ML17199G585
| ML17199G585 | |
| Person / Time | |
|---|---|
| Site: | Dresden, Quad Cities, 05000000 |
| Issue date: | 04/24/1987 |
| From: | Grotenhuis M Office of Nuclear Reactor Regulation |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML17199G584 | List: |
| References | |
| NUDOCS 8705140091 | |
| Download: ML17199G585 (23) | |
Text
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LICENSEE:
FACILITIES:
SUBJECT:
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 Apr*; l 24, 1987 ColT!llonwealth Edison Company Dresden Nuclear Power Station, Units 2 and 3 Quad Cities Nuclear Power Station, Units 1 and 2 JANUARY 20, 1987, MINUTES OF MEETING WITH BWR OWNERS GROUP TO DISCUSS SYSTEMS FOR COMBUSTIBLE GAS CONTROL DURING A LOSS OF COOLANT ACCIDENT On Tuesday, January 20, 1987, a meeting was held at NRC, Bethesda, Maryland, with representatives from GPU Nuclear (GPUN), Conmonwealth Edison, Northeast Utilities and Nebraska Public Power District (NPPD) on the systems used in their Mark I containment (Mark I) plants for cambustible gas control. These licensees have the following boiling water reactor (BWR) plants: Dresden 2/3 and Quad Cities 1/2 (Co11111onwealth Edison), Cooper (NPPD), Millstone 1 (Northeast Utilities) and Oyster Creek (GPUN). is the meeting sunmary which describes the significant items discussed and the actions, if any, taken or proposed. Attachment 2 is the list of the participants that attended the meeting. Attachment 3 contains the handout from the licensees for their presentation. The handout is arranged in the order of the licensees' presentation.
The staff requested that each licensee submit its plant-specific position on its compliance to 10 CFR 50.44(g). This submittal should include the assumptions made by the licensees to justify their position on 10 CFR 50.44. This submittal should also include the fnfonnation discussed during the meeting on the *reliability and capability of the containment fnerting system and the window of accident sequences for which this system would be effective in controlling combustible gases. The staff stated that a passive system, such as the fnerted containment, is not sufficient to meet 10 CFR 50.44(g) and that an active system, such as the containment inerting system, is required. The staff further stated that the reliability and capability of the existing containment inerting systems may be sufficient to meet, as a minimum, the intent of the GDC 41, 42 and 43 of 10 CFR 50.44(g). This is because the RG 1.7 hydrogen and oxygen source term indicative of large metal-water reactions may show that the licensee has sufficient time to respond with the existing system to the increasing combustible gasses concentrations in the containment from radiolysis of water b@fore the acceptable limits are exceeded.
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2 The time available until accept~ble concentrations are reached would allow the licensee to overcome the lack of redundancy in components and in providing power to the system.
This time period for the plant and the actions taken by*
the licensee should be*di~cussed in the l~censee's justification of the rel'iabil ity of its cpntainment inerting $ystem~
- : Attachments:
1 *. Sununary
- 2.
List of attendees
- 3.
Licertsee's handout cc *w/attachments:
- See next page for meeting Original ~igned by/
Marshali Grotenhuis, Project Manager
- Project Directorate-III-2
- Division of Reactor -projects
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ATTACHMENT 1
SUMMARY
OF JANUARY 20, 1987 MEETING WTTH BWR OWNERS GROUP INVOLVING COMBUSTIBLE SAS CONTROL The licensees began their presentation with a history of the licensing activity concerning combustible gas control systems. These are pages 1 through 5 in the handout.
The regulations governing the standards for these systems are contained in 10 CFR 50.44. These regulations are discussed below:
Paragraph 50.44(c)(3)(i) requires each Mark I containment be nonnally inerted during power operation. All these plants meet this requirement and the containments are inerted for power operation except for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> during startup to inert and shutdown to deinert.
Paragraph 50.44(c)(3)(i1) requires plants relying on a purge/repressurization system as the primary means of combustible gas control shall have an installed recombiner capability. The Comnission detennined in Generic letter 84-09 dated May 8, 1984, that Mark I plants did not have to have this capability if the plant met the 3 technical criteria listed in the letter. The 3 criteria are given on page 3 of the handout.
Paragraph 50.44(9) requires all combustible gas control systems to meet General Design Criteria (GOC) 41, 42 and 43. This regulation applies only to those plants which have the notice of hearing on its application for the construction pennit published on or before December 22, 1968. All of the plants involved in this meeting meet this condition and paragraph 50.44(g) applies to them.
The GOC are in Appendix A to 10 CFR Part 50.
