ML19296A103
| ML19296A103 | |
| Person / Time | |
|---|---|
| Site: | Waterford  |
| Issue date: | 01/16/1979 |
| From: | Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | Aswell D LOUISIANA POWER & LIGHT CO. |
| References | |
| NUDOCS 7901250016 | |
| Download: ML19296A103 (7) | |
Text
189 pa Pe cq UNITED STATES d'
'o, NUCLE AR REGULATORY COMMISSION y
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611 RYAN PLAZ A DRIVE, SUITE 1000
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January 16, 1979
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In Reply Refer To:
RIV Docket flo.
50-332/IE Circular 79-02 Louisiana Power and Light Co.
ATTri:
Mr. D. L. Aswell Vice President of Power Production 142 Delar:nde Street fiew Orlear.s, Louisiana 70174 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,
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- Karl V.
yfrit Director
Enclosures:
1.
IE Circular tio. 79-02 2.
List of IE Circulars Issued in the last 12 months
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790125cc(G
f UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.
20555 IE Circular No. 79-02 Date:
January 16, 1979 Page 1 of 2 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 degradation of botn 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 tnat 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 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 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.
I s
IE Circular No. 79-02 Date:
January 16, 1979 Page 2 of 2 (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 tr.e 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 tte potential problems of the types noted above.
It is recommended that the following items be considered in your revi1w 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 exceeaing the inverter component nameplate 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 availability 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.
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
IE Circular No. 79-02 January 16, 1979 LISTING OF IE CIRCULARS ISSUED IN LAST TWELVE MONTHS Circular Subject First Date Issued To No.
Of Issue 78-01 Loss of Well Logging 4/5/78 All Holdcis of Source Well Logging Source Licenses 78-02 Proper Lubricating 4/L)/78 All Holders of Oil for Terry Reactor Operating Turbines Licenses (OL) or Construction Permits (CP) 78-03 Packaging Greater 5/12/78 All Holders of Than Type A Reactor Operator Quantities of Low Licenses (0L),
Specific Activity Construction Radioactive Material Permits (CP), Fuel' for Transport Cycle, Priority I Material and Waste Disposal Licenses 78-04 Installation Error 5/15/78 All Holders of That Could Prevent Reactor Operating Closing of Fire Licenses (0L) or Doors Construction Permits (CP) 78-05 Inadvertent Safety 5/23/78 All Holders of Injection During Reactor Operating Cooldown Licenses (0L) or Construction Permits (CP) 78-06 Potential Common 5/25/78 All Holders of Mode Flooding of Reactor Operating ECCS Equipment Licenses (0L) or Rooms at BWR Construction Facilities Permits (CP)
Enclosure Page 1 of 3
IE Circular flo. 79-02 January 16, 1979 78-07 Damaged Components 5/31/78 All Holders of Of a Bergen-Paterson Reactor Operatics Series 25000 Hydrau-Licenses (01.) or lic Test Stand Construction Permits (CP) 78-08 Environmental Quali-5/31/78 All Holders of fication of Safety-Reactor Operating Related Equipment Licenses (OL) or at fluclear Power Construction Piants Permits (CP) 78-09 Arcing of General 6/5/78 All Holders of Electric Company i<eactor Operating Size 2 Contactors Licenses (OL) or Construction Permits (CP) 78-10 Control of Sealed 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 Stop BWR Operating Licenses (OL) or Construction Permits (CP) 78-12 HPCI Turbine Control 6/30/78 All Holders of Valve Lif t Rod BWR Operating Bending Licenses (0L) or Construction Permits (CP) with Similar HPCI Design 78-13 Inoperability of 7/10/78 All Holders of Service Water Pumps Reactor Operating Licenses (0L) or Construction Permits (CP) except for plants located in: AL, AK, CA, FL, GA,
LA, MS, SC Enclosure Page 2 of 3
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f IE Circular No. 79-02 January 16, 1979 78-14 HPCI Turbine Reversing 7/12/78 All Holders of Chamber Hold Down BWR Operating Bolting Licenses (0L) or Construction Permits (CP) for plants with a HPCI Terry Turbine excepting Duane Arnold and Monticello 78-15 Tilting Disc Check 7/20/73 All Holders of Valves Fail to Close Reactor Operating With Gravity ir Licenses (OL) or Vertical Position Cons +.ruction Permits (CP) 78-16 Limitorque Valve 7/26/78 All Holders of Actuators Reactor Operating Licenses (0L) or Construction Permits (CP) 78-17 Inadequate Guard 10/13/78 All Holders of Training /Qualifica-and applicants tion and Falsified for Reactor Training Records Operating Licenses (OL) 78-18 Underwriters 11/6/78 All Holders of Laboratory Fire Reactor Operating Test Licenses (0L) or Construction Permits (CP) 78-19 Manual Override 12/29/78 All Holders of (Bypass) of Safety Reactor Construction Actuation Signals Permits (CP) 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