 Complete the following phrase:  In his book Normal Accidents, Charles Perrow says that unexpected failures are built into societys complex and tightly coupled nuclear reactor systems. Nuclear power plants cannot be operated without some major accidents. Such accidents are unavoidable and cannot be designed around. An interdisciplinary team from MIT have estimated that given the expected growth of nuclear power from 2005  2055, at least four serious nuclear accidents would be expected in that period. To date, there have been five serious accidents core damage in the world since 1970 one at Three Mile Island in 1979; one at Chernobyl in 1986; and three at 