Pool Storage: Japanese nuclear power stations store spent fuel in concrete pools, where the fuel's radiation and heat are blocked and subsequently cooled by water and by thick concrete walls.

FROM THE OUTSET OF THE nation's efforts to develop nuclear energy for peaceful purposes in the late 1950s, the Atomic Energy Commission of Japan favored a program based on the utility of plutonium.

Why? Because uranium fuel can be recycled more efficiently if plutonium—which is formed as a by-product when uranium is "burned"—is also extracted during the reprocessing. By recycling both the unburnt uranium and the newly created plutonium and reusing the two as fuel for fast-breeder reactors (FBR), the result can be a manyfold boost in uranium-use efficiency.

Still, FBR technology will require some time to perfect. In the meantime, Japan is pressing ahead with the MOX utilization approach, the use of plutonium in light-water reactors. Because it calls for plutonium to be used in existing reactor designs, the technology is far closer to realization.

MOX program technology utilizes MOX (mixed-oxide) fuel-a mixture of uranium and plutonium oxides. MOX fuel is different from conventional uranium fuel in that the former replaces the enriched Uranium 235-usually about 3-5 percent Of the total-contained in the latter with anything from 4-9 percent plutonium.

Metal Cask Storage: Designed to shield against radiation and to diffuse heat, strong metal casks are used both to transport and store spent fuel. Casks can be dropped or burned without serious damage.