ML20035H053
| ML20035H053 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 04/28/1993 |
| From: | Andersen J Office of Nuclear Reactor Regulation |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 9305030040 | |
| Download: ML20035H053 (37) | |
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A UNITED STATES
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NUCLEAR REGULATORY COMMISSION Q'
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April 28,1993 Docket No. 50-245 LICENSEE: NORTHEAST NUCLEAR ENERGY COMPANY FACILITY: MILLSTONE NUCLEAR POWER STATION, UNIT 1
SUBJECT:
SUMMARY
OF APRIL 22, 1993, MEETING REGARDING PROPOSED MODIFICATIONS TO THE COMBUSTIBLE GAS CONTROL SYSTEM AND IMPLEMENTATION OF THE HARDENED WETWELL VENT On April 22, 1993, the NRC staff met with Northeast Nuclear Energy Company (NNECO) to discuss their proposed modifications to the combustible gas control system and implementation of the hardened wetwell vent at Millstone Unit 1. is the list of individuals who participated in the discussion. is NNECO's agenda and handout.
The following is a summary of the significant items discussed.
NNECO presented a detailed description of the current nitrogen inerting system and each of its components. NNECO stressed the reliability of the system and discussed the location, maintenance, accessibility under postaccident conditions, and potential redundant backups for all the major components.
NNECO also described the operation of the nitrogen inerting system under normal conditions and as it would be used during startup and shutdown.
NNECO then presented several upgrades which they are considering to the system. The upgrades would include an alternate nitrogen supply, an alternate pneumatic supply to some of the containment isolation valves within the nitrogen inerting system, and some minor modifications to the nitrogen skid piping. NNEC0 stated that these upgrades would improve the postaccident reliability of the nitrogen inerting system.
NNECO described the nitrogen inerting system vulnerability study which was conducted prior to the identification of the proposed modifications. The study concluded that most of the components could be repaired or that an alternate component could be used to achieve system success. Also, with the addition af the alternate nitrogen supply, nitrogen could be supplied to the inerting system, bypassing the storage tank, vaporizer, and the associated valves.
By providing the alternate pneumatic supply to several containment isolation valves within the nitrogen inerting system, the reliability of the containment isolation valves would improve under postaccident conditions, in that they could be opened totally independent of electrical power.
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i NNEC0 also presented an alternate design for the hardened wetwell vent. The alternate design is tied to the inerting supply system instead of the containment venting system. NNEC0 has committed to installing the hardened wetwell vent no later than the next refueling outage, which is scheduled for February 1994, or at an outage of sufficient duration (4-6 weeks). NNECO's alternate design could still be implemented in order to meet the February 1994 commitment date, but could not be installed during an outage of sufficient c
duration until the engineering design process is complete (should be completed by August 1993). The staff agreed with this new schedule, but recommended that NNECO update the docket to reflect the new installation schedule and design.
As a result of the discussion, the staff recommended that after NNECO has completed its review of the proposed modifications to the nitrogen inerting i
4 system, that they docket the information in order for the staff to conduct a
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formal review.
This review of the modifications, if found to be acceptable, t
would then resolve the open TAC number on the combustible gas control issue.
1 NNECO indicated that they would be able complete the engineering design process and docket the information presented at the meeting by approximately June 1993.
j Driginal signed by d
j James W. Andersen, Acting Project Manager l
Project Directorate I-4 2
i Division of Reactor Projects - I/II Office of Nuclear Reactor Regulation
Enclosures:
As stated 2
i cc w/ enclosures:
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Document Name:
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i Northeast Nuclear Energy Company l NNECO also presented an alternate design for the hardened wetwell vent.
The alternate design is tied to the inerting supply system instead of the l
containment venting system. NNEC0 has committed to installing the hardened wetwell vent no later than the next refueling outage, which is scheduled for l
February 1994, or at an outage of sufficient duration (4-6 weeks). NNEC0's alternate design could still be implemented in order to meet the February 1994 commitment date, but could not be installed during an outage of sufficient duration until the engineering design process is complete (should be completed by August 1993).
The staff agreed with this new schedule, but recommended that NNECO update the docket to reflect the new installation schedule and design.
As a result of the discussion, the staff recommended that after NNEC0 has completed its review of the proposed modifications to the nitrogen inerting system, that they docket the information in order for the staff to conduct a formal review. This review of the modifications, if found to be acceptable, would then resolve the open TAC number on the combustible gas control issue.
