05000255/LER-1992-038, :on 920825,reactor Tripped,Resulting from Loss of Preferred Ac Bus Y-20,coincident W/Blown Fuse in Second Channel of Rps.Caused by Failure of Inverter ED-07.All Fuses Checked & Plant Drawings/Vendor Manuals Updated
| ML18058B265 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 12/07/1992 |
| From: | Hillman C CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | |
| Shared Package | |
| ML18058B264 | List:
|
| References | |
| LER-92-038, LER-92-38, NUDOCS 9212140171 | |
| Download: ML18058B265 (9) | |
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I NRC Foim 366 19-831 1*
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U.S. NUCLEAR REGULATORY COMMISSION APPROVED OMB NO. 3160-0104 EXPIRES: 8131 /86 LICENSEE EVENT REPORT (LERI FACILITY NAME 111 I
DOCKET NUMBER 121 PAGE 131 Palisades Plant I
I 0 1. 5 I 0 I 0 I 0 I 2 I 5., 5 1 I OF 0 I 8 TITLE 141 REACTORTRIP CAUSED BY A LOSS OF THE PREFERRED AC BUS Y-20 COINCIDENT WITH A Bl.OWN FUSE IN A SECOND CHA.NNEI 111<' THI<
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] LER NUMBER 161 REPORT DATE 181 OTHER FACILITIES INVOLVED 181 YEAR FACILITY NAMES YEAR I
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COMPLETE ONE LINE FOR EACH COMP~NENT FAILURE DESCRIBED IN THIS REPORT 1131 I
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I On August 25, 1992 at 0129 hours0.00149 days <br />0.0358 hours <br />2.132936e-4 weeks <br />4.90845e-5 months <br />, with the plant operating at 100% power, and all systems in a normal full'
. power al i grment, the reattor tripped:
The reactor trip resulted from a loss of the preferre;d ac bus Y-20, coincident with. a* blown \\fuse in another portion ot the reactor protective system CRPS).
The automatic reactor trip was successfully c~leted with no major plant equipment problems identified.
The plant was maintained in hot shutdown for evaluation of the trip.
I The. cause of this event ;was the loss of preferred ac bus Y-20 that resulted
- in the loss. of one. channel of the reactor protective systetji CRPS),
coincident with a blown fuse in a second channel of the RPS, which resulted in the initiation of an RPS trip signal.
Preferred ac bus Y-20 was. lost due to the failure of inverter ED-07.
It was later determined \\that i!ll>roper internal wiring connecting the transformers within ED-07 caused accelerated aging of the, transformer coils and resulted in the failure of two transformers.
I Corrective action for th:is event included checking all the. fuses in the RPS system for proper sizing, c0111>leting a Procurement I Engineering Checklist for the SOLA transformers to identify critical characteristics to be used during the pq>curement
- process, updating plant* drawings and vendor manuals of the inverters. to properly show the use ofi functionally equivalent SOLA transformers,*
and reviewing this.event with electrical maintenance department
~rsonnel -to reinforce the illl>Ortance of requiring attention to the proper connection of components that have 11llJltiple windings.
Additional corrective action regarding the pressurizer level control circuitry is being* developed and will be reported in a supplemental licensee event report.
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921214017c~
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921207 05000255 pDR I
NRC Form 38SA 11-831 F.ACIUTY NAME 111 r
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.1. I LICENSEE EVENT REPORT (LERI TEXT CONTINUATION DOCKET NUMBER 121 YEAR LER NUMBER 131 SEQUENTIAL NUMBER U.S. Nl,ICLEAR REGULATORY COMMISSION APPROVED OMS NO. 3160~104 EXPIRES: 8/31186 REVISION i_._
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EVENT DESCRIPTION
On August 25, 1992 kt 0129 hours0.00149 days <br />0.0358 hours <br />2.132936e-4 weeks <br />4.90845e-5 months <br />, with th~*plant operating at 100% po~er and all systems in a normal full po:wer alignment, the reactor tripped.
