ML20086S882
| ML20086S882 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 10/22/1974 |
| From: | Stallings C VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | Moseley N NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| AO-S2-74-06, AO-S2-74-6, NUDOCS 8403060007 | |
| Download: ML20086S882 (7) | |
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Vanoixx A ELucrstic ANi> Pown n C o. waxy H re n n own.Vinm xr 4 c ou rn October 22, 1974 Mr. Nor:an C. Hosoley, Director Scrial No. 291 Directorato of ncquintcry operations P0&M/JrB:c1w United Staten Atcnic Encrgy Cot::sission Region II - Suite 818 Docket No. 50-231 23f) Peachtree Street, Northvent License No. DPR-37 Atlcnta, Georgia 30303 Dent Mr. Moacicy:
Purnucnt to Surry Foner Station Technical Spacification 6.6.B.1, the Virr. inia Elcetric ar.d Pour cc pany hereby aubaito forty (40) copion of Abnernal Occurrence Ecport No. A0-S2-74-06.
The cubutance of this rcrort han Leon reviewed by the Statica Euclear Safety rnd Opernting Comittee and vill be placed on the agenda for tha nort uncting of the Syoten IIucicer Safety and Operating Cotunittee.
Y:ry truly ycuro, v
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C. M. Stallings Vice President-Pct cr F;mply and Production Operations Enclocurna 40 copies of A0-S2-74-06 Mr. K. R. Coller, Accistant Director /
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ABNORMAL OCCURRENCE REPORT REPORT NO. A0-S2-74-06 j
FAILURE OF THE MAIN STEAM LINE TRIP VALVES (TV-MS-201A,B,C)
TO FUNCTION PROPERLY r
SEPTEMBER 9,1974 i
DOCKET NO. 50-281.
LICENSE NO. DPR-37 1
i SURRY POWER STATION-VIRGINIA ELECTRIC AND POWER COMPANY 4
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INTRODUCTION In accordance with Technical Specification 6.6.B.1 for Surry Power Station, Operating License No. DPR-37, this report describes an abnormal
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occurrence which occurred on August 3, 1974 and reported to Directorate i
of Regulatory Operations, Region II, on August 5, 1974. An interim report was submitted on August 13, 1974, Serial No. 236.
The occurrence reported herein is classified by Technical Specification i
1.0.I.6 which states that "An abnormal occurrence is defined as: Engineered safeguard system malfunction or other component or system malfunction which rendered or could render the engineered safeguard system incapable of performing its intended function."
This report describes the failure of the main steam trip valves (TV-MS-201A, B, C) to function properly during the performance of a periodic test.
The valves are manufactured by Schutte and Kcerting.
S II.
SUMMARY
OF OCCURRENCE On August 3,1974 the six (6) degree freedom of movement portion of PT-14 (Main Steam Te.p Valve Periodic Test) 'was being conducted on the Unit No. 2 main steam trip valves. At the time of the test the unit was operating at 58 per cent of rated power and 440 MWe.
When tested the first time for movement, no response was received from any of the three valves.
On the second test of TV-MS-201B, all the air was bled from its actuating cylinders; the valve went fully closed before limit switches could operate solenoid valves to restore air to the cylinders. A reactor trip occurrdd-as a result of "B" steam' generator _Lo-Lo Icvel.
During the unit trip, TV-MS-201A also closed; but TV-MS-201C remained open.
i-The reactor was brought to cold shutdown following the reactor trip-
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so an investigation and required maintenance could be carried out, l
necessary.
Subsequently, non-return valves "A",."B" and "C"'ere closed w
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- and two (2) of the three (3) trip valves (TV-MS-201A & B) performed correctly when tested at this time. TV-MS-201C was similarly retested, but it still did not function.
It was necessary to disassemble this valve to attempt to find the cause for its malfunction.
III. ANALYSIS OF OCCURRENCE The three (3) main steam trip valves (TV-MS-201A, B, & C) are installed in the main steam lines outside the reactor cortainment. They are similar in design to standard swing check valves; however, they are installed counter to the normal steam flow.
Their function is to close immediately upon a steam line break signal thus preventing rapid flashing and blowdown of the shell side of the steam generator.
When tested none of the three (3) main steam trip valves would initially move. TV-MS-201B inadvertently closed when tested for the secund time, and TV-MS-201A closed upon sensing the increased steam flow following closure of TV-MS-201B.
