05000255/LER-2005-005
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2552005005R00 - NRC Website | |
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Palisades 05000-255 2005 -- 005 -- 00
EVENT DESCRIPTION
On September 1, 2005, at 1025 hours0.0119 days <br />0.285 hours <br />0.00169 weeks <br />3.900125e-4 months <br />, with the plant operating at 100% power, the reactor [RCT;AB] was manually tripped due to a hydrogen leak associated with the main generator [GEN;TB]. The manual reactor trip was a precautionary measure to facilitate expeditious removal from service of the main generator to allow hydrogen to be isolated and purged from the main generator, and preclude the potential for formation of an explosive hydrogen/air mixture. Following the reactor trip, the auxiliary feedwater system [BA] started automatically to maintain steam generator [SG;AB] water level. The plant was stabilized in Mode 3 to investigate and repair the cause of the hydrogen leak.
This event is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in a manual actuation of the reactor protection system [JC] and automatic actuation of the auxiliary feedwater system.
CAUSE OF THE EVENT
The hydrogen leak was at a socket weld at a piping tee connection on the main generator's leak detection line. The primary purpose of the leak detection line is to allow detection of either a service water [KG] leak from the hydrogen coolers [CLR;TK] or a seal oil [TB] leak into the main generator.
The socket weld was repaired by grinding out the weld area and re-welding the connection. The grinding associated with the repair effectively precluded the ability to examine the socket weld and to positively determine a root cause. The most probable causes are cyclic fatigue of the weld due to vibration of the line and a weld flaw.
SAFETY SIGNIFICANCE
The safety significance of this event was minimal. All safety systems functioned as expected during the plant trip. This event does not involve a safety system functional failure.
CORRECTIVE ACTIONS
As noted above, the socket weld was repaired by re-welding the connection.
PREVIOUS SIMILAR EVENTS
None