ML20087E982
| ML20087E982 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 01/14/1992 |
| From: | William Cahill TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| CP-91-08, CP-91-8, TXX-92018, NUDOCS 9201220264 | |
| Download: ML20087E982 (2) | |
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Ref # 10CFR50.55(e)
TUELECTRIC January 14, 1992 Wimars J. Cahill, Jr.
Gwe Vice huislent U. S. Nuclear Regulatory Ccmmission Attn: Docur ent Control Desk Washington, D.C.
20555
SUBJECT:
COMANCHE PEAK STEAM ELECTRIC STATION - UNIT 2 DOCKET NO. 50-446 MSIV INTERNAL CORROSION
'SDAR CP-91-08 (FINAL REPORT)
Gentlemen:-
On October 15, 1991 TV Electric orally notified the NRC of a potentially reportable condition in which internai p1tting corrosion was found in all four MainSteamIsolationValvel(MS!Vs). The last report on this issue was logged TXX-91420 dated November 14, 1991.
It has now been determined that this condition is reportable pursuant to 10CFR50.55(e).
Descri;L. ion of Condition t
Pitting corrosion was discovered on internal bore surfaces of two Unit 2 MSIVs during preparation for rea v embly or September 16-18, 1991. The pitting in 2HV-2334A was identified over the entire bore surface with'the heaviest concentration in a circuttferential pattern about midway between the bonnet flange end the valve seat.
Numerous individual pits were found in 2HV-233#
near the valve seat.
The pits varied in depth fram 0.009 inch by pit gage to 0.018 by visual examination and were less than 1/8 inch in diameter.
Inspection of the other two MSIVs on September 30, 1991 revealed the same type of corrosion.
The four valves had been disassembled in July 1987 to allow plugs to be installed for a secondary hydrostatic test. The pistons were stored in the warehouse and plywood' covers were installed over the bores to maintain system cleanliness. Unit 2 work was placed on hcid before the test wa.t performed and the valves were not resssembled. Thus, the valves were not prope ly prepared forilong-terrr layup. The corrosion was aggravated by the fact that the area in which the MS!Vs are located was not weather-tight juring the layup period.
Safety implica.tlpD1 Although some of the individual pits exceeded 0.010 inch in depth, the manufacturer was more concerned with the areas of large concentrations of pits which were less than 0.010 inch deep. The balance chamber is critical for proper valve operation and the piston rings must seat against the bore surface. These areas of corros cn could possibly contribute to leakage al the piston rir.gs.
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TXX-92018 Page 2 of 2 Depending on the severity of the corrosion, both the cioning and closing times could be affected, and the possibility exists that piston binding could occur.
Thus, this deviation could create a substantial safety hazard were it to remain uncorrected.
Corrective Action i
The bore on all four MSIVs will be machined to 0.050 inch oversize and oversized piston rings will be installed to insure a proper seal between the piston and valve body bore.
The work will be accomplished by site personnel under vendor representative guidance prior to hot functional testing.
As part of the ongoing Unit 2 flush program, more than a hundred components have been inspected and no significant exampics of corrosion damage have been identified. Therefore, the unarotected condition that resulted in corrosion of the MSIV5 is considered to ae an isolated occurrence.
Sincerely, l
William J. Cahill, Jr.
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By:
D. R. Woodlan Manager, Docket Licensing cc
- n. D. Martin, Region IV ResidentInspectors,CPSES(2)
M. B. Fields NRR i-
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