IR 05000285/1990021
| ML20012D079 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 03/19/1990 |
| From: | Kelley D, Seidle W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | |
| Shared Package | |
| ML20012D077 | List: |
| References | |
| 50-285-90-21, NUDOCS 9003260431 | |
| Download: ML20012D079 (7) | |
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e APPENDIX U.S. NUCLEAR REGULATORY COMMISSION
REGION IV
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NRC Inspection Report:~ 50-285/90-21 Operating License: DPR-40 s
Docket:
50-285
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Licensee: Omaha Public Power District (OPPD)
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44a South 16th Street Mall Omaha, Nebraska 68102-2247 Facility Name: FortCalhounStation(FCS)
f Inspection At: ' FCS, Fort Calhoun, Nebraska
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Inspection Conducted: February 27 through March 2, 1990
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Inspector:
hu M BI.[A, h/9[fd Inspe GFr, Test Programs
$Fte D.T. Kelley,, Eeacto[f Reactor Safety
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Section Division o
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Approved:
M-J//f/1 8 l'
W. C. Seidle.,) Chief. Test Programs Section Date Division ofWeactor Safety
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Inspection Summary Inspection Conducted February 27 through March 2,1990 (Report 50-285/90-21)
. Areas Inspected: Nonroutine, unannounced, special inspection of the loss of offsite power event on February 26, 1990, and the subsequent' failure of the-low pressure safety injection (LPSI) pump to load shed.
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Results: Within the areas inspected, no violations or deviations were
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identified. The. inspector concluded that all systems responded as designed
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iwhen operating the LPSI pumps in the manual mode. However, during manual operation of the LPSI pumps, the automatic load shed and automatic diesel
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generator output breaker closure features would be inhibited when an actual
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undervoltage initiated event occurs. This inhibited action is in variance with
,the design description Updated Safety Analysis Report, Chapter 7 and Chapter 8.
Anopenitemregardingthisfindingisidentifiedinthereport(285/9021-01).
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.Theritem will remain open pending review of the design rationale concerning m
lmanualsoperation of the LPSI pumps.
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,c DETAILS
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PERSONS CONTACTED y
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- G. R. Peterson, Manager, Fort Calhoun Station U *D. J. Matthews, Supervisor, Station Licensing
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- J. D. Kecy. Supervisor, System Engineering
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- J. L.: Connolley, System Engineer. Emergency Safeguards Features t
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- R.-L'. Jaworski, Manager, Station Engineering
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- M. T. Frans, Lead System Engineer j
- C. F. Simmons, Station Licensing Engineer
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- C, J. Brunnet, Supervisor, Quality Assurance
W. Gartner, System Engineer, Main Generator l
R. Ronning, System Engineer, Diesel Generators
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L. T. Kusek, Manager, Nuclear Safety P.eview Group s
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. A..R. Patel, Nuclear Safety Review Group Specialist
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J.'A. Spilker, Operations Engineer
- J. Friedrichsen, System Engineer
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' Denotes those attending the exit meeting on March 2, 1990.
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During the inspection, the inspector also contacted other licensee personnel.
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LOSS-0F OFFSITE POWER EVENT (93702)
l The' purpose of this. inspection was to review the circumstances-surrounding the
' loss of the offsite power event of March 26, 1990, and the failure of LPSI
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- Pump SI-1B to load shed upon loss of voltage to the auxiliary 4.16 kV Bus 1A4.
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'2.1. Loss of Offsite Power Event Description
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The plant conditions on tiarch 26, 1990, prior to the event were:
- The reactor was shutdown and in Mode 5 (refueling shutdown mode).
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' Reactor cooling system (RCS) temperature was approximately 101'F, the RCS
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was vented, and the pressurizer level was approximately 52 percent.
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LPSI Pump SI-1B was running in the shutdown cooling mode.
' The 345 kV offsite power source was providing power to the plant.-
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The _161 kV offsite power source was unavailable because of maintenance,
a Diesel Generator D1 was red tagged "out-of-service" in preparation for j
inspection (no physical work had started and the diesel generator could i
have been returned to service in an estimated time of 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />).
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The main generator disconnect DS-T1 was opened, and power was being back fed through the main transformer T1 to 4.16 kV Busses IA1, IA2, IA3, and
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IA4 via unit auxiliary power transformers TIA-1 and TIA-2. Diesel i
generator D2 was available and in the auto start mode. The following breakers were closed: 345 kV Breakers 3451/2 and 3451/6.(345 kV
switchyard ring bus breakers); 3451/4 and 3451/5 (main eenerator output l
breakers);4.16kVBreakersIA11,1A13,IA22,and1A24(Unit
Auxiliary 4.16 kV bus input breakers).
