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On November 3, 2011, at 1550 PDT, operator … On November 3, 2011, at 1550 PDT, operators determined that control room ventilation system (CRVS) contained a single failure vulnerability whereby unfiltered air supplied to the control room could exceed the flowrates used in the licensing basis analyses of design basis accident (DBA) consequences. This vulnerability was discovered during performance of control room inleakage testing required by TS SR 3.7.10.5.</br>It was determined that the control room pressurization system airflow could bypass the supply filter if the CRVS booster fan in the associated train was not operating. This would allow as much as 800 cubic feet per minute of unfiltered air to be delivered to the control room following an accident that results in initiation of the CRVS pressurization mode. Operators would correct the condition approximately 10 minutes after a safety injection by manually selecting the train's redundant booster fan in accordance with existing proceduralized actions specified in the DCPP emergency procedure E-0 Appendix E. This period of unfiltered air supply to the control room due to a single failure of a CRVS booster fan had not been previously analyzed and could have potentially resulted in operator dose greater than contained in plant analyses. </br>Plant staff verified that all components and redundant components in each ventilation train are currently OPERABLE. Plant staff has implemented additional compensatory measures by issuing a shift order to require that TS Action 3.7.10.A be entered for unavailability of either of the two CRVS booster fans in each CRVS train. Additionally, evaluation of the new unfiltered inleakage may result in more restrictive administrative controls to ensure operator doses are maintained less than the FSAR accident analyses.</br>The licensee informed the NRC Resident Inspector.ensee informed the NRC Resident Inspector. +
22:50:00, 3 November 2011 +
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23:51:00, 3 November 2011 +
22:50:00, 3 November 2011 +
On November 3, 2011, at 1550 PDT, operator … On November 3, 2011, at 1550 PDT, operators determined that control room ventilation system (CRVS) contained a single failure vulnerability whereby unfiltered air supplied to the control room could exceed the flowrates used in the licensing basis analyses of design basis accident (DBA) consequences. This vulnerability was discovered during performance of control room inleakage testing required by TS SR 3.7.10.5.</br>It was determined that the control room pressurization system airflow could bypass the supply filter if the CRVS booster fan in the associated train was not operating. This would allow as much as 800 cubic feet per minute of unfiltered air to be delivered to the control room following an accident that results in initiation of the CRVS pressurization mode. Operators would correct the condition approximately 10 minutes after a safety injection by manually selecting the train's redundant booster fan in accordance with existing proceduralized actions specified in the DCPP emergency procedure E-0 Appendix E. This period of unfiltered air supply to the control room due to a single failure of a CRVS booster fan had not been previously analyzed and could have potentially resulted in operator dose greater than contained in plant analyses. </br>Plant staff verified that all components and redundant components in each ventilation train are currently OPERABLE. Plant staff has implemented additional compensatory measures by issuing a shift order to require that TS Action 3.7.10.A be entered for unavailability of either of the two CRVS booster fans in each CRVS train. Additionally, evaluation of the new unfiltered inleakage may result in more restrictive administrative controls to ensure operator doses are maintained less than the FSAR accident analyses.</br>The licensee informed the NRC Resident Inspector.ensee informed the NRC Resident Inspector. +
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00:00:00, 4 November 2011 +
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22:26:34, 24 September 2017 +
23:51:00, 3 November 2011 +
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0.0425 d (1.02 hours, 0.00607 weeks, 0.0014 months) +
22:50:00, 3 November 2011 +
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