ML18039A904

LER 99-010-00:on 990917,automatic Reactor Scram on Turbine Stop Valve Closure Occurred.Caused by High Water Level in Main Steam Moisture Separator 2C2.Unit 2C2 Reservoir Level Transmitter & Relays Were Replaced & Tested Satisfactorily

ML18039A904
Person / Time
Site:	Browns Ferry
Issue date:	10/15/1999
From:	Morris B TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML18039A903	List: ML18039A902 ML18039A904
References
LER-99-010, NUDOCS 9910260031
Download: ML18039A904 (12)

Text

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104 EKPIREs (6-1988) oersonoo 1 Estimated burden per response to comply with this manddtly information collection request: 50 hrs. Reported lessons learned are ncorporated Into LICENSEE EVENT REPORT (LER) the Ecensing process and fed back to Industry. Forward comments regarding burden estimate to.the Records Management Branch (T4 F33), U.S.

Nudear Regulatory Commission, Washington. OC 205554%1, and to the (See reverse for required number of Paperwork Reductbn Project (31504104), Office cf Management and digits/characters for each block) Budget Washington. OC 20503. If an information cotlection does not display a currently vaEd OMB control number, the NRC mdy not conduct or sponsor. and a person is not required to respond to, the Information collection.

FACILTTY NAME ul DOCKEr NUMBER (2) PAOE I31 Bfowns Ferry Nuclear Plant Unit 2 05000260 1 of 6 TITLE ldl Reactor Scram due to Moisture Separator High Level EVENT, DATE (5) LER NUMBER (6) REPORT DATE (7) OTHER FACI ITIES INVOLVED (8)

MONTH DAY YEAR SEQUENTIAL REVISION A ILI N DOCKET NUMBER NUMBER NUMBER NA DOCKET NUMBER 09 17 99 1999 010 000 10 15 99 NA OPERATING THIS REPORT IS SUBMITTED PURSUANT To THE REQUIREMENTS OF 10 CFR 5: (Check one or more) (11)

MODE (9) 20.2201(b) 20.2203(a) (2) (v) 50.73(a)(2)(I)(B) 50. 73(a) (2) (viii)

POWER 20.2203(a)(1) 20 2203(a) (3) (I) 50.73(a) (2) (II) 50.73 (a) (2) (x)

LEVEL (10) 30 20.2203(a)(2) (I) 20. 2203(a) (3) (II) ,

50.73(a)(2)(III) 73.71 20.2203(a) (2)(II) 20.2203(a)(4) 50.73(a)(2)(iv) OTHER

20. 2203(a) (2) (III) 50.36(c)(1) 50;73(a)(2)(v) Specify In Abstract below or In NRC Form 366A 20.2203(a) (2)(iv) 50.36(c)(2) 50.73(a) (2) (v(I)

LICENSEE CONTACT FOR THIS LER (12)

NAME TELEPHONE NUMBER (Include Area Coda)

B. C. Morris, Senior Licensing Project Manager (256) 729-7909 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE SYSTEM COMPONENT MANUFACTURER REPORTABLE To CAUSE SYSTEM COMPONENT MANUFACTURER'EPORTABLE I NPRDS TO NPRDS SB LT F180 SUPPLEMENTAL REPORT EXPECTED (14) EXPECTED MONTH OAY, YEAR YES NO SUBMISSION (If yes, complete EXPECTED SUBMISSION DATE).

x DATE (15)

ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines) (16)

On September 17, 1999, at 1702 Central Daylight Time, during reactor startup operations at 30 percent power, a high water level in main steam moisture separator 2C2 caused a Unit 2 main turbine trip. This resulted in an automatic reactor scram on turbine stop valve closure. Safety systems responded as expected and all control rods fully,inserted. The cause of the high level in the moisture separator was a failed high level controller for the 2C2 moisture separator drain reservoir. The 2C2 reservoir level transmitter and relays were replaced and tested satisfactorily. Unit 2 was restarted on September 18, 1999. a TVA is reporting this event in accordance with 10 CFR 50.73 (a)(2)(iv) as an event that resulted in an actuation of an engineered safety feature,-including the reactor protection system.

