Fuel rod, method of manufacturing the same, and fuel assembly

A lower end plug is welded to a fuel cladding tube made of a zirconium alloy. A plurality of uranium pellets having an average crystal grain size of from 30 to 60μm are filled in the fuel cladding tube. A gas such as air or the like in the fuel cladding tube is substituted with a He gas, and the pressure of the He gas is elevated to from 1 to 8 atm. An upper end plug is welded to the fuel cladding tube to seal the inside of the fuel rod in the chamber filled with the He gas in a state where the uranium pellets are urged by a plenum spring. The uranium pellets having an average crystal grain size of from 30 to 60μm are formed by adding alumina silicate to uranium fuels and then sintering them. With such procedures, high burn-up degree can be attained while maintaining the fuel integrity thereby enabling to reduce the production cost of fuel rods. Fuel rods suitable to be used for a BWR-type reactor can be obtained. (I.N.)