Unit cell ferrule spring relaxation jig in the spacer of boiling water type high burnup fuel assembly

摘要

PROBLEM TO BE SOLVED: To completely eliminate scratch generation with a simple operation of insertion and removal by a loosening jig used for a purpose that a fuel element to be elastically held in a spacer element in a spacer of boiling water fuel assembly for high burnup is not scratched by a ferrule spring for elastic holding. SOLUTION: A spring container 11 is fitted in the first and the second spacer element 3a and 3b of a unit cell 3A by holding a holder 10 and the first and the second facing branch pieces 7A and 7B of a ferrule spring 7 go into the path L formed by the press grooves 13f and 13g and are pushed and deformed. As the first and the second bent press plates 13A and 13B for insertion forming the path L are inserted along the first and the second spacer elements 3a and 3b, the inserted fuel element 2 never receives the spring force of the ferrule spring 7 and the duplication layer part 3m projecting above is fitted in a containing inlet 12b of thrust base 12 so that the fitting of the loosening jig is completed and the jig is removed after the insertion of the fuel element 2.