ML20238F777

Special Rept 87-010:inservice Tendon Surveillance Voids in Excess of 5% of Net Duct Vol Discovered.Cause Not Stated. Prevention of Tendon Corrosion Assured by Adequately Coating Tendon Wires & Anchorage

ML20238F777
Person / Time
Site:	Wolf Creek
Issue date:	09/11/1987
From:	Rhodes F WOLF CREEK NUCLEAR OPERATING CORP.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
87-010, 87-10, NO-87-0197, NO-87-197, NUDOCS 8709160340
Download: ML20238F777 (5)

Text

-

- - --- .g g

m. -

Lib W6) LF NUCLEAR CREEKOPERATING Forresi T. Rhodes Vice Prescent Nuclear Opereiens j.y . >  :

2 September 11, 1987 '!

7 k

G NO'87-0197 t 3

U.S. Nuclear Regulatory Commission

, ATTN: ' Document Control Cesk Washington D.C. .20555 ,

Subject:

Docket No. 50-482:' special Report 87-010 Gentlemen:

I

• The. enclosed ~Special Report is submitted pursuant to Technical

/ Specification 4 3.6.1.6 'and 6.9.2.

4

( ,y Very truly yours, A

. t.

Forrest T. Rhodes Vice-President Nuclear Operations 1

FTR/jad Enclosure cc: P. O'Connor (2)

R. Martin J. Cummins 1 a.w . j

)

l

'I S DfEhOCK3AO B70911 050004sp -

PDR 1

< gp }

P.O. BW 411/ Durtington, KS 66839 / Phone: (316) 364-8831 9 1 An Equal opportunity Employer M F HC/ VET

_ - _ _ _ _ _ _ _ _ _ _ _ l

Attachment to NO 87-0197

. September 11, 1987

-Page-1..'of 3, WOLF CREEK GENERATING S'DLTION L SPECIAL REPORP 87-19

. INSERVICE ' TENDON SURVEIIJAICE VOIDS L IN EXCESS OF 5 PERCENT CF NET DUCT VOLINE it 'This Special Report is being submitted pursuant to Technical Specifications-3.6.l'.6, action statement b, and 6.9.2 concerning the discovery of voids in excess of 5 percent of the net duct volume, thus exceeding the acceptance-criteria of surveillance 4.6.1.6.1.e.l.

The third year tendon surveillance at Wolf Creek Generating Station (WCGS) began in August, 1987. The surveillance inspection procedures required in part, inspection of tendon wire and anchorage components for evidence of corrosion and/or cracking, inspection of. concrete adjacent to the bearing plates for cracks, inspection of the tendon system for signs of water intrusion, verification of tendon lift-off force and elongation, and the

- measurement of sheathing filler grease voids. expressed as a percentage of the net duct volume. Figure 1 illustrates details of a typical vertical tendon anchorage and grease can assembly.

Technical Specification Surveillance. 4.6.1.6.1.e.1 requires in part, that the. OPERABILITY of the sheathing filler grease be assured by verifying that.

no voids 'in excess of 5 percent of the net duct volume exist. In order to 2 assess the. percentage of voids in the sheathing filler grease, hot grease is pumped into the. tendon duct under pressure and the volume of grease added by this method, less the volume of grease removed frcr;t the tendon duct and grease can assembly during tendon inspection, is ccnpared to the. net duct volume. 'Ihe pumping pressure was limited to assure that no damage to the containment structural integrity would occur during this process. This regreasing operation has been performed on four' vertical containment vessel tendons and'one-half of seven horizontal containment vessel tendons.-

During regreasing it was ' identified that the net refill volumes of the .

sheathing filler grease exceeded 5 percent of net duct volume for tendons -

listed below.  !

Percent Voids Date Tendon Number Of Net Duct Volume Discovered V18 12.8% 09/03/87 i

V47 6.8% 09/03/87 V1 28.9% 09/03/87 47BA 7.5% 09/11/87 35BA 9.0% 09/11/87

.These percentages reflect the annunt of sheathing filler grease added to the tendon ducts themselves and their associated grease can. -

1 1

Attachment to to 87-0197 September 11, 1987 Page 2 of 3 Technical Specification 3.6.1.6 , Action Statement b requires that, "With any abnormal degradation of the structural integrity . . . at a level below the acceptance criteria of Specification 4.6.1.6, 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 Comission within 15 days in accordance with Specification 6.9.2..."

Pursuant to this action statement Wolf Creek Nuclear Operating Corporation (WCNOC) has determined that the process used to measure and identify the voids in the sheathing filler grease immediately, ". . . restores the containment vessel to the required level of integrity . . .", provided no

/ other < evidence of abnormal degradation is present, by filling the identified

, Soids with sheathing filler grease.

Based on preliminary inspection and test results of additional aspects of the post tensioning system, such as grease coverage of tendon wires, absences of cracks, corrosion, and damage from tendon wires, and changes in the physical appearance of the filler grease, for the inspected tendons it was confirmed that the presence of voids in excess of 5 percent of net duct volume does not degrade the structural integrity of the Containment. The amount of grease found was more than adequate as all inspected tendon wires and anchorage cmponents had extensive grease coverage. There were ro signs of water or evidence of corrosion within the tendon ducts or grease can assemblies. Miitionally there was no evidence of concrete cracking adjacent tc the tenden anchorages.

