05000336/LER-2011-005
| Millstone Power Station - Unit 2 | |
| Event date: | 12-03-2011 |
|---|---|
| Report date: | 01-30-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material |
| LER closed by | |
| IR 05000245/2012003 (23 July 2012) | |
| 3362011005R00 - NRC Website | |
1. Event Description At 1230 on December 3, 2011, with Millstone Power Station Unit 2 (MPS2) operating at 100 percent power in Mode 1, the control room was notified that a door sweep became dislodged on a door credited as a boundary door for the Enclosure Building (EB) (door 205-(-25)-001). Operators declared the door inoperable and entered the Action for plant Technical Specification (TS) 3.6.5.2 Enclosure Building at 1235. TS 3.6.5.2 Action requires that the EB be restored to operable status with 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or be in Cold Shutdown within the next 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. Repairs to the door were completed and operators exited the Action at 1524 on December 3, 2011. The last known time where the door sweep was not dislodged was within 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> of the time of discovery.
The operability of the EB ensures that the release of radioactive materials from the primary containment atmosphere will be restricted to those leakage paths and associated leak rates assumed in the accident analyses.
TS Surveillance Requirement (SR) 4.6.5.2.2 stipulates that the Enclosure Building Filtration Train produces a negative pressure of greater than or equal to 1/4 inches water gauge (wg) in the Enclosure Building Filtration Region within 1 minute after an EBF Actuation Signal. When the door sweep dislodged, it created an opening estimated as 3/4 inch by 36 inches (27 square inches). Since there is currently no bounding analysis on the impact of this size opening on the ability of the Emergency Building Filtration System (EBFS)[BD] to produce the required negative pressure, the EB was declared inoperable.
This condition is being reported pursuant to 10 CFR 50.73(a)(2)(v)(C) as an event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material.
2. Cause The direct cause of the door seal failure was that the mounting hardware (screws) loosened and fell out. The apparent cause is the door was not being properly maintained.
3. Assessment of Safety Consequences The safety consequences of this event were low. The door was repaired within three hours of discovery and within 21 hours2.430556e-4 days <br />0.00583 hours <br />3.472222e-5 weeks <br />7.9905e-6 months <br /> of the last known operable condition. The safety function of the EBFS is to control and monitor radioactive releases from Containment and Emergency Core Cooling Systems (ECCS) leaks in the event of a Loss of Coolant Accident (LOCA). Operability of the EBFS is necessary to ensure doses to the public and control room operators do not exceed 10 CFR 50.67 limits in the event of a design basis LOCA. This function is achieved when EBFS is operational by maintaining a required negative pressure of 1/4 inches wg. It is not credited for any other design basis accidents.
Reactor coolant radioactivity levels were normal (significantly less than Technical Specification limits). Based on a review of effluent and containment radiation monitors, there was no indication of abnormal Reactor Coolant System, containment or ECCS leakage. Based on these conditions, there were no adverse consequences to the health and safety of the public or the plant and its personnel resulting from this EB boundary breach.
4. Corrective Action The door was repaired. Doors that are part of the Enclosure Building boundary have been added to the preventive maintenance program.
Additional corrective actions are being taken in accordance with the station's corrective action program.
5. Previous Occurrences MPS2 where the EBFS was not able to meet the acceptance criteria of a negative pressure of greater than or equal to 1/4 inch wg. The direct cause for not meeting the Enclosure Building drawdown acceptance criteria was that sliding bushings on the main steam safety valves exhaust piping had dislodged and not reseated.
Energy Industry Identification System (EllS) codes are identified in the text as [XX].