05000352/LER-2009-002
| Limerick Generating Station, Unit 1 | |
| Event date: | 12-09-2008 |
|---|---|
| Report date: | 04-22-2009 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3522009002R00 - NRC Website | |
Unit Conditions Prior to the Event Unit 1 was in Operational Condition (OPCON) 1 (Power Operation) at approximately 100% power. Unit 2 was in Operational Condition (OPCON) 1 (Power Operation) at approximately 100% power. There were no other structures, systems or components out of service that contributed to this event.
Description of the Event
On Friday November 21, 2008 a charcoal sample was removed from "A" Control Room Emergency Fresh Air Supply System (CREFAS) Subsystem (EIIS:UG) charcoal adsorber (EIIS:ADS) during performance of the 24-month "A" CREFAS Charcoal Analysis surveillance test (ST-4-078-801-0). The sample was shipped to a vendor for analysis. The analysis results became available on Tuesday December 9, 2008, at 0745 hours0.00862 days <br />0.207 hours <br />0.00123 weeks <br />2.834725e-4 months <br />, which was 18 days after the sample was taken. The analysis results failed the test acceptance criteria that required the methyl iodide penetration to be less than 2.5 percent.
The test results indicated that methyl iodide penetration was 5.013 percent. The "A" CREFAS subsystem was declared inoperable. The "A" CREFAS subsystem charcoal bed was replaced and the subsystem was returned to operable status on Thursday December 11, 2008 at 2022 hours0.0234 days <br />0.562 hours <br />0.00334 weeks <br />7.69371e-4 months <br />.
At the time the sample was removed there was no firm evidence that "A" CREFAS was inoperable. The sample analysis failure on December 9, 2008, provided firm evidence that the "A" CREFAS subsystem charcoal had exceeded the Technical Specification (TS) 3.7.2 CREFAS surveillance requirement for methyl iodide penetration to be less than 2.5 percent on November 21, 2008, when the sample was removed. The "A" CREFAS subsystem charcoal was restored to less than 2.5 percent methyl iodide penetration on Thursday December 11, 2008. This resulted in a period of 20 days that the "A" CREFAS subsystem was inoperable since it could not satisfy the surveillance requirement. TS 3.7.2 Action a.1 requires restoration of an inoperable CREFAS subsystem within 7 days. This requirement was not satisfied.
However, the subsystem was restored within three days of discovery of the condition.
This event resulted in the nuclear power plant being in a condition prohibited by Technical Specifications. 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 "B" CREFAS subsystem was operable during this period. In addition the "A" CREFAS subsystem was capable of operating at near design capacity. The potential increase in accident dose to the licensed operators in the main control room was determined to be negligible.
The TS surveillance requirement 4.7.2.1.c.2 states the following:
Verifying within 31 days after removal that a laboratory analysis of a representative carbon sample obtained in accordance with Regulatory Position C.6.b of Regulatory Guide 1.52, Revision 2, March 1978, shows the methyl iodide penetration of less than 2.5% when tested in accordance with ASTM D3803-1989 at a temperature of 30°C (86°F) and a relative humidity of 70%.
UFSAR section 6.5.1.2.1.d describes the design bases for the CREFAS charcoal adsorber. It states the following:
The charcoal adsorber is rated 95.0% for trapping of radioactive iodine as elemental iodine (I2) and 95.0% trapping of radioactive iodine as methyl iodide (CH3I) when passing through charcoal (2 inch bed depth) at 70% relative humidity. The air residence time in the 2 inch charcoal bed is not less than 0.25 seconds.
The vendor test in accordance with ASTM D3803-1989 specifies an acceptance criterion of 97.500 percent efficiency, which correlates to 2.5 percent methyl iodide penetration. The plant design basis assumes the charcoal is 95 percent efficient. Therefore, a successful analysis ensures that a safety margin factor of 2 is maintained.
The actual analysis determined the methyl iodide penetration was 5.013 percent with an efficiency of 94.987 percent.
This exceeded the plant design basis by 0.013 percent, which was less than the test uncertainty of plus or minus 0.052 percent.
Cause of the Event
The cause of the event was unplanned inoperability of the "A" CREFAS subsystem due to an increase in charcoal methyl iodide penetration. Charcoal bed performance may be adversely affected by several factors including bed age, run time, and contaminants. The TS allowed outage time was exceeded during the period when the routine sample was being analyzed by the vendor. Operations management was notified of the unsatisfactory analysis results when they became available but the seven-day TS allowed outage time had been exceeded prior to the notification.
Corrective Action Completed The "A" CREFAS subsystem charcoal bed was replaced and tested.
Charcoal bed age and penetration data have been added as inputs to bed performance monitoring and replacement decision making.
Previous Similar Occurrences There were no previous similar events during the last three years where charcoal sample analysis results rendered a safety system subsystem inoperable.
Component data:
System:�Control Room Emergency Fresh Air Supply System Component: ADS Adsorber Component Number:�0A-F161 Manufacturer: C780 CVI Corp Charcoal supplier: NUCON International, Inc.