ML20206L773
| ML20206L773 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 04/14/1987 |
| From: | Rice P GEORGIA POWER CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| REF-PT21-87 GN-1359, NUDOCS 8704170230 | |
| Download: ML20206L773 (5) | |
Text
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khtforA404 U481?4 404 %494i1 Georgia Power c~ a rn m m April 14, 1987 United States Nuclear Regulatory Cominission Document Control Desk File: X7BG03-M138 Washington, D. C. 20555 Log: GN-1359
Reference:
Vogtle Electric Generating Plant - Unit 2; 50-425 MSIV Overpressure Letter GN-1348, dated February 19, 1987 In previous correspondence, Georgia Power Company notified the NRC of a potentially reportable condition concerning the possibility for hydraulic and nitrogen pressure in the MSIV actuators to exceed design pressure.
Rockwell, the valve manufacturer, has indicated that when fully retracted and assuming a leaktight hydraulic system, the MSIV actuator could only accept a 12*F increase in temperature before the hydraulic pressure exceeds the rated operating pressure of the Keane solenoid valves.
Exercising the valve will relieve the overp'ressure, but when taken to the extreme, assuming a leaktight hydraulic system, this overpressure could prevent the Keane solenoid from operating which would result in a failure of the MSIV to close.
Georgia Power Company has completed its evaluation and has determined that a reportable condition as defined by the reporting requirerents of 10CFR21 and 10CFR50.55(e) does exist.
Based upon NRC suidance in NUREG-0302, Revision 1,
and other NRC correspondence, Georgia Power Company is reporting this condition for Unit 2 of the Vogtle Electric Generating Plant pursuant to the reporting requirements of10CFR50.55(e).
This response contains no proprietary information and may be placed in the NRC Public Document Room.
J. ).
P. D. Rice 8704170230 870414 PDR ADOCK 05000425 f
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s MSIV Overpressure File:
X78G03-M138 Log: GN-1359 Page two CWH/PDR/wk1 Attachment xc: USNRC - Region II Suite 2900 101 Marietta Street, NW Atlanta, Georgia 30323 H. G. Baker D. R. Altman L. T. Gucwa J. P. O'Reilly J. A. Bailey C. W. Hayes G. F. Head O. Batum G. A. McCarley R. E. Conway G. Bockhold R. W. McManus R. H. Pinson C. E. Belflower Sr. Resident (NRC)
- 8. M. Guthrie J. F. D'Amico C. C. Garrett (OPC)
R. A. Thomas W. D. Drinkard J. E. Joiner (TSLA)
E. D. Groover D. Feig (GANE)
NORMS
l i
EVALUATION OF A POTENTIALLY REPORTABLE CONDITION j
MSIV OVERPRESSURE i
A t
Initial Reoort: On January 23, 1987, Mr. C. W. Hayes, Vogtle Quality l
Assurance Manager, notified Mr. E. F. Christnot of the USNRC-Region II 1
of a potentially reportable condition associated with the Main Steam 1
Isolation Valves (MSIV's).
In subsequent correspondence with the NRC, Georgia Power Company indicated that a final report on this issue would i
be submitted by April 24, 1987.
I Backaround Information: During solenoid valve testing by Rockwell (the i
M5IV fabricator) a potential problem with Keane solenoid valve l
operability was discovered.
The problem involved the possibility that i
the valves could fail to properly stroke at pressures higher than the solenoid valve rating (approximately 6000 psig test pressure versus
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a ra ted pressure of 4500 psig).
The Keane solenoid valves are the 1
pilot valves used to open a hydraulic dump valve which allows the MSIV i
to close.
Failure of the pilot solenoid valve to shift as designed i
could cause a slow closure, or in the extreme case, a failure of the i
MSIV to close.
i i
i Unit 2 of the Vogtle Electric Generating Plant has two MSIV's in series
)
in each of the four main steam lines.
The MSIV's are supplied by 1
Rockwell International and are hydraulic / pneumatic actuated (Model A-290 actuators) gate valves.
These valves are designed to close in less than five seconds and isolate the secondary side of the steam generators to prevent the uncontrolled blowdown of more than ene steam 1
generator during certain accident conditions.
