ML19327A743

Forwards Addl Info on 890731 Request for Exemption from 10CFR50,App R Requirements Re Conduits Embedded in Concrete. Scope of Exemption Limited to Specific Set of Fire Areas

ML19327A743
Person / Time
Site:	Davis Besse
Issue date:	09/30/1989
From:	Shelton D TOLEDO EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
1719, NUDOCS 8910180027
Download: ML19327A743 (6)

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TOLEDO EDISON' A Centerer Errgy Cwnywy DONALD CL SHELTON vaenium- w r (419] P44 P300 Docket Number-50-346 License Number NPF-3 Serial Number 1719 September 30,-1989 1

United States Nuclear Regulatory Commission Document' Control Desk Washington,'D. C. 20555 Subj ec t : . Fire Protection, Appendix R Exemption Request Involving Conduits Embedded in Concrete.

Gentleman:

In' letter dated July 31, 1989 (Serial Number 1694), Toledo Edison requested.

three additional exemptior.s from the requirements of 10CFR50, Appendix R.

Subsequently, Toledo Edison determined the exemption request on embedded conduits required additional clarifying information and that the scope of the exemptionzrequested-should be limited.to a specific set of fire areas

-containing embedded conduits. The revised exemption request on embedded conduits is presented in Attachment 1.

If you'have any questions concerning this matter, please contact Mr. R. W. Schrauder, Nuclear Licensing Manager at (419) 249-2366.

Very truly yours,

/ j

-l KAS/ssg Attachment I

cc: P. M. Byron, DB-1 NRC Senior Resident Inspector A. B.-Davis,-Regional Administrator, NRC Region III D. J. Kubicki, NRC/NRR Staff Reviewer '

T. V. Vambach, DC-1 NRC Senior Project Manager pun

[ti { l THE TOLEDO EDISON COMPANY EDISON PLAZA 300 MAG: SON AVENUE TOLEDO, OHIO 43652

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e # , Docket Nuxber 50-346 m ' =.1 Lic:nsa Nur.b2r NPF-3 E  : Serial Number 1719 '

Attachment.1-L Page 1-EMBEDDED CONDUITS Exemption Requested certain circuits, required to achieve and maintain safe shutdown in the event of a fire, are enclosed in conduit and embedded in concrete valls, floors, duct banks or ceilings of the Davis-Besse Nuclear Power Plant. These s.ircuits were evaluated in the safe shutdown analysis for a fire. It was identified that the existing fire protection features for the safe shutdown embedded circuits in Rooms 252, 314, 323, 324, 334, 427, 428, 430, 431, 501, 515, ano 602 are not in accordance with the requirements of Section III.G of Appendix R to 10CFR50. However, as discussed below the fire protection features are sufficient to ensure one train of these circuits sould be free of fire damage.

An exemption is requested from Section III.G c: Appendix R to 10CFR50, pursuant to 10CFR50.12, to obviate the need for modifying the existing fire protection features for these circuits embedded in concrete in-Rooms 252, 314, ,

323, 324, 334, 427, 428, 430, 431, 501, 515, and 602.

Discussion The circuits that are embedded in concrete and required for safe shutdown in the event of a fire are presently listed under Fire Area EMB in Appendix B-2 of ti.e Davis-Besse Appendix R Compliance Assessment Report (CAR). The circuits are enclosed in conduits. These circuits were evaluated in the fire area (s) on either side of the vall, ceiling, or floor containing the embedded conduits. The analysis showed that there was no impact on safe shutdown capability for the circuits in embedded conduits except for the circuits in Rooms 252, 314, 323, 324, 334, 427, 428, 430, 431, 501, 515, and 602. Rooms 252, 314, 323, 324, 334, 427, 430, 431, 501, and 602 either have a combustible loading of 30 minutes or less or are protected by an automatic sprinkler system. -Rooms-428 and 515 have a' combustible loading of greater than 30 minutes and are not protected by automatic sprinkler systems.

Although the conduit embedment depth at Davis-Besse is not specifically dimensioned on design drawings, it is known that a minimum of 1 1/2 inches (2 inches nominal with a 1/2 inch tolerance) of concrete cover over the rebar for structures including those containing conduft was required. Two rebar mats are used in reinforced concrete valls at Davis-Besse, each may consist of two layers of rebar running perpendicular to eacn other. The minimum size of the rebar used in the subject valls, ceilings, duct banks or floors is a 3 combination of number _5 and 6 rebar resulting in a'l 3/8 inch thickness. This configuration of the reinforced concrete valls provides a minimum cond nt embedmont of 2 7/8 inches (1 3/8 inches of rebar covered by 1 1/2 in i t of concretc). This assumes the conduit is located directly behind the rebar mat.

