Electric arc apparatus for severing split-pin assemblies of guide tubes of nuclear reactors

In the replacement of old split-pin assemblies of a guide tube of a nuclear reactor by new split-pin assemblies, each old split-pin assembly is severed into readily removable fragments by metal disintegration machining apparatus. This apparatus includes a metal disintegration machining tool having an electrode which is guided precisely into arc-disintegrating relationship with the assembly by a glass block in such a way that the assembly is successfully severed into fragments without damaging the guide tube. The electrode is progressively fed into the assembly producing the separation by arc disintegration as it penetrates. The electrode is axially perforated and water under pressure is injected into the arc region through the perforation. A hole is produced in the assembly disintegrating the assembly into a fragment which includes a portion of the nut with a portion of the pin threaded to it and the remaining portion of the pin. The entrance to the hole is a short distance, about 0.08 inch, above the adjacent surface of the guide tube. The hole terminates at a region below the level where the threading of the nut on the pin terminates but before it penetrates through the nut in this region. The skirt of the nut below the region where the threading terminates is about 0.40 inch long. The electrode is in a holder which has a flange which engages a stop on the block to stop the electrode before the arc penetrates through the nut.