CREATE TABLE table_name_64 (reactortype VARCHAR(255), gross_capacity VARCHAR(255), electricity_grid VARCHAR(255))
Which Reactortype has a gross capacity of 417 mw and an Electricity Grid of 27.12.1971?
    
SQL: SELECT reactortype FROM table_name_64 WHERE gross_capacity = "417 mw" AND electricity_grid = "27.12.1971"