Part 1 of 2 Parts
I have been blogging about various aspects of dealing with radioactive waste in the past few columns. Today I am going to list a few suggestions and practices for repurposing radioactive waste.
One major type of radioactive waste is material left when nuclear fuel has been “burned” in a common light water fission reactor used for electrical generation. About ninety six percent of the waste consists of uranium isotopes. One percent is plutonium isotopes and the remaining three percent are a variety of isotopes of other elements. This type of waste makes up most of the radioactive waste in the world. Some of the isotopes in this spent nuclear fuel waste are radioactive and dangerous for thousand and thousand of years.
Fast Breeder Reactors
One suggestion for reducing the production of this waste consists of switching to what are called fast neutron reactors. These reactors “breed” non-fissile isotopes such as uranium-238 into plutonium-239 and plutonium-240 which are fissile and can be used to produce new nuclear fuel. There are designs for such reactors that can process out other actinides and use them as fuel for reactors. (Actinides are the 15 metallic chemical elements with atomic numbers from 89 to 103.) One of the major benefits is that these reactors are able to utilize almost all of the energy in uranium fuel. This reduces fuel use by sixty to one hundred times when compared to nuclear fuel used in conventional power reactors.
Fast breeder technology has not been widely adopted because of economic considerations. In the 1970s, new abundant deposits of uranium ore were discovered. This meant that is was much cheaper to just dig and refine uranium ore instead of developing expensive new technologies. A big concern about fast breeder reactors is that they can be used to create radioactive isotopes that are suitable for construction of nuclear weapons. This has impeded progress and adoption of such reactors. Some promising technologies have been developed but it is likely that major developments necessary to create safe and efficient fast breeder reactors are many years away.
Nuclear Batteries
Solar power is often used to provide power for satellites. However, when satellites are sent into the outer solar system far from the sun, solar power does not produce enough energy. This type of satellite and mission requires an alternate power source such as radioisotope thermoelectric generators (RTGs). Radioactive materials are placed in a container with thermocouples which utilize the heat generated by the materials to produce electricity. The heat produced by the radioactive materials also helps to keep the components in the satellites from freezing.
In the past, these RTGs have been used by the U.S. and Russia. The European Space Agency is also very interested in adopting this technology. They plan to extract radioactive americium-214 from the plutonium in the waste from reprocessed nuclear fuels. Such use of waste materials would have little impact on reducing the huge amount of such waste but would be good source of radioactive materials for RTGs. This is especially relevant because the U.S. stockpile of plutonium waste is rapidly diminishing because it is produced by the reactors that are used to produce plutonium for nuclear weapons and nuclear weapons production has be shut down in the U.S. The U.S. is working on producing more plutonium-238 but, for the moment, the British have an opportunity in this area.
Another idea for nuclear batteries is under development. This new type of battery is called a “beta-voltaic” battery. In this type of battery, a semiconductor material is used to capture electrons produced by the beta-decay of radioactive materials. The University of Bristol in the U.K. is working on such a battery that uses diamonds. This battery utilizes radioactive carbon-14 from the graphite blocks used as moderators in U.K. commercial power reactors. First, the outer layer which contains most of the carbon-14 is scraped off the graphite blocks. This material is used to produce manmade diamonds that release electrons as they decay. These radioactive diamonds are encased in non-radioactive carbon-12 which prevents the escape of electrons from the battery. The electrons which are produced by the beta-decay are very low energy so only a thin shielding layer is needed. These batteries will be able to produce hundred of microwatts of electricity for thousands of years.
Please read Part 2