Three Mile Island The most serious nuclear reac­tor accident in the United States occurred in 1979 at the Three Mile Island power plant in Pennsylva­nia. A partial meltdown of the reactor core took place. Had there been a complete meltdown of the fuel assembly, dangerous radioactivity would have been emitted into the surrounding countryside. Fortunately, the containment building kept virtu­ally nil the radioactivity released by the core mate­rial from escaping. Although a small amount of ra­diation entered the environment, there were evidently no substantial environmental damages and no immediate human casualties. A study con­ducted within a 10-mile radius around the plant ten years, after the accident concluded that cancer rates were in the "normal" range and that there was no association between cancer rates and radiation arm-ions from the accident.

The seriousness of the situation at Three Mile Island elevated public apprehension about nuclear power. It took six' years for Three Mile Island to be repaired and reopened, and in the aftermath of the accident, public wariness prompted construction delays and cancellations of a number of new nuclear power plants across the United States. On the positive side, the accident at Three Mile Island prompted new safety regulations—including evac­uation plans for the areas surrounding nuclear power plants—and reduced the complacency that had been commonplace in the nuclear industry.

Chernobyl: The worst accident ever to occur at a nuclear power plant took place at the Chernobyl plant in the former Soviet Union on April 26,1986, when one or possibly two explosions ripped a nuclear reactor apart and expelled large quantities at radioactive material into the atmosphere. The effects of this accident were not con­fined to the area immediately surrounding the power plant: in the atmosphere radiation quickly spread across large portions of the Northern Hemi­sphere. The Chernobyl accident affected and will continue to affect many nations, especially the former Soviet Union and the countries of Northern Europe.

The first task the Soviets faced after the acci­dent w s to contain the fire that had broken out after the explosion and prevent it from spreading to other reactors not the power plant. Local fire fight­ers, ma y of whom later died from exposure to the high levels of radiation, battled courageously to contain the fire. In addition, 116,000 people who lived within a 30-kilometer (18.5-mile) radius around the plant had to be quickly evacuated and resettled. Ultimately, more than 300,000 people were forced to resettle as a result of the accident.

Once the danger from the explosion and fire had passed, the radioactivity at the power station had to he cleaned up and contained so that it would not spread. Dressed in protective clothing similar to that worn by the people, workers were transported to the site in radiation-proof vehi­cles, and initially the radioactivity was so high that they could stay in the area for only a few minutes at a time. There are few photographs of the cleanup because camera film was quickly ruined by the radi­ation. After the initial cleanup, the damaged reactor

Building was encased in 300,000 tons of concrete. Then the surroundings country side had to be decontaminated: highly radioactive soil was removed, and building and roads were scrubbed down.

    Inhabitants in many areas of Byelorussia and the Ukraine still cannot drink the water or consume locally produced milk, meat, fruits, or vegeta­bles. Mothers cannot nurse their babies because their milk is contaminated by radioactivity. Hun­dreds of children are in hospitals, dying from leuke­mia (cancer of white cells in the blood and bone marrow). The health of approximately 350,000 Ukrainians is being constantly monitored.

    In the investigation that ensued after the acci­dent, it became apparent that there had been two fundamental causes. First, the design of the nuclear reactor was flawed—the reactor was not housed in a containment building and was extremely unstable at low power. Second, many of the Chernobyl plant operators lacked scientific or technical under­standing of the plant they were operating. As a re­sult of the disaster at Chernobyl, the Soviet Union developed a retraining program for operators at all the nuclear power plants in the country. In addi­tion, safety features were added to existing reactors.

    One of the disquieting consequences of Cher­nobyl was the lack of predictability of the course taken by spreading radiation. Chernobyl's radiation cloud dumped radioactive fallout over some areas of Europe and Asia, leaving other areas relatively untouched. This unevenness makes it difficult to plan emergency responses for future nuclear accidents.

The health effects of the accident at Chernobyl will be monitored for many years. Although only 31 people initially died from exposure to radiation,¹' it is estimated that as many as 24,000 people re­ceived dangerous doses of radiation {see Focus On: The Effects of Radiation on Living Organisms). An increase in mental retardation in newborns has been noted not only in the former Soviet Union but also in pans of Europe; this was expected, be­cause a similar pattern emerged in Japan after the bombings of Hiroshima and Nagasaki at the end of World War II. An increase in cancer deaths di­rectly attributable to Chernobyl is also expected, with'5,000 to 75,000 deaths projected. Psychologi­cal injuries to those living under the cloud of Cher­nobyl are also being assessed.

