ML17317B446
| ML17317B446 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 03/23/1979 |
| From: | INDIANA MICHIGAN POWER CO. |
| To: | |
| Shared Package | |
| ML17317B445 | List: |
| References | |
| NUDOCS 7908150320 | |
| Download: ML17317B446 (3) | |
Text
I.
NA 5 MICHIGAN POWER COMPANY DONALD C.
COOK NUCLEAR PLANT Operating License DPR-58 Docket No. 50-315 Special Report:
SI-12 SAFETY INJECTION ACTUATION MARCH 23, 1979 CONDITIONS PRIOR TO OCCURRENCE The Reactor was operating in Mode 1 at lOOX power with all parameters at normal values.
DESCRIPTION OF OCCURRENCE Power supplies to vital instrument Buses I and II failed, nearly simultaneously.
The first failure initiated Reactor and Unit trip.
The second failure initiated Safety Injection and Safeguard Train "B" actuation.
Steam Line isolation was also automatically initiated and all four Reactor Coolant Pumps tripped.
DESIGNATION OF CAUSE OF OCCURRENCE With the twin vital instrument bus failure, Safety Injection signals were initiated from false indication of "Steam Line Differential Pressure" and "Low Pressurizer Pressure"coincident with Low Pressurizer Level.
Steam Line isolation was initiated by false indication of "High Steam Flow" coincident with false indication Lo-Lo Tavg.
Reactor Coolant Pumps tripped because of false indication of "Underfrequency" on two of the four power busses of these pumps.
The two vital instrument buses were manually energized from the backup source.
After verification that all systems functioned properly and all operating parameters were within their normal ranges, the Unit was returned to Normal Hot Standby conditions in accordance with OHP 4022.008.003 "Termination of Safety Injection.
The failure of the two vital instrument power supplies was found to be the failure of a capacitor in each power supply.
The 250 volt D.C. battery that supplies the D.C. portion of Vital Instrument Buses I and II power supplies was under equalizing charge at. the time.
The 250 volt station batteries are normally operated at 260 volts and equalized at 280 volts.
The capacitor failures have been attributed to overvoltage.
The near simultaneous failure is attributed to the first failure causing a surge that resulted in the second failure.
ANALYSIS OF OCCURRENCE The following is a list of major items that were reviewed for their. Safety impli-cations.
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SAFETY INJECTION ACTUATION MARCH 23, 1979 SI-12
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PAGE TWO (2)
ANALYSIS OF OCCURRENCE Continued.
a)
Reactor Coolant System Cooldown Rate:
Mith the closure of the Steam Generator Stop Valves and the stopping of the Reactor Coolant Pump, this system was on natural circulation.
On the wide range loop temperature indicators T-hot reduced-from 600oF to 580oF and T-cold increased from 540oF to 550oF, for a net Tavg reduction of 5oF.
The temperatures stabilized in this area until a Reactor Coolant Pump was restarted, nearly 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> later, when all temperatures equalized at their normal hot standby value of 547oF.
b)
Thermal Effects of Safety Injection:
Safety Injection was terminated after 9 minutes of operation.
During this time the Centrifugal Charging Pump injected 1,350 gallons of bora-.
ted water with an initial temperature of 165oF into the Reactor Coolant System.
This is the twelfth (12th) inadvertant actuation of Safety Injection in which water was injected into the Reactor Coolant System and conservatively would constitute
.00030 of allowable thermal cycles.
Total accumulated, amounts to.00245 of allowable thermal cycles.
c)
Effects on the Emergency Core Cooling System Piping (ECCS)
The piping and supports in the ECCS were given a tho'rough visual inspec-tion to determine if any mechanical damage was experienced dut ing the Safety Injection.
There was no evidence of any mechanical damage or abnormal movements of the piping.
CORRECTIVE ACTIONS The voltage level for equalize charging of station batteries has been reduced to 275 volts.
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