ML20091K389
| ML20091K389 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 01/14/1992 |
| From: | Joshua Wilson TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| TAC-M75844, NUDOCS 9201240165 | |
| Download: ML20091K389 (6) | |
Text
_ _ - _ - _ _ _ _ _ - _ _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - _ _ _ _ - _ _ - - _ - - _ _ _ _ _ _ _ _ _ _
nn w n,n ve us-w wu tu v
,,w~r Jack 1. YO!!.on vu %3a sn,,.w w w -
January 14, 1992 U.S.. Nuclear Regulate:y Commisalon ATTNt Document Control Desk Washington, D.C. 20555 centlement in the Matter of
)
Docket Nos. 50-327 Tennessee Valley Authority
)
50-328 SEQUOYAll NUCLEAR PLANT (SQN)
UNITS 1 AND 2 - EAGLE 21 SIX-MONTil REPORT
References:
1.
TVA letter to NRC dated January 18, 1991, "Sequoyah Nuclear Plant (SQN) - Unit 1 - Eagle 21 Six-Month-Report" 2..
NRC letter to TVA dated October 31, 1990, " Reactor Protection System Upgrades and Enhancements (TAC 75844)
-(TS 89-27) - Sequoyah Nuclear Plant, Unit 7" 3.
TVA letter to NRC dated May 10, 1990, "Sequoyah Nuclear Plant (SQN) - Eagle 21 Functional Upgrade Commitments" In Reference 3. TVA committed to submit periodic reports at approximate:ly six-month intervals describir.g design hardware, design software, and
. maintenance problems encountered with the Eagle 21 reactor protection system during Unit 1 Cycle 5 operat!<an, The information in Enclosure 1 provides the last of'three reports and completes the Unit 1 commitment.
This report covers the period f rom June 11 to December 12, 1991.
By Reference 2, TVA is committed to' provide the same information during Unit 2 Cycle 5 operation at approximately six-month intervals. The information in Enclosure 2 provides the second of three reports to meet this commitment. This report covers the period fram Jure 11 to December 12, 1991.
9201240165 92'0114
)
PDR: ADOCK-ODOOO327 R
PDit i
l U.S. Nuclear ReCulatory Connission i
Page 2 January 14, 1992 Please note that the sum: nary report discussed in Reference 1 in regard to
- r. review of changes to the original Eagle 21 technical specification changes will not be provided. As discussed with NRC staf f, this sunaary report is no longer needed since previous submittals have adequately covered this topic.
If you have any questions concerning the enclosed infornation, please contact Keith C. Weller at (615) 843-7527.
Sincerely, hY$Ar-T L. Wilson Enclosures cc (Enclosures):
Mr. D. E.. LaBarge, Project Manager U.S. Nuclear Regulatory Commission one White Flint, North 11555 dockville Pike Rockville, Maryland 20852 NRC Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy Daisy, Tennessee 37379 Mr. B. A. Wilson, Project Chief U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 W
F 9
et rAwe 3
y e -
'r-="r w
T
-*Pr+4=-
'T 1
=..
ENCLOSURE 1 SEQUOYAH. NUCLEAR PLANT (SQN)
EAGLE 21 UNIT 1 EQUIPMENT / SYSTEM FAILURES AND PROBLEMS
.FROM JUNE 11.TO DECEMBER 12, 1991 Item 1 On Juu '8,1991, the 15/MULT power supp1, 'n Pack 1-R-12 was identified with
- high alternating-current ripple and degraoed voltv.a.
A tion Takent The degraded conditior. was identified during the weekly performance of a preventive maintenance instruction that was written to provide early detection of failed input filtering capccitors. This power supply that supplied he teater subsystem of the MULTIBUS was replaced before the test sequence processor (TSP) went into an error handling state. The root cause of the failure was due to corroded leads on the. input filtering capacitora made by Mepco/Centralab. This root cat.se is the same as that identified in the July 10, 1991, six-month j
repart from TVA to NRC in that the capacitor lead opened due to internal chloride corrosion. Tnis was the last poser supply degradation and/or failure of this type on Unit 1 as the MULT/15 and 15/MULT powar supplies with Mepco/Cantralab input filtering capacitorri have had the capacitor replacements completed with those of an acceptable vendor.
_ Item 2
' During a routine channel calibcation on December 12. 1991, in Rack 1-R-8, it was discovered-that the ralibration input signal for a steam generator level channel did not roperly re.spond; therehre causing the automatic surveillance fos chat channel to fail.
Action Taken: The routina chant.el calibration was being performed during the Unit i r' is-refueling outage. Troubleshooting within the rack ia n d f'
. an intermittent failure (i.e., loose connectbr
- the lead signal injection response (SIR) bus from the front tester panel to the firnt input / output (I/0) circuit card in termination frame one. The lead SIR bus was subsequently replaced. The SIR bus is basically a ribbon cable th<t injects. surveillance inputs from the high precision l
digital to a.nalog converters to the input cJreuit boards and is only required for surveillance testing. No impact to Eagle 21 safety functions was or could be created by this failure.
Itym 3 The following Eagle 21-deacription of work was not a result of an Eagle 21 failure.
[
==
Description:==
As a :. ult of a 10 CFR Part 21 notification by the vendor (Westinghouse Electric Corporation), all the Unit 1 Eagle analog
.nput, Eagle resistance input, and Eagle partial trip circuit boards we: e removed f rom the racks and inspected to determine the date of production of the component in question.
The
w
- 10 CFR Part 21 notification involved a-Burr-Brown direct-current to direct-current (de/de) converter that was environmentally qualified by Westir.ghouse. Approximately 97 of the I/O circuit boards inspected had de/dc converters that required replacement because of the date of. production.
