TIC Analysis
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Analysis of Thermally Induced Current


Background

Nuclear Site
The NRC has issued two information notices, IN 97-45 and IN 97-45 Supplement 1, alerting nuclear power plant staff to environmental qualification deficiencies in the coaxial cables used in high range radiation monitor (HRRM) systems. The supplement specifically addresses the potential for significant positive and negative current flow in HRRM coaxial cables when exposed to transient temperature conditions, potentially causing false high radiation indication or the “fail” alarm. The concern is that false high radiation indications could cause the operating staff to inappropriately enter an Emergency Action Level or fail to do so because of invalid HRRM indications under the influence of Thermally Induced Currents (TIC).

Analysis and Modification Support

The Analysis Division has completed multiple analyses evaluating the effects of thermally induced currents (TIC) on high range radiation monitors (HRRM) under accident and transient conditions. We have performed this analysis at several different sites for multiple clients. Our analysis evaluates the vulnerability of the affected cables to TIC under accident conditions and assists the clients in choosing replacement cabling, conduits, and the conduit routing.

At the start of the event, the conduit would be surrounded by air, its insulation intact. During a LOCA event, the water level on the reactor building floor may submerge it. Our approach is to use GOTHIC™ to evaluate the effect of conduit submergence on the cable temperature. The resultant temperatures, including accounting for submergence, are used to determine the thermally induced current and its effect on the HRRM readout. The currents can be evaluated for the current HRRM cable configuration and any potential alternative configurations.

For more information on our TIC analysis capabilities and how they can be used to analyze, develop, and implement a mitigation or modification strategy to address TIC, please contact Scott Ingalls or Anita Gates. The Analysis Division contact list is here.