ML19305A196
| ML19305A196 | |
| Person / Time | |
|---|---|
| Site: | Cherokee  |
| Issue date: | 01/16/1979 |
| From: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | Daily L DUKE POWER CO. |
| References | |
| NUDOCS 7901220323 | |
| Download: ML19305A196 (1) | |
Text
.
t " "84 UNITED STATES h
9
[,g jo NUCLEAR REGULATORY COMMISSION g, #7/
2 (g
Ni p 'p&
REGION ll
~'
{
g
\\v
/
a
-"' /E 101 M ARIETT A STREET. N.W.
' i uf f ATLANTA, GEORGIA 30303
%,. 6 4)[
o, JAN 161979 In Reply Refer To:
RII:JP0 50-413, 50-414 50-488, 50-489 50-490, 50-491 50-492, 50-493 Duke Power Company Attn:
Fk. L. C. Dail, Vice President Design Engineering P. O. Box 2178 Charlotte, North Carolina 28242 Gentlemen:
The enclosed Circular 79-02 is forwarded to you for information.
If there are any questions related to your understanding of the suggested actions, please contact this office.
Sincerely, C
wr r:es P. O'Reilly D rector
Enclosures:
1.
List of IE Curculars Issued in the last 12 months cc w/ encl:
D. C. Beam, Project Manager Catawba Nuclear Station P. O. Box 223 Clover, South Carolina 27910 J. T. Mcore, Project Manager Cherokee Nuclear Station P. O. Box 422 Gaffney, South Carolina 29340 7901220323
I UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.
20555 January 16, 1979 IE Circular No. 79-02 FAILURE OF 120 VOLT VITAL AC POWER SUPPLIES Description of Circumstances:
On September 16, 1978, Arkansas Nuclear One - Unit 2, while in hot functional testing preceding initial criticality, suffered a degrada-tion of both of the independent off-site power sources.
This produced an undervoltage condition on the Engineering Safety Features (ESF) Buses and caused an inadvertent ESF actuation.
The licensee determined that the ESF actuation occurred on a loss of at least two of the uninter-ruptable 120 volt vital AC power sources.
Immediate investigation revealed that all four of the Solidstate Controls, Inc., (SCI) inverter static switches had automatically transferred to the alternate power supply (the 120 volt AC being supplied by transformers directly off the ESF buses rather than from the inverter output.)
Figure 1 (attached) shovs the functional interconnection of the 120 volt AC power supply system.
A single conclusive cause of the undesired SCI inverter static switch transfer could not be identified. However, the following problems were discovered during subsequent investigation.
(a)
The SCI inverters have circuitry to monitor the incoming DC voltage level which, on sensing a low voltage (nominally 104 DC volts for these inverters) will trip both input breakers to the inverter component after an adjustable time delay.
The setting of these time delay relays were not verified during either preopcrational testing or subsequent maintenance.
The time delay is necessary in order to accommodate transient loading conditions which may be encountered.
(b) On one SCI inverter, a DC fuse within the inverter component was found blown.
The vendor indicated that this fuse will blow due to an excessive DC voltage to the inverter component caused by a transient on the 480 AC input. The licensee has subsequently reset the taps on the 480V to 120V three-phase AC input transformer to limit the DC voltage to the inverter to less than the nameplate maximum rating in the event of a high AC input voltage transient.
1 of 3 w
IE Circular No. 79-02 January 16, 1979 (c) The SCI inverter static switch is designed to transfer to an alternate source on inverter cutput overcurrent or undervoltage.
Initially, these trips were set at 125 percent overcurrent and 80 percent undervoltage.
An explanation for the transfer of two of the inverter static switches is that during one of the transfers of site loads, the instantaneous inductive load caused these trip set points to be exceeded.
The licensee has subsequently adjusted the transfer sensing circuitry to higher overcurrent and lower undervoltage trip settings to assure that the inverter will maintain load over the widest possible range of voltage and current.
(Note that in this case, once the SCl inverter transfers to the alternate source, it will not automatically transfer back to normal source.)
All holders of operating licenses should be aware of the potential problems of the types noted above.
It is recommended that the following items be considered in your review of this matter:
1.
Determine whether or not time delay circuitry is used in your inverter units.
If so, have they been adjusted to the appropriate set point as required by equipment and the integrated system designs?
2.
Determine if the AC input voltage and transformer tap settings are optimized to prevent exceeding the inverter component name-plate maximum rated DC input voltage in the event of a high AC input voltage transient.
3.
If an alternate 120 volt source is used in your design, determine if the protection transfer circuitry of the inverter has been optimized within design limits to ensure maximum possible avail-ability of the inverter system during transient loading conditions.
An operating history of inexplicable transfers may be indicative of the above.
4.
