ML20092G460
| ML20092G460 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 02/11/1992 |
| From: | Gates W OMAHA PUBLIC POWER DISTRICT |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| LIC-92-048S, LIC-92-48S, TAC-M80908, NUDOCS 9202200144 | |
| Download: ML20092G460 (4) | |
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Omaha Public Power District 444 South 16th Street Mall Omaha, Nebraska 68102-2247 February 11, 1992 402/6362000 LIC-92-048S U. 5. Nuclear Regulatory Commissior Attn Document Control Desk Mail Station P1-137 Washington, DC 20555
References:
- 1. Docket No. 50-285
- 3. Letter from NRC (L. J. Callan to OPPD (K. J. Morris) dated December 5,1988(IER88-39)
- 4. NRC Regulatory Guide 1.35, " Inservice Inspection of Prestressed Concrete Containments", Revision 3, dated July, 1990 5.LetterfromNRC(W.C. Walker)to0PPDdatedSeptember 26, 1991
'" Containment Tendon Meeting Summary" (TAC No.f/p0908)
Gentlemen:
Subject:
Special Re) ort on the Prestressing System - Excessive Grease Voids Found in tie Helical Wall Tendons The Omaha Public Power District (OPPD), holder of Operating License DPR-40, submits this special report pursuant to the requirements of the Fort Calhoun Station (FCS)UnitNo.1,TechnicalSpecification(TS)Sur/eillanceRequirement
- 3.5(7), "Prestressing System".
This report provides an interim status of actions taken in response to the results of surveillances conducted under this requirement.
TheFCSTSSurveillanceRequirementAcceptanceCriteria3.5(7)f.(v)(f) states that, "The difference between the amount of grease injected into a tendon to replace the amount which was removed during inspection shall not exceed 5% of the net tendon sheath (duct) volume when injected at the original installation pressure". TS3.5(7)(g)requiresanimmediateinvestigationtodeterminethe causes and extent of any non-conformance with the acceptance criteria, and it requires the results to be reported to the Commission within 90 days via a special report in accordance with TS 5.9.3.
From October 18, 1991 through November 13, 1991, the nineteenth year Prestressing System Surveillance was performed on the helical wall tendons of L
the FCS Containment Building by Precision Surveillance Corporation (PSC).
Grease was added to 21 tendons and then grease void measurements were performed I
on these 21 tendons. Grease void measurements on eight of the 21 tendons indicated greater than 5% net duct void which is reportable pursuant to TechnicalSpecification3.5(7)f.(v)(f). Results of the grease void
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measurements are presented in Attachment 1.
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9202200144 920211
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00-32-048S Page Two Reference 4, which is the basis for TS 3.5(7)f.(v)(f), requires reporting of measured grease voids in excess of 5% net. duct volume, however, industry experience shows-greater voids can be expected due to installation practices.
According to PSC,-a review of research completed by Inryco in 1984 and 1985
-found that there are three original installation factors which can lead to grease voids. These installation factors are:
1.-The coefficient of expansion of the grease which is injected at temperatures ranging from 120*F to 220*F.
- 2. Inadequate tendon bundle soak time (the void between the wires requires time to absorb grease.
- 3. Air entrapment.
Under original installation practice for Visconorust 2090-P filler grease, shrink back due to cooling could cause voids up to 6%; inadequate tendon bundle soak time could cause voids up to 7%; and air entrapment could cause voids up to 2%.- Therefore, a total of up to 15% net grease void could be expected.
According to PCS these observations have been consistent from site to site.
The PSC partici) ant on the American Society of Mechanical Engineers (ASME)
Section XI IWL fork Group Committee presented this research to the Committee in November, 1991.
As a result, the Committee adopted with the NRC participant's concurrence, acceptable void limits of 10% for tendons which are passively refilled and 15% for tendons-which are refilled with pressurized grease.
Five of the eight OPPD tendons with greater than 5% net grease void are considered acceptable under these criteria. Tendons 1087,'3105 and 4009, which failed to meet the Criteria of ASME Subsection IWL, " Requirement of Class CC Concrete Components of' Light-Water Cooled Power Plants", are discussed below.
Tendon 1087, which had a measured grease void of 17.8%, passes adjacent to one of the vents which leaks grease into Room 71.
The volume of grease which may
-have. leaked out of the vent is estimated at 1 to 2 cups of grease each year.
In the 19 years since tendon installation, approximately another 1.8 gallons would have leaked out-if 12 ounces of grease leakage per year is assumed. The volume of the vent is about 0.9. gallons.
Since tendon ~1087 was both pressure filled and passive-filled, a measured grease void of 15% could be expected due to installation practices.
Therefore, with 2.7 gallons leaking-into and-out of the concrete' vent, the remaining unaccounted void is less than 15%.
