05000255/LER-2006-006

LER-2006-006,

Docket Number
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material
2552006006R00 - NRC Website

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Palisades Nuclear Plant 05000-255 2006 -- 006 -- 00

EVENT DESCRIPTION

On November 1, 2006, with the plant in Model , a small service water [BI] leak (approximately 0.4 gallons per minute) was identified in VHX-4 containment air cooler (CAC) [CLR;BK]. The specific location of the through-wall flaw could not be physically verified, as the leak location was determined to be from the opposite side of the tube sheet. However, the leak is assumed to be from a pin-hole in a single cooling coil tube, similar to previous pin-hole leaks which have occurred in the cleanable­ bend area of the cooling coil, on the visible side of the tube sheet.

Since VHX-4 has no safety-related cooling function, Technical Specification (TS) Limiting Condition For Operation (LCO) 3.6.6, "Containment Cooling Systems" was not affected. However, the CAC cooling coil tubing is also a part of the containment [NH] boundary, and is required to be structurally sound to ensure that post accident containment leakage will not exceed allowable leakage (La).

Therefore, TS LCO 3.6.1, "Containment," is applicable for any through-wall defects noted in CAC cooling coil tubing.

Although analysis showed that the identified leak size would not challenge La, it was not possible to characterize the flaw and verify the structural integrity of the tube for post-accident conditions over the CAC's mission time. Therefore, in accordance with TS LCO 3.6.1.B.1, the plant was taken to Mode 3.

This event is reportable in accordance with 10 CFR 50.73(a)(2)(i)(A) as the completion of a shutdown required by plant Technical Specifications and 10 CFR 50.73(a)(2)(v)(C) as a condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material.

CAUSE OF THE EVENT

The probable cause of the through-wall flaw is loss of wall thickness due to flow induced erosion.

CORRECTIVE ACTIONS

The affected cooling coil was isolated by installing blanks on its inlet and outlet flanges. The VHX-4 CAC cooling coils are currently scheduled to be replaced during the Fall 2007 refueling outage.

SAFETY SIGNIFICANCE

The safety significance of this occurrence is considered to be minimal. For a worst case failure of a single CAC cooling coil tube, analysis has determined that all on-site and off-site dose limits would continue to be met for the bounding postulated post-accident scenario.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Palisades Nuclear Plant 05000-255 2006 -- 006 -- 00

PREVIOUS SIMILAR EVENTS

Licensee Event Report 05-006, "Inoperable Containment Due to Containment Air Cooler Through- Wall Flaw"