This is a term paper written for a course called Introduction to Nuclear Science. I learned quite a lot while writing it, so hope you will enjoy reading it!
On March 11, 2013, the second anniversary of the Fukushima nuclear plant explosion, 68,000 Taiwanese occupied the major cities of the island to protest an on-going nuclear power plant construction project, in the hopes of preventing a repeat of the Japan disaster.1 The debate between the economic benefits versus the unforeseen natural risks escalated over the following weeks, but the government had already invested billions of dollars into the project and was unlikely to halt the progress. The dispute over the benefits and dangers of nuclear power continues to be a point of disagreement in Taiwan as well as many other countries within the same region; these countries are struggling to find a balance between clean and efficient energy and safety from Fukushima-like events. With many of these nations’ nuclear power plants built on top of the coastal circum-Pacific seismic belt, the potential of natural disasters leading to possibly catastrophic nuclear explosions is resulting in enormous anxiety among the populations within the region.
The extant effects of the Fukushima nuclear incident have encouraged some countries to take on an initiative to reduce the construction of nuclear power plants. However, among many sustainable energy solutions, nuclear power still remains one of the most efficient energy sources. It is important to take a critical look at the incident in order to understand the fundamental design of the Fukushima Boiling Water Reactor (BWR), and consider safer future developments. Image 1. 2
On March 11, 2011, an underwater earthquake with a magnitude of 9.0 struck 43 miles east of Japan, causing a tsunami that surged at towering heights that reached 133 feet and at its peak, a speed of 6 miles per hour. Within a day, the unprecedented tsunami affected millions of households and killed approximately 16,000 Japanese. However, the tragedy did not end here. Immediately after the event, the Japanese national news broadcasting corporation, NHK, reported the breaking news of the meltdown of the Fukushima nuclear power plant, which led the government to announce a mandatory evacuation zone the following day, in response to the nuclear radioactive danger.
At the Fukushima Daiichi site the reactor units are built along the coast (as shown in Image 1). On the day of the tsunami, Units 4, 5 and 6 were under maintenance while Units 1-3 were operating normally. The first incident of meltdown occurred at Unit 1, where a confluence of events involving elevated temperatures and pressure levels within the reactor, and the exposure of an element, zirconium, to hydrogen, resulted in the nuclear disaster. After the tsunami reached the coast, the unit’s emergent condenser began to malfunction and as a result, failed to cool down the pressurized steam. This led to a hazardous rise in the temperature of the reactor, which began to produce increased amounts of highly pressurized steam. The steam then reacted with the container of fuel within the reactor. A volatile material called zirconium had been used to load the radioactive fuel inside the reactors. Zirconium is commonly used in places such as flashbulbs for generating instant flashes of light and is known to oxidize upon contact with heated vaporized water, and release hydrogen gas. Once a fair amount of hydrogen accumulated inside the system, the burning fuel rod ignited the oxygen and caused a hydrogen explosion. Within four days, the same scenario occurred in Units 2 and 3.
The news of the three consecutive explosions in Japan quickly circulated around the world and alarmed international communities. Following the third explosion, the New York Times commented on the imminent danger posed by the spent fuel pool: “The shutdown of the other reactors then proceeded badly, and problems began to cascade... A 1997 study by the Brookhaven National Laboratory on Long Island described a worst- case disaster from uncovered spent fuel in a reactor cooling pool. It estimated 100 quick deaths would occur within a range of 500 miles and 138,000 eventual deaths.” The article also reported that the lack of coolant inside the spent fuel pool could potentially catch on fire. To make matters worse, there was also a chance that the damaged spent fuel pool would leak out radioisotope caesium-137 which could contaminate the nearby soil with a half-life of 30 years.3 Meanwhile in Fukushima, the situation had become more dire as the earlier explosions in Units 1 through 3 had damaged the wall of the fourth unit, which was built adjacent to the spent fuel pool; a few fires were also reported at Unit 4.
These four reactors are known as BWR Mark 1, designed by General Electric. After the incident, General Electric released a statement: “The BWR Mark 1 reactor is the industry’s workhorse with a proven track record of safety and reliability for more than 40 years. ... Today, there are 32 BWR Mark 1 reactors operating as designed worldwide. There has never been a breach of a Mark 1 containment system”.4 Yet the statement made by GE is incongruous with the corporation’s actions, which indicate General Electric has been aware of the safety issues of the BWR Mark 1 for some time. In a company report from..., it is clear that throughout the decades, the actual design of the BWR has undergone a series of modifications and improvements, which have been integrated into General Electric’s subsequent model: Mark 3.5 It is important to note that the model from the Fukushima Daiichi plant, was in fact, BWR Mark 1, which had been commissioned as early as 1971.
