05000255/LER-2007-002

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LER-2007-002,
Docket Number
Event date: 01-19-2007
Report date: 03-19-2007
Reporting criterion: 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material
2552007002R00 - NRC Website

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Palisades Nuclear Plant 05000-255 2007 -- 002 -- 00

EVENT DESCRIPTION

On January 19, 2007, with the plant in Model, a small service water [BI] leak (approximately 60 drops per minute) was identified in VHX-4 containment air cooler (CAC) [CLR;BK]. The leak was subsequently determined to be from a pin-hole in a single cooling coil tube at the H-bend fitting.

The CAC cooling coil is 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, Technical Specification (TS) Limiting Condition For Operation (LCO) 3.6.1, "Containment," is initially applicable for any through-wall defect noted in a CAC cooling coil.

Although the size of the identified pin-hole would not have challenged La, it was not possible to characterize the flaw using the criteria prescribed in American Society of Mechanical Engineers (ASME) Code Case N-513-1 to verify the operability of the cooling coil for post-accident conditions over the CAC's mission time.

Therefore, this event is reportable in accordance with 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.

Since VHX-4 has no safety-related cooling function, TS LCO 3.6.6, "Containment Cooling Systems" was not affected.

CAUSE OF THE EVENT

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

CORRECTIVE ACTIONS

VHX-4 was repaired using an ASME accepted method by plugging tubes to isolate the H-bend flaw.

Subsequently, VHX-4 was completely isolated by installing blanks on the service water inlet and individual cooling coil outlet flanges.

The VHX-4 CAC cooling coils are currently scheduled to be replaced during the Fall 2007 refueling outage.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Palisades Nuclear Plant 05000-255 2007 -- 002 -- 00

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.

PREVIOUS SIMILAR EVENTS

Licensee Event Report 05-006, "Inoperable Containment Due to Containment Air Cooler Through- Wall Flaws" Licensee Event Report 06-006, "Inoperable Containment Due to Containment Air Cooler Through- Wall Flaw" Licensee Event Report 06-008, "Inoperable Containment Due to Containment Air Cooler Through- Wall Flaw"