A 235-ton reactor vessel at the start of its 1,075-mile rail trip, part way over the Southern, from Chattanooga, Tenn., to Shippingport, Pa. Described by its manufacturer, Combustion Engineering, Inc., as the heaviest unit of atomic power equipment yet made, it moved in a special train at a maximum speed of 15 miles an hour. Its width-12 feet, 11 inches-caused close clearances demanding extra-careful handling.