05000353/LER-2010-001
| Limerick Generating Station, Unit 2 | |
| Event date: | 04-29-2010 |
|---|---|
| Report date: | 06-25-2010 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3532010001R00 - NRC Website | |
Unit Conditions Prior to the Event Unit 2 was in Operational Condition (OPCON) 1 (Power Operation) at approximately 100% power. There were no structures, systems or components out of service that contributed to this event.
Description of the Event
On Thursday April 29, 2010, Limerick Unit 2 was operating at approximately 100% power. A test deficiency was identified during a review of a completed Unit 2 functional test on the reactor enclosure cooling water radiation monitoring system (RECW-RMS). The test contained an incorrect method for calculating the Hi Hi Alarm setpoint of three times background radiation. The test incorrectly directed use of the background radiation level from the previous month's test.
An investigation of tests performed over the past three years determined that the Unit 2 radiation monitor was rendered inoperable by the test deficiency on March 19, 2010 during performance of the functional test. The test directed use of the prior month's test background radiation level when determining the alarm setpoint. The radiation monitor was restored to operable status in April 22, 2010 following successful performance of the functional test which restored the alarm setpoint to the required value.
The radiation monitor was inoperable for 34 days.
Technical Specification (TS) 3.3.7.1 requires one operable RECW radiation monitor channel "at all times." With the radiation monitor inoperable, Table 3.3.7.1-1 Action 72 applies. Action 72 requires obtaining and analyzing RECW grab samples every 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The required grab samples were not collected until the radiation monitor was discovered to be inoperable following the identification of the surveillance test procedure error.
This event resulted in a condition prohibited by Technical Specifications. Therefore, this LER is being submitted pursuant to the requirements of 10CFR50.73(a)(2)(i)(B).
Analysis of the Event
There were no actual safety consequences associated with this event. The potential safety consequences of this event were minimal. The RECW-RMS Hi-Hi alarm setpoint was not within the required range but the Hi alarm setpoint was functional and would have alerted Operations of an increase in RECW radiation levels during the affected period. In addition, the RECW-RMS count rate was continuously indicated and recorded in the control room and was monitored during routine control panel walkdowns. The service water radiation monitor remained operable during the affected period.
The RECW-RMS is designed to detect leakage from contaminated systems into the RECW system, which provides a barrier to release to the environment. Service water provides the cooling medium for the RECW heat exchanger and is also designed with a process radiation monitor.
The RECW-RMS is described in Limerick UFSAR, Sections 7.7.9.12 and 11.5.2.2.13. The system is classified as a non-safety related process radiation monitoring system (PRMS). The system provides an upscale/downscale trip signal to an annunciator in the control room. The system provides no control trip function. Radiation data is continuously recorded in the control room.
Cause of the Event
The condition was caused by a technical human performance deficiency during revision of the affected surveillance test in 2003.
Corrective Action Completed The RECW radiation monitor functional tests for both units were revised to require use of the current background radiation level when calculating the alarm setpoints.
Previous Similar Occurrences There was one previous similar occurrence of reportable inoperability of TS equipment due to a surveillance test error in the past three years. Unit 2 LER 2008-003 reported that the RECW radiation monitor was rendered inoperable due to a personnel error by the technician performing the test. The corrective actions for the prior event addressed the test performance error and were not applicable to this event. The test revision error being reported occurred in 2003 which preceded this similar event.
Component data:
Component description: Reactor Enclosure Cooling Water Radiation Monitor Component number: RISH-013-2K606 Manufacturer: G080 General Electric Company Model number: 145C3284AAG001