ML20024H079

LER 91-002-00:on 910412,inadvertent Opening of Containment Purge Sys Isolation Valve Occurred.Caused by Opening of 3HV-9821 Using CR Handswitch for Valve.Valve Closed. Surveillance Procedure revised.W/910513 Ltr

ML20024H079
Person / Time
Site:	San Onofre
Issue date:	05/13/1991
From:	Krieger R SOUTHERN CALIFORNIA EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-002-02, LER-91-2-2, NUDOCS 9105210153
Download: ML20024H079 (8)

Text

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l',1,7' ['; May 13. 1991 2,C2, U. S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555

Subject:

Docket No. 50-362 30 Day Report Licensee Event Report No.91-002 San Onofre Nuclear Generating Station, Unit 3 Pursuant to 10 CFR 50.73(d), this submittal provides the required 30-day written Licensee Event Report (LER) for an occurrence involving the inadvertent opening of a containment isolation valve. Neither the health nor the safety of plant personnel or the public was affected by this occurrence, if you require any additional information, please so advise.

Sincerely,

/

l .-

Enclosure:

LER No. 91 002 cc: C. W. Caldwell (USNRC Senior Resident Inspector, Units 1, 2 and 3)

J. B. Martin (Regional Administrator, USNRC Region V)

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LICENSEE EVENT REPORT (LER)

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On April 12, 1991, at 1959, an outer containment mini purge isolation valve, 3HV 9821, was discovered open in violation of the requirements of Technical Specification (TS) 3.6.1.7.b. " Containment Ventilation System Limiting Condition for Operation." The valve was promptly closed by Control Room (CR) personnel.

Subsequent investigation determined that 3HV-9821 had been inadvertently opened at approximately 2339 on April 11, 1991 by a Control Operator (CO) (utility, licensed) during reset of the actuation circuitry for 3HV-9821. The actuation circuitry had been armed earlier in the day during surveillance testing of 3RE-7865-1 which had begun at 1030 on April 8. 1991.

3HV 9821 was opened cnd remained open as the result of a rumber of deficiencies in the areas of operator performance, surveillance procedt.res, plant status monitoring systems, and switch labeling, Corrective actions include: 1) the operator received appropriate guidance concerning performance in t.he area of problem solving and plant manipulation; 2) the' surveillance procedure will be revised prior to its next use to prevent a similar inadvertent valve opening during testing; 3) a review of the radiation monitor and containment purge valve logic circuitry is being performed; and 4) the plant status monitoring systems are being evaluated-for possibic enhancements.

There was no safety significance to this event since the inner containment isolation mini-purge valve remained closed at all times. Also, 3HV-9821 would have closed on receipt of 4.a ESFA3 signal or a high radiation signal from the containment purge vent stack radit. tion monitor,

i LICENSEE EVENT REPORT (LER) TEXT CONTINUATION ,

SAN ONorRE NUCLEAR GENERAT' I TATION DOCKET NUMBER LER NUMBER PAGE UNIT 3 05000362 91 002 00 2 of 7 Plant: San Onofre Nuclear Generating Station  !

Unit: Three Reactor Vendor: Combustion Engineering Event Date: 04 12 91 Time: 1900 A. CONDITIONS AT TIME OF THE EVENT:

Mode: 1, Power Operation B. BACKGROUND INFORMATION:

1. Cost.inment Purge System:

The isntainment purge system is comprised of two sub systems, each having a supply and exhaust unit, which are used under different >

circumstances to reduce airborne radioactivity to provide for personnel habitability inside containment [NH). The normal purge system is used when the unit is shutdown and the mini-purge system is used when the unit is in operation and personnel entry into containment is necessary. For each of these systems, a supply unit fan [ FAN) draws-outside air through a profilter [FLT) and discharges the air through two containment isolation purge valves [lSV) and ducting (DUCT) into the containment building, Each exhaust unit fan draws air from the containment building through ducting and two containment isolation purge valves and discharges the air to the containment purge stack, The mini-purge containment isolation  ;

valves are air operated and fail closed.

All containment mini-purge system isolation valves will close automatically on any.one or more of the following Engineered Safeguards Features Actuation System (ESEAS) signals: 1) Containment Purge Isolation Signal (CPIS), 2) Safety Injection Actuation Signal  !

(SIAS), and 3) Containment Isolation Actuation Signal (CIAS), All containment normal purge valves will close automatically on a CPIS signal. In addition, the outside containment purge system isolation  ;

i valves will close on high radiation from_the Containment Purge Stack

! Radiation Monitor [ MON), RE-7828 (or the Plant Vent Stack Wide Range Gas Monitor, RE 7865-1, when it is aligned to sample the containment purge stack). This non Engineered Safeguards. Feature (ESP) ensures that purge gaseous radiation release limits are not exceeded.