Determine if the administrative controls employed by your facility ensures operability of safety systems after its subcomponents (e.g., time delay relays, switches, etc.) have been subjected to maintenance or testing.
This Circular is also being forwarded to all holders of construction permits for their ir formation with regard to preoperational and startup testing.
2 of 3
IE Circular No. 79-02 January 16, 1979 No written response to this Circular is required.
If you require additional information regarding this matter, contact the Director of the appropriate NRC Regional Office.
Attachment:
Figure 1 3 of 3
4 EDG _
EDG EDG b
~ ~~
f).
7 - - - -: - -). -q _
NC I
T l
I 1-8 125 VDC 125 VDC BATTERY l
B ATTE RY - I CHARGER i
BANT lll l l
l l
h,NC i
t_
h 125 VDC BUS _
3.
.......x. _ ___ _ _. _ _ _ _
NC Uf
,3 N C
*\\
~
I t$U s
.Y_
lav V
's. -
j
' ' - - - ~ ~ ~~--7 5
hb"LT hl l A LT ERN AT E.
l bE I NVERT E R E
COMPONEAT l
Lu j
l-
~
W
. :. b
)
l NORM A'L jf s'
v b
E NE R G ENgSTATIC T R A NS'IE A SW1TCH l.
_.i
._ _ _ _ __ _ _. _ N,_,
i s-- -
120 VAC PANEL FIGURE I
SINGL E LINE DI AGRAM
'20.NAC
IE Circular No. 79-02 January 16, 1979 LISTING OF IE CIRCL*LARS ISSL'ED IN LAST IWELVE MONTHS Circular Subject Date Issued To No.
of Issue 78-01 Loss of Well Logging 4/5/73 All Holders of Source Well Logging Source Licenses 78-02 Proper Lubricating Oil 4/20/78 All Holders of for Terry Turbines Reactor JLs or cps 78-03 Packaging Greater Than 5/12/78 All Holders of Type A Quantities of Reactor OLs, cps, Low Specific Activity Fuel Cycle, Radioactive Material Priority I Material for Transport and Waste Disposal Licenses 78-04 Installation Error That 5/15/78 All Holders of Could Prevent Closing of Reactor OLs or Fire Doors cps 78-05 Inadvertent Safety Injection 5/23/78 All Holders of During Cooldown Reactor OLs or cps 78-06 Potential Common bbde 5/23/78 All Holders of Flooding of ECCS Equipment Reactor OLs or Rooms at BWR Facilities cps 78-07 Damaged Components of a 5/31/78 All Holders of Bergen-Paterson Series Reactor OLs or 25000 Hydraulic Test cps Stand 78-08 Environmental Qualification 5/31/78 All Holders of of Safety Related Equipment Reactor OLs or at Nuclear Power Plants cps 78-09 Arcing of General Electric 6/5/78 All Holders of Company Size 2 Contactors cps Enclosure Page 1 of 3
A IE Circular No. 79-02 January 16, 1979 LISTING OF IE CIRCULARS ISSUED IN LAST TWELVE MONTHS Circular Subject Date of Issued to No.
Issue 78-10 Control of Scaled 6/14/78 All Medical Sources Used in Licensees in hadiation Therapy Categories G and G1 78-11 Recirculation M-G 6/15/78 All Holders of Set Overspeed Stops BWR OLs or cps 78-12 HPCI Turbine Control 6/30/78 All Holders of Valve Lift Rod Bending BWR OLs or cps for plants with HPCI Terry Turbine 78-13 Inoperability of Multiple 7/10/78 All Holders of
-7 Service Water Pumps Reactor OLs and cps
"~
except for plants located in: AL, AK, CA, FL, GA, LA, MS, SC 78-14 HPCI Turbine Reversing 7/12/78 All Holders of BWR Chamber Hold Down Bolting OLs or cps for plants with a HPCI Terry Turbine excepting Duane Arnold and Monticello 7 P.- 15 Checkvalves Fail to 7/20/78 All Holders of Close In Vertical Reactor OLs or cps Position 7-16 Limitorque Valve 7/26/78 All Holders of Actuators Reactor OLs or cps 7-17 Inadequate Guard Training /
10/13/78 All Holders of Qualification and Falsified and applicants Training Records for Reactor OLs.
Enclosure Page 2 of 3
s IE Circular No. 79-02 January 16, 1979 LISTING OF IE CIRCULARS ISSUED IN LAST TWELVE MONTHS Circular Subject Date of Issued To No.
Issue 78-18 UL Fire Test 11/6/78 All Holders of Reactor OLs or cps 78-19 Manual Override (Bypass) 12/28/78 All Holders of of Safety Actuation Signals cps 79-01 Administration of 1/12/79 All Medical Unauthorized Byproduct Licensees except Material to Humans Teletherapy Medical Licensees and each Radiopharmaceutical Suppliers Enclosure Page 3 of 3 t-