ML20096D908
| ML20096D908 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 05/11/1992 |
| From: | Gates W OMAHA PUBLIC POWER DISTRICT |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| LIC-92-168S, NUDOCS 9205180301 | |
| Download: ML20096D908 (5) | |
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Omaha Public Power District 444 South 16th Street Mall Omaha, Nebraska 6810' -2247 c
02 6 2000 May 11, 1992 LIC-92-168S 1
U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Station PI-137 Washington, DC 20555
References:
1.
Docket No. 50-285 2.
NRC - Regulatory Guide 1.35,
" Inservice Inspection of Prestressed Concrete Containments', Revision 3, dated July 1990 Letter from OPPD W. G. Gates) to NRC 3.
dated February ll(,1992 (LIC-92-048S)(Document Control Desk)
Gentlemen:
SUBJECT:
Special Report on the Containment Tendon Prestressing System, Excessive Grease Voids found in Dome and Helical Wall Tendons Pursuant to Fort Calhoun Station (FCS) Technical Specification (IS) Surveillance Requirement 3.5(7) "Prestressing System", and as committed in Reference 3, Omaha Public Power District (OPPD grease voids found in the co)tainment dome and helical wall tendons.is submitting this special repo n
FCS Technical Specification Surveillance Requirement Acceptance Criteria 3.5(7)f.(v){f) states: "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."
1S 3.5(7)g requires an immediate investigation to determine the causes and extent of any nonconformance with the acceptance criteria and also requires the results to be reported to the Commission within 90 days via a special report in accordance with TS 5.9.3.
As described in Reference 3, tne nineteenth year Prestressing System Surveillance (PSS) was performed on the helical wall tendons of the FCS Containment Building from October 18, 1991 through November 13, 1991 by Precision Surveillance Corporatioa (PSC).
From January 22 1992 through February 13, 1992, the dome tendon portion of the nineteenth yea,r PSS was performed on the FCS Containment' Building by PSC. In accordance with commitments made in Reference 3, additional grease void measurements were performed during the dome tendon PSS.
These additional tests included: grease void measurements on tendons passing near vents and high temperature lines and a surveillance (including a liftoff test and wire removal) on a dome tendon which had lost grease through its main grease seal.
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4 LIC-92-168S Page 2 1
During the dome tendon phcse of the nineteenth year PSS, twenty tendons were inspected and measured for crease voids. The measurement results are summarized in Attachment 1.
These twenty tendons included: four randomly selected surveillance tendons, ten dome tendons with evidence of grease seal failure and an additional six helical wall tes Jons selected specifically to investigate the extent of grease voids as reported in Reference 3.
Grease voids greater than 5%
I net duct volume were found on six dome tendons and five helical wall tendons.
This is re ortable per FCS TS Surveillance Requirement Acceptance Criteria 3.5(7)f.(v)p(f) and NRC Regulatory Guide 1.35, Revision 3 (Reference 2).
As described in Reference 3, tendons filled with Visconorust 2090-P filler grease can experience voids of up to 15% (net) due to ori inal itstallation practices.
As a result, the American Society of Mechanical En ineers (ASME)Section XI IWL Work Group Committee adopted acceptable grease voi limits of 10% for passively refilled tendons and 15% for tendons refilled with pressurized grease. Seven of D229N, H1105, H2005, H3106) grease voids greater than 5% LDll4N, D120P, 0214N, the eleven tendons with net are acceptable under the IWL Limits. As discussed below, four of the eleven tendons with net grease voids greater than 5% (0318P, D218N, H1078, and H2015) failed to meet the IWL limits.
Main grease seal failures were found on eight of the ten dome tendons suspected of grease seal failure. The remaining two were determined to have leaking washer gaskets.
Four of the dome tendons with main grease seal failures had grease voids less than 5%; two had grease voids less than 15%: D318P had a grease void of 35.7% and D218N had a grease void of 36.0%.
