Can radiation waste from fission reactors be safely stored

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Can radiation waste from fission reactors be safely stored?

Viewpoint: Yes, radiation waste from fission reactors can be safely stored using existing technical expertise and drawing on the experience of test facilities that are already in operation.

Viewpoint: No, radiation waste from fission reactors cannot be safely stored, given the ever-present danger of human error and natural catastrophe during the thousands of years in which the waste must be stored.

The development of human societies has been characterized by an ever-increasing demand for energy. Until the industrial revolution this meant the muscle power of humans and animals, augmented by wind and flowing water for limited applications such as sailing and milling. Fuels—wood and sometimes coal—were burned for warmth but not for mechanical work.

With the invention of the steam engine, the energy content of wood and coal became available for such work, and the consumption of fuel dramatically increased. Forests were decimated and coal mines dug in great numbers. Eventually petroleum and natural gas deposits augmented coal as energy reservoirs, as the development of electrical technology put numerous horsepower at the disposal of the ordinary citizen in the industrialized world. However, the stores of these fuels would eventually not be enough to keep up with demand, and pollution of the air and water with the wastes of combustion would threaten the environment.

In the 1930s, physicists realized that the fission of uranium nuclei could be stimulated by neutron bombardment, and that the fission process released neutrons, which could stimulate additional fission events. The possibility of a self-sustaining chain reaction releasing immense amounts of energy was thus at hand. This discovery occurred, however, as the world headed towards World War II. In August 1939, a month before Germany invaded Poland, a number of leading physicists prevailed upon Albert Einstein to write a letter to President Franklin D. Roosevelt, recommending that the Unites States government fund nuclear research. This letter led to the development of the atomic bomb and its use as a weapon of war.

Following victory over Japan in 1945 and a period of debate between the proponents of military control over atomic energy and those favoring civilian control, the United States government set up the Atomic Energy Commission. New reactors were built: for research, to generate isotopes for medical use, and to generate electrical power. An "Operation Plowshare" was established to research civilian uses of nuclear explosives. Nuclear power plants were initially considered quite attractive as an energy source. They produced none of the air pollution inherent in the burning of fossil fuels, and the energy produced per pound of fuel was a million times greater. However, nuclear power had both political and practical drawbacks.

There are always political issues associated with nuclear power. Many Americans are intimidated by anything "nuclear" or radioactive. The cold war, with its nuclear bomb tests, air-raid drills in schools, and discussion of the need for shelters against radioactive "fallout," certainly did not make for peace of mind. But elements of overreaction can also be noted. When engineers developed a way of using the well-established technique of nuclear magnetic resonance (NMR) to image the soft tissues of the human body without exposure to x rays, hospitals soon found it necessary to rename the NMR imaging technique as "magnetic resonance imaging (MRI)" to reduce patient anxiety.

The practical drawbacks to nuclear power include the possibility of accident, the possible theft of nuclear materials or sabotage by terrorists, and the problem of waste disposal and storage. Accidents and theft can in principle be prevented by proper diligence and an engineering "fail-safe" approach. The problem of waste storage and disposal has proven more difficult to resolve. Reactor fuel elements eventually become unsuitable for continued use in the reactor but remain highly radioactive, while other shorter-lived radioactive waste is produced as a byproduct of reactor operation and fuel extraction.

Radioactive wastes are classified as low-level waste (LLW), intermediate-level waste (ILW), or high-level waste (HLW), depending on the time it will take for the radiation emitted to decay to background levels. This time can be calculated from the half-lives of the radioactive elements contained in the waste. Half-lives can vary from fractions of a second to millions of years. Low-level wastes contain short half-lived elements and typically decay to background levels in less than 100 years. Intermediate-level waste requires a somewhat longer storage period, but both LLW and ILW, which constitute the greatest volume of waste, can be buried in sites that can be trusted to be stable for a century or so.

High-level wastes, which include spent fuel rods, will remain radioactive for hundreds of thousand of years. Furthermore, uranium and plutonium are two of the most toxic substances known, so that a discharge of any amount into the environment presents chemical health risks in addition to those risks associated with radiation. The safe storage of HLW in a remote location would require that the cumulative risk of release from even highly improbable events remain small over time periods of hundreds of thousands of years. The risks involved in shipping HLW to this long-term storage would also have to be eliminated.

