High-Level Liquid Waste
- By Duncan Williams -
One of the most controversial topics regarding nuclear power is the issue of storing radioactive liquid waste. As a result of America’s decades-long processing of nuclear material, a fairly large amount of radioactive liquid waste has been generated and remains with us to this day. Some of this radioactive liquid waste is a result of once secret programs stemming back to the days of the Manhattan Project.
For example, beginning in the 1940s a site in eastern Washington State, known as the Hanford Site, produced plutonium for America’s defense program for decades. In addition, spent nuclear fuel from nuclear reactors was reprocessed at the Hanford Site in order to extract reusable uranium and plutonium. Although all reprocessing activities were discontinued at the Hanford Site in the 1980s, approximately 53 million gallons of radioactive and chemical waste are currently stored there in 177 underground tanks.
While the Hanford Site focused on plutonium production as a part of the Manhattan Project, another plant located in Oak Ridge, Tennessee, focused on producing uranium. As a result of this uranium experimentation and production, the Oak Ridge facility currently stores an unknown volume of radioactive liquid waste and sludge.
Another facility known as the West Valley Reprocessing Plant in West Valley, New York, recycled spent nuclear fuel from 1966-1972. During this period, at least 660,000 gallons of highly radioactive liquid waste were produced and stored in underground steel tanks.
Another facility, currently known as the Idaho Nuclear Technology and Engineering Center (INTEC), was established in the 1950s as yet another facility for reprocessing spent nuclear fuel. By the time reprocessing efforts halted in 1991, the facility generated roughly 9 million gallons of highly radioactive liquid waste.
Fortunately, there are a variety of technologies currently available, and in development, capable of safely immobilizing these radioactive liquid wastes. One of these methods, known as vitrification, converts the liquid waste into granules, and then encases the granules in glass. The process for converting liquid radioactive waste to granules has been in place at INTEC for decades and is described in U.S. Patent No. 4,065,400, issued on December 27, 1977. The process uses a container, known as a calciner vessel, for heating the liquid radioactive waste.
As can be seen in the diagram from the patent, the calciner vessel has a lower reaction portion (12) that is filled with silica (24). The silica (24) is then heated to between 752 F – 1472 F either by an electrical heating means or by igniting a flammable fuel source (44), such as oxygen and either propane or kerosene. A fluidizing gas source (20), typically air, is introduced into the bottom of the calciner vessel which is then directed upwards toward the silica (24). The fluidizing gas source (20) circulates the silica (24) in the lower portion (12) causing it to behave as if it were a fluid, creating what is known as a fluidized bed.
The radioactive liquid waste (45) is then atomized by a gas source (48), typically air, and sprayed into the lower reaction portion (12) containing the fluidized bed of silica. The heat converts the radioactive liquid waste into metal oxides, which is an ashy substance also known as calcine.
The fluidizing gas causes the calcine to eventually travel into the upper portion (28) of the calciner and exit through an exit port (29). The calcine is separated from the gas in a separator (31) and then travels to a receptacle (34) where it is collected. Since the calcine still emits radiation, the calcine is then taken from the receptacle so that it can be vitrified.
One method of vitrifying radioactive waste is disclosed in U.S. Patent No. 6,283,908, issued on September 4, 2001, and assigned to Radioactive Isolation Consortium, LLC, based in Falls Church, Virginia.
The patent describes an inner container (30) made from graphite and an outer container (10) made from stainless steel. A layer of insulation (20) is placed in between the inner container (30) and outer container (10). Calcine (100), or some other radiological waste, is introduced into the cavity of the inner container (30) through a feed pipe (60). A sand-like borosilicate glass called frit is also introduced through the feed pipe (60) in order to homogeneously mix with the radioactive material as the mixture begins to melt. As the level of the mixture begins to rise, a bottom segment of heating coils (25) is activated which melts the lower zone (40) of the mixture. As the level continues to rise due to more radioactive waste and frit being added, another set of heaters (35) are activated, causing the next zone (50) of the mixture to melt. This process continues until the calciner is filled and all of the heaters are activated. Once the contents are melted, all the heating coils are deactivated and the contents begin to cool and solidify. During this entire process, drying gases are introduced through the feed pipe (60) forcing any humidity to be vented through the exhaust pipe (70).