All the Unit 1 circuit boards heve had the potentially bad de/dc converters replaced during the Unit 1 Cycl., 5 outage.
This design concern was identified just af ter SQN Unit 1 start-up and the Eagle 21 installation. This concern was documented in the first Unit i Six-Month Report from TVA to NRC dated January 18, 1991, for the period of June 17 through December 16, 1990. The 10 CFR Part 21 notification was issued-just before SQN Unit 2 installation and was, cherefore, corrected by Westinghouse before Unit 2 start-up.
Update Eagle 2? problems with lockups o. ISP and loop calculation processors because of. timing deficiencies have become nonexistent following the replacement of the clock generators.
Eagle 21 problems with power supplies, software, and l-de/dc converters have also been corrected. -The remaining failures, which have be3n seen during the Unit 1 Cycle 5 operation, are considered random failures wi* no apparent generic implications.
f l
ENCLOSURE 2 SEQUOYAll NUCLEAR PLANT (SQN)
EAGLE 21 UNIT 2 EQUIPMENT / SYSTEM FAILURES AND PROBLEMS FROM JUNE 11 TO DECEMBER 12, 1991 Item 1, A_ test sequence processor (TSP) in Rack 2-R-3 experienced a luck-up on July 15, 1991.
Action Takent The TSP was reset and returned to service. This TSP had not
~
yet been upgraded to the new latel Corporation microprocessor.
As identified A the previous six-month report from TVA to NRC dated July 10, a991, Westinghouse Electric Corporation and Intel identified, with a high degree of confidence, that the cause of.the lock-ups was attributed to the Intel 82284 clock generator and that replacing the Intel clock generator with a Seimons model shculd eliminate the lock-ups. The Unit 2 loop calculation processors and TSPs were changed out as of
. July 21, 1991, and since that time there have been no lock-ups.
Item 2 During a channel functional test of a steam generator (0/G) level
- environmental allowance modifier and trip time delay channel in Rack 2-R-11 on August 14, 1991, all four S/G 1evel signals went offscale high.
Action Takent Before the surveillance testing and through the first automatic
-channel accuracy testing, all four channels were operating properly. A second automatic channel accuracy test was performed by instrument technicians to minimize analog to digital inaccuracies to near zero.
It was during this second automatic surveillance test that all four channels failed upscale high. As all four S/C level channels are processed through.an Eagle analog input (EAI) circuit board in termination f rame four, it'is suspected that a f ailure of this board was the cause. The EAI board was replaced and the channel 6 were returned to service.. The cause of the board failure is unknown, but a root-cause evaluation is in progress.. It does not appear that the EAI board failure was intermittent; therefore, it is unlike!y that it failed before the removal from service for the survelliance test. No further problems have been experienced.
Item 3
-During a channel functional test of a delta temperature and temperature average channel in Rack 2-R-6 on August 19, 1991, the TSP reported an error message, " Failure to Set Injection Relay NY-421Bl."
Action Takent The i_jection relays on the Eagle 21 input circuit boards are l
used to change the input f om the normal process signal to the surveillance signals. At the beginning of the functional test, L
the injection relay for a nuclear instrumentation system (NIS) input either failed to change state or the microcontroller
+
subsystem on the circuit board that processes the signal for the injection relay failed. The surveillance test was aborted, and NIS process inputs were verified to be operating normally through dynamic analog test points. The Eagle resistanc? input circuit board in termination frame four that contains the injection relay and microcontroller subsystem was replaced.
The channel functional test was reperformed and verified the channel to be operating properly. The cause of the board failure is presently unknown, but a failure analysis will be performed.
Item 4 During normal operation, several main control room annunciations were received, and indicators went downscale low on channels located in Rack 2-R-3 on October 9, 1991. The incident occurred for about ten m'outes and then all channels returned to normal.
Action Taken: A f ew minutes af ter the channels returned to normal, the rack was checked for obvious degradations including possible loose connections. The power supply was checked both for drif t and alternating-current ripple, but nothing was found. All indications and measurements, including the tester subsystem diagnostic routines, identified there were no problems. An action plan was developed to have a quick response of technicians on next occurrence, and planning was initiated to replace the Eagle 21 digital filter processor (DFP). The DFP is basically the analog to the dig; ital converter for the rack.
The next event took place early in the morning on October 22, 1991, at which time technicians were able to observe that the +12-volt, direct-current (VDC) light emitting diode (LLD) was not lit. The 12 VDC LED returned to normal when the technicians closed the rack door.
The MULT/15 power supply was replaced and seat to the vendor for a postmortem evaluation of the intermittent failure. To date, Weatinghouse has been unable to recreate failure of the +12-volt (V) power supply.
Item 5 During routine preventive maintenance monitoring of the Eagle 21 power supplies on November 21, 1991, the 15-VDC "B" nower supply in Rack 2-R-11 was found with a voltage ripple of approximately 46-milivolt alternating current (mVAC).
Action Taken: The acceptcnce criteria for the 15-V supplies are less than 35 mVAC. The 15-VDC "B" supply is located in the 15/MULT power supply drawer and is not normally used unless there is a failure in the primary 15-V
- pply. This high ripple does not appear to be indicative of an input filtering capacitor failure.
For an input filtering capacitor failure, the ripple typically would rise to at least 200 mVAC. Also, the input filtering capacitor failures, as seen in the past, occurred on only highly loaded supplies.
The power supply has been replaced and is being sent to Westinghouse for a failure analysis.
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - _ _ _ _ - _ _