I would like to have a discussion on issues surrounding radioactive waste.
You certainly have selected an important topic to review . . . and may we add, one of continuing social and political controversy. This Radioactivity Basics chapter serves as an introduction to radioactive waste issues and the management of these wastes.
I know. That’s why I want to learn more. So why is this topic so important?
Essentially, we are faced with an increasing dilemma in this country regarding the development of new disposal sites to harbor radioactive wastes generated from a variety of applications. As one California writer stated in a July, 2000 editorial in a San Jose newspaper: “We want the benefits of the atom….but we can’t agree on what to do with the “leftovers”. Well put, don’t you think?
The topic of radioactive waste seems pretty broad. Can it be broken down a bit?
Absolutely. And, as is the case with many other radiation and radioactivity topics, this is a specialized area requiring a fair degree of selectivity in a forum such as this one. So to make this introduction reasonably well focused, we’ll limit ourselves to the following topics: Sources of radioactive waste, waste classifications, treatment options, the controversy surrounding waste disposal, disposal options, the regional compact issue and access limitations, and costs. In addition, we will briefly discuss mixed waste issues.
Do I need much of a science background to understand this topic?
There are indeed several areas of study important to a true appreciation of the technical aspects of the radioactive waste issue. If you have already reviewed the other “Radioactivity Basics” modules, then you have a good start on understanding basic radiation and radioactivity concepts. In addition, knowledge of chemistry, physics, biology, earth science (e.g., geology, hydrology, etc.), and meteorology are important as well for different reasons. Collectively, they are essential to a better understanding of this issue. However, we’ll continue our discussion in a non-technical manner so that you will come away with insights, but without overly taxing the brain!
Ok. I’m game. Where do we start?
A logical question indeed! Perhaps the best place is with an understanding of what is meant by a “radioactive waste”.
Alright. What is it?
Well, it depends on your perspective! In general, it refers to radionuclides produced either naturally, or through manmade means such as reactors or accelerators, that eventually end up in a form or level of radioactivity no longer useful to the organization responsible for its use. From a regulatory point of view, it is waste that contains radionuclides at concentrations or activities greater than those specified by federal and/or state regulatory authorities. This means a certain “threshold” has to be reached before this designation kicks in.
Could you provide a regulatory example of a threshold?
Here’s one for you. In their regulations, the United States Nuclear Regulatory Commission (USNRC) states that radioactivity concentrations of Carbon-14 (C-14) and Hydrogen-3 (H-3) less than 0.05 microcuries do not constitute a radioactive waste and can be disposed of without regard for their radioactive content. Notice we are not saying radioactivity is absent, but rather it is below a level that warrants disposal at a properly licensed facility.
Ok. Then what categories do qualify as radioactive wastes?
Well, hold on to your hat – there are several because there is no one approach to classifying these wastes! Three categories of particular importance are High-level Radioactive Waste (HLW), Transuranic or “TRU” (i.e, “beyond uranium”) wastes; and Low-Level Radioactive Waste (LLRW or LLW). Other categories include wastes exempt from the regulations (such as medically-generated wastes which can be released directly into the sanitary sewer system if certain conditions are satisfied), naturally-occurring radioactive materials or “NORM”, naturally-occurring or accelerator-produced radioactive material known as “NARM”, spent nuclear fuel, byproduct materials, and the proverbial “other” category.
Whew. That sounds like a lot!
Don’t breathe a sigh of relief yet. Still other types and categories exist. For example, “intermediate” wastes fall between the HLW and LLRW/LLW categories.
Where do all these wastes originate?
There is quite a legacy here. Initially, large volumes of nuclear wastes were produced during World War II when in the interest of national security, an intensive research and development effort known as the “Manhattan Project” was undertaken to accumulate sufficient uranium and plutonium to construct and eventually detonate atomic bombs in Japan. These were known as defense wastes. One result of this effort was the accumulation of wastes from chemical reprocessing techniques used to recover the fissionable plutonium isotope of interest (Pu-239) from neutron bombardment of uranium-238 (U-238).
And since then?
Radioactive wastes now originate from a variety of sources, including not only the defense wastes associated with the government and the military, but commercial sources as well. These include wastes generated from industrial, medical, academic, scientific, and agricultural disciplines.
