ML20149H727
| ML20149H727 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 07/18/1997 |
| From: | Tulon T COMMONWEALTH EDISON CO. |
| To: | Beach A NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| Shared Package | |
| ML20149H729 | List: |
| References | |
| NUDOCS 9707250141 | |
| Download: ML20149H727 (5) | |
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T o,ommnwehh FAvm Conhunf 3nidwem! tkoeraung Mation Ron:eal.Cox M a
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July.18,1997 Mr. A. B. Beach NRC Regional Admmistrator, Region III United States Nuclear Regulatory Commission 801 Warrenville Road i
Lisle, Illinois 60532 - 4351
Subject:
Braidwood Nuclear Power Station Unit 2
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NRC Docket No. 50-457 g
Special Report Identifyirg Abnormal Containment Tendon Degradation References Braidwood Station Technical Specification Bases 3/4 6.1.6 Containment Vessel StructuralIntegrity
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- The Braidwood Technical Specifications require that upon the identification of any abnormal i
degradation of the containment structuralintegrity below the acceptance criteria that an engineering evaluation be performed and a special report provided to the Commission within 15 days. It b the purpose of this letter to transn.it such a report summarizing the findings i
resulting from a recent inspection of the containment tendons.
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On July 1L P 7 during the annual In Service Inspection (ISI) of tendons, Braidwood Unit 2 containmc.
foop Tendon H4ED was conservatively determined to be in a condition of abnormal degradation, in that a larger quantity of protruding and broken tendon wires were found than was originally identified during station construction.-
Attached is a summary of the report, the required engineering evaluatica, and the corrective actions being taken to address this issue.
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' ' ', iIfyou have any, questions please contact T. W Simpkin, Regulatory Assurance Supeivisor at
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1 raidwood Station Manager-
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A.' B. Beach, Region 111 G. F. Dick, Project Manager, NRC C.;J. Phillips, Sr. Resident inspector, Braidwood i
F. Nizio' lek, Div. of Engr., IDNS 6
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Special Report Summary y
Description of Abnormal Deuradation:
Tendon H4ED 'was included in the 1997 containm' nt te. don water and visual inspection
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e scope. These inspections are performed on an annual frequency to identify free water.
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. intrusion _and to perform chemical analysis on' the sheathing filler to ensure it continues to protect the tendons as designed. The inspections were performed.under Braidwood NWR i
,970056944 and per approved contractor procedures.!' The contractor employed to perform
' the inspections was Precision Surveillance Corporation.
I The inspections _were performed by a qualified Quality Control inspector. The subject tendon had'not been examined since the initial pre-se vice examinations. The degradation involved the identification of a larger quantity of protruding / broken wires than originally documented.
On Nov.10,1982, the original installing contractor identified 4 broken and 4 unseated wires on the shop end of the tendon and 3 broken and 4 unseated wires on the field end. The
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4 original installing contractor was not required to take measurements to determine if the j
button heads were seated in the anchor head.
A visual inspection was the only method 4
employed.
l On July 1,1997 Precision Surveillance Corporation identified 11 protruding wires on the -
shop and. The current procedures require that measurements be taken to determine if button heads are properly seated. The measurements for wire protrusion ranged from 0.1" to 4.1"
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The three lowest values are 0 I", 0.15", and 0.25" In order to identify the scope of j
' degradation, the contractor was requested to perform an inspection of the field end of the
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tendon. This inspection activity was completed on July 8, revealing 8 protruding wires and 1 y
W missing button head. The measurements for the protruding wires ranged from 0.1" to 3.5" The two lowest values were 0.1" and 0.15".
After comparing the results of the inspections i
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. performed by the installing contractor to those performed by Precision Surveillance Corporation and after consulting the Architectural Engineer, it was conservatively
. determined that the tendon may have further degraded since plant start up.
This 3_
' determination was made on July 11, 1997. Free water was identified during the recent
-inspection. Seventy two ounces was collected from the shop end and 36 ounces was collected from the field end. Grease and v>ater samples are being analyzed to determine if the free water degraded the protection capabilities of the grease.
