|Other Waste Types
Mixed Waste (MW)
Mixed waste contains both hazardous waste (as defined by RCRA and its amendments-see below) and any type of radioactive waste (as defined by AEA and its amendments). It is jointly regulated by NRC and EPA (or State-level equivalent agencies). The fundamental and most comprehensive statutory definition is found in the Federal Facilities Compliance Act (FFCA) where you can find: "The term 'mixed waste' means waste that contains both hazardous waste and source, special nuclear, or byproduct material subject to the Atomic Energy Act of 1954." Mixed Low-Level Waste (MLLW) is just mixed waste with a radioactive component consisting of "low-level" radioactive waste.
Special Nuclear Material (SNM)
SNM has considerable percentages of fissionable material to be a special concern to management. Includes plutonium, uranium-233, or uranium enriched in the isotopes uranium-233 or uranium-235. SNM is defined as "(1) Plutonium, uranium-233, uranium enriched in the isotope 233 or in isotope 235, and any other material that the NRC, determines to be SNM, but does not include source material; (2) or any material artificially enriched by any of the foregoing but does not include source material." SNM is important in the fabrication of weapons grade materials and as such has strict licensing and handling controls.
Management at LLW dumps must demonstrate to have had training and experience handling fissionable materials before the site can be allowed to handle SNM. SNM is obviously a national security issue.
Source Material is the uranium or thorium ores mined from the earth. Source material is defined as "(1) Uranium, or thorium or any combination of uranium and thorium in any physical or chemical form; or (2) Ores that contain, by weight, one-twentieth of 1 percent (0.05 percent), or more, of uranium, thorium, or any combination or uranium and thorium." Source material does not include special nuclear material or byproduct material.
Special Case Waste
Waste that is not high-level or transuranic waste, but requires greater confinement than of standard radioactive waste disposal methods.
Depleted uranium (DU) is in such surplus that massive amounts sit stored in corroding tanks at the enrichment plants in gaseous form (uranium hexaflouride- UF6). The primary use of depleted uranium is by the military, which use its characteristics as one of the densest elements known for armor and for aircraft wing counterweights. They also make armor-peircing missles which use a chemical characteristic of DU. When DU weaponry is fired at a tank, it superheats upon impact and burns up, drilling a hole through the target, and dispersing powdered DU throughout the immediate area. When this material is airborne, such as in conditions like Desert Storm in Iraq, it has been found to go downwind anywhere in a 60-mile radius. DU is an alpha emitter, and has an extremely long halflife. As a solid metal, it is not dangerous aside from minor exposure to the skin on contact. Risk is raised considerably when it is in a gas or airborne powder as produced when burned up. The risk of lung cancer is raised, but microscopic particles can also pass through to many parts of the body through the bloodstream.
Veterans and their families have amassed enormous amounts of information on the toxic effects of DU. Many of them have had personal experiences where either themselves or a loved one had contracted medical complications after the Gulf War. Often they had been given nonfunctional treatments based on misdiagnosis by doctors, and turned away. They found that they were not alone, and pooled their research with nongovernmental Veterans groups. The main reason the US military denies the effects of DU is simple- if DU is considered a chemical weapon, the US would be harshly criticized for violating the Geneva Convention. (DU is not a "nuclear weapon", since its use does not involve triggering a fission chain-reaction) Many veterans have died, some of them had posed for pictures next to tanks covered in white DU dust in the Middle East. Often, veterans recall that their commanding officers sometimes had worn protective clothing while GI's were not briefed or informed that they were handling a toxic substance.
Hazardous Waste and Hazardous Substances
Hazardous waste is waste, which is defined by the Resource Conservation and Recovery Act (RCRA), and does not contain materials, which are considered radioactive from a regulatory standpoint. It can be waste, which a generator has declared to be hazardous, or contains any of a wide variety of organic and inorganic material, heavy metals, and/or other hazardous constituents.
Some materials are not regulated under RCRA, but are hazardous. These materials are generally considered hazardous under either the Toxic Substances Control Act (TSCA) or the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA, widely known as Superfund), and include contaminants such as PCB's, asbestos, and petroleum products. These materials are not considered hazardous waste, and are called "hazardous substances."
Nuclear Waste Storage
Main problem of nuclear waste is what to do with it. In fact, one of the biggest (and perhaps the single biggest) expenses of the nuclear power industry could eventually be the storage of nuclear waste. Currently there are several ways in which nuclear waste is stored. Most of these methods are temporary. In most cases a viable long-term solution for waste storage has yet to be found. This is because the time period for storage is so incredibly long.
