On March 27, 1979, Metropolitan Edison's Three Mile Island Nuclear Power Plant, near Middletown, Pennsylvania, was running at 97% full power. Like most of the 110 nuclear power plants in the United States, both TMI-1 and TMI-2, were pressurized-water reactors, as shown in Figures 6.3a and 6.3b. In
Figure 6.3. (a) View of Three Mile Island with its twin cooling towers and reactor building off to the left (courtesy of TMI); (b) the major components of a pressurized-water reactor (courtesy of the Nuclear Energy Institute); (c) schematic diagram showing greater detail within the reactor and the piping leading to the turbine, generator, and cooling towers (courtesy of the Nuclear Regulatory Commission).
Figure 6.3. Continued
Figure 6.3. Continued
PWRs, the water pumped through the pressure vessel, at the rate of 90,000 gallons per minute, is kept under high pressure. As the water passes through the core, it is heated to about 600°F (315°C), and the 2200 pounds per square inch (lb/in.2) of pressure prevents the water from boiling. The pressure vessel that housed the core was 36 feet high and had 9-inch-thick steel walls.
Water circulates through the core, then proceeds to the steam generator, where boiling occurs, creating the steam that drives the turbine in the adjacent building. After transferring its heat, the steam is cooled to liquid water and returns to the core to continue its endless cycle.
As evening slipped into dawn of March 28, trouble was nowhere in sight. TMI-1 was out of service for refueling, and TMI-2 was functioning normally. The staff working the graveyard shift were veterans, highly qualified professionals, having obtained their nuclear training and experience in the U.S. Navy's nuclear submarine program. They had years of experience in both the Navy and at TMI.
At 4 a.m . , a pump tripped in the nonnuclear section of the plant. What should have been no more than a minor event escalated into a crisis. The main feedwater pumps stopped running, preventing the steam generators from removing heat. Both the turbine and the reactor automatically shut down, thus increasing the pressure in the nuclear portion of the plant. To relieve the pressure, the pilot-operated relief value (PORV), at the top of the pressurizer (see upper left, above control rods in Fig. 6.3c), opened. It was here at the PORV that, unbeknownst to the staff, trouble mounted. The valve should have closed when pressure decreased, but it failed to do so. Signals at the control room did not show the valve as being open. With the valve open, cooling water poured out of it, causing the core to overheat. This is where confusion ran riot. As there was no instrument to show the water level in the core, the operators judged the level according to the level in the pressurizer, and as it was high, with water pouring out of the core, into the pressurizer and out of the PORV, they judged the core to be adequately covered with cooling water. As alarms rang and warning lights flashed, the operators had no way of knowing that a loss of coolant was occurring in TMI-2. Then it got worse. Believing that there was sufficient coolant in the system, they further reduced the flow. The nuclear fuel now overheated to the point that the zirconium tubing containing the nuclear fuel pellets ruptured, allowing the pellets to melt. This was the meltdown, the so-called worst-case scenario, in which predictions held that a meltdown would breach the reactor' s 9-i nch-thick steel walls, the steel shielding lining the 36-i nch-thick reinforced concrete containment building, and spew radioactive material around the countryside, radiating and killing thousands of people—literally. This was the "China syndrome," and was too vivid for the press to resist. Their steady drumbeat of impending disaster caused thousands to flee the area. Little had been learned since Hiroshima and Nagasaki, in which the press trumpeted the allegations that Hiroshima would be uninhabitable for decades, if not centuries, and would see epidemics of misshapen monsters, both animal and plant. Of course, none of this occurred. In fact, just months after the bombing, reconstruction was under way. Today, both Hir-shima and Nagasaki are lovely cities attracting tourists from the world over.
