ML20215J882
| ML20215J882 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 06/19/1987 |
| From: | DUKE POWER CO. |
| To: | |
| Shared Package | |
| ML20215J870 | List: |
| References | |
| NUDOCS 8706250140 | |
| Download: ML20215J882 (10) | |
Text
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'l ATTACFMENT 1 i
l 8706250140 870619 PDR ADDCK 05000369 P
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'3/4.7.6 CONTROL' AREA VENTILATION SYSrEM LIMITING CON 0! TION FOR OPERATION
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g1 13.7.6-Two; independent-Control Area ventilation Systems'snall be OPERA 8LE.
f.i APPLICA8ILITY:
A LL ;. MODE S -
' ACTION: '(UnP 1 and 2)
MODES 1'.2, 3-and 4:
With-one Control: Area Ventilation ~S stem inoperable, restore the inoperable' system'to OPERABLE;statusLwithin 7 ays or be in at least HOT STAN08Y within-
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the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and.in COLD SHUT 00WN witnin the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.
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MODES'S and'6:
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- With' one Control. Area Ventilation System inopjrable, restore the.
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-inoperable' system'to OPERABLE status within rdays or initiate and
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. maintain' operation of the remaining OPERABLE Control Area Ventilation j
System in the recirculation mode; and
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With both Control Area Ventilation Systems inoperable, or with the
-OPERABLE Control Area Ventilation System,-. required to be in the recirculation mode' by ACTION a,, not capable. of 'be,ing _ powered by-an OPERABLE emergency power source, suspend all operations involving CORE ALTERATIONS or positive reactivity, changes..
The provisions of Specification 3.0.a'are not applicable.
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- SU VEILLANCE REQUIREMENTS
.4.7.6 Each Control Area Ventilation System snall be demonstrated OPERABLE:
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At least once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, by '.>erifying that the control room a.
air temperature is less than or equal to 120 F; STAG'ERED TEST BASIS, by initiatina.
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b, At least once per 31 days an 3 I
flo the)ugn tne HEDA filters and Cn3rcoa?
from the control room, adsorbers and verifying tnat tre system operates for at least 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> with the heaters operating; 4'An allcWGd " f
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co;co hg Amendment No.
(Unit 2)
McGUIRE UNITS-1 and 2 3/4 7-13 Amendment No.
(Unit 1)
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'l ATTACHMENT 2 l
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Justification and Safety Analysis
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Introduction:==
The proposed change to the Technical Specifications is to allow extended outage time for each train of the control area ventilation system (VC) to allow system modifications to improve system reliability. The one time extension to twentyJone days (for each train, one at a time) will allow completion of the modifications while one or both units are on-line; otherwise it would be necessary to shutdown both units to complete the modification.
The modification, described in detail below, will replace the Outside Air Pressure Filter Train fans. While these fans are inoperable, it will not be possible to pull air through the filter pack of the affected VC train. As the affected train would be unable to meet the Surveillance Requirements for operability of the filters or pressurization of the control room, the affected VC train must be considered to be inoperable.
Justification for Allowed Outage Time Extension:
The present allowed outage time of seven days is insufficient to complete the modifications as planned. A centative schedule is enclosed (Table 1).
It is based upon this preliminary schedule that Duke is proposing the one-time
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allowed outage time extension to twenty-one days to facilitate the modifi-cations. A firm schedule will not be available until work is about to begin.
Duke believes that twenty-one days will be sufficient to complete the modif1-cations, and will take steps to reduce that time as much as possible.
Some of the methods to reduce the downtime include continued planning, work on " mock-ups", prefabrication, and organization of parts and components. However, some areas, such as the curing time for the grout, cannot be substantially reduced, and all problems cannot be anticipated.
l Description of Modification:
The modification will replace the Outside Air Pressure Filter Train (OAPFT) fans with one nuclear grade fan per filter unit.
The present 0APFT fans were bought from Brod-XcClung-Pace, Inc. The existing fans were bought as light duty, commercial grade fans by CTI Nuclear (defunct) and sold to Duke Power as part of a nuclear grade package.
However, the manufacturer will not sell repiscement parts that are nuclear grade. The frames are weakening from stress cracks and bearing replacement is common.
