ML20154S825

Submits Response to NRC for Addl Info Requested During Course of 980930 Telcon Re Containment Tendon long-term Corrective Action Plan

ML20154S825
Person / Time
Site:	Calvert Cliffs
Issue date:	10/23/1998
From:	Cruse C BALTIMORE GAS & ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9810280104
Download: ML20154S825 (6)

Text

Wd CHARLES II. CROSE Bahimore Gas and Electric Company Vice Pree ient Calvert Cliffs Nuclear Power Plant Nuclear energy 1650 Calvert Laffs Parkway Lusby. Maryland 20657 410 495-4455 October 23,1998 U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION:

vocument Control Desk

SUBJECT:

Calvert Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Nos. 50-317 & 50-318 Re;ponse to Verbal Request for Additional Information Regarding Containment Tendon Long-Term Corrective Action Plan

REFERENCES:

(a)

Letter from Mr. A. W. Dromerick (NRC) to Mr. C.11. 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 froin Mr. C. H. Cruse (BGE) to NRC Document Control Desk, dated May 14.1998, Containment Tendon Long-Term Corrective Action Plan (c)

Letter from Mr. C. II. Cruse (BGE) to NRC Document Control Desk, dated August 20, 1998, Response to Verbal Request Regarding Containment Tendon Long-Term Corrective Action Plan (d)

Letter from Mr. C.11. Cruse (BGE) to NRC Document Control Desk, dated October 28,1997, Containment Tendon Engineering Evaluation In response to the NRC requirement contained in Reference (a), by letters dated May 14 and August 20,1998, we provided our long-term corrective action plan regarding the Calvert Cliffs Nuclear Power Plant Units 1 and 2 Containment tendon degradation (References b and c, respectively). On September 30,1998, we held a teleconference with the NRC staff to discuss the long-term corrective action plan provided in References (b) and (c). This letter provides the additional information requested by the staff during the course of the September 30,1998, teleconference.

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9810200104 981023

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• ' Docum:nt Control Desk October 23,1998 Page 2 NRC Reauest No.1 Provide a tabulation of the updated Containment vertical tendon wires' failure historyfor both Units l

(Table 4 ofAttachment 1, Reference d), and a summary ofbroken wiresfor Unit 2 vertical tendons.

BGE Response Attachment (1) to this letter contains the requested information.

NRC Reauest No. 2 The long-term action plan (Reference b) addresses the action youplan to take on the problems related to the vertical tendon wire corrosion in Units 1 and 2. In the earlier inspections (1985,1991,1997), you had experienced low prestressingforce measurements, and reddish brown color on stressing washers of some of the sampled hoop tendons (Reference d), Root causes of thesefindings were not identified. In view of thefact that some of the hoop tendons (particularly those below grade) are subjected to water intrusion and may have unprotected wires, provide information as to why the hoop tendons in both units should not be included in the long-term corrective action plan.

BGE Response As described in detail in Reference (d), we have determined that the root cause of vertical tendon wire corrosion was inadequate design of the tendons' upper end stressing washer / shim stack arrangement, coupled with a poor end cap (grease can) design. These contributed to a condition where the tendon wires directly below the upper stressing washer were not adequately coated during initial greasing, and the poor end cap design allowed intrusion of water / moist air from the outside environment. This combination created a corrosive environment that, in turn, caused wire failure either by general corrosion or by hydrogen-induced cracking.

Both the hoop and dome tendons have the same grease can design as the vertical tendons. The dome tendon grease cans are oriented such that rainwater is unlikely to pool on the grease can and leak in.

They are also shielded from the weather by siding. Therefore, a failure mechanism requiring substantial water leakage is unlikely to affect the dome tendons. The hoop tendons have the potential to be affected by water in leakage. Several hoop tendons are below ground level and have been submerged for periods of time during plant history. To determine if these hoop tendons have been affected by in-leakage, they were visually inspected. That inspection revealed no abnonnal degradation or corrosion of the tendons. Since these tendons were found to have no corrosion, it is unlikely other hoop tendons will be affected. The hoop and dome tendons are also oriented so that a void would not form immediately below the stressing washer since the stressing washer surfaces are not horizontal. With adequate grease coverage, BGE believes the potential for corrosion attack is minimal. The fact that no corrosion was observed on vertical tendon wires at elevations lower than 6.5 inches below the bottom of the stressing washer, where the wires were immersed in grease in all cases, is evidence that adequate grease coverage prevents corrosion.

