ML20195F591

Special Rept:On 980812,addl Unseated Wires Were Discovered. Cause Is Unknown at Present Time.Util Evaluated Number of Unseated/Ineffective Wires & Determined Effect on Containment Structural Integrity.Commitments,Encl

ML20195F591
Person / Time
Site:	Braidwood
Issue date:	09/11/1998
From:	Tulon T COMMONWEALTH EDISON CO.
To:	Paperiello C NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
NUDOCS 9811200032
Download: ML20195F591 (4)

Text

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• • ' * . liraidwood Generating Station Route 01. llox H4 liruceville. II. 6040* *Xil9 Tel Hi&4 W2Hol September 11,1998  ;

l United States Nuclear Regulatory Commission l t

Attention: Carl Paperiello 801 Warrenville Road Lisle, Illinois 60532-4351

Subject:

NRC Docket Nos. 50-456 and 50-457  !

l Braidwood Nuclear Power Station Units 1 and 2 Submittal of Special Report Identifying Abnormal Containment Tendon Degradation  !

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References:

Braidwood Station Technical Specification Bases 3 / 4 .6.1.6 Containment Vessel StructuralIntegrity NRC Code of Federal Regulations,10CFR 50.55a Codes and Standards ASME Section XI Boiler and Pretsure Vessel Code, Subsection IWL, 1992 Edition with the 1992 Add mda The Braidwood Technical Specifications require a Special Report be provided to the Commission within 30 days upon die identification of any abnormal degradation of the containment structural integrity beyond the acceptance criteria. It is the purpose of this letter to transmit a Special Report summarizing the results of a recent inspection of the containment tendons. An Engineering Evaluation will be produced in accordance with 10CFR50.55a and ASME Section XI, Subsection IWL, and included in the ISI Summary Report in accordance with IWA-6000 within 90 days following the completion of AIR 07.

During preparation for the Steam Generator Replacement Outage (AlR07), sheathing for Unit 1 Containment Hoop Tendon 65CB was breached while drilling for anchor bolts for the temporary construction elevator. A Bechtel Nonconformance Report (NCR # BD 98-006) was generated to document this breach. As part of the NCR disposition, the grease cans at each end of the teadon were removed and the tendon anchorages examined. This examination revealed that 6 wires were unseated and therefore ineffective. This differed t from the installed condition records, which identified only two wires as ineffective. \

The immediate corrective action was to evaluate the number of unseated / ineffective wires and determine their effect on the containment structural integrity. This evaluation demonstrated that the tendon capacity is adequate to maintain containment structural integrity. Braidwood will perform future monitoring of this tendon to assure that no y 9P further degradation occurs. Attached is the Summary Report to address the issue.

j 9811200032 980911 PDR S ADOCK 05000456 PDR A t'nkom compan3 d '

4 Document Control Desk September 11,1998 Page 2 -

l Comed is committing to the following actions:

The development of a reinspection plan, which is being tracked by NTS Item # 456-201-98-CAQS02140. Any other actions described in this submittal represent intended or planned actions by Comed and are being described for the NRC's information and are not regulatory commitments.

Sincerely, thy J.Tulon

' e Vice Preeident raidwood Nuclear Generating Station Attachent l

cc: Steward Bailey-Braidwood Project Manager-NRR C. J. Phillips-Senior Resident Inspector-Braidwood F. Niziolek-Office of Nuclear Safety-IDNS nrcS8057tjt. doc I

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Special Report Descrintion of Potential Derradation and Condition of the Tendon 61GB During preparation for the Steam Cenerator Replacement Outage (AIR 07), sheathing for Unit 1 Containment Hoop Tendon 65CB was breached while drilling for anchor bolts for the temporary construction elevator. A Bechtel Nonconfonnance Report (NCR # BD-98-006) was generated to document this breach. De depth of drilling was such that tendon wire would not have been impacted by the drill bit-However, as pan of the NCR disposition, grease cans were required to be removed at each end of the tendon for inspection to verify number of unseated wires. This inspection was performed as a Level !!!

VT 1 Examination, and revealed that 6 wires were unseated, and therefore ineffective. This is contrary to the prior condition, where only two wires were identified as ineffective. The discovery of the additional unseated wires occurred on August 12,1998.

E':cortma Reauirements Braidwood Station Technical Specification 6.9.1.11 states:" Any abnormal degradation of the containment structure detected during the tests required by the Containment Vessel Structural Integrity Program shall be reported to the NRC v ithin 30 days. The report shallinclude a description of the tendon condition, the condition of the concrete (especially at the tendon anchorages), the inspection procedures, the tolerance on cracking, and the corrective actions taken."

The Code of Feder:1 Regulations,10CFR 50.55a,. Codes and Standards b(E) states "For Class CC applications, the licensee shall evaluate the acceptability ofinaccessible areas that could indicate the presence of or result in degradation to such inaccessible areas. For each inaccessible area identified, the licensee shall provide the following in the ISI Sumniary Repon required by IWA-6000: (1) A description of the type and estimated extent of degradation, and the conditions that led to the degradation:"

Braidwood considers an increase in the number ofineffective wires in a tendon as Abnormal Degradation.

Results of Visual Examination:

As required by the disposition of the NCR, Bechtel Quality Control performed an inspection of both tendon end anchorages for horizontal tendon 65CB. This was subsequently followed up by an independent inspection by a Level 111 VT-1 inspector from the Braidwood Station for the field end (B buttress), which provided confirmation of the Bechtel inspection. The inspections revealed a total of 6 unseated / ineffective wires at the B Buttress, and no unseated / ineffective wires at the C Buttress. The inspection at the B Buttress was contrary to the prior inspection which documented only two unseated wires.

Potential Causes of

Dearadation:

The cause of the increase from two to six unseated / ineffective wires at the B Buttress on horizonta 65CB is unknown at this time. This condition is considered an anomaly, based on the overall post-tensioning system inspection program results at the Braidwood Station. Other inspections performed in parallel with horizontal tendon 65CB for the Steam Generator Replacement Project provided consistency between current inspections and previous inservice inspections and original construction documentation.

' The twd wires with the greatest protrusion are consistent with those shown unseated during initial inspections.

I Corrective Actions Taken:

The immediate corrective action was to evaluate the number of unseated / ineffective wires and determin their effect on the containment structuralintegrity. This evaluation was documented in

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a Calculation 5.2.2-BRW 98-0770 S, which demonstrates that the tendon capacity is adequate.

Nature. Extent. and Freauency of Additional Exams-A Braidwood will perfonn future monitoring of this tendon to assure that no further degradation occurs. The development of the reinspection plan is being tracked by NTS item # 456-201 98-CAQS02140.

Accentability of the Concrete Containment Without Renair:

Although degradation of the tendon capacity has occurred, it has been demonstrated by analysis that the overall structural integrity of the post tensioning system and the concrete containment has not been compromised.

design function.

T here is no impact on operability, and the post tensioning system continues to perform its 9

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