ML20126A876
| ML20126A876 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 02/25/1980 |
| From: | Brown S VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20126A880 | List: |
| References | |
| 1111B-113079, NUDOCS 8002260720 | |
| Download: ML20126A876 (3) | |
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February 25, 1980 Mr. Harold R. Denton, Director Serial No. 11118/113079 Office of Nuclear Reactor Regulation PSE&C/JMD:adw:mc l
Attn: Mr. O. D. Parr, Chief Light Water Reactors Branch No. 3 Docket No. 50-339 Division of Project Management U. S. Nuclear Regulatory Commission Washington, D. C.
20555
Dear Mr. Denton:
STAFF POSITION ON ELECTRICAL PROTECTION OF CONTAINMENT PENETRATIONS FOR NORTH ANNA POWER STATION, UNIT 2 As we indicated in our February 15, 1980 letter, Serial No. 1111C/113079, this is our final submittal for containment penetration primary protection. Our pre-vious submittals addressed power and instrument circuits; this submittal addresses control circuits.
In our enclosure listing the control circuits, there are five circuits which require the protective device to be changed to a lower setting.
These circuits are:
Enclosure pages 2 and 6 1.
Position 6C-2 Load f (2-RS-P-01A VIB. SW) 2.
Position 19C-2 Load c (2-RS-P-01B VIB. SW)
The devices listed above are vibration sensors which are very low signal devices. The listed 35A fuses will be replaced with 15A fuses which coordinate with the type IB penetration limits.
Enclosure pages 4 and 8 3.
Position 6D-2 Load n PS-13-2 4.
Position 6D-2 Load o PS-14-2 5.
Position 190-2 Load t PS-12-2 These devices are pressure switches which indicate that hydraulic pressure is adequate in the RCP lift pump system to permit starting an RCP.
The 30A fuses will be replaced with 15A fuses which will coordinate with the type IB penetration limits.
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Mr. Harold R. Denton 2
The purpose of this portion of the submittal is to explain an apparent discrepancy in our protection philosophy for control circuit penetrations when compared to power circuit design considerations.
The difference appears in the Long Time Region of. the following control circuit curves:
IB-2, IB-3, IB-4, 2IB-6, IB-7 and IB-10. The last point verified by test on the penetra-i tion 1 t curve'is at 1500 sec. The continuous load capability lies at a 2
current lower than this point. The continuation of the 1 t characteristic from the 1000 sec, point to the continuous current value is an estimated pro-jection. To insure that the protection covers the full fault range, the overcurrent device has been set so that at the last verified test point, 1000 sec., the protective device trip current is below the penetration con-tinuous current rating. This is not the case with the above listed curves.
The continuous current value, Point "D", is the current rating under absolute worst case conditions; that is,12 amperes in each of the 140 conduc-tors. Since this loading is not feasible case for control circuits of this nature, we have taken credit for a diversity factor.
This factor is considered conservative an'd has been proven by test.
The diversity factor is based on a shared load of 20 amperes in 138 of the 140 conductors (98.6%). This current equals a minimum of twice the full load expected and is applied simultaneously to the conductors where the actual loads occur intermittantly.
Under this condition, any 2 conductors of the 140 total conductors are capable of carrying 25 amperes continuously.
This rating has been derived by test.
With this test point taken into consideration, the overcurrent protection trip current at the 1000 sec. point is lower than the penetration continuous rating of 25 amperes.
Therefore, overcurrent protection is provided over the full range of faults with a conservative diversity factor taken into account.
The protection scheme is designed around the highest possible fault current available. The current shown on the curves is the current calculated using only line impedance from the circuit's source.
No credit has been taken for power supply or Controller Impedances.
In addition, internal protection devices located in power supplies or controllers are not incorporated into the analysis, even though these factors decrease available fault current and offer addi}ional steps of protection.
Mr. Harold R. Denton 3
If you have any questions please contagt this office.
~7gryy/ ruly t
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(
- gwn, Senior Vice President Power Station Engineerinc and Construction s
Enclosures i
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