ML20133C469
| ML20133C469 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 09/16/1985 |
| From: | Hukill H GENERAL PUBLIC UTILITIES CORP. |
| To: | Murley T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| 5211-85-2146, NUDOCS 8510070371 | |
| Download: ML20133C469 (4) | |
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GPU Nuclear Corporation 68 Post Office Box 480 i
Route 441 South Middletown, Pennsylvania 17057 0191 717 944 7621 TELEX 84 2386 Writer's Direct Dial Number September 16, 1985 5211-85-2146 Dr. Thomas E. Murley Region I, Regional Administrator U.S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, Pa.
19406
Dear Dr. Murley:
Three Mile Island Nuclear Station Unit 1 (TMI-1)
Operating License No. DPR-50 Docket No. 50-289 ICS/NNI Subfeed Power Failure This is to inform you of an event that occurred on August 21, 1985 at TMI-1 involving a partial loss of ICS/NNI power.
Because this type of an event has been of interest to the NRC since the major loss of ICS/NNI power at Crystal River 3 on February 26, 1980, this information is being provided to update you on the details of this minor event at THI-1 and how the improvements made since the Crystal River 3 event helped operators to diagnose and respond quickly. The August 21, 1985 event at TMI-1 is not considered reportable under 10CFR50.72 or 10CFR50.73.
On August 21, 1985, TMI-1 was at stable hot shutdown conditions with the reactor coolant system at 532*F and 2165 psig.
THI-1 was maintaining this condition in anticipation of a favorable court decision on restart. At approximately 1330 hours0.0154 days <br />0.369 hours <br />0.0022 weeks <br />5.06065e-4 months <br />, a control room operator was withdrawing the Make-Up Tank level recorder on the main console to the park position. This recorder is designed with a coiled power cable connecting the recorder frame to the recorder in order to permit this repositioning. As a result of worn insulation on this coiled connector cable, a short to ground occurred at this o.
time which caused the Make-Up Auto Power breaker to open in the NNI cabinet.
Jg This Auto subfeed is one of eight in the ICS/NNI Auto power system. The gga.
failure of the Make-Up Auto power was not immediately recognized as being a og result of taking the Make-Up Tank Level recorder to the park position. As a 0o result, the operators in the control room were responding to a partial loss of power from an unknown cause.
by 28 provides the listing of alarms received and actions observed. Of g<
significant importance relative to diagnosing the problem were the indicators o
installed as part of LM-43A modification "ICS/NNI Loss of Power Indication".
Gig This modification provided an indicating light status panel in the relay room aan.u) and an alarm in the control room for loss of the various feeder circuits. The Main Annunciator window (H-1-5) "ICS/NNI power lost" was immediately received c/
which directed the operators to the ICS/NNI subfeed power indicators on Panel GPU Nuclear Corporation is a subsidiary of the General Public Utilities Corporation 9~
g
f 5211-85-2146 September 16, 1985 Center Lef t (PCL). With the white indicating light for "Subfeeds-Auto / Hand" extinguished, the operators were directed to the ICS/NNI Power Monitoring Cabinet located in the Relay Room (one floor below the Control Room where the ICS/NNI power cabinets are also located). With only the "Make-Up Auto" light extinguished on the monitoring cabinet, the operators in the control room quickly confirmed that the failure was affecting only portions of the Make-Up and Purification system.
The Operators in the Relay Room, based upon the indications on the Power Monitoring Cabinet went to the NNI cabinet for the Make-Up system and discovered the breaker for Make-Up Auto power in the
" trip-free" position. Without the provisions installed by LM-43A, the boundary of the affected systems could not have been recognized in such a rapid manner (estimated at less than 2 minutes),
Plant conditions were evaluated as normal using computer indications for RCP i
Temps, MU Tank Level using LI778A (installed to be independent of ICS/NNI power by LM-43C), and secondary plant status by normal indications. Due to loss of seal injection indication, two operations personnel were immediately dispatched to the Reactor Bldg. to monitor seal injection and seal leakoff flows at the RCP stations.
Since letdown was secured when MU-V3 closed, an operator was dispatched to MU-V70A to bypass the Make-Up demi.1eralizers. MU-V6A was closed in preparation for reinitiating letdown to reduce pressurizer level (the maximum level increase was approximately 50").
