ML19327C262

LER 89-012-00:on 891018,reactor Tripped Due to lo-lo Steam Generator Level Due to Closure of Governor Valves.Caused by Design Error in Digital electro-hydraulic Control Sys.Valve Position Limiter Feature removed.W/891114 Ltr

ML19327C262
Person / Time
Site:	Farley
Issue date:	11/14/1989
From:	Hairston W, Dennis Morey ALABAMA POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-012, LER-89-12, NUDOCS 8911220017
Download: ML19327C262 (4)

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• Alabama Power Company 40 inverness Center Paikway -

Post Office Box 1295 Birmingham. Alabama 35201

..*, . Telephone 205 868 5581 W. G. Heireton, lli Senior Vice President November 14, 1989 s

Nuclear Operation.

Alabama Nur

"***ffcWidWT Docket No. 50-364 F

U. S. Nuclear Regulatory Commission ' '

ATTN:- Document Control Desk Vashington, D.C.' 20555

Dear Sir:

Joseph M. Farley Nuclear Plant - Unit 2 L

Licensee Event Report No. LER 89-012-00 l Joseph M. Parley Nuclear Plant, Unit 2, Licensee Event Report No. LER 89-012-00 is being submitted in accordance with 10CFR50.73.

• If you have any questions, please advise. k Respectfully submitted, e

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,p W. G. Hairston, III VGH,III/ JAR:md 8.46 Enclosure i cc Mr. S. D. Ebneter b Mr., G. F. Maxwell 8911220017 891114 gDR ADOCK0500g4 I

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NiaiCe%e"'c' F ACILITY 9eatet (1) DOCMET NUGASS R (Il FADI G1 Joseph M. Farley - Unit 2 o i s ; o ; o l o l 3l 6] 4 i lorl q 3 TITLE t4l Reactor Trip Caused By Design Error In The Digital Electro-hydraulic Control System SVGNT DAf t 40) LER NUGADER ISI REPORT DAf t (71 OTHER F ACILITIES INVOLVED tel

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At 1407 on 10-18-89, with the unit operating at 100% power, the reactor

! tripped due to lo-lo steam generator level. The lo-lo steam generator l level occurred when the turbine generator governor valves closed. This i closure resulted from a digital electro-hydraulic control (DEHC) system i design feature enhancement which causes the governor valve position limiter to lower to zero as a backup to closing the governor valves when both overspeed protection channel (OPC) power supplies fail.

This event was caused by a design error in the DEHC system. This error allowed a momentar/ data loss to be created when the operator requested l' the "Re-enable Highway" function at the DEHC Operators / Alarms Console.

This resulted in the same system control action that is taken when both OPC power supplies fail.

l The valve position limiter feature which lovers to zero as a backup to I closing the governor valves when the OPC power supplies fail has been I removed from the Unit 1 and Unit 2 DEHC systems. Vestinghouse has been

! directed to determine if there are other DEHC features available to the operator which may cause a turbine trip or turbine valve closure.

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. NRC Form 300 (64iH

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i Plant and System Identification Vestinghouse - Pressurized Water Reactor Energy Industry Identification S; stem codes are identified in the text as [XX].

Summary of Event

( At 1407 on 10-18-89, with the unit operating at 100% power, the reactor [AB]

L tripped due:to lo-lo steam generator level.- The lo-lo steam generator level

! cccurred when the turbine generator [TB] governor valves closed. This closure resulted from a digital electro-hydraulic control (DEHC) system design feature cnhancement which causes the governor valve position limiter to lower to zero as a backup to closing the governor valves when both overspeed protection channel (OPC) power supplies fail.

Description of Event On 10-18-89, the unit was operating in steady state at 100% power. _A Unit Operator was investigating a problem with the generator stator temperature s

'clarm. He pressed the DEHC selector for the system status function while he was  ;

trying to determine the cause of the alarm. Once in this system status function group he selected "Re-enable Highway", a subgroup. When this was depressed, the t turbine governor valve position limiter was automatically run to a minimum.

This caused the governor valves to go closed and the subsequent reactor trip.

-The valve position limiter function of the DEHC.had been installed to run the limiter to zero in the event that both overspeed protection channel power -

supplies failed. The DEHC design was such that when the operator requested the' "Re-enable Highway" function, the same system control action results as when both OPC power supplies fail. This in turn actuates the governor valve closure.

Following the trip, the operators implemented FNP-2-EEP-0 (Reactor Trip or Safety Injection) and .FNP-2-ESP-0.1 (Reactor Trip Response), ensuring that the unit vt.s safely in Mode 3 (Hot Standby). The unit was maintained in a normal '

statle condition.

'Cause of Event This evant was caused by a design error in the DEHC system. This error allowed  ;

l' c momentary data loss to be created when the operator requested the "Re-enable l

Highway" function at the DEHC Operators / Alarms Console. This resulted in the same system control action that is taken when both OPC power supplies fail.

l NRC f orm 30sA (6801

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oIo nit OF Ab i text en am = = n, we.wanc w asumm l Reportability Analysis and Safety Assessment This event is reportable because of the actuation of the reactor protection system. After the trip, the following safety systems operated as designed: main feedvater was isolated with flow control valves and bypass valves closed, cuxiliary feedvater pumps started automatically and provided flow to the steam generators, source range nuclear instrumentation automatically energized, and pressurizer heaters and spray valves operated as required to maintain system pressure. There was no effect on the health and safety of the public.

Corrective Action The valve position limiter feature which lovers to zero as a backup to closing the governor valves when the OPC power supplies fail has been removed from the Unit 1 and Unit 2 DEHC systems. In addition, the DEHC system status selector switch has been caution tagged to prevent its operation without the support of Computer Services personnel until additional training is given to plant operators concerning the system status function.

Westinghouse has been directed to determine if there are other DEHC features cvailable to the operator which may cause a turbine trip or turbine valve closure.

Additional Information The unit returned to criticality on 10-19-89 at 0600.

No similar LERs have been submitted by Farley Nuclear Plant.

1 No components failed during this event.

This event would not have been more severe if it had occurred under different operating conditions.

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NRC Fue 3ebA (649)

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