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A review of industry operating experience … A review of industry operating experience regarding the impact of unfused Direct Current (DC) ammeter circuits in the control room has determined the described condition to be applicable to Palo Verde Nuclear Generating Station resulting in an unanalyzed condition with respect to 10 CFR 50 Appendix R analysis requirements. The original plant wiring design and associated analysis for the Class 1E Train B and D batteries and chargers (including the BD Swing charger) control room ampere indications do not include overcurrent protection features to limit the fault current. </br>In the postulated event, a fire in the control room could cause one of the ammeter wires to hot short to the ground plane; simultaneously, the fire causes another DC wire from the opposite polarity on the same battery to also hot short to the ground plane. This would cause a ground loop through the unprotected ammeter wiring. This event could result in excessive current flow (heating) in the ammeter wiring to the point of causing a secondary fire in the raceway system. The secondary fire could adversely affect safe shutdown equipment and potentially cause the loss of the ability to conduct a safe shutdown as required by 10CFR50 Appendix R.</br>The train B and D DC circuits were reviewed first since they are part of alternate safe shutdown capability for the control room fire event. An extent of condition review is ongoing for the A and C train DC circuits and other similar circuit designs that could potentially cause a secondary fire.</br>This condition is reportable in accordance with 10 CFR 50.72(b)(3)(ii)(B) as an unanalyzed condition. Compensatory measures (fire watches) have been implemented for affected areas of the plant. </br>The NRC Resident Inspector has been notified. NRC Resident Inspector has been notified. +
16:46:00, 4 October 2013 +
49,411 +
18:20:00, 4 October 2013 +
16:46:00, 4 October 2013 +
A review of industry operating experience … A review of industry operating experience regarding the impact of unfused Direct Current (DC) ammeter circuits in the control room has determined the described condition to be applicable to Palo Verde Nuclear Generating Station resulting in an unanalyzed condition with respect to 10 CFR 50 Appendix R analysis requirements. The original plant wiring design and associated analysis for the Class 1E Train B and D batteries and chargers (including the BD Swing charger) control room ampere indications do not include overcurrent protection features to limit the fault current. </br>In the postulated event, a fire in the control room could cause one of the ammeter wires to hot short to the ground plane; simultaneously, the fire causes another DC wire from the opposite polarity on the same battery to also hot short to the ground plane. This would cause a ground loop through the unprotected ammeter wiring. This event could result in excessive current flow (heating) in the ammeter wiring to the point of causing a secondary fire in the raceway system. The secondary fire could adversely affect safe shutdown equipment and potentially cause the loss of the ability to conduct a safe shutdown as required by 10CFR50 Appendix R.</br>The train B and D DC circuits were reviewed first since they are part of alternate safe shutdown capability for the control room fire event. An extent of condition review is ongoing for the A and C train DC circuits and other similar circuit designs that could potentially cause a secondary fire.</br>This condition is reportable in accordance with 10 CFR 50.72(b)(3)(ii)(B) as an unanalyzed condition. Compensatory measures (fire watches) have been implemented for affected areas of the plant. </br>The NRC Resident Inspector has been notified. NRC Resident Inspector has been notified. +
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100 +
00:00:00, 4 October 2013 +
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18:20:00, 4 October 2013 +
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16:46:00, 4 October 2013 +
Postulated Fire Event Could Result in a Hot Short That Could Adversely Impact Safe Shutdown Equipment +
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