05000296/LER-1996-008-03, :on 961217,loss of ECCS Division II Instrumentation Caused ECCS Equipment to Be Inoperable. Replaced Cleared Fuse & Shorted SCR
| ML18038B807 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 01/15/1997 |
| From: | Jay Wallace TENNESSEE VALLEY AUTHORITY |
| To: | |
| Shared Package | |
| ML18038B806 | List:
|
| References | |
| LER-96-008-03, LER-96-8-3, NUDOCS 9701210398 | |
| Download: ML18038B807 (12) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(viii) 10 CFR 50.73(a)(2)(ii) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(x) |
| 2961996008R03 - NRC Website | |
text
NRC'FORM 366 (4-95)
U.
UCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
(See reverse for required number of digits/characters for each block)
ROVED BY OMB NO. 3150<104 EXPIRES 04/30/98 ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS MANDATORYINFORMATIONCOLLECTION REQUEST:
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U.S.
NUCLEAR REGULATORYCOMMISSION. WASHINGTON,DC 20555.0001, FACILITYNAME IT)
Browns Ferry Nuclear Plant (BFN) Unit 3 DOCKET NUMBER (2) 05000296 PAGE (S) 1 OF 6 TITLE te)
Loss of the Emergency Core Cooling Systems (ECCS) Division il Instrumentation Renders ECCS Equipment Inoperable.
EVENT DATE (5)
LER NUMBER 6)
REPORT DATE (7)
OTHER FACILITIES INVOLVED(6)
MONTH 12 DAY YEAR 17 96 SEQUENTIAL REVISION NUMBER NUMBER 96
008
00 MONTH 01 DAY YEAR 15 97 FACILITYNAME N/A FACILITYNAME N/A DOCKET NUMBER OPERATING MODE (9)
N UANT TO THE REQUIREMENTS OF 10 CFR I): (Check one THIS REPORT IS SUBMITTED PURS 50.73(a)(2)(i)(B) 20.2203(a)(2)(v) 20.2201(b) or more) (11) 50.73(a)(2)(viii)
POWER LEVEL (10) 99 20.2203(a)(1) 20.2203(a)(2)(l) 20.2203(a)(2)(ii) 20.2203(a)(2)(iii) 20.2203(a)(2)(iv) 20.2203(a)(3)(l) 20.2203(a)(3)(ii) 20.2203(a)(4) 50.36(c) (1) 50.36(c) (2)
LICENSEE CONTACT FOR THIS LER (12) 50.73(a)(2)(ii) 50.73(a)(2)(iii) 50.73(a)(2)(iv) 50.73(a)(2)(v) 50.73(a)(2)(vii) 50.73(a)(2)(x) 73.71 OTHER low Specify in Abstract be or in NRC Form 366A NAME James E. Wallace, Compliance Licensing Engineer TELEPHONE NUMBER tinctude Ares Code)
(205) 729-7874 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)
CAUSE
SYSTEM COMPONENT MANUFACTURER REPORTABLE TO NPRDS
CAUSE
SYSTEM COMPONENT MANUFACTURER REPORTABLE TO NPRDS X
AD X
AD FU SCR B569 H177 SUPPLEMENTAL REPORT EXPECTED (14)
YES (Ifyes, complete EXPECTED SUBMISSION DATE).
ABSTRACT (Limitto 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)
(16)
EXPECTED SUBMISSION DATE (15)
MONTH DAY YEAR On December 17, 1996, with Units 2 and 3 at approximately 100 percent and 99 percent power, respectively, and Unit 1 shutdown and defueled, Unit 3 operators declared ECCS Division II instrumentation inoperable, in accordance with TS 3.2.B. This event was caused by a cleared fuse and shorted Silicon Controlled Rectifier (SCR) in the ECCS Division li Analoq Trip Unit Inverter, which resulted in the loss of the inverter output.
Unit 3 entered several limiting condition for operations (LCO).
TVA considers this event as the fourth Unit 3 inverter failure as identified in LER 50-296/96004.
Final corrective actions for this event will be included in a supplemental report to LER 50-296/96004.
Immediate corrective actions taken for this event were the replacement of the cleared fuse and shorted SCR.
Based on these replacements, TVA concluded that the ATU inverter was operational, and the inverter was returned to service.
This report is being submitted in accordance with 10 CFR 50.73 (a)(2)(vii) as any event where a single cause or condition caused at least one independent train or channel to become inoperable in multiple systems designed to remove residual heat or mitigate the consequences of an accident.
Additionally, this event is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) for a condition prohibited by Technical Specifications.
Previous LERs on similar events were: 260/94001, 260/94006, 260/94010, 296/96004, and 296/96006.
9701210398 970115 PDR ADOCK 05000296 S
1 Ol(4-95)
U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
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PLANT CONDITIONS
At the time of discovery, Units 2 an'd 3 were operating at approximately 100 percent power and 99 percent power, respectively.
Unit 1 was shutdown and defueled.
ZI.
