ML20149H139
| ML20149H139 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 02/18/1988 |
| From: | Gridley R TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| NUDOCS 8802190137 | |
| Download: ML20149H139 (3) | |
Text
e TENNESSEE VALLEY AUTHORITY CH ATTANOOGA. TENNESSEE 374ot SN 157B Lookout Place FEB 181988 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C.
20555 Gentlemen:
In the Matter of
)
Docket Nos. 50-327 Tennessee Valley Authority
)
50-128 SEQUOYAH NUCLEAR PLANT (SQN) - CRITERIA FOR SEPARATION OF SAFETY-RELATED CONDUITS - NRC INSPECTION REPORT NOS. 50-327/87-1f AND 50-328/87-18 Enclosed is our response to S. D. Richardson's December 31, 1987 letter to S. A. White regarding NRC's concern over safety-related conduit separation criteria.
Very truly yours, TENNESSEE VALLEY AUTHORITY
,/
R. Gridley, D ector Nuclear Licensing and Regulatory Affairs Enclosure cc (Enclosure):
Mr. K. P. Barr, Acting Assistant Director for Inspection Programs TVA Projects Division Office of Special Projects U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 Mr. G. G. Zech, Assistant Director for Projtets Mail Stop 7F23 TVA Projects Division office of Special Projects U.S. Nuclear Regulatory Commission 7920 Norfolk Avenue
- 7 go l Sethesda, Maryland 20814 Sequoyah Resident Inspector
/
Sequoyah Nuclear Plant l
2600 Igou Ferry Road Soddy Daisy Tennessee 37379 8802190137 880218 PDR ADOCK 05000327 O
DCD An Equal Oppodanity Employer
ENCLOSURE SQN's raceway separation requirements are based upon Institute of Electrical and Electronic Engineers (IEEE) 279 (1971), IEEE-308 (1971), and Regulatory Cuide (RG) 1.6, revision O.
Because none of these documents provided specific raceway separation distance requirements, SQN's separation requirements were determined based upon industry-accepted practices.
SQN's Final Safety Analysis Report (FSAR),
section 8.3.1.4.2, and design criteria SQN-DC-V-12.1 reflect these standards.
With respect
'.o NRC's concern that an electrical f ault in one raceway might cause internally generated fires that affect the functional integrity of redundant safety-related circuits in adjacent raceways, TVA offers the following analysis justifying the adequacy of SQN's existing conduit / cable tray installations.
Calculations performed as part of SQN's Appendix R analysis demonstrated that all cables routed in safety-related cable trays and conduits are protected from fault-induced fires by an overcurrent protection device (fuso or circuit breaker). A potential event in one divisional cable tray or conduit is mitigated by these overcurrent protective devices as they prevent automatic ignition of cable insulation because of an electrical fault.
SQN's class 1E cable tray installations are comprised of IEEE-383 vertical-flame-test-qualified cables and non-IEEE-333 qualified cables coated with Flamemastic fire retardant. The use of fire-retardant cables or fire-retardant coatings in conjunction with overcurrent protective devices provides assurance that an internally generated fire in a cable tray would r.ot affect the functional integrity of redundant rafety-related circuits in adjacent cable trays or conduits.
I Typically, SQN's class lE conduit installations, because of required support methods, result in the presence of a one-inch air gap between conduits.
Installations where the one-inch separation may not be maintained are of no consequence because there is no propagation path for an internally generated fire in one conduit to affect the functional integrity of circuits in an adjacent conduit.
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The specific example stated in Inspection Report 50-327 -328/87-18, in which a division A conduit was installed less than one inch from a division B i
uncovered cable tray, was investigated by TVA.
Identification of the cables j
carried by the referenced raceways verified that redundant safety-related channels were not involved.
NRC resident inspectors reviewed and concurred with TVA's findings.
i l
l i
The above design features were previously reviewed by NRC and found acceptable as indicated in the NRC's Safety Evaluation Report (sed) related to operation of SQN units 1 and 2 (March 1979), section 8.5.3 whien states:
"On the initial site visit, we questioned the implementation of separation criteria in instances where non-divisional cable trays were routed between redundant divisional cable tray stacks, unsupported cable bundles run vertically between cable trays in the same stack, and trays of different divisions cross. The applicant has (1) coinmitted to coat all cabling in the spreading room with fire retardent coating, (2) provided adequate sprinkler coverage (3) supported and will encase the vertical runs in fire retardent coating, and (4) committed to provide barriers at interdivisional crossings.
We conclude that these provisions adequately address our concerns and are acceptable."
With respect to circuit breakers used for isolation of non-1E loads from 1E power systems, section 8.5.4 of the SER states:
l "We confirmed that circuit breakern actuated by f ault current are used as isolation devices in this plant. This usage conflicts with the current recomnendations of Regulatory Guide 1.75, ' Physical Independence of Electric Systems.' However, because this design preceded the issuance of Regulatory Guide 1.15, this use is permitted.
In addition, the breakers are qualified as I
Class 1E equipment and will be periodically tested to verify that the originally designed coordination continues to be available. We conclude that this is acceptable, and requirements for such testing will be included in the technical specifications."
In conclusion, it can be stated that, because of SQN commitments, analyses provided by engineering calculations, and typical class-1E cable tray and conduit installations, elsetrical faults in one raceway (conduit or cable tray) will not cause internally generated fires that affect the functional integrity of redundant safety-related circuits in adjacent raceways at SQN.
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