991026003i 99iQi5 PDR ADQCi('5000260 S PDR NRC FORM 366B (6-1996)

i~

NRC FORM 366A 'U.S. NUCLEAR REGULATORY COMMISSION

'iI I6 1998)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAIVIE 1 DOCKET LER NUMBER 6 PAGE 3 YEAR SEQUENTIAL REVISION NUMBER 2 of 6 Browns Ferry Nuclear Plant - Unit 2 05000260 1999 010 000 TEXT (If more space is required, use additional copies of NRC Form 366A/ I 17 I I. PLANT CONDITIONS Prior to the initiation of the event, Unit 2 was at 30 percent power and Unit 3 was at 100 percent power. Both units were in Mode 1. Unit 1, was shutdown and defueied.

II. DESCRIPTION OF EVENT A. Event:

During a reactor startup on Friday, September 17, 1999, at 1530 hours0.0177 days <br />0.425 hours <br />0.00253 weeks <br />5.82165e-4 months <br /> Central Daylight Time (CDT), the Unit 2 main control room received an annunciation indicating a high water level in main steam moisture separator 2C2 level control reservoir [SB]. The Outside Unit Supervisor (US) was dispatched to investigate the situation at the local control panel. The high level controller for the 2C2 moisture separator reservoir was observed to be indicating downscale and the normal level controller was indicating full scale. The other moisture separator reservoirs were at various levels as indicated by the normal and high controllers. The US directed that the heat-up and drain alignment for the moisture separators be completed by opening the drain pump suction valves, and observed water level reducing on 5 of the 6 level control reservoirs. The 2C2 level control indicators did not respond, which was diagnosed by the US as an instrument reference leg'problem. A work order was written to investigate and correct the problem. At 1702 hours0.0197 days <br />0.473 hours <br />0.00281 weeks <br />6.47611e-4 months <br /> CDT, a Unit 2 main turbine trip occurred on moisture separator 2C2 high level. Reactor power was 30 percent at the time.

The resulting turbine stop valve closure initiated an automatic scram and trip of both recirculation pumps as would be expected. The post trip investigation indicated that the high level controller for the 2C2 moisture separator level drain reservoir had failed, which resulted a high level in the 2C2 moisture separator. The controller level transmitter [LT] and associated relays [RLYJ were replaced and tested, and restart operations were resumed on September 18, 1999.

The scram resulted in the expected automatic actuation or isolation of the following PCIS [JE] systems and components on low reactor water level. Some of these components are in their isolated positions during normal operations. The scram and isolation signals were reset by 1709 hours0.0198 days <br />0.475 hours <br />0.00283 weeks <br />6.502745e-4 months <br /> CDT, and the systems were returned to normal alignment.

~ PCIS group 2, Shutdown cooling. mode of Residual Heat Removal (RHR) [BO] system; drywell floor drain isolation valves; drywell equipment drain isolation valves [WP].

~ 'CIS group 3, Reactor Water Cleanup (RWCU) system [CE].

~ PCIS group 6, primary containment purge and ventilation,[JM], Unit 2 reactor zone ventilation [VB];

refuel zone ventilation [VA]; Standby Gas Treatment system [BH]; Control Room Emergency Ventilation system [VI].

~ PCIS group 8, Traversing Incore Probe (TIP) [IG].

This event is reportable in accordance with 10 CFR 50.73 (a)(2)(iv), as an event that resulted in the actuation of an engineered safety feature, including the reactor protection system.

NRC FORM 366 {6-1998)

0 4!

h,

NRC FORM 366A U.S. NUCLEAR REeULATORY COMMISSION (6.1998I LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME 1 DOCKET LER NUMBER 6 PAeE 3 YEAR SEQUENTIAL REVISION NUMBER 3 of 6 Browns Ferry Nuclear Plant - Unit 2 05000260 1999 010 000 TEXT (if more space is required. use additional copies of NRC Form 366AJ {17)

B. Ino erable Structures Com onents or S stems that Contributed to the Event:

None.