The licensees stated that their plants comply with the above regulations. The containments are inerted during power operation except briefly (24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />) during startup and shutdown. This is allowed by the plant Technical Specifi-cations (TS).
It is the licensees' position that the primary means of combustible gas control is the inerted containment and not a purge/repressurization system, and the licensees have addressed in submittals to NRC how the 3 criteria in GL 84-09 are met at their plants. Therefore, the licensees stated that a hydrogen recombiner capability is not required, the combustible gas control system of Paragraph 50.44(g) is the inerted containment and it meets GDC 41 to
- 43. The basis for the licensees' conclusion that the inerted containment is sufficient to assure peak combustible gas concentrations are below acceptable limits without the need to take any action to purge, repressurize or provide a recombiner is General Electric Report NE00-22155, "Generation.and Mitigation of Combustible Gas Mixtures in Inerted BWR Mark I Containments" ~ated 1982.
The licensees stated that the NRC has identified some concerns in its review of NE00-22155. This report was part of the NRC staff's basis for ~nd was indirectly addressed in GL 84-09. The licensees explained that these concerns, listed in page 5 of the handout were addressed in a submittal dated November 5, 1982, from Millstone 1 which had additional infonnation not given in NED0-22155.
This additional information was not discussed in this meeting.
l l The licensees di.scussed the typical system used to inert or de-inert the containment at their plants. The figure on page 6 is a typical containment inerting system for these plants. This system is operated during startup to inert the containment with nitrogen. This is through the nitrogen (N2) makeup line and purging the containment throuqh the ventilation exhaust line.
The containment atmosphere is reduced to less than 4% oxygen for power operation. During shutdown, the containment atmosphere is increased to atmospheric conditions using the nitrogen purge line and the ventilation exhaust line. The containment is inerted during startup and de-inerted during shutdown to allow personnel to be in containment with a breathable atmosphere and conduct needed surveillance of the reactor coolant system while the reactor is at high temperature and pressure. This period of time is restricted by TS to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> for startup and 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> for shutdown.
The licensees explained that this containment inerting system is a backup to the inerted containment for controlling combustible gases during a LOCA.
This system could be used to purge the containment of such gases or to pressurize the containment to dilute the concentration of the gases. The licensees presented page 8 of the handout which compares the inerted containment and the containment inerting system to GOC 41, 42 and 43 of 10 CFR 50.44(g). The licensees concluded that the containment inerting system almost meets these GDC except for loss of power to the system and lack of some redundancy in components.
The "features" referred to on page 8 are the plant-specific features in the systems at each plant. These features might be different for each plant. The licensees explained that the containment inerting system is used continually
- during power operation. Besides startup and shutdown, these systems are used during power operation to maintain pressure in the atmosphere at about 1 psi gauge and to reduce containment pressure for the monthly tests of the torus-to-drywell vacuum breakers. The licensees stated that no additional surveillance should be needed for these systems to meet GDC 42 and 43.
The licensees further explained that the difference between the existing inerting system and a system meeting GDC 41 is the lack of redundancy in components and in supplying power.
The existing inerting systems do not meet GDC 41 on single failure.
The staff stated that it did not consider the containment inerting system as a backup to the inerted containment. This system could not itself deal with the metal water reaction which generates large quantities of hydrogen at a high rate at the beginning of an accident. The production rate of hydrogen is too high for the current inerting system alone to keep combustible gases within acceptable limits. The inerted containment is the safety system to keep the hydrogen from the metal water reaction within acceptable limits. For the duration of an accident, an active combustible gas control system is required to maintain the hydrogen and oxygen concentrations from the radiolysis of water within acceptable limits.
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...:. The licensees continued their presentation with a discussion on when the inerting systems would be effective during accidents. This is pages 9 to 15 of the handout.
The licensees stated that these systems are effective only for accident sequences where the metal water reaction is between 1% and 10% of the fuel cladding and channels in the core. The licensees explained that this is based on the report NED0-22155 which shows that for above 10% the amount of hydrogen in containment will suppress the generation of oxygen and hydrogen generated from the radiolysis of water. This would be through the recombination of oxygen and hydrogen.
The licensees' conclusions of this discussion are on pages 14 and 15 of the handout.
Page 14 is the accident event tree for the containment inerting system for Millstone Unit 1. The system is effective for only 1.7% of all core damage accident sequences.
For this 1.7%, the system is effective 99.5% of the 8 time.
The existing system failure rate with core damage is only 2.6 x 10-events/year.
The licensees stated that requiring the existing containment inerting system to meet 10 CFR 50.44(g) could at best only raise the effectiveness of the system by 0.5% from 99.5%.to 100.0%.