    The world has learned much from this nuclear disaster. Most countries are taking nuclear power more seriously, hoping to prevent more accidents. Safety features that are commonplace in North American and European reactors are being incor­porated into new nuclear power plants around the world. In addition, nuclear engineers learned a great deal from the cleanup and entombment of Chernobyl; this knowledge will be useful in the decommissioning of power plants. For example, remote-controlled bulldozers and robots were rela­tively ineffective in the cleanup process because their electronics failed, probably as a result of expo­sure to high levels of radiation. Doctors learned more about effective treatment of people who have been exposed to massive doses of radiation. In the years to come, health researchers will learn more about the relationship between cancer and radia­tion as they follow the health of the thousands who were exposed to radiation from Chernobyl. Also,

the area within a 10-kilometer radius around Chernobyl has been designated an ecological reserve char will be left to recover on its own. The only people allowed inside will be scientists who study the effects of high levels of radiation on plants and animals and monitor the environment's recovery.

Proponents of Nuclear Power Say That Newly Designed Nuclear Power Plants Are Safer

New reactors are being designed that arc considered by nuclear experts to be much safer than the current generation of reactors operating in this country. Some of the new reactors will not have a meltdown even in a worst-case scenario. Because the' fuel can­not melt, radiation cannot be released into the environment during the plant's operation. Some of the designs utilize a gas (helium) rather than water to turn the turbines and cool the system. Helium, being much less corrosive than steam, is another safety feature, because it is less likely to cause leaks by corroding pipes. According to the nuclear power industry, the new generation of nuclear power plants will also be smaller, simpler in design, and less expensive to build. Nevertheless, they will still have many of the unresolved problems of tradi­tional designs, including what to do with radioac­tive wastes.

Radioactive Wastes

Radioactive wastes are classified as either low-level or high-level. Low-level radioactive wastes ik radioactive solids, liquids, or gases that give off small amounts of ionizing radiation. Produced by

Nuclear power plants, university research, hospitals (nuclear medicine), and industries, low level radio active wastes have traditionally been stored in steel drums in six special government-operated landfills. High-level radioactive wastes produced during nuclear fis­sion include the reactor metals (fuel rods and as­semblies), coolant fluids, and air or other gases found in the- reactor. Fuel rods, for example, can be used for only about three years, after which they become the most highly radioactive waste on Earth; their dangerous level of radioactiv­ity requires that they be handled in special ways. In addition to nuclear wastes produced during fission, considerable tailings—piles of loose rock—are pro­duced when uranium is mined and processed. A third type of waste, the nuclear power plant itself once it has outlived its usefulness, will he consid­ered separately.

    Some radioactive wastes are created when neu­trons are absorbed by the uranium fuel rods, thereby forming radioactive isotopes. As the iso­topes decay, they produce considerable heat, are extremely toxic, and remain radioactive for ex­tended periods of time.

    Clearly, the safe disposal of radioactive wastes is one of the main difficulties that must be over­come if nuclear power is to realize its potential. Many people question whether we can safely guar­antee the storage of wastes that must be isolated from living organisms for millennia. High-level radioactive wastes, which have very long half-lives, must be stored in an isolated area where there is no possibility they can contaminate the biosphere. The storage site must also have geological stability (imagine the consequences of storing wastes near an earthquake zone!) and little or no water flowing nearby (which might transport the waste away from its original site).

    What are the best sites for the long-term stor­age of high-level radioactive wastes? Some experts think we could store the wastes in stable rock for­mations deep in the Earth. However, many experts think that deep salt deposits are the best solution for long-term storage. Salt is an effective barrier to radiation; further, the presence of 200-million-year-old undisturbed salt deposits indicates their stability in the Earth's crust. Another suggestion for the long-term storage of radioactive wastes is mau­soleums, which would be aboveground sites built in remote locations such as deserts. If we built

Mausoleums, however, we would not be able to simply I acre the wastes and forget about them. Mausoleums would have Co have cooling systems {to re­move the excess heat produced during radioactive decay) and adequate security to guarantee their safety. Other long-term possibilities that have been considered include storage in ice sheets, burial be­neath the ocean floor, and storage in deep ocean trenches. Most experts today support underground geologic disposal in either rock formations or salt deposits. The selection of these sites is further complicated by people's reluctance to have radioactive wastes stored near their homes.

    The enormity of this problem is demonstrated by the fact that there are no permanent storage fa­cilities for radioactive wastes in any country. In the United States, there are about 100 sites at which our radioactive wastes have been "temporarily" stored for decades. In 1982 the pas­sage of the Nuclear Waste Policy Act put the bur­den of developing permanent waste sites on the federal government and required the first sire to be operational by 2010. The federal government has selected Yucca Mountain in Nevada as a storage site for high-level nuclear wastes from commer­cially operated power plants. High-level nuclear wastes from military weapons are being stored at Carls­bad, New Mexico. Neither site is perfect. The yucca mountain site is controversial because it is near a young volcano and active fault lines; earth-quakes might possibly disturb the site and raise the water table, which could result in radioactive con­tamination of air and groundwater. There is con­cern that oozing brine at the Carlsbad site, a net­work of rooms carved out of rock salt, could corrode the steel waste drums and contaminate groundwa­ter with radioactivity.