NNECO indicated that they would be able complete the engineering design process and docket the information presented at the meeting by approximately June 1993.
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r James W. Andersen, Acting Project Manager Project Directorate I-4 Division of Reactor Projects - I/II Office of Nuclear Reactor Regulation
Enclosures:
As stated cc w/ enclosures:
See next page i
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Distribution:
Docket File NRC &- Local PDRs PD I-4 Memo T. Murley/F. Miraglia J. Partlow S. Varga t
J. Calvo 3
J. Andersen i
S. Norris OGC E. Jordan
.D. Jaffe J. Stolz i
A. Dromerick M. Thadani R. Lobel W. Long ACRS (10)
V. McCree, EDO L. T. Doerflein, RI J
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l Mr. John F. Opeka Millstone Nuclear Power Station Northeast Nuclear Energy Company Unit-1 i
l cc:
Gerald Garfield, Esquire R. M. Kacich, Director Day, Berry and Howard Nuclear Licensing Counselors at Law Northeast Utilities Service Company City Place Post Office Box 270 i
Hartford, Connecticut 06103-3499 Hartford, Connecticut 06141-0270 I
W. D. Romberg, Vice Presi_ dent J. P. Stetz, Vice President Nuclear Operations Services Haddam Neck Plant-I Northeast Utilities Service Company Connecticut Yankee Atomic Power Company l
Post Office Box 270 362 Injun. Hollow Road l
Hartford, Connecticut 06141-0270 East Hampton, Connecticut 06424-3099 l
t Kevin McCarthy, Director Regional Administrator Radiation Control Unit Region I Department of Environmental Protection U.S. Nuclear Regulatory Commission State Office Building 475 Allendale Road l
Hartford, Connecticut 06106 King of Prussia, Pennsylvania.19406
.}
Allan.Johanson, Assistant Director First Selectmen j'
Office of Policy and Management Town of Waterford Policy Development and Planning Division Hall of Records 80 Washington Street 200 Boston Post Road l
Hartford, Connecticut 06106 Waterford, Connecticut 06385 S. E. Scace, Vice President P. D. Swetland, Resident Inspector Millstone Nuclear Power Station Millstone Nuclear Power Station Northeast Nuclear Energy Company c/o U.S. Nuclear Regulatory Commission l
Post Office Box 128 Post Office Box 513 i
Waterford, Connecticut 06385 Niantic, Connecticut 06357 i
H. F. Haynes, Nuclear Unit Director G. H. Bouchard,-Director i
Millstone Unit No. I Nuclear Quality Services Northeast Nuclear Energy Company Northeast Utilities Service Company Post Office Box 128 Post Office Box 270 Waterford, Connecticut 06385 Hartford, Connecticut 06141-0270.
I Nicholas S. Reynolds Winston & Strawn 1
1400 L Street, NW l
Washington, DC 20005-3502 i
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COMBUSTIBLE GAS CONTROL AND HARDENED VENT ATTENDANCE LIST NAME ORGANIZATION Dave Jaffe NRR/PDI-4 John Stolz NRR/PDI-4 Jim Andersen NRR/PDI-4 Alex Dromerick NRR/PDI-4 Mohan Thadani NRR/PDII-4 Richard Lobel NRR/SCSBA William Long NRR/SCSBA Nirmal Jain NU G. E. Cornelius NU Jack Quinn NU D. N. Harris NU Don Cleary NU Peter Miner NU i
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MILLSTONE UNIT NO.1 DOCKET NO. 50-245 I
I NRC/NU MEETING l
HARDENED WETWELL VENT APRIL 22,1993 t
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AGENDA T
f INTRODUCTION P. J. MINER PURPOSE OF MEETING P. J. MINER SYSTEM DESCRIPTION D.S.CLEARY PROPOSED PLANT IMPROVEMENTS J. M. QUINN SYSTEM EVALUATION N. K. JAIN POSTACCIDENT OPERATION N. K. JAIN HARDENED WETWELL VENT PROJECT G. E. CORNELIUS
SUMMARY
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MP1 ENGINEERING G. E. CORNELIUS PROJECT SERVICES D..N. HARRIS NUCLEAR LICENSING N. K. JAIN NUCLEAR ENGINEERING P. J. MINER NUCLEAR LICENSING J. M. QUINN MP1 ENGINEERING l
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INTRODUCTION NU BELIEVES MILLSTONE UNIT NO 1 COMPLIES WITH 10CFR50.44 WILLING TO EXPLORE COST-EFFECTIVE IMPROVEMENTS IN AN EFFORT TO BRING ISSUE TO CLOSURE NRC ISSUED SER TO OYSTER CREEK REGARDING NITROGEN INERTING SYSTEM (NIS) ENHANCEMENTS NU REQUESTED TO REVIEW SER RELATIVE TO MILLSTONE UNIT NO.1 NU IDENTIFIED THE IMPORTANT DESIGN CHARACTERISTICS OF NIS RELATIVE TO COMBUSTIBLE GAS CONTROL c
PERFORMED VULNERABILITY STUDY RESULTS OF EVALUATION INDICATE THAT SIMPLE DESIGN MODIFICATIONS COULD BE MADE TO FURTHER IMPROVE THE POSTACCIDENT RELIABILITY OF THE EXISTING NIS 4
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PURPC'SE OF MEETING TECHNICAL EXCHANGE OF INFORMATION WITH NRC' STAFF PROVIDE A DESCRIPTION OF THE EXISTING NIS PRESENT PROPOSED IMPROVEMENTS TO THE EXISTING NIS TO INCREASE POSTACCIDENT RELIABILITY PROVIDE THE STAFF WITH THE RESULTS OF OUR EVALUATION OF THE NIS AND POSTACCIDENT OPERATION OF NIS DISCUSS THE SYNERGY WITH HARDENED WETWELL VENT
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SYSTEM DESCRIPTION NITROGEN SUPPLY LIQUID NITROGEN TANK (CAPACITY IS APPROXIMATELY 950,000 SCF)
MINIMUM INVENTORY IS 400,000 SCF STANDING PURCHASE ORDER.WITH VENDOR MANUAL CONNECTION FOR TANKER HOOK-UP
- LOCAL TANK LEVEL INDICATION LOCAL TANK PRESSURE INDICATION PRESSURE BUILD-UP COIL r
-COMPONENTS LOCATED IN YARD i
WOULD BE ACCESSIBLE POSTACCIDENT 6-
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VAPORIZER
- STEAM VAPORIZER SIMPLE HEAT EXCHANGER DESIGN LOCATED IN YARD HOUSE HEATING STEAM (HHS) UTILIZED AS HEAT SOURCE 2 BOILERS POWERED BY MILLSTONE UNIT NO.1 1-BOILER POWERED BY MILLSTONE UNIT NO. 2 WOULD.BE UTILIZED DURING LOSS-OF-NORMAL POWER (LNP)
AT MILLSTONE UNIT NO.1 BOILERS LOCATED IN TURBINE BUILDING MILLSTONE UNIT NO. 2 REBOILER COULD BE UTILIZED AS BACKUP, IF AVAILABLE.
CAPABILITY EXISTS FOR CONNECTION OF PORTABLE BOILER PREVIOUSLY UTILIZED WOULD BE ACCESSIBLE POSTACCIDENT
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- PROCESS CONTROL CONTAINMENT ISOLATION VALVES (CIVs)
' AC-5, -6, -17 PROVIDE AUTOMATIC CONTAINMENT ISOLATION FUNCTION ON GROUP ll SIGNAL ELECTRICAL POWER TO SOLENOID OF AIR OPERATED VALVES FROM INSTRUMENT AC PNEUMATIC SUPPLY FOR AIR OPERATED VALVES FROM INSTRUMENT AIR CIVS FAIL CLOSED ON LOSS OF AIR OR ELECTRICAL POWER INTERLOCKS MUST BE BYPASSED TO OPEN CIVS WHILE GROUP ISOLATION SIGNAL IS PRESENT CAPABILITY TO BYPASS INTERLOCKS CURRENTLY EXISTS FROM CONTROL ROOM (CR)
