05000389/LER-2004-005
| Event date: | |
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| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3892004005R00 - NRC Website | |
REPOR TABLE
TO EPIX
- On December 27, 2004, Unit 2 was in Mode 1 at 10 percent reactor power preparing to latch the turbine.A At 1751 hours0.0203 days <br />0.486 hours <br />0.0029 weeks <br />6.662555e-4 months <br />, the turbine was latched and the "A" steam generator inventory took a step increase.A Approximately 140 seconds following the turbine latch, the 2A main feedwater (MFW) pump automatically tripped on high level in the "A" steam generator. With no MFW pump in service, the "B" steam generator narrow range water level decreased to the low level 40 percent reactor protection system pre-trip operators performed standard post-trip actions and stabilized the plant in Mode 3.
The event was caused by a combination of human error and the malfunction of a main feedwater regulating valve controller that allowed the steam generator overfeed condition that ultimately resulted in manual reactor trip due to low steam generator water level.A Corrective actions included controller replacement, procedure revisions, and training on the event.A The unit was returned to service on January 2, 2005.
2. DOCKET1. FACILITY NAME 6. LER NUMBER 3. PAGENUMBER
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Description of the Event
On December 27, 2004, Unit 2 was in Mode 1 at 10 percent reactor power preparing to latch the turbine. Steam generator inventory was maintained with the 2A MFW pump [EIIS:SJ:P] in service providing flow through the low power feedwater control system (LPFWCS) 15 percent bypass valves LCV-9005 ("A") and LCV-9006 ("B") [EIIS:SJ:LCV].
LIC-9005 was in automatic control and LIC-9006 [EIIS:SJ:LIC] was in manual control.
The steam generator inventories were below setpoint but within normal range in anticipation of latching the turbine.
When the turbine was locally latched from front standard at 1716 hours0.0199 days <br />0.477 hours <br />0.00284 weeks <br />6.52938e-4 months <br />, steam generator "A" inventory took a step increase. Approximately 140 seconds following the turbine latch, the 2A main feedwater (MFW) pump automatically tripped on high level in the "A" steam generator. High steam generator level initiated an automatic turbine trip. Although attempts were made to restart the 2A MFW pump, it was recognized that the attempts would most likely be unsuccessful because the high level in the "A" steam generator was close to the reset point. With no MFW pump in service, the "B' steam generator narrow range water level decreased to the low level operators manually tripped the reactor at 1721 hours0.0199 days <br />0.478 hours <br />0.00285 weeks <br />6.548405e-4 months <br />.
Operations performed standard post trip actions and the plant was stabilized in Mode 3 with decay heat removal being performed by the auxiliary feedwater (AFW) system and atmospheric dump valves (ADVs). However, main feedwater was available once the "A" steam generator level decreased below the high level reset.
An event response team was formed to investigate the steam generator overfeed event and subsequent low steam generator water level trip. Reactor startup commenced on January 1, 2005 and the unit was brought online on January 2, 2005.
Cause of the Event
The event response team identified two significant causes for the steam generator "A" overfeed event and subsequent manual trip on low steam generator level on the "B" steam generator.
The first significant cause for the overfeed of the "A" steam generator was a human error by the failure to follow procedure during post trip activities from the December 25, 2004 manual reactor trip. Plant procedure 2-EOP-99, Appendix X, "Secondary Post Trip Actions," Section 2, requires that a control room operator ensure that both main feedwater regulator valve (MFRV) block valves are closed.
However, the MFIV block valves were not closed and there was no requirement that that the procedure steps be independently verified. With the MFRV block valves (MV-09-5 and MV-09-6) open, a path exists to feed the steam generators through the MFRVs, FCV 9011 and FCV-9021. FCV-9011 for the "A" steam generator opened due to a controller output malfunction in the automatic mode when the turbine was latched. Regardless, had the MFRV block valves been closed as required by procedure, this event would have been prevented.
The other significant cause for the overfeed of the "A" steam generator was the automatic opening of FCV-9011 [EIIS:SJ:LCV], the "A" MFRV for the "A" steam generator. FIC-9011 [EIIS:SJ:FIC], the controller for the "A" steam generator MFRV, was in the automatic mode. When the operators latched the turbine FIC-9011 provided an open signal to FCV-9011. However, the "A" controller malfunctioned and rapidly positioned FCV-9011 to approximately 25 percent open following the turbine latch.