Based on the length of conduit runs that enter and exit each of these rooms, it is highly improbable that the conduit is placed on only one layer of rebar.

Toledo Edison has also analyzed the potential impact of anchor bolts on the fire resistance of the concrete valls, floors, duct banks or ceilings. The

t- ** , Docket Number 50-346 9 a~ Licens] Number NPF-3 Serial Number 1719 Attachment 1

! Fage 2 vorst case anchor bolt conduit configuration has been analyzed. This analysis was based on the configuration of the minimum conduit embedwent, an anchor bolt aligned directly with the conduit and the standard heat input specified by ASTN E-119 time-temperature curve. The analysis determined that the circuits' temperatures vould not exceed 310*F in 30 minutes. Once the heat source is removed or extinguished, the hottest temperature in the conduit vill continue to rise to approximately 370*F and then drop off. These temperatures are enveloped by the environmental qualification data for the cable used in the circuits embedded in these rooms /and thus the circuits vill remain operable.

Evaluation Toledo Edison has evaluated the existing fire protection measures provided for embedded conduits in Rooms 252, 314, 323, 324, 334, 427, 428, 430, 431, 501, 515, and 602 and has determined that these measures provide a level of protection equivalent to Section III.G of 10CFR50, Appendix R. These measures are:

1-. An analysis of the vorst case configuration (i.e., a minimum conduit embedment of 2 7/8 inches and snehor bolts in the concrete) was performed.

The circuits' temperatures vould not exceed 310'F in 30 minutes. Once the heat source is removed or extinguished, the hottest temperature in the conduit vill continue to rise to approximately1 370'F and then drop off.

These temperatures are enveloped by the envircnmental qualification data for the cable used in the circuits embedded in these rocas/and thus the circuits vill remain operable.

2. Rooms 252, 314, 323, 324, 334, 427, 430, 431, 501, and 602 either have a combustible loading of 30 minutes or less or are protected by an automatic sprinkler system. In those rooms with a combustible lesding of 30 minutes or less, the passive protection of the concrete vill maintain the circuits at an acceptable temperature and thus they vill remain operable. In those rooms with a combustible loading of greater than 30 minutes and an automatic sprinkler system, the passive protection of the concrete and the nctive protection provided by the automatic sprinkler system vill maintain the circuits at en acceptable temperature and thus they vill remain operable.

3. Room 420 has a combustible loading greater than 30 minutes and is not protected by automatic sprinkler systems. In this ream the passive protection of the concrete vill maintain the circuits at an acceptable temperature and thus they vill rerain operable. Room 428 is provided with fire detection zones which would al.ert Control Room personnel to a fire and l they would-initiate the response of the Fire Brigade. Vithin 30 minutes, the firs trigade would respond to extinguish the fire and the circuit I temperature vill remain at an acceptable temperature and thus they vill remain operable. '

1

4. Room 515 has a combustible loading greater than 30 minutes and is not protected by an automatic sprinkler system. However, ninety-five percent of the total combustible load is charcoal which is contained in three charcoal filters that are within heavy metal plenum boxes as part of the ventilation system. The charcoal has an extremely slov burn rate. Also it is

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License Number NPF-3 s Serial Number 1719

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, reasonable to assume that only one of the charcoal filter plenums vould be on fire at a time. Even though the combustible loading exceeds 30 minutes, the effect of any potential fire is very limited and the passive protection of the concrete vill maintain the circuits at an acceptable temperature and thus remain operable.

5. The Davis-Besse Fire Brigaae has a minimum shift size of five members and is onsite at all times in accordance with Technical Specification 6.2.2.f. The Fire Brigade does not include the members of the minimum shift crev necessary for safe shutdown of Davis-Besse during a fire emergency. The Fire Brigade has established training programs and fire drills under l- existing administrative controls. Normal fire brigade response at

, Davis-Besse has been timed in drills at less than 15 minutes from alarm initiation to providing vater on the fire.

