ST-HL-AE-4064, Special Rept:Discovered That Tendon Filler Grease Voids Exceeded Surveillance Requirement 4.6.1.6.1.d.2 Max of 5% Net Duct Vol.Caused by Spaces in Tendon Bubble.Adequate Grease Protection Exists for Tendons

Special Rept:Discovered That Tendon Filler Grease Voids Exceeded Surveillance Requirement 4.6.1.6.1.d.2 Max of 5% Net Duct Vol.Caused by Spaces in Tendon Bubble.Adequate Grease Protection Exists for Tendons

ML20095G411
Person / Time
Site:	South Texas
Issue date:	04/22/1992
From:	Jump W HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ST-HL-AE-4064, NUDOCS 9204290003
Download: ML20095G411 (5)

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The Light

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c o mp a ny South Texas Project Electric Generating P.O.Station A. 289 Wadsworth, Texas 77 483 llouston Lighting & Power April 22, 1992 ST-IIL-AE-4064 File No.: G02 10CFR50.36 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 South Texas Project Unit 1 Docket No. STN 50-498 Special Peport Regarding An Evaluation of The Unit i Fif th Year Containment 'lendon Surveillance Pursuant to the South Texas Project Electric Generating Station Technical Specifications 3.6.1.6, Houston Lighting & Power submits the attached Special Report regarding an evaluation of the Unit 1 fifth' year containnent tendon surveillance.

If you should have any questions on this matter, please contact Mr. C. A. Ayala at ($12) 972-8628 or me at (512) 972-7205.

lawt *f William J. Jun Manager Nuclear Licensing JMP/12

Attachment:

Special Report Regarding An Evaluation of the Unit 1 Fifth Year Containment Tendon Surveillance 8

SWEP\92-098.002 VI

/\ Subsidiary of Houston industries Incorporated l 9204290003 920422 PDR ADOCK 05000498 S PDR

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L South Texas Project Electric Generating Station .-

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. Regional-Administrator,-Region IV Rufus S. Scott Nuclear Regulatory Commission Associate General-Counsel-611 Ryan Plaza Drive,. Suite 400 Houston-Lighting & Power Company Arlington,;TX- 76011- P. O. Box 61867 George Dick, Project Manager

.U.S. NuclearzRegulatory Commission INPO

= Washington, DC- 20555 Records Center 1100' Circle 75 Parkway.

LJ. I. Tapia .

-Atlanta, GA 30'339-3064

-Senior Resident Inspector- .

c/o U._-S.-Nuclear Regulatory Dr. Joseph M.. .Hendrie 1 Commission 50 Bellport Lane

P . -' O . Box 910 Bellport, NY 11713

-Bay City, TX 77414-D. K. Lacker

~- J . R.1Newman, Esquire ~

Bureau of Radiation Control Newman & Holtzinger, P.C. Texas Department of Health Ll615-L Street,-N.W.- 1100 West 49th Street Washington, DC ;20036 Austin, TX 78756-3189

-- D. - E . - Ward /T . c M . Puckett_  : (

' Central Power ~and Light Company-P..O.cBox 2121' Corpus-Christi,LTX 78403

-J. C.;.Lanier/M. B. Lee -

City of Austin _

Electric Utility Department

- P . O . . - Box -1,.0 8 8 -

Austin, TX 78767.

K.fJ. Fiedler/M. T.-Har'dt City Public Service Board-

-P. O.-Box 1771-San Antonio, TX 178296 s.

Revised 10/11/91 L4/NRC/-

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Attachment ST-HL-AE-4064 Page 1 of 3 South Texas Project Unit 1 Docket No. STN 50-498 Special Report Regarding An Evaluation of The Unit 1 Fifth Year Containment Tendon Surveillance Technical Specification 4.6.1.6 rcquires 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 fifth year surveillance it was discovered that _ tendon filler grease voids in excess of the Surveillance Requirement 4.6.1.6.1d.2 maximum of 5 percent of not duct volume L existed. Compliance with the associated action statement required -

L restoration of containment structural integrity, which was not L compromised by the_ voids, performance of an engineering evaluation and submittal of this Special Report. Note that refilling of grease is accomplished-simultaneously with the discoveries of voids as a result of-the inspection process used.

Ten Reactor Containment Building tendons are required to be inspected for.the surveillance. At this time, the Unit 1-fifth

_ year surveillance is not complete. To date, two containment tendon '

inspections have been completed with grease voids of 6.2% and 7.2%.

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 and continue pumping 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 -Js 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 alth grease over its entire length including filling the grease caps, thus encasing the tendon-end anchorages.

'In addition, the tendon wires were ccated 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 2090 p-4 (grease)

_ during installation where the temporary corrosion preventative material had been scraped off and to lubricate the tendon for SREP\92-098.002

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Attachaent ST-HL-AE-4064 Page 2 of 3 insertion into the duct. This insured 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.

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

The grease (Visconorust 2090 P-4) has a coefficient of expansion which yields an expansion of about 1% per 20'F.

Initial installation temperatures are typically greater than 18 0'F . Depending on the ambient temperature, l shrinkage can be in excess of 4%.

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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 dif ficult to fill all spaces between the wires during initial installation because the tendon is at ambient temperature. As the hot grease surroundtd 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 dact 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 initial installation process took care to eliminate duct voids as much as possible; however, it does introduce air into the duct during the pumping of the grease. 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 ent) :iped while the grease _is pumped from one end of the s: sathing 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 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 SREP\95098.002

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Attachment ST-HL-AE-4064 Page 3 of 3 visual examination of exposed anchorage components was performed at both ends of the tendons and there was no evidence of degradation.

. previously stated, the tendon wires and anchorage system were coated with storage or filler grease prior to installation and the ducts were complctely 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 not included in this surveillance is maintained.

Previous surveillances at other plants which have similar installation of tendons have shown that the existence of grease voids in the ducts have not had adverse affects on the tendons.

Additionally, the manufacturer of the grease has suggested against eliminating voids from the tendon duct due to the coefficient of expansion 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 ins *alled throughout the entire length of the tendon ducts and grease sverage was assured.

The-grease will adhere to the tendon and protect the wires from corrosion. There is a vapor phase inhibitor in the Visconorust 2090-P-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 grease leakage is evident, therefore, containment integrity is assured.

HL&P expects that the remaining tendon inspections will result in grease voids similar to the tendon voids experienced in previous surveillances. If it is determined that an abnormal degradation of the containment building exists, then additional information will be provided in a supplemental report to the Commission.

SREP\92 098.002