ML19274D488
| ML19274D488 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 01/16/1979 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Daltroff S PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| References | |
| NUDOCS 7902010244 | |
| Download: ML19274D488 (8) | |
Text
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UNITED STATES o
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NUCLEAR REGULATORY COMMISSION f,t 3(Q(
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MING OF PRUSSI A, PENN5YLVANt A 19406 January 16, 1979 Docket Nos. 50-277 50-278 Philadelphia Electric Company ATTN: Mr. S. L. Daltroff Vice President Electric Production 2301 Market Street Philadelphia, Pennsylvania 19101 Gentlemen:
The enclosed IE 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, Boyce H. Grier Director
Enclosures:
1.
IE Circular No. 79-02 2.
List of IE Circulars Issued in the last 12 months cc w/encls:
W. T. Ullrich, Station Superintendent Troy B. Conner, Jr., Esquire Eugene J. Bradley, Esquire Raymond L. Hovis, Esquire Warren Rich, Esquire 7yso/ 02y
UNITED STATES NUCLEAR REGULATORY COMMISSION
]D,Mn 0FFICE OF INSPECTION AND ENFORCEMENTo o J
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20555 IE Circular No. 79-02 Date:
January 16, 1979 Page 1 of 3 FAILURE OF 120 V0LT 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 degradation 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.
Itrnediate 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).
F5 pre 1 (attached) shows 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 settings of these time delay relays were not verified during either preoperational 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.
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IE Circular No. 79-02 Date: January 16, 1979 Page 2 of 3 (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 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 shoulu 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 information with regard to preoperational and startup testing.
IE Circular No. 79-02 Date: January 16, 1979 Page 3 of 3 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:
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IE Circular No. 79-02 Date: January 16, 1979 Page 1 of 3 LISTING OF IE CIRCULARS ISSUED IN LAST TWELVE MONTHS Circular Subject Date of Issued To No.
Issue 78-01 Loss of Well Logging 4/5/78 All Holders of Source Well Logging Source Licenses 78-02 Proper Lubricating 011 4/20/78 All Holders of for Terry Turbines Reactor OLs 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 Errors That 5/15/78 All Holders of Could Prevent Closing Reactor OLs or of Fire Doors cps 78-05 Inadvertent Safety 5/23/78 All Holders of Injection During Reactor OLs or Cooldown cps 78-06 Potential Common Mode 5/23/78 All Holders of Flooding of ECCS Reactor OLs or Equipment Rooms at cps BWR Facilities 78-07 Damaged Components on a 5/31/78 All Holders of Bergen-Paterson Series Reactor OLs or 25000 Hydraulic Test St.d cps 78-08 Environmental Qualifica-5/31/78 All Holders of tion of Safety-Related Reactor OLs or Equipment at Nuclear cps Power Plants
IE Circular No. 79-02 Date: January 16, 1979 Page 2 of 3 LISTING 0F IE CIRCULARS ISSUED IN LAST TWELVE f10NTHS Circular Subject Date of Issued To No.
Issue 78-09 Arcing of General Electric 6/5/78 All Holders of Company NEMA Size 2 cps Contactors 78-10 Control of Sealed Sources 6/14/78 All Medical Used in Radiation Therapy kc' seat in Categories G and G1 78-11 Recirulation M-G Set 6/15/78 All Holders of Overspeed Stops BWR OLs or cps 78-12 HPCI Turbine Control 6/30/78 All Holders of Valve Lift Rod BWR OLs or cps Bending for plants with HPCI Terry Turbine 78-13 Inoperability of 7/10/78 All Holders of Multiple Service Reactor OLs and cps Water Pumps except for plants located in: AL, AK, CA, FL, GA, LA, MS, SC 78-14 HPCI Turbine Re-7/12/78 All Holders of BWR versing Chamber OLs or cps for Hold Down Bolting plants with a HPCI Terry Turbine excepting Duane Arnold and Monticello 78-15 Checkvalves Fail to 7/20/78 All Holders of Close in Vertical Reactor OLs or Position cps 78-16 Limitorque Valve 7/26/78 All Holders of Actuators Reactor OLs or cps 78-17 Inadecuate Guard 10/13/78 All Holders of Trai;tng/ Qualification and applicants and raisified Training for Reactor OLs Records
4 IE Circular No. 79-02 Date: January 16, 1979 Page 3 of 3 LISTING OF IE CIRCULARS ISSUED IN LAST TWELVE MONTHS Circular Subject Date of Issued To No.
Issue 78-18 UL Fi' e 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 Supplier