Yes it is. Most of it is associated with the commercial “nuclear fuel cycle” which begins with the mining and milling of uranium, followed by uranium enrichment (i.e., increasing the natural percentage of the fissionable isotope U-235) and subsequent fabrication of the uranium into “fuel assemblies” for use in nuclear reactors as a generator of electricity. Reactors presently constitute the largest civilian generator of radioactive waste. The cycle then culminates with disposal of the “spent” fuel assemblies. We’ll get to this one more a bit later when we talk about high level waste repositories.
But what about the other stuff in the list?
Exempt wastes, byproduct materials, and those classified as NORM and NARM are probably not worth discussing further in this chapter except to briefly define what they are.
Okay. What is byproduct material, exactly?
Byproduct material basically refers to materials made radioactive by an irradiation process, such as in a nuclear reactor, or the residue (e.g., “tailings” or waste) produced by the extraction or concentration of uranium or thorium from any ore processed primarily for its uranium or thorium content.
Hm-m-m. Well then what is NORM?
NORM refers to radioactive materials naturally occurring throughout our planet and atmosphere. When the concentrations of these materials are enhanced (elevated) through man-made activities, such as the production of chemical fertilizers, oil production, phosphate mining, etc., the designation TENORM or “Technologically Enhanced Naturally Occurring Radioactive Materials” applies. NARM pertains to NORM or accelerator produced materials subject to regulation by individual states, not the NRC.
What physical forms do all of these wastes exist in?
Solid, liquid, and airborne (and either gaseous and/or particulate) forms exist.
Do I take it there is a wide range of radioactivity levels in waste materials?
You bet! High activities, up to curie quantities and more, are typically associated with the nuclear fuel cycle – a prime example being the wastes associated with reactor operations. On the other end of the spectrum, scientific/research laboratories, such as on a university campus, utilize much smaller, i.e., “tracer” (microcurie) quantities. However, these definitely aren’t rules of thumb. Medical and industrial facilities, and even university campuses can generate high concentration materials as well, depending upon what types of licensed activities they have going on there.
You mentioned high-level wastes previously. Tell me about them.
Using a definition provided by the International Atomic Energy Agency (IAEA), we are referring to a waste originating from the reprocessing of spent nuclear fuel or any other waste with an activity similar to fuel reprocessing wastes. In addition, the waste generates a high rate of heat.
If it is an international designation, does it hold true for this country?
Pretty much. High-level wastes include spent nuclear fuel from commercial nuclear reactors and reprocessing wastes (both liquids and solids) from the nuclear weapons program. For your information, the vast majority (~99%) of these wastes originate from military uses.
I take it “pretty much” means there are some differences.
And you would be correct! A prime exception between the IAEA and regulatory policy in the United States is that the U.S. no longer allows reprocessing of spent nuclear fuel.
So we used to commercially reprocess spent nuclear fuel?
Yes, but only for a limited time. From 1966-1972, reprocessing of several hundred tons of spent fuel occurred at a commercial facility near West Valley, New York.
Why did the operation stop? It seems like reprocessing would be a useful way of dealing with waste products.
I agree with you there. However, while social and political reasons influenced the decision, the inability of the plant to operate economically was the primary reason its operations were terminated.
Well, what happened then?
The Nuclear Waste Policy Act was passed in 1982. The Act mandated that high-level waste and spent nuclear fuel would not be processed. Instead, it was going to be stored in geologic repositories designed to provide adequate radiological safeguards for many thousands of years.
And intermediate/low-level wastes . . . are these similar?
Not quite. Both of these types are defined as wastes having radionuclide and heat production levels below those of high-level wastes.
Can you provide a better descriptor of intermediate wastes?
Probably the best way to do so is based on the amount of radioactivity present. The distinction is arbitrary, but generally speaking, intermediate wastes have radioactivity concentrations that are greater than microcuries per gallon but lower than curies per gallon. Using this distinction, low level and high level wastes fall into the microcurie and curie range, respectively.
Are there any particular problems associated with intermediate wastes?
These wastes unfortunately fall into a “no man’s land” where treating them is often a serious economic liability. Therefore, one of two approaches are taken: These wastes are either concentrated to produce high level wastes or diluted to produce low level wastes . . . with the end result being only two categories instead of three.
What are low-level wastes?
Believe it or not, low-level wastes, according to the IAEA classification system, are defined as any wastes not classified as high-level wastes! In other words, they are classified in terms of what they are not, instead of what they are. In general, low-level radioactive wastes carry that designation because, as the name implies, they pose relatively lower risk than do other radioactive wastes. This is because while the preponderance of radwaste, meaning the total volume involved, is large, it contains only a small percentage of the total waste radioactivity.