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CIV POSITION INDICATED IN CR OPERATED FROM CR CIVs LOCATED IN REACTOR BUILDING (RB)
CIV SOLENOIDS ENVIRONMENTALLY QUALIFIED SURVEILLANCE / TESTING ADDRESSED IN TECHNICAL SPECIFICATIONS 8
PROCESS VALVES i
AC-16, -89 l
AC-16 PROVIDES FLOW CONTROL i
AC-89 PROVIDES LOW TEMPERATURE / LOW STEAM PRESSURE PROTECTION ELECTRICAL POWER TO SOLENOID OF AIR OPERATED VALVES FROM INSTRUMENT AC PNEUMATIC SUPPLY FOR AIR OPERATED VALVES FROM INSTRUMENT AIR VALVES FAIL CLOSED ON LOSS OF AIR OR ELECTRICAL POWER POSITION INDICATED IN CR 5 OPERATED FROM CR VALVES LOCATED IN YARD WOULD BE ACCESSIBLE POSTACCIDENT
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REMAINING VALVES ARE MANUAL VALVES l
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INSTRUMENT AC REQUIRED FOR NORMAL PLANT OPERATION L
NORMAL AND BACKUP POWER SUPPLIES
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INSTRUMENT AIR 2 AIR COMPRESSORS (RECENTLY UPGRADED) 1 COMPRESSOR AUTOMATICALLY LOADED ONTO GTG OTHER CAN BE MANUALLY LOADED ONTO DG RECENT MODIFICATIONS TO INCREASE AIR RESERVOIR SIZE STATION AIR COMPRESSOR MAY BE UTILIZED A,S BACKUP
< MILLSTONE UNIT NO. 2 AIR SYSTEM MAY BE CONNECTED AS BACKUP AIR MAY BE MANUALLY SUPPLIED FROM PORTABLE BOTTLES 11
INSPECTION AND TESTING SYSTEM WALKDOWN BY PLANT EQUIPMENT OPERATOR EACH SHIFT INCLUDES TANK LEVEL AND PRESSURE
- CIV SURVEILLANCE TESTING IN-SERVICETESTING STROKE TIME TESTING APPENDIX J LEAKRATE TESTING SYSTEM OPERATIONAL TESTING TESTED BY ROUTINE OPERATION OF THE SYSTEM TF.STED BY INERTING THE PRIMARY CONTAINMENT DURING STARTUP OR FOLLOWING DRYWELL ENTRY h
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MAINTENANCE UNIT PERSONNEL PERFORM MAINTENANCE ON SYSTEM FAMILIAR WITH SYSTEM ROUTINE PREVENTIVE MAINTENANCE ON CIVs CORRECTIVE MAINTENANCE INITIATED BY TROUBLE REPORT NO AREAS OF CONCERN WITH PERFORMANCE OF COMPONENTS INSTRUMENTS CALIBRATED NITROGEN FLOW TRANSMITTER - ANNUALLY VAPORIZER LOW TEMPERATURE CUTOFF SWITCH - EVERY TWO YEARS 6
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ALTERNATE NITROGEN SUPPLY ALTERNATE FILL CONNECTION WOULD BE PROVIDED OUTSIDE OF RB DISCUSSIONS WITH CURRENT NITROGEN SUPPLIER INDICATE
- ADDITIONAL NITROGEN COULD BE PROVIDED WITHIN 8 HOURS NITROGEN GAS CURRENTLY PREFERRED CHOICE DUE TO AVAILABILITY ALTERNATE PNEUMATIC SUPPLY TO CIV ACTUATORS 2
INSTRUMENT TUBING WOULD BE PROVIDED TO ACTUATE AIR OPERATED VALVES.WITH PNEUMATIC SUPPLY FROM OUTSIDE OF RB MINOR MODIFICATION TO NITROGEN SKID PIPING THREADED FITTINGS WOULD BE INSTALLED TO ADDRESS-VULNERABILITY STUDY FINDINGS 14 c
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SYSTEM EVALUATIC'N IDENTIFIED IMPORTANT DESIGN CHARACTERISTICS REVIEWED APPROPRIATE PROCEDURES EVALUATED POSTACCIDENT SYSTEM PERFORMANCE PERFORMED VULNERABILITY STUDY t
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NIS VULNERABILITY STUDY.