At approximately 2:50 p.m. on March 26, 1990, Fort Calhoun Station experienced a total separation of the remaining offsite power source (345 kV) because of the bumping of a relay by a licensee employee who was working inside the main control board _in the control room. The relay, 86-x/BF 5, is an intermediate relay in
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Breaker 3541/5's backup trip system. The backup trip operates if Breaker 3541/5 i
fails to open upon receipt of a trip signal from the master trip relay. The
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breaker failure protection system first attempts to open Breakers 3451/2 and i
3451/6, if breaker 3451/5 does not open.
If these breakers fail to open, the t
backup trip attempts to open the four breakers feeding the plant's auxiliary 4.16 kV busses. Relay 86-x/BF 5, when bumped, energized relay 86-2/BF 5, which
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is a second order backup trip, and this relay tripped the four 4.16 kV bus input feeder breakers locking them out.
The resultant. loss of voltage on the auxiliary 4.16 kV busses caused the load shed undervoltage relays and the diesel generator undervoltage start relays to pickup. The auxiliary 4.16 kV busses were stripped of their loads by the load shed relays (except for the operating shutdown cooling Pump SI-1B), and the diesel generator started. The diesel generator came up to speed and voltage, but the output breaker did not automatically close because shutdown cooling
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Pump SI-1B had not been stripped from the bus by the load shed undervoltage
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relays.
The control room operators took recovery action as described in Procedure E0P-02,
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" Loss of Offsite Power / Loss of forced Recirculation." The procedure addresses the situation where the diesel generator is running, but its breaker has not
closed in on it's bus. The operators checked-tripped the loads on the diesel generator bus, thereby completing the load shed, the diesel generator output breaker then automatically closed, and the operators restarted the shutdown
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cooling pump. The diesel generator was loaded in approximately 1 minute and
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shutdown cooling was restored in approximately 2 minutes. During this time, i
there was no RCS temperature increase as the unit had been shut down for
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10 days. Offsite power was restored to the auxiliary 4.16 kV busses in approximately 14 minutes.
The inspector concluded that all systems responded as designed when operating the LPSI in.the manual mode.
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No violations or deviations were identified during this portion of the inspection.
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2.2 Investigation of the failure to Load Shed
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During the event, the diesel generator output breaker failed to close automati-O cally, even though it was in the auto close mode. As noted in'the event
description of NRC Event 17844 of February 26, 1990, the shutdown
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cooling pump (SI-1B) did not load shed on undervoltage to the auxiliary 4.16 kV
~l Bus IA4. AreviewofElectricalDrawings11405-E-17(ControlSchematicfor i
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LPSIPumpSI-1B),161FS98(AutoCloseCircuitforDieselGeneratorD2 Output
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Breaker 1AD2), and 11405-E16 (4.16 kV Switchgear Schematics and Switch r
Developments) revealed the following:
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The circuit breaker for LPSI Pump SI-1B must be open to complete the auto
close permissive circuit for Diesel Generator ID2 Output Breaker 1AD2.
Anytime LPSI Pump SI-1B is started in manual, it will not-load shed, even
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though the undervoltage relays 'perate because the control switch contact
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positions in the "after start" :osition do not complete the portion.of the
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trip circuit containing the undervoltana trip contacts. This trip circuit
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is only lined up in the "after trip" ' acod by) position.
An additional review was conducted of the remaining auxiliary 4.16 kV loads i
(seetheattachmenttothisreport)includedinthedieselgeneratoroutput
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breaker permissive circuit. The review also included six 480 V motors,(three-
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HPSI> pump motors and three containment spray (CS) pump motors). 'The review revealed that the two LPSI, the three HPSI and the three CS pumps all have the J
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same. control switch scheme. This wiring scheme will prevent these pumps from
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i being-load shed if they have been started manually. However, the two LPSI pumps are the only pumps that will inhibit the diesel generator output breakers'
auto close permissive circuit.
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Additional reviews were conducted to ascertain if events similar to this one
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had occurred in the past and what controls existed for minimum power
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requirements for shutdown cooling, especially shutdown cooling in reduced RCS.