Essentially all the HLW generated by nuclear power plants in the United States is stored at the sites at which it is generated, and storage space is running out. The notion of deep burial in geological formations believed to be stable has some support, but responsible opponents point to the difficulty of assuring that the waste will not be released by earthquakes or seepage into groundwater. There is also the possibility that radiation released by the waste will, given enough time, compromise the physical integrity of the disposal site. However, even if nuclear power generation is abandoned, enough HLW already exists that there is no alternative to finding an adequate long-term storage or disposal method. The dispute over what that method is will be a major issue confronting twenty-first century science.

—DONALD R. FRANCESCHETTI

Viewpoint: Yes, radiation waste from fission reactors can be safely stored using existing technical expertise and drawing on the experience of test facilities that are already in operation.

Radioactive waste from fission reactors is already being stored safely all over the world. Although the majority of radioactive waste (rad-waste) is buried, a small amount of the most dangerous waste is currently stored by the reactors that produce it, and it is the permanent disposal of this waste that is currently causing concern. If politics were left out of the equation, then the safe permanent disposal of all radioactive waste is possible today. The scientific knowledge and technical know-how already exists, the plans have been on the drawing board for many years, and test facilities have been running in a number of countries. However, the political will to make legislative changes, and the public acceptance of such disposal sites, are necessary before these plans can be put into operation.

Storage Versus Disposal

It is important to note the difference between the temporary storage of radwaste, and the permanent disposal of such waste. Most reactor-made radwaste is first stored on-site at the reactor facilities. The vast bulk of radioactive waste, about 95% by volume, is stored only for a few months or years before being buried. The remaining radwaste, which mainly consists of spent fuel rods, is stored in temporary facilities. This waste has been mounting up for decades, as there are currently no permanent disposal sites in operation. Spent fuel rods are the most active and "hot" waste. Within their metal cladding, they contain numerous fuel pellets, each about the size of a fingertip; each pellet contains potential energy equivalent to 1,780 lb (808 kg) of coal, or 149 gal (565 L) of oil. Because of their small size, 40 years worth of spent fuel rods in the United States is only about 44,000 tons (40,000 t), and would cover an area the size of a football field to a depth of about 5 yd (4.5 m).

Spent fuel rods are classified as high-level waste (HLW), for despite their small size they are very radioactive, produce a large amount of heat, and remain dangerous for 100,000 years before their activity finally falls to background levels. The most common type of radwaste is low-level waste (LLW), consisting of solid material that has levels of radioactivity that decay to background levels in under 500 years. Ninety-five percent of LLW decays to background levels within 100 years or less. Large volumes of LLW are produced in the mining of radioactive material, the storage and transport of such goods, and even by being in close proximity to radioactive sources. LLW can include anything from equipment used in a nuclear power plant, to the seemingly harmless contents of a wastepaper basket from a laboratory. Practically, for rad-waste disposal purposes, intermediate-level waste (ILW) and LLW are grouped together, while the more dangerous HLW is treated separately.

Radwaste disposal aims to keep the waste secure until such time as its emissions reach background levels. For LLW and ILW, the methods are simple, cheap, and very effective, with the vast majority of waste being disposed of in "shallow" burial sites. While the term "shallow" may give some cause to worry, it is only shallow in comparison to the proposed deep disposal methods for HLW discussed in the following section, and can actually be up to 110 yd (100 m) below the surface. Simple trenches are used for some types of very short-lived LLW, and engineered trenches are created for other waste. An engineered trench may be many tens of yards deep and lined with a buffer material such as clay or concrete. Containers of waste, themselves highly engineered, are then placed in the trench, and the trench can then be backfilled with a buffer material, adding yet another level of protection. There are also other, less common, methods for disposing of LLW, such as concrete canisters, vaults, and bunkers. The sites for burial must be away from natural resources, isolated from water, and in areas of low geological activity. Such sites come under strict national and international controls, and are constantly monitored.

