Emergency Response and Solutions for Damaged Fuel Assembly Handling Events Lessons learned from a 2013 fuel positioning issue

摘要

In 2013, during the refueling of a French 1300 MWe reactor, a fuel assembly was damaged by a fuel assembly positioning tool in the reactor vessel. The upper part of a corner rod of the fuel assembly was twisted and the top end grid was torn off. Because of the protruding fuel rod, the assembly could not be easily transferred for repair to the fuel storage pool via the transfer tube. This unexpected and rarely encountered situation was assessed jointly by EDF and AREVA NP. AREVA NP relied on the expertise of its teams located in France, USA and Germany to assess the different options which could be envisaged. The chosen option was to directly perform the field service inside the reactor building in cells generally used for intermediate storage during refueling This operation, performed by EDF and AREVA, involved removing the twisted rod and positioning it in a special-purpose canister by means of a gripper-type tool for removal and a gripper for holding the rod in place. The special-purpose canister was designed, ordered and supplied by a sub-supplier within one week. As part of the operation, a field service document file was promptly prepared and submitted to the safety regulator; the gripper, which had been designed for in-pool operation, was also requalified. This was a first-of-a-kind in France. The operation, which was performed on the outage critical path, was completed in one day after a week of preparation, thanks to close cooperation between the AREVA NP teams in charge of the operation and the EDF teams. It was also made possible thanks to the field services crisis organization in the AREVA on-site services department which includes a hotline, a worldwide expertise network in the three AREVA regions and an active list of qualified sub-suppliers which can be mobilized at any moment. For EDF, the experience feedback from this operation was the basis for defining an organizational setup for fuel operations in case of a random event affecting the fuel. EDF also reviewed the fuel assembly positioning tools to reduce the risk of a recurring event of this type.