05000341/LER-2013-003
| Fermi 2 | |
| Event date: | 11-24-2013 |
|---|---|
| Report date: | 01-22-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material |
| 3412013003R00 - NRC Website | |
Initial Plant Conditions:
Mode 1 Reactor Power 100 percent
Description of the Event
On November 24, 2013, at approximately 00:01 hours EST, the non-safety related Reactor Building Heating Ventilation and Air Conditioning (RBHVAC) [VA] system tripped due to improper drainage of a steam coil heater [CL] through its steam trap. Secondary Containment [NH] differential pressure rose above -0.125 inches water column (WC), reaching a maximum of +0.08 inches WC. At 00:04 hours EST, the Standby Gas Treatment System (SGTS) was manually started and Secondary Containment differential pressure decreased to less than -0.125 inches WC.
Technical Specification Surveillance Requirement (SR) 3.6.4.1.1 verifies that Secondary Containment vacuum is greater than or equal to 0.125 inches of vacuum water gauge. Limiting Condition for Operation 3.6.4.1, Condition B, Secondary Containment inoperable was entered due to not meeting SR 3.6.4.1.1, and later exited when Secondary Containment pressure was restored to less than -0.125 inches WC. The Emergency Operating Procedures (EOPs) were entered based on high Secondary Containment differential pressure and later exited at 00:09 hours EST.
The RBHVAC system has 14 steam coil heaters and 14 corresponding low temperature switches. The switches monitor the temperature of the heater coils to ensure they do not freeze. If any switch trips on low temperature, the RBHVAC system automatically trips. In this event, one of the switches tripped on low temperature (35°F decreasing) causing a trip of the RBHVAC system.
Upon determination of the cause of the trip and replacement of the steam trap, the RBHVAC system was restarted and the SGTS shutdown at 23:46 hours EST on November 24, 2013.
The loss of Secondary Containment function is reportable under 10 CFR 50.73(a)(2)(v)(C) as an event or condition that could have prevented the fulfillment of a safety function needed to control the release of radioactive material. An 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> NRC event notification (No. 49575) was previously made to the NRC based on meeting the reporting criteria of 10 CFR 50.72(b)(3)(v)(C).
Significant Safety Consequences and Implications The purpose of SR 3.6.4.1.1 is to verify Secondary Containment integrity. This SR ensures that the Secondary Containment boundary is sufficiently leak tight to preclude exfiltration under expected wind conditions.
The non-safety related RBHVAC system is not relied upon to mitigate consequences of an accident. Secondary Containment, in conjunction with the SGTS, is designed to minimize release of radioactive material which may result from an accident.
The two principal accidents for which Secondary Containment integrity is assumed are a loss of coolant accident (LOCA) and a fuel handling accident (FHA). Neither of these accidents occurred coincident with this event.
The SGTS is designed to start automatically to maintain the reactor building at a negative pressure relative to the outside atmosphere during transient and accident conditions. The SGTS can also be manually started from the Main Control Room [NA]. During this event, Division 1 of SGTS was manually started (no transient or accident had occurred that would automatically start SGTS) and restored the required Secondary Containment vacuum approximately 3 minutes after RBHVAC tripped. There were no radiological releases associated with this event.
Therefore, this event did not pose an actual threat to the health and safety of the public.
Cause of the Event
RBHVAC tripped on low heater coil temperature due to lack of steam flow through a heating coil caused by improper draining of the downstream steam trap. Investigation revealed corrosion and a cracked drain seat in the associated steam drain.
Corrective Actions
The malfunctioning heating coil steam trap was replaced and tested. The RBHVAC system was returned to normal operation. Secondary Containment differential pressure was stabilized at less than -0.125 inches WC, and the SGTS was shutdown at 23:46 hours EST on November 24, 2013.
Since this event was potentially caused by a corrosion related failure, preventive maintenance is being scheduled to inspect, and clean or replace the RBHVAC steam traps and strainers.
Additional Information
A. Failed Component: Steam Drain Component: Steam Trap [TRP] T4100D043N Function: Discharge condensate as it is formed Manufacturer: SPIRAX SARCO Model Number: FT-15, 3/4" — 1" Failure Cause: Corrosion and a cracked drain seat B. Previous Licensee Event Reports (LERs) on Similar Problems:
equipment malfunction. However, the cause of that event was related to damper sequencing. Therefore, the corrective actions for that event would not have precluded this event.