ML17206A628
| ML17206A628 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 01/16/1979 |
| From: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | Robert E. Uhrig FLORIDA POWER & LIGHT CO. |
| References | |
| NUDOCS 7901220193 | |
| Download: ML17206A628 (11) | |
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UNITED STATES JAN 16 579 NUCLEAR REGULATORY COMMISSION REGION II
'I01 MARIETTASTREET, N.W.
ATLANTA,GEORGIA 30303 In Reply Refer To:
RII:JPO 50-335$
50-389 50-250$
50-251 Florida Power and Light Company Advanced Systems and Technology Attn:
Dr. R. E. Uhrig, Vice President P. 0. Box 529100 Miami, Florida 33152 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, 9~83 mes P. O'Reilly D rector
Enclosures:
l.
List of IE Curculars Issued in the last 12 months
JAM 16 1979 Florida Power and Light Company cc w/encl:
N. Weems, Assistant QA Manager P. 0.
Box 128 Ft. Pierce, Florida 33450 C. M. Wethy, Plant Manager St. Lucie Plant P. 0. Box 128 Ft. Pierce, Florida 33450 H. E. Yaeger, Plant Manager Turkey Point Plant P. 0. Box 013100 9250 West Flagler Street Miami, Florida 33101
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCKKNT 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) 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 ad5ustable 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.
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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 loads, the instantaneous inductive load caused these trip set points to be exceeded.
The licensee has subsequently ad)usted 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.
8 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 sub)ected 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.
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IE Circular No. 79-02 January 16, 1979 No written response to this Circular is required.
Xf 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 January 16, 1979 LISTING OF IE CIRCULARS ISSUED IN LAST IWELVE MONTHS Circular Subject No.
Date of Issue Issued To 78-01 Loss of Well Logging Source 4/5/78 All Holders of Well Logging Source Licenses 78-02 Proper Lubricating Oil for Terry Turbines 4/20/78 All Holders of Reactor OLs or CPs 78-03 78-04 Packaging Greater Than Type A Quantities of Low Specific Activity Radioactive Material for Transport Installation Error That Could Prevent Closing of Fire Doors 5/12/78 5/15/78 All Holders of Reactor
- OLs, CPs, Fuel Cycle, Priority I Material and Waste Disposal Licenses All Holders of Reactor OLs or CPs 78-05 Inadvertent Safety Injection 5/23/78 During Cooldown All Holders of Reactor OLs or CPs 78-06 Potential Common Mode Flooding of ECCS Equipment Rooms at BWR Facilities 5/23/78 All Holders of Reactor OLs or CPs 78-07 Damaged Components of a Bergen-Paterson Series 25000 Hydraulic Test Stand 5/31/78 All Holders of Reactor OLs or CPs 78-08 Environmental Qualification of Safety Related Equipment at Nuclear Power Plants 5/31/78 All, Holders of Reactor OLs or CPs 78-09 Arcing of General Electric Company Size 2 Contactors 6/5/78 All Holders of 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 No.
Date of Issue Issued to 78-10 Control of Sealed Sources Used in Radiation Therapy 6/14/78 All Medical Licensees in Categories G
and Gl 78-11 78-12 78>>13 Recirculation M-G Set Overspeed Stops HPCI Turbine Control Valve Lift Rod Bending Inoperability of Multiple Service Water Pumps 6/15/78 6/30/78 7/10/78 All Holders of BWR OLs or CPs All Holders of BWR 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, MS, SC 78-14 78-15 HPCI Turbine Reversing Chamber Hold Down Bolting Checkvalves Fail to Close In Vertical Position 7/12/78 7/20/78 All Holders of BWR OLs or CPs for plants with a HPCI Terry Turbine excepting Duane Arnold and Monticello All Holders of Reactor OLs or CPs 7-16 7-17 Limitorque Valve Actuators Inadequate Guard Training/
gualification and Falsified Training Records 7/26/78 10/13/78 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 TWELVE MONTHS Circular Subject No.
Date of Issue Issued To 78-18 78-19 79-01 UL Fire Test Manual Override (Bypass) of Safety Actuation Signals Administration of Unauthorized Byproduct Material to Humans 11/6/78 12/28/78 1/12/79 All Holders of Reactor OLs or CPs All Holders of CPs All Medical Licensees except Teletherapy Medical Licensees and each Radiopharmaceutical Suppliers Enclosure Page 3 of 3
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