ML20209B425
| ML20209B425 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 01/26/1987 |
| From: | Hukill H GENERAL PUBLIC UTILITIES CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 5211-87-2013, NUDOCS 8702040040 | |
| Download: ML20209B425 (2) | |
Text
u GPU Nuclear Corporation 4
g gf Post Office Box 480 Route 441 South Middletown, Pennsylvania 17057 0191 717 944 7621 TELEX 84 2386 Writer's Direct Dial Number:
January 26, 1987 5211-87-2013 U.S. Nuclear Regulatory Commission Attn:
Document Control Desk Washington, DC 20555
Dear Sir:
Three Mile Island Nuclear Station Unit 1 (TMI-1)
Operating License No. DPR-50 Docket No. 50-289 10 CFR 50 Appendix R - Associated Circuits GPUN letter to NRC, dated July 22, 1986 (5211-86-2124), provi ded clarifications of the analysis and review performed on associated circuits by common power discussed in the TMI-1 FHAR, Rev. 7.
The following discussion is intended to identify the additional studies and field verification being performed to further assure adequate protection is provided for associated circuits by common power source.
The review of the 4160 volt and 480 volt power distribution systems was limited to the lE equipment required for an Appendix R shutdown.
Electrical drawings were reviewed for existence and rating of overcurrent protection on all power circuits connected to the Appendix R required power sources (i.e.,
both A and B trains). All of the circuits were walked down in the field.
This walkdown verified the interrupting devices at the switchgear. An overcurrent protection study, which compared the incoming main breaker and the largest outgoing feeder breaker, was performed on the B train of the 1E buses required for the Appendix R shutdown. The results were considered to be applicable to the A train based on the review of overcurrent protection ratings because both trains were designed, installed and maintained to the same standards for identical loads.
Subsequent to FHAR Rev. 7, GPUN decided to perform two additional studies on the TMI-1 AC distribution system for all 1E buses. These studies are (a) a detailed system coordination study and (b) a bus short circuit study to check interrupting ratings of the circuit
&g breakers.
"8' Regarding DC power system coordination studies, please be advised that field Po gg verification of the rating and type of certain fuses not accessible during operation has been performed and any deficiencies identified are being corrected during the 6R Outage.
00 SE Subsequent to the FHAR Rev. 7 review of instrument power circuits identified that some instrument cables containing 120 VAC conductors from the NNI/ICS cabinets to the non-Appendix R instrument transmitters and controllers were eE C$u.
not provided with individual overcurrent protection.
A f ault on one of these circuits could result in the loss of the auto power and/or hand power bus of 0%
0 I
GPU Nuclear Corporation is a subsidiary of the General Public Utilities Corporation
I 5211-87-2013 January 26, 1987 the NNI/ICS system, because their instrument power circuits were not individually fused. An " Appendix R Associated Power Review of the NNI/ICS Cabinets" was performed and coordination deficiencies identified, and modifications are being implemented. A non-Appendix R modification being performed during the 6R outage will install fuses on individual instrument circuits in the NNI/ICS cabinets which will also correct the Appendix R coordination concerns. An Appendix R review of the modification engineering package is being conducted to verify the Appendix R associated power concerns have been corrected.
The AC Distribution panels evaluated prior to the FHAR, Rev. 7 were the vital power supplies required for the Appendix R shutdown.
The vital power supplies were evaluated based on a general comparison of the main breaker and feeder breakers. However, inherent current limiting characteristics of the equipment could result in unsatisfactory performance due to other faults, such as degraded voltage.
A more detailed study of the vital power supplies is being performed to confirm system coordination.
The additional studies and verifications identified subsequent to the FHAR, Rev. 7, are being completed during the 6R Refueling Outage. Any deficiencies found will be corrected during the 6R Outage by providing an adequately sized breaker or fuse.
If any additional information is required, please contact us.
Si ncerely, H. D. Hu fil Vice President A Director, TMI-l HDH:DJD:1705g cc:
J. F. Stolz J. Thoma F. Young D. Kubicki A. Krasopoulos