. J. Miller, NRC J. E. Silberg, Esquire Resident Inspector, NRC S. S. Bajwa, NRC R. I. McLean, DNR A. W. Dromerick, NRC J. II. Walter, PSC
__.