PNP 2011-009, Special Report of Inoperability of Main Steam Line Gross Gamma Activity Monitor

Special Report of Inoperability of Main Steam Line Gross Gamma Activity Monitor

ML110410549
Person / Time
Site:	Palisades
Issue date:	02/10/2011
From:	Patricia Anderson Entergy Nuclear Operations
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
PNP 2011-009
Download: ML110410549 (2)

Text

Entergy Nuclear Operations, Inc.

Palisades Nuclear Plant 27780 Blue Star Memorial Highway Covert, MI 49043 Tel 269 764 2000 Paula K. Anderson Licensing Manager PNP 2011-009 February 10, 2011 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001

SUBJECT:

Special Report of Inoperability of Main Steam Line Gross Gamma Activity Monitor Palisades Nuclear Plant Docket 50-255 License No. DPR-20

Dear Sir or Madam:

The Palisades Plant Offsite Dose Calculation Manual, Appendix A, Table A-1, Action 4, requires that a special report be submitted to the Nuclear Regulatory Commission within 30 days for the inoperability of RIA-2324, Main Steam Safety and Dump Valve Discharge Line Gross Gamma Activity Monitor, when the instrument is not restored to operable status within 7 days. The enclosed report summarizes the actions taken, the cause of the inoperability and the plans and schedule for restoring the instrument to operable status.

Summary of Commitments This letter contains no new commitments and no revisions to existing commitments.

PKAITAD Enclosure (1)

CC Administrator, Region III, USNRC Project Manager, Palisades, USNRC Resident Inspector, Palisades, USNRC

ENCLOSURE MAIN STEAM SAFETY AND DUMP VALVE DISCHARGE LINE GROSS GAMMA ACTIVITY MONITOR 1

BACKGROUND RIA-2324, Main Steam Safety and Dump Valve Discharge Line Gross Gamma Activity Monitor, was declared inoperable on January 11,2011, for replacement of the analog type monitor with a new modern digital monitor.

ACTIONS TAKEN The preplan ned alternate method of monitoring was placed in-service as a compensatory measure. Installation of the new digital monitor was completed and it was returned to operable status on January 28, 2011. However, the new digital monitor exhibited regula,r indication spikes, similar to previous indications seen on the analog monitor, which resulted in numerous unexpected control room alarms. On February 3, 2011, the monitor was again declared inoperable to allow troubleshooting the cause of the intermittent spikes.

CAUSE OF INSTRUMENT INOPERABILITY Troubleshooting identified that electromagnetic interference was inducing noise on the preamplifier power input from the monitor. This noise would enter the preamplifier and be amplified and returned to the monitor. The monitor interpreted the noise as a high radiation signal, resulting in spiking and subsequent alarms. The cause of the electromagnetic interference was determined to be insufficient grounding of the cabling for both the monitor and the preamplifier.

PLANS AND SCHEDULE FOR RESTORING INSTRUMENT OPERABILITY On February 9, 2011, a jumper was connected from the preamplifier board terminal board ground to the junction box chassis. This grounded the high voltage, signal, and overall cable shields at the preamplifier end of the cabling. Grounding of the cabling on both the monitor and the preamplifier ends has improved the overall shielding, resulting in elimination of the spikes. No noise (spiking) has been present on RIA-2324 since the time this jumper was installed.

RIA-2324 will be monitored for an appropriate period of time, with the compensatory measure remaining in place, before declaring the monitor operable. RIA-2324 is expected to be restored to operable status not later than March 11,2011.

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