by Rosie Sugrue
Grey smoke swarmed into the air from one of the reactor sites at Japan’s Fukushima Daiichi plant. It was March 12, 2011, a day after a forty foot tsunami seared through the northeast coast of Japan demolishing everything in its path following a record breaking 9.0 magnitude earthquake. Those of us in MIT’s Department 22, Nuclear Science and Engineering, were frantically emailing, blogging, and glued to news sites seeking additional information about the crisis. We knew that the Fukushima facility consisted of six reactors, one of which was due to retire the following week. We also knew that all of Japan’s eleven nuclear plants were automatically programmed to shut-down in the event of an earthquake. What we did not know was that the resulting tsunami would flood the back-up generators creating an impending crisis when the third layer of redundancy, back-up DC batteries, were exhausted.
The rising haze indicated that nuclear operators were venting a pressure build-up within at least one of the reactor containment units. Such venting would prevent excess pressurization but would also leak miniscule amounts of radioactive particles into the surrounding area. More seriously, some of the vented gases could flow into the non-ventilated reactor building creating a build-up of dangerously high levels of hydrogen. When this build-up created an explosion which blew the roof off the Unit 1 facility, we knew that public fear would increase dramatically and that intensive media attention would be focused on the safety of nuclear energy.
It is not surprising, of course, that such an accident would evoke high levels of anxiety, fear, and concerns about the use of nuclear power. After all, radiation is colorless, invisible, and can cause damage that may not be apparent for several years. Some studies have even found that individuals unfamiliar with nuclear technology believe reactors are capable of exploding in the same way as the atomic bombs dropped on Hiroshima and Nagasaki during the late stages of World War II.i Images from that time period and John Hersey’s well known book on the horrible after effects are well known. In fact, the invisible, terrifying dangers associated with radiation are so creepy that they have been labeled “Radiation Bogey Man Factors.”ii
As engineers and scientists, however, we rely on data and evidence to determine the potential health impact of exposure to radiation. Now that more time has elapsed since the first problems occurred at the Fukushima facility, information is being released, and assessments of radioactivity have and are being taken. Such data can be compared with analyses from past disasters to more accurately assess the health (and ecological) risks for the population of Japan. To better understand what the future consequences might be, it makes sense to review the numerous studies published on the effects of the melt down at Chernobyl, the worst nuclear plant disaster in history. Before doing so, however, the “Bogey Man,” himself, needs to be defined.
Radiation: the “Bogey-Man”
The term ‘radiation’ is commonly used for what is actually termed ionizing radiation. The Biological Effects of Ionizing Radiation (BEIR) VII report published by the U.S. National Research Council in 2006 is the definitive source of information on radiation and the associated health risks. Ionizing radiation is conceptualized as “the radiation that has sufficient energy to displace electrons from molecules….and these free electrons, in turn, can damage human cells.”iii Measurements of radiation exposure are typically denoted based on the quantity of absorbed doses using an international unit called the Gray (Gy). The term Sievert (Sv) is used interchangeably with Gy for low levels of ionizing radiation (although Sv is actually defined in risk assessment work as equivalent dose vs. absorbed dose).
The reality is that all of us are exposed daily to a variety of natural radiation sources including radon, cosmic rays, rocks, soil, and a large number of foods such as sunflower seeds, various nuts, and even some types of beans. In addition, Professor Jacqueline Yanch, a nuclear engineering professor and expert in radiation physics associated with MIT, points out that natural background radiation varies from location to location across the globe, with the lowest average ranges in Denmark and the highest average rates in certain parts of Iran. Besides these natural background sources, man-made radiation such as medical X-rays and CT scans, consumer products like tobacco, and airline travel contribute to annual radiation exposure. Taken together, natural background and man-made sources of radiation amount to an average yearly dosage of about 2.8 mSv. The U.S. National Council on Radiation Protection and Measurements specifies that the maximum (safe) dose levels for individuals exposed to radiation (in addition to natural or man-made sources) is about 50 mSv/year, which would apply primarily to workers in occupations such as medical technology and nuclear facilities.iii
A key question to ask is “how do these annual average rates compare to the situation at Fukushima?” Needless to say, the information coming from various news reports and engineers is still sketchy, although some dose rates have been recorded. What has been particularly frustrating, however, is the inconsistency of the reported data. For example, three days after the Unit 1 reactor became inoperable, a dose rate of 11.9 mSv per hour was recorded in the containment area which dropped to 0.6 mSv six hours later. This seemed to indicate that the attempted cooling efforts with sea water were successfully achieving a decrease in radiation. Later that day, however, readings as high as 400 mSv were measured in the area between reactor units 3 and 4, leading to an immediate evacuation of workers (all of whom returned a few hours later when the readings again decreased significantly).
