ES&T
OUTLOOK
Nuclear waste disposal When the nuclear era began, radioactive waste disposal was considered a rather minor technical problem that could easily be taken care of in a few years. Now, almost four decades later, an acceptable solution for highlevel wastes has still not been devised. Because of political and corporate inertia, what used to be a negligible risk may perhaps be growing into one of the most critical hazards for the next generation. During the 1950s and 1960s billions of dollars were spent to develop nuclear power and produce nuclear weapons. But during this same period, the government spent a few tens of millions for research on ways to solve the waste problem. Major expenditures to find waste disposal methods were made only in recent years. At present, controversy surrounds almost all aspects of nuclear waste management. The only principle about which there is little argument is that the issue is a serious one requiring concentrated effort. The sheer volume of nuclear waste accumulated to date would suggest that the problem is important: • 2.3 million cubic meters of lowlevel waste • 77.6 million gallons of highly radioactive liquid waste • 331 000 cubic meters of transuranic waste • 175 million tons of radioactive uranium mine tailings • 6700 metric tons of spent nuclear reactor fuel. Currently the spent fuel rods are being stored in pools at the nuclear power plants; the high-level liquid wastes in tanks; the nondefense lowlevel wastes at six commercial sites, three of which are now closed; and the mill tailings in piles at the uranium mines. 0013-936X/82/0916-0271 A$01.25/0
A case of benign neglect? Spent fuel rods are generating a great deal of concern because a number of power plants are running out of storage capacity for them. The continued operation of the nuclear power industry depends in part on finding a way to dispose of these wastes safely. Four states—California, Wisconsin, Iowa, and Maine—have passed laws prohibiting further nuclear plant construction until the U.S. government demonstrates a workable method for the management of spent fuel rods. For this same reason, during the last administration both the Council on Environmental Quality and the Government Accounting Office called for a limitation on the use of nuclear power. In the past three years no new construction permits have been granted for nuclear power plants and 37 have been deferred or terminated, in part because of their high cost and a lessthan-anticipated demand for electricity. An additional factor has been the uncertainty about how to handle the waste problem. At least 22 states have passed laws barring or limiting nuclear waste disposal within their borders. Limited storage space So far the history of nuclear waste management is a mixed one in which
© 1982 American Chemical Society
many of the problems seem to have been institutional rather than technical. About 25 years ago, when the nuclear power industry began, it was believed that spent fuel would be stored in pools at the plants for only a year or at most a few years and then shipped to a reprocessing plant. Between 1966 and 1972 a plant at West Valley, N.Y., reprocessed some spent fuel but then closed because the operation was not profitable and because it incurred several major infractions of its license. Since that time no nondefense spent fuel has been reprocessed; all of it has been stored in massive reinforced concrete pools that are normally lined with welded stainless steel sheet and housed in a building. The fuel is held by racks made of stainless steel or aluminum alloy containing boron (an element that stops neutrons from colliding with fissionable uranium atoms). Boric acid is also added to the pool water. Spent fuel, which is clad with either zircalloy or stainless steel, has been stored on-site at some facilities for 20 years, and most scientists believe it can be stored in water for 50 years or longer. The Nuclear Regulatory Commission ( N R C ) has given permission to about 40 of the 72 licensed operating nuclear plants to put more spent fuel rods in their existing storage pools; 11 more applications are pending for approval. This means the fuel rods are packed closer together in most pools than was originally planned. Some people fear that having less space between the rods is a safety hazard. Under most circumstances, their fears do not seem to be justified. Boric acid in the pools and boron in the racks (if aluminum racks are used) absorb neutrons, and the rods would have to be packed tighter than N R C regulations permit to allow fissioning Environ. Sci. Technol., Vol. 16, No. 5, 1982
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to occur. The pool water is constantly circulated to maintain a temperature between 80 and 125 ° F . However, there are some circum stances that could cause the cooling system at a pool to fail and result in a major nuclear accident. If a massive earthquake occurred, it could crack an older pool and allow the water to run out. If a severe accident were to hap pen at the reactor itself, the site might be evacuated, leaving the pool unat tended. In this case, there would be no one to keep the cooling system oper ating. In either of these situations, the pool water could become hot and begin to boil off. An interaction could then take place between the zirconium cladding on the rods and steam, which would release a large amount of hy drogen. In a matter of minutes, an ex plosion could occur, destroying the building over the pool and exposing radioactive materials to the environ ment. Even with reracking, utilities will begin to run out of storage space by 1985 unless dry storage is begun, new pools are built, or fuel is shipped be tween power plants. Dry storage is a method of storing fuel rods in sealed casks and keeping them in ventilated buildings. So far no dry storage technologies have been licensed in the U.S. If all possible reracking and in