Image 2. 6
General Electric’s primary developments from BWR Mark 1 and 2 to Mark 3 were focused on the reactor’s containment system. Image 2 shows the actual design of the reactors of Daiichi BWR Mark 1, which operates under typical circumstances as follows: pure water is injected under the fuel core to act as a coolant and moderator. The fuel core boils the water off, thus creating steam, which is dried out and passed through the turbines and eventually ends up condensed to liquid water and ready to be reused as a coolant. BWR is designed with a negative void coefficient of reactivity.7 A negative void coefficient indicates that the loss of water as a coolant will decrease the power output. With more steam acting as a moderator in the system, the neutron multiplication for the fuel core would decrease and eventually stabilize an over-heating system. However, the self-stabilizing mechanism is not built to tolerate a sudden shift in steam pressure, so in addition to self-stabilizing, the suppression pool is designed to lower the excessive steam pressure. GE’s modifications throughout the years have mainly been made to the modulation of steam pressure within the system; this is because the manufacturer recognized that an over-pressurized environment could damage the containment vessel.and the stability of the reactor. Consequently, “quenchers” were installed to break up the steam bubbles in an attempt to reduce a sudden shift in pressure inside the suppression pool. However, BWR Mark 1 and Mark 2, are particularly criticized for their small containment systems. The containment system for a typical Pressurized Water Reactor has a size up to ten times larger the systems in the BWR Mark 1 and 2 designs. The latest design, BWR Mark 3, not only has a larger containment system, but also includes a mechanism that would ignite the excessive hydrogen gas exceeding a dangerous concentration.
The risks of BWR Mark 1 were reported as early as thirty-five years ago. A former General Electrics engineer, Dale Bridenbaugh, stated on an ABC News interview, “The problems we identified in 1975 were that, in doing the design of the containment, they did not take into account the dynamic loads that could be experienced with a loss of coolant”.8 In Fukushima, the Daiichi reactors were automatically shut down after the first earthquake, but there was a failure to foresee that the tsunami could damage and turn off the water pump generator, cutting off the supply of the coolant within the reactor. Thus, the focus of the recovery plan devised by the Tokyo Electric Power Company (TEPCO) was to cool down the reactors in an attempt to prevent any further meltdown. In the following weeks, TEPCO employees manually fed up water to cool down the fuel core, injected nitrogen gas to reduce the combustive oxygen concentration, and dumped water from helicopters to maintain water levels within the spent fuel pool. On March 27, a record high amount of 1000 milliSieverts (mSv) of radiation per hour was measured close to the plant (comparable to the 6000 mSv of radiation that was measured near the Chernobyl plant in 19869). Along with the radioactive water that was used to cool down the reactors, other radioactive wastes such as iodine-131, caesium-134 and caesium-137 had quickly contaminated the nearby area. At this point, the Japanese government extended the evacuation zone from a radius of 6 miles to one of 19 miles, consequentially relocating approximately 160,000 Japanese to temporary shelters following the events of the tsunami.
A typical BWR contains enriched uranium-235 between 1.7% to 2.5%. When uranium-235 undergoes fission, the most probable byproducts split into an atomic mass of 95 and 137, producing caesium-137 and strontium-90; another pair of byproducts is that with an atomic mass 140 and 94, which eventually beta decays from xeon-140 and strontium-94 into caesium-140, and zirconium-94. Of all the byproducts, iodine-131, caesium-137 and strontium-90 are the most dangerous, and were all detected near Fukushima.
Image 3. 10
The public reaction to nuclear events such as the Fukushima incident is often an immediate response of fear of illness and disease from exposure to radiation; however, the actual biological effects of radiation is dependent upon the amount of exposure. A low exposure is defined to be 100 mSv or less.11 Typically, a small dose of radiation does not induce immediate symptoms, but will increase the likelihood of cancer. For example, the inhalation of plutonium could cause lung cancer; the intake of strontium could cause leukemia; and caesium, considered to be the most poisonous to living organisms, could cause various types of cancer. According to the survey conducted by the Japanese government, the highest dose received by people living in Fukushima was 23mSv, thus deserving a classification of “low exposure”. The data shows that in general, people were not exposed to highly dangerous amounts of radiation. Image 3 shows that the radiation exposure around Fukushima had approximately decreased by half within 18 months of the explosion. However, a group of Japanese called the “Fukushima 50” that started as a group of around fifty people who voluntarily remained in the evacuation zone, rescuing onsite after the nuclear incident received a dangerous amount of exposure, and were later hailed for their heroic action by the Japanese public. The typical short term symptoms for these individuals who had undergone high levels of radiation exposure were nausea, diarrhea, loss of appetite, loss of hair, bone marrow, skin burns, etc. The long term symptoms include a higher susceptibility to the cancers described earlier.