The next day, March 16, doses of 250 mSv were recorded by planes above the unit 3 reactor creating speculation that the containment structure was compromised. Some hours afterwards, it turned out that this was not the case. Between March 26-27, recordings of ionizing radiation in the region 30 – 40 km from Fukushima showed variability ranging from 0.9 – 17 mSv/hour. During the same time period, the International Atomic Energy Agency (IAEA) measured dose rates of 0.08 – 0.14 mSv in various regions of Tokyo, levels which are only slightly above normal background radiation. More recently, a key concern has been the recordings in the overflow tunnels surrounding units 1 through 4. The highest reading, so far, has been 1000 mSv in a tunnel outside of unit 2.
The million dollar question, of course, is what do these elevated levels mean for the surrounding population, and in particular, what are the likely health risks? A trip back in time to the Chernobyl disaster may shed light on what may and may not occur.
The Incident at Chernobyl
The Chernobyl Nuclear Power Plant is located in the northern Ukraine area, 7 km south of the Ukrainian-Belarusian border, in an area covered with meadows and forests.iv There are numerous reports and books that describe what happened at the Chernobyl power station in the early morning hours between 1 and 2 am on April 26, 1986. Called the “most severe accident ever in the nuclear industry,”v the explosion of unit 4 in the 30-year old reactor was primarily due to human error. In order to carry out an experimental procedure, a number of safety systems were disabled simultaneously, something which is prohibited in all U.S. facilities. When two explosions occurred in the reactor core, the reactor closure head was blown off, exposing the core to air. Although all reactors in the U.S. and most of the rest of the world encase reactors in steel- reinforced, concrete containment structures, the Chernobyl plant did not have any type of containment vessel. (The containment structure, in fact, was the reason that when the core meltdown occurred at Three Mile Island in 1979, minimal radiation was released and not a single injury occurred).
To make matters worse at Chernobyl, the Russian reactor design utilized highly flammable graphite blocks, which are prohibited in U.S. reactor systems. Thus, when the reactor began to melt down, numerous fires and explosions also occurred which led to the death of at least two emergency responders. During the ten day meltdown process that ensued, large amounts of radioactive materials were released directly into the surrounding environment particularly over Belarus, as well as the Ukraine, Europe, and Russia.
Although estimates vary, over 200,000 km² of European territory was impacted by this accident, with Belarus, the Ukraine, and Russia being the most affected.vi Radioactive materials were deposited on soil, vegetation, wetlands, rivers, and buildings depending on the wind and other climatic conditions at the time (e.g., it was raining in some parts of Russia, so the level of radioactivity varied from one town to another). The International Atomic Energy Agency determined that 25,000 km² was “contaminated”, with 14,600 km² in Belarus, 8,100 km² in Russia and 2,100 km² in the Ukraine. Over five million individuals lived in these contaminated areas, another 116,000 were evacuated from the area closest to the plant, and approximately 270,000 more were evacuated during the four years following the accident. In addition to the residents of contaminated areas, approximately 600,000 emergency personnel (“liquidators”) were exposed to the Chernobyl fallout.
Most estimates indicate that the liquidators received an average dose of 100 mSv. However, a number of workers in this group were early responders to the accident (e.g., firemen), arriving on-site without proper equipment or protective materials, and apparently received more than 250 mSv.vii Subsequently, a total of 134 liquidators were diagnosed with acute radiation syndrome (ARS) and 28 died shortly after the accident. Another two deaths were due to the impact of the (graphite) reactor explosions and nineteen more individuals with ARS died between 1987-2004, although it is not clear that their deaths were directly caused by radiation exposure.viii
The majority of individuals impacted by Chernobyl were exposed to low levels of radiation over a prolonged period of time. According to researchers who presented their findings at the Chernobyl Forum in 2006, the average accumulated doses were estimated to be in the range of 10-20 mSv for the several million individuals who resided in the surrounding regions. Given that exposure from natural radiation averages approximately 2.8 mSv, it is clear that the Chernobyl exposures rates were considerably higher than normal.