The reactor trip resulted from a lo~s of the prefer~ed ac bus Y-20 [ED;PL]; coincident with a blown fuse in a second chann.el o.f the reac;tor protective system (RPS).
Preferred ac bus Y-20 provides ac power to the Engineered S'afeguards System electrical loads including the reactor protective system (RPS) [JC]. I The automatic reactor trip was successfully completed with no major plant equipment prolblems identified.. The control room immediately initiated emergency operating procedur~s (EOP~) EOP-1, "Standard Post Trip Actions," and EOP-2, "Reactor Trip Recovery."
Th~e required actions for the EOPs were successfully completed and the I
procedures were exi~ed.
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During the actions ~aken for the reactor trip, it was noted that the "B" channel of the.
RPS was de-energize;d indicating a loss of Y-20.
Pressurizer level control was operating in the "B" channel ~hich is powered from Y-20; therefore, the control room operators
- immediately swapped pressurizer level control tu the redundant "A" channel, ih accordance with th~ Off-Normal Procedure (ONP) 24.2, "Loss of Preferred AC Bus Y-20,"
and expected additi~nal automatic charging p~mp starts of the standby charging pumps to be initiated based ~n p~essuriz~r level.. After a short period of time with no additional charging pump starts~ the control room operators manually started an additional chargin~ pump in accordance with the EOPs to regain ptessurizer level.
At the time the contro~ room operators manually started a charging pump, pressurizer level
. was approximately 312% with the pressurizer level control setpoint at 42%.
I The plant ~as mai~~ained in hot shutdown for evaluation of the trip.
Preferred ac bus Y-20 was re-energi~ed through the bypass regulator at approximately 0330 hours0.00382 days <br />0.0917 hours <br />5.456349e-4 weeks <br />1.25565e-4 months <br /> on August 25, 1992.
On August 26, 1992, at 0925 hours0.0107 days <br />0.257 hours <br />0.00153 weeks <br />3.519625e-4 months <br /> preferred ac bus Y-20 was returned to its normal powe~ supply and the limiting condition of operation (LCO) action statement was exit~d.
This event is repor!tabl e fo the NRC in accordance with 10CFRSO. 73 ( ~)(2)( iv.) as an event that resulted in t~e automatic actuation of the reactor protective system (RPS).
I CAUSE OF THE EVENT i I
. The cause of this ~vent was the loss of preferred ac bus.Y-20 that resulted in the loss of one channel of ~he reactor protective system (RPS), coincident with a bltiwn fµse in a second channel of the RPS, which resulted in the initiation of an RPS trip signal.
- Preferred ac bus Y-!20 was lost due to the failure of inverter ED-07.
It was later determined th~t improper internal wiring connecting the transformers within ED-07 caused accelerated aging df the transformer coils an~ re~ulted in the failure of two transformers.
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This event involve~ the failure of equipment important to safety.
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ANALYSIS OF THE EVENT
- ~ailed Preferred aJ Bus Y-20 I.
Preferred ac bus yj20 is a 120V ~c electrical distr{butio~ panel that pro~ides ac power
- to the Engineered S~afeguards electrica'l loads.
Y-20 is normally powered from the
, station batteries ~hrough an inverter.. lhe inverters in use at Palisades employ output*
transformers to fil:ter and regulate the output of the inverter.
The inverter uses
- three, one-third c*pacity, constant voltage transformers made by SOLA Electric Co. to perform this task. I These SOLA transformers are a static magnetic voltage regulator that
- includ~ capacitors !as part of a ferro-~esoriant circuit.
SOLA supplies their units as a*
complete package; ~ransformer, terminal block, and several capacitors.
I Equipment History df SOLA. Transfrirmer~
The orig~nal SOLA ~rahsformers were supplied with a single primary winding for input connect ions.
Curr.~nt pl ant drawings and controlled vendor manuals. reflect this wiring configuration.
j In 1980, SOLA infonmed the inverter manufacturer that the original SOLA transformers with a single prim~ry winding were no longer available. *SOLA recommended a substitute with two primary wi~ndi ngs.
