ML17296A280
| ML17296A280 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 01/16/1979 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Vanbrunt E ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR |
| References | |
| NUDOCS 7901220222 | |
| Download: ML17296A280 (12) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION REGION V SUITE 2021 WALNUT CREEK PLAZA 1950 N. CALIFORNIABOULEVARD WALNUT CREEK, CALIFORNIA 94556 January 16, 1979 NOTE TO:
ALL THOSE ON IE CIRCULAR DISTRIBUTION LIST FROM:
IE, REGION V
SUBJECT:
IE CIRCULAR NO. 79 FAILURE OF 120 VOLT VITAL AC POWER SUPPLIES The attached IE Circular 79-02 was issued this date to the following licensees:
l.
Arizona Public Service Company (Palo Verde 1, 2 5 3, Docket Nos.
50-528, 50-529, 50-530) 2.
3.
4.
Pacific Gas 8I Electric Company (Humboldt Bay Unit 3, Diablo Canyon Units 1
8 2, Docket Nos.
50-133, 50-275, 50-323)
Portland General Electric Company (Trojan, Docket No. 50-344)
Sacramento Municipal UtilityDistrict (Rancho
- Seco, Docket No. 50-312) 5.
Southern California Edison Company (San Onofre Units 1, 2, 3, Docket Nos.
50-206, 50-361, 50-362)
=-6.
Washington Public Power Supply System (WNP-l, WNP-2, WINP-3, WNP-4, and WNP-5, Docket Nos.
50-460, 50-397, 50-508, 50-513 and 50-509)
Region V has made distribution to the Accessions Unit for the
- PDR, Local
Enclosures:
1.
Transmittal Ltr.
2.
IE Circular No. 79-02 o~o>~~
UNITED STATES NUCLEAR REGULATORY COMMISSION REGION V SUITE 202'ALNUT CREEK PLAZA 1990 N. CALIFORNIABOULEVARD WALNUTCREEK, CALIFORNIA 94596 JAN I< 579 Docket Nos. 50-528~
50-529 50-530 Arizona Public Service Company P. 0.
Box 21666 Phoenix, Arizona 85036 Attention:
Mr. E.
E. Van Brunt, Jr.
Vice President, Construction Projects Gentlemen:
The enclosed IE Circular No. 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, R.
H. Engelken
~ Director
Enclosures:
l.
IE Circular No. 79-02 2.
List of IE Circulars Issued in the last 12 months cc:
F. tl. Hartley, APS
FAILURE OF 120 VOLT VITAL AC POllER SUPPLIES IE Circular Ho. 79-02 January 16, 1979 Paqe 1 of 2 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) shows the functional interconnection of the 120 volt AC power supply
'ystem..
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 was not verified during either preoperational testing or subsequent maintenance.
The time delay is necessary in order to accommodate transient loading condi-tions which may be encountered.
(b)
On one. SCI inverter, a
DC fuse within the inverter component was'ound 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 r eset 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.
(c)
The SCI inverter static switch is designed to transfer to an alternate source on inverter output overcurrent or undervoltage.
Initially, these trips were set at 125 percent overcurrent and 80 percent undervoltage.
An explanation for the transfer of two
IE Circular No. 79-02 January 16, 1979 Page 2 of 2.
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 SCI 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.
-.3.
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.
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-abi.lity of the inverter system during transient loading conditions.
An operatinq history of inexplicable transfers may be indicative of the above.
C 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 information with regard to preoperational and startup testing.
No written response to this Circular is r equired.
If you require additional information regarding this matter, contact the Director of the appropriate NRC Regional Office.
Attachment:
Figure 1
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IE Circular No. 79-C2 January 16, 1979 Circular Subject No.
LISTING OF IE CIRCULARS ISSUED IN LAST TMELVE MONTHS Date of Issue Issued To 78-01 78-02 78-03 78-04 '.
78-05 78-06 78-07 78-08 78-09 Loss of Mell Logging Source Proper Lubricating Oil for Terry Turbines Packaging Greater Than Type A Ouantities of Low Specific Activity Radioactive Material for Transport Installation Error That Could Prevent Closing of Fire Doors Inadvertent Safety Injection During Cooldown Potential Common Mode Flooding of ECCS Equipment Rooms at BMR Faci'lities Damaged Components of a Bergen-Paterson Series 25000 Hydraulic Test Stand Environmental gual ification of Safety Related Equipment at Nuclear Power Plants Arcing of General Electric Company Size 2 Contactors 4/5/78 4/20/78 5/12/78 5/15/78 5/23/78 5/23/78 5/31/78 5/31/78 6/5/78 All Holders of Mell Logging Source Licenses All Holders of Reactor OLs or CPs All Holders of R'eactor OLs, CPs, Fuel Cycle, Priority I Material and Maste Disposal Licenses All Holders of Reactor Q.s or CPs
. All Holders of Reactor OLs or CPs All Holders of Reactor OLs or CPs All Holders of Reactor OLs or CPs All Holders of Reactor OLs or CPs All Holders of CPs Enclosure Page.l. of 3
IE Circular No. 79-02 i)anuary 16, 1979 LISTING OF IE CIRCULARS ISSUED IN
. LAST TMELVE f'10NTHS 78-10 Control of Sealed Sources Used in Radiation Therapy Circular Subject No.
Date of Issue 6/14/78 Issued to All t1edical Licensees in Categories G
and G1
'8-11
,78-12 78-13 78-14 78-15 78-16 78-17 Recirculation H-G Set Overspeed Stops HPCI Turbine Control Valve Lift Rod Bendinq Inoperability of Multiple Service Mater Pumps WPCI Turbine Reversing Chamber Hold Down Bolting Checkvalves Fail to Close In Vertical Position Limitorque Val ve Actuators Inadequate Guard Training/
gualification and Falsified Training Records 6/15/78 6/30/78
,7/10/78 7/12/78 7/20/78 7/26/78 10/13/78 All Holders of BMR OLs or CPs All Holders of BMR OLs or CPs for plants with HPCI Terry Turbine All Holders of Reactor OLs and CPs except for plants located in: AL, AK, CA, FL, GA, LA, HS, SC All Holders of BMR OLs or CPs for plants with a HPCI Terry Turbine excepting Duane
'rnold and Honticello=
All Holders of Reactor OLs or CPs All Holders of Reactor OLs or CPs All Holders of and applicants for Reactor OLs.
Enclosure Page 2 of 3,.
IE Circular No. 79-02 January 16, 1979 LISTING OF IE CIRCULARS ISSUED IN LAST TIJELVE MONTHS 78-18 UL Fire Test Circular Subject No.
Date of Issue 11/6/78 Issued To All Holders of Reactor OLs or CPs 78-19 79-01 Manual Override (Bypass) of Safety Actuation Signals
/
Administration of'nauthorized Byproduct Material to Humans 12/28/78 1/12/79 All Holders of CPs All Medical Licensees except Teletherapy Medical Licensees and each Radiopharmaceutical Suppliers Enclosure Page 3 of 3