Selecting and building the sites doesn't solve the entire nuclear waste problem, as there are also concerns about transporting the high-level nuclear

wastes to these sites. Wastes would be transported by truck or train across the country, and residents of areas through which waste disposal vehicles would pass are naturally worried about what would happen if an accident caused the wastes to he spilled.

Radioactive Wastes with Relatively Short Half-Lives

Some radioactive wastes are produced di­rectly from the fission reaction. U-235, the reactor fuel, may split in several different ways, forming a number of smaller atoms, many of which are radio­active. Most of these, including strontium 90 {half-life 28 years), cesium 137 (half-life 30 years), and krypton 85 (half-life 10.4 years), have relatively short-term radioactivity. In 300 to 600 years they will have decayed to the point where they are safe. (Recall that a radioactive material produces negli­gible radiation after ten half-lives.)

    The safe storage of fission products with relatively short half-lives is of concern because fission produces larger amounts of these materials than of the materials with extremely long half-lives. Also, health concerns exist because many of the shorter-lived fission products mimic essential nutrients and tend to concentrate in the body, where they con­tinue to decay, with harmful effects. For example, one of the common fission products, strontium 90. is chemically similar to calcium. If strontium 90 were to be accidentally released into the environ­ment from radioactive waste that had not been stored properly, it could be incorporated into human and animal bones and teeth in place of cal­cium. In like manner, cesium 137 replaces potas­sium in the body and accumulates in muscle tissue, and iodine 131 concentrates in the thyroid gland.

Decommissioning Nuclear Power Plants

Nuclear power plants can operate for only 25 or 30 years before certain critical sections, such as the reactor vessel, become brittle or corroded. At the end of their operational usefulness, however, nu­clear power plants cannot simply be abandoned or

demolished, because many parts have become contaminated with radioactivity. In addition, highly radioactive spent fuel, which is usually placed in water filled storage ponds in the plant throughout its operation, must safely, and disposed of.

Entombment, in which the entire power plant is permanently encased in concrete, is not considered a viable option by most experts because the tomb would have to remain intact for thousands of years. It is likely that accidental leaks would occur during that time. Also, we cannot guarantee that future generations would inspect and maintain the "tomb."

    The third option for the retirement of a nuclear power plant is to decommission, or dismantle, the plant immediately after it closes. The workers who dismantle the plant must wear protective clothing and masks. Some portions of the plant are too "hot" (radioactive) to be safely dismantled by workers, although advances in robotics may make it feasible to tear down these sections.

    Several small nuclear power plants have been decommissioned. Shipping port, the nation's first commercial nuclear power plum, was dismantled in 1989 and transported by barge more than 8,000 miles from its working site in Pennsylvania to Hanford Military Reservation, a military dump site in Washington State. The decommissioning of a large nuclear power plant will not he possible, however, until advances in robotics provide the technology to safely dismantle it (Shipping port’s reactor vessel was small enough to be kept intact) and until there-are permanent storage sites for all the radioactive pieces.

    Decommissioning nuclear power plants is the responsible thing to do once a plant is no longer operable. There are risks, including dangers to workers during the decommissioning process and accidental discharges of radiation into the environment

either during dismantling or during transport of radioactive debris to a permanent site.

    Worldwide, many nuclear power plants are nearing retirement age. In 1990 approximately 35 plants were 25 years old or older; by 1995 there will be 66, and by 2000 there will be 150 retirement-age plants. As we enter the 21st century, we may find that we are paying more in our utility bills to close old plants than to have new plants constructed.

The Link between Nuclear Energy and Nuclear Weapons

Fission is involved in both the production of elec­tricity by nuclear energy and the destructive power of nuclear weapons. Uranium 235 and plutonium 239 are the two fuels commonly used in atomic fission weapons. As you know, plutonium is produced in breeder reactors. It is also possible t. process spent fuel from conventional fission reac­tors to make weapons-grade plutonium.

Many countries are using or contemplating using nuclear power to generate electricity. The possession of nuclear power plants gives these countries relatively easy access to the fuel needed for atomic weapons. Many world leaders are con­cerned about the proliferation of nuclear warheads and the consequences of terrorist groups and na­tions building atomic weapons (see Focus On: The Effects of Nuclear War). Also, the transport of nu­clear wastes to storage sites increases the chance that terrorist groups will steal the wastes and use, them to make nuclear weapons. These concerns' have caused many people to shun nuclear energy, Particularly breeder fission, and to seek alternatives that are not so intimately connected with nuclear 'weapons.