Is the same true in the U.S.?
In this country, low-level waste also refers to radioactive waste not classified as high-level radioactive waste. But in addition, it is also waste that is not transuranic waste, spent nuclear fuel, or byproduct material as defined in the Atomic Energy Act (AEA).
Where do low level wastes originate?
On the commercial side, the majority of the volumes and levels of radioactivity associated with LLW is generated from nuclear power plants. Defense facilities also generate some LLW.
I’m a little puzzled. How does a nuclear plant produce this type of waste?
Good question! During the course of operation, neutrons can interact and “activate” materials within the plant, making them radioactive. These are referred to as “activation products”. A prime example is activation of stainless steel – an important structural component in a nuclear plant – which produces isotopes of iron, cobalt, nickel, and manganese. Secondly, the fission process produces “fission products” which end up in various places in the plant.
How are they classified?
Per regulations issued by the NRC in 10 CFR Part 61, “Licensing Requirements for Land Disposal of Radioactive Waste”, low-level wastes are further classified as Class A, Class B, and Class C.
What are the distinctions between these classifications?
The particular class designation is based on the type and quantity of radioactivity present. Class A wastes have the lowest potential hazard and require minimal precautions for disposal, while, on the other end of the scale, Class C wastes must be protected/isolated from a potential intruder due to their greater hazard. In addition, because of their relative hazards, these wastes are buried in trenches specifically designed to provide containment for a specified period of time.
Well, Class A wastes are buried in trenches designed to contain the wastes for 100 years, Class B wastes are buried in separate trenches designed for 200-300 year containment periods. And Class C wastes are segregated further, into other trenches designed for 500 year time frames. Class C wastes are also buried deeper in the ground than the other waste categories to minimize access by and reduce potential radiation exposures to an intruder.
Would this be an example of what is meant by “radioactive waste management”?
Yes, it is one good example, but not the only one. Managing the particular type of waste – whether high/low level waste and solid, liquid, or gaseous in nature – to control contamination and provide internal and external radiation protection is the key objective. So when we bury the wastes according to their relative hazards – as we do for Class A, B, and C wastes – we are managing these wastes in the best way possible based on our present knowledge
How can radioactive waste management issues be adequately handled?
It really boils down to issues involving two different sets of criteria: On one hand, there are scientific and engineering aspects to consider. At the same time, social and political considerations must be evaluated.
Tell me about the “science” first.
The science and engineering examine more “quantitative” aspects of the process, that is, things we know or at least can reasonably assess. These include the amount of radioactivity present, half-life of the waste, the physical quantity of the waste, the non-radioactive material the radioactivity is dispersed within, and the form of the waste (i.e., solid, liquid, or gas).
And the socio-political considerations?
Well, this includes several difficult issues such as where the waste will be placed (the “Not in My Backyard” or “NIMBY” syndrome) and public policy decisions.
Can we really “dispose” of radioactive wastes?
In a manner of speaking, no. Radioactive elements lose their radioactivity only through the passage of time and the process of radioactive decay. Many non-radioactive substances, on the other hand, can be treated in a variety of chemical, physical, or biological ways to reduce their “toxicity”.
So we cannot treat radioactive wastes?
Actually, we can. However, the types of treatments employed will not reduce the amount of radioactivity, but rather minimize the risk that these wastes will enter the world in which we live.
What is the difference between “storage” and “disposal”?
Generally speaking, we distinguish between the two terms in this way: Storage implies the waste can be retrieved at some future date, whereas no expectation in this regard exists for disposal. In other words, when we “dispose” of a waste, the intent is to abandon it and never recover it.
You mean to say you simply walk away from a disposal site? That sounds very convenient for the people that generated it, but a bad situation for those who reside near it.
Absolutely not. While the intent may be to abandon the waste, the waste disposal site is not abandoned. Rather, the site itself is kept under watch and regulatory control for an indefinite period of time. In addition, ongoing surveillance and environmental monitoring, such as collecting and analyzing samples of ground and surface water, soil, fish, and vegetation on an ongoing basis, are performed.
Where can low-level radioactive wastes be disposed of in the United States?