Recall that the accident at TMI occurred only several days after the film The China Syndrome, starring Jane Fonda and Jack Lemon, was released. The press had a field day with that. In the film, Jane Fonda, a news anchor at a California TV station doing a series on nuclear energy, is at a nuclear power plant with a cameraman, and is raising the prospect of how unsafe the plant is. In the film, Fonda's character speaks with a safety expert who says that a meltdown could force an area "the size of Pennsylvania" to be evacuated, and the fictional near-accident in the film stems from a plant operator's misunderstanding of the amount of water within the core. Jane Fonda began lobbying against nuclear power. The physicist Edward Teller began lobbying in favor of nuclear power. It was during this period that Teller, then 71, suffered a heart attack, which he blamed on Fonda, noting that "You might say that I was the only one whose health was affected by the reactor near Harrisburg. No, that would be wrong. It was not the reactor. It was Jane Fonda. Reactors are not dangerous "  .
Given the media circus surrounding the TMI accident, what have we actually learned about adverse health effects of the accident now that almost three decades have passed? Studies of the consequences have been conducted by the Nuclear Regulatory Commission, the EPA, the Department of Health and Human Services, the Department of Energy, and the State of Pennsylvania, as well as independent studies by the University of Pittsburgh, School of Public Health, and Columbia University's School of Public Health. Consensus governmental estimates are that the average dose to about 2 million people in the area was about 1 mrem, or 0.01 mSv. By way of comparison, exposure from a set of chest X rays is approximately 6 mrem (0.06 mSv), compared to the natural background of about 100-125 mrem (1-1.25 mSv) per year; thus the collective dose was minuscule. As for the reactor building, it has become clear that most of the radiation was contained, and the actual release, if there was any, had negligible effects on the population and the physical environment. Perhaps most illuminating was the finding that iodine-131 in the core did not remain in the gaseous state long enough to escape, but had dissolved in water or had attached to metal surfaces of the reactor building .
At the request of the Three Mile Island Public Health Fund (created by federal court order in 1981, to supply financial support for analysis of radiation effects in the area), the Division of Epidemiology, School of Public Health, Columbia University, conducted a study to determine whether cancer occurrence following the March 28 accident was related to radiation releases from TMI-2.
New cancer cases from 1975 to 1985, among the 160,000 residents living within a 10-mile radius of TMI-2, were obtained from all hospitals within 30 miles of TMI. During those 11 years, 5493 new cases were diagnosed. How were they interpreted? No associations were seen for leukemia in adults, nor for childhood cancers as a group. In fact, a negative trend was found for adults. Here again, it must be recalled that cancer is a fact of life, and studies must distinguish between which are related to the study question and which are not. Interestingly enough, one of the observations found that rates of leukemia among children in the area were low compared to both regional and national rates, which may speak to both the fact of any accidental emissions as well as living near a nuclear power plant. Also, the authors tell us that they "failed to find definite effects of exposure on cancer types and population subgroups thought to be most susceptible to radiation." They concluded that, "overall, the pattern of results does not provide convincing evidence that radiation releases from the Three Mile Island nuclear facility influenced cancer risk during the limited period of follow- up" [ 10]. Furthermore, their computer simulations found that projected exposure patterns agreed with the data obtained by TMI dosimeters used at the time of the accident.
Recognizing that there would be wide interest and concern in the results of this study, the editor of the American Journal of Epidemiology requested Dr. Colin R. Muirhead of the National Radiology Protection Board, Oxfordshire, UK, to provide an independent evaluation of the publication. Muirhead began by stating that "There are a number of problems associated with performing this study. Doses received as a result of the accident are estimated to be less than the annual background gamma dose of 1 mSv." Too many people who ought to know better have either overlooked that fact or prefer to ignore it. He noted, too, that "consequently it would not be expected to detect any increased risk associated with these emissions," and concluded by stating that "the authors conclusion that their study does not provide convincing evidence that radioactive emissions from Three Mile Island influenced the risk of cancer during the period of follow-up therefore seems to be reasonable" .