terpool transfers are allowed, the onsite storage pools at U.S. plants would not be filled until at least 1990, ac cording to the DOE. However, many utilities do not want to accept spent fuel rods from other plants, and some state, county, and city governments prohibit the shipment of spent fuel rods within their territory. For several years DOE was pushing for government-owned facilities where spent fuel could be stored away from the power plants. This idea was aban doned mostly because the majority of legislators felt that the utilities should bear the cost of storing their own spent fuel. Whether storage space runs out in 1985, or 1990, or even the year 2000, a disposal solution will have to be found eventually. Pros and cons of reprocessing Many people believe that repro cessing would solve the disposal prob lem for spent fuel. Reprocessing re moves uranium and plutonium 239 from the fuel, and these elements can then be used in new fuel or the pluto nium can be used in weapons especially if a new laser technique is used to pu rify it into better bomb-grade material. However, reprocessing produces high-level liquid wastes and transuranic wastes that have just as much initial radioactivity and require just as
much repository space as the spent fuel rods. In addition, the high-level liquid wastes that result from reprocessing have to be solidified before they are permanently stored. Spent fuel rods are ceramic already and can be put •into repositories without initial solidi fication. A possible advantage of reprocess ing would occur 100 years later, when the radioactivity of the products of reprocessing would have decayed to a level that is somewhat less than the radioactivity of the spent fuel rods themselves. The only immediate ad vantages are that reprocessing would extend uranium resources and could perhaps provide fuel for weapons. However, most experts are strongly opposed to the use of any commercial reprocessing for defense purposes be cause it would blur the distinction be tween military and commercial uses of nuclear materials, possibly leading to further nuclear proliferation. Reprocessing has many drawbacks, such as the additional chances for error involved in the extra shipping and handling of nuclear waste before it is stored permanently, and the opportu nities for diversion of radioactive ma terials by terrorists or foreign enemy nations. President Reagan favors re processing of domestic spent fuel. In September 1981, a bill was introduced
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Environ. Sci. Technol., Vol. 16, No. 5, 1982
^^,Cumulative amount of fuel •*^
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by Rep. Manuel Lujan (R-N.M.) to start reprocessing at Barnwell, S.C., but final action is not expected until some time this year. Liquid waste management The first high-level liquid wastes were generated by the nuclear weapons program and were stored in large, single-walled carbon steel underground tanks at the U.S. Hanford Nuclear Reservation at Richland, Wash. The earliest tank leak occurred in 1956. Eventually, about 450 000 gallons of high-level waste leaked from 20 of the 149 tanks there, but caused no serious groundwater contamination. In the early 1950s tanks of double-wall . construction were built for liquid defense wastes at Idaho Falls, Idaho, and Savannah River, S.C. About 100 gallons of high-level waste leaked from the tanks at Savannah River, contaminating some groundwater. In the 1960s the Atomic Energy Commission (AEC) began to solidify high-level liquid wastes, evaporating them to a damp salt cake or to calcine, a dry granular material; however, no permanent repository has been developed for these materials, which is the case for all other types of high-level waste. A shortage of low-level waste sites Scientists would probably agree that the technical capability currently exists to select low-level waste sites properly and to package, handle, transport, and isolate these wastes safely. But they have also been a subject of concern and controversy. In the 1940s and 1950s they were buried in shallow pits or put in steel drums and dumped at sea. The last license for sea disposal was granted in 1960. Later six commercial low-level sites were established, and the system appeared to be operating smoothly. Then between 1975 and 1978 three sites were closed. Two sites, the one at West Valley, N.Y., and the one at Maxey Flats, Ky., closed because of water control problems caused by design defects in the caps used to seal the trenches. The third site in Sheffield, 111., shut down because it was filled to capacity and the state refused to authorize further expansion. Here some very low concentrations of tritium have moved a short distance outside the disposal area. Now, of the three operating disposal areas, only one is located in the east, the site at Barnwell, S . C , which in 1979 was accepting 80% of all commercial waste; it has cut in half the amount it will take. The state of Washington banned out-of-state non-
Radioactive wastes defined High-level wastes Spent fuel
consists of used-up fuel assemblies from nuclear reactors. They contain considerable amounts of fission products and transuranic elements.
