NOC-AE-000250, Special Rept:Discovered That Tendon Filler Grease Voids in Excess of SR Max of 5% of Net Duct Vol Existed.Caused by Shrinkage of Grease & Spaces Existing Between Wires in Tendon Wires.Installed Grease Throughout Tendon Ducts

Special Rept:Discovered That Tendon Filler Grease Voids in Excess of SR Max of 5% of Net Duct Vol Existed.Caused by Shrinkage of Grease & Spaces Existing Between Wires in Tendon Wires.Installed Grease Throughout Tendon Ducts

ML20237B536
Person / Time
Site:	South Texas
Issue date:	08/12/1998
From:	Thomas S HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NOC-AE-000250, NOC-AE-250, NUDOCS 9808190025
Download: ML20237B536 (5)

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August 12, 1998 NOC-AE-000250 File No.: G02 10CFR50.36 STI: 30682749 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 )

South Texas Project Unit 1 Docket No. STN 50-498 Special Report Regarding a Evaluation of the Unit 1 Tenth Year Containment Tendon Surveillance Pursuant to South Texas Project Technical Specifications 3.6.1.6 and 6.9.2, the STP Nuclear Operating Company submits the attached Special Report regarding an evaluation of the Unit I tenth year Containment tendon surveillance.

If you have any questions on this matter, please contact Mr. K. J. Taplett at (512) 972-8416 or me at (512) 972-7162.

S. E. Thomas Manager, Design Engineering  ;

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Attachment:

Special Report Regarding an Evaluation of the Unit 1 Tenth Year Containment )

Tendon Surveillance.

9808190025 980812 PDR ADOCK 05000498 S PDR, c:\wp\nl\nrc-wk\srep-98W250. doc

. .. NOC-AE-000250 File No.: G02 Page 2 Ellis W. Merschoff Jon C. Wood

' Regional Administrator, Region IV Matthews & Branscomb

- U. S. Nuclear Regulatory Commission One Alamo Center 611 Ryan Plaza Drive, Suite 400 1% S. St. Mary's Street, Suite 700 Arlington, TX 76011-8064 - San Antonio, TX 78205-3692 Thomas W. Alexion Institute of Nuclear Power Project Manager, Mail Code 13H3 Operations - Records Center 4 U. S. Nuclear Regulatory Commission 700 Galleria Parkway I Washington, DC 20555-0001 Atlanta, GA 30339-5957 David P. Loveless Richard A. Ratliff ,

Sr. Resident Inspector - Bureau of Radiation Control c/o U. S. Nuclear Regulatory Commission Texas Department of Health P. O. Box 910 1100 West 49th Street Bay City, TX- 77404-0910 Austin, TX 78756-3189 J. R. Newman, Esquire D. G. Tees /R. L. Balcom -

Morgan, Lewis & Bockius Houston Lighting & Power Co.

I800 M. Street, N.W. P. O. Box 1700 Washington, DC 20036-5869 Houston,TX 77251 M. T. Hardt/W. C. Gunst Central Power and Light Company City Public Service ATTN: G. E. Vaughn/C. A. Johnson P. O. Box 1771 P. O. Box 289, Mail Code: N5012 San Antonio,TX 78296 Wadsworth,TX 77483 A. Ramirez/C. M. Canady U. S. Nuclear Regulatory Commission City of Austin Attention: Document Control Desk Electric Utility Department Washington, D.C. 20555-0001 721 Banon Springs Road Austin,TX 78704  !

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Attachment NOC-AE-000250 File No.: G02 Page 1 of 3 Special Report Regarding an Evaluation of  ; '

the Unit 1 Tenth Year Containment Tendon Surveillance i

Technical Specification 4.6.1.6 requires that the structural integrity of the Containment tendons be demonstrated at the end of 1,3, and 5 years following the initial Containment structural integrity test and at 5 year intervals thereafter. During the performance of the Unit I tenth year surveillance it was discovered that tendon filler grease voids in excess of the Surveillance Requirement 4.6.1.6.1 d.(2) maximum of 5 percent of net duct volume existed.

Six Reactor Containment Building tendons were inspected for the surveillance. Grease voids in excess of 5% were present in 2 out of the 6 tendons. The voids for the two tendons were 11.8%

and 12.4%. It should be noted that refilling of grease is accomplished simultaneously with the discoveries of voids as a result of the inspection process.

