ML20079D967
| ML20079D967 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 09/27/1991 |
| From: | Tuckman M DUKE POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9110040261 | |
| Download: ML20079D967 (4) | |
Text
m-
+ - -
g; l
!) uke 1% rr Com;>any M S 11i um hise lYoJu;Iw1: fir; t Vn e l'reudr at
' l'O Rv.n lotii
~
b lair Oprutwns (krlottcz 5 C lGi fleil
(:nt'i;;I D TI DUKEPOWER September 27, 1991 U.S. Nuclear Fegulacory commission ATTN: Document Control Desk
'3ashington, D.C. 20555
Subject:
McGuiro Nuclear Station Docket Nos. 50-369, -370 Inspection Report No. 50-369, -370/91-09 Electrical Distribution System Functional Inspection Response to Finding on Breaker Miscoordination Gentlemen:
Please find attached Duke Power Company's response to the subject finding. This resp se addresses our plans and schedu'le for resolving this finding. An adoitional response will be submitted as indicated in the attachment to provide the resulta of the evaluation regarding the feasibility of providing full coordination in DC panelboards for branch circuit protection.
Should there be any questions concerning this matter, contact L.J. Rudy at (704) 373-3413.
Very truly yours.
W%
M.S. Tuckman LJR/s Actachment xc (W/ Attachment):
S.D. Ebneter Regional Administrator, Region II T.A. Reed, ONRR P.K. VanDoorn Senior Resident Inspector 9110040261 910927 l
PDR ADOCK 05000359
)
)
O PDR
-.. - ~ _
-_-.--~
~
a p.
j l
MODITICATION DESCRIPTION L
a l
As noted in the NRC Inspection Report, the 125 VDC Vital Instrumentation and Control (EPL) system is not selectively coordinated above a certain level of fault current.
Since the system is shared betveen units 1 and 2, this could potentially result in a trip of both units i f this specific f ault were to 4
occur.
Each of-the four batteries supply one distribution center which in turn supplies one DC panelboard per unit Coordination cannot bc guaranteed
- in-the instantaneous region of the molded case circuit breakers located in j
the distribution center and the panelboards.
This characteristic may cause j
the battery circuit breaker to operate due to a fault in a panelboard.
5 Several options have been evaluated to improve coordination of the CPL sys-tem.
A search did not uncover a molded case circuit breaker which would im-prove coordination.
The more advanced features of AC molded case circuit bronkers are not available for DC applications.
4 The most feasible solution is to replace the charger circuit breaker, bat-tery circuit breaker, main circuit breaker and cross-tic circuit breaker (indicated by an asterisk on the attached drawing) with n.m-fusible and fusible switches.
The addition of fuses will rllow the circuit breakers
+
closest to the fault to clear before isolattng the battery from the bus.
- This will decrease the possibility of a fault causing a loss of power which
- would trip both units.
In the cross-tied configuration, the fuses will help
- insure that the bus without a battery will be cleared successfull" under a fault condition without isolating the battery from the other bus.
s Even with the replacament of the circuit breakers described no, one unit
_could trip as a result of a fault beyond one of the panelboard branch cir-cuit breakers.
Both the panelboard feeder circuit breaker and the branch circuit breakers have thermal-magnetic elements, so they will not coordi-
- nate during the instantaneous' region.
However, this is similar in conse-
- quence to the case postulated in the FSAR where the panelboard is lost and the other train is used.
The feasibility of providing full coordination in DC panelboards for branch circuit protection has not heen fully determined.
Concerns such as space limitations and plant operation during the modification must be considered 4
further.
The evaluation of this option will continue for the nsxt 90 days and an additional response will be submitted, i
TIME F"U2DULE In order to maxinize plant reliability and personnel
- safety, the circuit breaker replacements should be performed while the bus is not energized.
^
The EPL system is shared therefore, all its buses-are normally energized.
By aligaing the inverters to their regulated bus and providing a
temporary feed to the-DC panelboards, the distribution center can be de-energized.
In order to align the system, replace the breakers and return the system to normal, more than the Technical Specification limit of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> will be needed.
Therefore,
- a. Technical Specification change will be required to ex-I tend the time for this modification.
i a
y
+
~.
2 m
.-__._.___....__m.....
r
-It is_. preferable to replace this equipment while one unit is_in an outage.
LThe planned schedule is for two. of the busen.to be changed during; unit 1
outage Eoc-9. scheduled-for. March 1994,-with the remaining two buses changed-
~
during the unit 2 outage EOC-9 scheduled for September 1994.
This will pro-
- vide-adequate time-to procure-and qualify equipment, complete--the design and address the details necessary to install the new equipment.
This time schedule considers the replacement of_the charger, battery, main and cross-tic circuit. breakers.
The time schedule for the panelboard changes will be included in the succeeding response.
b t
ft 8
F
.n. - ~
,n
.. ~,
>v.
,=Q-.
\\,
y l
t l
e 2EMMA EMXA 2EMx8 SEMXS SEMIM 2E,MMM IEMxA tEMza Euxa 2EMsg
- c
- d r-k' J
[
.s
)--a - ECo-s c,,,,,Ece4 L)..gT Co....,
I I
s ECn. C.......Ece-2 l> -a --l) g) -x.)
C"*"*'
EC8-3 i
i3..,.r
)
')
standby
.)
DOllery
)
Q Q
',.'t j
j EYCD g
EVCC C a, '.
Ch0F9'r EVCB Cn. e E*C"
')
)
')
l EVCS y
j
)
Dotte W- )
M ) EVCdr
-f )
- Bottery Bottery D888F lEYD*
M )
EVCD EvCC EVCA
)--x - - 4 I
M ')
y)
- I }
I I
I.
WI D;su; ta ;,n ry sx CceFors es Is es
@ ftl)
Ml,)
h3 Y I h EvDo l
Yr g)
- ,)
h Evoc
-#l) v g
N )
)
)
)
')
)
I) f)
')
I)
I)
')
I)
)
f) f)
')
S ' I * '" d '"
Evos tvDA 2EVDCf IEvDO 2EvDO IEvDB 2EVD8 IEVDC VITAL. lHS1FUMt.NTATION IEVDA 2EvDA 7
AND CONTR01. PWl_R (EPG)
)
)
,)
L1
)
)
)
)
l
^
d DC Pane.l beaccis ll