Based on the fact that the fans see limited run time and do have preventative maintenance performed on them but still fail frequently, we cannot consider ?. hem reliable.
Presently, each filter train contains two 50% capacity fans that operate in parallel. The system is described in the McGuire FSAR, Section 6.4 and is l
depicted in FSAR Figure 6.4.2-1.
A simplified sketch (Figure 1) and the affected portion of the FSAR figure (Figure 2) are enclosed.
The modification will replace the two 50% capacity fans with a single 100% fan per filter train. Present parallel ducting from the fan discharge to the Control Room return duct will be replaced with a single duct. One of the two existing ducts will handle 100% flow, therefore one of the ducts will simply be de-leted. Along with the duct, its respective humidity sensor, pressure switches, firestat, and flow instrumentation will be deleted.
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. Safety Analysis:
Duke has assessed the safety significance of this planned modification and has determined the safety significance of the change to be minimal as the probabil-ity of an accident requiring use of the inoperabic VC train during the addi-tional two weeks is negligibly small.
The filtration system is needed only in q
the event of a toxic gas spill or a core melt. A core melt is precluded by the operability of the emergency core cooling systems. The ECCS will remain operable as required by the Technical Specifications. For a substantial radioactive release to occur requiring use of the filter train of the VC, multiple failures would have to occur:
the various ECCS subsystems and ultimately containment in concert with a LOCA.
Such an event is not con-sidered credible, especially in light of leak before break and Technical Specification limits on reactor coolant system leakage. The probability of either of these events occurring during the 21-day period is very low.
As discussed in FSAR Section 6.4.3, gaseous chlorine is the only toxic gas I
normally onsite that might be drawn into the VC intake. Normally, two 150 pound chlorine cylinders are stored as to be of potential concern (one connected, one spare). Chlorine detectors (OVCMT 5010, 5020, 5030, 5040, shown on FSAR figure 6.4.2-1) are installed just downstream of the radiation monitors.
For chlorine to be drawn into the intake, a storage cylinder would have to rupture, then the gas would need to travel about 450 feet around the turbine building to the elevated intake. As discussed in FSAR Section 6.4.3, this is a highly improbable event (chlorine gas is heavier than air and will therefore stay on the ground, any wind would tend to disperse and dilute the chlorine).
Upon receipt of a radiation signal or a high chlorine signal, the affected intake will automatically isolate. The system would then operate from the uncontaminated air intake. As normal operation is from both intakes, no further realignments are required to assure safety function following the isolation of a single intake.
Cross connecting ductwork assures that air from either intake may be drawn through either filter train. As the intakes are physically independent (opposite sides of the auxiliary building), the ability of the system to deal with a toxic gas or radioactive release is unimpaired by the proposed change.
In addition, for toxic gas or radioactive material to enter the control room area, the operable train of filtration would also have to fail.
This is not considered to be a credible event as operability of the required train will be assured by testing and maintenance prior to declaring the opposite train inoperable. With the exception of control room temperature, all Technical Specification surveillances are on a thirty-one day basis, thus it will not be necessary to perform any surveillance on the required train while the opposite train is being modified.
The second train to be modified will have further assurance that the opposite train will be operable as it (the operable train) will have recently been overhauled and subjected to post modification system i
testing, and the new OAPFT fan will be more reliable. Therefore, the impact of this one-time A0T extension on public-health risk is insignificant.
l The extended allowed outage time would increase the probability of a required
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shutdown due to both trains of VC being inoperable. McGuire is taking meas-ures to assure that while one train is inoperable for the modifications, the operable train remains operational. As the control area ventilation system is
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. a shared system, the support systems may be from either unit; that is, if the operable system is aligned to the Unit I diesel generator and nuclear service
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water system, it may be realigned to the Unit 2 support systems if any trouble is encountered.
In order to assure the operability of the operable train, normal performance i
testing and preventative maintenance will be performed on the system in order to identify and resolve any problems prior to starting modifications (on the
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opposite train), and the performance of preventative maintenance on the system j
will ensure maximum reliability for the system. As previously discussed, no i
Technical Specification surveillance will come due during the extended A0T, and the second train to be modified will have further assurance of the re-quired opposite train being operable as the required train will be fully tested in accordance with post modification testing, a more reliable OAPFT fan, and the previously discussed measures.
The operators will be fully aware of the situation. The impact of losing the I
operable train would be the shutdown of both units within seven hours of the initial event (one hour to return the train or shutdown within the following six hours). The impact of a station shutdown on McGuire (thermal cycling of equipment) and on the Duke system is a situation that Duke seeks to avoid, thus McGuire will be examining other measures that may be taken to prevent
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degradation of the operable train during modifications of the redundant train.
However, should the operable train become degraded and declared inoperable, a shutdown of both units will be initiated in accordance with Technical Specifi-cation 3.0.3.
The modifications will be completed one train at a time, thus one VC train will be fully available at all times.
If neither VC train is fully operable, the station will be in Technical Specification 3.0.3, which would require that one train be returned to operability within one hour or the units be in Hot Standby within the following six hours, Hot Shutdown within the next six hours, and Cold Shutdown within the next twenty-four: hours.
Additionally, while a train 45 tnopers>1e for modifications, the chiller package of that train is available, if heeded. While the filter section is out of service for the modificatlon, dampers may be manipulated to bypass the filter section.
Referring to Figure 2 (FSAR Figure 6.4.2-1), to bypass filter package number 1, dampers CR-0AD-1, 3, and 4 would be closed while CR-0AD-2 would be opened; to bypass package 2, CR-0AD-5, 7, and 8 would be closed while CR-0AD-6 would be opened.
This would not be done to meet requirements in the Technical Specifications for system operability, but would merely be available to provide cooling for the control room systems to assure an orderly shutdown (no spurious signals due to overheating of solid state systems) pursuant to Technical Specification 3.0.3.
Also, as previously discussed, the failure sequence of ECCS and containment to where the filter train would be required is not a credible event.
The systems that would be required to fail are covered by Technical Specifications and are thus maintained and tested as such to preclude a core melt accident.
- Again, in addition to the core melt the operable filter train would have to fail to affect safety.
Such a total failure during the additional two week A0T is not considered a credible event.
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3 As one train is all that is nectssary to provide ventilation, and one train i
will be operable at all times, no loss of safety function is involved.
Analysis of Significant Hazard Considerations:
Pursuant to 10CFR50.91, this analysis provides the information and conclusion that the proposed amendment does not involve any Significant Hazard Considera-tions as defined by 10CFR50.92.
The proposed change would not involve a significant increase in the probabil-ity or consequences of an accident previously evaluated. The proposed change will affect only the VC_ system which is designed to maintain the habitability of the control room area as described in the FSAR, Section 6.4 and will not i
affect the probability of an accident. One train is fully adequate for all conditions, either train can draw outside air from either independent intake, and one train will be operable at all times, or the station will reduce power or shutdown in accordance with Technical Specification 3.0.3.
As the trains are totally redundant, including the ability of each train to draw outside air from either independent intake (should one intake become contaminated), or place the system in recirculation, control room doses ~due to inleakage, as presented in Chapter 15 of the McGuire FSAR (Table 15.6.4-12) and the NRC Safety Evaluation Report for Facility Operating License amendments numbers 51 (NPF-9, _ Unit 1) and 32 (NPF-17, Unit 2) dated March 5,1986, are unaffected.
The additional allowed outage time thus will not affect the probability or consequences of an accident.
The proposed change will not create the possibility of a new or different kind of accident from any accident previously evaluated.
The proposed allowed outage time extension is to allow system modifications to enhance system reliability. Neither the extension or the planned modifications are of a nature which could lead to any new accident scenarios.
The proposed changes would not involve a significant reduction in a margin of safety. With one train of VC. operable, all margins are satisfied; control room doses are unaffected. Presently, one train may be inoperable for up to seven days before a station shutdown would be required.
The addition of fourteen days allowed outage time on a one time basis for each train will not have an impact on any safety margins.
Based upon the preceding analyses, Duke Power concludes that the proposed amendment does not involve a significant hazard consideration as defined by 10CFR 50.92.
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