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The use of remote robotic equipment has proven invaluable in the task of removing the fuel from General Public Utility's damaged Three Mile Island Unit 2 reactor . The. March 28, 1979 accident at Three Mile Island redistributed an estimated 300,000 pounds of core debris throughout all regions of the reactor vessel . Portions of the debris accumulated in areas that are inaccessible without major demolition efforts. The final stage of fuel removal requires gaining access to the regions below the lower core support assembly and behind the baffle plates where an estimated 67,000 pounds of fuel debris is trapped (1). The Automated Cutting Equipment System (ACES ), a robotic manipulatorcontrolled plasma are cutting system, was developed to cut through the five plates comprising the lower core support assembly as well as the baffle plates, creating a passage to the fuel debris entrapped in these areas. This paper will provide a thorough description of the ACES system and its major components , as well as address the design challenges that. had to be met to perform the designated task. 1. Overview of the Reactor Vessel Defueling Effort To perform the fuel removal. process, the reactor head and plenum were removed and a rotating shielded work platform was installed on top of the vessel. This platform provides radiation shielding for personnel as well as a means of safe access for deployment of defueling tools via an open work slot in the top of the platform. Below the platform , the reactor vessel is flooded with water which is borated with boric acid and buffered with sodium hydroxide, a highly conductive solution that acts as a neutron absorber to prevent criticality by the remaining fuel in the vessel. Defueling tools are used to dislodge, flush, vacuum, and transport fuel debris into canisters for shipping and offsite disposition. These activities are observed and supervised from the Coordination Center, a remote station located 700 feet from the reactor vessel, via audio and video equipment. . At, this stage of the defueling effort, all fuel assemblies have been removed and the remaining fuel in the vessel is inaccessible without severing the lower core support assembly and baffle plates. 1.1 Lower Core Support Assembly and Baffle Plate Description The lower core support assembly consists of a series of five horizontal stainless steel plates, varying in thickness from 1 inch to 13 inches, which are submerged under 29 to 35 feet of water. Each plate has a unique geometry and hole pattern. The incore guide tubes,

Dismantling the Damaged Three Mile Island Reactor Vessel by Remote Plasma Arc Cutting