Continuing concern by residents prompted the University of Pittsburgh, School of Public Health, in cooperation with the Pennsylvania Department of Health, to undertake another study of the residents in the area. This one looked at the mortality experience and specific cancer risks of the 32,135 individuals enrolled in the study. At the outset, it is of paramount importance to know the levels and types of radiation that residents may have been exposed to. From this study we learn that investigators from the Pennsylvania Department of Health determined that the average likely and maximum whole-body gamma doses were 9mrem (0.09mSv) and 25mrem (0.25mSv), respectively. Compared to 300mrem (3 mSv) annual effective natural background dose received by the residents of the United States, the emissions from Unit 2 were Lilliputian. As for beta radiation, with its shorter range in air, and poor penetrating power, and given clothing, shelter, and other shielding factors, the impact of beta radiation was substantially reduced, but to an uncommon level. The researchers concluded that "the radiation released from Unit 2 did not provide evidence that low-dose radiation had any impact on the deaths among the cohort studied. And, as the latency period for most cancer is at least 15 years, more likely 20 or more, continued follow-up may provide a more comprehensive description of the mortality experience" .
The University of Pittsburgh's first report on health affects from the TMI accident covered the period 1979-1992. Their follow-up study covered an additional 6 years: 1974-1998, and the 32,135 individuals involved in the first study were again available. A major observation was that "overall cancer mortality among this cohort was similar to the local population." Again they remarked that radioactivity released during the accident had no impact on the overall mortality of the residents. Nevertheless, given the timeframe, they suggest four areas for future investigation: the alcohol and smoking consumption of the cohort, continued monitoring of the children, studying the natural background as it relates to cancer rates, and continued follow-up of the overall mortality experience of this cohort.
March 28, 2004 was the 25th anniversary of the accident. It seems fitting that a 30-year follow-up could be useful as children at the time of the accident would then be adults, and young adults at the time would be entering the period when cancer normally exacts a heavy toll. But it is also evident that some people will never believe that TMI was not the cause of their ailments . More than likely one day a journalist will admit that for them, TMI was no more than a media circus. By the way, has anyone inquired as to the adverse health affects acquired by the dozen or more operators who remained on duty during TMI's meltdown? Surely they should have received doses of radiation far in excess of doses received by any nearby residents. In fact, they had no radiation-related injuries—- omething more to consider, as is the fact that 325,000 cancer deaths from all causes are normally expected in the population of 2 million people living within 50 miles of TMI.
Unfortunately current terrorist concerns have mandated that visits to nuclear power plants be curtailed. Security is the order of the day. The former open-door policy permitted many the luxury of a highly educational guided tour, with questions and answers, from which you came away comfortable in the knowledge that these plants are in capable, professional hands. Worse yet, public opinion was so adamant that Metropolitan Edison decided, after the cleanup, not to reopen Unit 2. It has been standing idle ever since its cleanup, and will be decommissioned shortly. Of course the public has to find its electricity elsewhere. Over the past two decades one would have suspected that public opinion would have changed. But Chernobyl intervened. It will be instructive to see if the most recent data out of Chernobyl have a salutary effect on Pennsylvania residents. So, let us now consider Chernobyl.
Chernobyl was different from Three Mile Island. Situated some 80 miles north of Kiev, and 12 miles south of the border with Belarus, forming a triangle with Chernigov and Kiev, the Chernobyl nuclear power complex consisted of four nuclear reactors of the RBMK-1000 design. The RBMKs are Soviet designed and built, graphite - moderated pressure - tube - type reactors, using slightly enriched (2% 235U) uranium dioxide fuel. As shown in Figure 6.4, it is a boiling, light-water reactor, with direct steam feed to the turbines, without an intervening heat exchanger. Water pumped to the bottom of the fuel channels boils as it progresses up the pressure tubes, producing steam that feeds two 500-MW electric turbines. The water acts as a coolant and also provides the steam used
to drive the turbines. The vertical pressure tubes contain the zirconium-alloy-clad fuel around which the cooling water flows  .
