Light water reactor fuel assembly, light water reactor core and MOX fuel assembly production method

A method of producing a light water reactor fuel assembly, comprising:

• setting conditions at least concerning an operation cycle period and average discharge burnup;
• setting an initial enrichment of enriched uranium to 5% or more;
• calculating excess reactivity of a light water reactor core where light water reactor fuel assemblies including the enriched uranium are burned until an end stage of a final operation cycle;
• determining whether excess reactivity is positive through the operation cycle and 0.3% Δk at an end of a first operation cycle in the calculating of the excess reactivity;
• returning to the setting of the initial enrichment, if the determining determines that the excess reactivity is not positive and 0.3% Δk, or deciding an enrichment of the enriched uranium if the determining determines that the excess reactivity is positive and 0.3% Δk;
• and
• placing the enriched uranium determined in the determining to have the excess reactivity that is positive and 0.3% Δk as fuel pellets into a cladding tube configured to house the enriched uranium pellets, the cladding tube being configured as a LWR fuel rod suitable for in the light water reactor fuel assembly in an array of LWR fuel rods and burnable poison-containing fuel rods.