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Ro:On 730612,electromatic Relief Valve Failed to Close Properly Following Manual Actuation from Control Room. Caused by Sticking Valve Due to Scoured Valve Rings & Leaking Union on Pilot Tube Extension.New Rings Installed
	ML20090D392
Person / Time
Site:	Nine Mile Point
Issue date:	06/21/1973
From:	Burt P; NIAGARA MOHAWK POWER CORP.
To:	Skovholt D; US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20090D394	List: ML20090D392; ML20090D396;
References
	5015, NUDOCS 8302280102
	Download: ML20090D392 (3)
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NIAGARA MOH AWK POWER CORPORATION

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Nine Mile Point Nuclear Station 3

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Lycoming, New York 13093 June 21, 1973 Mr. Donald J. Skovholt Assistant Director for Reactor Operations Division of Reactor Licensing United States Atomic Energy Commission Washington, D. C.

20545

Dear Mr. Skovholt:

Re:

Provisional Operating License:

DPR-17 Docket No.:

50-220 k

The purpose of this letter is to report a failure of one of f

the six electromatic relief valves to close properly following manual actuation from the control room. This event which occurred on June 12, 1973 at 0808 hours0.00935 days 0.224 hours 0.00134 weeks 3.07444e-4 months , was reported by phone to Directorate of Regulatory Operations - Region I that same day and followed with a telegram sent that evening containing as much preliminary data as was availabic at that time. During the Spring 1973 refueling outage of Nine Mile Point, f

Unit #1 all six of the electromatic relief valves were overhauled.

There are three 6" Consolidated electromatic relief valves, Type 1525-VX, installed on each of the two steam lines within the drywell for a total of six. Three are required for depressurization in the loss of coolant accident and five are required to maintain pressure margin between peak transient pressure and the lowest safety valve setting on turbine trip without bypass transient. These valves were operated at low reactor power following the spring outage to ascertain their ability to function properly prior to power operation.

The reactor was operating at approximately 12% power with most of the steam being generated, bypassed to the condenser. Reactor pressure was 950 psig, torus water temperature 75'F and torus water level approximately 3.2-3.4 feet of submergence. Testing of the electromatic relief valves was in progress following' their outage overhaul.

All valves had responded satisfact-orily up to this time and operation of the fifth electromatic (#113) began at 0808 hours0.00935 days 0.224 hours 0.00134 weeks 3.07444e-4 months .

The indicated bypass steam flow to the condenser dropped from 30%

indicated (100% bypass equals 40% total steam) to 16% indicating approximately 400,000 #/hr. of steam was flowing through valve #113.

Electromatic valve #113 was then given a close signal (duration of cycle 1.32 seconds) however the indicated bypass steam flow remained at 16%. Special Procedure No, 9 (Inadvertant Operation of an Electromatic Relief Valve) was initiated and an orderly shutdown of the reactor begun.

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O Mr. Donald J.q. ovholt June 21, 1973 U. S. Atomic Energy Commission Attempts were made to close the valve by pulling the fuses and depressing the reset button.

In addition the containment spray system was aligned to cool the suppression chamber water should it be needed.

The drywell was not inerted' at this time and personnel were dispatched to close the manual blocking valve upstream of the operating electromatic.

The blocking valve was successfully closed and bypassed steam flow returned to 27% indicated.

(The reactor was being shutdown therefore the difference between starting and ending flows). Torus temperature peaked q

at 125'F indicated and torus level increased to approximately 3.6 foot sub-O me rgence.

Reactor water level and pressure remained essentially unchanged during the valve operation. The electromatic valve operated for 43 minutes and released approximately 25,000 gallons of coolant to the torus (207,000 pounds of steam). Torus coolant activity increased to 586 c/m/ml from 470 e/m/ml.

The torus temperature returned to nonnal within an hour of the incident with use of the containment spray system heat exchanger as set forth in Special Procedure No. 9.

The reactor was shutdown in an orderly manner to less than 110 psig at 1300 hours0.015 days 0.361 hours 0.00215 weeks 4.9465e-4 months the same day. No pressure changes were noted in either the drywell or torus.

Subsequent investigation of the electromatic valve revealed the valve rings were scoured (Fig. 4, part K) causing the valve _to_ stick in the opened position.

In addition a possible leeking union on the pilot valve ' hbe"exteision (part D, Fig. 4 attached) was found. This could t

have caused leakage from chamber C and thus may have reduced the motive force to close the valve. The union was replaced and new rings and guide were installed in the valve. A retest of the valve showed satisfactory operation upon three openings and closures of the valve.

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As the transient occurred from low reactor power, coolant coverage of the mactor provided no problem. Sufficient inventory is available from not only the condenser hotwell but also the condensate storage tanks; demineralized water storage at all power levels. This inventory is so established to provide normal core coverage should this transient occur from 100% power. Therefore, no unreviewed safety questions existed nor did this incident present any significant hazard to the health and safety of the general public.

Very truly yours, P. Allister Burt General Superintendent Nuclear Generation PAB: cm Enc.

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ML20090D392

Text

Dear Mr. Skovholt:

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