High-Level Waste Disposal

High-level waste does not leave the nuclear power plant in which it is produced. The spent fuel is stored in steel-lined, concrete vaults filled with water, which cools the fuel and never leaves the plant itself, to avoid any possible contamination. However, such monitored storage is not an acceptable long-term solution, and nuclear power plants were not designed to be the final resting places for such waste. Because of its extreme longevity, HLW requires a disposal solution that will remain safe and secure without human monitoring. Many options have been suggested, but all have their problems.

The idea of launching radwaste into space, completely outside Earth's environment, is in some ways a very attractive option. The waste would have little or no effect on space, which is already a radioactive environment. However, the possibility of a launch accident such as the 1986 Challenger space shuttle disaster highlights the key problem with such a method. In addition, even if a completely safe launch method could be devised, the cost of space disposal would be astronomical.

Many early efforts to dispose of HLW focused on the notion of reprocessing spent fuel cells so they could be used again. However, reprocessing proved to be very expensive and produced vast quantities of highly toxic liquid waste, which was even more problematic than the used fuel cells. Although a number of reprocessing plants were built, and a few operated, their use has more to do with politics than a sensible solution to HLW disposal. Nuclear incineration, a process that can turn HLW into LLW, suffers from similar cost and contamination problems.

Some countries, including Sweden and Canada, have suggested disposing of HLW in ice formations. One advantage of this method is that the heat-producing radwaste would sink itself deeper. However, the costs of transporting the waste to such remote areas would be prohibitive. In addition, there is no scientific data concerning the extreme long-term behaviour of ice formations, and there are a number of legal constraints.

Sea burial of radwaste is one of the few proposed methods for which there is a large amount of data, mainly thanks to the ill-advised, and sometimes illegal, sea dumping of the past. Sea burial relies not only on containment, but also on the diluting power of the oceans to quickly reduce any leaks to background levels. The data show that sea burial is a very effective method that provides safety to the human environment and has only a localised effect on the immediate surroundings. However, all nuclear waste-producing nations have signed international agreements banning the use of the sea for radwaste disposal. In part this is due to the reckless early dumping done before the impact had been studied, and also because of political pressure from nonnuclear waste-producing countries.

Geological Disposal of HLW

The most promising potential solution is deep geological disposal, which basically means burying HLW deep underground. The aim of deep disposal is to isolate the HLW from the environment for as long as possible, partly by mimicking natural processes, and also by over-engineering to ensure a higher degree of safety. A number of natural burial sites have kept naturally occurring radioactive material shielded. At Oklo, Gabon, Africa, a large amount of radioactive ore has been shielded by bedrock for two billion years, and under Cigar Lake in Canada, a body of uranium ore embedded in clay acts as a natural repository.

Deep burial sites can be engineered to avoid the shortcomings of other proposed methods. Multiple barriers would separate the radwaste from the outside world, much like a set of Russian dolls, where removing one doll reveals another. The first level of protection would be the packaging of the HLW itself, such as a metal canister. This would in turn be over-packed inside a second metal or ceramic container. These canisters would then be placed inside the underground facility, up to a 0.33 mi (0.5 k) underground. Once full, the facility would be back-filled with buffer material to fill up the spaces between the canisters and the walls. Over the next 100,000 years, the contents of the deep disposal facility would slowly decay to background levels, and eventually become one with the surrounding rocks. Underground burial protects the waste from both natural disasters and human interference. For example, underground sites are much more resistant to earthquake damage than surface sites. Physical barriers, the remote location, and the choice of a site well away from potential resources will deter all but the most determined and large-scale attempts to gain access to the waste.

Deep geological disposal is the preferred HLW disposal method for all countries producing nuclear waste, but it does have its opponents. Some critics have suggested that more needs to be known about the implications of deep disposal before such facilities are opened. To that end test sites have been collecting data around the world, and hundreds of studies and experiments have been carried out modelling potential hazards and their solutions. The impact of everything from volcanoes to meteorites has been considered, as well as more likely concerns such as climate and groundwater changes.