The main purpose for the sheathing filler material grease is to provide long-term corrosion protection for the tendon wires and anchorage components. Initial installation of the sheathing filler material involved pumping the heated grease into the tendon sheathing (duct) from one end of the horizontal tendon until the hot grease (temperature > congealing point) is ejected from the opposite end of the horizontal tendon with a continuous stream of hot grease flow, free of air bubbles and foreign substances. Additionally, for horizontal tendons routed above discontinuities such as a penetration, the sheathing was vented to release entrapped air during grease injection.

Filling the vertical tendons is basically the same, except pumping is performed from both ends of the tendon until the hot grease is ejected from the high point vent located at the apex of the dome.

This installation procedure assured that the tendon had been thoroughly coated with grease over its entire length including filling the grease caps, thus encasing the tendon-end anchorages. In addition, the tendon wires were coated with a temporary corrosion preventative, Visconorust 1601-Amber, after fabrication for storage and handling of the tendon coil. Furthermore, the tendon wires were hand-coated with Visconorust 2090P-4 (grease) during installation where the temporary corrosion preventative material had been scraped off and to lubricate the tendon for insertion into the duct. This ensured that all of the tendon wires were coated with corrosion inhibitor at the time of installation and maintained corrosion-free through their entire service life.

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. NOC-AE-000250 t File No.: G02 Page 2 of 3 l

. Grease voids are expected in the tendon ducts. The percent voids can be in excess of the 5% limit l

for several reasons'which are explained below:

1) Shrinkage of grease occurs since the grease was initially injected at a temperature between 150 and 250 degrees F. The grease (Visconorust 2090P-4) has a coefficient of expansion which yields an expansion of about 1% per 20 degrees F. Initial installation temperatures are typically greater than 180 degrees F. Depending on the ambient temperature, shrinkage can be in excess of 4%.

2)- Spaces exist between the wires in the tendon bundle. The tendon is made up of 186 tightly wound wires. This condition makes it very difficult to fill all spaces between the wires during initial installation because the tendon is at ambient temperature. As the hot grease surrounded the tendon, it is possible that it worked its way into the middle spaces of the tendon bundle. These spaces make up a minimum of 3% of the net duct volume for a given tendon. In addition, this migration of grease may occur in areas where the tendon is in contact with the sheathing, which is not considered in the previous 3%.

3) The process of pumping grease into the duct entrains air inside the grease. This entrained air can surface from suspension between the time the duct is filled and the surveillance is -

performed. Additionally, air becomes entrapped while the grease is pumped from one end of the sheathing to the other end, which can be as long as 600 feet. This introduction of entrained and entrapped air can account for a significant percentage of the additional grease pumped into the tendon duct during the surveillance.

Therefore, voids of 20% or less are considered reasonable. There was no evidence of grease leakage as determined by performing a visual inspection of the accessible Containment surfaces and by holding the pressure for one hour after replacing the grease. A visual examination of exposed anchorage components from the surveillance tendons as well as the wires removed from the detensioned tendons has shown no evidence of degradation. i As previously stated, the tendon wires and anchorage system were coated with storage or filler grease prior to installation and the ducts were completely filled with filler material from one end of the tendon to the other at initial installation. Special consideration was given to the formulation of the filler grease as the original specification required it to have a liquid vapor phase inhibitor for the prevention of corrosion within the voids. The filler material was also required to contain additives to enhance the corrosion-inhibiting and wetting properties, as well as to form a chemical bond with the tendon steel. Therefore, the corrosion protection for the tendons is maintained.

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Attaciunent i NOC-AE-000250 File No.: G02 Page 3 of 3 Additionally, the manufacturer of the grease has suggested against eliminating voids from the tendon duct due to the coefficient of exparsion of the grease discussed in item 1 above, when the grease is installed while Containment ambient temperature is below the upper operating range.

The duct needs some void area to allow the grease to expand in order not to be detrimental to the tendon sheathing.

In conclusion, grease was initially installed throughout the entire length of the tendon ducts and grease coverage was assured. The grease will adhere to the tendon and protect the wires from corrosion. There is a vapor phase inhibitor in the Visconorust 2090P-4 for the prevention of corrosion within voids as well as additives to enhance corrosion-inhibiting properties of the grease. The tendons which had voids have been filled and there is no evidence of grease leakage from the sheathing. The remaining tendons in the containment structure are adequate in their existing condition since minimum grease coverage still exists to provide corrosion protection for {

the post-tensioning system. Adequate grease coverage exists for the tendons to maintain corrosion protection and no significant grease leakage is evident. Therefore, Containment integrity is assured.

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