DESCRIPTION OF EVENT
Event On December 17, 1996, at 1236 hours0.0143 days <br />0.343 hours <br />0.00204 weeks <br />4.70298e-4 months <br /> Central Standard Time (CST),
the Unit 3, Division II Emergency Core Cooling Systems (ECCS)
Analog Trip Unit (ATU) inverter power was lost due to a cleared fuse and a shorted Silicon Controlled Rectifier (SCR) in the ECCS Division II Analog Trip Unit Inverter.
(NOTE:
TVA considers this event as the fourth failure of the Unit 3 ATU inverters as identified in LER 50-296/96004).
This failure affected two of the four channels of the drywell pressure and reactor water level sensors.
These sensors feed both divisions of initiation logic for the ECCS (Residual heat removal (RHR)
[BO] system, core spray (CS)
[BG] system, high pressure core injection (HPCI)
[BJ]
- system, automatic depressurization systems (ADS)[JC], Anticipated Transient Without Scram (ATWS) [JC],
and the Unit 3 diesel generators (EDG)
[EK]).
The above ECCS were declared inoperable due to the loss of logic inputs as delineated in Technical Specifications (TS) Table 3.2.B.
Since the ADS was declared inoperable, the plant was placed in limiting condition for operations (LCO) requiring the unit to be in hot shutdown within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
Additionally, TS 3.5.A.3 and 3.5.B.S for RHR and CS require the unit to be in cold shutdown within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
These were the most restrictive LCOs.
At 1500 hours0.0174 days <br />0.417 hours <br />0.00248 weeks <br />5.7075e-4 months <br />, the ECCS ATU Inverter was repaired by the replacement of the cleared fuse and the shozted SCR.
At that
- time, LCO 3.2.B was exited.
At 1522 hours0.0176 days <br />0.423 hours <br />0.00252 weeks <br />5.79121e-4 months <br />, a four-hour notification was made to the NRC in accordance with 10 CFR 50.72(b)(2)(iii) as any event or condition which alone could have prevented the fulfillment of the safety functions of systems that are needed to remove residual heat or mitigate the consequences of an accident.
This repozt is being submitted in accordance with 10 CFR 50.73 (a)(2)(vii) as any event where a single cause or condition caused at least one independent train or channel to become inoperable in multiple systems designed to remove residual heat or mitigate the consequences of an accident.
This event is also being submitted in accordance with 10 CFR 50.73(a)(2)(i)(B) for any operation or condition prohibited by Technical Specifications.
1 0
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NRC'FORM 366A (4-95)
U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
Browns Ferry Unit 3 DOCKET 05000296 NUMBER NUMBER PAGE
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)
3 of 6
96 008 00 TEXT (I more space is required, use addiuona copies of N orm
) (17)
B.
1'no erable Structures Co onents or S stems that Contributed to the Event:
None.
C.
Dates and A roximate Times of Ma'or Occurrences:
December 17,
- 1996, at 1236 hours0.0143 days <br />0.343 hours <br />0.00204 weeks <br />4.70298e-4 months <br />, CST Unit 3 ECCS ATU Inverter power failed due to a cleared fuse and a shorted SCR.
at 1500 hours0.0174 days <br />0.417 hours <br />0.00248 weeks <br />5.7075e-4 months <br />, CST Unit 3 inverter fuse and SCR were
- replaced, and the inverter was returned to service.
LCO 3.2.B was exited.
at 1522 hours0.0176 days <br />0.423 hours <br />0.00252 weeks <br />5.79121e-4 months <br />, CST NRC was notified.
D.
Other S stems or 'Seconda Functions Affected:
None.
E.
Method of Discove This event was promptly discovered when control room alarms indicated ECCS Division II instrumentation problems,.
One of the received alarms was ECCS ATU Trouble alarm.
erator Actions:
There were no TS safety initiations required of the control room operators.
The steps taken to identify the problem and initiate maintenance actions were appropriate.
G.
Safet S stem Res onses:
None.
CAUSE OF THE EVENT
A.
Immediate
Cause
The immediate
cause of the event
was a loss of Unit 3 ECCS ATU inverter output.
~i(4-95)
U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME 1)
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) (17)
B.
Root Cause:
The apparent
cause of the event
was a cleared fuse and a shorted SCR.
The fuse and the shorted SCR were replaced.
At that time, the inverter was returned to service.
TVA considers this event as the fourth Unit 3 ATU inverter failure as identified in LER 50-296/96004.
At this time, the root cause for the failures has not been determined.
Efforts are continuing to identify the
cause
When the cause is determined, it will be reported in a supplement to LER 50-296/96004.
C.
Contributin Factors:
None.
Iv.
ANALYSIS OF THE EVENT
The failed ECCS Division II ATU Inverter caused a loss of level and/or pressure input signals to the HPCI, CS,
This event did not result in a condition outside the plant's design basis for the following reasons:
This event resulted from a power supply failure to the instrumentation logic of the Division II of the ECCS.
- However, Division I instrumentation remained available for automatic initiation of ECCS Division I and Division II equipment during this event.
Division I and Division II ECCS equipment remained available with the following exceptions:
(1)
HPCI would not automatically inject water into the reactor vessel as a result of a loss of flow controller power.
