FISSILE MATERIAL FOUND IN ELECTRICAL JUNCTION BOX AT NUCLEAR FUEL SERVICES, INC.

摘要

On October 29, 2014 at Nuclear Fuel Services, Inc., while troubleshooting a failed heater control circuit, fissile material was found in a small electrical junction box that contained a Resistance Temperature Detector (RTD). The RTD was mounted inside a stainless steel thermowell located in a uranium recovery boildown loop. Over time, the end of the thermowell had become pitted allowing fissile solution to penetrate the thermowell and collect in the electrical junction box. Conduit connected the small electrical junction box to an unfavorable geometry electrical panel, providing a credible scenario where an unsafe volume of fissile liquid could potentially collect in an unfavorable geometry. This postulated upset scenario had not been analyzed by Nuclear Criticality Safety (NCS). Prior to restart of the operation, a corrective action was taken to replace the damaged thermowell. Additionally, a review of other fissile systems was completed to identify all unfavorable geometry electrical panels where the potential for a similar accident scenario existed. Drain holes were drilled in the bottom of all those identified. Analysis of the damaged thermowell is ongoing. Expanded details of the incident, the short term and planned long term corrective actions, and lessons learned are discussed.