ler 90-001-00:on 900308,relay failed to operate properly ... s ,. ,:42 ~- 414 nicollet mall...
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~- 414 Nicollet Mall . . .! Minneapolis, Minnesota 55401 1927 --
Telephone (612) 330 5500 - ,
April 9, 1990 '10 CFR Part 50 Section 50.73 ,
- (' | Director of Nuclear Reactor R'egulation- -i
U S Nuclear Regulatory Commission Attn: Document Control Desk Washington,'00' -20555'
' PRAIRIE ISLAND NUCLEAR' GENERATING PLANT .I
j'Docket Nos. 50 282 License Nos. DPR-42 50-306 DPR-60-
' Unit 2 Reactor Trip from Generator Lockout ,
Caused by Faulty Relav in Test Circuitry - I >
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The Licensee Event Report for this occurrence is attached.
This. event was reported via the Emergency Notification System in accordance with 10 CFR Part 50, Section 50.72, on March 8, 1990. Please contact us if . ' you require additional information related to this event.
Thomas M Parker ,
Manager Nuclear Support Services
c: Regional Administrator - Region III, NRC NRR Project Manager, NRC Senior Resident Inspector, NRC MPCA
Attn: Dr J V Ferman
Attachment i 1
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EVENT DESCRIPTION * *
On March 8, 1990, Unit 2 was at 100% power. An Operations Instructor and a trainee were making operator rounds in the Turbine Building. The bus duct cooler local panel test was to be demonstrated to the trainee. When the test button was depressed, a relay (EIIS Component Identifier: RLY) failed to operate properly and a main generator lockout signal was produced, resulting in a turbine trip and reactor trip at 1104. Plant response to the trip was as expected for a secondary side initiated reactor trip; some water hammer occurred in secondary side piping. After the circumstances of the trip were reviewed and corrective action taken, the unit was restarted.
The Generator Bus Duct Cooling System is provided to cool the generator output busses. Each of these three busses is located inside of a duct which provides protection, insulation and cooling for the bus. The bus duct cooling system
| consists of an air filter, two blowers and two water cooled heat exchangers. The system filters, cools and circulates the air inside of the bus ducts. One
| of the blowers and its associated cooler is normally in service and the other ; in standby. The standby blower / cooler unit will start if the primary unit j trips or if the bus duct temperature exceeds 62 degrees C. If the bus duct '
temperature exceeds 80 degrees C the generator is tripped automatienlly. A local control and alarm panel is provided near the bus duct coolers. The j alarm panel on this local panel is tested occasionally by the Turbine Building |operators as they make their rounds of the plant. The test circuitry is ! designed to test the trip signals without actually causing a trip to occur.
| [AUSE OF THE EVENT |
Cause of the event was failure of a test relay to operate properly, allowing a trip signal to be generated. The circuit is designed so that when the test
| button is depressed, relay K3 deenergizes, removing the trip relay (23 X) from | the circuit prior to simulating a high temperature condition. The K3 relay 1 | contacts failed to open as designed. Thus, when the high temperature i condition was simulated, a trip signal was generated, producing a generator | lockout'and resulting in a turbine trip and reactor trip.
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