05000338/LER-2015-003
| Event date: | 05-08-2015 |
|---|---|
| Report date: | 07-01-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3382015003R00 - NRC Website | |
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1.0 DESCRIPTION OF THE EVENT On May 11, 2015, it was identified that, on May 8, 2015 at 0358 hours0.00414 days <br />0.0994 hours <br />5.919312e-4 weeks <br />1.36219e-4 months <br />, both ventilation fans (EIIS Component FAN) for the Unit 2 Motor Driven Auxiliary Feedwater (AFW) Pump House (EIIS System BA) were simultaneously tagged out for preventive Motor Driven AFW Pump House were returned to operable on May 8, 2015 at 1630 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20215e-4 months <br />.
Based on the identification that both ventilation fans for the Unit 2 Motor Driven AFW Pump House were simultaneously tagged out for maintenance, a past operability review for the previous three years was performed for North Anna Units 1 and 2. This review identified that there were four occasions on each Unit where the Motor Driven AFW Pump House ventilation fans were tagged out simultaneously which challenged operability of the Motor Driven AFW Pumps (EIIS Component P) as required by Technical Specification 3.7.5.
Technical Specification 3.7.5 requires three AFW trains to be OPERABLE (two motor driven trains and one turbine driven train). The Technical Specification definition of OPERABILITY is "A system, subsystem, train, component, or device shall be OPERABLE or have OPERABILITY when it is capable of performing its specified safety function(s) and when all necessary attendant instrumentation, controls, normal or emergency electrical power, cooling and seal water, lubrication, and other auxiliary equipment that are required for the system, subsystem, train, component, or device to perform its specified safety function(s) are also capable of performing their related support function(s)." The ventilation fans for the Motor Driven AFW Pump House are considered other auxiliary equipment within the context of the Technical Specification definition of OPERABILITY. Tagging out both Motor Driven AFW Pump House fans simultaneously challenged operability of the safety related Motor Driven AFW Pumps as required by Technical Specification 3.7.5.
The ventilation fans are powered from emergency power sources to ensure the Motor Driven AFW Pump House temperature is maintained less than 120 degrees Fahrenheit (F) following a design basis event. A calculation was/previously performed and determined that the Motor Driven AFW Pump House would reach 120 degrees F in 8.7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> (assuming conservative ambient air and wall temperatures) following a loss of forced ventilation when both of the Motor Driven AFW Pumps are in service.
The Updated Final Safety Analysis Report (UFSAR) states that "The auxiliary feedwater system must be capable of functioning for extended periods, allowing time either to restore normal feedwater flow or to proceed with an orderly cooldown of the plant to the reactor coolant temperature where the residual heat removal system can assume the burden of decay heat removal." The UFSAR also states "A source of feedwater will be available for in excess of one week.
This issue was determined to be reportable to the NRC in accordance with 10 CFR 50..73(a)(2)(i)(B) for "any operation or condition which was prohibited by the plant's Technical Specifications.
2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS No significant safety consequences resulted from this event because the Motor Driven AFW Pump House ventilation was returned to operable on May 8, 2015, at 1630 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20215e-4 months <br />, without exceeding design basis temperatures. Also, the Turbine Driven AFW Pump was operable during the event and would perform its design function. During a design basis event with the Motor Driven AFW Pumps in service, operators would enter the pump house to refill the Emergency Condensate Storage Tank (El IS Component - TK) and would note any elevated room temperatures. Action could readily be taken at that time to restore ventilation. The health and safety of the public were not affected by this event.
3.0 CAUSE A cause evaluation determined the event was due to the design basis for the Motor Driven AFW Pump House ventilation fans not being universally understood across the organization which led to the fans being simultaneously tagged out for maintenance.
4.0 IMMEDIATE CORRECTIVE ACTION(S) The ventilation fans for the Unit 2 Motor Driven AFW Pump House were returned to operable on May 8, 2015 at 1630 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20215e-4 months <br />.
5.0 ADDITIONAL CORRECTIVE ACTIONS A Unit 1 and Unit 2 Limiting Condition for Operation (LCO) tracking information action has been entered to prevent removing from service any safety related ventilation fans that cool the ambient temperatures inside valve houses, pump houses and enclosures that are necessary to maintain operability of safety related systems (e.g., AFW, Service Water, Rod Drive); and are not explicitly referenced in the Technical Specifications, Technical Specification Bases or the Technical Requirement Manual.
6.0 ACTIONS TO PREVENT RECURRENCE Lessons learned from this event are being reviewed for incorporation into appropriate training programs.
The cause evaluation report addresses additional corrective actions that are being tracked in the Corrective Action Program.
7.0 SIMILAR EVENTS None 8.0 ADDITIONAL INFORMATION North Anna Units 1 and 2 continued operating in Mode 1, at 100 percent power during this event.