The choices differ quite a bit based on whether government or commercial disposal is desired. If its disposal has been authorized through the Department of Energy, or DOE, several government contractor sites have and still do dispose of these wastes. These include facilities located in Hanford, Washington; Idaho Falls, Idaho; Los Alamos, New Mexico; the Nevada Test Site (near Mercury, Nevada); the Oak Ridge National Laboratory, Oak Ridge, Tennessee; Sandia Laboratory, New Mexico; the Savannah River Site, near Aiken, South Carolina; and several smaller sites in a variety of locations.
And for commercial waste?
Unfortunately, the choices here are quite limiting at the moment. Four of the six pre-existing sites originally licensed in the 1960’s were closed in the 1970’s for several reasons, including the discovery of radioactivity leaking from storage containers into the groundwater. (Another one closed to most users in 2008. and while a new opportunity has opened in the State of Texas, that site’s acceptance criteria are limiting and participation is compact-driven.)
So what was done?
In 1980, the United States Congress passed the “Low-Level Radioactive Waste Policy Act of 1980”, making each state responsible for radioactive waste disposal within its borders.
Was there anything special about this Act?
Yes. States were to form agreements or “compacts” with other states whereby one of the states within the compact would serve as the “host”, and the other states would be allowed to dispose of their low-level radioactive wastes within their designated host compact state.
Then what happened?
In December 1985, Congress passed the “Low Level Radioactive Waste Amendments Act of 1985”, a revision of the 1980 policy act. It approved the first seven regional compacts involving thirty-seven states and allowed existing burial sites to remain open to non-compact states beyond the originally mandated January 1, 1986 closure date. It also mandated a new deadline of January 1, 1993 for new burial sites to be in full operation in all compacts.
So that took place, right?
Unfortunately, no. Progress has been slow in this area. Several states initially formed low-level waste compacts with the intent of having one disposal facility per compact in a host state, only to later disassociate their involvement with their respective compact. As of 2001, the present makeup of compacts consist of the: Northwest, Midwest, Southwestern, Rocky Mountain, and Texas. However, only one new disposal facility has been been constructed to date, and that one is in Texas.
Wait a minute. I thought I read about a new facility in California.
Sorry, a bit of wishful thinking happened there. Here’s the deal. In 1993, a well known company, US Ecology, received the first license in over twenty years to operate a shallow land burial site in Ward Valley, California. That site is located twenty-two miles west of Needles, California. Even though the site has been extensively studied and has several notable attributes including low annual rainfall and a deep ground water table, several issues, including the transfer of federally-owned land on which the site rests to the State of California, still await resolution. Therefore, there is no new facility – only the hoped for one.
Then what commercial LLW sites are available for commercial disposal today?
There are four LLW sites available today. The first is located in Clive, Utah, called the “Envirocare” facility. The second is the Barnwell site, located in South Carolina, but that one is only open to Atlantic Compact generators. And the third is the U.S. Ecology site, located near Richland, Washington, access to which is restricted to the Northwest and Rocky Mountain compacts. The fourt, Waste Control Services, is located near Pasadena, Texas but is again compact-restricted.
How is the “fitness” of a low-level waste disposal site determined?
The process is certainly not trivial. Aside from the always present political and social issues, which only result in delay in constructing promising sites such as Ward Valley, there are many technical issues such as hydrogeology which influences to a great extent the movement or migration of radioactivity away from the site (not good!) or the migration of radioactivity into the groundwater (also not good!).
Is the low-level site expected to totally prevent the release of any radionuclides to offsite locations?
That certainly is a noteworthy objective, but the honest answer is that this cannot be guaranteed. However, the design of these sites is intended to ensure that any releases are of such a minor nature that they represent no harm either to the public or the environment. And keep in mind, these sites are typically placed in unpopulated and very arid locations, further reducing the probability of radiological impacts on the general public.
I’ve heard the term, “shallow land burial” before. What is it and why is it used?
It is one means of burying low-level radioactive wastes. As the name implies, the waste is placed in the ground near the surface. Essentially, shallow trenches are dug, and then the waste, which is placed first in a container, such as a steel drum or box to help contain the waste for a sufficient period of time, is covered with dirt or other suitable material. The principal objective is to confine the radioactivity and contain it long enough so as not to present an unacceptable risk to members of the general public.
Where is shallow land burial utilized?
It is used for both federal (e.g., Department of Energy) and civilian applications.
Is anything done to reduce the amount of space required at a shallow land burial site?
