05000395/LER-2006-004
| Docket Number | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv), System Actuation |
| 3952006004R00 - NRC Website | |
PLANT IDENTIFICATION
Westinghouse — Pressurized Water Reactor
EQUIPMENT IDENTIFICATION
XSG0002A-RC Steam Generator A XSG0002B-RC Steam Generator B XSG0002C-RC Steam Generator C
IDENTIFICATION OF EVENT
On November 22, 2006 at approximately 0430, during secondary plant startup, the "B" steam generator (SG) water level increased to the high level (P-14) setpoint. The P-14 signal isolated feedwater (RN), tripped the FW pumps and the main turbine.
EVENT DATE
11/22/2006
REPORT DATE
01/19/2007
CONDITIONS PRIOR TO EVENT
Mode 2, Startup from Refueling
DESCRIPTION OF EVENT
On November 22, 2006, V. C. Summer Nuclear Station (VCSNS) was stable with reactor power being maintained between 1 to 3 % power. The Main Turbine was reset and was on the turning gear. Operators commenced secondary plant startup and power escalation in accordance with General Operating Procedure GOP-4A. The operators initiated a transfer of feedwater (RN) from emergency feedwater (EF) to main FW with the FW pump (FWP) Master Speed Controller and the bypass feedwater regulator valves (FRVs) in manual control. As the FW Operator opened the Bypass FRVs and throttled down on EF, he did not note positive SG level response. The operator raised demand on the Bypass FRVs and adjusted the FWP Master Speed Pump Controller in an attempt to increase RN flow to the SGs. The operator still did not note appropriate SG level response and informed the Shift Supervisor (SS). The SS observed that the FW flow to all three SGs was in excess of that required for the current power level, and directed that the FW flow be reduced. The Bypass FRVs were closed and the FWP Master Speed Controller setpoint were reduced to minimum.
As a result of the excessive FW flow, the SG levels started to increase and Reactor Coolant System (RCS) temperature started to decrease. The Reactor Operator adjusted rods to control RCS temperature. The increasing RCS temperature and narrow range (NR) SGWL lagging actual level caused SG level indication to continue to rise.
At approximately 0430, SG "B" level reached the P-14 setpoint causing FW isolation, FWP trip and Main Turbine trip.
Once it was recognized that excessive FW flow was present, the crew responded properly. During the transient, RCS temperature decreased below the minimum temperature for criticality for approximately one minute, letdown isolated on low pressurizer level, and pressurizer heaters tripped. After the transient, the crew established EF flow to the SGs, restored RCS temperature and pressure to normal, restored pressurizer heaters, and then restored letdown.
CAUSE OF EVENT
The major issue was a failure of the operators to utilize all available indications and anticipate plant response. Contributing factors include: equipment issues with the FWP Master Speed Controller not being able to control speed in automatic during no or low FW flow conditions. FW flow indications are not accurate at low flow conditions. Narrow range (NR) SGWL lags actual level at low power. These factors contributed to the FW Operator not recognizing adequate flow to the SGs.
ANALYSIS OF EVENT
At the time of the event, the plant was at less than 3% reactor power. Operators were performing secondary plant startup. The FWP Master Speed Controller and the Bypass FRVs were in manual due to low flow conditions. All plant systems functioned as designed and remained operable. The P-14 signal isolated FW, tripped the main FWP turbines, and tripped the Main Turbine.
CORRECTIVE ACTIONS
After the transient, the crew established EF flow to the SGs, restored RCS temperature and pressure to normal, and then restored letdown. The oncoming operations crew received simulator training on the startup evolution. The crew then assumed the watch and successfully raised power, and continued with the secondary plant startup.
Condition Evaluation Report C-06-4275 was initiated to document actions and evaluations for this event.
Corrective actions to preclude recurrence include improving pre-job briefings and just-in-time (JIT) training for the startup evolution to include equipment issue awareness. Additionally, licensed operators will be provided training on the event during the next scheduled Licensed Operator Requalification training cycle and simulator training on this evolution will be added to the Licensed Operator Requalification Program. These actions will be completed by April 1, 2007.
PRIOR OCCURRENCES
There have been no similar events that have occurred at VCSNS during the last five years.