Part 2 of 2 Parts (Please read Part 1 first)
Depleted Uranium
    Another major product of the nuclear power industry is depleted uranium. This is the uranium left over after the ratio of fissile U-235 to non-fissile U-238 is increased from low natural levels to three to five percent. This byproduct is mainly U-238 and is less radioactive than natural uranium ore because the U-235 has been removed.
     Depleted uranium is a heavy, dense metal which makes it useful for military applications. One of these applications is anti-tank ammunition. Depleted uranium shells have excellent penetration ability and can blast through tank armor. When depleted uranium hits a target, it flakes off as it passes through the armor and the projectile stays sharp. The cloud of depleted uranium particles is ignited by the heat of the impact. One big concern about this use is the fact that depleted uranium dust is spread around the battlefield and can be a threat to public health.
    Another application for depleted uranium is in chemical processing. Researchers at the University of Sussex in the U.K. have been able to create a catalyst from depleted uranium which can help convert ethylene into ethane. This is a common chemical process using other methods but it is a novel application for depleted uranium.
    There are thousands of tons of depleted uranium in stockpiles around the world. This new use in chemical processing would be preferable to either storing it or using it in warfare. It does have to be handled carefully because although it is not very radioactive, it could still pose a health threat.
Remaining Roadblocks
    There are still multiple issues of concern in the repurposing of nuclear waste. In many cases, the uses proposed here could result in nuclear waste materials being stolen or diverted adding to the risk of nuclear proliferation.
    It only takes a few pounds of plutonium to make a nuclear warhead. If nuclear waste is reprocessed on industrial scales, the amount needed for a nuclear bomb could easily be stolen or diverted without being noticed. It is a serious problem that depends on the exact isotopes and processes in use. Currently, spent nuclear fuel from light water reactors is too hot to be easily handled which reduces the risk of theft or diversion. However, technologies such as the reprocessing of spent nuclear fuel could be adapted to producing weapons-grade nuclear materials which undesirable.
     Another issue that has been raised is that recycling and/or reprocessing of nuclear fuel could divert interest and resources from the quest for permanent geological repositories for spent nuclear fuel. Many countries that use nuclear power and produce spent nuclear fuel have been slow to create viable long-term disposal methods for such waste. Considering the danger from long-lived isotopes in spent nuclear fuel, creating such long-terms storage should be a priority.
Final Thoughts
    The powerful radioactivity and dangerous nature of nuclear waste raises many challenges for countries that use nuclear power. The way in which this waste is currently handled is to let the stockpiles build up while the debate about ultimate solutions goes on and on. It would be best if new technologies were developed to deal with nuclear waste in a safe and efficient manner. In the meantime, there are a host of difficult political decisions that must be made with respect to the use of nuclear power.

Ambient office  = 101 nanosieverts per hour

Ambient outside = 123 nanosieverts per hour

Soil exposed to rain water = 119 nanosieverts per hour

English cucumber from Central Market = 101 nanosieverts per hour

Tap water = 135 nanosieverts per hour

Filtered water = 119 nanosieverts per hour

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

Ambient office  = 99 nanosieverts per hour

Ambient outside = 145 nanosieverts per hour

Soil exposed to rain water = 139 nanosieverts per hour

Ahaheim pepper from Central Market = 77 nanosieverts per hour

Tap water = 122 nanosieverts per hour

Filtered water = 97 nanosieverts per hour

     Recently an important article was published in the journal Chemistry about a means of more safely and efficiently reprocessing spent nuclear fuel. Nuclear energy currently produces about ten percent of the electricity in the world. However, the nuclear fuel that is used in nuclear power reactors becomes less efficient over time and needs to be replaced about every five years.
    Spent nuclear fuel is still very radioactive and produces a lot of heat. Prior to being reprocessed or permanently disposed of, spend nuclear fuel is immersed in special cooling ponds under more than forty feet of water. The water provides shielding for the spent fuel and is continuously cooled and recirculated to remove the heat. It takes over a year in the cooling pool for the spent fuel rods to cool to the point where they can be reprocessed to remove uranium and plutonium which can then be used to create more fuel.
     The elements americium, curium and neptunium, which are called the minor actinides, are produced by the nuclear reactions of the fissioning nuclear fuel. After the uranium and plutonium are removed, the minor actinides are still present and they account for most of the residual radioactivity and heat. These elements remain dangerously radioactive for about nine thousand years. This makes either storage or disposal very dangerous.
     The removal of these actinide would make nuclear power a much safer and more sustainable power source. The remaining spent fuel following the removal of the actinides would only be dangerously radioactive for about three hundred years which is a more manageable time frame.
     There are molecules called trazines that can be used to selectively remove or extract the actinides from spent nuclear fuel. These trazines have been known for quite some time. Researchers decided to determine how the modification of selected part of these molecules could alter their ability bind and extract the minor actinides at a molecular level. If useful modifications could be identified and exploited, it should be possible to design better versions of the molecules that would be more efficient for reprocessing spent nuclear fuel in the future.
     The researched altered the size of the aliphatic rings in the current benchmark molecules. They were changed from six-part rings to five-part rings. It turned out that this minor alteration had surprising effects on the efficiency of these molecules to bind and extract minor actinides. The new configuration is much more efficient than the benchmark molecules. The researchers then used a variety of experimental techniques to discover exactly how the change in configuration improved efficiency.
     Dr. Frank Lewis is a senior lecturer in organic chemistry in Northumbria University’s Department of Applied Sciences. He said, “The findings are significant as they could allow better molecules to be designed in a more rational way, rather than simply by trial and error. The knowledge and insights we have gained by tuning the cyclic aliphatic part of these molecules could pave the way for the rational design of improved actinide selective ligands for reprocessing spent nuclear fuels. Modifying these molecules in different ways to improve their extraction properties could make future reprocessing more efficient and could be essential if they are to be used industrially in future. We believe that these results are of great importance to the field of nuclear energy, and this has been confirmed by the panel who reviewed the paper before publication.”