Although tendon 4009 passes through the repoured area, it does not pass near a vent. Row 4000 tendons are the closest to the Containment liner, and the vents penetrate through the 1000 and 2000 rows. Also, the sheath for tendon 4009 L
does.not 3 ass close to any known vents. The measured void is only 1.6 percent l~
greater tian what may be. expected from construction practice, which amounts to 1.34 gallons.
Except for possible minor grease dripping from the Stressing Gallery grease cap (which has been observed from many tendons), no observable
-leak path exists for tendon 4009.
4 -
y LIC-92-0485 Page Three
. The net grease void-in tendon 3105 was measured by passive fill at 11.1 gallons or 13.5 percent of net duct volume. Based on the information cited above, up to 10% net grease void could be expected from construction practices, therefore, at least 2.9 gallons has leaked out.. Only a grease film was discovered on the top anchorage when the top grease can was removed, where other tendons had at least a gallon of grease coating their top anchorages.
While inspecting the containment along the path of tendon 3105, grease filled pfnt blisters were discovered in the Upper Electrical Penetration Room at M
D".
This area is.immediately underneath the penetrations of the Main re #
er and Main Steam lines. Tendon 3105 passes adjacent to penetration M-
% ca a Main Feedwater line. During operation, the temperature in the tendon
%+ near the Main Feedwater and Main Steam line penetrations exceeds the
'y lting point'of the originally installed Visconorust 2090-P filler grease, thus, pressurizing the grease causing it to flow wherever it can find a path.
Tendons 1087, 3105 and 4009 will be inspected for grease voids during the next tendon surveillance which is currently scheduled for 1996.
Several tendons in the vicinity of vents and high temperature lines are currently being ins 3ected for grease voids as part of the surveillance being performed by PSC on tie dome tendons.
In addition, a liftoff-test and wire removal on one of the dome tendons,:which has-lost a significant amount of filler grease, will be performed by PSC, as discussed in the meeting between OPPD and NRR on September 13, 1991 (Reference 5).
Tests results will demonstrate the anti-corrosion effectiveness of thin films of grease.
Since no grease voids, in excess of the IWL acceptance criteria discussed above were' identified in tendons 2121, 3075, 3087, 3091 and 3104, O'PD has no additional actions presently planned regarding inspecting the:e' tendons.
OPPD will submit a supplement to this special report within ninety days, discussing the results of the ongoing tendon investigations.
If you should have any questions,-please contact me.
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Sincerely, Av.N &
W. G. Gates Division Manager l
Nuclear Operations
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LAttachment l
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Precision Surveillance Corporation, R. D. Hough, President LeBoeuf, Lamb, Leiby & MacRae R. D. Martin, NRC Regional Administrator D. L. Wigginton, NRC Senior Project Manager R. P. Mullikin, NRC Senior Resident Inspector
Greace Void Measurements Tendon Het Duct Grease Loss Refill Grease Volume Gallons Gallons Net Void Refill Tendon Gallons Top Bottom Top Bottom Gallons Percent Method 1018 83.05 3.0 3.5 8.5 0.0 2.0 2.4%
Passive 1046 83.02 1.5 4.0 2.0 1.0
-2.5
-3.0%
Pressurized / Passive 1058 83.02 1.3 3.0 5.8 0.0 1.5 1.8%
Passive 2029 84.59 3.0 40.0 5.8 37.8 0.5 0.6%
Pressurized / Passive 2121 84.74 2.0 21.0 8.0 23.8 8.8 10.3%
Pressurized / Passive 2145 83.70 2.5 7.3 13.5 0.0 3.8 4.5%
Passive 3008 82.31 1.0 18.0 20.0 0.0 1.0 1.2%
Passive 3105 82.50 0.0 23.5 34.6 0.0 11.1 13.5%
Passive 3104 82.34 1.0 0.0 8.0 0.0 7.0 8.5%
Passive 4141 81.90 3.0 30.5 31.0 2.0
-0.5
-0.6%
Pressurized / Passive 4154 82.25 2.0 16.5 21.8 0.0 3.3 4.0%
Passive 1083 82.96 0.0 0.0 3.0 0.0 3.0 3.6%
Passive 1087 82.98 0.0 0.0 6.0 8.8 14.8 17.8%
Pressurized / Passive 1092 83.29 0.0 0.0 2.0 0.0 2.0 2.4%
Passive 2010 84.65 0.0 0.0 2.0 0.0 2.0 2.4%
Passive 3075 82.31 0.0 0.0 6.0 0.0 6.0 7.3%
Passive 3079 82.40 0.0 0.0 4.0 0.0 4.0 4.9%
Passive 3087 82.38 0.0 0.0 7.0 0.0 7.0 8.5%
Passive 3091 82.40 0.0 0.0 5.0 0.0 5.0 6.1%
Passive 4009 83.98 0.0 0.0 9.8 0.0 9.8 11.6%
Passive 4012 81.97 0.0 0.0 2.3 0.0 2.3 2.7%
Passive