The licensees concluded their presentation with the following:
(1) the Mark I plants meet 10 CFR 50.44(g) with the inerted containment and (2) the existing non-safety containment inerting systems are sufficient for addressing those accident sequences where the metal water reaction is between 1% and 10%. This is page 16 of the handout.
The staff stated that the window of accident sequences where the containment inerting system is effective may be too small. It further stated that the arguments presented had been reviewed when the staff reviewed NED0-22155 prior to issuing GL 84-09.
The staff did not agree with the report conclusion that above 10% metal water reaction the hydrogen generated suppressed the further generation of oxygen and hydrogen from the radiolysis of water. It stated that the uncertainties listed on page 5 of the handout were the basis for the staff's position that Regulatory Guide {RG) 1.7 should be used to calculate the generation of combustible gases during an LOCA.
In response to the staff, the licensees stated that if RG 1.7 were used, the number of accident sequences in which the inerting system could be used does increase. The licensee further stated that the existing system should be sufficiently reliable to handle these additional sequences; however, if this increase in accident sequences is high enough, it would be the justification for having the system meet SOC 41, 42 and 43.
The staff requested that each licensee submit its plant-specific position on its compliance to 10 CFR 50.44(g). This submittal should include the assumptions made by the licensees to justify their position on 10 CFR 50.44.
This submittal should also include the infonnation discussed during the meeting on the reliability and capability of the containment inerting system and the window of accident sequences for which this system would be effective in controlling combustible gases. The staff stated that a passive system, such as the inerted containment, is not sufficient to meet 10 CFR 50.44(g) and
that an active system, such as the containment inerting system, 1s required.
The staff further stated that the reliability and capability of the existing containment inerting systems may be sufficient to meet, as a minimum, the intent of the GDC 41, 42 and 43 of 10 CFR 50.44(g'. This is because the RG 1.7 hydrogen and oxygen source terms indicative of large metal-water reactions may show that the licensee has sufficient time to respond with the existing system to the increasing combustible gasses concentrations in the containment from radiolysis of water before the acceptable limits are exceeded.
The time available until unacceptable concentrations are reached would allow the licensee to overcome the lack of redundancy in components and in providing power to the system. This time period for the plant and the actions taken by the licensee should be discussed in the licensee's justification of the reliability of its containment f nerting system.
!r-l ATTACHMENT 2 MINI-OWNERS MEETING TO DISCUSS SYSTEMS FOR COMRIJSTIBLE GAS CONTROL JANUARY 20, 1987 NAME T. Rotella I. Johnson J. Zwolinski D. Farrar E. Rowley R. Benero G. Lainas J. Donohew T. Pickens L. Nexbitt J. Lachenmayer G. Smith C. Grimes P. Blasioli J. Stang J. Shea C. Wright P. Hearn J. Kudrick J. Hulman L. Gifford M. Laggart Commonwealth Edison (CECo)
GPU Nuclear (GPUN)
Nebraska Public Power District (NPPD)
Northern States Power (NSP)
Northeast Utilities {NU)
ORGANIZATION NRC/NRR/DBL/RWDl CECo-Nuclear Licensing NRC/NRR/DBL/BWDl CECo-Nuclear Licnesing CECo-Engineering t4RC/NRR/DBL NRC/NRR/DBL NRC/NRR/OBL/BWDl NSP-Licens1ng GE San Jose Engineering GPUN NPPD Licensing NRC/NRR/DPLB/ISAPD NU-licensing
~RC/NRR/DBL/BWDl NRC/NRR/DPLB GE-Licensing NRC/NRR/DBL/PSB NRC/NRR/ORL/PSB NRC/NRR/DBL/PSR GE-Licensing GPUN
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LICENSING HISTORY ATTACHMENT 3 o 1978 - Issuance of 10 CFR 50.44{g) A Combustible.Gas Control System.
- Purge system is acceptable if radiation dose limits are met and designed in conformance with GDC 41, 42 and 43.
Otherwise,
- Another type of combustible gas system control in conformance with GDC 41, 42 and 43 shall be provided o 1981 - Issuance of 10 CFR 50.44(c)(3)(ii)
- Required either an internal re~ombj;ler or the capability to install an external recombiner for those reactors that rely upon a purge/repressurization system as the primary means for combustible gas control.
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o 1982 NED0-22155 'Generation and Mitigation of Combustible Gas Mixtures in Inerted BWR Mark I Containments" was prepared.
- Conclusions from Report
- Peak oxygen concentrations for Mark I plants with inerted containments is below the Regulatory Guide 1.7 combustible gas concentration limit without the need for containment venting.