The Unit 4 reactor was to be shut down on April 25, 1986 for routine maintenance. To take advantage of this shutdown, a test was set in motion. Its aim was to determine whether cooling the core could continue safely if there were loss of power. As the shutdown proceeded, the reactor was operating at about half power. Then the emergency core cooling system was switched off. Standard operating procedure required that a minimum of 30 control rods, of the total 231, were necessary to maintain control of the reactor. In the test, only about 7 were used. There was an increase in coolant flow and a resulting drop in steam pressure. The automatic trip that would have shut down the reactor when steam pressure was low, was bypassed. The reactor became unstable. The loss of cooling water exaggerated the unstable condition by increasing steam production in the cooling channels, and the operators could not prevent an overwhelming power surge.
At 1:23 a.m. Saturday, April 26, 1986, two explosions destroyed the core of Unit 4 and the roof of the building. The two explosions sent fuel, core components, structural items, and burning graphite into the air. The smoke, radioactive fission products, and core debris rose a half- mile into the air, with an unprecedented release of radioactive materials. The lighter materials were carried by the prevailing wind to the northwest of the plant and on into European countries. Fires raged in what remained of Unit 4. But these were not graphite fires. Graphite played no part in the fires as high - purity, nuclear - grade graphite doesn ' t burn.
Over 100 firefighters were needed, and it was this group that received the highest levels of radiation exposure and sustained the highest losses of personnel. By 5 p.m., the fires were extinguished, but many of the firefighters continued their radiation exposure by remaining on site. The intense heat of the graphite was responsible for the dispersion of radionuclides high into the atmosphere, which continued for about 20 days.
The Chernobyl accident was the result of a poorly designed reactor, with no containment building and poor safety regulations and conditions. The operators performing their test had no idea that what they planned was a recipe for disaster, and they failed to comply with established operational procedures. The combination of poor reactor design and human error created the worst nuclear reactor calamity in history. There were dire predictions that thousands, tens of thousands of people—men, women, and children—in the Soviet Union and Europe might die of radiation-related illnesses. What, in fact was its legacy?
Twenty years after the accident, a clear understanding of its impact had yet to be obtained by the countries and individuals involved. To fill this void, the Chernobyl Forum was established in 2003 by the International Atomic Energy Agency in cooperation with six specialized UN agencies—the World Bank and the governments of Belarus, the Ukraine, and the Russian Federation—as the Soviet Union no longer exists. The IAEA convened an expert working group of scientists from around the world to deal with the environmental effects, while WHO convened a panel of experts to consider the health effects. Their efforts produced a stunning report: Chernobyl's Legacy: Health, Environmental and Socio-economic Impacts and Recommendations to the Governments of Belarus, The Russian Federation and Ukraine, published in September 2005  ' No sooner had the UN-commissioned report been issued, when it was attacked by environmental groups as a biased attempt to whitewash the potential dangers of nuclear power. The fact that this report was a consensus document prepared by and contributed to by eight agencies and several countries mattered little to these naysayers. But we can let the report speak for itself.
With the exception of the on- site reactor personnel and the emergency workers present near the destroyed reactor, most of the people living in the contaminated territories received relatively low-dose whole-body radiation— comparable to background levels. Some of the reactor staff and emergency workers received doses of external gamma radiation of 2-20 Gy; 28 of them died within the first 4 months from radiation and thermal burns, and another 19 died over the years to 2004. The number of deaths attributable to Chernobyl has been of the greatest import to the public, scientists, the media, and government officials. The claims of the number of deaths that would ensue has, of course, been thoroughly exaggerated. The total number that could have died, or could die in the future due to exposures from Chernobyl in the most contaminated areas, is estimated at about 4000. This includes some 50 emergency workers who died of acute radiation syndrome, 9 children who died of thyroid cancer, and an estimated 3940 that could die from cancer as a result of radiation exposure.
The report makes it clear that confusion about the impact of Chernobyl has arisen because thousands of emergency and recovery operation workers as well as people who lived in contaminated areas died of a range of natural causes not attributable to radiation. Widespread expectations of illness, and a tendency to attribute all health problems to Chernobyl, have led residents to assume that Chernobyl-related fatalities were higher than they actually were. Of additional interest was that fact that among the general population, radiation doses were low, and acute radiation syndrome did not occur.