The research literature on Chernobyl is extensive. Abel Gonzalez, a scientist with the Argentine Nuclear Regulatory Authority, published a comprehensive review in 2007 which reported that over 25,000 studies have been conducted since 1986 and slightly over 10,000 have assessed the impact of the radiation exposure on health. Three years after the incident occurred, the USSR opened its doors to the international community of researchers, and in 1990 the International Chernobyl Project was initiated which found that although the contaminated area extended for well over 1000 miles, the whole- body lifetime radiation doses for most of the population was below 160 mSv. In 2003, the International Atomic Energy Agency organized the Chernobyl Forum to continually update and review research on the event.ix
The majority of Chernobyl investigations found a significant increase in thyroid cancer among children and adolescents living in three exposed countries (Belarus, Ukraine, Russia) who were between the ages of 0 and 18 at the time of the Chernobyl accident. Thyroid cancer is among the rarest forms of malignant tumors, and the percentage of the radionuclide iodine-131 that localizes in the thyroid gland is much higher for children than for adults. This is due to the fact that the thyroid glands in children are very active and small so that the dose per cubic millimeter of tissue is much higher than what would be expected in adults exposed to an equivalent amount. Children were particularly vulnerable (even in lower contamination areas) because they ingest a high level of milk from cows whose food supply was contaminated. Close to 5,000 excess thyroid cancer cases (over and above what would normally be expected) have been documented among those individuals who were children or adolescents at the time of the accident in the three country region between 1991 and 2002. However, since thyroid cancer is among the easiest to treat, there are only 15 known instances of resulting fatalities.x
One of the other types of cancers investigated relative to the Chernobyl accident is leukemia, which was shown to increase in exposed Japanese groups after the atomic bombings.xi Extensive research conducted by the European Childhood Leukemia-Lymphoma Study did not show an increase in leukemia during the five years following Chernobyl. In fact, to date, none of the case or cohort studies performed have found significantly higher (excess level) leukemia rates for individuals, adults, or children, in any of the surrounding Chernobyl regions. Similarly, the majority of those investigations which have tried to ascertain the link between low-level radiation doses and other types of cancer, besides that of thyroid and leukemia, have been inconclusive. A few studies of breast cancer in the Ukrainian region, however, has found slightly increased rates compared with the general population, and there are also increased reports of breast cancer in Belarus particularly those areas where dose exposure was higher than others.xii
In general, data gathered on over 470,000 individuals between 1980-2004, including 360,000 residents of contaminated areas and 60,000 recovery workers, have only indicated a significant increase in various cancers for the recovery workers who received higher dose rates than the general population and who were not wearing protective clothing when they responded to the incident.xiii One recent review, in fact, found chromosomal abnormalities in the Chernobyl clean-up workers in the years following the accident.xiv This type of damage, as well as some forms of cancer, may not show up in terms of adverse health consequences until considerably later in life.xv
Overall, the clearest long-term health impact associated with Chernobyl was the relationship between children who drank milk contaminated with iodine -131 and the incidence of thyroid cancer. The approximately 49 fatalities associated with the accident, however, were caused by high levels of radiation exposure to individuals who were required to immediately respond at the accident site, and who were not prepared in terms of proper safety equipment or protective radiation gear.
Predictions from Chernobyl for Fukushima
If there are any positives concerning the Chernobyl tragedy, they have to do with the fact that the international community learned a great deal after the incident was analyzed. When it became clear that radiation levels were increasing within the reactor units at Fukushima, the government acted quickly to evacuate the immediate surrounding areas, and gradually increased the evacuation zones as the potential for radioactive fallout increased. In addition, potassium iodide tablets were given to individuals in the surrounding areas to protect the thyroid gland from the adverse effects of iodine-131, a major byproduct of the fallout. To date, there has not been a single fatality associated with the accident. In the Chernobyl case, the government waited days before beginning an evacuation process, and preventative measures (such as the allocation of potassium iodide tablets) were not taken. Perhaps most importantly, unlike the Chernobyl plant, all of the Japanese reactors were housed in containment structures which minimized the extent to which ionizing radiation could escape into the atmosphere and surrounding land areas. Although it is likely that one of the containment units was compromised, the amount of radioactivity released was considerably less than the release from the Chernobyl meltdown.xvi
To shed more light on the situation at Fukushima, the faculty of MIT’s Nuclear Science and Engineering Department held an open panel session on March 15 to answer questions and address concerns that constituents from the broader MIT community might have about this nuclear incident. One of my former professors, Dr. Jacqueline Yanch, referred to above, participated in the panel telephonically as an expert on the potential health effects. Her feeling was that the preventive actions of the Japanese authorities, particularly the quick evacuations from the immediate surrounding region and the distribution of potassium iodide pills to negate the impact of radioactive iodine in water and milk supplies, should prevent major cases of thyroid cancer in the years ahead. In fact, Professor Yanch pointed out that the over 5000 cases of thyroid cancer caused by the Chernobyl accident could have been prevented if such measures had been taken expeditiously.
Professor Yanch also noted that the recorded radiation levels at Fukushima did not come close to those produced from the Chernobyl disaster. Also, although iodine- 131 has been measured at significantly high rates following the Fukushima incident, it has a relatively short half life of about eight days. The most problematic radionuclide detected is caesium-137, which has a half life of about 30 years and tends to bind securely to vegetation and soil.xvi The Japanese government is monitoring all crops and has enforced evacuation zones to minimize the impact from both radionuclides. At Chernobyl, however, extensive dispersion of iodine-131, caesium-137, as well as numerous other radionuclides were emitted into the surrounding region. Despite this – twenty years after the meltdown – less than 1% of these threats remain in the contiguous areas.
