ENS 50786
ENS Event | |
|---|---|
15:34 Feb 4, 2015 | |
| Title | Control Room Ventilation Inoperable Due to Mispositioned Ventilation Inspection Port |
| Event Description | At 0934 CST hours on Wednesday, February 4, 2015 during a housekeeping inspection, an inspection port (18x18 inch opening) on the Control Room Fresh Air (CRFA) System was discovered open. The opening of the inspection port resulted in the loss of safety function for both trains of CRFA as a loss of control room envelope boundary.
The cause of the inspection port being open is currently unknown and is under investigation. The Control Room was notified and an operator immediately secured the inspection port returning both trains of CRFA to operable status. The reactor was at approximately 100 percent power at the time of the discovery of the event. The Limiting Condition for Operation (LCO) Technical Specification 3.7.3, Control Room Fresh Air (CRFA) System, is two CRFA subsystems shall be OPERABLE. This Technical Specification is applicable in MODES 1, 2, and 3, and during operations with a potential for draining the reactor vessel. This condition is reportable as an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> call in accordance with 10 CFR 50.72(b)(3)(v). The licensee has notified the NRC Resident Inspector.
Grand Gulf Nuclear Station is retracting this event notification based on the following: Regulatory Guidance in NUREG-1022, Revision 3, Event Reporting Guidelines 10 CFR 50.72 and 50.73, Sections 2.8 Retraction and Cancellation of Event Reporting and 4.2.3 ENS Notification Retraction. Once the inspection port was discovered open, the control room was notified and an operator immediately secured the inspection port. After the port was secured, detailed engineering calculations were initiated to analyze the situation. Due to the time needed to perform the detailed calculations versus the time required for notification (8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />) a conservative decision was made to report the event based on knowledge at the time of the event and rough calculations. Subsequently detailed calculations were performed to evaluate and support system operability evaluation. The calculations evaluated dose sensitivity analysis for the increased Control Room in-leakage due to the open inspection port. A test determined the control building in-leakage to be 585 cfm, the in-leakage from other sources to be 15 cfm, and the calculation determined the flow rate through the opening to be 1245 cfm. This total in-leakage rate of 1845 cfm is below the maximum allowable control building in-leakage of 2000 cfm. The calculation performed a sensitivity analysis with recent ILRT results applied and concluded that 4200 cfm in-leakage is permissible to maintain within the limits of 10CFR50.67. By subtracting the measured in-leakage assuming all ports closed ( 585+15= 600 cfm) from the in-leakage permissible to maintain within the limits of 10CFR50.67 (4200 cfm), there Is a resulting margin of 3600 cfm. Technical Specification 3.7.3, Control Room Fresh Air (CRFA) System, requires TWO CRFA subsystems shall be OPERABLE, and the calculations show that the CFRA was OPERABLE. The calculations lead to the conclusion that the system would have fulfilled its safety function needed to mitigate the consequences of an accident. Therefore, this event is not an 8-hour notification under 50.72(b)(3)(v). The licensee informed the NRC Resident Inspector. Notified R4DO (Allen). |
| Where | |
|---|---|
Grand Gulf  Mississippi (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+2.38 h0.0992 days <br />0.0142 weeks <br />0.00326 months <br />) | |
| Opened: | Ryan Meyer 17:57 Feb 4, 2015 |
| NRC Officer: | Daniel Mills |
| Last Updated: | Feb 13, 2015 |
| 50786 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |