ML19345D850

LER 80-187/03L-0:on 801118,found Vital Instrument Power Board 2-III Being Powered from Maint Power Supply.Caused by Failure of Vital Inverter 2-III.Inverter Restored

ML19345D850
Person / Time
Site:	Sequoyah
Issue date:	12/15/1980
From:	Cottle W, Maddox S TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19345D846	List: ML19345D845 ML19345D850
References
LER-80-187-03L, LER-80-187-3L, NUDOCS 8012170605
Download: ML19345D850 (4)

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EVENT DESCRIPTION ANO PnCB ABLE CONSECUENCES h 4

[o ( 21 l At 1200 (c) on 11/17/80 a mode change was made from mode 3 to mode 2 with vital l gl instrument power board 2-III being powered from the maintenance power supply due to a [

1o 4 41 l f ailtrre of vital inverter 2-III. A deterriination was subsequent 1v made by the NRC ]

g I that a vital instrument board is inoperable when its vital inverter is out of service, f

[016] l Durine the oeriod of time between 11/9/80 and 11/23/80, there were a total of 9 vital l g i inverter 2-III failures. There was no effect on public health or safety. Previous l l0iAl l occurrences - 5. I SYSitu CAu$t C Au$f COv' vatvt CCCE CQct SusCODt CC88*cNENT COct Su8CCDs SueC0ct l0igj lE lD i@ W@ l A l@ l Gl El N l E l R l A l@ lF l@ g @ 19 20 2 3 9 10 13 12 IJ to

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ITITl l Thd vital instrument power board had been considered coerable in sccorence with I W I Technical Specification 3.0.5. At 0935 (c) on 11/18/80, notification was received i l i F21 I from NRC that a loss of an inverter makes the corresponding vital instrument board IiiJll inoperable. For all subsequent inverter failures. the applicable' vital instrument f

, i s i n I l board has been considered inoperable until the inverter was restored.

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Name of Preparer W. T. Cottle/S. G._Ma_dd_ox Phone 615-842-8261

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Tennessee Valley Authority Sequoyah Nuclear Plant

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i LER SUPPLEMENTAL INFORMATION h

SQRO-50-327/80187 Technical Specification involved: 3.8.2.1 l

Reported Under Technical Specification 6.9.1.13.b l Dates of Occurrences: 11/09/80 Times of Occurrences: 2250 (c) 11/10/80 0325 (c) 11/10/80 1250 (c) 0246 (c) 4 11/11/80 11/16/80 2135 (c) 11/17/80 1400 (c) 11/18/80 0940 (c) 11/19/80 1000 (c) 11/23/80 1235 (c) 1 Identification and Description of Occurrences:

! During the period 11/09/80 through 11/18/80, a vital instrument power board was not considered to be inoperable upon loss of a vital inverter if the j board was immediately shifted to its alternate maintenance power supply.

The basis for this decision was Technical Specification 3.0.5 which allows

, a component or system to be considered operable if (1) the normal or emer-gency power source is operable and (2) all the redundant components or systems l.

are operable. Vital instrument power board 2-III was receiving power from the j maintenance power supply at 1200 (c) on 11/17/80, at which time a mode change

' from made 3 to made 2 was made. At 0935 (c) on 11/18/80, notification was received from NRC that Technical Specification 3.0.5 was being inappropriately appliel and that the loss of an inverter makes the associated vital instrument power beard inoperable. A commitment was made by plant management to comply with the interpretation given by NRC and all subsequent inverter failures have resulted in the applicable vital instrument power board being declared inoperable i and the appropriate Technical Specification Action Statement entered. In addition, plant management agreed to provide a Licensee Event Report detailing the failures of vital inverter 2-III.

). 1. On 11/09/80, at 2250 (c) with unit 1 in mode 4, vital inverter 2-III trip--

' ped on blower failure. Vital instrument power board 2-III was declared inoperable which resulted in entering the Action Statement of LCO 3.8.2.1.

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Investigation revealed a failed resistor. The resistor was repla'ed c and l

the system was declared operable on 11/10/80, at 0205 (c).

2. On 11/10/80, at 0325 (c)' with u nit 1 in mode 4, vital inverter 2-III trip-ped. Vital 1 atrument power board _2-III was declared inoperable which resulted in entering the Action Statement of LCO 3.8.2.1.

Investigation revealed a fuse in the clipper circuit had blown and resistor-A25R1 had failed. The fuse and resistor ~were replaced and the system was l

declared operable at 1124 (c) on 11/10/80.

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LER SUPPLEMENTAL INFORMATION (Continued) 3., On 11/10/80, at 1250 (c) with unit 1 in mode 4, vital inverter 2-III tripped. Vital instrument power board 2-III was declared inoperable

, which resulted in entering the Action Statement of LCO 3.8.2.1.

Investigation revealed that resistor A25R1 had failed. This resistor was replaced and the system was declared operable at 1730 on 11/10/80.

4. At 0246 (c) on 11/11/80, with onit 1 in mode 3, vital inverter 2-III

tripped. Vital instrument power board 2-III was declared inoperable j

which resulted in entering the Action Statement of LCO 3.8.2.1.

When the inverter tripped, the vital instrument power board 2-III was immediately transferred to its maintenance supply while the vital in-verter was being repaired. Investigation revealed that the K-1 relay, RC9 temperature sensing board, and the U-9 integrated circuit located

' on the control board had failed. These parts were repladed and the 4 inverter was returned to operation at 0824 (c) on 11/11/80. At this time the vital instrument power board was still being powered from its maintenance supply and operable vital instrument power board 2-III was considered operable in accordance with the requirements of Technical Specifications 3.0.5.

On 11/12/80, at 1035 (c), vital instrument power board 2-III was removed from its maintenance supply and placed back on the vital inverter after completion of additional testing of the inverter.

5. At 2135 (c) on 11/16/80, vital inverter 2-III tripped. Vital instrument l power board 2-III was immediately shifted to the alternate maintenance power supply and was considered to be operable.

At 1200 (c) on 11/17/80, a mode change was made from mode 3 to mode sith the vital instrument power board 2-III being powered from the maintenance power supply.

? Investigation revealed that R147, Q12, and U9 intergrated circuit located on the control board had failed. These parts were replaced and the inverter was returned to operation at 1654 (c) on 11/17/80, supplying vital instrument power board 2-III.

6. At 1400 (c) on 11/17/80, vital inverter 2-III tripped. Vital instrument

> power board 2-III was immediately shifted to the alternate maintenance power supply and was considered to be operable.

Investigation revealed that the output fuses and the CR6' diode'ha'd' failed.

These components were replaced and the inverter was returned to operation at 1654 (c) on 11/17/80, supplying vital instrument power board 2-III.

1 NOTE: On 11/18/80, at 0935 (c) notification was received from NRC that the provisions of Technical Specification 3.0.5 were not appli-cable to the loss of an inverter. A loss of an inverter makes the corresponding vital instrument power board inoperable even though the vital instrument power board may be powered from its maintenance supply.

LER SUPPLEMENTAL INFORMATION (Continued) 7' . At 0940 (c) on 11/18/80, with unit 1 in made 1 at 50% RTP, vital in-verter 2-III tripped rendering vital instrument power board 2-III inoperable. This resulted in entering the Action Statement of LCO 3.8.2.1.

Investigation revealed that the RBS control board had failed. This control board was replaced and the vital instrument power board 2-III was declared operable at 1235 (c) on 11/18/80.

8. At 1000 (c) on 11/19/80, with unit 1 in mode 1 at 50% RTP, vital in-verter 2-III tripped rendering vital instrument power board 2-III inoperable. This resulted in entering the Action Statement of LCO 3.8.2.1.

Investigation indicated a loss of control voltage from the internal A10 power supply. The A10 power supply was replaced and control voltage was restored. The vital instrument power board was declared operable at 1150 (c) on 11/19/80.

9. At 1235 (c) on 11/23/80, during the performance of Startup Test 1.1, blackout at 30% RTP, vital inverter 2-III tripped rendering vital instru-ment power board 2-III inoperable. This resulted in enteri-g the Action Statement of LCO 3.8.2.1.

Investigation revealed that resistor RlB located on the A10 power supply had failed. This resistor was replaced and vital instrument power board 2-III was declared operable at 1730 (c) on 11/23/80.

NOTE: The failures of vital inverter 2-III and subsequent losses of vital instrument power board 2-III, had no adverse effect on unit 1 operations as a result of the inverter trips addresseo in this report. Although this vital instrument power board does supply control power to various separation and miscellaneous auxiliary relays associated with systems and components that are either unit 1 or shared by both units, our research has thus-far not revealed any interactions which would have a significant impact on engineered safety feature systems' performance or the capability to safely shutdown Ard cooldown unit 1.

Corrective Action:

In each instance, immediate action was taken to re-energize vital instrument power board 2-III from the alternate maintenance supply. Short term correc-tive action has been to repair vital inverter 2-III and return the inverter to service. Extensive use has been made of temporary brush recorders to attempt to determine why this particular vital inverter has experienced an unusually 1

high failure rate. This diagnostic effort is continuing.

Preparations are in progress to replace all four of the unit 2 vital inverters (2-I, 2-II, 2-III, and 2-IV) with new inverters identical to those installed in unit 1. The unit 1 inverters have demonstrated a significantly higher level of reliability since their replacement with the new units.

Studies are being made to evaluate (1) the feasibility of simplifying the

, inverter protection circuits to increase overall inverter availability and l

(2) alternate class IE instrument power supplies which might be utilized either in parallel with or in place of the inverters.

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