ML19225A118

RO 50-267/76-19A on 760617:while Reactor Was in Shutdown Condition,One Steam Water Dump Valve in Each Loop Opened. Caused by Design Problem.Failure Modes & Effects Analyzed & Steam Water Dump Circuits Revised

ML19225A118
Person / Time
Site:	Fort Saint Vrain
Issue date:	07/12/1979
From:	Gahm J PUBLIC SERVICE CO. OF COLORADO
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19225A117	List: ML19225A116 ML19225A118
References
NUDOCS 7907180444
Download: ML19225A118 (7)

Text

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NAME: l* N* CdhU NCNE: (303) 785-2253

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P2 PORT DATE: July 12, 1979 A3 NORMAL OCCURRENCE 76-19A Page 1 of 6 OCCURRE' ICE DATE: June 17, 1976 FORT ST. VRAIN NUCLEAR GENERATING STATION PU3LIC SERVICE COMPANY OF COLORADO P. O. BOX 361 PLATIEVILLE, COLORADO 80651 REPORT NO. 50-267/ 76-19A Final IEI.;TIFICATION OF OCCURRENCE:

On June 17, 1976, one steam / water dump valve in each loop was open. This has been identified as an abnormal occurrence per the Fort St. Vrain Technical Specifications, Section 2.1, paragraph f.

CONDITIONS PRIOR TO OCCURRENCE: S teady State Power Routine Shutdown Hot Shutdown Routine Load Change X Cold Shutdown Other (specify)

Refueling Shutdown Routine Startup The major plant parameters at the time of the event were as follows:

Power RTR 0 YJth ELECT 0 YJe Secondarf Coolant Pressure

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1,000 psig Temperature 174 *F Flow 100,000 #/hr.

Primary Coolant Pressure 340 psig Temperature 194 *F Core Inlet 194 *F Core Outlet Flow *

1. /hr.

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ABNORMA1. OCCURRENCE 76-19A Page 2 of 6 CONDITIONS PRIOR TO OCCURRENCE (continued) :

• Circulators lA 1,500 RPM on Feedwater 13 1,500 RPM on Feedwater 1C 1,500 RPM on Feedwater 1D 1,500 RPM on Feedwater DESCRIPTION OF O CCURRE' ICE :

The reactor operator was =aking a routine check of the plant control boards and noticed that a s ea=/ water du=p valve in each loop was open and the alarm light was lit.

APPARENT CAUSE I 0F OCCURRENCE: X Design Unusual Se rvice Cond.

I Including Environ =ent Manufacture Co=penent Failure Ins tallation/Const. Other (specify)

Op era tor Procedure ANALYSIS OF OCCURRENCE:

Reference attached Figure 1 which shows two parallel du=p valves in a loop and the trip signals which will open a du=p valve. Loop 1 and Loop 2 du=p valves discharge to a co==en s team / water du=p tank. Figure 2 shows the inter-locks which were required to be closed to open a s team / water dump valve. If a loop steam / water du=p valve is open, its relay must be energized. Th e en-ergized relay and position switches on the open valve interlock and should prevent automatic opening of either steam / water du=p valve in tF1 other loop.

The seal in circuit also insures that operator action is required to close an open valve by utilizing the hand switch.

The manual bypass can open a valve in each loop but this also requires opera-tor action.

The steam water du=p valves were tested on June 16, 1976, per approved surveil-lance test S R 5 - 3.1-Q .

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ABNORMAL OCCL"ARENCE 76-19A

? age 3 of 6 CORRE CTIVE ACTION:

f Approved test, T-46, tested the s team water du=p valve circuitry. The relay l logic system operated as specified and thers was no explanation f or the simul-taneous opening of a s team / water du=p valve in each loop.