The U.S. plans to store the waste in Nevada in the same area as has been used for underground nuclear tests. This plan is still tied up in long-term indecision. In 2002 a big step forward was taken when the President signed a bill to over-rule the objections of the State of Nevada.
Fuel Rod Storage Pool (Temporary Storage)
The spent fuel rods from a nuclear reactor are the most radioactive of all nuclear wastes. When all the radiation given off by nuclear waste is tallied, the fuel rods give off 99% of it, in spite of having relatively small volume. There is, as of now, no permanent storage site of spent fuel rods. Temporary storage is being used while a permanent site is searched for and prepared.
When the spent fuel rods are removed from the reactor core, they are extremely hot and must be cooled down. Most nuclear power plants have a temporary storage pool next to the reactor. The spent rods are placed in the pool, where they can cool down. The pool is not filled with ordinary water but with boric acid, which helps to absorb some of the radiation given off by the radioactive nuclei inside the spent rods. The spent fuel rods are supposed to stay in the pool for only about 6 months, but, because there is no permanent storage site, they often stay there for years. Many power plants have had to enlarge their pools to make room for more rods. As pools fill, there are major problems. If the rods are placed too close together, the remaining nuclear fuel could go critical, starting a nuclear chain reaction. Thus, the rods must be monitored and it is very important that the pools do not become too crowded. Also, as an additional safety measure, neutron-absorbing materials similar to those used in control rods are placed amongst the fuel rods. Permanent disposal of the spent fuel is becoming more important as the pools become more and more crowded.
Another method of temporary storage is now used because of the overcrowding of pools. This is called dry storage (as opposed to "wet" storage which we outlined above). Basically, this entails taking the waste and putting it in reinforced casks or entombing it in concrete bunkers. This is after the waste has already spent about 5 years cooling in a pool. The casks are also usually located close to the reactor site.
Fuel Rod Disposal (Permanent Storage)
There are many ideas about what to do with nuclear waste. The low-level (not extremely radioactive) waste can often be buried near the surface of the earth. It is not very dangerous and usually will have lost most of its radioactivity in a couple hundred years. The high-level waste, comprised mostly of spent fuel rods, is harder to get rid of. There are still plans for its disposal, however. Some of these include burying the waste under the ocean floor, storing it underground, and shooting it into space. The most promising option so far is burying the waste in the ground. This is called "deep geological disposal". Because a spent fuel rod contains material that takes thousands of years to become stable (and non-radioactive), it must be contained for a very long time. If it is not contained, it could come in contact with human population centers and wildlife, posing a great danger to them. Therefore, the waste must be sealed up tightly. Also, if the waste is being stored underground, it must be stored in an area where there is little groundwater flowing through. If ground water does flow through a waste storage site, it could erode the containment canisters and carry waste away into the environment. Additionally, a disposal site must be found with little geological activity. We don't want to put a waste disposal site on top of a fault line, where 1000 years in the future an earthquake will occur, releasing the buried waste into the environment.
The waste will probably be encapsulated in large casks designed to withstand corrosion, impacts, radiation, and temperature extremes. Special casks will also have to be used to transfer fuel rods from their holding pools and dry storage areas next to the reactor to the permanent geological storage site.
Plutonium Waste Storage
Besides fission products, spent fuel rods contain some plutonium produced by the U-238 in the reactor absorbing a neutron. This plutonium and leftover uranium can be separated in a reprocessing plant and used as reactor fuel. The Japanese had their spent fuel rods reprocessed in Europe and shipped the plutonium back home for use in reactors. Thus, plutonium is more easily addressed in nuclear waste management when compared to the fuel rods.
In terms of nuclear fuel, about 1/4 as much as the U-235 that was in the fuel rods in the first place. Thus running a reactor for four years produces enough plutonium to run it for one more year provided the plutonium is extracted and put into new fuel rods.
Accidents involving Nuclear Waste
A number of incidents have occurred when radioactive material was disposed of improperly, shielding during transport was defective, or when it was simply abandoned or even stolen from a waste store. In the former Soviet Union (a nation possessing a high level of technical expertise and experience with nuclear issues), waste stored in Lake Karachay was blown over the area during a dust storm after the lake had partly dried out. In other cases lakes or ponds with radioactive waste accidentally overflowed into the rivers during exceptional storms.