In response to the international concerns, the World Health Organization in 2013 released a health risk assessment for Fukushima, and concluded that “no discernible increase in health risks from the Fukushima event is expected outside Japan. With respect to Japan, this assessment estimates that the lifetime risk for some cancers may be somewhat elevated above baseline rates in certain age and sex groups that were in the areas most affected”.12 For example, after being exposed to low radiation levels, infants, the highest-risk group, have a lifetime increase of 7% in leukemia, 6% in breast cancer, and 70% in thyroid cancer. The baseline of thyroid cancer rate in Japan is 0.75% for infants, therefore an increase of 70% brings the risk up to approximately 1.25%.
The two main sources of radiation at Fukushima came from iodine and caesium, which have a half-lifes of 8 days and 30 years, respectively. Although the radiation from iodine quickly diminishes within a few months to less than 1%, iodine in a human body ends up concentrated in the thyroid, creating a high concentration of radioactivity. With a much longer half-life, caesium contaminates an area for decades, and takes centuries to decay down to 1%. Caesium is known to be very dangerous for its chemical structure. It chemically resembles the structure of potassium, which is an essential chemical inside a living organism. Therefore, the intake of caesium could affect the entire human body; and the beta decay of caesium has a chance of yielding gamma emissions that contain high energy harmful to human cells.13 Near the Fukushima plant, agricultural products and seafood had been detected with high amounts of iodine and caesium. In February 2013, a greenling, caught near Fukushima, was reported with a caesium radiation that was 7400 greater than what is commonly considered safe for human consumption.14 While the radiation levels from the Fukushima area will continuously decrease, the real danger is the accidental consumption of these radioactive chemicals. Inevitably, both of these chemicals have already entered the food chain and continue to critically threatened the ecosystem around Fukushima, with broader effects still waiting to be felt.
Within a year of the disaster, the Japanese government had poured billions of dollars into the clean-up of the damaged reactors, the restoration of the contaminated area, relocation of the evacuees, and the decommissioning of the Daiichi reactors. The decommission plan is expected to take as long as 40 years15, but the most challenging task of all will surely be the reconditioning of the contaminated environment. So far, there is still a lot of work to be done by TEPCO. Currently there are 1000 tanks storing 400,000 tons of radioactive water at the site, and leakage has been a primary concern for the international community. Another challenge will be the removal of the molten cores. The mixture of the molten cores-- the cladding, concrete, and steel-- remains to be dug up and safely contained before depositing at the waste site. In addition to the decommissioning, TEPCO has also set up fish net around the plant to prevent the contaminated fish from swimming into the clean external ecosystem.16
The government agency in charge of the clean up project is known as the Japan Atomic Energy Agency. The JAEA has sponsored companies to develop efficient ways to clean up the nearby cities. One of the ideas developed was to use pressurized water to scour off the caesium on the road, and recycle and filter the contaminated water to reuse17. While most citizens were evacuated, some volunteered to help out with decontamination by manually wiping off the surface of a public school, and digging up the top layer of areas with contaminated soil. The common perception of the public was summarized by the Guardian, “Who should the public trust? In nuclear issues it can be hard to know. The engineers with most experience, those best placed to make a dangerous site safe, are industry insiders. Nuclear is their livelihood. But who does not have biases? Are anti-nuclear activists better qualified, more honest? Are academics more independent? University staff who work on nuclear technology are often funded by, or have close links to the industry. Perceived biases can be just as harmful to trust as real ones.”18 There is confusion, uncertainty and fear; and it is clear from the rising numbers of Japanese who are volunteering themselves for the clean-up work, the citizens have slowly lost faith in the Japanese government.