Now, what of the children? Iodine-131 was one of the main radionuclides released by the explosion. As part of normal metabolism the thyroid gland accumulates iodine from the bloodstream. Consequently fallout of radioactive iodine led to considerable thyroid exposure via inhalation and ingestion of contaminated foods, especially milk. The thyroid gland is one of the most susceptible to cancer induction by radiation, and children are the most vulnerable. During 1992-2000, about 4000 cases of thyroid cancer, were diagnosed among those up to 18 years of age at the time of the accident. The survival rate was 98.8%. Eight children died of thyroid cancer, and 6 died of other causes. There is reasonable certainty that the cancer deaths were due to radiation. The report also makes it clear that "There is no convincing evidence that incidence of leukemia has increased in children or adult residents of the exposed populations. "
Examinations of children's eyes and those of the emergency and recovery operation workers shows that cataracts do develop as a result of exposure. Doses as low as 250 mGy may be cataractogenic. Because of the relatively low dose levels to which the general population was exposed, there is no evidence, nor is there expected to be, of decreased fertility among men and women as a result of exposure. This is similar to the results seen in Hiroshima and Nagasaki. Birth rates may be lower in contaminated areas because of concerns about having children, but there is no discernable evidence of hereditary effects. In fact, the greatest public health hazard has been psychiatric. Because of greatly undue fear of the risks in the area, many have become alcoholic, abuse drugs, or are unemployed, anxious, or unable to function. So, as of mid-2005, no more than 50 deaths were deemed attributable to radiation from the Chernobyl eruption; almost all of these deaths were rescue workers and firefighters who had been directly exposed to the radiation resulting from the accident. A total of up to 4000 people may eventually die of radiation in the years ahead, but this is an estimate that could be revised upward or downward. Obviously it is important that the true scale of the accident 's consequences become widely known and understood. These data offer means for coping with major releases of radiation whether caused by accident or terrorism and should improve the level of confidence in nuclear reactors as sources of much-needed electricity.
Paralleling the Chernobyl Forum report, and of singular importance, is the news that in October 2005, farming resumed in the radiation zone. The summer crop of rye, barley, and rapeseed came in at a record 1400 tons, and none tested radioactive, and the winter rye was sprouting green. Families have begun returning to this area of Belarus 150 miles from Chernobyl, which has been among the most contaminated spots on earth. Interestingly enough, among the Chernobyl Forum's recommendations was that authorities in Russia, Ukraine, and Belarus move to reverse the psychological trauma caused by the chaos after the explosion, and encourage investment and redevelopment. Lands where agriculture was banned can be safe for growing crops once again, but farmers cannot sell their produce without a government certificate of approval .
Adding a lighter touch to the increasingly positive developments, curiosity being what it is, Chernobyl has become a tourist attraction; its very name lures people in. Chernobyl may be a dead zone to some, but Chernobylinterinform, the zone ' s information agency, conducts chaperoned, guided tours that they maintain do not carry health risks. Although tourists are not allowed to wander about on their own, the guided tours are extensive and close -up. One -day group excursions cost $200-$400, including transportation and meals. For many tourists this is an extraordinary photo opportunity, and a bird-watcher's nirvana, cataloging the zones resurgent life .
The investigations by Ronald K. Chesser and Robert J. Baker, both of Texas Tech University, at Chernobyl taught "tough lessons about politics, bias, and the challenges of doing good science" . They found radiation exposure to be less hazardous than generally believed. Shades of Hiroshima and Nagasaki. Their article "Growing Up in Chernobyl" is must read for undergraduate and graduate students planning a career in science. I also recommend this insightful essay to all those trying to negotiate between fact and fiction.
Having considered warfare and nuclear plant accidents, we now turn our attention to environmental and occupational exposures as well as exposures to populations living in areas of unusually high natural backgrounds.
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