ML20147A526
| ML20147A526 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1981-037-00 | |
| Download: ML20147A526 (5) | |
Text
PRECURSOR DESCRIPTION AND DATA NSIC Accession Number:
171667 Date:
December 15, 1981
Title:
Loss of Two Instrument Buses at Davis-Besse I The failure sequence was:
- 1. With the reactor at 74% power, "A"
control rod drive breaker was deenergized as part of a Control Rod Drive Breaker Logic Test.
- 2.
Construction personnel inadvertently caused a mechanical shock to nonessential breaker HAAEZ which caused a ground fault relay to activate and trip the breaker, resulting in loss of bus E2.
This caused loss of the control rod drive Inductrol Power Supply which, in conjunction with the "A" CRD breaker being open for testing caused a loss of power to the control rods and a reactor trip.
- 3.
The loss of bus E2 deenergized the power supply (E23) to the regu-lated instrumentation distribution panel YAR.
- 4.
The inverter supply (YVA) for uninterruptable instrumentation distribution panel YAU had previously transferred to its alternate supply YAR due to a defective static sensing and transfer logic card in the static switch.
Because of this, YAU was also deenergized when YAR deenergized.
Panel YAU provides power to the following:
Integrated control system Y-bus Nonnuclear instrumentation Y-bus Control rod drive system bus 2 Station annunciator Communication system A CRD redundant position indicator Computer peripherals Main feed pump turbine 1-1 control Reactor coolant pump 1-1-1 and 1-2-2 speed switches
- 5.
Loss of YAU resulted in loss of indication on both saturation meters (due to a requirement for both saturation meters to be powered from both noninterruptible power supplies YAU and YBU),
loss of auxiliary feed pump I flow indication, and trip of makeup pump 1 (when the makeup tank level time delay relay powered from YAU deenergized).
Makeup pump 1-2 was in operation at the time.
- 6.
During recovery, the auxiliary feedwater pumps were manually actuated using the steam and feedwater rupture control system and AFW pump 2 did not respond properly due to a maladjusted governor slip clutch and bent low speed stop pin.
- 7.
Main steam safety valve SP17B4 opened and failed to properly reseat and was gagged.
- 8.
Approximately 13 minutes after unit trip, bus E2 was reenergized from its alternate source by manually connecting bus E2 to its alternate feed on the B bus.
Corrective action:
- 1. All type ITH relays at the unit were adjusted to as wide a gap as possible consistent with proper relay operation.
- 2.
The defective static sensing and transfer logic card in inverter YVA was replaced and YAU was returned to its normal power supply.
- 3.
The 2 AFW pump turbine governor slip clutch was adjusted and the low speed stop pin straightened.
The governor was subsequently replaced with a space.
- 4.
Saturation margin meter wiring was modified to power the meters from one power supply each.
Design purpose of failed system or component:
- 1. Uninterruptible buses provide a continuous source of power to instrumentation and control circuity that cannot tolerate short-term power interruptions (for example, during diesel start and loading following a LOOP).
- 2.
The auxiliary feedwater pumps provide cooling water to the steam generators when the main feedwater system is unavailable.
- 3.
The makeup pumps provide RCS makeup during normal operation (separate HPI pumps are provided on Davis-Besse).
- 4.
Safety valves provide overpressure protection.
Reactor at Breaker HAAEZ Inverter supply Bus YVA de-AFW pump Main 74% power inadvertently YVA previously energized due
- 2 fails steam and "A" struck and transferred to to deenergiza-to start relief control rod trips, result-YAR due to tion of YAR.
when manu-valve drive breaker ing in loss of defective static Resultant loss ally actuated SPI7B4 deenergized bus E2, deen-sensing and of indication due to mis-fails as part of ergization of transfer logic on both satura-adjusted to CRD breaker panel YAR and cord tion meters, governor slip fully logic test reactor trip loss of AFW clutch and bent reset pump #1 flow low speed stop indication, and pin trip of makeup pump 1-1 Potential Severe Core Damage No -
AFW pump #1 available for core cooling No -
AFW pump #1 available for core cooling No No No No No No No No No No No NSIC 171667 - Actual Occurrence for Loss of Two Instrument Buses at Davis-Besse 1
Loss of Reactor Auxiliary PORV PORV or High Long Term Potential Sequence SMain Trip Feedwater and Demanded PORV Isola-Pressure Core Severe No.
Feedwater Secondary tion Valve Injection Cooling Core Heat Removal Closure Damage No 1
No 2
Yes 3
Yes 4
C(D)
No 5
No 6
Yes 7
Yes 8
No 9
No 10 Yes 11 Yes 12 (F)
Yes 13 NSIC 171667 -
Sequence of Interest for Loss of Two Instrument Buses at Davis-Besse 1
CATEGORIZATION OF ACCIDENT SEQUENCE PRECURSORS NSIC ACCESSION NUMBER:
171667 LER NO.:
81-037 Rev.
1 DATE OF LER:
December 15, 1981 DATE OF EVENT:
June 24, 1981 SYSTEM INVOLVED:
Vital power, auxiliary feedwater COMPONENT INVOLVED:
Breaker, inverter, auxiliary feedwater pumps, safety valve CAUSE:
Mechanical shock to breaker, faulted static sensing and transfer logic card SEQUENCE OF INTEREST:
Loss of feedwater ACTUAL OCCURRENCE:
Loss of vital bus REACTOR NAME:
Davis-Besse 1 DOCKET NUMBER:
50-346 REACTOR TYPE:
PWR DESIGN ELECTRICAL RATING:
906 MWe REACTOR AGE:
3.9 years VENDOR:
Babcock & Wilcox ARCHITECT-ENGINEERS:
Bechtel OPERATORS:
Toledo Edison LOCATION:
21 miles east of Toledo, Ohio DURATION:
N/A PLANT OPERATING CONDITION:
74% power TYPE OF FAILURE:
Inadequate performance; failed to start; made inoperable DISCOVERY METHOD:
Operational event COMMENT: