Except that, from what I have read, when they take the unit down for inspection, they store active fuel rods temporarily in the spent fuel pool. Unit 4 was down for maintenance; but, I have not read if they were inspecting the core.
This process is carried out periodically to also rearrange the fuel rods. The rods in the center of the core burn hotter due to the higher neutron density. During inspection and maintenance the outer fuel rods are moved to the center. T