For the substitute to be used at Pali saed jumpers would be used to properly cdnnect the transf6rmers.
Th~ plant drawihgs or vendor manuals were not ~hanged to ref~ect the installation of jumpers.
In 1981 another suqstitution was made by SOLA.
The 1981 substitute included multiple primary windings and capacitors..Again, the use of jumpers to properly connect the transformers was r~quired; however, the plant drawings and vendor manuals were not changed.
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In 1984 transformeri T-21 was replaced in ED-07.
The replacement SOLA transformer that was removed from stock was equipped with multiple input connections.
Jumpers were pr~perly attached; ihowever,* the source of the information to install the jumpers was not documented in the ~aintenance order package, and was.als~ not reflected in pl~nt drawings or the ve~dor manual.
In 1985, SOLA suggJsted that all three transformer/c:apacitor pairs be replaced as a group.
This wouldl~nsure that each of the three paralleled SOLA~ ~qually share load.
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!&-8.31 FACILITY NAME.111 Palisades Plant I I I I I I I
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LICENSEE EVENT REPORT (LERI TEXT CONTINUATION DOCKET NUMBER 121 LER NUMBER 131.
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In July 1986, contrary to the information provided by SOLA, only two transformers {T-20 and T~22), but all1 three sets of capacitors were replaced in ED-07~ The work order summary for the re'placement did not indicate that transformers T-20 and T-22 had the required jump~rs ir~talled.
Current Status I
i Following the reac:tor trip on.August 25, 1992, troubleshooting revealed that the output volta~e ffom.pref~rred ac bus v~20 had dropped t~ 24 volts.
Further troubleshooting indicated that in~erter ED-07 had failed and that tfansformers T-20 and T-22 within inverter ED-07.ha~ shorted windings and required replacement.
Based on equipment*
history informatio:n obta.ined in 1985 concerning replacement of SOLA transformers, all three SOLA transf~rmer~ (T-20, T-21 and T~22) and their "matching" capacitors w6uld need to be replaced. lhree SOLA transformers were in stock and were used as replacements for the fail~d transf~rmer components:
Post maintenance testing of th~ replacement transformers found the output voltage of inverter ED-07 to jbe unsatisfactorily low at ~100 vo~ts:
Tro~bles~ooting identifi~d tha~ the replacem1nt tra~sformers had four primary wrndrngs with different connection options. The:plant drawings and the controlled vendor manual.had not been updated for correct placement jof jumpers to provide the required output voltage, therefore, no jumpers were inst~lled during the replacement of the damaged transformers. Jumpers were subsequently inst~lled following engineering direction and review of the vendor manual
- that was shipped with the replacement SOLA transformers;
- The output voltage was fully acceptable after ~he installation of the necessary jumpers. *.
Si.nee the SOLA trJnsforme~s that failed {i-20 and T-22) on August 25, 1992 had been in service since 198~, a ~uestion was raised as to whether or not inverter ED-07 was capable of providing power output to meet both normal and emergency loads.
An analysis was performed to ~etermine_both normal operating and e~ergency power demands on ED-07.
The analysis concluded that the normal continuous load on ED-07 is 4,390 volt-amps while the emergency load on ED-07 adds an additional 1,082 volt-amps for a total of 5,472 volt-amps.
Durin~ the 19~2 refueling outage, technical specifications surveillance procedtire {TSSP)
~T-8D, "Engineered Safeguards System - Right Channel" was performed.
This TSSP tested inverter ED-07 with both normal loads.and emergency loads.
The results of TSSP RT-SD dem0nstrated that the inverter.ED-07 was fully capable of serving both normal and emerge~cy loads.
Furthermore, prev~ntive maintenance is performed on the inverters using t~e periodic and predetermined activity control system {PPACS).
PPAC SPS019, which measures the output voltage of the transformers in inverter ED-07 and was last performed on March 17, 1992, was reviewed.
This review det'ermined that the
. measured output v~ltage of the transfor~ers in inverter ED-07 were acceptabl~.
