ML20247R071

Special Rept 89-10:on 890810,fifth-yr Inservice Containment Vessel Tendon Surveillance Failure Identified.Caused by Void Existing within Tendon Duct Boundary.Future Tests Will Monitor Containment to Detect Any Potential Degradation

ML20247R071
Person / Time
Site:	Callaway
Issue date:	09/14/1989
From:	Blosser J UNION ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
89-10, ULNRC-2074, NUDOCS 8909290170
Download: ML20247R071 (8)

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CMlaway Plant d

September 14, 1989 U. S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555 ULNRC-2074  ;

Gentlemen:

DOCKET NUMBER 50-483 CALLAWAY PLANT UNIT 1 FACILITY OPERATING LICENSE NPF-30 SPECIAL REPORT 89-10 STH YEAR INSERVICE CONTAINMENT VESSEL TENDON SURVEILLANCE FAILURE This letter amends the subject Special Report dated September 5, 1989 (ULNRC-2066). The percentage given on the bottom of page 2 within the body of the evaluation should read 12.08% rather than 19.23%.

The enclosed Special Report which reflects the above change, was submitted to satisfy Technical Specification action statement 3.6.1.6(b) regarding sheathing filler grease voids in excess of 5%.

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4. D. Blosser j Manager, Callaway Plant 10h% (;$ f WRC/JAh/DLBn UG/cmk Enclosure ces Distribution attached 8909290170 890914 FDR ADOC.K 05000483 27.-

5 FDC Ig Mailing Acuress PO Box 621 Futton MO 65251

'* i cci l distribution.for ULNRC-2074.

. ;, Mr. A.-.Bert Davis, Regional Administrator.

.U.S. Nuclear Regulatory Commission Region.III 799 Roosevelt Road

Glen Ellyn, IL 60137 Mr..R. W -DeFsyette Chief, Reactor Projects Section 3A U.S. Nuclear Regulatory Commission

Region III'

~799 Roosevelt Road

' Glen Ellyn,_IL 60137 Mr.;T..W.~ Alexion (2)

F Office-of Nuclear Reactor Regulation

.U.S. Nuclear Regulatory Commission

-Mail'Stop 13-E-21 Washington, D.C. 20555 Manager, Electric Department Missouri.Public Service Commission P.O. Box-360 Jefferson. City, MD 65102

'Mr. B. H. Little NRC Senior Resident Inspector I.

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EVAL'JATION OF THE FIFTH YEAR INSERVICE TENDON SURVEILLANCE

i. FOR THE CALLAWAY NUCLEAR PLANT -

The Callaway Plant Technical Specification 4.6.1.6.1 requires the demonstration of containment vessel structural integrity through e

a surveillance of the containment post-tensioning system at the end of 1.5, 3.5 and 5.5 years following the initial structural integrity test, and at 5 year intervals thereafter. The 5.5 year surveillance ~

l of the system began on July 17, 1989 On August 10, 1989, it I .-

was discovered that the net refill volume of the sheathing filler-grease p-i exceeded 5% of the net duct volume for tendons (see Attachmnent 1, Ten- c-don Greasing Summary). This void condition failed to meet Tech. Spec.

4.6.1.6.1(d)(2) which requires verification of operability of the sheathing filler material, by assuring the " amount of grease replaced does not exceed 5% of the net duct volume, when injected at 110% of the specified installation prese:Jre." Since a void greater than 5% was discovered after filling, restoration of the tendon sheathing ,

filler grease, specification action statement 3.5.1.6(b), was immedi-ately satisfied with the cxception of the Special Report. The NRC staff ...

a conevred with this position in a meeting on the same subject for the first year surveillance on July 19, 1985.

The Callaway containment vessel is a post-tensioned, reinforced concrete structure comprised of a vertical cylinder with a hemispheri-cal dome roof and is supported by a reinforced concrete slab. A con-tinuous access gallery is provided beneath the foundation slab for inspection of the vertical tendons. Three concrete buttresses are I provided for anchorage of the horizontal tendons. Anchorages are #

designed such that the tendons con be defensioned, inspected and reten-sioned readily during the life of the plant. The vertical cylinder -'

wall is provided with a system of vertical and horizontal (hoop)

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tendons. Vertical tendons are continuous to form inverted D's that'

' extend over the dome. The configuration of the tendons in the dome is based.on a three-way system consisting of two groups of vertical tendons oriented at 90 degrees with respect to each other and.a-horizontal'(honp)fgroup extending from the spring line to approxi-o

- mately 45 degrees from.the horizontal. Hoop tendons in both the wall

' and the dome are_placed in:a 240 degree system in which-three tendons form two completed rings using.three buttresses for anchoring the tendons.' Each' tendon is comprised of 170 - 1/4" wires, terminating at each end with a cold formed buttonhead at the anchorage fixture.

