05000455/LER-2012-001
| Docket Number Sequential Revmonth Day Year Year Month Day Yearnumber No. N/A | |
| Event date: | 02-06-2012 |
|---|---|
| Report date: | 04-06-2012 |
| 4552012001R00 - NRC Website | |
Description of Event
Event Date/Time: February 6, 2012 / 1719 hours0.0199 days <br />0.478 hours <br />0.00284 weeks <br />6.540795e-4 months <br /> Unit 2 was in Mode 1 — Power Operation The Unit 2 Reactor Coolant (RC) [AB] System was at normal operating temperature and pressure for 25% power. No structures, systems, or components were inoperable at the start of this event that contributed to the event. The 2C Feedwater (FW) [SJ] Isolation Valve (FWIV) was degraded due to mechanical binding issues when opening. A warming blanket was installed on the valve to aid in stroking it open without binding.
At approximately 1700 hours0.0197 days <br />0.472 hours <br />0.00281 weeks <br />6.4685e-4 months <br />, on February 6, 2012, the Unit 2 Operating crew was in the process of conducting a unit startup in accordance with startup procedures. At approximately 25% reactor power, the Reactor Operator (RO) responsible for Steam Generator (SG) FW flow and level control and the RO responsible for opening the FWIVs were ready to perform the steps that transfer FW flow from the Steam Generators (SGs) [SB] upper nozzles to the lower nozzles through the four FWIVs. The Unit 2 Senior Reactor Operator (SRO) was overseeing the evolution. To open the FWIVs, three water hammer prevention interlocks ensuring adequate FW flow and temperature needed to be satisfied. The startup procedure has the FW Regulating Valves (FRVs) in manual control for this evolution. Additionally, the 2C FWIV was to be the first valve to open due to issues with it potentially binding.
At the start of the evolution, the SG RO was focused on maintaining subcooling in the 2C FW tempering line by opening the 2C FRV and providing more FW through the line. The SG RO was also concerned with satisfying the water hammer prevention flow and temperature interlocks. The FWIV RO began opening the 2C FWIV and the 2C SG level began to rise as expected. As the 2C FWIV was opening, the SG RO continued to focus on maintaining subcooling and satisfying the waterhammer prevention interlocks and not closely monitoring the 2C SG level increase. During this time, the Unit 2 SRO was focused on the proper performance of the 2C FWIV due to its degraded condition and not maintaining proper oversight of the overall evolution.
Another RO, assisting in the startup, noticed and communicated to the SG RO and Unit 2 SRO that the 2C SG level was above 70% and rapidly rising. The SG RO reduced FW flow to the 2C SG; however, the level continued to increase and approach the high level setpoint of 80.8% (i.e., P-14), which causes an automatic turbine trip and FW isolation. In anticipation of reaching this setpoint, the Unit 2 SRO directed a manual reactor trip at 1719 hours0.0199 days <br />0.478 hours <br />0.00284 weeks <br />6.540795e-4 months <br />. Almost simultaneous to the manual reactor trip, the 2C SG level reached the P-14 setpoint. The reactor trip signal and P-14 both generate an automatic turbine trip and FW isolation signal. The turbine tripped and FW isolated, as designed. The Operating crew responded to the reactor trip using appropriate emergency procedures. At 1734 hours0.0201 days <br />0.482 hours <br />0.00287 weeks <br />6.59787e-4 months <br />, in accordance with reactor trip response procedures, the 2A and 2B Auxiliary Feedwater (AF) [BA] pumps were manually started to provide water to the SGs. The AF pumps operated as expected and were secured at 1954 hours0.0226 days <br />0.543 hours <br />0.00323 weeks <br />7.43497e-4 months <br /> and 2037 hours0.0236 days <br />0.566 hours <br />0.00337 weeks <br />7.750785e-4 months <br /> for the 2A AF and 2B AF pumps, respectively. Unit 2 remained stable in Mode 3 pending post reactor trip event review.
An Emergency Notification System notification was made to the NRC in accordance with 10 CFR 50.72 (b)(2)(iv)(B) and (b)(3)(iv)(A). In addition, an LER is required to be submitted in accordance with 10 CFR 50.73 (a)(2)(iv)(A).
RC FORM 36E0-2010)
A. Cause of the Event
The root cause was determined to be an overly complex procedure requiring the FRVs to be in manual control during this point in the reactor startup process. Coordination of the opening of the FRVs and FWIVs, while the SG RO was reacting to other issues such as maintaining subcooling in the tempering lines and satisfying water hammer prevention interlocks, became overly distracting and led to the 2C FRV to be opened to far. A benchmark of the Braidwood Station startup procedure indicates having the FRVs in automatic control at this point in the startup is less complex and a more effective means to perform this evolution.
Contributing causes include:
Inadequate personnel performance issues by the licensed operators involved in the event.
Distraction created by the degraded 2C FWIV.
Less than adequate Operations crew teamwork performance during the evolution.
Lack of Unit 2 specific SG level control simulator modeling. The Unit 1 and Unit 2 SGs are different models and have different level setpoints and level control. The site simulator is modeled after the Unit 1 configuration. Consequently, Operators do not receive simulator experience controlling the Unit 2 SG level.
B. Safety Significance
There were no safety consequences impacting plant or public safety as a result of this event. The reactor trip system, P-14, and the AF system functioned as designed. A risk analysis also indicates this event was not risk significant.
C. Corrective Actions
The Unit startup procedure will be revised to have the FRVs in automatic control during the opening of the FWIVs.
Other shutdown and startup procedures will be reviewed against Braidwood Station's corresponding procedures to ensure the sites are aligned to the best practices.
The priority of repair for the 2C FWIV will be reassessed.
Performance weaknesses with the operators involved have been remediated.
To correct the crew teamwork performance, enhanced pre-planned organizational responses are being developed and will be deployed when operating personnel performance issues warrant intervention.
The simulator's design will be reviewed to determine if the Unit 2 SG level control should be modeled.
E. Previous Occurrences
Low Steam Generator Level Due to Inadequate Surveillance Testing," dated April 19, 2010 Some personnel performance issues in this event were similar to this previous event. Beyond crew remediation for this event, management oversight and corrective actions to address crew team performance should maintain future high standards in individual and crew performance