Prevention of corrosion of the tendons is assured by adequately coating the tendon wires and anchorage components. The material used in the WCGS post-tensioning system, Visconorust 2090P-4, accomplishes its corrosion protection function by the filler material's affinity to adhere to steel structures, its ability to emulsify any moisture in the system nullifying its rusting ability, and by its resistance to moisture, mild acids and alkalis. As long as suf ficient grease has been introduced into the system to coat the wires and anchorages completebr, corrosion protection is assured. Protection is also afforded by each tendon wire being individually precoated with Amber 1601 prior to installation. The degree of filling the interstitial spaces, which comprise the net duct volume, is not directly related to the degree of coating which occurs and, consequently, is not of significant import w e as an indicator of operability of the sheathing filler material.

Due to the physical characteristics of the sheathing filler material and industry standard installation techniques, voids up to approximately 15 percent coulo be expected af ter the initial filling operation. Voids in the tendon sheathing may be attributed to a number of additional factors:

(a) Visconorust 2090P-4 has a coefficient of expansion which yields an expansion of about 1 percent per every 20 degrees Fahrenheit.

Initial filling temperatures of the filler material can average 160 degrees Fahrenheit. Cold weather conditions can cool the filler material to 40 degrees Fahrenheit, giving a contraction of 6 percent of the net duct volume.

L Attachment to NO 87-0197 September-11, 1987 j Page 3 -'of.3-(b) Calculated voids between the wires which comprise the tendon bundle are approximately 7 percent of the net duct volume. .If during the

. initial filling operations the tendon bundle is cold (ambient temperature of 65 degrees Fahrenheit) and, as the filler material is pumped into the sheathing void, it solidified on the surface of the tendon bundle, small voids will be left between.the wires. As tendon bundles gradually heat and cool over time, it is likely that the voids between the wires allow migration of the filler material into the tendon bundle. In addition, this type of migration could also occur at other areas such as where tendons are in contact with the sheathing.

(c) Characteristics of the initial filling method may induce air entrapnent into the filler material. Pumping operations can introduce air into filler material and may add up to as much as 2 percent of the net duct volume. This void value could be higher for horizontal tendons due to the lower pumping head used when ccznpared to the vertical tendons.

' Visual inspection of the exterior concrete, the containment under plate, grease cans and the tendon gallery revealed no signs of grease leakage or liner plate bulging. 'Ihe reasons for the voids in excess of 15 percent identified in tendon V1 are not clear at this time. An investigation is being performed including a review of original installation records to determine potential causes of these voids. The surveillance program may be modified as deemed appropriate based on the conclusions of the investigation.

The presence of sheathing filler material voids does not alone indicate the presence of post-tensioning degradation. Each individual tendon wire is individually pre-coated with Amber 1601 (a corrosion inhibitor) and the tendon bundle is coated with grease prior to installation. In addition, the grease becomes liquid when heated at initial installation and pumping the grease fluid over the tendon bundle will adequately coat the bundle. A tendon wire was removed from V1 and subsequent inspection revealed that no corrosion existed. Samples et the wire are being tested for ultimate strength, but test results are not currently available. Samples of the grease removed from the tendon duct are also being tested for impurities but again test results are not available at this time. In addition, the surveillance inspection has not reported any signs of moisture within the tendon duct system.

Based on the above discussions it has been determined that the identification of sheathing filler grease voids in excess of 5 percent of the net duct volume alone is not evidence of degradation and does not adversely affect the structural integrity of the Containment Building.

.. ~, - e_

I s i

VERTICAL TENIGi (Callery - In Det*Il_) '

s TEffDON WIRES a . /

r.;)  ! /

ilf' ,

TRUMPET TUBE i ,

!;' l 80

-EEARI;40 PLATE i

L ,

r

! i l,' .er N L l. g et + j HOUNTING 3 . [;}

. CA5KET- - I: *

• 1

[.I BOLT 5 .

I ,

T/!

g.;i

.i.

("

,.y e.:o

• .f. .

t

.x}

.i  %

N' h..tghe,;,fbg a i CALLERY CEILING j

ll . _

l CASKET RETAINER t

.NA-l b W SilIMS Sil!H ' ,

~

i  ! CX '

- STACK, , _

! l' p

' J

ANCHORACE V

'g. ,_

BUTTONHEADS VJ///////////sts/ D dN FILLER BUSilINC This can will be completely full of grease. BpSHINC PLUG There fw no shrinkage ut titis end I of the Tendon. FIGURE 1 4t m___;____.:_______._ _ _ _ _ _ _ _ _

l l

l'

,- ,<4 l

N (D '

.g-en .

C3 i (*

.c3 m . ~&

l Z l

D Qc4

=>

r=~

i

_ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ . . . _ _ _ _ _ _ . _ _ _ 1