Lif toff tests performed on tendons D318P and 0218N found that both met the respective acceptance criteria and no abnormal deterioration was discovered.
Light corrosion was found on the anchor head of tendon D318P, which most likely was caused by contaminants introduced during one of the surveillances conducted in 1974. Tendon D318P was detensioned for inspection twice in 1974, and had a wire removed duris g the second surveillance. Although approximately 20 gallons of grease was unaccounted for, tendon 0318P's anchorage was well coated with grease because it is below the main grease seal. Tendon 0318P was refilled with grease and accepted "as is."
Light corrosion was also found on the shim of tendon D218N's anchorage, most likely due to failure of its main grease seal.
Tendon D218N has never been opened for inspection prior to this surveillance. Tendon D218H was detensioned to allow removal of a sample wire for tensile testing.
A small spot of rust suspected to have been caused by contamination introduced during construction was found on the sample wire. The sample wire passed the tensile test. Tendon D218N was refilled with grease and accepted "as is."
To investigate the anti-corrosion effectiveness of thin films of grease, OPPD committed (Reference 3) to test a dome tendon that had lost a significant amount of grease.
The surveillance testing of dome tendon D218N ful fill s this commitment. The results show that enough grease adheres to the tendon wires to i
l protect them from corrosion even when large grease voids occur.
Following l
completion of surveillance testing, all ten dome tendons which had failed main grease seals or leaking washer gaskets were repaired and refilled with grease.
LIC-92-168S Page 3 Helical wall t,
,s H1078 and H2015 were tested for grease voids as part of the investigation in the effect that the ungrouted concrete vents have on nearby tendons.
These vents are in containment wall pour CW-10 and were used to construct containment wall pour CW-9A over the Personnel Airlock.
Tendon H1078, which had a measured grease void of 15.7%, passes adjacent to the concrete vent located near the east wall of Room 69. Since tendon H1078 was both pressure filled and passive filled, a measured grease void of 15% could be expected due to installation practices. A consistent slow leakage of grease from this vent is known to have occurred although the volume that has leaked out is not documented. Tendon H1078 will be reinspected for grease voids again during the next tendon surveillance currently scheduled for 1996.
Tendon H2015 had a measured grease void of 29%. Since tendon H2015 was passive filled, a measured grease void of 10% could be expected due to installation practices.
Tendon H2015 passes adjacent to the concrete vent in Room 71 (discussed in detail in Reference 3).
Except for this concrete vent, no other visible leakage location could be found along the path of tendon H2015. Tendon H2015 will be included in the 1996 tendon surveillance for liftoff testing and detensioning for wire removal.
In Reference 3, helical wall tendons H3105, H1087, and H4009 were reported to have net grease voids in excess of the IWL acceptance limits.
To measure the extent of the problem, OPPD committed to perform grease void tests on several other tendons which pass near high temperature lines and the concrete vents.
Grease void tests on tendons H1105 and H3106, which are parallel to tendon H3105, showed grease voids of 8.0% and 8.5% respectively.
In November 1991, a grease void of 8.5% (Reference 3) was measured on tendon H3104, Wch is also parallel to tendon H3105.
All three tendon (H1105, H3104 ano H3106) grease void measurements are within the 10% IWL acceptance limit. Therefore, the grease void measurement on tendon H3105 is considered to be an isolated case.
Because the grease void measurements (Reference 3) on tendons H1087 and H4009 were outside of the IWL acceptance limits, additional greas6 void measurements were performed on tendons H1078, H1082, H2005 and H2015.
Grease void measurements on tendons H1082 and H2005 were within the IWL acceptance limits while measurements on tendons H1078 and H2015 exceeded the IWL acceptance limits.
As a result, additional tendons with grease voids exceeding 15% are suspected among the one hundred tendons passing through the area of the Personnel Airlock.
