ML20079L874

Special Rept 1-SR-91-003:on 910927,reactor Trip Occurred, Resulting in Opening of Turbine Control Valve & Causing Primary Sys Temp to Decrease Below 1,837 Psia.Caused by Valid Low Pressurizer Pressure.Isolation Sys Reset

ML20079L874
Person / Time
Site:	Palo Verde
Issue date:	10/31/1991
From:	James M. Levine ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
1-SR-91-003, 1-SR-91-3, 192-00752-JML-T, 192-752-JML-T, NUDOCS 9111070167
Download: ML20079L874 (3)

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Arizona Public Service Comjuny CAL O V[ h['[ tqlX L [ AH G[ 94[ H AT !tgG 5,1 A 1 C N l' t. i 0; > s !-; i u h . y 4 a.

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"#$'d%')'lff October 31,1991

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U. S. Nuclear Regulat ory Commluton Attentlon: Document Contiol Desh Hall Station PI-37 Washington, D.C. 20$$$

Subject:

Palo Verde Nuclear Generating Station (PVNGS)

Unita 1 and 3 Docket No. STN $0 528 (License No. NPF 41)

Docket 140. STN $0 530 (License No. NPT 74)

Special Report 1 SR 91 003 filt: 91 020d!)/t Attached please find Special Report 1 SR 91 003 prepared and t.ubmitted pursuant t o Emergency plan Implement ing Procedure (EPIP 03) . This report discusses a condition requiring the declaration of a NOTIFICATION or UNUSUAL EVENT due to an event resulting in Safety injection Actuation System (SIAS) actuation, caused by a valid low pressurizer pressure. The event occurred in both Palo Verde Units 1 and 3.

If you have any questiens, please cont act D. Alan Johnsen, Compliance Supervisor at (602) 393 3703 Very t ruly yours, L g/

JML/TRI5/KR Attachment cc: W. F. C onway (all with attachment)

J. 11 Martin D. 11. Coe }

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Palo Verde Nuclear Generating Station Units 1 and 3 Notification of Unusual Event Docket Nos. 50 528 and 50 530 License Nos. NPP 51 and NPF 74 Special Report No. 1 SR 91 003 This Special Report is being provided pursuant to Doergency Plan Implementing Procedure (EP1P 03), " Notification of Unusual Event Implementing Actions" to report a condition requiring the declaration of a Notification of Unusual Event for both Palo Verde Units 1 and 3 at approximately 0729 HST on October 27, 1991, lhe Notifications of Unusual Event were terminated at approximately 0905 MST on October 27, 1991.

On October 27, 1991, at approximately 0722 MST, Palo Verde Uruts 1 and 3 were operating at approximrtely 100 percent power in Mode 1 (POWER OPERATION) when a reactor trip occurred in each unit. At approximately 0721 MST, prior to the reactor trips, the control boards in bot units indicated that Main Turbine / Main Generator large load fluct_.tions were in progress. The Main Turbine Electro llydraulic Control System (EHC) Power Load Unbalance (PLUB) circuitry initiated a Turbine Control Valve (TCV) fast closure, closing two TCVs in Unit 1 and four TGVs in Unit 3. This PLUB feature in installed in order to prevent overspeed af ter a load reject and subsequent acceleration.

The Steam Bypass Control System responded as designed to the resulting change in steam flow (i.e. , TCV closures) with a quick open signal to the steam bypass control valves (SBCVs) in order to control the secondary side pressure.

The opening of the SBCVS, combined with the reopening of the TCVs when the PLUB annunciation cleared, resulted in an excess steam demand causing primary temperature to decrease and reactor power to increase. Unit 3 received a reactor power cutback signal. The resulting reactor power transient was -

terminated by the Core Protection Calculator generated auxiliary trip signal on Variable Overpower. This resulted in a reactor trip and subsequent Main Turbine / Main Generator trip. Unit l's response to the reactor power transient was similar to Unit 3's with the exception of the receipt of the reactor power cutback signal immediately following the reactor trip.

Followinr, the reactor trip, the combination of tae modulating SBCVs and the '

reopened TCVs caused primary system temperature to decrease resulting in a pressure decrease below the low pressurizer pressure setpoint of 1837 psia. A valid actuation of the Safety Injection Actuation System (SIAS) and the ,

Containment Isolation Actuation System (CIAS) occurred in both units due to low pressurizer pressure. The Emergency plan Implementing Procadures require the declaration of a Notification of Unusual Event (NUE) for an event resulting in Safety Injection Actuation System (SI AS) actuations, caused by a valid low pressurizer pressure. By approximately 0743 MST, on October 27, 1991, the appropriate state and local agencies were notified of the condition requiring the ceclaration of a Notification of Unusual Event (i.e., event resulting in SIAS actuations). The Nuclear Regulatory Commission (NRC)

Operations Center van notified at approximately 0740 and 0756 MST on October 27, 1991, by Unit 3 and Unit 1, respectively.

, t NRC Document Control Desk Special Report 1 SR.91 003 i Page 2 By approximately 0755 MST, the SIAS and CIAS vere reset in both units. By ,

approximately 0805 MST, Control Room personnel in both units stopped Trains A  !

and B Containment Spray pumps, liigh Pressure Saf ety injection pumps, and Low i Pressure Safety injection pumps. The plants were stabilized in Mode 3 (HOT STANDBY). At approximately 0905 MST on October 2/, 1991, the Notifications of  ;

Unusual Event were terminated in accordance with EpIP.03. By approxinintely 0940 MST on October 27, 1991, the appropriate state and local agencies and the NP,C Operations Center were notified of the termination of the Notifications of Unusual Event.  !

i Turther investigation into the circumstances surrounding this event is being performed in accordance with the PVNGS Incident Investigation Prograin. The results of the investigation will be reported pursuant to 10CrR50.73. Unit 2 is in a refueling outage and was not affected by the electrical porturbation,  !

other than minor control board Class 1E inverter annunciations indicating a i disturbance (e.g., loss of synchronization).

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