ML19296A111
| ML19296A111 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 01/16/1979 |
| From: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | Burstein S WISCONSIN ELECTRIC POWER CO. |
| References | |
| NUDOCS 7901250040 | |
| Download: ML19296A111 (8) | |
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Jry,,,m Docket No. 50-266 Docket No. 50-301 Wisconsin Electric Power Company ATTN:
Mr. Sol Burstein Senior Executive Vice President Power Plants 231 West Michigan Milwaukee, WI 53201 Gentlemen:
The enclosed IE Circular No. 79-02 is forwarded to you for information. If there are any questions related to your under-standing of the suggested actions, please contact this office.
Sincerely, konbu JamesG.Kepf1(r Director
Enclosures:
1.
IE Circular No. 79-02 2.
List of IE Circulars Issued in the last 12 months cc w/encls:
Mr. G. A. Reed, Plant Manager Central Files Director, NRR/DPM Director, NRR/ DOR PDR Local PDR NSIC
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UNITED STATES NUCLEAR REGULATORY COMMISSION IOFFICE OF INSPECTION AND ENFORCEMENT r.
REGION III 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 het functional testing precceding 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 (EST) 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 of f the ESF buses rather than from the inverter output.) Figure 1 (attached) shows the functional intcrconnection of the 120 volt AC power supply systet.
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 preoperational testing or subsequent main-tenance. The time delay is necessary in order to accom-modate transient loading conditions which may be encount-ered.
(b) On one SCI inverter, a DC fuse within the inverter component was
.fo.und 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 naceplate maximum rating in the event of a high AC input voltage transient.
IE Circular No. 79-02 January 16, 1979 (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 leads, 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 it will not automatically transfer back to normal alternate source, 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 information with regard to preoperational and startup testing.
IE Circular No. 79-02 January 16, 1979 i
No written response to this Circular is required. If you require e
additional information regarding this catter, contact the Director of the appropriate NRC Regional Office.
Attachment:
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IE Circular No. 79-02 January 16, 1979 I
LISTING OF IE CIRCUL/.RS ISSUED IN LAST TWELVE MONTHS Circular Subject Date Issued To No.
of 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 Error That 5/15/78 All Holders of Could Prevtat 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 Mode 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 Environcental 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
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 Radiation 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 Service Water Pumps Reactor OLs and cps except fer plants located in: AL, AK, CA, FL, GA, LA, MS, SC 78-14 HPCI Turbine Reversing 7/12/78 All Holders of BWR Chanber Hold Down Bolting OLs or cps for plants with a HPCI Terry Turbine excepting Duane Arnold and Monticc2 76-15 Checkvalves Fail to 7/20/78 All Holders of Close In Vertical Reactor OLs or cps Position 78-16 Limitorque Valve 7/26/78 All Holders of Actuators Reactor OLs or cps 78-17 Inadequate Guard Training /
10/13/78 All Holders of Qualification and Falsified and applicants Training Records for Reactor OLs.
Enclosure Page 2 of 3
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 Medica:
Licensees and each Radiopharmaceutica]
Suppliers Enclosure Page 3 of 3