Within 30 minutes, letdown was i
initiated by manually holding MU-V3 open using the valve control switch on control room console center which overrides the false closing signal. As provided in the existing Emergency Procedure (EP 1202-42) however, the high temp interlock for MU-V3 was removed and the valve was cycled to verify control capability.
To ensure minimum Make-Up Tank pressure, an operator was sent to the fiake-Up Valve Alley to monitor Make-Up Pump 1B (MU-PIB) suction pressure at the local j
pressure gauge (MU-PI-413).
1 i
Deliberate and timely trouble-shooting and circuit ground checks in the relay room NNI cabinet by the maintenance personnel isolated the fault to the Make-Up Tank level recorder connector cable. The connector cable was removed and power restored to all affected equipment except the Make-Up tank recorder i
in approximately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. The Make-Up Tank recorder connecting cable was then replaced and the recorder was restored to service within an additional I hour.
As a result of this experience the following changes have been or are being l
implemented:
j 1.
A Preventive Maintenance procedure and schedule has been implemented to periodically inspect and replace console recorder connector cables as necessary.
O f
5211-85-2146 September 16, 1985 1
2.
Emergency response procedures have been changed to more clearly designate which components are affected by failures in specific j,
ICS/NNI Auto-Hand Subfeeds.
3.
An indepth review and procedure development is in progress to add <.ess power failures in the remaining ICS/NNI subfeed supplies (Hex, Hey, Auto). This procedure will be available by October,1985.
4.
An operator aid is being developed to more easily read the ICS/NNI power system schematic. This simplified "one-line" schematic showing source, interruption devices, and loads should be available by the end of this year.
5.
Console ICS/NNI subfeed power labeling is under review to determine if additional changes are desirable.
A(. no time during this event was plant control in any significant jeopardy.
The Make-Up tank decrease and pressurizer level increase was a slow controllable transient. Even if the plant had experienced this same failure at 100% power, plant control and response would have been essentially the same.
Sincerely, f
j N. D. Hu 11 Director, TMI-1 HDH/MRK/spb:0350A cc:
J. Thoma R. Conte f
1 l
ATTACHMENT 1 Alarms Received:
"B" HPI Flow Hi/ Low (H-2-3); ICS/NNI Power Lost (H-1-5); MU Flow Hi (G-1-8);
RC Pump Seal Supply / Return Filter d/p Hi (G-3-7); MU Letdown Storage Tank Press Hi/Lo (F-1-2); MU Letdown Cooler Outlet Temp Hi (F-1-3); RCP Seal Inj d/p to (F-1-4); RC Pump Seal Total Injection Flow Hi/Lo (F-1-5); MU letdown Storage Tank Level Hi/Lo (F-2-1); MU Letdown Demin/ Filter Diff Press Hi (F-2-2); RC Pump Labyrinth Seal d/p Lo (E-1-3); Inverters A/C/E Frequency High/ Low (PRF-3-2).
Actions Observed:
MU-V-3 closed; ICS/NNI power indicator for subfeeds - Auto / Hand was out; MU-V-32 auto light was out; MU-14-LR (Level Recorder) glitched up and then stopped (Recorder would not advance or indicate level. The MU Tank digital, LI-778A, still operated properly).
Instruments That Failed Mid Scale:
MU-42-FI (Total Seal Inj. Flow); MU-24-FI (Makeup Flow); MU-2-PI (Make-Up Pump Discharge Press); MU-17-FI (MU Tank Press); MU-18-DPI (MU & Purif Filter d/p);
MU-5-TI (letdown temp); MU-4-FI (letdown flow); MU-41-DPI (RCP Seal Inj Filter); MU-40-DPI (RCP Seal Return Filter); RC-18-DPI - 1/2/3/4 (RCP Labyrinth Seal d/p); MU-13-DPI - 1/2/3/4 (RCP #1 Seal d/p); RC3A-PT5 (Low Range RCP Press - Digital); MU-23-FI 3/4 (HPI Flow); MU-43-FR (RCP #1 Seal Leakoff Record - No power).
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