Yup. First, every generator makes a conscious effort to minimize the amount of waste generated for shipment to these sites. Secondly, the volume of these wastes, once generated, is then minimized. Regarding the latter, significant efforts are made to reduce the volume of waste through some type of compaction technique in order to maximize the amount of waste that can be placed in a single container. By the way, these two procedures are additional and important parts of a waste management program.
What means are employed to manage the wide range of radioactivity levels in waste?
There are essentially two governing principles. High radioactivity content is typically “concentrated and contained”, whereas much smaller amounts are often “diluted and dispersed”.
Could you clarify the distinction please?
Certainly. In the first case, the levels of radioactivity are sufficiently high that these wastes must be relegated to a specific location designed for this purpose and confined or maintained at this location. The levels of radioactivity are just too high to effectively reduce them by dilution. In the latter case, however, small levels of radioactivity can be diluted, which diminishes the amount of radioactivity on a mass or volume basis, and then dispersed or released into a sanitary sewer . . . as long as applicable federal and state regulations are kept.
There is a third means of dealing with radioactive waste and that is to simply let the waste decay through the radioactive decay process. Of course, this is designed for radionuclides with very short half lives, typically on the order of several days or a few weeks.
How is solid rad waste managed?
There are several useful techniques employed to reduce the volume of wastes produced. These include filtration, ion exchange, evaporation, compaction, incineration, and solidification. These techniques are designed to concentrate the waste which reduces the volume.
You mentioned volume reduction before. Why is this so important?
Two principal reasons: The increasing cost of burial and decreasing amount of available land for burial sites.
I’d appreciate a short explanation of each of those volume reduction methods.
Glad to oblige. To draw some analogies about filtration, think about the types of filters in your home to trap dust, some of which are designed to collect fairly small particles, and the filters in your coffee pot used to strain the grounds. The same principle applies here. The objective is to strain the solid and liquid components through a filter which allows the liquid to pass through and the solids to be collected on the filter. The contaminated filter is then placed in a suitable container, such as a 55 gallon drum, for disposal.
And ion exchange?
This technique is used to handle wastes that cannot be filtered – for example, wastes that are in liquid form. Charged ions in the solution are passed through a resin bed and are exchanged with non-radioactive ions. At some point, the resin becomes saturated with radioactive ions and must be disposed of as waste unless it can be cleaned and re-used.
Evaporation sounds like some boiling process might be involved.
Right you are! Boiling off the water in a waste solution as steam leaves the waste more concentrated. Typically a sludge or something like that is produced.
Tell me about compaction.
Think of a trash compactor you might have in your household, but bigger! Industrial compactors are designed to reduce the volume associated with a container of radioactive waste by crushing the container, often a conventional 55 gallon drum or something like that, under pressure. A hydraulic ram is used to provide the desired compression.
What reduction factor occurs using this kind of compaction?
The amount of volume reduction is going to vary with the material, but to cite one example, a factor of three to seven can be achieved for radioactive waste containing ordinary trash. However, there are also “super compactors” available, that as you might envision, can really do a number on a drum! For example, while ordinary compactors apply a pressure on the order of ten to fifty tons, a super compactor can apply pressures significantly higher – on the order of 1500 metric tons!
Doesn’t crushing a drum containing radioactive waste create other problems?
Yes. The process of crushing the drum can result in the potential for release of airborne contaminants. This radiation protection problem is solved through a combination of applying air suction to remove the contaminants away from the compactor and personnel, and filters to trap particulates prior to discharge to the environment. In addition, the fact that radioactivity is present within the drum presents a potential external radiation exposure for personnel, especially when super compactors are used. This is solved through engineering and proper planning, the latter emphasizing the implementation of the As Low As Reasonably Achievable (ALARA) philosophy and the established exposure reducing principles of time, distance, and shielding.
You haven’t mentioned what happens to the drums.
Good point. The compacted drums are placed into approved Department of Transportation (DOT) containers and shipped to the designated burial site. If you’re interested and have not done so already, you should check out the “Radioactivity Transport” chapter in this section of the Plexus-IEM web page.
And incineration – you mentioned that before, didn’t you?
Yes I did. Incineration is another technique used to reduce the volume of solid radioactive wastes. Examples include paper, cloth, wood, and plastics. In general, burning wastes provides a greater degree of waste reduction than compaction. It is the ability of this particular technique to reduce the volume of waste that has made it a very important waste processing option.
