ML20082G926
| ML20082G926 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 08/15/1991 |
| From: | Parker T NORTHERN STATES POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9108220101 | |
| Download: ML20082G926 (3) | |
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No'them States Power Company 414 recollet Mall Minneapolis, Minnesota 55401 1927 Telephone (612) 330-5500 August 15, 1991 Tech Spec 3.13.G 2 US Nuclear Regulatory Commission Atte Document Control Desk Was hington, D.C.
20555 MONTICELID NUCLEAR GENERATING PIANT i
Docket No. 50-263 License No. DPR-22 Special Report Inonerable Petu=1 ration Fire Barrier This special report is being submitted per Technical Specification 3.13,G.2.
Technical Specification 3.13.G.2 requires that "If Specification 3.13.G.1 cannot be met,... verify the operability of fire detectors on at least one side of the non functional fire barrier and establish an hourly fire watch patrol.
Restore the inoperable penetration fire barriers tu Operable status within 14 days or submit a special report to the commission within 30 days outlining the cause of the inoperability and the plans and schedule for restoring the barrier to Operable statun".
BACKGROUND On 19 July 1991, several fire protection related issues in the area of the diesel fuel oil system were identified by the NRC Resident Inspector.
These included:
1.
The vents on both Emergency Diesel Generator base tanks are connected with the vent on one of the day tar hi in a single pipe that runs through three different fire areas, then cutside to a flame arrestor and the atmosphere.
2.
The fuel supply to 12 Emergency Diesel Generator goes from the day tank to the engine in a trench in the floor of the 11 Emergency Diesel Generator room.
3.
The overflow lir:es from both 11 and 12 day tanks return to the - fuel oil storage tank in separate trenches in the floor of both Emergency Diesel Generator rooms, and t.he overflow lines tie together under the floor of 12 Emergency Diesel Generator room.
4.
The Emergency Diesel Generator base tanks apparently do not have the emergency vent caprbilit.y required by NFPA 30.
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URNRC NORTHERN STATES POWER COMPANY August 15, 1991 Page 2 Initial evaluation of these concerns by plant staf f personnel indicated that the possibility of propagating a fire through these vents or other piping and thus crossing the fire barrier was improbable.
However, until this situation could be fu'.ly evaluated, operability of fire detectors on at least one side of the fire barrier was verified and an hourly fire watch patrol was established in accordance with Technical Specification 3.13.G.2.
A Professional Fire Protection Engineer with a background in nuclear power plant issues has evaluated the situation from both an Appendix R compliance and a Fire Hazards Analysis perspective. The conclusion of this evaluation is that equivalert protection to that required by Appendix R is provided.
This is based on the fact that the spread of fire alon5 the vent pipe is extremely unlikely oecause this would require multiple failures of the diesel, its associated support _ systems and the fire suppression system, and because of the limited combustibility characteristics of diesel fuel. Manifolding of vent lines, although not recommended, is acceptable in some circumstances under the-NFPA code.
In addition, for the piping in trenches in the floor, thermal plume effects would mean that the heat of the fire-would reach the floor last.
This would be after the firo protection system has actuated and filled the trencht with water.
These factors, coupled with the defense-in depth fire protection strategy of the plant, support the conclusion that the prenent installation provides acceptable protection.
Emergency venting of fuel oil tanks is required because of the possibility of exposure fires which might. excessively heat the oil.
The present-vent provides pressure protection in the unlikely event of an exposure fire, although it is not adequately sized to meet the NFPA code requirements.
This is considared acceptable for the near term because, with the installed automatic detection and suppression system, the chance of an exposure fire of sufficient energy to cause tank failure is minimal.
A modification to install emergency venting capability is planned for the next reft: ling outegn.
Based on the above analysis, no penetration fire barriers between the diesel-rooms or diesel fuel day tank rooms are considered inoperable. Technical Specification 3.13.G.2 was entered as a conservative precaution until plant personnel could evaluate all aspects of this issue.
This letter is submitted because it has taken more than 14 days to resolve this issue and it is our desire that the NRC be fully aware of our actions.
Because there is no inoperable fire barrier, the fire watch has been removed.
CAUSE
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The cause of the potentially inoperable fire barrier is the use of some less conservativo, but technically acceptable, design alternatives in the original plant construction.
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URNRC NORTHEGN STATES POWER COMPANY August 15, 1991 Page 3 I'L6NS AND SCHEDULE It is rec.gnized that the cross connected vent piping, although technically acceptable, is not the preterred installation. Therefore, the vents from each Emergency Diesel Generator Base Tank and the 12 Diesel Fuel Day tank will be rerouted so that these vents are no longer manifolded together. This modification is planned to be installed in the 1993 refueling outage.
A modification to install improved emergency venting capability is also planned for the 1993 refueling outage.
Please contact us if yeu require additional information.
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- Thomas M. Parker Manager Nuclear Support Services cc: Regional Mministrator-III, NRC NRR Project Manager, NRC Resident Inspector, NRC J Silberg
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