Scavenging of abandoned radioactive material has been the cause of several other cases of radiation exposure, mostly in developing nations, which may have less regulation of dangerous substances (and sometimes less general education about radioactivity and its hazards) and a market for scavenged goods and scrap metal. The scavengers and those who buy the material are almost always unaware that the material is radioactive and it is selected for its aesthetics or scrap value. Irresponsibility on the part of the radioactive material's owners, usually a hospital, university or military, and the absence of regulation concerning radioactive waste, or a lack of enforcement of such regulations, have been significant factors in radiation exposures.
Transportation accidents involving spent nuclear fuel from power plants are unlikely to have serious consequences due to the strength of the spent nuclear fuel shipping casks.
The Problems of Nuclear Waste
And, why do it? Creating a deep underground storage/disposal site is easily and cheaply done by conventional mining and tunneling methods. This is what is proposed for the Nevada Yucca Mountain site which is only twenty miles, or so, from the weapons test area. Also, Yucca Mountain is dry and above the water table. Most, or all, of the nuclear test caverns are below the water table and now flooded.
The hazards of radioactivity are not expressed in "cubic yards" but in terms such as "mega curies" "relative biological effectiveness", "half-life", "environmental mobility" and other similarly arcane terms. These hazards are measured in terms of "trillions" and greater. A factor of 2.5 up or down has no practical significance in arriving at a long-term solution. In fact, because of isotopic decay, radioactive hazards decrease with time, unlike most toxic chemicals, which will remain hazardous forever.
Nuclear Waste Treatments
Synthetic rock is a more sophisticated way to immobilize such waste, and this process may eventually come into commercial use for civil wastes (it is currently being developed for U.S. military wastes). Synroc was invented by the late Prof Ted Ringwood (a geochemist) at the Australian National University. The Synroc contains pyrochlore and cryptomelane type minerals. The original form of Synroc (Synroc C) was designed for the liquid high-level waste (PUREX raffinate) from a light water reactor. The main minerals in this Synroc are hollandite (BaAl2Ti6O16), zirconolite (CaZrTi2O7) and perovskite (CaTiO3). The zirconolite and perovskite are hosts for the actinides. The strontium and barium will be fixed in the perovskite. The caesium will be fixed in the hollandite.
In the nuclear industry it is the most common for medium active wastes to be treated with ion exchange or other means to concentrate the radioactivity into a small volume. The much less radioactive bulk (after treatment) is often then discharged. For instance, it is possible to use a ferric hydroxide floc to remove radioactive metals from aqueous mixtures. After the radioisotopes are absorbed onto the ferric hydroxide, the resulting sludge can be placed in a metal drum before being mixed with cement to form a solid waste form. In order to get better long-term performance (mechanical stability) from such forms, they may be made from a mixture of fly ash, or blast furnace slag, and Portland cement, instead of normal concrete (made with Portland cement, gravel and sand).
Where does stored nuclear waste go?
Waste resulting from the nation's nuclear weapons program lie in a remote location in southeastern Washington State called Hanford. Beneath this desert landscape about two million curies of radioactivity and hundreds of thousands of tons of chemicals are captured within the stratified vadose zone below which gives rise to complex subsurface flow paths. These paths create uncertainties about where the contaminants go and what happens to them. With the mighty Columbia River bordering much of the site, where these nuclear wastes migrate, their composition and how fast they are traveling are of vital importance to both environment and the people.
To better understand the migration of these contaminants, Researchers have investigated Hanford’s vadose zone, ultimately reducing or stemming their flow toward the Columbia River, thereby protecting the river and the people living downstream. By studying the geologic, biologic, geochemical and hydrologic conditions at the Hanford site, the researchers seek to understand and manipulate the factors that control contaminants’ fate and transport.
Studies show that fine-grained sediment layers along with rain, snowfall and other climatic conditions affect contaminant transport. For three decades, scientists have studied what happens when water enters and exits the soil, particularly under various conditions how it affects the movement of the contaminants.
Chemical studies indicate that a number of contaminants, such as cesium, react strongly with Hanford sediments and move only under extreme conditions. Researchers found that another contaminant, uranium, reacts with the sediments in complex ways and its migration varies under different conditions. Other contaminants, such as tritium and nitrate, are relatively mobile. These contaminants have been transported deep into the vadose zone and reached the groundwater. Carbon tetrachloride and other organic compounds have moved in complex ways, as both vapor and liquid, and reached the groundwater.