ST-HL-AE-3451, Submits Special Rept Re Evaluation of third-yr Containment Tendon Surveillance.Tendons Which Had Voids Have Been Filled & No Evidence of Grease Leakage from Sheathing Exists

Submits Special Rept Re Evaluation of third-yr Containment Tendon Surveillance.Tendons Which Had Voids Have Been Filled & No Evidence of Grease Leakage from Sheathing Exists

ML20042F117
Person / Time
Site:	South Texas
Issue date:	05/01/1990
From:	Rosen S HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ST-HL-AE-3451, NUDOCS 9005070239
Download: ML20042F117 (5)

Text

.

. g, -

1. -.

' The Light COIttpBIly n<,mn,n u i,ong a,-> w.n<,x nm nomn,n.wxas 77oni (vi3>u28 92ii n

5/1/90 ST IIL AE 3451 File No.: CO2 10CFR50.36 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 South Texas Project Electric Generating Station' Unit 1-Docket No. STN 50 498 Special Report Regarding An' Evaluation of The Unit 1 Third Year Containment Tendon Surveillance-Pursuant to the South Texas Project Electric Generating Station.

' Technical Specifications =3.6.1.6, Houston Li hting & Power submits the attached Special Report regarding.an evaluat on of the Unit 1 third year containment tendon surveillance.

If you should have any questions on this matter, please contact Mr. C. A. Ayala at (512)-972-8628 or myself at (512) 972 7138, hku

/

S.-L. Rosen Vice Presiden Nuclear Engine ing-

.BEM/n1

Attachment:

Special Report Regarding An-Evaluation of the Unit 1 Third Year Containment Tendon Surveillance A1/042.N13 9005070239' 900501

'( { t PDR ADOCK 05000498 9-PDC

\\

-,. ~..

4;

.i

' llouston lj hting k P<nn:r Com[niny g

Attachment..

ST.HL AE-3451 Page 1 of 4 South Texas Project Electric Generating Station-Unit 1

. Docket No. STN $0 498-Special Report Regatoing An Evaluation of The Unit 1 Third Year Containment Tendon Surveillance 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 ysars L

following the initial containment structural integrity test and at 5 year H

intervals thereafter. During the performance lof the year three surveillance -

'it was-discovered that tendon filler grease voids in excess-of the L

Surveillance Requirement 4.6.1.6.le.1 maximum of 5 percent of net duct volume existed.- Compliance with-the associated action statement required restoration ~

of containment' integrity, ion and-submittal of this Special Report.which was not compromised by th of an engineering evaluat Note that voids as a result of the inspection process used. y with.the discoveries of refilling of grease was accomplished simultaneousl Ten Reactor Containment Building tendons were inspected to satisfy the=

surveillance. The tendon identification numbers and grease void' volumes were as follows:

Void Volume Tendon #

(percent of duct ~ volume)

L l

1H091-8.0%

1 l

1H127 7.6%

.l 2H039 14.3%

2H075 15.5%

l L

3H011 6.2%

3H029 6.5%-

V126 5.1%

V212 5.9%

V113

'7.1%

V247 6.8%

A1/042.N13

i

-e :

• e v

Ilouston Lighting & Power Cornpany Attachment

-ST IIL AE 3451 Page 2 of 4 The.aain 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 i

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 bet grease flow, free of air bubbles and foreign substances. AdditionclP/, for horizontal tendons routed above discontinuities

- t such as a penetration, t.he sheathing ves vented to release entrapped air during grease injectica.

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 done. 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 2090 P-4 (grease) during.inctallation where the temporary corrosion preventative material had been scraped off'and to 1pbricate the tendon for insertion into the duct.

This insured that all of tha tendon wires-were coated with corrosion inhibitor at the time of installation and maintained corrosion free through their' entire service life.

Crease 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 180'F.

Depending on the ambient temperature, shrinkage can be well in excess of 4%.

2)

Spaces txist 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 possibly worked _its way into the middle spaces of the terdon 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 l

in the previous 3%.

i L

2 A1/042.N13

,m_.

~

m

, ~

~

11ouston Ughting & Power Company Attachment ST.HL AE 3451 Page 3 of 4 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 i

can surface from suspension between the time the duct is filled and'the surveillance is performed. Additionally, air becomes-entrapped wn'.le 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 additlonal grease pumped into tho tendon duce during the surveillance.

2.

Therefore,: voids in-the range of 5.14 to 15.5% discovered'during this surveillance are reasonable.. There was.no evidence of grease.lcakage.as

. determined by erforming a visual inspection of the accessible containment surfaces and b holding the pressure for one hour:after replacing the grease, A thorough eva uation of exposed anchorage components was performed at both '

ends of the tendons and there was no evidence ^of degradation.

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 withifiller 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.

.11guld 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 expressed some concern about eliminating voids from the tendon duct due to the coefficient of expansion of the grease discussed in item 1 above, i

when the grease is-installed while containment ambient temperature is1below the upper operating range.. The duct needs some void area to allow the greaso to expand in order not to be detrimental to the tendon sheathing.

l l

L t

n A1/042.N13

(*,-4

.(

e.

llouston Lighting & Power Coinpany Attachment ST llL AE.3451-Page 4 of 4 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 2090 P-4 for the prevention of corrosion within voids as well as additives to enhance corrosion inhibiting properties of the grease. Chemical properties of the grease from samples removed during if the surveillance were tested and the results were acceptable. 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.

l l

4 A1/042.N13 1

A

.