Okay. Well then how does solidification work?
Well, our intent here is to mix a liquid waste with a solid material that, once disposed of, will not be adversely affected by the degrading properties of water. In other words, the waste form will remain stable, avoiding the possibility of leaching and subsequent contamination of the ground and, potentially, the groundwater.
So what do we use?
Concrete and asphalt are popular choices.
This doesn’t sound real “high tech” to me.
It isn’t! But if it works, is there anything wrong with a simple approach?
Nope. But are there any disadvantages to these methods?
Every one of the volume reduction techniques described above has its drawbacks. The success of incineration is dependent on a number of factors such as the type of waste being burned. The process also produces particulates, gases, and ashes from incomplete burning. The particulate component in particular must be effectively trapped to prevent environmental pollution while the residual ash must be treated as LLW. This necessitates a more detailed engineering design than found with compactors. (In case you were not aware, air quality emission standards for incineration must be met – not an easy task.) In addition, public perception regarding this technique is mixed at best.
What types of radionuclides fall into the category of high level wastes?
In general, we are referring to radionuclides with atomic numbers (the number of protons in the nucleus) greater than that of uranium. These radionuclides are known as “transuranic” (“beyond uranium”) wastes.
What approaches have been discussed to manage these wastes?
There have been several ideas proposed over the years, employing a combination of retrievable and non-retrievable methods. The word “retrievable” refers to the possibility of locating the material and removing it at some point in the future. Discussions of retrievable methods have included: 1) the deep hole method – a hole is bored several miles deep in the ground and the waste inserted; 2) placing the waste in a nuclear test hole produced following a planned underground nuclear detonation; 3) the use of granitic rock; and 4) deep underground salt deposits.
What about non-retrievable methods?
Non-retrievable methods have included placing these wastes on the polar ice sheet in the South Pole, burying them in a sea bed, placing them in the direct path of the lava from an active volcano, sending them into outer space (or shooting the wastes into the sun), and transmutation, whereby long-lived radioactive elements could be transformed into other elements with shorter half-lives using neutron irradiation.
What is the problem with these wastes that would require such interesting storage and disposal options?
Many of these radionuclides have very long half-lives, which increase the time period for potential release to the environment. They also routinely decay by alpha emission with its higher degree of biological effectiveness – compared to other ionizing radiations – if inhaled or ingested in sufficient quantity.
What consequence does this have for storage and disposal?
The long half-lives require a special engineered facility to confine the wastes until significant radioactive decay has occurred. Unfortunately, for some transuranic radionuclides, this could require a period of million of years to reach background levels.
Do these facilities exist?
Once again, a yes and no response is required.
But what about that Yucca Mountain thing I have been hearing about? Isn’t that what it was supposed to do?
Yucca Mountain is the site of a proposed government repository for high level solid wastes. Spent fuel assemblies from nuclear power plants would be placed in canisters and stored in holes drilled into the floor of tunnels running through out the mountain. The site is located approximately 100 miles northwest of Las Vegas, Nevada, bordering between Nellis Air Force Base and the Nevada Test Site (NTS).
Why did you say “proposed”?
The site was one of three that were first proposed in 1984 by the DOE after extensive study. Since then, extensive site characterization and tunnel boring activities have begun and continue to this day. Unfortunately, controversy continues to surround the suitability of this site, primarily as it regards the potential for earthquakes, and rain to seep in, causing premature degradation of the canisters, and release of radioactivity into the groundwater. While a license application has been submitted to the U. S. Nuclear Regulatory Commission, political pressure has reduced and may soon eliminate funding for the project. Instead, another “blue ribbon committee” has been proposed to study the options yet again.
If I wanted to learn more about this issue, where can I find further information?
Further information about Yucca Mountain can be found at the U. S. Department of Energy’s Office of Civilian Waste Management web site.
And the Waste Isolation Pilot Plant – what’s the deal with it?
The Waste Isolation Pilot Plant, known as “WIPP” for short, is the DOE’s underground disposal facility for transuranic waste produced as a result of nuclear weapons production. As I mentioned a bit earlier, transuranic waste contains radionuclides with atomic numbers greater than that of uranium (i.e., “92”). The site is located twenty-six miles east of Carlsbad, New Mexico. The waste is placed in underground tunnels carved out of a massive salt deposit.
Where does the project presently stand?