6. Figure 7-8E of the NFPA Handbook, 16th Edition, indicates that 2 7/8 inches of concrete provides over 45 minutes of fire resistance. The anslysis considered the impact of the anchor bolts which could reduce the fire resistance of the concrete. The analysis has a number of conservatisms that if removed from the calculation, vould cause the fire resistance to approach the equivalent fire resistance of the concrete without considering the anchor bolts. The analysis is conservative fsr the following reasons:

a. The heat input _to the calculation was the ASTM E-Il9 time-temperature curve. The actual combustible loading in the rooms vould not result in the assumed heatup rate.

b. The calculation assumed the anchor bolt is in direct alignment with the conduit and is the largest size normally allowed with a embedment of 2 7/8" or less. Actually, it is highly improbable that the anchor bolt is in direct alignment with the conduits or is near the conduits due to the small surface area of the conduit relative to the large surface area of the vall, floor, duct banks, or cciling. Also the minimum conduit embedment is based on combining the minimum concrete cover and rebar sizes which are both not likely to occur where an anchor bolt is located.

Consequently, Toledo Edison has determined that the existing fire protection features provided for the embedded conduits vould ensure one train of equipment necessary to achieve and maintain safe shutdown in the event of a fire is free of fire damage and, thereby, provide an equivalent livel of fire protection as c required by Section III.G of Appendix R. Additionally, the imposition of l

additional modifications simply to satisfy the methods specified by Appendix R of 10CFR50 for the embedded conduit vould not significantly enhance the level of fire protection currently provided.

L Applicable Special Circumstance l Toledo Edison has determined that the requested exemption conforms to (Se L applicable exemption criteria of 10CFR50.12(a). There are no prohibitions of law to preclude the activities that would be authorized by the requested

, exemption, and the requested exemption, if granted, vould have no impact on the L-

I c Docket Number 50-346 1 Licans3 Nu:ber NPF-3 Serial Number 1719 Attachment 1 Page 4 common defense and security. Additionally, the requested exemption does not present an undue risk to the public health and safety since an eqt'ivalent level of fire protection as required by Section III.G of Appendix R is provided as described above.

Special circumstances are applicable to the requested exemption in accordance with 10CFR50.12(a)(ii) in that application of the regulation for these particular circumstancea is not necessary to achieve and maintain hot standby.

The underlying purpose of the rule is satisfied by the requested exemption since the existing fire protection features described above provide an equivalent level of fire protection as required by Section III.G of Appendix R and the installation of modifications simply to satisfy the methods specified by Appendix R is not necessary.

Additional special circumstances are applicable to the requested exemption in accordance with 10CFR50.12(a)(iii) in that the application of the regulation would represent an unwarranted burden on Toledo Edison rescurces. The modification of the current fire protection features for the embedded conduits vould result in the considerable expenditure of engineering, construction and plant staff resources for its design and installation. Modification of the existing valls, ceilings, and floorr with the installed equipment present is extremely impractical and would reqeire an extended outage. Also rerouting of the circuits vould to be extremely difficult and vould require an extended outage. The associate costs vould include:

• Engineering, construction, and installation of additional fire barriers on valls, ceilings, and floors or increase the concrete embedment to achieve a three hour fire rating through many rooms of the plant or to provide circuit reroutes.

Additional fire barriers on valls, ceilings, and floors or the increase in the concrete embedment vould significantly increase congestion in the plant, complicating future pleat modifications and operation.

$1milarly, rerouting embedded circuits outside the fire areas vould increase congestion and complicate future plant modifications and operations.

The high costs associated with modification of the existing fire protection features for embedded conduits vould represent an unvarranted burden on Toledo Edison resources considering the resulting negligible safety benefit and the alternative means of fire protection described above.

In conclusion, Toledo Edison considers that special circumstances in accordance with 10CFR50.12(a)(2)(11) and 50.12(a)(2)(iii) are present to justity the requested exemption. The imposition of additional modifications simply to satisfy the methods specified by Appendix R of 10CFR50 is not necessary to satisfy the underlying purpose of the rule since the existing fire protection features provided for embedded conduits vould ensure one train of systems necessary to achieve and maintain hot standby is free of fire damage and, thereby, provide an equivalent level of fire protection as required by Section III.G of Appendix R. Additionally, the imposition of additional modifications

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simply to satisfy the methods'specified ')y Appendix R ~of.10CFR50 represents an

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