Nuclear plants produce two classes of radioactive waste. The first is slightly radioactive material consisting of contaminated pipes, tools, excess coolant, ion-exchange resins, and protective clothing. The second is fuel materials that are no longer capable of producing energy in the reactor.
        The pebble bed modular reactor (PBMR) design reduces both types of waste. Inert coolant gas minimizes low-level waste by reducing equipment contamination. Corrosion, the source of most radioactive contamination in conventional nuclear plants, will be virtually eliminated. Since there is no liquid coolant, there is no need to discharge excess water during reactor start-up.
        The PBMR will also improve on the already impressively small amount of leftover fuel materials. The coated particle fuel allows a PBMR to obtain approximately 3--4 times as much heat per unit heavy metal as is possible in a conventional nuclear plant. PBMRs are also about 30 percent more efficient than steam nuclear plants at converting thermal power to electrical power, which is the end product that really counts. Finally, the designers claim that the fuel coatings will keep fission products isolated from the environment for a million years, long enough for all products to decay into stable elements.
        The PBMR design includes enough storage space under the reactor to hold all the fuel by-products produced during the power plant's 40-year life. Once the plant is retired, the material will remain in place while the radioactivity decays away.