05000251/LER-2010-008

LER-2010-008, Turkey Point Unit 4 05000251 1 of 3

Docket Number
Event date:	12-9-2010
Report date:	10-20-2011
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
Initial Reporting
ENS 46471	10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation
2512010008R01 - NRC Website

DESCRIPTION OF THE EVENT

At 22:00 on December 9, 2010, Unit 4 had indication (high sodium) of a condenser tube leak. A rapid power reduction was commenced in accordance with plant procedures 4-ONOP-100, "Fast Load Reduction", 4-0NOP-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).

Chemistry confirmed that the high sodium level was due to salt water intrusion from the 4BN Main Condenser tube bundle. A management decision was made to shutdown the reactor in accordance with plant procedures by manually opening the reactor trip breakers at about 22:58:13 from approximately 17.5% power. All systems functioned as designed and there was no impact on the health and safety of the public.

The NRC was notified (Event Number 46471) at approximately 01:25 (EST) on December 10, 2010.

CAUSE OF THE EVENT

Corrective actions involved plugging the failed tube and four other tubes with minimal indications. The failed tube was removed during the next refueling outage (RFO PT4-26) and sent for analysis. Analysis indicated the root cause to be axial cracking caused by high cycle fatigue.

ANALYSIS OF THE EVENT

The seawater contamination event and 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." The Reactor Protection System (RPS) including reactor scram or reactor trip is included in the systems listed. All systems operated as expected during the reactor shutdown and there was no impact on the health and safety of the public.

Review of the operating history of Units 3 and 4 revealed no similar tube leakage events in Unit 3 or Unit 4.

Both units have had previous tube leaks due to other causes, e.g. damage from flashing, plug leakage, rolled joint failures, and vibration. The Units 3 and 4 condensers have some tube bundles from the same manufacturer.

CORRECTIVE ACTIONS

Corrective actions involved plugging the failed tube and four other tubes with minimal indications. The failed tube was removed during the next refueling outage (RFO PT4-26) and sent for analysis. Analysis indicated the root cause to be axial cracking by high cycle fatigue. Eddy Current Testing was performed during RFO PT4-26 with conservative plugging criteria to plug all tubes with indications of greater than 50% wall-loss. Long term, the Unit 3 and Unit 4 condenser tube bundles are currently planned for replacement under the Extended Power Uprate Project.

ADDITIONAL INFORMATION

component function identifier (if appropriate)].

SIMILAR EVENTS

A review of the station condition reports and LERs revealed that there have been no similar Turkey Point events in the last five years .