Groundwater is the most likely method for disposed radwaste to move back to the human environment, and the biggest concern for those involved in the design of disposal sites. All rocks contain some amount of water, and it moves through pores and fissures, leeching out mineral deposits as it flows. Such is the power of water flow that, no matter how over-engineered a deep disposal facility may be, water will eventually cause the release of waste. The aim is to make the timescale during which such leakages occur a geological one by selecting dry sites well above the water table, and using innovative engineering, such as the Swedish WP-cave design which isolates the entire facility from any possible groundwater leakage by using a hydraulic cage.

Politics and Public Relations

However, the biggest obstacles by far for deep geological disposal are not technical, but political and public-relations problems associated with radwaste. In many ways the nuclear power industry has only itself to blame. Early burials were often haphazard and made with little concern for the environment, and many early LLW trenches were prone to flooding and leaching of radioactive material into the local groundwater. Since the 1970s there have been much stricter regulations controlling the disposal and storage of all industrial waste, and a much greater appreciation for the danger these represent to humans and the environment. As a result the burial of nuclear waste is one of the most regulated activities on the planet, and the nuclear power industry can proudly claim to have all of its recent waste safely contained, unlike many other industries.

However, the nuclear power industry has a history of poor public relations. Combined with early mistakes, this has led many to protest against nuclear power and the dumping of waste, and to resist moves to open burial sites in their vicinity. The nuclear power industry is now trying to redefine its image within the community, stressing the clean air aspects of nuclear generation, and the benefits to consumers in terms of quantity of power and cost savings. These public relations moves are important, as deep disposal sites must gain many public consents. Even though a disposal site may benefit a nation, it is often hard to convince those who will be living closest to the site to see the positive side.

Another reason for opposition to deep disposal sites is the issue of the transportation of HLW to such areas, which in some cases passes close to human settlements. Yet the safe and efficient transportation of hazardous waste (including ILW and LLW) already occurs in many countries, and there are about 100 million shipments of toxic waste annually in the United States. The safety record for radwaste transports in the United States is astoundingly high, with only four transportation accidents since 1973, with no resulting injuries. Other countries have similar, or better, safety records. However, accidents in other industries, most notably with oil shipping, have left the public unwilling to accept industry assurances about the safety of waste transport.

Only one country, Finland, has made a positive decision regarding the final disposal of high level radwaste: it hopes to have an final disposal facility operating around 2020. Other countries seem poised to follow suit, but face further political and public hurdles.

The safe disposal of radwaste is not a technical problem, but rather a political one. The scientific and technical details for the disposal of nuclear waste have been studied in extraordinary detail, and the need for permanent disposal is pressing. Even if all nuclear waste production, industrial, medical, military and scientific, were to cease tomorrow, there would still be a legacy of waste that will last over 100,000 years. In addition, the growing demands on power consumption, and public demands for more power stations and cleaner, cheaper power all suggest that the number of nuclear power stations around the world is likely to increase. When this happens, the need for a permanent disposal sites will become more urgent.

—DAVID TULLOCH

Viewpoint: No, radiation waste from fission reactors cannot be safely stored, given the ever-present danger of human error and natural catastrophe during the thousands of years in which the waste must be stored.

After the detonation of the first atomic bomb in 1945, Robert Oppenheimer, the key scientist in the Manhattan Project, which developed the bomb, was quoted as saying, "I have become Death: the destroyer of worlds." Oppenheimer could not have known exactly how prophetic these words were. From that fateful moment in the middle of the last century, we have been living in the nuclear age. However, with the end of the Cold War in the early 1990s, the threat of nuclear war was greatly diminished. Although we no longer had to focus on the destructive power of the atomic bomb, we suddenly found ourselves with a much greater problem right in our own backyards—what to do with radioactive waste. This waste came not from the development of weapons, but rather from the production of electrical power. Because we thought science would soon come up with a solution, we weren't too alarmed at first. However, as it turned out, the problem would be with us for a long time to come.

What Makes Radioactive Waste Such a Problem?

