ENS 48429
ENS Event | |
|---|---|
05:10 Oct 22, 2012 | |
| Title | Potential Condition Could Bypass Flooding Barriers and Affect Residual Heat Removal Equipment |
| Event Description | During a walkdown evaluating potential for adverse consequences of site flooding, per 10CFR50.54(f) request, a condition was identified which had the potential to adversely impact the ability to address external flooding conditions. The old Emergency Offsite Facility (which currently houses information technology offices) has a drain pipe which connects to Sump AA in the Augmented Radwaste (ARW) building and bypasses the flooding barriers erected per maintenance procedure 7.0.11 in the event of site flooding.
Per the USAR, the basis for site flooding is a flood with concurrent surge effects on exposed safety related structures reaching an elevation of 905 feet. This elevation is 2.0 feet above the grade elevation of 903 feet. Flooding protection for important site facilities is provided by installing temporary barriers protecting to elevation 906 feet. Primary and Secondary Flood Barriers are installed at the ARW building external entrances on the 903 feet elevation to protect the Reactor Building from external flood water. The drain piping from the old EOF floor drain and shower is piped directly to Sump AA in the ARW building basement. This is a 3 inch pipe which drains by gravity. There are no isolation features on the pipe, and no barriers to flooding are provided for this facility, thus the potential exists to bypass the flood barriers which would be erected around the ARW Building. Flooding of the building basement could result, disabling processing equipment. If the basement fills up, flood waters could enter the Reactor Building through the internal entrance, which has no additional protection installed. Floodwaters could then affect equipment which is required to remove residual heat. This condition has been determined to be reportable per 50.72(b)(3)(v) - Any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of SSCs that are needed to remove residual heat. The potential condition was identified on 10/20/2012. Evaluation of the condition and the potential impact was completed and reportability determined on 10/22/2012. The condition has been entered into the Corrective Action Program. The licensee notified the NRC Resident Inspector.
During a walk down evaluating the potential for adverse consequences of site flooding per 10CFR50.54(f) request, a condition was identified which had the potential to adversely impact the ability to address external flooding conditions. The Optimum Water Chemistry (OWC) building has 5 floor drains, at ground level elevation 903 ft, which connect to a common 3 inch drain pipe which connects to a sanitary sump located in the Turbine building, at an elevation of 882 ft, and bypasses all flooding barriers erected per maintenance procedure 7.0.11 in the event of site flooding. Per the USAR, the basis for site flooding is a flood with a concurrent surge effect on exposed safely related structures reaching an elevation of 905 ft. This elevation is 2 ft above the grade of the floor drains. Flooding protection for important site facilities is provided by installing temporary barriers which provide protection to an elevation of 906 ft. Primary and secondary barriers are installed at the Turbine building external entrances to protect the Reactor building from external flood waters. Additional secondary barriers are erected inside the Turbine building to provide additional protection to the Diesel Generator rooms. The drain piping from the OWC building floor drains is piped directly to the sanitary sump located in the Turbine building. There are no isolation features on the piping and no barriers to flooding are erected between the Turbine building and Reactor building thus the potential exists to bypass the flood barriers erected around the Turbine building. Flooding of the Turbine building could result in the accumulation of water in sufficient quantities to fill the Turbine building 882.5ft elevation to the height of the external floodwaters which would then be allowed to flow unimpeded by flooding barriers to the Reactor building through the internal entrance which has no additional barriers installed. These floodwaters could then affect equipment, located within the Reactor building, which is required to remove residual heat. This condition has been determined to be reportable per 50.72(b)(3)(v) - Any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of SSC's. that needed to remove residual heat. This condition was identified at 1550 [CDT on] 10/22/2012 and has been entered into the Corrective Action Program. The licensee informed the NRC Resident Inspector. Notified R4DO (Hagar).
This notification is being made to retract Event Notification EN #48429 which reported a loss of safety function due to the discovery of two flow paths (one from the old Emergency Operating Facility and one from the Optimum Water Chemistry building) where an external event flood event at 905 feet would result in flooding of the Turbine and Radwaste basement and eventually the Reactor building basement. Upon further review, the design basis Probable Maximum Flood for CNS is 903 feet. The two water entry points discussed in the Event Notification are above the 903 foot elevation. Wave energy would be dissipated before reaching any of the main buildings so there would be a minimal influx of water into the structures. As such, there is no loss of safety function for equipment in the Reactor building basement. NPPD therefore retracts Event Notification EN #48429. The NRC Resident Inspector has been notified. Notified R4DO (Farnholtz). |
| Where | |
|---|---|
Cooper  Nebraska (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat | |
| Time - Person (Reporting Time:+-1.35 h-0.0563 days <br />-0.00804 weeks <br />-0.00185 months <br />) | |
| Opened: | John Myers 03:49 Oct 22, 2012 |
| NRC Officer: | Donald Norwood |
| Last Updated: | Nov 9, 2012 |
| 48429 - NRC Website | |