Plutonium isotopic composition of high burnup spent fuel discharged from light water reactors

► Pu isotopic composition of fuel affects FBR core nuclear characteristics very much. ► Spent fuel compositions of next generation LWRs with burnup of 70 GWd/t were obtained. ► Pu isotopic composition and amount in the spent fuel with 70 GWd/t were evaluated. ► Spectral shift rods of high burnup BWR increases the fissile Pu fraction of spent fuel. ► Wide fuel rod pitch of high burnup PWR lowers the fissile Pu fraction of spent fuel.