After years of political and social controversy, the first shipment of transuranic wastes arrived at the site in 1999. There have been many more shipments since that time. Further information and updates about WIPP can be found at a USDOE web site, with additional information located at a USEPA web site.
What are high-level liquid wastes?
These are wastes principally associated with the chemical processing of used (or “burned up”) reactor fuel. The high level refers again to the concentrations of radioactivity which can be on the order of several hundred curies per gallon – not a level to be taken lightly!.
How are these wastes managed?
As with many issues we deal with in everyday life, we learn as we go. No exception here. In the distant past, liquid wastes were first reduced in volume through evaporation followed by storage in specially designed underground tanks.
This sounds reasonable to me. What’s the problem?
Glad you asked! While the tanks were designed for strength, resistance to corrosion, heat removal, and monitoring for leaks – an excellent short-term solution – they were not designed for a life span of many hundreds of years. This long time frame raises at least two principal concerns.
The first is the potential for release of certain wastes associated with the fission process which produces a variety of radionuclides from the splitting of uranium atoms in reactors. These wastes, if released to the environment, could concentrate in plants and animals, affecting our food supply and resulting in an internal dose to the human population. The potential for an external radiation dose from exposure to the radioactive waste, though smaller in magnitude than the internal hazard, is the second concern.
All right then, what have we done to address these concerns?
Something pretty neat in the case of the internal exposure pathway! We enclose the radioactivity in materials that prevent its release.
One interesting way is through a process known as “vitrification”.
Say that again?
Sorry! Vitrification is a fancy word for a process that takes radioactive atoms and places them into the chemical makeup of glass beads. In this way, the radioactivity is contained in a glass-like matrix.
This sounds very interesting. But can’t the glass break down and release the radioactivity to the environment?
Yes, that could possibly happen . However, based on extensive research conducted with a special type of naturally occurring volcanic glass, the time for this to happen would be measured in geological time frames, rather than much shorter (historical) time periods. Accordingly, this approach has distinct advantages.
So vitrification is the way to go, right?
Well, yes and no. While vitrified glass removes heat fairly well and leaches (dissolves) at a slow rate, scientists are not satisfied it is the ultimate end product for long term storage. Experiments with ceramics are continuing, for example, to find the “perfect” solution (if one exists) for our long term storage needs.
Ok, I see. How about the external dose hazard?
I see you’re a tough person to convince! We solve the potential external dose problem by placing the glass beads or whatever alternative materials are selected into specially designed containers and burying these containers in deep underground repositories where the hazard to people would be eliminated.
Do these deep underground storage locations exist?
Yes, they do. Examples include deep tunnels used in times past to conduct underground nuclear bomb tests and salt domes. Both of these also have the desired advantage of being geologically stable!
So the bottom line is . . .
The bottom line is we render high level radioactive wastes nonhazardous by eliminating all human exposure pathways of concern.
Let’s move on to intermediate and low level liquid wastes, shall we?
How do we dispose of these wastes?
Let’s look first at what we used to do. Historically, several methods have been used. For one, these wastes were typically discharged into the oceans based on the premise that dilution and dispersion would work quite well. In the United States, four different ocean sites – two in the Atlantic and two in the Pacific Ocean – were used. However, due to uncertainties and questions that arose, principally regarding the distribution of radionuclides in the oceans and the effect on the human food chain, this mode of disposal was stopped in 1994 through an international agreement.
But that’s not all. Another method was direct disposal into the ground utilizing the principle of “delay for decay”. In essence, the ground served as a barrier, allowing the radionuclides time to decay to acceptable, i.e., insignificant levels.
Tell me more about this particular disposal method.
One practice entailed building a pit or “crib” filled with gravel. The liquid wastes were introduced to the crib, and allowed to slowly percolate through the gravel to the ground below.
Were there any flaws in this approach?
As you might suspect, yes. The concern with this approach was the possibility that the groundwater would become contaminated. Therefore, this disposal method is no longer being pursued.
What treatment/decontamination options are there for intermediate/low-level wastes?
One standard approach is through chemical means. The acidity/alkalinity of the wastes can be adjusted to allow precipitation and ionic exchange (As we mentioned previously, ionic exchange means radioactive ions – those with a positive or negative charge – can be exchanged with non-radioactive ions.). Another approach is through evaporation, a process relegated to nonvolatile radionuclides. The objective is to reduce the volume of radioactivity. This process is expensive, however, and is generally worthwhile only when extensive decontamination is required.