TV-MS-201C remained fully open throughout the transient.
The investigation of TV-MS-201C revealed slight chemical buildup and mechanical binding of the rockshaf t in its stuffing box bushings.
Investi-gation af ter the disassembly of the valve revealed that chemical buildup in conjunction with rockshaft deflection caused the binding.
The binding was aggravated by a slight deflection in the rockshaft as it passes through the stuffing box bushings.
Clearance between the rockshaft and this bushing is.007.011 inches.
IV.
CORRECTIVE ACTION TO PREVENT RECURRENCE
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After having determined the probable cause for failure, the stuffing l
box bushings on TV-MS-201C were removed; cnd the oilite bushings were l
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relieved in the area which is in close proximity to the splined portion of the rockshaft, to preclude any possible interference. The chemical buildup was removed by honind.
Similar maintenance was performed on the other two (2) valves.
Extensive testing was performed on all three trip valves following maintenance and it was found that they functioned properly.
Unit No. 2 has now been in operation for approximately one and a half years, and this is the first such occurrence of chemical buildup binding in 1
the main steam trip valves.
However, a number of abnormal occurrences have 4
i been experienced with the subject valves as enumerated in the following reports:
A0-S1-73-04, A0-SI-73-05, A0-S1-73-07, A0-SI-73-10, A0-SI-73-11, A0-S2-73-07 and A0-S2-73-09.
The AEC has issued a Regulatory Operations' Information Request No. 74-2 and is investigating main steam line trip valves on a generic basis. The results of this' investigation will be reviewed in relation to the valves installed at the Surry Power Station.
1 The chemical buildup has been identified as a buildup of phosphate deposits. The source of the phosphate is a carry-over in the steam from the steam generators. Phosphate treatment is used in the feedwater to
' prevent corrosion of the steam generator tubes.
Several modifications have been made to the steam generators to. reduce 1
the carry-over; however, these have been unsuccessful. The Westinghouse Electric Corporation has recently recom= ended volatile chemistry control
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Unit No. I will initiate volatile treatment after.the refueling scheduled.
on or about October 18, 1974.
Unit No. 2 is presently shutdown for main-tenance and volatile treatment will be init'iated upon start-up..The climination of the source of phosphates will, eliminate the source of the' T
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phosphate deposits on the main steam line trip valves rockshafts.
V.
ANALYSIS AND EVALUATION OF SAFETY IMPLICATIONS OF THE OCCUliRENCE The occurrence described herein occurred as a result of improper valve performance during a periodic test.
The test was' designed to i
verify the freedom of movement of each trip valve. The actual conditions requiring main steam line isolation did not exist; therefore, there were i
no safety implications associated with this particular occurrence.
Section 14.3.2 of the Final Safety Analysis Report, Surry Power Station, presents the analysis of the. rupture of a main steam pipe.
As stated in this section, "A rupture of a main steam line is assumed to include any accident which results in an uncontrolled steam release from a steam generator. The release can occur due to a break in a pipe line or due to a valve malfunc61cn."
As stated previously, each. main steam line has a fast closing trip valve and a non-return valve. These six (6) valves prevent blowdown of more than one steam generator for any break location even if one valve fails to close. For exampic, for a break upstream of a trip valve in one line, closure of either the non-return valve in that line or the trip valves in the other lines prevents blowdown of the steam generators.
In the case of this occurrence, it is felt that in an emergency situation r
there was not sufficient binding in two of the three. main steam trip valves to prevent them from closing.
Only TV-MS-201C remained open.
If an actual steam line rupture had occurred, the requisite five (5) isolation valves would have performed their intended function;- therefore, the failurelof one (1) rain steam trip valve would not have created a significant safety hazard or an unreviewed' safety question.
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VI. CONCLUSIONS 4
j The licensee concludes that:
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The failure of the three (3) main steam line 1
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trip valves (TV-MS-201A, B, & C) to function
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binding between the rockshaft and the stuffing i
box bushings, slight chemical buildup, and i
deficction of the rockshaft as it passes through the close tolerances of the stuffint h x bushings.
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It is felt that the corrective measures taken i
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are sufficient to prevent similar recurrence 4
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of the problem.
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The occurrence described herein did not affect the safe operation of the station.
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The occurrence described herein did not present 4
l any danger to the public health or safety.
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