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At 1903 CST, on 04-10-08 the Plant Shift Superintendent (PSS) was notified that an alarm was received in the C-335 Area Control Room for the C-335 Unit 2 Cell 7 UF6 Release Detection (PGLD) System. Operators responded to the local panel and found all detector heads in alarm. Operators attempted to reset the system and the system would not reset, all heads remained in alarm. Operators then responded to the Unit 2 Cell 7 cell floor with the proper PPE and confirmed there was not a UF6 release. This PGLD System contains detectors that cover the C-335 Unit 2 Cell 7 cell housing roof and cell exhaust duct and sections 3 & 4 of the cell bypass housing. At the time of this alarm, C-335 Unit 2 Cell 7 and sections 3 & 4 of the cell bypass were operating above atmospheric pressure. TSR 2.4.4.1 requires that at least the minimum number of detector heads in the cell housing roof, cell exhaust duct, and cell bypass housing are operable during steady state operations above atmospheric pressure. With all the Unit 2 Cell 7 PGLD system heads locked in alarm, none of the required 3 heads in the cell housing roof and cell exhaust duct were operable and less of the required 3 heads in the cell bypass housing sections were operable. This PGLD System was declared inoperable, TSR LCOs 2.4.4.1.A.1 and 2.4.4.1.C.1 were entered and a continuous smoke watch was put in place within one hour. An investigation is ongoing to attempt to determine the cause of the failure. This event is being reported as a 24 hour event in accordance with 10CFR 76.120(c)(2)(i). This is an event in which equipment is disabled or fails to function as designed when: a.) the equipment is required by a TSR to prevent releases, prevent exposures to radiation and radioactive materials exceeding specified limits, mitigate the consequences of an accident, or restore this facility to a pre-established safe condition after an accident; b.) the equipment is required by a TSR to be available and operable and either should have been operating or should have operated on demand, and c.) no redundant equipment is available and operable to perform the required safety function. The NRC Resident Inspector has been notified of this event. PGDP Assessment and Tracking Report No. ATRC-08-1089; PGDP Event Report No. PAD-2008-10; Worksheet No. 44134 Responsible Division: Operations

• * * UPDATE FROM B. WALLACE TO J. KNOKE AT 1021 EDT ON 6/4/08 * * *

The update is a retraction. Investigation has attributed the false alarm to a moisture problem and not a loss of power. The system did not fail. The licensee notified the NRC Resident Inspector. Notified R2 (Robert Haag) and NMSS (Jack Guttmann)