- The existing inerted Mark I containment design is sufficient to assure peak combustible gas concentrations which are below allowable limits without the need to vent the containment, repressurize the containment or to install recornbiner capability.
- Owners provided evaluations demonstrating applicability of NED0-22155 to their plants
- Conclusions are valid for the Design Basis Accident LOCA which includes that described in 10 CFR 50.44
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o 1984 Generic Letter 84-09 was issued
- The Commission has determined that a Mark I BWR plant will be found to not rely upon purge, repressurization systems as the primary means of hydrogen control, if certain technical criteria are satisfied.
- 1.
The plant has technical specifications (limiting conditions for operation) requiring that, when the containment is required to.be inerted, the containment atmosphere be less than four percent oxygen, and
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The plant has only nitrogen or recycled containment atmosphere for use in all pneumatic control systems within containment, and
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- There are no potential sources of oxygen in containment other than that resulting from radiolysis of the reactor coolant. Consideration of potential sources of inleakage of air and oxygen into containment should include consideration of not only normal plant operating conditions but also postulated loss-of-coolant-accident conditions. These potential sources of inleakage should include instrument air systems, service air systems, MSIV leakage control systems, purge lines, penetrations pressurized with air and inflatable door seals.
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Utility Compliance with Regulations The primary means of combustible gas control for Mark I containments is an inerted containment.
- Utilities have addressed the 3 criteria in Generic Letter 84-09, therefore hydrogen recombiner capability is not required.
- Regulation does not limit the option to hydrogen recombiners or a purge repressurization system that meets criteria 41, 42 and 43 of Appendix A.
- Inerted Mark I containments constitute a means of combustible gas control as required by 10 CFR 50.44{g).
1985 -
RECENT NRC CORRESPONDENCE.
o NRC HAS IDENTIFIED SOME CONCERNS FOR WHICH A NARROW BAND OF ACCIDENT SEQUENCES COULD RESULT IN ADDITIONAL OXYGEN GENERATED.
AMONG THESE ARE:
- 1.
DURATION OF BOILING WITHIN THE CORE
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DEGREE OF FUEL ROD DAMAGE
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EFFECT OF WATER CONTAMINATION ON THE OXYGEN GENERATION PROCESS o
WITHIN THE ENVELOPE OF 10 CFR 50.44 THESE CONCERNS WERE ADDRESSED BY THE MILLSTONE SUBMITTAL IN 1982 ~
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V-28-Z7 DRYWELL V-28-47 NITROGEN COMPRESSORS FROM ROCTOA
- BLO<i.ATllOSPHCAE
CONTAINMENT INERTING SYSTEM*
o DESIGNED TO INERT CONTAINMENT WITHIN 24 HOURS o
SUPPLY SYSTEM CTORUS & DRYWELL)
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- LIQUID NITROGEN TANK MANUAL CONNECTION FOR TUBE TRAILER HOOK-UP o
FILL SYSTEM CTORUS & DRYWELL)
PURGE LINE MAKE UP LINE o
VENTING SYSTEM CTORUS & DRYWELL)
REACTOR BUILDING VENTILATION STAND BY GAS TREATMENT CSAFETY RELATED)
REDUNDANT CONTAINMENT ISOLATION VALVES ON ALL LINES NORMALLY OPERATED SYSTEM 1
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0 I CRITERIA 41 I PRIMARY SYSTEM CONTAINMENT ATMOSPHERIC CLEANUP INERTED CONTAINMENT
- CONTROL OF HYDROGEN & OXYGEN COMPLY
- REDUNDANCY IN COMPONENTS AND FEATURES NIA
- LEAK DETECT I ON COMPLY
- ISOLATION AND CONTAINMENT CAPABILITIES COMPLY
- ACCOMPLISH SAFETY FUNCTION WITH:
LOSS OF ON-SITE AND OFF-SITE POWER ASSUMING SINGLE FAILURE 0 I CRITERIA 42 INSPECTION OF CONTAINMENT ATMOSPHERIC CLEANUP SYSTEMS
- DESIGNED TO PERMIT INSPECTION OF COMPONENTS o
CRITERIA 43 TESTING OF CONTAINMENT ATMOSPHERIC CLEANUP SYSTEMS
- DESIGNED TO PERMIT APPROPRIATE PERIODIC TESTING COMPLY COMPLY COMPLY e
B8C~UP SYSIH'1 VENT & PURGE FEATURES PROVIDED FEATURES PROVIDED FEATURES PROVIDED FEATURES PROVIDED FEATURES NOT PROVIDED FEATURES PROVIDED OPERATIONALLY TESTED
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VENT AND PURGE SYSTEMS ARE EFFECTIVE FOR THOSE ACCIDENT SEQUENCES WHERE METAL WATER REACT I ON IS 7 1% BUT 4C 10°% OF CLADDING AND CHANNELS CAPPROXIMATELY 2% ro 20% OF ACTIVE FUEL CLADDING) I ABOVE 10% THE AMOUNT OF HYDROGEN SUPPRESSES ANY OXYGEN FROM RADIOLYSIS.
TIME DURATIONS TO REACH 1% AND 10% MWR BASED ON MARCH CODE ANALYSIS AND ENGINEERING JUDGEMENT EVENTS:
1% MWR 10% MWR A)
REACTOR ISOLATION WITH LOSS OF ALL RPV COOLANT 45 MIN.
50 MIM.
INJECTION AT TIME ZERO.
B)
REACTOR ISOLATION WITH LOSS OF COOLANT INJECTION AT 5 HOURS FROM SCRAM 510 MIN.
540 MIN.
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- Excluded Scenarios:
- Events for which containment will eventually f aii due to overpressurization {Loss of Residual Heat Removal and ATWS).
- Line Break LOCA events -- Core damage cou"ld start within first 15 minutes.
- Those events where time duration is from 510 min. to 540 min. -- Very small contribution to core damage frequency due to high probability of power recovery and successful mitigation during the first 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
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- Transient Accident sequences are most likely to be recovered before 10% MWR is reached. These sequences have t~e following characteristics:*
- Loss of coolant injection
- Recovery time duration is in the order of 15 min. to 30 min.
after 1/2 hour
- Recovery from hardware failures is unlikely due to the short time limit
- Recovery actions by plant personnel within the short time window are difficult
- Scenarios which require electrical power recovery are the most probable
- Sequences where Vent and Purge system is effective are those initiated by loss of off-site power followed by failure 9f Isolation Condenser, Feedwater and Depressurization FunctTon.
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- Conservative Core Damage Frequency (CDF) of 3 x E-4 events
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- 3.4% of total accident sequences have a chance of being recovered in the 1% to 10% MWR range. (Sequences where Vent and Purge systems are effective)
- Probability of recovery of electrical power within 45 min. is estimated to be 0.505 (NUREG/CR-3085 - Page C-22)
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VENT AND PURGE SYSTEM UNAVAILABILITY CONSERVATIVELY ASSUMED THAT ALL AIR OPERATED VALVES ARE TESTED ONLY AT 18 MONTH INTERVALS.
RECOVERY OF VENT AND PURGE SYSTEM COMPONENTS WHEN SYSTEM IS DEMANDED WAS NOT CONSIDERED~ <CONSERVATIVE, SINCE ADEQUATE TIME EXISTS <AT LEAST 24 HOURS) FOR RECOVERY OF THE MOST LIKELY FAILED COMPONENTS.)
MAJOR CONTRIBUTOR TO UNAVAILABILITY IS CONTROL POWER.
TOTAL CALCULATED UNAVAILABILITY IS 5 X E-3/DEMAND WHICH CONSISTS OF:
- 3.48 X E-3/DEMAND DUE TO HARDWARE FAILURES 1.40 X E-3/DEMAND DUE TO CONTROL POWER FAILURES
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' RECUVEREU SF:r.11 IENCES RJ:.CrJVERED VEMT
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PURGE SYSTEM SUCCESSFUL
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CONSEQUENCES
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1 0.995
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0.966 5.J.3E-6 2.6E-8
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VENT t~ PURGE
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~ PURGE SYSTEM FAILURE cur-;*E OAM~GI:: -
SEQUENCES NOT nECOVERED Cr:l11E DAMAGE -
MrJM RECO'JERADLE SEQUENCES FI Gum:: i.:
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~*. PURGE SYSTEM EVENT TREE FOR MI LLSTrJf'.IE 1
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Conclusions:
- Vent and Purge system provides effective mitigat1on for only 1.7% of total population of core damage accident* sequences.
(p = 0.034 x 0.505 = 1.7%)
- For the 1.7% of sequences where mitigation by Vent and Purge system is possible, the system is effective 99.5% of the time
- Calculated CDF where current standard Vent and Purge system fails is 2 x E-8 events/yr.
- Assuming we had a perfect system (better than system designed to criteria 41, 42 and 43) the maximum possible benefit would be a reduction in CDF of 2 x E-8 events/yr.
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I LICENSING CONCLUSIONS BWR Mark I units meet the requirements described in 50.44(g) with inerted containments.
An Event Which Exceed that Described in 50.44 Non-safety related syste~s ar~ sufficient to address those events where MWR is :>1% but <10% and use of Vent and Purge-system is effective.