You mentioned earlier the disposal of radioactive wastes into sanitary sewers. Does that apply here?
Possibly! If the decontaminated water associated with the treatment of intermediate wastes or the very low level wastes from laboratory operations meet regulatory criteria, discharge into sanitary sewers can be entertained. Note that regulatory controls are in place to avoid indiscriminate decision making.
I am also interested in treatment options for airborne wastes. Can you help?
I’ll try. First, there is no question that the ideal situation would be to control the initial production of airborne wastes. These wastes contain either particles or gases (or both simultaneously). If controlling production is not entirely successful or possible, decontamination measures must be employed, followed by dilution and discharge to the atmosphere.
So what do we do about the gaseous component?
For short-lived gases, especially commonly encountered iodines and noble gases, one option is to trap the gases on a charcoal bed, and allow radioactive decay to take its course. This process is known as “adsorption” and is used effectively at nuclear power plants. A quicker option is to discharge the gases from a very high stack, employing dilution to reduce radioactivity levels to acceptable levels. There are several other treatment options as well.
And the particulates?
Treatment options for radioactive particulates are also varied. The most common approach to control these wastes is to trap the particles on filters that have a very high efficiency for small particles in particular. Once filtered, any particles small enough to pass through the filter are discharged to the atmosphere.
What are mixed wastes?
The name implies we are dealing with a mixture – in this instance, both radioactive and hazardous (chemical) species. Hazardous materials are characterized by being either toxic, corrosive, inflammable, or explosive.
Is that a problem?
It is at least from a regulatory perspective. Disposal of these wastes must meet both NRC and Environmental Protection Agency (EPA) requirements which, to a great extent in the past and less so (but not eliminated) now, were contradictory and incompatible.
Can you provide an example?
It’s like this. Unless special licensing is obtained by federal authorities, a low level radioactive waste (LLRW or LLW) site must reject a mixed waste because hazardous constituents are present. At the same time, hazardous waste processors reject the waste because radioactivity is present. Tough situation, would you not agree?
Is there a way to summarize essentially the bottom line regarding treatment and disposition of radioactive wastes?
Sure. Barring natural decay processes, it is impossible to reduce the level of radioactivity in waste. However, treatment options are available to render these wastes nonhazardous to people. These options include: 1) volume reduction through waste concentration, followed by burial; or 2) dilution to acceptable levels and subsequent release to the environment. Social and political considerations, in addition to technical and engineering considerations, are important drivers in determining the best treatment and disposition methods.
Where can I learn more?
There is a tremendous amount of information available on this topic. This chapter hopefully gave you an initial insight into some of the issues involved in the production, treatment, and disposal of radioactive wastes. I can give you a few more suggestions you might want to pursue.
That would be great.
Basic health physics texts provide useful introductory material. In fact, I often rely on Herman Cember’s Introduction to Health Physics (3rd edition), Daniel Gollnick’s Basic Radiation Protection Technology (3rd edition [though a 4th edition is now available]), and Jacob Shapiro’s Radiation Protection, A Guide for Scientists and Physicians (3rd edition) for some really interesting discussions on radioactive waste. All three of these texts are available in local university or technical libraries. Another very useful text is Raymond L. Murray’s “Understanding Radioactive Waste” (Look for the latest edition because the author updates the present state of knowledge on this evolving area every few years.) For an interesting perspective from the DOE, the book “Linking Legacies: Connecting the Cold War Nuclear Weapons Production Processes to their Environmental Consequences” is available from the DOE Office of Environmental Management. If you’re interested, contact the Center for Environmental Management Information toll free at 800-736-3282 [800-7-EM-DATA]. The book number is DOE/EM-0319.
You’re welcome. However, because of the ongoing and important nature of the radioactive waste issue, many other resources – including online (internet) resources – are available as well. Regarding the internet, you should definitely check out http://www.radwaste.org, a website with links to hundreds of other sites dealing with this issue. The DOE and NRC home pages at http://www.doe.gov and http://www.nrc.gov, respectively, should be used as starting points for locating relevant links and information. One particular NRC “NUREG” document (NUREG/BR-0216) has been published. Entitled “Radioactive Waste: Production, Storage, Disposal”, it can be found and downloaded at http://www.nrc.gov/NRC/NUREGS/BR0216/index.html.