Nuclear power plants produce power through the use of a fission reactor. Uranium is processed into fuel rods, which are then placed into the reactor core. The heat created through the nuclear reaction produced by these rods through the splitting of atoms, provides us with electricity. However, this reaction begins to diminish as fuel is "spent." Before long, usually 12 to 18 months, the rods must be withdrawn from the reactor and replaced with new ones. Although they are no longer useful in producing energy, these spent fuel rods are now high-level waste (HLW) and incredibly dangerous.

To understand how dangerous these rods are, one must consider that an exposure to 5,000 rems (a unit of radiation dosage applied to humans) will instantly debilitate a human being, with death following within seven days. On average, an unshielded spent fuel rod can provide a 20,000 rem dose each hour of exposure to within a few feet. A significantly smaller dosage of radiation can cause cancer years—or even days—later.

Nor do these spent fuel rods lose their radioactivity in a short period of time. Radioactive elements are characterized by a quantity called a half-life, which determines the amount of time it would take for half the element to decay into a more stable form. HLW normally takes 10 to 20 half-lives to lose its hazardous qualities. To put this in perspective, Plutonium-239, a common element in spent fuel, has a half-life of approximately 24,400 years. This means it could provide a lethal dose of radiation well over 200,000 years after it is removed from a reactor core. Anyone that interacts with this material, even millennia from now, must remain shielded or risk deadly exposure.

With the vast potential for harm this HLW possesses, as well as the incredible period of time for which it remains dangerous, the question of safe disposal methods has become a serious matter. However, even now the question remains, for the most part, unanswered. Many suggestions have been made, but as yet none have been viable. This is a terrifying prospect considering the fact that although HLW makes up only 3% of all radioactive waste, it contains 95% of the dangerous radioactivity.

Problems Associated with Current Storage Methods

Currently, spent fuel rods are stored on-site at their producing reactors. Not one ounce of this HLW, during 40 years of production, has been placed into a permanent disposal facility. For now, the rods remain in cooling pools, where they are stored until they become safe for transportation. Because of the heat and radiation they produce, the rods will have to remain in this form of storage for several decades before they can be considered manageable.

This wet form of storage produces numerous problems and concerns. For example, this form of storage is only a temporary solution. It was, indeed, intended to be temporary, as it was assumed that a better solution would be discovered as time passed. Optimists thought that scientists would work on the problem and the temporary storage method would buy them time to find a solution. Time is, however, running out. Although the pools are able to contain the HLW for the moment, space is limited, as each pool can only hold a certain number of rods at one time. Each year, more HLW is created and thus requires storage. With the incredibly slow turnover rate (the time it takes to move the old rods out to make space for the new ones), HLW will begin to back up much sooner than most would like.

Some facilities in the United States have already reached their pool capacity. In these cases, the rods have been placed into dry storage—contained in a cask made of metal or concrete, which is then filled with inert gases. Even so, this form of storage can only be used several years after the rods have been cooled off in storage pools.

The cooling pools themselves are also at risk from damage by outside influences, such as earthquakes, tornadoes, or hurricanes. Improper storage or human error could also create serious problems, as the pools require constant upkeep and surveillance. Should the water levels drop too low or the rods become too close to one another, the rods will begin the early stages of a nuclear reaction. At best, this will produce massive amounts of dangerous heat and radioactivity. At worst, it would lead to a horrific meltdown that could not be contained.

The Yucca Mountain Depository—Is It the Answer?

Every country in the world has different options for its long-term HLW disposal plans, ranging from reprocessing to burying it deep in the earth. The United States has begun to focus on the Direct Disposal option. In this plan, the spent fuel rods progress through the cooling off phase in on-site standing pools until they eventually become ready for shipment. Once manageable, the rods are transported across the country to an underground depository. The proposed location of this depository is beneath the Yucca Mountains in Nevada, where emplacement tunnels about 985 ft (300 m) beneath the surface will then serve as the final resting place for the HLW.

There are two major problems with this plan, both short term and long term. In the short term, one must consider the extreme risks inherent with the transportation of the HLW to the disposal site. In some cases, this could involve distances of thousands of miles. Transportation of the spent fuel rods will be done with large trucks. The HLW itself will be contained in casks similar to those used for dry storage, which must remain completely intact for several thousand years to prevent the radioactive material from escaping. The longer these casks are in transit, the greater the risk of them being damaged through human error or natural disasters. Consider the damage that might be unleashed by a road accident, during which a breach could spill deadly radioactivity into the environment. Should several casks be damaged, the rods contained within could react to one another just as violently as they could in a cooling pool accident. In both cases, the result would be catastrophic, with long-lasting ramifications.