- However, RCIC was available to initiate and to inject water into the reactor vessel, and (2)
Core Spray (CS) loop Il would also not inject water into the reactor vessel due to the loss of the inboard injection valve control circuit to sense a reactor pressure less than 450 psig.
- However, CS loop II inboard injection valve could be manually opened to allow water to inject into the reactor vessel.
The BFN Final Safety Analysis Report (FSAR), Section 6.5.2, states in part "...the reliability and the redundancy of the controls and instrumentation of the Emergency Core Cooling Systems show that no failure of a single initiating sensor either prevents or falsely starts the initiations of these cooling systems.
No single control failure prevents the combined cooling systems from providing the core with adequate cooling."
The event did not result in any plant transient described in the BFN FSAR, Chapter 14, Accident Analyses.
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Therefoze, based on the above, this event did not result in a condition outside the design basis of the plant, nor did it adversely affect the health and safety of plant personnel or the public.
CORRECTIVE ACTIONS
A. Immediate Corrective Actions:
The cleared fuse and the shozted SCR were replaced in the Unit 3 ECCS Division II ATU Inverter.
The instrumentation logic was restored.
The LCOs were exited.
B. Corrective Actions To Prevent Recurrence:
TVA considers this event as the fourth Unit 3 ATU inverter failure as identified in LER 50-296/96004.
Final long-term corrective actions to resolve this fourth inverter failure will be addressed in a supplemental report to LER 50-296/96004.
Corrective Actions Taken or Planned:
TVA sent a failed SCR to an independent laboratory and one to the SCR vendor.
Results of their analysis are due by January 21, 1997 and by March 1, 1997, respectively.
Based on the results of the independent laboratory, TVA plans to conduct in situ monitoring to detect any transient condition that might have caused/contributed to the inverter failures.
Division II had new SCRs with higher steady state amperage ratings installed.
TVA plans to replace Division I SCRs during the next refueling outage.
Additionally, TVA plans to change fuse sizes on Division I and II during the next Unit 3 refueling outage.
Finally, TVA plans to install an alternate power supply to each ECCS ATU inverter cabinet that is independent of the cabinet's associated ECCS ATU inverter.
This modification will be implemented during the next Unit 2 and Unit 3 refueling outages, respectively.
As a result of this modification, one 120 VAC to 24 VDC power supply will be removed from each ECCS ATU inverter cabinet and replaced with a 250 VDC to 24VDC converter allowing uninterrupted operation of the ATUs in the event of an inverter failure.
vz.
ADDITZONAL ZNFORMiiTZON A. Failed Co onents:
~
BUSS Semiconductor
- fuse, Part No.
FWH-125A, 550v AC/DC manufactured by Bussmann, Inc.
II(4-95)
U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
Browns Ferry Unit 3 DOCKET 05000296 NUMBER NUMBER PAGE 6 of 6 96 008 00 TEXT (I more space is required, use addiuooa copies o orm 36 (17)
~
Silicon Controlled Rectifier, Part TD 42 F-HDR 681310 13C1 manufactured by HDR Power Systems, Inc.
B. Previous LERs on Similar Events:
TVA has reviewed previous BFN LERs to detezmine if similar events have occurred.
Five previous events have occurred:
LER 260/94001 was written as a result of a Unit 2 ATU DC input fuse failure.
- However, the root cause of the event was determined to be a failure of the ECCS ATU Inverter control board.
A control board failure was not involved in this LER 50-296/96008 event.
LER 260/94006 described the failure of a Unit 2 ECCS Division I ATU
- Inverter, 250v DC reactor motor operator valve (RMOV) breaker trip.
This ECCS RMOV breaker tripped as a result of a shorted SCR.
The LER 260/94006 event occurred on Unit 2 while LER 50-296/96008 happened on Unit 3(See SCR issue in LER 296/96004 writeup below).
LER 260/94010 addressed the failure of Cl capacitor in the Unit 2 Division II ATU Inverter capacitor bank.
This failed capacitor was a result of a manufacturing defect.
A failed capacitor was not the cause of the LER 50-296/96008 event.
LER 296/96004 addressed two failed SCRs of the Unit 3 Division I ATU Inverter.
As a result of these SCR failures, an Design Change Notice (DCN) was initiated to replace the SCRs in Unit 3 Division II inverter circuit.
However, at the time of the 50-296/96008
- event, the DCN had not been implemented.
A supplemental report for LER 50-296/96004 is scheduled to be submitted on February 5,
1997.
This supplemental report will address final corrective actions to prevent recurrence foz the July 17,
- 1996, and August 6,
- 1996, events as well as for 50-296/96006 and this event, 50-296/96008.
LER 50-296/96006 addressed the third Unit 3 Division I inverter failure due to a cleared fuse.
Final corrective actions to preclude recurrence will be addressed in the supplemental report to LER 50-296/96004 along with the LER 50-296/96008 event.
VII.
COMMITMENTS
None.
Energy Industry Identification System (EIIS) system and component codes are identified in the text with brackets (e.g.,
[XX)).
l'