<Tr> <Td> Dec. 1980 </Td> <Td> U.S. 96th Congressional session passes U.S. legislation establishing a five - year nuclear safety, research, demonstration, and development program . </Td> </Tr> <Tr> <Td> July 1984 </Td> <Td> The reactor vessel head (top) was removed . </Td> </Tr> <Tr> <Td> Oct. 1985 </Td> <Td> Defueling began . </Td> </Tr> <Tr> <Td> July 1986 </Td> <Td> The off - site shipment of reactor core debris began . </Td> </Tr>

What part of a nuclear power plant is under thousands of pounds of pressure