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Docum nt Control Desk October 23,1998 Page 3 8

0 Should you have further questions regarding this matter, we will be pleased to discuss them with you.

Very truly yours, 7

d gg 64 w y

CilC/GT/ dim

Attachment:

(1) Table (1)- Updated Vertical Tendon Wires Failure liistory-Unit 1 & 2, Table (2)- Summary of Unit 2 Broken Vertical Tendon Wires cc:

R. S. Fleishman, Esquire

11. J. Miller, NRC J. E. Silberg, Esquire Resident inspector, NRC S. S. Bajwa, NRC R.1. McLean, DNR A. W. Dromerick, NRC J. II. Walter, PSC i

l ATTACHMENT (1) m 1

TABLE (1) - UPDATED VERTICAL TENDON WIRES FAILURE HISTORY - UNITS 1 & 2 TABLE (2) -

SUMMARY

OF UNIT 2 BROKEN VERTICAL TENDON WIRES Baltimore Gas & Electric Company Docket Nos. 50-317 and 50-318 October 23,1998

l o

ATTACHMENT (1)

~

RESPONSE TO VERBAL REQUEST FOR ADDITIONAL INFORMATION REGARDING CONTAINMENT TENDON LONG-TERM CORRECTIVE AcrION PLAN Table (1) l Updated Vertical Tendon Wires Failure History - Unit 1 & 2 Sample Size Tendons Unit Surveillance Year (Number of with Failed Failed wires Tendons)

Wires 1

1 year 1974 5

0 0

1 3 year 1976 6

0 0

1 5 year 1978 6

1 2*

1 10 year 1984 3

0 0

1 15 year 1991 3

0 0

1 20 year 1997 202 19 117 2

1 year 1977 5

0 0

2 3 year 1979 5

0 0

2 5 year 1982 5

0 0

2 10 year 1985 5

1 1**

2 15 year 1991 3

0 0

2 20 year 1997 204 27 102 l

l 1

ATTACHMENT (1)

RESPONSE TO VER!AL REQUEST FOR ADDITIONAL INFORMATION REGARDING CONTAINMENT TENDON LONG-TERM CORRECTIVE ACTION PIAN Table (2)

Summary of Unit 2 Broken Vertical Tendon Wires Tendon

1. Indeter- #During La ratory Wmal Exam g

Field Visual Exam Results Broken Ductile Brittle minate lift Observations J

l 12Vi1 1

1 heavy corrosion, no grease 2

12V17 1

1 1

extreme corrosion, no grease ductile-fresh break 3

12V18 1

1 1

extreme corrosion, no grease ductile-fresh break l

4 23V6 1

1 extreme corrosion, film coat ofgrease 5

23Vl9 12 9

3 9

extreme corrosion, no grease, old, very corroded, indeterminate moisture or ductile fresh break aner lift-off 6

23V22 1

1 1

extreme corrosion, no grease ductile-fresh break 7

23V25 1

1 i

extreme corrosion, no grease, ductile-fresh break moisture 8

23V28 5

5 extreme corrosion, no grease old, very corroded, indeterminate 9

34V23 1

1 extreme corrosion, little dried old hard grease, moisture 10 34V3 2

2 heavy corrosion, no grease, moisture 11 45V19 1

1 heavy corrosion, no grease 12 45V25 13 7

6 7

extremely heavy corrosion, very old, probably ductile but no grease indeterminate or fresh ductile aner lift-off 13 45V33 1

1 1

extreme corrosion, hard dried ductile-fresh break grease 14 56V11 1

1 heavy corrosion, no grease 15 56V13 12 12 extreme corrosion, no grease, moisture 16 56V22 9

9 extreme corrosion, no grease, old I

moisture j

17 56V24 8

8 extreme corrosion, little grease, moisture 18 56V25 2

2 extreme corrosion, partial grease 19 56V27 9

9 extreme corrosion, no grease old 20 56V29 4

4 4

extreme corrosion, no grease i very thin - ductile fresh break j

ductile 21 56V32 3

1 2

1 extreme corrosion, little dark old, very corroded hard dried grease, moisture possible or fresh ductile after lif1-l off I

22 56V4 1

1 1

extreme corrosion, no grease, ductile-fresh break i

moisture i

23 61V13 4

4 4

extreme corrosion, no grease ductile-fresh break 24 61V17 5

2 3

2 extreme corrosion, no grease old, very corroded, indeterminate or fresh ductile after lift-off j

25 61Vl9 1

1 light corrosion, small amount of grease 26 61V28 1

1 1

extreme corTosion, no grease 27 61V34 1

1 i

extreme corrosion, no grease ductile-fresh break i

Totals 102 34 48 20 34 2