I.
In addition, all three transformers were removed from inverter ED-07 and were sent to CPCo's Equipment ~nd Services laboratory for testing.
- Of the three transformers, T-21 had been properly!connected since 1984 therefore, it was available for testing and evaluation.
Transformers T-20 and T-22 were examined to determine the cause of their I
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NRC Form JeeA il-831 FACILITY NAME.111 Palisades Plant LICENSEE EVENT R.EPORT (LERI TEXT CONTINUATION OOCKE'T NUMBER 121 lER NUMBER 131 U.S. NUCLEAR REGULATORY.COMMISSION APPROVED OMB NO. 3160~10*
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,8 failures. Test results indicated that the *transformers operate at a higher temperature with only one primary winding connected which could cause accelerated aging.
'Furthermore, the test results indi_cated that even with only one primary winding.
. connected, the transformers would be able to provide output power of the proper voltage, frequency and wave form; Incorre~tly Sized Fuse in the "C".Channel RPS Trip Lotjic Troubleshooting performed on the RPS system following the Aug~st 25, 1992 reveal~d a blown fuse in the "C" channel of.the logic circuits for the RPS.
The RPS contains.six logic l~dders representing the 2 out of 4 logic combinations; AB, AC, AD, BC, BO, & CD.
Each log i.c ladder is powered by two auctioneered 28 volt power supplies.
The power supply and ac feed to the power supply correspond to the.particular matrix ladder.
For example, the B-C. matrix is powered on one side by a "B" channel 28 vblt ~upply which is fed fro~ preferred ac bus Y-20.
The other side is powered by a "C" channel 28 volt power supply fed from preferred*ac bus Y-30.
When the Y-20 bus was lost (due to the failure.of ED-07), three of the si~ logic ladders that involve the "B" channel (AB, BC, & BD) lost one (the B supply) of their auctioneered 28 volt power supplie~. For ~atrix logic ladders AB and BD, the remaining redundant 28 volt power supplies picked.up the load and kept the matrix trip relays energized.
For the BC logic ladder, the remaining redundant 28 volt po~er supply suffered a blown fuse.
Although the power supply was capable of carrying the load, the blown fuse prevented the "C" channel power supply from picking up the ~atrix trip relays for the BC logic ladder, therefore~ the BC matrix trip relays de-energized and~ full RPS trip was generated.
A review of the vendor supplied wiring diagrams indicated that the required fuse size was 1,0 amp; however, the blow~ fuse removed from th~ circuit was a 0.5 a~p fuse.
It could n6t be determined whether the fuse had blown prior to the
- August 25, 1992 event or blew as a result of the failure of preferred ac bus Y-20.
A majority of the RPS system was replaced during the 1992 reftielin~ outage.
The existence of the 0.5 amp fuse was not determined duri~g post-modification testing.
The instrument and control (l&C) technicians assigned to the RPS upgrade project* ~ere interviewed and responded that they had not replaced ~ny of the 28 volt de power supply fuses.
The RPS hardware vendor performed an internal investigation regarding their QA practices employed during the assembly, inspection and testing of-the RPS hardware.
From this investi~ation the vendrir could not c~nclude whether the incorrett sfze fuse was or was not installed pricir to shipment to CPCo.
Failure of Charging Pump Auto;start Pressurizer level control was operating in the "B" channel which is powered from Y-20, therefore, the control room operators immediately swapped pressurizer level control to the red~ndant "A". channel, in accordance with the Off-Normal Procedure (ONP) ahd expected additional automatic charging pump starts initiated by the pressurizer level controller. After a short period of time with no additional charging pump starts, the
NRC Form.388A 111*831 FACILITY NAME 111 Palisad~s Plant LICENSEE EVENT REPORT (LERI TEXT CONTINUATION OOCKET*NUMBER 121.
LER NUMBER 13)..