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No concrete ' amage or cracks d
The remainder of the inspection attributes were acceptable.
were identified.in the area around the bearing plates. No reportable corrosion was identified and the wire button heads were determined to be in excellent condition. No pitting was identified on any of the components. The tendons above and below tendon H4ED, (H3ED and H5ED ) were inspected in the summer of 1996. No degradation was identified.
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b Reportina Reauirements; I
-Section ' C.8 ' of Proposed Revision 3 to Regulatory Guide ~ ~.35, - Recorting ' to the j
1 Commission:
i The reportable conditions of regulatory position C.7.1.3, C 7.1.4, C.7.3, or C.7.4 could l
indicate possible abnormal degradation - of the containment structure (a boundary designed to contain radioactive materials). ' Any such condition should be reported to the Conunission in accordance with the recom. mended reporting program of Regulatory
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. Guide 1 16," Reporting of Operating Information Appendix A Technical
. Specifications "
Braidwood Technical Specification.6.6.1.6 Containment Systems, Action Statement 3.6.1.6b.
"With any abnormal degradation of the structural integrity other than ACTION at a level below' the acceptance criteria of Specifications 4.6.1.6.1, 4.6.1.6.2, and 4.6.1.6.3, restore the containment vessel to the required level of integrity within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and
- perform an engineering evaluation of the containment and provide a special report to the Commission within 15 days in accordance with Specification 6.9.2 or be in HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />." Technical Specification section / 6.1.6.2 of the Surveillance Requirements, specifies the inspection requirements for tendon end anchorage and adjacent concrete j
surfaces.
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4.6.1.6.2 End Anchorage and Adiacent Concrete Surfaces.
"The structural integrity of the end anchorage of all tendons inspected pursuant to Specification 4.6.1.6.1 and the adjacent concrete surfaces shall be demonstrated by determining through inspection that no apparent changes have occurred in the visual appearance of the end anchorage since last inspected. Inspections of the concrete shall i-be performed during the containment vessel tendon tests (reference 4.6.1.6.1)",
i This requirement entails a complete visual inspection of the tendon anchorage and the surrounding concrete. The anchorage includes the anchorage head, wire buttonheads, bushing, shirns, and bearing plate. The scope of the concrete exam includes an area one foot beyond the edge of the bearing plate.
E Braidwood Technical Specification Bases section 3/4 6.1.6, third paragraph states, "The required Special Reports from any engineering evaluation of containment abnormalities i
shall include a descriptionLof the tendon condition, the condition of the concrete 1.
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(especially-. at the tendon anchorage), the inspection procedure, the toleiance on cracking, the results of the engineering evaluation and the corrective actions taken. "
Corrective ~ Actions Taken:
' An Engineering Evaluation was performed on the Unit 2 Containment Structure. This evaluation determined that the Unit 2 containment structure remained capable of performing
- its. intended design function with Tendon' H4ED in the existing condition. The containment
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was determined to.be operable and not degraded and the stress levels remain below the allowable. This evaluad, a is included in this report. The tendon has been restored and the i
grease canisters filled with new grease, 3 Operations Shift Supervision was made aware of the problem at approx.1400 on July 11,1997.
Potential Causes ofDegradation:
i The actual cause for the apparent additional degradation is unknown at this time. The Braidwood Engineering Department will further evaluate the condition 'for root cause determination. The evaluations will include but 'not be limited to researching the differences between the construction inspection techniques and those implemented during the recent inspection to determine if additional degradation has tmly occurred.
Additional inspections on tendon H4ED will be performed to monitor the apparent additional degradation. The grease cans on H4ED will be removed and the anchorage will be inspected annually until the aext scheduled physical test. Unit e tendons are currently scheduled for physical-testing in 2001. In the event additional degradation is identified, additional evaluations and augmo u testing including a continuity test on the defective wires will be
_ performed as required on tendon H4ED. This tendon will be tested in addition to the normal physical testing scope during the next scheduled physical surveillance.
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