ASSUMPTIONS RB IS INACCESSIBLE NO REPAIR IN THE RB IS CREDITED REPAIR OR REPLACEMENT OF COMPONENTS OUTSIDE RB IS CREDITED IF COMPONENT-IS:
~ ACCESSIBLE, AND SCREWED OR FLANGED, AND MAY BE ISOLATED FROM NITROGEN TANK NO REPAIR OF WELDED COMPONENTS IS CREDITED q
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FOR SOME COMPONENT FAILURES, EASY ALTERNATIVES ARE AVAILABLE -
UTILIZE ONSITE EQUIPMENT SOME COMPONENT FAILURES WOULD REQUIRE ALTERNATE NITROGEN SUPPLY RELATIVELY SIMPLE MODIFICATIONS COULD SIGNIFICANTLY IMPROVE THE RELIABILITY OF NIS l'
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4 RESULTS OF VULNERABILITY STUDY
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VULNERABILITY ACTION
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FAILURE OF PRESSURE BUILD-UP REPAIR, REPLACE, OR CIRCUlT FOR LIQUID NITROGEN UTILIZE NITROGEN BOTTLE TANK-WITH A REGULATOR (FOR-PRESSURIZATION); OR PROVIDE ALTERNATE l
NITROGEN SUPPLY FAILURE OF PRESSURE, REPAIR, REPLACE, OR TEMPERATURE, OR. MANUAL UTILIZE MANUAL OPERATION e
VALVES IN NITROGEN SUPPLY WITH ACTUATOR (S) i LINE BYPASSED; OR PROVIDE ALTERNATE NITROGEN SUPPLY-i LOSS OF HHS PROVIDE. ALTERNATIVE i
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UTILIZE BACKUP STEAM
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VULNERABILITY ACTION FAILURE OF VAL \\/ES IN HHS SUPPLY REPAIR, REP' LACE, OR BYPASS ; OR PROVIDE ALTERNATE NITROGEN SUPPLY FLOW, TEMPERATURE, AND REPAIR, REPLACE, OR PRESSURE CONTROL INSTRUMENTATION BYPASS FAILURE OF AC-5 OR -6 ALTERNATE INJECTION LOCATION WOULD BE SELECTED FAILURE OF SOLENOIDS ON AC-5 OR -6 ALTER.NATE INJECTION LOCATION WOULD BE SELECTED; OR UTILIZE ALTERNATE PNEUMATIC SUPPLY TO ACTUATOR 19
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VULNERABILITY ACTION
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LOSS OF INSTRUMENT AIR TO AC-5,-6 REPAIR; OR UTILIZE BACKUP AIR SUPPLY; OR UTILIZE ALTERNATIVE PNEUMATIC SUPPLY TO ACTUATOR LOSS OF INSTRUMENT AC TO AC-5,-6 REPAIR OR BYPASS; OR UTILIZE ALTERNATE PNEUMATIC SUPPLY TO ACTUATOR 5
20
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-- DESIGN AND OPERATIONAL CHARACTERISTICS OF AC-17 VALVE IS A QUARTER TURN BUTTERFLY VALVE RUGGED VALVE VALVE IS USED ROUTINELY ALWAYS NITROGEN'INERTED NORMALLY OPERATED WITH LITTLE OR NO AP EXCELLENT OPERATIONAL HISTORY
. NO RECORDED FAILURES TO OPEN REVIEW ENCOMPASSED LAST 9 YEARS SURVEILLANCE / TESTING ADDRESSED IN TECHNICAL
. SPECIFICATIONS PREVENTIVE MAINTENANCE IS PERFORMED ON THE VALVE
ACTUATOR IS SPRING-RETURN AIR-OPERATED
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RUGGED DESIGN NO RECORDED FAILURES IN RECORDS ATTRIBUTED TO ACTUATOR ASSEMBLY REVIEW ENCOMPASSED LAST 9 YEARS SOLENOID ENVIRONN dNTALLY QUALIFIED POWER SUPPLY IS INSTRUMENT AC SOLENOID COULD BE BYPASSED BY SUPPLYING AIR DIRECTLY TO THE ACTUATOR CONCLUSION A NON-CORRECTIBLE FAILURE OF AC-17 IS VERY-UNLIKELY NEED NOT BE POSTULATED -
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-RESULTS OF SYSTEM EVALUATION NIS IS USED ROUTINELY 1
PROCEDURES EXIST FOR NIS OPERATION NIS CAN BE USED IN AN LNP CAPABILITY TO BYPASS CIV INTERLOCKS CURRENTLY EXISTS FROM CR PRELIMINARY RESULTS INDICATE NIS CAPABLE OF PRESSURIZING CONTAINMENT TO 50% OF DESIGN (31 PSIG)
PRELIMINARY RESULTS INDICATE POSTACCIDENT NITROGEN
- FLOW RATES ARE:
>1,100 SCFM AT LOW DRYWELL (DW) PRESSURE ABOUT 500 SCFM AT 50% DESIGN PRESSURE-PROBABILISTIC RISK ASSESSMENT EVALUATION SHOWS ONLY MINIMAL BENEFIT OF UPGRADING NIS BENEFIT < O.5 MAN-REM / YEAR 23
~
POSTACCIDENT OPERATION CURRENT EOPs CONSISTENT WITH REV. 4 EMERGENCY PROCEDURE GUIDELINES CONTAINMENT IS NOT PRESSURIZED TO CONTROL H2/02 CONCENTRATION CONTAINMENT IS VENTED THROUGH THE VENT VALVES NIS IS USED TO SWEEP GASES IN CONTAINMENT AND DILUTE VENT FLOW VENTING FLOW PATH IF DW RADIATION < 40,000 R/HR TO THE STACK THROUGH SOFT DUCTS WITH RB FANS-OPERATING IF DW RADIATION > 40,000 R/HR TO THE RB SBGT IS ALIGNED TO TAKE SUCTION FROM THE RB 24
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'h EOPS FOLLOWING INSTALLATION OF HARDENED VENT CURRENTLY PLANNED TO BE USED FOR VENTING DUE TO HIGH.
