|Turkey Point Unit 3|
|Reporting criterion:||10 CFR 50.73(a)(2)(iv)(A), System Actuation|
|ENS 46660||10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation|
|LER closed by|
|IR 05000250/2012002 (26 April 2012)|
|2502011001R01 - NRC Website|
DESCRIPTION OF THE EVENT
At approximately 11:35 on March 6, 2011, a sodium spike was detected in the 3AS hotwell. Subsequently the 3A1 and 3A2 circulating water pumps (CWP) were stopped. However, approximately four hours after stopping the CWPs a higher sodium spike was detected again in the 3AS hotwell [SG] (3BS hot well sample pump was not in service.) At approximately 16:20 (EST), steam generator sodium concentrations exceeded 3-0NOP-071.1, "Secondary Chemistry Deviation from Limits" and 0-ADM-651, "Nuclear Chemistry Parameters Manual" as the sodium levels increased to greater than 250 ppb (action level 3). A rapid power reduction was commenced in accordance with plant procedures 3-0NOP-100, "Fast Load Reduction", to approximately 23% power. A manual reactor trip was initiated per procedure at 16:44 (EST). Unit 3 was stabilized in Mode 3. All rods [AA, ROD] fully inserted and all safety systems functioned as required and there was no impact on the health and safety of the public. The NRC was notified of the event due to manual actuation of the Reactor Protection System (Event Number 46660) at approximately 19:38 (EST) on March 6, 2011.
CAUSE OF THE EVENT
A root cause analysis was performed. The cause of the sodium intrusion event was due to a tube flaw near the tubesheet interface of tube R305/T5. High cycle, low stress fatigue, and cold work induced residual stresses likely contributed to the event. Corrective actions involved plugging several tubes and applying an overcoat of Duromar after tube plugging. Eddy Current Testing was performed on a selected tube population. A combination of foam/dimple plug testing was also performed. There was evidence of leakage near a tube-to-tubesheet interface [SG, COND]. Several tubes [SG, TBG] of the 3AN and 3BS water boxes were plugged and coated.
ANALYSIS OF THE EVENT
The sodium level increase led to the decision to shutdown the reactor in accordance with plant procedures and therefore is reportable under 10 CFR 50.73(a)(2)(iv)(A) as "any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B) of this section." All systems operated as expected during the reactor shutdown and there was no impact on the health and safety of the public.
Corrective actions involved plugging several tubes in water boxes 3AN and 3BS.
Long term, the Unit 3 and Unit 4 condenser tube bundles will be replaced under the Extended Power Uprate Project.
component function identifier (if appropriate)].
Turkey Point Unit 4 had a condenser tube leak, LER 2010-008-00, that resulted in a manual plant shutdown on December 9, 2010.