C.. Dates and A roximate Times of Ma or Occurrences:

September 17, 1999, at 1530 hours0.0177 days <br />0.425 hours <br />0.00253 weeks <br />5.82165e-4 months <br /> CDT Received a.2C2 moisture separator level control reservoir high alarm in the control room indicating a high water level in the reservoir. Dispatched US to investigate. Completed heat-up alignment for moisture separators. Work order written to investigate 2C2 level indicators.

September 17, 1999, at 1702 hours0.0197 days <br />0.473 hours <br />0.00281 weeks <br />6.47611e-4 months <br /> CDT Turbine trip/stop valve closure was'initiated by moisture separator 2C2 high level signal resulting in a automatic reactor scram and recirculation pump trip.

September 17, 1999, at 1709 hours0.0198 days <br />0.475 hours <br />0.00283 weeks <br />6.502745e-4 months <br /> CDT Reset isolations, secured SGTS and CREV, and restarted reactor building and refuel zone ventilation following reset of isolation logic.

September 17, 1999, at 1954 hours0.0226 days <br />0.543 hours <br />0.00323 weeks <br />7.43497e-4 months <br /> CDT A four-hour non-emergency report is made to the NRC pursuant to 10 CFR 50.72 (b)(2)(ii).

D. Other S stems or Seconda Functions Affected:

None.

E. Method of Discove Operators received high water level alarm in 2C2 moisture separator, followed by a turbine trip and reactor scram.

F. 0 erator Actions:

Operations personnel responded to the event in accordance with applicable plant procedures.

G. Safet S stem Res onse:

All required safety systems operated as designed.

III. CAUSE OF THE EVENT A. Immediate Cause:

The immediate cause of this event was high water level in 2C2 moisture separator.

NRC FORM 366 I6-1998)

IS !!

l

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION I6-I998)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME 1 DOCKET LER NUMBER 6 PAGE 3 YEAR SEQUENTIAL REViSiON NUMBER 4 of 6 Browns Ferry Nuclear Plant - Unit 2 05000260 1999 - 010 000 TEXT iifmore spece is required, use addi tionel copies of NRC Form 366Ai I17)

B. Root Cause:

The root cause of the failure was a malfunction of the high level controller for the 2C2 moisture separator level control reservoir. The failed transmitter will be disassembled and inspected to determine if a specific failure mechanism can be identified.

C. Contributin Factors:

None.

IV. ANALYSIS OF THE EVENT Six moisture separators are provided to remove moisture from steam exiting the high pressure turbine.

Additionally, to protect the main turbine from excess water in the moisture separator tanks, a turbine trip is initiated on high water level in any of the six moisture separators. Water level control for the moisture separators is provided by controlling level in separate moisture separator level control (drain) reservoirs.

Two Level Indicating Controllers (LIC), a normal and high controller, are installed on each drain reservoir.

During low reactor power operationthe normal controller is operated in manual mode and the high level controller is maintained in automatic. At high power levels, both controllers operate in automatic with the normal level controller as the primary control element and the high level controller as a back-up.

Following the high water level annunciation in the 2C2 moisture separator level control reservoir, the Outside US was dispatched to investigate'the situation locally. On arrival, the US found the drain reservoir normal and high LICs in the proper mode for low power warm-up and drain of the moisture separators. The 2C2 high L'IC was indicating downscale and the 2C2 normal LIC was indicating full scale. Reservoirs A1 and A2 were indicating high level and the high level dump valves were open, and Reservoir B1 went high after his arrival. Reservoirs B2 and C1 were high on the normal range. The US's initial review of the indications and system alignment, and.communication with the control room identified that the warm-up valve alignment of the moisture separators was not complete in that the drain pump suction valves were yet to be opened. The moisture separator drain pump suction valves were opened from the control room, completing the warm-up alignment of the moisture separators. When the drain pump suction valves were opened, the US observed level lowering on the other five drain reservoirs as would be expected due to filling of the downstream drain piping. However, the 2C2 level indication did not lower as would be expected in this alignment. The US diagnosed that the full scale reading on the 2C2 normal LIC was being caused by an instrument leg problem, and believed that the 2C2 high LIC would operate to control level when required. A work order was then written to investigate the 2C2 moisture separator level control reservoir instrumentation indications.