The result of this process is vitrified radiological waste, as shown in this picture taken from Radioactive Isolation Consortium’s website. However, vitrification is not the only known method of solidifying radiological waste. For example, U.S. Patent No. 7,476,194, issued on January 13, 2009, and assigned to Studsvik, Inc., based in Atlanta, Georgia, describes a process called mineralization. In order to mineralize the radioactive waste, the waste is transferred into a treatment container and mixed with mineralization additives.
These additives include clays, zeolite, silica, phosphates, calcium, magnesium, titanium, iron, and/or aluminum.
The mixture is then heated to between 300 F and 1112 F. Heating the mixture to the higher end of this range ensures that all the water, volatile organic compounds, as well as all nitrates, are vaporized. The end product is a mineralized substance that prevents the leaching of radioactive waste for long periods of time.
Another company, called Clean Technologies International, Inc., based out of Austin, Texas, has patented a method of solidifying nuclear waste in metal. U.S. Patent No. 7,034,197, issued on April 25, 2006, describes a process that results in the radiological waste being solidified in metal ingots. The ingots are created by melting the radiological waste and mixing it with an alkaline metal as well as a radiation absorbing metal. Examples of an alkaline metal include aluminum, magnesium, lithium, calcium, iron, zinc, or copper. Although the patent recommends using tungsten as the radiation absorbing metal, it also suggests using beryllium, cadmium, vanadium, yttritium, ytterbium, zirconium, or lead. The patent indicates that the resulting metal ingots are very stable, will not leach any of the immobilized radioactive waste, and emits a low amount of radiation due to the presence of the radiation absorbing metal.
Despite the numerous technologies available, vitrification has become the most widely used technology for immobilizing America’s radioactive liquid waste. About 98% of the liquid waste stored at the West Valley Site in New York has been successfully solidified using vitrification methods. In 1996, the Savannah River Site’s Defense Waste Processing Facility began vitrifying radioactive sludge that was stored at various sites around the country. Since its startup, it has produced over 9 million pounds of glass and has immobilized over 2 million gallons of radioactive sludge. Additionally, the U.S. Department of Energy has contracted Bechtel National, Inc., to design and build another radioactive waste treatment plant located at the Hanford Site. The treatment plant, known as the Hanford Waste Treatment and Immobilization Plant, will use vitrification to immobilize and permanently store radiological waste. Construction of the plant began in 2002, and is currently scheduled to become operational in 2019.
The rise in use of vitrification in America should come as no surprise. Vitrification methods have been successfully used for solidifying radioactive liquid waste in America, as well as foreign countries for decades. In the 1960s, France and England began experimenting with solidifying liquid waste in glass. Today, both France and England receive radioactive waste from other countries so that it can be vitrified and then returned to the country of origin for storage. Thus, vitrification has a long, and safe, history.
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MOX Fuel From Weapons-Grade Plutonium - By Duncan Williams - On February 25, 2010, the U.S. National Nuclear Security Administration (NNSA) announced that it entered into an inter-agency agreement with the government owned Tennessee Valley Authority (TVA) in order to evaluate the use of a nuclear fuel made from surplus weapons ...
About Duncan WilliamsDuncan Williams graduated from the University of Florida in 1994 with a B.S. in Physics, and a minor in mathematics. Upon graduation, he was commissioned in the U.S. Navy where he completed training in the Navy’s Nuclear Propulsion program. He then served onboard an 
aircraft carrier, the USS Theodore Roosevelt, as a reactor control division officer. Onboard, he was responsible for the operation and maintenance of the electrical and mechanical components that make up the reactor control systems. This includes the control rod drive mechanisms, the reactor safety and emergency systems, the reactor coolant pump systems, and the ion exchangers. He also developed and implemented ship-wide reactor safety drills in order to educate sailors in reactor safety.
Duncan then transferred to the U.S. Naval Academy, where he served as a senior instructor teaching Thermodynamics to senior cadets. While serving as an instructor at the Naval Academy, Duncan attended night law school at the George Washington University Law School. After receiving his J.D. in 2004, he resigned his commission and began working as an intellectual property associate with Kenyon & Kenyon LLP. While at Kenyon & Kenyon, he drafted numerous patents relating to medical devices, electronic devices, telecommunications, as well as other technologies. He also has experience in all stages of patent litigation, and has represented numerous Fortune 500 companies in protecting their intellectual property rights. Duncan is currently an intellectual property associate at Blank Rome LLP.
If you have questions, comments, or know of a patent that you think Duncan should review E-mail Duncan Williams>> duncan@nuclearstreet.com