2. Radiation Monitors:

3RE 7828 generates an alarm and initiates the closure of the four outside containment purge / mini-purge istlation valves on high .

radiation levels, radiation monitor inst.ument failure, or on loss of power to the monitor.

m._ an __ _____;_.u___._____ _ , _ _ _ . _ , _ . . _ _ , _ _ , _ . ,_ , _ . _ _

• l LICENSEE EVENT REPORT (LER) TEXT CONTINUATION SAN ONOFRE NUCLEAR CENERATION STATION DOCKET NUMBER LER NUMBER PACE-UNIT 3 '05000362 91-002 00 3 of 7 l 3RE-7865 1 can be aligned to sample either the plant vent stack or the containment purge stack. If aligned to the plant vent stack, 3RE-7865 1 generates en alarm (AIJt) and initiates closure of the vaste gas discharge header flow control valve [FCV) on high radiation levels, radiation monitor instrument failure, or loss of power to the monitor. If aligned to the containment purge stack, 3RE 78651 generates an alarrn and initiates closure of the four outside containment purge /tnini purge isolation valves on high radiation levels,-radiation monitor instrument failure, or loss of power to the radiation monitor.

3. Containment Purge System Isolation Valve Controls .

1 As previously described, the raini purge containment isolation valves l are air operated. Air to open the valves is provided through two l fail closed solenoid valves [FSV) installed in series between the i air supply and the valve actuator for each valve. Or.e of these solenoid valves (which is normally open) is controlled by the selected non ESF radiation monitor. The other solenoid valve (which

. is normally closed) is controlled by the valve's Control Room (CR) handswitch [HS) and the previously discussed ESFAS signals, such that an ESFAS actuation signal (to close the valves) cannot be overridden by a CR handswitch open signal.

Upon a loss of power or a high radiation alarin [RA) to radiation '

monitors, 3RE 7828 or 3RE-7865-1, the non ESF solenoid valves are de energized closing the associated purge valve and a reset switch in the CR is illuminated. When the close signal from the radiation monitor is' cleared, this reset switch allows-the non-ESF radiation >

monitor controlled solenoid valves to be opened. If the other solenoid valve ir. also open, the containment isolation valve will open.

This arrangement assures that an ESFAS signal to the containment purge system will close the outer containment purge isolation valves irres.pective of the position of the non ESF solenoid valve.

4 Technical Specification (TS): '

TS 3.6.1.7.b, " Containment Ventilation System Limiting Condition for

~

l Operation," requires the containment purge supply and exhaust isolation valves to be OPERABLE, and each 8 inch containment mini-purge and supply isolation valve to be closed to the maximum extent practicablo. -These valves may be open for purgo system operation for pressure control, for ALARA and respirable air quality considerations for personnel entry, and for surveillance tests that require the valve to be open.

TS 3.6.1.7 action "a.2" requires that with the 8-inch containment =

l mini-purge supply and/or exhaust isolation valve (s) open for reasons l other than as stated in Specification 3.6.1.7.b, the open valve (s)

-.- - - - - . - . _ - . , , . - . . , . - - . . - . . . - . - , - - . ~ . . - . - - . . - - - . . - . - - - . . - _ - - . _ - , , - .

l .

i LICENSEE EVENT REPORT (LER) TEXT CONTINUATION ,

SAN ONOFRE NUCLEAR GENERATION STATION DOCKET NUMBER LER NUrCER PAGE UNIT 3 , 05000362 91 002 00 4 of 7 must be closed or isolated by a blind flange within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> or the plant must be taken to 110T STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SilUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

Y t

C. DESCRIPTION OF Ti!E EVENT:

1. Event:

On April 12, 1991, at 1959, an outer containment mini purge isolation valve, 318V 9821, was discovered open contrary to the requirements of TS 3.6.1.7.b. The valve was promptly closed by ,

Control Room (CR) personnel (utility, licensed) after determining ,

that no activity was in progress which required it to be open.

• Subsequent investigation determined that 311V 9821 had been inadvertently opened at approximately 2339 on April 11, 1991 by a Control Operator (CO)-(utility, licensed) during reset of the actuation circuitry for 311V 9821. The actuation circuitry had been armed earlier in the day during surveillance testing of 3RE 78651 which had begun at 1030 on April 8, 1991. i

2. Inoperable Structures, Systems or Components that Contributed to the Event:

Not applicable.

3, Sequence of Events:

DAIE IIt1E ACTION 4-8 91 -1030 3RE 7865 surveillance initiated.

4 11 91 1812 311V 9821 opened. for loss o! power test on 3RE 7865 1, 4 11 91 1813 31tV 9821 closed upon receipt of a loss of power signal from 3RE 7865-1, 4-11-91 ~1900 surveillance test of 3RE 7865-1 is completed for the shift.

4 11-91 2339 Unit 3 CD depresses the reset switch for 311S 7828 and 311V 9821 opens.

4-12-91 1959 31tV 9821 is discovered open and is closed.

4 14 91 1800 3RE-7865 1 su;veillance is completed.

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LICENSEE EVENT REPORT (LER) TEXT CONTINUATION SAN ON0FRE NUCL" EAR GENERATION STATION DOCKET NUtiBER LER NUMBER PAGE UNIT 3 0,1000362 91 002 00 5 of 7

4. Method of Discovery:

CR personnel discovered 3HV 9821 open during routine control board walkdowns.