U.S. NUCLEAR REGUV.TORY COMMISSION APPROVED OMS NO, 3160.()104 EXPIRES: 8/31/86 PAGE 141 SEOUE)\\ITlAL REVISION YEAR NUMBER NUMBER Q
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- 1 Q. 6 OF. Q control room operators m~nually started an add1tional charging pump to regain press~rizer level in accordarice with tha EOPs.
At the time the control room operat6rs initiated a manual charging p~mp start pressurizer level was approximately 32% with the pressµrizer level tontrol setpoint at 42%.
System Engineering, Operations and I&C reviewed the electrical prints depicting the pressurizer level control system design. This review conclud~d that the charging pumps would not start for the plant conditions which existed following the _reactor trip on
.August 25, 1992.
Th~ normal level control signal was configured such that no additional charging pumps would start while the back~up level control signal was configured to start additional charging pumps~ Testing was performed tq verify that the pressurizer level controllers were operating.as designed.
. During the event pressurizer level control was swap~ed to the "A" channel following the loss of Y~20 in accordance with the ONPs.
The redundant c6ntroller (in this case the "A" channel) is normally in the manual mode with a 50% normal level control signal that calls for the additional charging pumps to be tripped.
As a result of the trip and the loss of Y-20, with the pressurizer level decreased to-the point where the back-~p level control sigrial would have initiated additional charging pump starts. Since the normal pressurizer level control signal was still not requiring additional charging pump starts, a standing trip signal was present while the back-up pressurizer level control signal was configu~ed for additional charging pump starts; however, the breakers for the charging pump~ are equipped with an anti-pump relay.
With both a start signal and.a trip signal being fed to the charging pump breaker, the anti-pump relay activated and would nbt allow the additional charging pumps to start. The control room operators correctly identified the failure tif the ~harging pumps to start and placed the charging pumps in manual control, thereby allowing a charging pump to start. It is important to note that both the man~al charging pump start signal and the safety injection sjstem (SIS) charging pump start signal will defeat the. anti-pump relay allowing the charging pumps to be starte~.
Further investigation revealed.that the design f~ature regarding the inability to start a charging pump with a standing trip signal energized had been previously identified in D-PAL-90-053 and has not been modified.
Prop9sed corrective action for D-PAL~90-053 included modifying the* charging pump circuitry so that the back-up level controls could start the charging pumps without relying on the normal level controls to clear the standing trip signal.. The modification to the control circuitry has been rescheduled to*
the 1994 refueling outage.
NRC Form 399A 111-&31 FACILITY NAME 111 LICENSEE EVENT REPORT (LERI TEXT CONTINUATION DOCKET NUMBER 121 LER NUMBER 131 U.S.. NUCLEAR REGULATORY C_OMMISSION APPROVED OMB NO. 3160.,010*
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CORRECTIVE ACTION
Prior to plant start-up the.fuses in the rema1ntng eleven 28V de power s~pplies located in RPS Channels A, B, C, & 0 were checked and found satisfactory.
In addition, fuses are in other locations in the RPS circuitry were checked and found satisfactory.
Inverter E0-07 Further investigation into the reasons why the plant wiring diagrams did not adequately reflect the correct jumper installation for the transformers within inverter E0-07 and why vendor supplied information-was not pre~iously incorporated.into plant design
_documents was deemed necessary.
This information is documented in corrective action document O-PAL-92-227.
- The incorrect connecti.on of the two SOLA transformers was caused by:
- 1.
Failure to identify during the procurement process that substitute SOLA transformers, Jlthough thought to be functional ~quivalents, had physical size anq electrical connection differences.
- 2.
Failure to perform detailed design engineering during the justification of functionally equivalerit replacement parts.
- 3.
- Failure to identify on pl ant drawings and vendor manuals that replacement transformers in stock would require* both physical and el~ctrical modifications before their use.
- 4.
Inattention to detail during the installation process.
Cor~ective action for the events pertaining to the failure of inverter ED-07 are
- documented in O-PAL-92-227 and include the following actions.
. 1.
Complete a Procurement Engineering Checklist for the SOLA transformers to identify critical characteristics to be used during the procurement process.
