ML20010B172
| ML20010B172 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 08/10/1981 |
| From: | Delgeorge L COMMONWEALTH EDISON CO. |
| To: | Schwencer A Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0519, RTR-NUREG-519 2402N, NUDOCS 8108140181 | |
| Download: ML20010B172 (5) | |
Text
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'"'N Commonwealth Edison
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'D Address Reply to: Post Office Box 767
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AUG 131981 T
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Mr. A. Schwencer, Chief Licensing Branch 2 Division of Licensing U.S. Nuclear Regulatory C$mmission Washington, DC 20556
Subject:
LaSalle County Station Units 1 and 2 Supplemental Information Concerning Fire protection and Cable Separation Rev11w NRC Docket Nos. 50-373/374_
Dear Mt. Schwencer:
Attached for your information is information provided to resolve questions raised by the NRC Staff in connection with the LaSalle County fire protection and cable separation review.
This information was provided informally to Mr. A. Bournia of your staff on July 31, 1981 and is formally documented here.
If there are any questions in this regard, please direct them to this office.
Very truly yours, Vf L. 0. DelGeorge l
Director of Nuclear Licensing l
l Enclosures l
cc:
NRC Resident Inspector - LSCS 2402N (30*$
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a
o Enclosure _1 Supplemental Information Concerning
- Fire Protection Review The telephone conferences between the Nuclear Regulatory Commission (NRC), Commonwealth Edison-Company (CECO.), and Sargent &
Lundy (S&L) have reduced the NRC's concerns as we understand them to two areas of the Fire Protection Systems:
Structural upgrading in some fire zones and electrical duct fire harrier design.
The NRC requested that structural sections of fire zones 4C2, 4C3, 5813, and SC11 be upgraded in fire ratings or fire suppression systems be provided.
We do not believe that fire suppression system installation is required.
We have reviewed the analysis of fire zones 4C2 and 4C3.
We revised our approach to the classification of ceiling assembly in construction in these zones.
Under the previous analysis, we did not conduct a detail analysis to obtain the maximua fire ratings possible for structural elements.
Because of the low fire loadings (1/2 hour) in the zone, we documented only that the fire barriers exceed the fire loading.
Our analysis was performed using unrestrained assemblies, which are the more conservat ive and constitute the majority of construction.
In our re-antlysis of the fire zones, we are employing Underwriters Laboratories acceptance criteria, U.L. 263-Standard for Fire Tests of Building Construction and Materials, Section 60.C-conditions of acceptance for restrained assemblies.
Underwriters Laboratories acceptance criteria allows the use of unrestrained beam designs in a restrained floor / ceiling assembly.
For restrained assembly ratings greater than one hour the unrestrained beam fire rating used shall be for a period of 1/2 the classification of the floor assembly or one hour, whichever is greater.
For a 3 hour3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> restrained floor / ceiling assembly the'use of 1 1/2 hour unrestrained beam is acceptable.
We have documented that at least 3/8" of Pyrocrete 102 fireproofing was installed.
According to U.L. design N721, 3/3" of Pyrocrete 102 for an unrestrained beam provides 1 1/2 hours of protection.
Therefore using the restrained ceiling assembly application over fire zones 4C2 and 4C3, we qualify the fire zones as constructed.
The questions about fire zones 5813 and SCll were addressed in previous discussions.
A commitment was given to NRC to upgrade to three hours the barrier separating the two zones.
The upgrading construction is in progress or has been completed.
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. In order.to resolve the NRC's concern for electrical' bus duct fire / vapor barrier, Commonwealth Edison agrees to. install a fire stop in addition to the fire / vapor barrier.
Theafire stop will be made of a silicone elastomer material and-a fire test'will be performed to. verify it has an adequate' fire rating.
We will' engage Tech-Sil Inc. to install the fire stop and perform the fire test.
The details and schedule for installation of the-fire stop and performing the fire test are being developed.
This project-is expected to be completed prior to fuel loading on Unit 1.
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Supplemental Information Concerning Cable Separation Review (NUREG-0519 Supplement 1, Open item )
In response to comments by the NRC Staff concerning the conformance of the LaSalle County raceway design to Regulatory Glide 1.75, the following supplemental information is provided.
It shoeld be understood that this material was developed on the suggestion of the Staff that demonstration of adequate fire resistance of the installed cable system to fault induced fires would resolve the concern identified in NUREG-0519.
This information is judged to clearly demonstrate the adequacy of the present design and supports conclusions on adequacy previously discussed with the Staff.
1.
NUREG PR-0381, a preliminary report on Fire Protection Research Program Fire Barriers and Fire Retardant Coatings Tests, dated September, 1978, describes test configurations similar to those found at LaSalle County Station.
In those cases where IEEE-383 qualified cable was installed in a solid bottom tray, no fire developed after six cycles of the external ignition source.
Also, there was no apparent damage to the cables in the tray.
Where IEEE-383 qualified cable was installed in a ladder rack tray, a small fire was observed after the 4th, 5th and 6th cycles of the external ignition source.
This fire self-extinguished after four minutes of completion of the 6th cycle.
In no case did fire propagate from one tray to another, when solid bottom trays were used, even after igniting non-qualified cable in the lower tray.
2.
This same report describes cases where the effects of vented top covers and fire retardant coatings were tested.
In these cases, some damage occurred to the insulating and jacketing materials, apparently because the gases generated from overheating were
.ontained.
Cables in a solid bottom, open top tray are less likely to ignite if uncovered.
3.
A Summary of Fire Protection Research Sponsored by the U.S.
Nuclear Regulatory Commission presented by Gary L. Benneit, Chief of the Nuclear Regulatory Commission Research Support Branch to the 1979 Joint Power Generation Conference includes the following statement relative to Program Element 1 - Cable Tray Separation.
"The principal conclusion was that a f ully developed fire in the bottom cable tray of a stacked array may propgate to a retardant safety division without fire suppression systems (as expected).
On the other hand, electrically initiated fires do not propagate because they do not result in a fully developed cable tray fire."
(Emphasis added) 4.
This same paper contains the following statement under Program Element 2 - Effectiveness of Fire Shields (This includes solid bottom trays with no cover.)
"The results of the Sandia research showed that all fire shield designs offered some protection.
None of the cable which passed the flame retardancy
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test in IEEE Standard 383-1974 ignited.
It is passible to ignite the cable which did not pass this flame retardancy test; however, no propagation was observed past the fire shields."
This information is directly applicable to LaSalle County Station for which only cable which satisries IEEE 383-1974 is used.
Moreover, those areas where the LaSalle County design are in marginal conflict with the guidance provided in RG 1.75, are typically solid bottom-open trays which were shown to be as good as fire retardant coatings and vented covered trays.
In as much as the LaSalle Count; fire protection design hcs been accepted by the NRC Staff as adequate, the referenced fire testing sponsored by the NRC Staff showed electrically initiated fires do not propagate, and the backfit proposed by the NRC Staff has as yet not been justified on a technical basis other than by reference to a regulatory guide the effective date of which makes it inapplicable to LaSalle County, thu present design is considered adequate.
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