Failure modes and effect analysis was perfor=ed. For the s team water du=p circuit as it existed, the analysis did not identify any other unacceptable

, system consequences than were known to exist. These were (1) the potential l for a concurrent du= of Loops 1 and 2 with the permissible nu=ber of moisture

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monitors out of service and tripped acco=panied by an instrument bus f ailure, and (2) du=p inhibit of Loops 1 and 2 due to single integrated circuit chip failures. For the proposed modified design, the analysis indicated both the

unacceptable system consequences stated above were eliminated and no others

! were introduced. Based on the results of these analyses, it was concluded

[ that the design modifications to the steam / water du=p system satisfy all Plant Protective System requirements and are consistent with the original design

{, basis of the plant.

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i The following describes the modifications resulting from various analysis of i the Fort S t. Vrain steam water dump system circuitry. The modifications are as follows:

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l. Made the auto =atic trip upon moisture monitor system f ailure a manual action; and revised the logic to per=it individual manual trip of the associated =cisture monitor (as opposed to disabling by pairs) .

The moisture monitor trip outputs (reflected light) were revised to transmission logic. The alar =.s and indications have been reviewed to assure that the operator is advised of moisture monitor system failure and enable him to readily ascertain manually tripped channels.

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2. Revised the relay interlocks to eli=inate an undesirable single f ailure

nhibit problem. See Reportable Occurrence Report No. 50-267/77-

'7(14)A.

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, 3. Removed the temporary time delay relay modification.

I l The modified circuits have b een functionally tested successfully, i

l The applicable operating procedure has been revised.

l l No further corrective action is anticipated or required.

FAILURE DATA /SIMILAR REPORTED OCCURRENCES:

None PROGRA"MATIC IMP ACT:

None CODE IMPACT:

None )k!

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ABNOFXAL OCCUIL" '!CE 7G-19A

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l HYDRAULIC Y I LOOP 1 VALVES SET , 1 STEAM GENERATOR

1. ENE.~GlZE "

MODULES l

TO CLOSE l AAAAAA CHECK Y VALVE bl

vs N k i FEEDWATER BLOCK REGULATING 6._ __ _ _ _ _ _ _ _ _ . _ _ _ ,

VALVE VALVE I I y . .. _ _

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T HIGH REACTOR I

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MOISTURE q/ \/ HYDRAULIC

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LEVIL SIGNALS

---t VALVES SET I

ENERGlZE

-  :# E TO OPEN l From Loo; HV-2215 y 2 Dump HIGH REACTOR l

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{ h Valves OUMP -

PRESSURE SIGNALS

---i VALVES y

l L.O. L.O.

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I g OTHER PLANT ,,,_,___J '

SIGNALS DUMP TANK l V /

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. h Steam / water du=p syste= (Loop 1)

FIGURE 1

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A3:!OR".AL OCCURRE!!CE 76-19A Page 5 of 6

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Stea=/ water dump actuating signals (1) Both Loop 2 du=p valve relay CR-2216 and CR- --

2218 de-energized % (1 T --

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(2) Both Loop 2 dump valves Manual Bypass closed (position switches }

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on Loop 2 valves). r- gg 11-

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In (3) Loop 1 or Loop 2 feedwater flow low.

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1 Prior to Circuit Revis ion f

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T (4) -Open whee _ Loop 2 T

(S) Hand switch. #l I CR Loop 1 du=p valve (6).

l (1) Relay contacts are open if the Loop 2 dump relay is energized; closed if de-energized.

(2) Valve position switches are on each Loop 2 dump valve. Contacts open it valve is not fully closed, closed if valve is closed.

(3) Contacts open if Loop 1 or Loop 2 feedwater flow is low.

(l. ) Open if Loop 2 is shutdown by PPS.

(5) Hand switch utilized to terminate a stea=/ water du=p whan required; contact no r= ally closed.

(6) Relay controlling or.e Loop 1 du=p valve relay cust energize to open a Loop 1 dump valve.

FIGURE 2 3 t(7 036 -

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A3 NORMAL OCCURRENCE 76-19A Page 6 of 6 Prepared by: W A, Micpael J. Ferr1[- j Technical Services Engineer Reviewed by-J G4h5 f W.

chnical Services Supervisor Reviewed by: 6 Frank M. Mathie Operations Manager Approved by: W4vu '

Don Warembourg Manager, Nuclear Productuan bk 0

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