This will help justify any changes in model and part numbers.
- 2.
Update plant drawing~ of the inverters to properly show the use of
- functionally equivalent SOLA transformers.
- 3.
Update plant vendor manuals for the invert~rs to properly show the use of functionally equivalent SOLA transformers.
4.- Review this event with electrical maintenance department personnel to reinforce the importance of requiring attention to the proper connection of components that have multiple windings.
" NRC For;,, 388A 11-831 FACILITY NAME 111 Palisade.s Plant LICENSEE EVENT REPORT !LERI TEXT CONTINUATION..
DOCKET NUMBER 121 YEAR LER NUMBER 131 SEQUENTIAL NUMBER U.S. NUCLEAR REGULATORY COMMISSION APl'ROVED OMB NO. 3160-010*.
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Incorrectly Siz~d Fuse in the "C" Channel *RPS Trip Logic The results of investigation as to the existence of the-0.5 amp fuse in the RPS circuit as opposed to the required 1.0 amp fuse are documented in corrective action document D-PAL~92-230 and include the following actions.
- 1.
Check the fuses in th~ ~emaining el~ven 28V de power supplies located in RPS channels A, B, C, & D.
Also, other fuses in the logic.circuits were verified to be properly.sized. This action was completed prior* to plant re-start and all fuse~ were found to be correctly sized. -
- 2.
Revie~ response from the vendor of the RPS hardware concerning this event and determine if additional corrective action is warranted.
The vendor investigation could not confirm that the incorrectly sized fuse was installed by the -vendor..
.Failure of Charging Pump Auto-start The failure of.the charging pump auto-start circuit was evaluated.
The corrective action identified in the previous corrective action document {D~PAL-90-053) was determined to be adequate.
The modification to the charging pump-circuitrj to allow the
. back-up level controls to start the charging pumps without relying on the normal level controls to clear the ~tanding trip si~nal is scheduled for completion in the 1994 refueling outage.
.ADDITIONAL INFORMATION None
- - e LICENSING CORRESPONDENCE\\COMMITMENT TRACKING RECORD SUMMARY
.DATE:
December 7., 1992 DOCKET S0-255 LICENSE DPR~20 - PALISADES PLANT SUPPLEMENTAL LICENSEE EVENT REPORT 92-038~01 - REACTOR TRIP CAUSED BY A LOSS OF THE PREFERRED AC BUS Y-20 COINCIDENT WITH A BLOWN FUSE IN A SECOND CHANNEL OF THE REACTOR
..
- PROTECTIVE* SYSTEM SUMMARY:.
Transmits supplemental LER 92-038~01 which describes the August 25, 1992 reactor trip.
The trip was coincident.with a loss of the preferred AC bus Y-20.
The supplemental report provides the fin*a1 results of testi~g perfor_med ~n the SOLA constant voltage transformers and the results of an evaluat1on of the fa1lure of the charging pump auto-start circuit.
Previous NRC Letters Dated:
- LC----
LC LC __ _
VFI NO:
950-73*20*01*01
.Ori9inator:
CTH1 l l man Special Distribution:
Concurrences:
TJPalmisano PMDonnelly KEOsborne Previous CPCo Letters Dated:
09/24/92 LC Lt--
Concurrences:
JLKuemin MTNordin RSWesterhof PSE' LOG NA PRC MTG NA NPAO LOG NA LC LC--
. Individuals Providing Info:*
HMEsch TJSwieciki COMMITMENT TRACKING COMMITMENTS MAOE:
- 1.
Modify the charging pump auto-start circuit.
Assigned Individual: TJSwieciki
- Related CA Document No:
D-PAL-90~053 Commitment To Be Made Resident?
COMMITMENTS CLOSED:
1994 REFOUT CTS Commitment No:
Resident Document:
Provide suplemental report to NRC by November 30, 1992.
Related CA Document No:
E-PAL-92-065
. CTS Cammi tment No:
.Additional Information Needed for CTS Entry:
System Code:
Suggested Keywords: