WM SYMPOSIA, SPONSORED FEATURE | ARC SAW TECHNOLOGIES, LLC
Arc saw segmenting of CANDU shield plugs
A novel non-contact cutting tool is being deployed at the Gentilly unit two nuclear power plant to reduce shield plugs and compensation bars so they will fit into standard CANDU spent fuel storage containers
Authors: Thomas S. LaGuardia, PE, CCP, Richard F. Simoneau CCNuclear, LLC, Julien Moussalam, P. Eng.
General Description The arc saw is a circular, toothless saw blade that cuts any conducting metal without contacting with the work piece. There are no reaction forces between the blade and the work piece. Cutting is by a high current electric arc between the blade and the work piece. The blade, made of any electrically conducting metal such as stainless steel, tool steel, mild steel, or copper, rotates at 300-500 RPM removing molten metal (dross) created by the arc in the kerf of the cut. The molten metal solidifies as highly oxidized pellets expelled from the kerf. The depth of the cut (up to 26 in.) is determined by the blade diameter and the electric power delivered to the blade.
Gentilly Unit -2 so they would fit into CANDU standard spent fuel storage containers. The Shield Plugs provide shielding at both ends of each fuel channel assembly in the reactor, and accordingly are highly radioactive. Therefore, all segmentation must be done underwater for shielding.
Description of Shield Plugs There are a total of 109 Shield Plugs to cut. The Plugs are 38.61 in. long and 3.96 in. dia. Each Plug will be cut in half to fit vertically in spent fuel baskets and dry-stored in existing power plant facilities. The material is stainless-steel 410 annealed and has undergone radiation hardening through its lifetime.
Right, figure 1: Arc saw
Description of Compensation Bars There are 21 Compensation Bars (Comp Bars), 15 Long Bars (165.75-in.) and 6 Short Bars (74.88-in.). The Bars have a cylindrical sleeve of 3 in. dia. with thickness ranging from 0.06 to 0.13 in. The arc saw will be used to cut the Long Bars into 7 equal lengths of 19.5 in. and the Short Bars into 2 sections with a smaller 5.8 in. section. Each Comp Bar has an inner rod ranging from 0.5 in. to 0.6 in. dia. which will be cut by either a hydraulic shear or the Arc Saw. The material is stainless-steel 304.
Right, figure 2: Shield plug and ground clamp
Advantages of the Arc Saw Materials are cut rapidly and cleanly. The arc saw can be operated under water or in air. However, under water is preferred since in-air cutting produces greater noise, a rougher cut and more challenging dross management. Cutting in air requires blade cooling using a fine mist spray. Underwater cutting produces a small quantity of steam bubbles, which quickly condense as they rise within the pool. The Arc Saw blade is driven by a Hydraulic Pressure Unit (HPU), and the Saw Head driven by a Stepper Motor.
CANDU Shield Plug and Compensation Bar Project Following an exhibition of an Arc Saw mockup at the 2021 Waste Management Symposia, CCNuclear, LLC (CCN) of Montreal, Canada contracted with AST to design, fabricate and test an Arc Saw to segment CANDU reactor Shield Plugs and Compensation Bars. The Plugs and Bars will be segmented at the Hydro-Quebec Nuclear Power Plant
36 | February 2023 |
www.neimagazine.com
Need for Precise Clean Cut Without Slag The segmented Plugs and Bars are to be placed in a standard CANDU spent fuel container for ultimate storage/ disposal. Any slag or protruding edge will interfere with loading the containers underwater. The Arc Saw makes clean, through cuts. The blades were designed so spent blades may be placed in the spent fuel container when Plug and Bar loading is complete.
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