Perhaps the most concerning piece of information about Fukushima is the discovery of nuclear contamination seeping into the water channels as well as the surrounding ocean ecosystem. Kimberlee Kearfott, a professor of nuclear engineering at the University of Michigan, notes that this will require extremely careful monitoring of seafood, especially kelp and shrimp. “Fish can act like tea or coffee presses. When you push down on the plungers, the grounds all end up on one side. In this case, that is the fish.”xvii Unfortunately, Chernobyl did not provide insight into the impact such a disaster might have on fishing in the immediate area and more broadly, the ocean ecosystem. Thus, if there is a Bogeyman this time around, it may come from the ocean floor.
i) Shull, W.J. (1995). Effects of atomic radiation: A half century of studies from Hiroshima and Nagasaki. New York: Wiley and Sons, Inc.
ii) Friedman, G. and Egold, I. (Summer 1987). Reporting on radiation: A content analysis of the Chernobyl coverage. Journal of Communication, 37 (3), 58-66.
iii) NRC, National Research Council (2006). Health risks from exposure to low levels of ionizing radiation (BEIR VII). Washington, D.C.: National Academies Press, p.1
iv) United Nations Development Program. (Jan 25, 2002). The human consequences of the Chernobyl nuclear accident: a strategy for recovery. Report commissioned by the UNDP and UNICEF with support of OCHA and WHO. New York: United Nations.
v) Turner, J.E (2007). Atoms, radiation, and radiation protection. Germany: Wiley-VCH,p. 418.
vi) Balonov, M. (2007). Third annual Warren K. Sinclair keynote address: Retrospective analysis of the impacts of the Chernobyl accident. Health Physics, 93, 383.
vii) Boice, J.D. (1997). Leukemia, Chernobyl, and epidemiology. Journal of Radiological Protection, 17, 129-133.
viii) UNSCEAR, (2000) United Nations Scientific Committee on the Effects of Atomic Radiation. “Sources and effects of ionizing radiation.” 2000 Report to the UN General Assembly, with scientific annexes.
ix) Gonzalez, A. J. (July 2007). Chernobyl vis-à-vis the nuclear future: an international perspective. Health Physics, Volume 93, 5, p. 571-592.
x) Cardis, E. et al (2006). Cancer consequences of the Chernobyl accident: 20 years on. Journal of Radiological Protection, 26, 127-140.
xi) Howe, G. R. (2007). Leukemia following the Chernobyl incident. Health Physics, 93 (5), 512-515.
xii) Cardis, ibid.
xiii) Prysyazhnyuk, A. et al. (2007). Twenty years after Chernobyl: Solid cancer incidence in various groups of the Ukranian population. Radiation Environmental Biophysics, 40, 43-51.
xiv) Alexanin, S. et al. (2010). Chromosomal aberrations and sickness rates in chernobyl clean-up workers in the years following the accident. Health Physics, 98 (2), 258-260.
xv) Cardis, ibid.
xvi) For the best technical assessment of the Fukushima-Daichii accident, refer to J. Buongiorno et al, “Technical lessons learned from the Fukushima-Daichii accident and possible corrective actions for the nuclear industry: An initial evaluation.” MIT-NSP-TR-025, May 2011, Center for Advanced Nuclear Energy Systems.
xvii) Jolly, D., J. Tabuchi, and K. Bradsher. (March 27, 2011). “Tainted water at 2 reactors increases alarm for Japanese.” The New York Times.
Rosie Sugrue is a Course 22 (Nuclear Science and Engineering) major in the five year BS/SM program with a completion date of June 2012. She has worked as a nuclear operations intern for the Turkey Point Nuclear Facility in Florida and has spent the past two summers working within the risk assessment branch of the Nuclear Regulatory Commission. Her UROP projects in MIT’s Center for Nanotechnology have given her insight into the potential for increasing the safety and efficiency of nuclear power which she believes will be a key component in any future comprehensive energy policy. Rosie was honored to receive second prize in the 2011 Dewitt Wallace Scientific Writing for the Public competition for a paper she wrote on the Florida Everglades. Her major hobbies and interests include photography, playing the saxophone, and watching a variety of sports, particularly football and basketball.
This article was written for Course 21W.732 in the few weeks following the worst earthquake and tsunami in Japan’s history, events which led to massive loss of life as well as billions of dollars in property damage. During the devastating aftermath, much of the world’s attention was focused on the nuclear accident at Japan’s Fukushima-Daichii plant and more generally, on the risks associated with nuclear energy. Like most course 22 students, I was obsessed with learning more about what had gone wrong at the plant, what might be done to prevent such accidents in the future, and understanding what the eventual consequences would be in terms of public health and the future of nuclear energy.