Ambient office  = 94 nanosieverts per hour

Ambient outside = 120 nanosieverts per hour

Soil exposed to rain water = 114 nanosieverts per hour

Organic Hawaiian avocado from Central Market = 87 nanosieverts per hour

Tap water = 104 nanosieverts per hour

Filtered water = 93 nanosieverts per hour

     One of the main problems with nuclear power is how to store and dispose of nuclear waste produced by develop and manufacture of nuclear weapons. Currently, vitrification is used for permanent long-term storage of nuclear waste in underground geological repositories. Nuclear waste is mixed with other materials that form glass or ceramics when heated and then enclosed in metallic cylinders. Unfortunately, scientists have now found that the glass and ceramic materials used in vitrification can interact with the stainless steel of the cylinders. This can result in an acceleration of corrosion of the cylinders.
     This accelerated corrosion will definitely affect the estimated service life nuclear waste storage. This, in turn, could increase the risk of the release of radioactive materials into the environment. Pollution of drinking and irrigation water as well as injury to public health would be a probable result.
      Xiaolei Guo is the lead author of the sturdy. He is the director of Ohio State’s Center for Performance and Design of Nuclear Waste Forms and Containers. He says, “Under specific conditions, the corrosion of stainless steel will go crazy. It creates a super-aggressive environment that can corrode surrounding materials.” Nuclear waste can remain radioactive and dangerous to human beings and the natural environment for hundreds of thousands of years.
    In response to this longevity of risk, countries that possess nuclear waste related to nuclear weapons have created plans to store this high-level waste up to three thousand and two hundred feet below the ground in a deep geological repository. This deep storage should prevent contamination of ground water and a threat of the release of radioactive materials into the environment. High level waste is created in liquid form during nuclear weapons production. Guo said, “In the current disposal plan for many countries, the high-level nuclear waste will be primarily mixed with other materials to form glass or ceramic waste forms.”
     Dr. Gerald Frankel at Ohio State University and his team carried out experiments for this study. They pressed pieces of stainless steel against vitrification materials such as a borosilicate glass and titanate-based ceramics. They studied the rate of corrosion in the stainless steel and found that the degree of corrosion was much faster in areas where the vitrification materials were in contact with the stainless steel.
     Guo said, “’Severe’ corrosion was found between stainless steel and both borosilicate glass and the ceramic waste form. Our study showed that the release rate could be enhanced due to the corrosion interactions between different materials used to isolate these wastes. Specifically, the corrosion of metallic canisters creates a highly aggressive environment that can corrode the surrounding materials faster than what was predicted.”
     The accelerate corrosion could be the result of chemical changes that take place in a confined space over time. This research should be carefully reviewed when assessing the safety of nuclear waste disposal and materials when selecting the material that will be used to enclose the waste.
     Guo says, “The corrosion that is accelerated by the interface interaction between dissimilar materials could profoundly impact the service life of the nuclear waste packages, which, therefore should be carefully considered when evaluating the performance of waste forms and their packages. Moreover, compatible barriers should be selected to further optimize the performance of the geological repository system.”
     In the United Kingdom, HLW treatment is carried out at Sellafield which is a two square mile site that is near Seascale on the coast of Cumbria. The site does not have a deep geological repository. Sellafield spokesmen say that the U.K. government is searching for a site for a deep geological repository but they are storing HLW for the time being on site.
     In the U.S., there are over ninety thousand metric tons of nuclear waste that await disposal. For the moment, the waste is stored onsite near the reactors in temporary canisters. A permanent deep geological repository has been proposed for Yucca Mountain in Nevada but work was halted in 2009.
    Only Finland has begun construction on a deep geological repository for HLW. Guo said, “At this stage, it is still a plan for most countries, but there have been continuous research and risk assessment efforts on this topic. Eventually, it is very likely to occur.”