Combined mechanical and electrical testing of a full-scale TF shear key prototype

To assist in the ongoing research and development program for the International Thermonuclear Experimental Reactor (ITER), a full-size prototype of the toroidal field (TF) shear keys to be used in ITER was tested at 77 K. The most critical aspect of the shear key design is the composite insulation, which must withstand mechanical and electrical loads, have good fatigue characteristics, and maintain its properties under high levels of radiation. All components included in the current ITER design, such as the TF shear plates, composite insulation, shear key liners, and shear keys, were included in the prototype test. The preimpregnated insulation system, combined with an electrical barriers was fabricated using a vacuum bag/autoclave process. The mock-up was tested in tensile fatigue with a maximum load of 3.2-MN (720-kip). A 5-kV potential was placed across the composite insulation at regular intervals during the test, with no drop in resistance recorded. Both mechanical and electrical testing was conducted while the prototype was submersed in liquid nitrogen (77 K). The test was planned to proceed to a maximum of 8 X 105 cycles, but failure of the test rig assembly occurred at 5.75 X 104 cycles, causing the termination of the test. The composite insulation system performed well throughout the test