(HLWs) a are a byHigh-level wastes product of the reprocesing of spent fuel. Most result from the reprocessing of nuclear fuels for the purpose of extracting plutonium for nuclear weapons. HLWs contain fission products and some transuranic elements not separated by reprocessing. Without chemical treatment, they are liquid. Chemicals are often used to convert them to a liquid with settled-out sludge, a damp salt cake, or calcine.
fuel and the manufacture of plutonium for nuclear weapons. These are less intensely radioactive than fission products and are sometimes termed low-level waste, but they take much longer to decay than fission products. Some have half-lives of 1000 years or more.
Low-level wastes defined as wastes containing less than 10 nanocuries of transuranic elements per gram of material, result from almost all processes involving nuclear materials. Examples are cleaning, rinsing, and decontamination solutions, contaminated wiping rags, etc.
defined as wastes containing more than 10 nanocuries of transuranic elements per gram of material, are produced mostly from the reprocessing of spent
consist of fine sand that is a byproduct of the uranium mining and milling operation. Low concentrations of naturally occurring radioactive materials are present in this sand.
* Confusion results from the nomenclature because spent fuel, transuranic wastes, and high-level wastes all belong to the main category
of high-level wastes, so the term high-level wastes is both a main category and a subcategory.
medical waste from its only site (Hanford), but in June 1981, the ban was overturned by a federal judge. At present, with Barnwell's volume limitation, about half the waste generated in the east must be shipped to the two western sites. The states of Washington, Nevada, and South Carolina would rather not be the dumping grounds for all commercial wastes and are trying to establish a regional network of state-controlled sites. Mill tailings Uranium mill tailings, fine sand remaining from the mining and milling of uranium, was at first a neglected form of radioactive waste. During its 28-year lifetime before it was abolished in 1974, the AEC said it had no jurisdiction over tailings because they could not be defined as source material. When uranium mines closed, the tailings (totalling 27 million tons) were left uncovered and unprotected, and some of them were blown close to buildings and onto grazing lands. Some were also incorporated into the concrete foundations of buildings, many of which are located in Grand Junction, Colo.; these foundations have had to be replaced. In July 1979 at a uranium mine site in Church Rock, N.M., about 1100 tons of mill tailings poured through a 20-foot crack in an earthen dam; traces of these tailings
were found 75 miles away. The Uranium Mine Tailings Radiation Control Act passed in 1978 requires the government to cover the tailings piles at closed mines or move and treat the piles if they cannot be rendered harmless in place. Now the N R C has authority to require uranium mills to manage the tailings properly. However, the Senate recently passed an ammendment suspending the current licensing requirements for uranium mill tailings. The issue must be resolved in a congressional conference. Mined repositories Many methods have been considered for the disposal of all kinds of high-level waste (see box). To date, study has been mostly given to mined geologic repositories, a system in which the waste would be buried in a suitable geologic medium, and it now seems that research on this option could be completed and a repository could be put into operation earlier than any other disposal method. For this system, the waste would be solidified (if not already solid), covered with a canister, surrounded with an overpack, and buried in a mine 300-1500-m deep in a selected rock formation. The mine would then be filled with what is called backfill. In this way, multiple barriers would stand between the radioactive materials and the human environEnviron. Sci. Technol., Vol. 16, No. 5, 1982
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Quantities of existing radioactive waste (April 1979) Types of waste
Volume of waste (measurements in thousand cubic meters)
Commercial Spent fuel
2
Defense
Major storage sites
Commercial
Defense
0
At reactor sites and reprocessing ilants at Morris, II. and West Valley. N.Y. High-level 2.3 283 West Valley, N.Y. Hanford, Wash.; waste Idaho Falls, Idaho; Savannah River, S.C. Transuranic Volume not 311 Beatty, Nev.; Hanford, Wash.; waste available Hanford, Wash.; Idaho Falls, (approx. 125 Maxey Flats, Ky.; Idaho; Los kg) Sheffield, III.; Alamos, N.M.; West Valley, N.Y. Oak Ridge, Tenn.; Savannah River, S.C. Low-level 515 (Jan. 1, 1470 Barnwell, S . C ; Hanford, Wash.; waste 1978) Beatty, Nev.; Idaho Falls, Hanford, Wash.; Idaho; Los Maxey Flats, Ky.; Alamos, N.M.; Sheffield, III.; Oak Ridge, Tenn.; West Valley, N.Y. Savannah River, S . C ; Nevada test site Uranium 125 25 Piles are located in AZ, CO, mill tailings NM, ND, OR, PA, SD, TX, UT WA, WY. Source: Copyrighted by the League of Women Voters Education Fund. Adapted from "A Nuclear Waste Primer," 1980.