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inventory conditions. Anadditionalareareviewedwasthelicensee'sresgonse
'T to the " station blackout rule" (10 CFR Part 50.63, " Station Blackout Rule ),
specifically in the area of controlling RCS decay heat removal. The inspector
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determined that three similar events had occurred in.the past. These events
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weredescribedinlicenseeeventreports(LERs)87-008 87-009, and 88-026.
i li Theplant'sresponsewassimilarforthethreeeventsfi.e.,therunningLPSI
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y pump did not load shed, and operator action was required to load the emergency diesel). The Technical Specifications do not address minimum electric power requirements below 300'F. However, Operating Procedure OP-6." Hot Shutdown to Cold Shutdown," and Operating Instruction 01-SC-1, " Initiation of Shutdown
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I Cooling," both require that each pump to be used must have a backup power L
source. This includes operation of shutdown cooling at reduced RCS inventory
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conditions. Notwithstanding these procedural requirements, plant operation L
could still be performed with the same initial electrical conditions of this event and require the same operator response due to plant design.
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The licensee's response to the " station blackout rule" was that for the blackout period of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, the plant decay heat removal would be controlled by
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natural circulation and the turbine driven auxiliary feedwater pump. The j
licensee also pointed out that for the 4-hour period, RCS inventory losses
would not result in uncovering the core,
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The conclusions of the inspector were that the plant did respond as designed when operating the LPSI pumps in the manual mode. However, during manual
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operation of the LPSI pumps, the automatic load shed and automatic diesel i
generator output breaker closure features would be inhibited when an actual L-undervoltage initiated event occurs. This is in variance with the design
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description of Updated Safety Analysis Report, Chapter 7. Section 7.3.2.1,
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" Auto-Start of Diesel Generators," and Chapter 8. Section 8.4.3.2, " Description and Operation," and Section 8.4.3.3, " Design Analysis." As configured, if the l
event is repeated or an actual loss of offsite power occurs, the same operator i
actions described in paragraph 2.1 would be required to effect recovery. One
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question that remains unanswered refers to what the design basis is for the
control wiring scheme of the LPSI pumps. As of the date of the exit meeting, documentation had not been located, which discussed the design rationale of manual LPSI pump operation. The design rationale question will be identified
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as Open Item 285/9021-01, pending review of the design documentation.
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There were no violations or deviations identified during this portion
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inspection.
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EXIT MEETING
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An exit meeting was held March 2, 1990, with the individuals noted in paragraph 1 of this report. At the meeting, the scope of the inspection and the findings were> summarized. The licensee did not identify as proprietary any of the information provided to, or reviewed by, the inspector.
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i ATTACHMENT I
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h The following documents were reviewed during the conduct of this inspection:
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Drawings
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11405-E-1 Main One Line Diagram 11405-E-347,345/161 kV Mimic Bus Indication and Breaker Failure Backup
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. Relay Schematic Diagram
11405-E-144, 480 Y Switchgear Schematics 11405-E-142, 480 V Switchgear Schematics 11405-E-143, 480 V Switchgear Schematics 11405-E-136, Schematic and Switch Developments for Motor Driven Aux.
Feedwater Pump FW-6 11405-E-17, 4.16 kV Switchgear Schematics 11405-E-24, 4.16 kV Switchgear Schematics 11405.E-11, 4.16 kV Switchgear Schematics 11405-E-12, 4.16 kV Switchgear Schematics 11405-E-15, 4.16 kV Switchgear Schematics 11405-E-16, 4.16 kV Schematics and Switch Developments 161F598, Diesel Generator D2 Auto Close Permissive Circuit 161F597, Diesel Generator D1 Auto Close Permissive Circuit 2.
Procedures and Other Documents OP-6, Hot Shutdown to Cold Shutdown 01-5C-1, Initiation of Shutdown Cooling g
E0P-02, Loss of Offsite Power / Loss of Forced Recirculation LER 87-008, Loss of Offsite Power c
LER 87-009, Loss of Offsite Power Due to Personnel Error
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I LER 88-026 Inadvertent Start of Diesel Generator Due to Personnel Error (.-
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OPPD Letter to NRC, LIC-39-331, Subject: OPPD Response to the Station j,;
Blackout Rule as It Applies to Fort Calhoun Station Nl[ '
USAR Chapter 7, Section 7.3.2.1, Auto-Start of Diesel Generators
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USAR Chapter 8, Section 8.4.3, Automatic Transfer and Load Shedding Controls
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