|Reporting criterion:||10 CFR 50.73(a)(2)(iv)(A), System Actuation|
|ENS 52718||10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation|
|4432017001R00 - NRC Website|
|Person / Time|
NextEra Energy Seabrook
Document Control Desk, Office of Nuclear Reactor Regulation
|Download: ML17178A359 (5)|
comments regarding burden estimate to the Information Services Branch (1--2 F43), U.S. Nuclear Regulatory Commission. Washington, DC 20555-0001, or by e-mail to rifocollects.Resource@rrc.gov, and to the Uesk Officer, Office of Information and Regulatory Affairs.
used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to: the information collection.
05000- Seabrook Station 443
Description of the Event
On April 29, 2017 at 18:44, the Reactor [AC,RCT] was manually tripped by the operators at approximately 12% power in response to a feedwater [SJ] isolation caused by High Steam Generator (SG) Level on the 'B' Steam Generator [AB, SG].
The control room operators were manually controlling SG levels while starting up the unit and were in the process of opening the main feedwater regulating valves. During low power operations, the wide range indication is used to more accurately control SG water levels as SG wide range level indication will lead narrow range level indication as feedwater flow to the steam generator changes.
The feedwater isolation signal P-14 was automatically actuated at 1843 when the 'B' SG level reached the setpoint of 90.8% narrow range level. The P-14 signal closes the main feedwater isolation valves, all feed regulating valves, and trips the main feedwater pumps. The plant was being started up following the major work performed for Refueling Outage 18.
Post-trip investigation revealed that FW-LT-502-V1L (the variable leg pressure isolation for FW-LT-502) had not been restored to the required open position during routine instrument line filling and venting. On April 26, 2017, l&C performed backfilling of the reference legs on multiple steam generator level channels, including FW-LT-502, the 'B' SG wide range level instrument. FW-LT-502-V1L not being restored to the open position caused the 'B' SG wide range indication to respond slowly to level changes.
The operating crew processed through E-0, Reactor Trip or Safety Injection (exited the procedure at Step 4 a RNO) to ES-0.1, Reactor Trip Response (exited at step 14 a RNO) to OS1000.11, Post Trip to Hot Standby.
Cause of the Event
The cause of the event was determined to be failure of the l&C technician to properly implement maintenance fundamentals during the restoration of FW-LT-502. A contributing cause was determined to be improper characterization of SG level backfill activity as skill-of-the-craft.
Analysis of the Event
Feedwater isolation on a high steam generator level prevents continuous addition of excessive feedwater, which could result in carryover of water into the steam lines and excessive cool down of the primary system.
Upon the P-14 actuation, the plant functioned correctly. All automatic functions occurred as designed, in the expected time frame. The Feedwater Isolation function was completed within seven seconds (based on a review of available computer points). The loss of feed flow required the operators to manually actuate a reactor trip at 18:44:26.
Without forward feed flow, SG levels quickly dropped. The emergency feedwater (EFW) actuation signal occurred due to two 'C' SG level instruments dropping below the 20% lo-lo set point. The 'B' EFW pump breaker closed immediately, and the turbine-driven EFW pump began to develop discharge pressure and was at normal operating pressure 11 seconds later.
Estimated burden per response tc comply with this mandatory collect:on request:80 hours
. Reported comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington. DC 20555-0001, or by e-mail to Infccollects.Resource@nrc.gov. and to the Desk Officer: Office of Information and Regulatory Affairs:
NEOB-10202, (315C-0104). Office of Management and Budget. Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor. and a person is not reouired to respo".d to, the informatron collection.
05000- Seabrook Station 443 An EFW actuation also results in a SG blowdown isolation, and this function was performed within five seconds. Due to a lack of decay heat, the RCS temperature cooled to approximately 535 deg. F and a subsequent automatic letdown isolation occurred due to low pressurizer level at 17%. The crew then successfully stabilized the plant in Mode 3 at normal operating pressure and temperature and normal letdown and SG levels were restored. The event posed no actual or potential hazard to public health or safety.
The event resulted in a valid actuation of the reactor protection system and met the reporting criteria of 10 CFR 50.72(b) (2)(iv)(B) and 10 CFR 50.72(b)(3)(iv)(A). A four hour report was made to the NRC at approximately 2119 on April 29, 2017 (event number 52718). Plant operators responded to the plant trip in accordance with approved procedures, and safety systems functioned as expected. No adverse consequences resulted from this event and this incident had no adverse impact on health and safety of the public or the plant and its personnel. This event did not involve a safety system functional failure.
Completed Corrective Actions
1. Individual performance was corrected.
2. All similar transmitter valve positions were verified. All valves were found in their correct position.
Planned Corrective Actions
1. Develop and present a case study on this event to l&C technicians that captures the specific details of this event and lessons learned.
2. Develop a maintenance procedure that provides specific step-by-step instructions to perform SG level channel backfilling operations.
Similar Events There have been no previous licensee event reports at Seabrook for a similar event.