In situ testing following the reactor scram demonstrated that the level transmitter for the high LIC was stuck downscale. Therefore, it was concluded that the upscale reading on the normal LIC was correct at the time.

With the high LIC stuck downscale, the high level dump valve to the condenser would not auto-operate to drain water from the 2C2 level control reservoir,.which subsequently. accumulated and backed-up into the 2C2 moisture separator causing a turbine trip at 1702 hours0.0197 days <br />0.473 hours <br />0.00281 weeks <br />6.47611e-4 months <br /> CDT.

A.review of maintenance records did not reveal similar problems with the LIC transmitters which are currently on a refuel cycle schedule for Preventive Maintenance (PM). The event investigation also concluded there were some Operator knowledge deficiencies regarding the moisture separator level control reservoir instrumentation operation.

NRc FoRM 366 I6-1999)

i~ I, NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (6-1998)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME 1 DOCKET LER NUMBER 6 PAGE 3 YEAR SEQUENTIAl. REVisiON NUMBER 5 of 6 Browns Ferry Nuclear Plant - Unit 2 05000260 1999. - 010 '000 TEXT (If more spece is required, use edditionel copies of NRC Form 366A J (17 i V. ASSESSMENT OF SAFETY CONSEQUENCES The evaluation of plant system and component responses to the event concluded, that responses were as expected. The normal heat removal path was not lost during this event since the condenser was used for decay heat removal and no main steam relief valves opened. Personnel performance in response to the scram was also evaluated and found to be appropriate an event of this type. In addition, there was no radioactive material released and no actual or potential safety consequences as a result of this event.

VI. CORRECTIVE ACTIONS A. Immediate Corrective Actions:

The Operations crew stabilized the reactor following the scram using the appropriate operating instructions. The 2C2 moisture separator high LIC transmitter and relays were replaced and tested satisfactorily.

B. Corrective Action to Prevent Recurrence:

A corrective action document was issued to further evaluate the Operator response to the level alarm and to determine if additional training on the moisture separator level control system is warranted.'he PM'activity for the moisture separator level control. reservoir LICs will be evaluated. In addition, the failed transmitter will be disassembled and inspected to determine if a specific failure mechanism can be identified.'he Alarm Response Procedures for the moisture separator level control reservoirs have been revised to provide directions to take manual control of moisture separator level in the event of level controller system malfunctions.'II.

ADDITIONALINFORMATION A. Failed Com onents:

Level transmitter 2-LT-006-0083B, a Foxboro Model 15A, failed causing the high level in the 2C2 moisture separator.

B. Previous Similar Events:

None.

'TVA does not consider these corrective actions as regulatory commitments. Completion will be tracked in TVA's Corrective Action Program.

NRC FORM 366 (6-1998)

Cl l[

NRC FORM 366A NUCLEAR REGUL'ATORY COMMISSION (6. I 998)

LICENSEE EVENT REPORT (LER)

CONTINUATION'.S.

TEXT FACILITY NAME DOCKET LER NUMBER 6 'PAGE 3 YEAR SEQUENTIAL REVISION NUMBER 6 of 6, Browns Ferry Nuclear Plant - Unit 2 05000260 1999 010 000 TEXT fifmore space is required, use additional copies of NRC Form 366Ai (17)'.

Additional Information:

This event did not result in loss of the normal heat removal path as described in draft NEI 99-02, Rev. C, since the condenser was used for decay heat removal.

D. Safet S stem Functional Failure:

This event did not result in a safety system functional failure in accordance with draft.NEI 99-02, Rev..C.

VIII. COMMITMENTS

.None.

NRC FORM 366 {6-1998I

!I II