DW PRESSURE VENTING PATH TO CONTROL H2/02 WOULD REMAIN THROUGH VENT VALVES NIS WOULD CONTINUE TO BE USED TO SWEEP GASES IN CONTAINMENT 1
PLAN TO REVISIT VENTING STRATEGY USE OF NIS TO PRESSURIZE CONTAINMENT WOULD BE DEFERRED UNTIL RESOLUTION OF GENERIC ISSUE WITH BWROG I
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PROJECT AS A RESULT OF REVIEW OF NIS, AN ALTERNATE HARDENED WETWELL VENT DESIGN WAS IDENTIFIED INITIATIVE TO INVESTIGATE FEASIBILITY OF ALTERNATE DESIGN ONGOING PRELIMINARY INDICATIONS ARE THAT ALTERNATE DESIGN COULD RESOLVE BOTH THE COMBUSTIBLE GAS CONTROL AND HARDENED WETWELL VENT ISSUES WITH CONSIDERABLE COST SAVINGS MODIFICATIONS WOULD REMAIN SCHEDULED FOR INSTALLATION DURING CYCLE 14 PURSUIT OF ALTERNATE LEAST-COST DESIGN WOULD RESULT IN-DELAY OF PREVIOUS COMMITMENT TO IMPLEMENT MODIFICATION I
DURING SCHEDULED OUTAGE OF SUFFICIENTDURATION j
EXPECT THAT DESIGN COULD BE. FINALIZED BY AUGUST 1993 26
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. ADVANTAGES OF ALTERNATE DESIGN j
COST OF COMBUSTIBLE GAS CONTROL ALTERNATE PNEUMATIC i
SUPPLY TO AC-5,-6,-17 INTEGRAL TO MAKING HARDENED WETWELL VENT AC-INDEPENDENT ALTERNATE NITROGEN SUPPLY CONNECTION WOULD BE INSTALLED ON VERTICAL SECTION OF HARDENED WETWELL VENT PIPING SIMPLIFIED DESIGN ELIMINATES ADDITION OF DC MOTOR-OPERATED CIV AND ASSOCIATED CONTROLS ELIMINATES ADDITION OF-RUPTURE DISK INSTALLATION OF LARGE REACTOR BUILDING PENETRATION NOT REQUIRED SIGNIFICANT PORTIONS OF MODIFICATION COULD BE INSTALLED DURING PLANT OPERATION 27 f
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i CHARACTERISTICS OF ALTERNATE DESIGN MEETS BWROG/NRC DESIGN CRITERIA FOR TW SEQUENCE VENT FLOWRATE IS APPROXIMATELY 50,800 SCFM AC-INDEPENDENT DISCHARGE ON SIDE OF RB UTILIZES EXISTING RADIATION MONITOR O
t 28
SUMMARY
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THE EXISTING NIS IS A RELIABLE SYSTEM AND COULD FUNCTION UNDER CERTAIN ACCIDENT CONDITIONS A THOROUGH EVALUATION HAS BEEN CONDUCTED AND VULNERABILITIES OF THE EXISTING NIS HAVE BEEN IDENTIFIED PROPOSED IMPROVEMENTS WOULD RESULT IN ONLY MINIMAL BENEFIT TO SAFETY PROPOSED IMPROVEMENTS WOULD.lNCREASE POSTACCIDENT SYSTEM RELIABILITY AND CAPABILITY BY ADDRESSING VULNERABILITIES PROPOSED IMPROVEMENTS TO THE NIS SHOULD BRING THIS LONG STANDING ISSUE TO CLOSURE SYNERGY BETWEEN COMBUSTIBLE GAS CONTROL ISSUE AND HARDENED WETWELL VENT INSTALLATION COULD RESULT.IN CONSIDERABLE SAVINGS 29
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