05000425/LER-2013-001
| Vogtle Electric Generating Plant - Unit 2 | |
| Event date: | 02-26-2013 |
|---|---|
| Report date: | 04-22-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4252013001R00 - NRC Website | |
A. REQUIREMENT FOR REPORT
This report is required per 10 CFR 50.73(a)(2)(iv)(A) due to an unplanned manual actuation of the Reactor Protection System (RPS) [JC] and an automatic actuation of the Auxiliary Feedwater System (AFW) [BA].
B. UNIT STATUS AT TIME OF EVENT
At the time of this event, Unit 2 was In Mode 1 at 94 percent rated thermal power with End of Life (EOL) coastdown in progress.
C. DESCRIPTION OF EVENT
The event occurred following restoration of the Reactor Coolant System (RCS) filter to service following cartridge replacement. Three of the four Reactor Coolant Pump (RCP) seal leakoff flows began increasing within 5 minutes after returning the RCS filter and Chemical Volume Control System (CVCS) demineralizers to service, and completing a 50 gallon dilution. RCP Seal number one leakoff gradually trended upward over the next hour on all four RCPs. The restoration of flow through the CVCS demineralizers and the dilution lowered charging temperature. The Waste Gas System was not in service to remove any gases introduced into the Volume Control Tank (VCT). The gases dissolved back into solution and were introduced into the seal injection lines resulting in thermal expansion differences within the seal materials affecting the seal taper angle causing a gradual increase in flow rate through the seals.
operators initiated a manual reactor trip due to RCP #4 number one seal leakoff flow exceeding the operating limits.
D. CAUSE OF EVENT
The direct cause of the transient was the addition of air into the CVCS charging system as a result of less than adequate filling and venting of the RCS Filter following replacement.
E. SAFETY ASSESSMENT
When the reactor was manually tripped all rods fully inserted. As a result of the reactor trip, the turbine tripped, the Feedwater System isolated and the AFW system actuated in accordance with plant design.
Control Room operators responded appropriately to stop RCP #4 and isolate the number one seal leakoff flow per plant operating procedure and the plant was stabilized in Mode 3 by controlling feedwater flow and rejecting decay heat to the condenser. The Mode 3 decay heat removal requirements are low enough that a single RCS loop with one RCP running is sufficient to remove core decay heat. Based upon these considerations, there was no adverse effect on plant safety or on the health and safety of the public as a result of this event.
F. CORRECTIVE ACTION
Procedure changes have been implemented to provide instruction to significantly reduce the amount of air intrusion from the RCS filter change by ensuring adequate fill and venting of the RCS filter, providing improved guidance on returning the CVCS demineralizers to service prior to realigning the letdown flow to the CVCS Volume Control Tank, and requiring the Waste Gas System to be in service prior to replacement of a RCS Filter to ensure removal of any gases introduced to the system.
G. ADDITIONAL INFORMATION
1) Failed Components:
None 2) Previous Similar Events:
OE 18570 Kewaunee Unit 1, High dissolved oxygen concentration results in increased seal leakoff flow.
3) Energy Industry Identification System Code:
[CB] — Chemical and Volume Control / Makeup and Purification System [JC] — Reactor Protection System [BA] — Auxiliary Feedwater System 4) Other Systems Affected:
None 5) Commitment Information:
This report does not create any new permanent licensing commitments.