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ment—the waste form itself, the canister, overpack, backfill, and the repository—to isolate it for what scientists believe is necessary, at least 10 000 years. The method sounds simple and straightforward, and seems to require no major scientific breakthroughs, but the research program, which has been carried on since the mid-1960s, has been fraught with conflict. Several different rock formations have been
considered for repositories, dome and bedded salt, granite, shale, basalt, alluvium, volcanic tuff, and argillite. For many years, salt beds and salt domes were believed the most suitable geologic formations for a number of reasons: They seemed stable geologically because they had been there for millions of years; no groundwater seemed to flow through the formations; salt is plastic under pressure and heals itself after being fractured by earth-
Alterrtatives to mined geologic repositories Subseabed disposal the burial of canisters in geologically stable ocean sediments consisting of red clay (ES&T, Vol. 16, No. 1 , 1982). This concept is now being researched intensively. the burial of wastes in holes drilled up to six miles deep in stable rock. disposal—placing the waste form in a shallow hole and allowing it to melt ice and descend about two miles to the bottom of the ice sheet with solidification of the melted ice above it. This concept has been dropped because geologists are not sure that the ice sheets would remain stable for 100 0 0 0 years. S p a c e disposal· shooting the waste form into space where it assumes an
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orbit stable for one million years, or shooting it into the sun. This concept has been abandoned because of the high cost and the risk of a launch a c cident. Transmutation reprocessing the spent fuel, bombarding the byproducts with neutrons inside a reactor to transmute a portion of them into stable short-lived isotopes, and burying the remaining radioactive materials in mined geologic repositories. This idea is not being considered seriously because it would not eliminate the necessity of a disposal method for some highly radioactive materials. iisposal—keeping spent fuel rods or canisters of solidified high-level waste in pools or air-cooled vaults for a century or more while scientists decide upon a permanent solution.
quakes; cracks through which groundwater might flow seemed absent because the very existence of the salt formation seemed to indicate that groundwater was not dissolving it. Recently, however, several disadvantages of salt formations have surfaced. Salt itself invariably contains tiny traces of water. Groundwater seems to enter certain salt beds and change them in ways not yet understood nor detectable from the surface. Brine pockets exist in some formations that could burst from the heat of radioactive materials. Salt solutions are more reactive than previously believed; they are highly corrosive to a number of waste containers under study such as carbon steel. If groundwater were to enter a salt bed repository and dissolve radioactive materials, it could carry them much further through rock and soil than if the materials were carried by fresh water. Also, salt formations usually exist near other natural resources such as oil, gas, and gypsum. In comparison, the disadvantages of other rock formations such as granite, basalt, and tuff are that they usually have fissures which do not heal themselves, and fewer studies have been completed to characterize them. Therefore, if one of these were chosen, it would take longer to do the research necessary for designing and building a repository there. On the other hand, rocks like granite and basalt have much higher absorptive powers for radioactive materials than salt, so would not allow dissolved materials to be carried as far. Salt, with all its disadvantages, remains one of DOE's choices for a test repository, and this has caused a number of scientists to be highly critical of the agency's program. But before any rock site is chosen as the final repository, many studies will be performed at the actual site in order to model effects and to establish a range of uncertainty for the effects that are not completely understood. Researchers do not believe it necessary to have a complete understanding of all phenomena before a repository is built; they plan to determine an upper and lower bound for those effects that cannot be quantified exactly. Some scientists argue that even if groundwater were to enter a repository and dissolve some nuclear material, the radioactivity in the water would have decayed to less than background levels before it reached the surface. Is glass the best medium? All high-level wastes except for spent fuel rods have to be solidified into some chemically stable form before
they can be placed in a repository. The medium used for solidification has also been a subject of great argument. It must satisfy a number of requirements: resist leaching; tolerate temperature change; remain stable in the presence of intense alpha and gamma radiation fields; be compatible with all high-level wastes that, like witches' brews, vary widely in composition; and be manufactured by a fairly simple process that can be remotely controlled. A number of materials have been considered, but three have received the most attention—glass, crystalline ceramics, and cement-based encapsulants. For nearly two decades, the waste form of choice was borosilicate glass, a special glass spiked with boron, which is relatively unleachable compared to other kinds of glass; almost all research in the U.S. and Europe centered on glass. It is cheap, and the technology for making it is simple. France already has a plant that consolidates nuclear waste into glass. In the last few years, however, glass has been called into question as a suitable waste form. The leach rate of glass has been found to be greatly accelerated by high temperature and steam over long periods of time, just the kind of conditions that might result if water entered a repository. Hot salt brines etch their way through glass in a matter of days. In short, glass is relatively unstable and chews up easily.
