05000331/LER-2014-002
| Duane Arnold Energy Center | |
| Event date: | 02-18-2014 |
|---|---|
| Report date: | 04-17-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material |
| Initial Reporting | |
| ENS 49838 | 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material |
| 3312014002R00 - NRC Website | |
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I. Description of Event:
On February 18, 2014 at 0944 CST, while operating at 100% power, the Control Room Supervisor (CRS) received a call that Door 245 and Door 239A, both in Secondary Containment Airlock 222 were opened concurrently. The doors being open at the same time caused a failure to meet SR 3.6.4.1.2 to verify that either the outer door(s) or the inner door(s) in each Secondary Containment access opening are closed. The identified condition caused Secondary Containment to be considered inoperable per TS LCO 3.6.4.1. The individuals involved each closed their respective doors upon encountering this unexpected condition. This action allowed SR 3.6.4.1.2 to be met, and restored Secondary Containment to an operable status. The CRS stationed individuals to control access to the door to ensure no other violations occurred.
This resulted in an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> reportable event. The Resident Inspector was notified, and Event Notification Number 49838 was made pursuant to 10 CFR 50.72(b)(3)(v)(C) due to a condition at the time of discovery that prevented the fulfillment of the Secondary Containment safety function. Secondary containment-leak tightness is required to ensure that the release of radioactive materials from the primary containment is restricted to those leakage paths and associated leakage rates assumed in the accident analysis and that fission products entrapped within the secondary containment structure will be treated by the Standby Gas Treatment System prior to discharge to the environment.
The Secondary Containment airlock utilizes an interlock device with an adjustable permanent magnet (mounted on the door), and an electromagnet (on the door frame) arranged in an electrical circuit so that door(s) are held closed and/or are allowed to open. It was determined that the adjustable permanent magnet on Door 245 allowed the airlock to sense Door 245 was closed prior to it latching closed. Because of this, the interlock no longer prevented Door 239A from opening, which ultimately led to both doors being opened concurrently. The Door 245 permanent magnet was adjusted, and surveillance testing was performed satisfactorily per Surveillance Test Procedure (STP) 3.6.4.1-02, Secondary Containment Airlock Verification, to verify the airlock was functioning properly. The airlock was then restored to functional status at 1323 on February 18, 2014.
There were no radiological releases associated with this event. There were no other structures, systems or components inoperable at the start of this event that contributed to the event.
II. Assessment of Safety Consequences:
There were no actual safety consequences associated with this event; the potential safety consequences were minimal. Both doors on the airlock were open simultaneously for less than 10 seconds, and were able to close immediately upon discovery of the condition.
This event will not be reported as a safety system functional failures since an engineering analysis (Corrective Action ACE1941869-02) was performed which determined that the system was capable of Duane Arnold Energy Center 05000-331 performing its safety function during events when the airlock was open for less than 10 seconds. The post-LOCA dose calculation does not credit secondary containment integrity for mitigation of on-site and off-site doses for the first 5 minutes of the event. Therefore, this event is bounded by the existing dose calculation.
This event did not result in a safety system functional failure. There were no automatically or manually initiated safety system responses.
Cause of Event:
An Apparent Cause Evaluation was completed. The evaluation identified the apparent cause of Door-245 and Door-239A being open at the same time as excess permanent magnet strength.
After the permanent magnet was adjusted, the interlock was able to prevent both doors from opening.
IV. Corrective Actions:
An operational check of the Secondary Containment door interlocks is performed monthly via STP 3.6.4.1-02, Secondary Containment Airlock Verification. STP 3.6.4.1-02 has been revised to check the permanent magnet for proper adjustment by verifying that the red interlock light(s) turn OFF as close to when the door latches as possible. The permanent magnet will then be adjusted as needed.
V. Additional Information:
Previous Similar Occurrences:
A review of DAEC Licensee Event Reports from the past 5 years identified one similar occurrence, reference LER 2013-006.
A review of the corrective action program identified additional occurrences of airlock conditions causing momentary secondary containment inoperability - two additional occurrences in the past year and nine occurrences in the past two years.
EIIS System and Component Codes:
I EL Interlock Reporting Requirements:
This event is being reported 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, 10CFR50.73(a)(2)(v)(C).