ML20077N799
| ML20077N799 | |
| Person / Time | |
|---|---|
| Site: | Pilgrim |
| Issue date: | 08/08/1991 |
| From: | Gina Davis BOSTON EDISON CO. |
| To: | Martin T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| 91-101, NUDOCS 9108150106 | |
| Download: ML20077N799 (6) | |
Text
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P V < uth 'Jana:.MeMs P2300 August 8,
1991 George W. Davis BECo Ltr.91-101 s~ v<e wem - w w Mr. Thomas T. Martin Regional Administrator, Region I U.S. Neclear Regulatory Commission 475 Allendale Rd.
King of Prussia, PA 19406 Docket No. 50-293 License No. DPR-35
Subject:
Response to NRC Electrical Olstribution System Functional Inspection (EDSFI) Switchgear/ Battery Room HVAC Concern
Dear Sir:
The purpose of this letter is to provide Boston Edison Company's (BECo) response to a concern raised during the EDSFI conducted July 22-26, 1991.
The concern and our assessment / corrective measures are discussed below.
This information is based on an assessment of operability that has been reviewed by the Pilgrim Operations Review Committee.
BACKGROUND The Switchgear and Battery Rooms contain safety-related equipment cooled with non safety-related ventilation.
The normal cooling air supplied to each switchgear area is 10.500 cfm at a design outside air temperature of 88 degrees Fahrenheit maximum to maintain the area at a normal operational design maximum of 105 degrees fahrenheit.
Engineering judgements or analyses during original plant design are not available and the design basis cannot be verified at this time.
Therefore, the operability of the equipment located in the Switchgear and Battery Rooms after a loss of the non safety-related HVAC is indeterminate.
The possibility exists for a loss of non safety-related Turbine Building ventilation during normal operation or a design basis accident. Ventilation can conceivably be lost due to a loss of off-site power, a major seismic event, a loss of instrument air, or a loss of Bus A3.
Preliminary analyses are indeterminate regarding the operability of the Switchgear and Battery Room equipment following a loss of ventilation.
Temperature limits above the Switchgear and Battery Room 105 degree Fahrenheit equipment design temperature for the required 30 day mission time are being evaluated.
Due to the current extent of the room heatup modeling and the lack of design basis information regarding the assumed continuous room heat loads and outdoor air temperatures, a final determination of room heatup profiles has not been completed.
1 910815 _0106 910508 n n ~_
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aPage 2 The affected safety-related electrical equipment in the Switchgear and Battery Rooms include the following:
Emergency 4KV Buses A5 and A6 X21 and X22 Stepdown Transformers B1 and 82 Emergency 480 VAC load Centers Dl, D2 and 03,125 VDC and 250 VDC Batteries D4 and DS, 125 VDC Chargers D10, 250 VDC Power Bus Dil and D12, Normal 125 VDC Charger D13, Normal 250 VDC Charger D14 and D15, Backup 125 VDC and 250 VDC Chargers D16 and 017, 125 VDC Buses D29, D30 and D31, Current Limiters fo, fault Protection D32 and D33, Sensing and Control Logic for Y10 Transfer AA504 and AA604 Undervoltage Relays for 4KV Associated Cabling e
Equipment imp,ortant to safety in Switchgear Rooms:
E/S 2600A and B, ATHS Inverters ENGINEERING ANALYSIS Since the operability of the above equipment due to a loss of ventilation is indeterminate at this time, operability is considered conditional based on the compensatory measures discussed below.
The compensatory measures will restore, as a minimum, adequate ventilation to the Switchgear and Battery Rooms for all postulated loss of ventilation events.
These measures are designed to meet the environmental design basis specified above.
This analysis is based on these actions being completed by operators and maintenance personnel in three hours.
To meet these time frames, compensatory measures specify prompt initiation of these actions based on available indications and alarms of a ventilation problem.
Temperature versus time heatup profiles were developed for the Switchgear and Battery Rooms for 100 percent power, LOCA with offsite power available, LOCA with a Loss of Offsite Power, and a Pipe Break Outside Containment. Comparison of the heatup profiles indicates the LOCA with of fsite power available heatup load is bounding.
- Page 3 A three hour, worst case room heatup profile based on LOCA heat loads and assuming
. an i'nitial room. temperature of 105 degrees Fahrenheit was used as the basis of equipment evaluation.
The worst case profile for the lower switchgear room indicates an increase to less than 122 degrees Fahrenheit over three hours.
Ventilation will then be restored that will reduce temperature below 105 degrees Fahrenheit within approximately thirty (30) minutes.
Based on published industry and vendor information, manufacturer's engineering assessment, and BECo engineering assessments, safety-related electrical equipment in the switchgear and battery rooms will be operable for at least a four hour transient above 105 degrees Fahrenheit and below 130 degrees Fahrenheit.
Therefore, sufficient time is available to implement compensatory measures without loss of operability assuming the bounding scenario.
The difference between the estimated maximum profile and the operability limits provides conservative margin.
Additional margin to equipment operability temperature limits is expected with further analysis.
Heat loads in the warmest Battery and Switchgear Room are approximately 245,NO BTU /HR.
To maintain room temperature at 105 degrees Fahrenheit, with a design
-outdoor air te.nperature of 88 degrees Fahrenheit a flow of approximately 16,000 cfm is required to each Switchgear Room.
The compensatory air flow configuration will direct all flow from a 115,000 cfm Turbine Building supply fan to Zone IV, which includes both Switchgear Rooms.
The Turbine Building supply fan can provide this flow at an increased duct pressure without causing duct failure.
Therefore, the compensatory flow configuration can remove the worst postulated room heat loads while maintaining design conditions in the rooms.
The analysis of equipment operability during room heatup with no ventilation assumed an initial temperature of 105 degrees Fahrenheit.
If this analyzed operability limit is reached, a controlled plant shutdown will be initiated.
The decision to complete plant shutdown will be based on the rate and direction of room temperature change and the current and forecast outdoor air temperatures.
POSTULATED FAILURE MODES AND COMPENSATORY MEASURES The following is a discussion of the postulated events and the compensatory measures planned to ensure equipment operability.
A loss of instrument air may cause the outside air damper for the Turbine Building supply fans to fall closed without causing a fan trip.
This damper will be blocked open whenever a supply fan is operating to preclude possible damage to the supply duct and fan.
Flow alarms will annunciate so that compensatory actions can be taken quickly to restore ventilation.
A loss of offsite power or a loss of Bus A3 de-energizes all Turbine Building ventilation except the Battery Room fans that are powered from safety buses.
Compensatory actions for these conditions include connecting a portable diesel generator to repower one Turbine Building supply fan at Load Center B3 and three Turbine Building roof ventilators at Motor Control Center (MCC) B19A from Load Center 87.
Prestaged cable will be terminated at Load Centers B3 and B7 on the l
load side of the breaker.
This action will defeat Turbine Building supply fan control circuit permissives and interlocks for low outdoor air temperature, low flow, and exhaust to supply plenum differential pressure.
Equipment protection l
will be provided by in-line fuses.
i Fans will operate to maintain a negative Turbine Building pressure while providing flow through the Switchgear and Battery Rooms.
Volume dampers at the supply plenum will be blanked off to all areas except Zone IV.
The volume damper to the Switchgear Rooms will be fully opened.
This ensures adequate flow rates to the Switchgear Rooms and that failure of ducting to other zones will not affect flow to the Switchgear Rooms.
These actions effectively restore normal or increased air flow conditions to the Switchgear and Battery Rooms.
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~a AD J A Page 4 A sdismic event represents the last mechanism for failure-of Turbine Building ventilation since this equipment, including the Battery Room fans, was not origirially designcd to seismic class I criteria.
A seismic event has the potential
-to cause a loss of power to Turbine Building. fans as well as failure of nonsafety related fans, ducting, conduit, MCCs or other associated equipment.
To address this event, the following actions have been or will be taken.
Field walkdowns of the eavipment associated with the compensatory measures are being performed.
The components and configurations are being evaluated for functionality during a Safe Shutdown Earthquake :SSE) using the Seismic Qualification Users Group (S0Z) Generic Implementation Procedure for Seismic "erification of Nuclear Power riant Equipment".
The evaluation includes inspections for seismic II,'1, ;patial interaction and anchorage consistent with the SQUG methodology as well as appropriate representation in the seismic experience database.
This evaluation is expected to conclude that the equipment can be relied upon to restart and operate after a SSE.
However, modifications may be required as a result of the ongoing evaluation.
The analyses and modifications to support seismic verification of this equipment will be completed within 36 days of plant startup.
The probability of a seismic event that could cause equipment failure is estimated to be IE-4.
The risk of a damaging seismic event is considered acceptable if the required work is performed within this time frame.
ACTIONS CEING TAKEN The following is a description of the specific actions planned to provide reasonable assurance of equipment operability during design basis events.
These measures are to remain in place until our analysis is complete or the appropriate permanent changes are made as necessary.
The actions to ensure equipment operability have been incorporated into station procedure 2.4.153, " Loss of Switchgear Area Ventilation" and are discussed below.
Switchgear and Battery Room temperatures will be monitored once a day.
A recorder is set to alarm at 95 degrees Fahrenheit for both Switchgear and Battery Rooms.
This alarm annunciates at Control Room Panel 905L-A2.
Turbine Building ventilation alarms annunciate at Control Room Panel C7L-A1.
If the temperature in any Switchgear or Battery Room reaches 95 degrees Fahrenheit, the Switchgear and Battery doom temperatures will be monitored and logged hourly until temperatures drop belas 95 degrees Fahrenheit.
The following actions will be considered, as r ressary, to improve cooling to these rooms:
The nornial lighting in the Switchgear and Battery Rooms will be de-energized.
Both Battery Room doors will be blocked open.
The plant heating water to the ventilation heating coils will be isolated and the electric heating coils will be de-energized.
-The double doors at the south end of the lower Switchgear Room will be opened.
The rollup steel fire doors at the south end of both Switchgear Rooms will be verified open.
One Battery Room exhaust fan will be verified to be running.
Both may be operated in parallel.
' Page 5 The use of blowers or upright fans may be considered with the blowers / fans properly located and secured to preclude seismic hazards.
If temperatures exceed 105 degrees Fahrenheit, a plant shutdown will be initiated unless temperatures are trending down or are stable and indicatilig a decrease based on decreasing outdoor air temperatures.
If ventilation is lost to the Switchgear Rooms the following actions will be taken as necessary:
Temperatures will be monitored every 30 minutes until ventilation is restored.
Normal Turbine Building ventilation wi oe restored, if possible.
Power to Load Centers 83 and B7 will be restored, if possible.
If-these measures _ fail to restore ventilation, then the compensatory measures will be implemented that connect the portable diesel generator to power a Turbine Building supply fan and three Turbine Building exhaust fans.
The total horsepower required to run the fans is approximately 130 HP.
The portable diesel generator is adequately sized to supply the loads.
Provisions are in place to supply additional diesel fuel prior to onsite stores being depleted so the diesel generator will be available for at least 30 days.
The portable diesel generator will be electrically connected to 480 VAC Load Centers 83 and B7.
The cables have been routed (per Plant Design Change 91-51) from the portable diesel generator to the Load Centers.
The cable is secured in the rooms and prestaged for installation.
The tools to perform the required connections are located in a dedicated tool box in the Turbine Building.
In order to maximize flow to the Switchgear and Battery Rooms, six prefabricated duct covers will be installed on the inside of the Turbine Building supply plenum.
The portable diesel generator will then be started and one Turbine Building supply fan and three Turbine Building exhaust fans will be started.
The room temperatures will continue to be monitored.
The following items have been or will be completed to ensure the required actions can be properly implemented:
Preoperational testing of the portable diesel generator was satisfactorily 1
completed.
A walkdown of the implementing procedure will be done prior to startup to confirm these actions can be completed within the allowable time frame of three hours.
A procedure is being developed to periodically test the portable diesel generator to ensure its availability.
Training, including a walkdown of the procedure, will be completed for each operating shif t prior to the shif t assuming watchstanding responsibilities after plant startup.
Administrative controls are in place to ensure availability of the required t -
equipment.
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- Page 6 SIGVIrICANT HAZARDS CQN$1 ERAT 10N BECo evaluated this condition and determined that operating with the compensatory _
. measures in. place would not involve a significant increase in the probability or-
-consequences of an accident previously evaluated.
This condition would not create-
--the possibility of a new or different kind of accident from any accident previously evaluated because the proposed modifications and procedures provide added assurance of safe shutdown equipment operability.
In addition, this condition would not involve a significant reduction in a margin of safety.
This is based on the low probability of any of the initiating events occurring which would require use of the compensatory measures.
Based on the above, BECo concluded operating with this condition would not involve a significant hazards consideration.
CONCLUSIQE Based on the engineering assessment of the design and the compensatory measures outlined above, we believe reasonable assurance of equipment operability is established so that electrical equipment can perform its safety function.
An acceptable basis for plant startup and operation is established until the ongoing system analyses can be completed.
This information is provided for your review and concurrence.
Please do not hesitate to contact me if you have any questions -regarding this issue.
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G. H. Davis
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U.S. Nuclear Regulatory Commission Attn:
Document Control Desk Hashington, D.C.
20555 Mr. R. B. Eaton Division of Reactor Projects I/II Office of NRR - USNRC One White Flint North - Mail Stop 14D1 11555 Rockville Pike Rockville, MD 20852 i
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