2. DOCKET1. FACILITY NAME 6. LER NUMBER 3. PAGENUMBER � The "A" controller automatic tracking malfunction along with the open "A" steam generator MFRV block valve provided the main feedwater flowpath and subsequent overfeed event on the "A' steam generator. Had the MFRV controller responded as expected or been in the manual mode in hold with zero output, this event could have been prevented.
Contributing causes for the inadequate MFRV configuration control were latent procedure weaknesses and human performance issues during turnover.
The secondary post trip actions of 2-EOP-99, "Appendices/Tables/Figures/Data Sheets,' Appendix X correctly configure feedwater for LPFWCS operation by closing both MFRV block valves. However, a latent procedure weakness existed. The operators were not required to take action on the MFRVs because the MFRVs would be in the post turbine trip mode with the controller output grounded (regardless of the selected mode, automatic or manual). This presented a human performance trap for feedwater alignment and challenged operations when the controller remained in the automatic mode and malfunctioned when the turbine was latched.
Procedure 2-G0P-201, "Reactor Plant Startup - Mode 2 to Mode 1," permits steps to be marked N/A based on system configuration control. As such, the configuration is based on other procedures correctly providing the configuration alignment before latching the turbine. This weakness contributed to operating the MFRVs in the automatic mode rather than aligning the MFRVs in manual mode in hold with zero output. Therefore, when the turbine latch removed the controller output ground, the MFRV responded to demands based on steam generator level.
Analysis of the Event
This event is reportable under 10 CFR 50.73(a)(2)(iv)(A) as a manual actuation of the RPS.
Analysis of Safety Significance This event was an uncomplicated plant trip and is an analyzed event, so this had no adverse impact on the health and safety of the public. Although the high "A" steam generator level caused the momentary loss of main feedwater and subsequent manual trip based on low level in the "B" steam generator, main feedwater was available once the high level in the "A" steam generator was reset.
The procedural deficiencies identified during this event also existed in the St.
Lucie Unit 1 procedures. These St. Lucie Unit 1 latent procedural issues were corrected as part of the corrective actions for this event.
St. Lucie Unit 2 has experienced past issues related to the MFRV controllers during automatic transfer from the LPFWCS to the MFRVs (automatic transfer is unique to Unit main feedwater control issues, the feedwater regulating system was scheduled to be completely replaced with a Foxboro digital control system during SL2-16 (spring 2006). However, this event resulted in significant impact just prior to SL2-15 and a SL2-15 refueling outage. As part of the Life Cycle Management (LCM) program, FPL will implement an upgrade to the St. Lucie Unit 2 LPFWCS digital control system during the SL2-16 refueling outage. The LCM program is also upgrading the digital main and LPFWCS feedwater systems for St. Lucie Unit 1 in future refueling outages.
Corrective Actions
1.To ensure proper alignment of the feedwater system during startups, the St. Lucie Units 1 and 2 plant procedures 1/2-GOP-201, "Reactor Plant Startup - Mode 2 to Mode 1," and 1/2-GOP-502, "Data Sheets Required for Heatup," were revised to require closure of the MFRV block valves and to place the MFRV controllers in the manual mode prior to turbine startup.
2.To ensure that EOP actions are independently verified, Operations Policy 521, "Emergency Operating Procedure Implementation," was revised to require that EOP actions performed by an operator be verified by another operator when conditions permit.
3.To ensure proper alignment of the feedwater system post-shutdown, the St. Lucie Units 1 and 2 plant procedures 1/2-EOP-99, "Appendices/Tables/Figures/Data Sheets," Appendix X will be revised to require that the MFRV controller be placed in the manual mode in hold with zero output during the next EOP update. This action will be completed by August 31, 2005.
4.The Unit 2 "A" MFRV controller FIC-9011 and LIC-9011 were replaced and tested satisfactory prior to Unit 2 return to automatic MFRV control under work order 35000042.
5.A new Foxboro digital main feedwater control system plant modification was implemented during the January 2005 St. Lucie Unit 2 SL2-15 refueling outage under PCM 05002.
Other Information Although not specifically identified as a corrective action for this event, additional digital feedwater system modifications and upgrades had previously been planned as part of the Life Cycle Management (LCM) program. The modifications currently scheduled for the next refueling outage for each unit will further enhance the operation of the FRV's through software integration with the plant's distributed control system as well as provide an improved human/machine interface system for the operators.
Failed Components Identified Flow Indicating Controller for Feedwater Regulating System 2A Equipment:� Manufacturer: Fischer & Porter Co.
Model: D200D-3000 Similar Events None