The essentiel criterion for +he operability of the sheathing filler material is to prevent corrosion of both the tendon wires and the anchorage components. The material used in the Callaway Plant post-

' tensioning system, Visconurust 2090P-4, accomplishes this by a charac-teristic which'gives the filler grease an affinity to adhere to steel surfaces, an ability to emulsify any moisture in the system which nullifies its rusting tendency, and resistance to moisture, mild acids and alkalis. In addition, protection is afforded by each tendon wire l being individually pre-coated with a grease, Amber 1601, prior to l

installation.

Ren:ults from the first and third year tendon surveillance revealed

. voids in excess of 5% for all tendons surveyed, without a loss of integrity to the system. From lab test on the removed wires and grease, and from visual inspections of the tendon components, the filler grease is performing its intended function of prohibiting corrosion of the tendon.

The void in the tendon sheathing, as indicated by the refill volume and varied from 6.83% to 12.08% (see Attachment 1),

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may be attributed'to a number of factors:

. 1) 'Visconorust'2090P-4 has a coefficient of expansion which yields an expansion of about 1% per every 20'F. Initial filling temperatures of the filler. grease. averaged.160*F.

\ Cold weather conditions can cool the' filler material to 40*F, -

giving a contraction of 6% of the net duct volume. During the fifth' year inservice surveillance of the tendons, the temperature of insitu filler grease average '90*F, giving

.a contraction of 3 to 4% from initial fill.

- 2) Characteristics of the initial filling method may induce air entrapment into the filler grease. Pumping operations can introduce air into filler material and may add up to as much as 2% of the net duct volume. The tendons at Callaway Plant were initially greased between April and October, 1981 by t

INRYC0 using current industry standard filling procedures.

3) Calculated voids between the wires which comprise the tendon bundle'cre approximately 7% of the net duct volume. During the initial filling operations, the tendon bundle was cold (ambient temperature of 65'F) and as the heated filler grease (exit temperature of 140'F) was pumped into the sheathing void, it solidified on the surface of the tendon bundle, leaving small voids between the wires. As the filler

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grease gradually heated the tendon bundle, it is likely that the voids between the wires allowed migration of the filler grease into the tendon bundle. Because this process is slow and gradual, it is reasonable to expect that it took place sub-stantially after the filling operation was complete and i

possibly during the surveillance refill operation. In

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p addition,-this type of migration could also occur at.other E

areas such as where tendons are in contact with the sheathing.

,In addition, visual inspection of 'the exterior concrete of.the containment building after the initial greasing and during the surveil-

. lance revealed no signs of grease seepage from the tendon duct. There-fore,-refillivolumes in excess of the lost grease during.the surveillance indicates that the void existed within the tendon duct boundary.

'The'Callaway Plant' tendons, requiring net refill volume of the filler material in excess of'the 5% criteria, have'not shown any

- abnormal visual deterioration. The lift off force for those tendons

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was found to fall within the predicted I;mits. Laboratory examination of_the filler grease has been performed as of this date and found to be within the tolerance limits as specified in the Tech. Spec.

Visual inspection of the different components of the anchorage system revealed proper coverage by the filler material with no signs of

< corrosion or presence of water.

As indicated by the above, the function of the filler grease protecting the post-tensioning system was maintained. As long as sufficient filler grease has been introduced into the system to completely coat the wires and anchorage system, corrosion protection is assured. Voids can be expected due to the characteristics of the filler grease and initial filling operations as noted above. Since each' wire is individually pre-coated with Amber 1601, the degree of filling interstitial spaces, which comprise the net duct volume, is not directly related to the degree of coating which occurs, and ther-efore, is not a major indicator of the operability of the post-tensioning system. Based on the lift off results, visual inspection

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and results from the first and third year surveillance, we have con-cluded that the. structural integrity of the tendon and anchorage system has not been adversely affected by the measured void.

Addition.11y,.since compliance with all remaining surveillance requirements for Tech. Spec. 4.6.1.6.1 was demonstrated, it is concluded that " voids in excess of 5% of the net duct volume" have not resulted in any degration of the post-tensioning system, assuring the structural integrity of the containment vessel structure.

In addition, future scheduled surveillance of the post-tensioning system and full pressure integrated leak rate tests will monitor the structural parameters of the' containment to detect any potential abnor-mal dest adation, assure continued operability of the system, and verify containment vessel structural integrity on a continuing basis.

This report has been filed to meet the 30 day action statement as specified in Technical Specification Action Statement 3.6.1.6(b).

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,- . . Attachment 1 TENDON SURVEILLANCE GREASING

SUMMARY

TENDON.  % GREASE ADDED V41 10.8

- V84 6.83 12AC 7.96 20AC 12.08 42AC 10.38 52AC 9.13 20CB 12.70 20BA 11.87 44BA 8.92 j

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