To continue the investigation, the following actions will be included in the scope of the 1996 tendon surveillance:
Tendon H1078 will be inspected for grease voids.
Liftoff testing and removal of a sample -wire for tensile testing will be conducted on tendon H2015.
Grease void inspections will be conducted on a sample of ten of the tendons passing through the area between containment pours CW-10 and CW-9A. The sample will be taken from the remaining eighty-six tendons passing through this area that were not tested during the nineteenth year PSS.
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l LIC-92-168S Page 4 In conclusion, four tendons were found during the dome tendon surveillance to exceed the IWL acceptance criteria.
For these four tendons, the source of the leakage has been determined or additional actions are planned for the 1996 surveillance.
As noted above, repairs have been completed on the ten dome tendor.s found to have a main grease seal failure or a leaking washer.
Investigations of tendons with grease voids in excess of IWL acceptance criteria have shown that thin films of grease are effective in preventing excessive corrosion, thus assuring the mechanical integrity of the tendon.
During the nineteenth year PSS, no abnormal deterioration of the containment tendons was detected.
Therefore, OPPD is confident in the ability of the containment structure to continue to perform its safety rela'.ed function.
If you should have any questions, please contact me.
Sincerely, j
4ts. N./h.i W. G. Gates Divi.sion Manager Nuclear Operations WGG/sel Attachment c:
LeBoeuf, Lamb, Leiby & MacRae R. D. Martin, NRC Regional Administrator, Region IV D. L. Wigginton, NRC Senior Project Manager S. D. Bloom, NRC Project Engineer R. P. Mullikin, NRC Senior Resident Inspector R. D. Hough, President, Precision Surveillance Corporation i
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i to LIC-92-168S Grease Void Measurements l
Tendon Het Duct Grease Loss Refill Grease Volume Gallons Gallons Net Void Refill t
Tendon Gallons Top Bottom Top Bottom Gallons Percent Method Dome Tendons i
Dll4N*
56.97 0.0 1.0 2.0 4.5 5.5 9.7%
Pressurized l
Dll8N*
55.98 1.0 0.0 3.0 0.0 2.0 3.6%
Pressurized D119P 54.94 1.8 1.3 2.8 2.0 1.8 3.2%
Pressurized i
D120P 54.09 1.0 1.0 2.3 2.5 2.8 5.1%
Pressurized 0214N 58.33 0.0 1.0 7.0 0.0 6.0 10.3%
Pressurized D216N 57.62 0.0 0.0 0.0 0.8 0.8 1.3%
Pressurized 0216P*
57.51 0.0 1.0 3.0 0.0 2.0 3.5%
Pressurized D218N*
56.18 1.3 1.3 20.8 2.0 20.3 36.0%
Pressurized D229N*
46.69 1.0 0.0 7.0 0.0 6.0 12.9%
Pressurized l
0235P*
38.69 0.0 1.0 0.0 1.8 0.8 1.9%
Pressurized i
i D30lP 62.78 2.3 1.3 3.0 2.0 1.5 2.4%
Pressurized
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D318P*
57.76 0.0 2.8 0.0 23.4 20.6 35.7%
Pressurized D330N*
46.18 1.0 0.0 3.0 0.0 2.0 4.3%
Pressurized Helical Tendons H1078 84.47 0.0 0.0 5.3 8.0 13.3 15.7%
Pressurized / Passive H1082 82.97 0.0 0.0 2.8 0.0 2.8 3.3%
Passive H1105 84.23 0.0 0.0 5.8 0.0 6.8 8.0%
Passive H2005 82.69 0.0 0.0 5.3 0.0 5.3 6.4%
Passive H2015 82.76 0.0 0.0 22.8 1.3 24.0 29.0%
Passive i
H3106 82.15 0.0 0.0 6.5 0.5 7.0 8.5%
Pressurized / Passive H4104 82.00 1.0 0.0 4.8 0.0 3.8 4.6%
Passive f
- Main grease seal failure
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