A new reactor vessel head, shrouded in a protective wrap, arrived at Diablo Canyon nuclear power plant Monday morning. The equipment will be installed on the plants Unit 1 reactor during a refueling shutdown in the fall. The large component was shipped via a 185-foot-long special transport vehicle from Mt. Vernon, Ind., that is the equivalent of three semitrucks. The reactor head itself is 17 feet in diameter, 8 feet tall and weighs 70 tons. As the name implies, the component sits on top of the reactor. The cost of replacing both vessel heads at the plant is $141 million.