05000454/LER-2013-001
| Byron Station, Unit 1 | |
| Event date: | 09-17-2013 |
|---|---|
| Report date: | 11-18-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4542013001R00 - NRC Website | |
A. Plant Condition Prior to Event Event Date/Time: September 17, 2013 / 1140 hours0.0132 days <br />0.317 hours <br />0.00188 weeks <br />4.3377e-4 months <br /> CST Unit 1 - Mode 1 - Power Operations, Reactor Power 100 percent Reactor Coolant System [AB]: Normal operating temperature and pressure.
B. Description of Event
On September 17, 2013, the plant was in Mode 1 with reactor power at 100 percent. At 1140 hours0.0132 days <br />0.317 hours <br />0.00188 weeks <br />4.3377e-4 months <br />, charcoal adsorber [ADS] samples were removed from the A Train VC recirculation charcoal bed filter, OVCO2FA, to perform charcoal sample removal/analysis in accordance with the Ventilation Filter Testing Program as required by Control Room Ventilation System Technical Specification (TS) Surveillance Requirements 3.7.10.2 (Perform Required VC Filter Testing) and 5.5.11.c (Laboratory test of a sample of the charcoal adsorber). The samples were transported to a vendor for analysis with results due within 31 days per Technical Requirements Manual (TRM) Appendix K, Section 1.5.1.f.2 (Verify Carbon Sample Methyl Iodide Penetration less than 4.0 percent).
On September 26, 2013, the charcoal sample analysis results were received from the test vendor, showing the charcoal penetration value was 6.197 percent. The limit for charcoal penetration per the surveillance procedure is less than 4.0 percent, thus the sample results did not satisfy the procedural acceptance criteria. Main control room operators were notified of the charcoal sample analysis results at 0645 hours0.00747 days <br />0.179 hours <br />0.00107 weeks <br />2.454225e-4 months <br /> and they entered Action A.1 requirements of TS 3.7.10 that requires restoration of the inoperable A Train CREFS to operable status within 7 days.
The degraded charcoal in the A Train CREFS was replaced and retested satisfactorily on September 27, 2013. The A Train CREFS was declared operable on September 27, 2013, at 2057 hours0.0238 days <br />0.571 hours <br />0.0034 weeks <br />7.826885e-4 months <br />.
C. Cause of Event
The cause of the unsatisfactory sample test result is that the applicable charcoal banks had reached their end of life. No direct correlation with the degraded charcoal performance to this point in operating life was able to be identified.
D. Safety Significance
The purpose of the control room emergency filtration system is to provide clean filtered air to control building occupants to limit post accident radiation exposures to 5 Rem Total Effective Dose Equivalent (TEDE) or less. Exelon Engineering compared the documented test results for methyl iodide penetration of the charcoal sample with the values assumed in analyses for the Fuel Handling Accident (FHA) and for Loss of Coolant Accidents (LOCA) in Chapter 15 of the Updated Final Safety Analysis Report (UFSAR). The Byron Technical Specifications assume an overall efficiency of 96 percent; however, Alternate Source Term design criteria for Byron demonstrate that an efficiency of 90 percent is sufficient for the filter unit to perform its prescribed safety function. Based on the above, the level of degradation of the charcoal found in the surveillance test would not have prevented the filter/adsorber units from performing the assumed design safety function. The B Train CREFS was not affected by this event and remained operable. Therefore, the significance of this issue is considered low.
E. Corrective Actions
The A Train Control Room Emergency Filtration System charcoal bed was replaced and tested on September 27, 2013.
F. Previous Occurrences
There have been no previous occurrences of this nature in the previous three years.