A sequential set of barriers will be used to isolate the radionuclides in a mined geologic repository Radiophases containing radioactive elements encapsulated in metal, glass, or ceramic
Canister Overpack -Liner
Host rock (including possible waste rock interaction) The "Russian doll' concept — so named because of its redundant layers — includes a sequential set of barriers to retain radionuclides in solid, inert phases. At the center, the waste is solidified in a radiophase of either ceramic or glass or encapsulated by ceramic, concrete, or metal. Next is a canister to protect the ceramic or glass. Then an absorbent overpack protects the canister from inbound corrosives and the environment from radioactive materials leached from the canister. Next is a liner, and finally is a host rock, originally conceived as salt, now generally expected to be salt, granite, basalt, or shale. A fifth barrier may result from chemical interaction between the host rock and the waste containers. The system includes protection at all levels — atomic (radiophase), microstructural (encapsulant), and macrostructural (canister). Source: Technology Review, April 1981.
A much-disputed, unpublished National Academy of Sciences report concluded in 1978 that glass is generally much inferior to crystalline materials such as ceramics, but that glass might be suitable for use as a "first demonstration" of a waste solidification and disposal system. Despite its disadvantages, borosilicate glass remains one of DOE's choices for a waste form. Glass and ceramics are the two media that will get federal approval for further work in the next fiscal year. In 1984 DOE will decide between the two finalists, and the government will spend S850 million to build a plant at Savannah River to solidify wastes in the selected medium. What is the present program? DOE's schedule calls for identifying three specific sites for geologic repositories by 1983, at which time the construction of exploratory shafts will begin at all three sites. The agency hopes to start design and construction for a test and evaluation facility for high-level waste in 1984 with completion planned for 1989. An exploratory shaft for a Waste Isolation and Pilot plant (WIPP) has been built at a site in southeastern New Mexico. This will be a storehouse for transuranic wastes and a test facility for other high-level wastes. The choice of the WIPP site is especially controversial. The first site was chosen in 1975, a salt bed in the Delaware Basin in southeastern New Mexico. This was eventually rejected because the geologic structure was found to be complexly distorted and a pocket of brine was discovered there. Another site six miles away has been selected in the Delaware Basin. A brine pocket was found here too, 600 feet from the proposed test repository. If this pocket is joined with others, the site may have to be given up. Roger Anderson, a professor of geology at the University of New Mexico, believes that the proposed site is located where salt beds are still actively dissolving in subterranean areas. His theory is not widely accepted by geologists, but it will be given more credence if additional brine pockets are .found joined to the original pocket. W I P P has been funded $125 million in the proposed 1983 budget. D O E estimates that the first full-scale repository will be ready for use by 1998. Obstacles to progress Almost all aspects of nuclear waste disposal—from locating low-level waste sites to deciding upon a site for the first geologic repository—generate
intense conflict, which makes it difficult to take steps toward a solution of the nuclear waste problem. This causes many of those who are involved and especially those who favor nuclear power to become frustrated sometimes with the democratic process, and to wish there were a board of experts that could make arbitrary and binding decisions. In nuclear waste management, the democratic process is indeed put to a test. It is almost impossible for a large number of people to be well informed about this highly technical issue. They tend to divide into opposing camps, which might be characterized very generally as those who strongly object to nuclear power and those who favor it. The result of such confrontation is that decision making becomes slow, even in such minor areas as where to place the next low-level waste site. But it may not be so much the democratic process itself as the distrust that surrounds almost all decisions the government makes in this area that presents the greatest obstacle to decision making. In the past, the government said nuclear waste would be easy to manage. It is clearly not easy to dispose of. In the past, the public was assured that nuclear power was safe. The accident at Three Mile Island has eroded that belief. Another barrier to decision making is that motives and issues are interwoven and confused. The radioactive waste issue is used by some people who object to nuclear power as one means of opposing it. They may try to thwart progress in waste management because they fear this will lead to an expansion of the nuclear power industry. Others who oppose atomic weapons may also use the failure to solve the waste problem as one of their arguments against these weapons and try to hinder advances in waste disposal. The issue is further confused because the current administration is considering reprocessing commercial spent fuel rods and using the recovered plutonium in weapons. Because the public is skeptical of almost all decisions the government makes about nuclear waste, and because the issues are blurred and confused, it is difficult to make rational choices. But even if all nuclear power plants and weapons production stopped tomorrow, the radioactive waste already generated would remain and require eventual disposal. What is perhaps most irrational may be the failure to have found a permanent solution over a period of almost four decades. —Bette Hileman Environ. Sci. Technol., Vol. 16, No. 5, 1982
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