IMPROVED FUEL BUNDLE DISASSEMBLY USING ELECTRICAL DISCHARGE MACHINING


11th International Conference on CANDU® Maintenance and Nuclear Components - 2017 Oct. 01-04

Presented at:
11th International Conference on CANDU® Maintenance and Nuclear Components
2017 Oct. 01-04
Location:
Toronto, ON Canada
Session Title:
Fuel Channel Life Management

Authors:
R. Meguerian (Laveer Engineering)
J. Hulcoop (Laveer Engineering)
R. Lewis (Bruce Power)
  

Abstract

Inspecting fuel bundles that have been removed from CANDU reactors is a common occurrence. The results of these inspections are used to ensure there is an adequate understanding of the fuel condition such that the assumptions in relevant safety and fitness-for-service assessments are demonstrated to be valid, and unexpected conditions are identified for trending and communication to interfacing system groups for assessment. When suspected fuel defects reside on the interior facing surfaces of the bundles, these cannot be easily viewed, if at all, with underwater vision systems. To facilitate more detailed inspection and investigation, a bundle must be disassembled. The disassembly process is a time-consuming activity, typically utilizing manual tools (screwdrivers and pliers on long poles) which currently necessitate an “outside-in” disassembly and bundle disposal through alternate nuclear waste stream given the change in bundle geometry. Presently, hard barriers do not exist to prevent excessive force and sheath contact with the current tools which could lead to a breach of the sheath as well as damage to the feature of interest – preventing the cause from being identified and mitigated. Moreover, the current approach requires multiple operators to coordinate manipulation of the bundle, observe tool interactions with the bundle, and handle the tools. A semi-automated, proof-of-concept system has been designed and built to support disassembly of a fuel bundle using electrical discharge machining (EDM). This process imparts no mechanical stress on the fuel components, minimizing the risk of damage to the desired evidence, allows selective removal of any element without removal of adjacent elements, and yields a partial bundle that still has integrity for disposal. The automated process, requires only a single operator to monitor the system while it “cuts”, reduces effort for and duration of bundle disassembly, decreases the likelihood of human performance errors and reduces waste requiring disposal.

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