Process Window Based on Vibration and Torque for Dry Disc Milling of Thick Steam Generator Shells in Nuclear Decommissioning

Dry disc milling cuts thick carbon-steel components in nuclear decommissioning without liquid waste, but no catalogue gives a safe spindle speed and feed for a large remote module. This paper sets out an application-specific procedure for the longitudinal module on the 75 mm shell of a VVER-440 steam generator. A portable analyser and the drive log are the only measurements. Vibration depends on spindle speed, and torque depends on feed per revolution. Seven velocity spectra (60–120 rpm) were recorded on a test stand. Torque comes from 599 records of the module installed in the cell. At 80 rpm a 690–780 Hz band reaches 3.47 mm/s. Order tracking is consistent with a speed-locked order crossing a fixed band; the natural frequency was not measured. At 110 rpm the band is 0.22 mm/s, the lowest value of that sweep for five band definitions. In 65 cuts at 90 rpm and 2 mm/s, the mean torque is 11.3 N·m and the 99th percentile is 26.4 N·m. The mean matches the supplier’s calculation at that one condition. A 45 N·m limit on the 99th percentile—taken only from jam precursors on an earlier thinner (35 mm) cut, not from the 75 mm wall of the window—gives a model-predicted condition at 110 rpm and 240 mm/min: a kinematic removal rate of 108 cm3/min, twice current practice, and 56% less test-stand vibration than at 90 rpm. The torque at 110 rpm is extrapolated, and that point has not been cut. The speed remains 110–120 rpm in all 36 sensitivity cases. Doubling the removal rate requires the 45 N·m limit.