05000389/LER-2010-001
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. | |
| Event date: | |
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| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3892010001R00 - NRC Website | |
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)
Description of the Event
During the performance of response time testing of Unit 2 CROAI radiation monitors (RIM-26-61, RIM-26-62, RIM-26-65 and RIM-26-66), an unexpected failure mode of the radiation monitors was encountered. Testing was being performed in two modes: (1) high radiation and (2) high radiation with loss-of-offsite power (LOOP). The CROAT radiation monitors [EIIS: IL] failed to generate a high radiation alarm signal after a LOOP. Engineering was contacted and testing was performed on all channels with the same results. The high radiation with the LOOP test failed and the CROAIs were declared inoperable and the appropriate Technical Specifications actions were taken.
On June 30, 2009, St. Lucie Plant notified General Atomics of the anomaly regarding the Model RM-80 radiation monitoring system. The firmware was updated, installed and successfully tested on all four CROAI radiation monitoring channels.
An extent of condition review determined no immediate operability concerns existed for the other safety-related or Technical Specification monitors..
Cause of the Event
General Atomics' Part 21 identified the defect to be in the RM-80 firmware which is manifested by a failure of the RM-80 to maintain alarm relays in an alarm condition under certain specific conditions. Specifically, if the radiation monitor is already in a High and/or alert alarm state, and subsequently suffers a loss of power, then upon restoration of power to the unit, the RM-80 high and/or alert alarm relays are not re-energized by the RM-80 firmware. This in turn prevents the relays that are located in the RM-80 from performing their safety function of starting the emergency filtration fans during emergency diesel generator.(EDG) load sequencing. A failure to actuate the fans could result in a potential safety hazard to personnel by not filtering infiltration with the control room.isolated which could result in unintended overexposure to radiation.
The error in firmware only affects annunciator panels or safety-related equipment that is connected to the RM-80 alert and high alarm relays.
Analysis of the Event
Evaluation of the event determined the RM-80 firmware anomaly resulted in the radiological consequences for a SGTR accident potentially exceeding those analyzed in UFSAR. During the SGTR with concurrent LOOP, the RM-80 firmware anomaly would result in the failure to start the associated emergency filtration fans, HVE-13A and HVE- 13B, during EDG load sequencing. This results in isolation of the control room without any filtered recirculation flow. Based on an assumed quantity of unfiltered in-leakage into the control room, delayed manual initiation of HVE-13A or HVE-13B, and re-quantifying control room dose, it .was concluded the radiological consequences for such a SGTR accident would exceed the 10 CFR 50.67 limit of 5 REM TEDE, exceeding UFSAR Section 15.6.3 results. Therefore, this event is reportable in accordance with the requirements of 10 CFR 50.73(a)(2)(v).
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Analysis of Safety Significance This is a legacy issue. RIM-26-61, RIM-26-62, RIM-26-65, and RIM-26-66 were modified via MSP 09097, Revision 1 to correct the firmware anomaly. For the period in question (between September 3, 2006 and June 29, 2009) operators would have been able to recognize the failure of the HVE-13A and HVE-13B fans to automatically start.
Emergency Operating Procedure 2-E0P-04, "Steam Generator Tube Rupture," provides guidance for coping with a SGTR with a concurrent LOOP. Emergency Operating Procedure 2-EOP-04 requires operators to ensure that proper actuation of engineered safety features actuation system (ESFAS) components has occurred. The delayed manual initiation of HVE-13A and/or HVE-13B would have permitted the operators to establish control room habitability to permit successful event termination after receiving a dose judged to marginally exceed 5 rem TEDE.
Corrective Actions Taken The corrective and supporting actions are entered into the site correction action program (CAP). Any changes to the proposed actions will be managed under the CAP.
Immediate Corrective Actions Taken 1. Notified General Atomics of RM-80 anomaly.
2. Updated firmware was. successfully installed and tested on all four CROAI radiation monitoring channels.
3. Extent of 'condition review was performed and determined no immediate operability concerns existed for the other safety-related or Technical Specification monitors.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)
Corrective Actions
1. Created Work Order 39016634-01 to track and verify installation of the RM-80 firmware versions.
2. Perform a human factors evaluation to address the loss of annunciation functions for RM-26-11 and RM-45-1. If the functionality of the local alert lights, local high radiation lights, or local alarm horns is affected, then an evaluation will be performed; and if warranted, a firmware modification will be obtained from General Atomics.
Similar Events A search of the corrective action database for St. Lucie was performed to identify events related to General Atomics Model RM-80 Radiation Monitoring System and none were found. This event is not considered a repeat event.
Failed Components
General Atomics Electronic Systems, Inc. radiation monitoring system Model RM-80 firmware. GA-ESI assembly firmware number: SID136.02. Affected plant tag numbers:
RIM-26-61, RIM-26-62, RIM-26-65, and RIM-26-66.