The MSIV tag numbers are: 2-HV-3006A & 8, 3016 A & B, 3026 A & B, and 3036 A & B.
i Engineerina Evaluation:
It was detennined that certain ambient temperature increases with the MS!V open, including a postulated small break in a steam line in the MSIV area, could cause a substantial j
increase in the actuator hydraulic and nitrogen dome pressures.
P The nitrogen dome pressure, which is the motive force used to close I
the MSIV's, will also increase with increasing temperature.
There i
was a concern that the gas pressure could become excessive and result j
}
in structural failure of the actuator pressure boundary, thereby causing j
the loss of the MSIV motive closing force.
i i
This overpressure condition was not considered in the original equipment qualification test because the valves are closed relative 1y early during i
a large steam line break scenario.
Later, when small breaks in a steam i
l line were considered, the increased temperature effects on the components I
were addressed, but the increased pressure due to thermal expansion l
of the internal fluids was not addressed.
A small break in a steam i
line results in a higher actuator temperature of concern than a large steam line break because the MSIV's may remain open for a longer period j
of time af ter the small break.
Analysis of Safety !molications: Had this condition gone undetected, it is postulated that soth M5IV's on one or more main steam lines may i
f
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MSIV OVERPRESSURE Page 2 not have closed within the required five seconds.
This could have allowed an uncontrolled blowdown of more than one steam generator following a main steam or feedwater line break.
This situation is not bounded by the current FSAR accident analyses.
The root cause of this condition was detemined to be an incomplete consideration for the pressure increases which could be caused by themal expansion of the internal fluids in an assumed leaktight system.
The pressure increase has safety implications onl if the increase in temperature occurs while the valves are open. y Each time the valves are cycled the pressure is relieved.
Other hydraulic actuators installed at Vogtle were examined to detemine if any are susceptible to similar failures.
The hydraulic actuators examined are supplied by the following vendors:
Anchor Darling - Main Feedwater Isolation Valves Paul Munroe - Atmospheric Steam Dump Valves Borg Warner - Various Valve Operators ITT General Controls - Various HVAC Damper Operators Based on review of vendor data and equipment qualification reports, it has been detemined that similar failure modes do not exist for these pieces of equipment.
Evaluation of Quality Assurance Program Breakdown: A quality assurance review of this condition and discussion with the involved parties has concluded that failure to consider this particular situation in the design and testing of the MSIV's is an isolated instance and does not represent a significant quality assurance program breakdown at Rockwell, Bechtel, or GPC.
==
Conclusion:==
Based on the results of the above analysis, the plant safety could possibly have been adversely impacted had the condition gone uncorrected.
Therefore, Georgia Power Company has concluded that a reportable condition as defined by the criteria of 10 CFR 50.55(e) and 10 CFR 21 does exist.
Based on the guidance in NUREG-0302, Revision 1, concerning duplicate reporting of an event, Georgia Power Company is reporting this event per the criteria of 10 CFR 50.55(e) for Unit 2.
This condition was reported in LER 50-424/1987-002 for Unit 1.
Corrective Action:
The corrective actions will be accomplished commensurate with the Unit 2 construction schedule and include the addition of a relief valve in the hydraulic system of the MSIV actuator to limit hydraulic Tracking System (MTS) pressure. This change will be tracked by Master number WI-AB002.
Rockwell completed testing on 2/14/87 for an A-290 actuator equipped with a relief valve.
This testing demonstrated the operability of the actuator during a postulated design basis accident environment.
o.
MSIV OVERPRESSURE Page 3 The test environment was established to conservatively encompass the expected environment following a small break in a steam line (i.e.,
the actuator was left in an open position while the environmental temperature was increased to 320*F).
During the test it was observed that hydraulic pressure did not exceed 4000 psig and therefore did not challenge the Keane solenoid valve rating of 4500 psig.
- Also, it was observed that nitrogen hemisphere pressure did not exceed 3000 psig; i.e.,
the pressure did increase beyond the hemisphere design pressure of 2800 psig, but stayed well below the hemisphere pneumatic test pressure of 3500 psig.
This condition has been reviewed by Bechtel Power Corporation and has been determined to be acceptable.
The observed test results indicate that the addition of the relief valve is a conservative resolution for the reported condition.
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