05000219/LER-2013-001, Regarding Automatic Reactor Scram Due to an Invalid Intermediate Range Monitor (IRM) Scram Signal
| ML14051A545 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 02/06/2014 |
| From: | Peak R Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RA-14-012 LER 13-001-00 | |
| Download: ML14051A545 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2) |
| 2192013001R00 - NRC Website | |
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t.4 RA-14-012 10 CFR 60.73 February 6,2014 U. S. Nuclr Regulatory Commiwon Atn: Documwt Cotrol Desk Washington, DC 20656 -0001 Oyster Croek Nuclear Generating Stdon Renewed Facility Operafti Uicnse No. DPR-16 NIRc Q*
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Subject:
Lcensee Event Report (LER) 2013-0000, Aunadc R tor SCRAM due to an Invald Intermediate Range Moni (lM) SC.RM SignW, Revision I Enclosed is LER 20134O01-01, Automailc Reactor SCRAM due toan invalid Intm fd Range Monitor ONR)
SCRAM SiOWa, Revision 1. The LER "a rvise to aft9 supploemeal Infomnation a quhpd by Revision 0. T~s ovet did not affect the NOW and safety of to ptulic or plant peronn.
This event did not re*ult In a safety system functional failure. There are no regulatory conNiMmens made In "* LER submttl.n Should you have 'ay questions To this ltt.
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Respectfuly, Russell R. Peak Oyster Creek Nuclea Genertin Statio Enclosure: NRC Form 366, LER 2013.W0011 cc:
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w ajfi sjwnwr4J On 10/3/13 at 0643 EDT, during reactor startup, with the reactor critical and power in the intermediate range, an automatic reactor scram occurred due to an Invalid (noise) Intmermedlate range monitor (IRM) scram sial processed on both RPS trip systems. The SCRAM was caused by both Reactor Protection Systems (MPS) channels recelving simultaneous IRM Hi-Hi signals on IRM channels 12, 13, 14, 17, and 18.
Testing cxodcted by Analysis and Measurement Services (AMS) identified low shield to ground insulation resistances on mul"ip channels of the IRM system. This condition allowed significant noise coupling to occur which resulted in the erratic behavior of the IRM channels that led to the full reactor SCRAM. The noise which was received by the IRM channels has been determined to be caused by a shorted SRM 22 detector. The short circuit provided a path to ground for the high voltage potential used to bias the SRM detector.
The root cau of the SCRAM was the susceptibility of the Intermediate Range Monitor (IRM) channels to electrical noise due to low shield to ground insulation resistance. Contributng to tfts event was an interal fault of Source Range Monitor (SAM) detector 22 which caused a significant amount of noise to propagate onto the IRM channels resulting In spiking. SRM-22 was replaced during a subsequent maintenance outage on November 20, 2013.
There were no safety consequences as a result of this event. Al control rods fury inserted and plant response was as expected. This event Is being reported pursuant to: I0CFR50.73(a)(2)(Qv)(A) due to an automatic actuation of the Reactor Protection System (RPS).
NRC FORM NO6 (10-2010)
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, 3 2013 001 01 NARRAIVE Plant Conditions Pior To Event Event Date: October 3, 2013 Event Time: 0643 EDT Unit 1 Mode: Startup Power Level: 0%
Descrption of Event An automatic reactor SCRAM occurred on October 3, 2013 at 0843 EDT during the plant startup from 1M30. The SCRAM was caused by both Reactor Protection Systems (RPS) channels receiving simultaneous IRM HI-Hi signals on IRM channels 12, 13, 14, 17, and 18. The IRMs all became erratic at the same time, cycling between Hi-HI and downscale. Source Range Monitors (SRMs) 23 and 24 also became erratic at Otis time. These erratic output signals occurred coincidentally with Source Range Monitor (SRM) 22 withdrawal to maintain counts in their acceptable range.
Testing conducted by Analysis and Measurement Services (AMS) Identified low shold to ground Insulation resistances on multiple channels of the IRM system. This condition allowed significant noise coupling to occur which resulted in the erratic behavior of the IRM channels that led to the full reactor SCRAM. The noise which was received by the IRM channels has been determined to be caused by a shorted SRM 22 detector. The short circuit provided a path to ground for the high voltage potential used to bias the SRM detector.
Analys of Event A full SCRAM was received due to actuation of RPS sub-channel relays I KI, 1 K2, and 2K(2. It was determined from PPC trend data that IRM9 12-14, 17, and 18 caused the SCRAM. Atthe time of the event, IRMs 11 and 16 were bypassed. Further troubleshooting identified that the SCRAM occurred while withdrawing SRM detectors out of the core. It was identified that SRM 22 motion caused spiking of all IRM channels.
There were no safety consequences as a result of this event. Al control rods fully inserted and plant response was as expected. This event is being reported pursuant to: 10CFRS0.73(a)(2)(v)(A) due to an automatic actuation of the Reactor Protection System (RPS).
Cauea of Event Troubleshooting has identified the motion of SRM-22, In and out of the core, as the souroe of noise causing spiking on the IRMs. When the high voltage to the SRM-22 detector was disconnected, there was no IRM spiking when the SRM detector was moved.
The root cause of the SCRAM was the suscepdt of the Intermediate Range Monitor (lRM) channels to electrical noise due to low shield to ground insulation resistance. Contributing to this event is an internal fault of Source Range Monitor (SRM) detector 22 which caused a significant amount of noise to propagate onto the IRM channels resulting in spiking.
NRC FORM 86A (10-2010)
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NUCLEAR REULATORY COMMISSION (10-2010)
LICENSE EVENT REPORT (LER) us OL om o CONTINUATION SHEET
- 1. FACNJT HARIG DOCKET_ -
LE NUMIR Oyster Creek, Unit 1 0 50 0 02 19 3
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2013 001 01
NARRATIVE
SRM-22 high voltage cable was disconnected per the simple troubleshooting process. When the high voltage to the SRM-22 detector was disconnected, there was no IRM spiking when the SRM detector was moved. SRM-22 was not initially repaired, but electrically Isolated. SRM-22(General Electric Part number 112C3144G037) was subsequently replaced during a Maintenance outage on November 20, 2013.
I Actions were created to troubleshoot and repair low insulation resislances on IRM channels and implement a mitigation strategy to address EMI issues with the Nuclear Instrumentation System.
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oce There have been no similar Licensee Event Reports associated with this component failure submitted at OCNGS In the last two years.
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