5. Personnel Actions and Analysis of Action:

Upon discovery of the opened valve, CR personnel promptly closed 3HV 9821-

6. Safety System Responses:

Not applicable.

D. CAUSE OF THE EVENT:

SCE's investigation of this event to nd that during surveillance testing of 3RE 78651, 3HV 9a21 tas opened ec 1812 on 41191 using the CR handswitch for.the valv<.. One mitiute later, 3HV-9821 closed as the result of a loss of power signal to 3RE-7865-1 as a part of the surveillance test. Following automatic closure of the mini-purge valve, the 3HV-9821 CR handswitch 5as left in a condition which resulted in the valve opening when the commot reset switch for 3RE 7865 1 and 3RE-7828 was depressed.

Procedure The surveillance procedure did not ensure that the logic.for 3HV 9821 was reset to the normal valve closed' condition by requiring that the CR close handswitch button be depressed immediately after testing the valve closure logic on a-loss of power-to the-radiation monitors, >

Labeling ,

As previously described, the radiation monitor and containment purge isolation valvo logic circuitry design (which controls the containment purge / mini purge valves),-reopens-the non-ESF air supply solenoid valve (s) when the reset. switch _is depressed. The reset switch was labeled

" Containment Purge Stack Radiation Monitor 3HS 7828" indicating that it only affected the one radiation monitor. It did not contain any reference to its reset function with respect to 3RE-7865-1. As a result, prior to depressing the illuminated reset. switch, the CO did not recognize that radiation monitor 3RE 7865 1 could also have actuated-the reset switch.

Operator Performance The CO did not follow established guidance-for operator performance in the areas of problem solving and plant manipulation by 1) not fully investigating all reasons.why the reset light was illuminated and 2) not cor.sulting with other CR personnel who were fully aware of the status of the in progress surveillance and t he consequence of his action.

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LICENSEE EVENT REPORT (LER) TEXT CONTINUATION SAN ONOFRE NUCLEAR GENERATION STATION DOCKET NUMBER LER NUMBER PAGE UNIT 3 05000362 91 002 00 6 of 7 '

In addition, during shift relief, ptocedures direct the operators to check the status of all ESF valves that have main control board indication, which includes this valve. This review was inadequately performed during the next two shifts and.as a result the misalignment of 3RV 9821 was not detected during this period.

Plant Status Monitoring When the reset switch was depressed, the change in 3HV 9821 po.ition was indicated on the main control panel, the valve position status indication on one of the display pages of the Critical Functions Monitoring System (CFMS) and as an entry on the Plant Monitoring System (PHS) computer. The design of these systems does not initiate an audible alarm which would

, have alerted the operators to the change of valve position.

l E. CORRECTIVE ACTIONS:

1. Corrective Actions Taken:

a. The CO who depressed the reset switch received appropriate guidance concerning performance in the area of problem solving and plant manipulation.

b. A sign was posted adjacent _ to _ the reset switch warning CR personnel to check purge / mini purge valves after resetting the

-reset switch to insure they are in the required position for the plant mode-or evolution.

2. Planned Corrective Actions:

a. Applicable radiation monitor surveillance procedures will.be revised prior to their next use to require that the containment purge isolation valve open signal be removed at the handswitch immediately after each test of valve closure by a signal from a radiation monitor,

b. A review of the radiation monitor and valve logic circuitry which controls the main-purge / mini-purge valves is in progress to evaluate a design enhancement to eliminate valve reopening upon reset of the radiation monitor,

c. As a result of a corrective action described in LER 90 010 (Docket-Nos. 50 362), an engineering evaluation is being i- performed to identify critical Engineered Core Cooling System L valves and Containment Spray system valves not having audiblo annunciation of misalignment whose initial position is critical to component or system operability. As a result of the late discovery of_the misalignment of 3HV 9821, the_ scope i of this evaluation is being expanded to include other valves l

l 1

• *,e

___ a LICENSEE EVENT REPORT (LER) TEXT CONTINUATION

' SAN ONOFRE NUCLEAR GFM'lATION STATION DOCKET hdMBER LER NUMBER PAGE 1 UNIT 3- 05000362 91-002-00 7 of 7 which can be remotely positioned from the CR and can impact the containment isolation function. Appropriate corrective

-action will be implemented.

d. The reset switch and the adjacent warning label will be relabeled to fully identify all equipment affected,

e. This event will be reviewed with CR personnel emphasizing the function of the reset switch, shift turnover requirements, valve indication status, and CR communications,

f. The existing computer based data systems are being evaluated to deteraine if they can be modified to provide the Operations staff with greater visibility of the status of critical valves. This evaluation is a result of a corrective action described in LER 90 010 (Docket Nos. 50 362).

F. SAFETY SIGNIFICANCE OF THE EVEhT:

There was no safety significance to this event since the Janer containment isolation mini-purge valve renained closed at all times. Also, 3HV-9821 would have closed on receipt cf a CPIS, SIAS, CIAS or a high ra 'intion signal from the_ radiation monitor.

G. ADDITIONAL INFORMATION:

1. Component Failure Information:

Not applicable.

2-. Previous LERs for Similar Events:

None, l

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