Even if the HLW should reach its destination at the Yucca Mountain depository without incident, numerous other problems remain. When considering the risks of permanent HLW storage, the dangers cannot be thought of in terms of years, decades, or even centuries. Indeed, we must think in the terms of millennia, perhaps even longer than the human race has been on Earth. In the tens and hundreds of thousands of years it will take for the HLW to become safe, the planet itself can change drastically. The geologic processes that shaped Earth are still at work, and could have dramatic consequences on a facility such as the Yucca Mountain depository.

There are 33 known geologic fault lines near or in the Yucca Mountain area, and each has the potential of unleashing a devastating earthquake. Should an earthquake occur, the storage facility could be severely damaged and, in turn, break the HLW casks. The water table beneath the facility, which feeds the Amargosa Valley, risks serious contamination in such an event. Farming communities making use of this water would be devastated and turned toxic for generations. While the fault lines may not be active at this moment, this does not mean they could not become active in the future. There is another worry, a volcano that is only 10 miles away from the site. By itself, it has the potential of creating seismic events that could damage the facility and its contents irreversibly.

The human element in the equation must also be considered. For one, sabotage or human error could be viable threats to such a facility. It would only take one mistake to unleash a disaster of unimaginable proportions, although admittedly the facility would be well guarded. Also, the facilities must be maintained throughout several generations to make sure none of the casks are leaking and to keep an eye on potential geological threats. Even though such a staff would be small and easy to manage, they would have to be vigilant long into the future. Also, the casks containing the HLW will eventually erode and begin to leak after about 1,400 years. Although several elements will have become inert before this time, others, like plutonium, will hardly be through their first half-life and still be extremely dangerous. Nothing but bare rock would stand between these elements and the outside world. Nor will there be anything between them and other HLW, posing a risk for nuclear reaction.

In the end, we are left with a deadly threat that will not go away for thousands of years. At the moment, the only solutions for dealing with it are unsafe and temporary. Even in the long term, there are no trustworthy resolutions, and quick fixes cannot be relied upon to solve this potentially catastrophic problem. The situation worsens with each passing day, as the amount of HLW increases. Because of the devastating effects of radioactivity on the environment, the storage of HLW cannot be considered to be solely a national problem—it is a global threat, and one that must be addressed immediately. Safe solutions must be found. Otherwise, the ramifications could be felt not just beyond this generation and the next, but also for a thousand generations to come. The risk is just too high for half-measures.

—LEE A. PARADISE

KEY TERMS

BACKGROUND RADIATION:

The natural amount of radiation that surrounds us everyday. It comes from a variety of sources, but mostly from natural sources in Earth left over from its creation, and also from space.

GEOLOGICAL DISPERSAL:

Method of disposing of radioactive waste by burying it deep within a stable geological structure, such as a mountain, so that it is removed from the human environment for a geological timespan, allowing it to decay to background levels.

HALF-LIFE:

Time for a given radioisotope in which half the radioactive nuclei in any sample will decay. After two half-lives, there will be one-fourth of the radioactive nuclei in the original sample, after three half-lives, one-eighth the original nuclei, and so on.

HIGH-LEVEL WASTE:

Highly radioactive material resulting from the reprocessing of spent nuclear fuel.

RADIOACTIVITY:

Spontaneous disintegration of an unstable atomic nucleus.

RADWASTE:

Commonly used abbreviation of the phrase "radioactive waste"; applied to everything from spent fuel rods to train carriages used in the transportation of radioactive material.

REM:

Derived from the term "Roentgen equivalent man," a rem is a radiation unit applied to humans. Specifically, a rem is the dosage in rads that will cause the same amount of damage to a human body as does one rad of x-rays or one rad of gamma rays. The unit allows health physicists to deal with the risks of different kinds of radiation on a common footing.

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