Image 4. 19
With an ambitious regulatory plan, the Japanese government created excessive public fear of radiation. Image 4 shows the updated human radiation consumption limits that the government began to enforce in April 2012. The new legislation attempts to minimize the radioactive remnants in the food chain; as a result, many common food products from Fukushima, including their rice and beef goods, were banned. The public began to pay more attention to the radiation levels in foods and grew more health- conscious. These new limits have damaged the agricultural economy in Fukushima and contributed to a mass suspicion of Fukushima products from citizens living outside of the prefecture. Post-explosion anti-radiation/nuclear energy legislation has had sizeable negative impact on the residents, merchants and farmers of Fukushima, those who were hit hardest in the explosion in the first place. In October 2013, David Ropeik from the New York Times pointed out the disconnect between the public’s fear of radiation and the scientific facts behind the effects of radiation: “Without a much broader and persistent effort by various branches and levels of government to help the public understand the actual biological effects of radiation, we will continue to face the threat of deep historic nuclear fears that simply don’t match the facts.”20
Image 5. 21
Unsurprisingly, the anti-nuclear movement surged in Japan and resonated globally. Of all the nations that supported the anti-nuclear propagation campaign, Germany was one of the countries that efficiently planned out an actual decommission plan for nuclear energy. Germany projected a complete nuclear reactor phase out by the year 2022. Unlike Germany that was able to fall back on their matured infrastructure of wind and solar power, Japan and other countries continue to fight to set up the groundwork that will serve as the foundation for a swift transition from nuclear energy to alternative energy. Image 5 shows that after the 2011 Fukushima incident, the main source of electricity has strongly depended on fossil gas and coal power plants, but searching for an alternative energy source has recently reached a new milestone in Japan. In November 2013, the Los Angeles Times reported, “Japan’s wind energy potential could generate 1,570 gigawatts, or five times current national electricity output, the Japan Daily Press said in its report on the turbine start-up. It hailed the project as reflecting the hope that nuclear power, which supplied nearly one-third of Japan's electricity needs before the Fukushima disaster, can be significantly reduced or phased out.” The country’s is located 13 miles away from Fukushima and generates electricity to support 600 households22. Japan’s search for renewable energy has yielded a new solution for its legacy of nuclear fear.
Since the Fukushima accident, the relationship between the Japanese government and its citizens is gaping with mistrust. Similar to Japan, other countries that are searching for a substitute for nuclear energy must strive to find an alternative energy source with a comparable economic cost and fewer environmental risks. While the modern nuclear power plant continues to serve as a an efficient method of generating electricity without emitting greenhouse, the fear of nuclear radiation governs the anti- nuclear movement across the world. The protesters will have to face a temporary burden of higher electricity bills and worsening air quality conditions until the current nuclear system can be completely replaced by renewable energies. Perhaps, the real victim to the movement is the possible sustainable nuclear solution such as nuclear fission that does not contain radioactive byproducts, but has simply suffered from being named “nuclear”. From the Fukushima accident, it is not only important to see the engineering problem in the current system-- it is imperative to see the social impacts of a highly informed (or misinformed) population that will be making the decisions for future generations.
1. Sun, Yu-Huay. “Taiwan Anti-Nuclear Protests May Derail $8.9 Billion Power Plant” Bloomberg 11 March 2013. |↩
3. William J. Broad and Hiroko Tabushi. “In Stricken Fuel-Cooling Pools, a Danger for the Longer Term” The New York Times 14 March 2011. |↩
4. General Electrics. “The Mark I Containment System in BWR Reactors” GE Reports 16 March, 2011. |↩
5. United States Nuclear Regulatory Commission “Resolution of Generic Safety Issues: Issue 157: Containment Performance” U.S NRC 29 March 2012. |↩
8. Yang, Jia Lynn. “Nuclear experts weigh in on GE containment system” The Washington Post 14 March 2011. |↩
10. World Nuclear Association. “Fukushima Accident” World Nuclear Association 25 November 2013. |↩
6. 9. 11. Wilson Andrews, Alberto Cuadra, et al. “Japan’s nuclear emergency” The Washington Post. 25 March 2011. |↩
12. World Health Organization “Health risk assessment from the nuclear accident after the 2011 Great East Japan Earthquake and Tsunami based on a preliminary does estimation” World Health Organization 2013. |↩
7. 13. John Lilley. “Nuclear Physics Principles and Applications” John Wiley & Sons Ltd. 2001 |↩
14. 16. Tokyo Electric Power Company “Nuclide Analysis Results of Fish and Shellfish” Tokyo Electric Power Company 15 March 2013. |↩
15. 18. Ian Sample. “Fukushima two years on: a dirty job with no end in sight” The Guardian 3 December 2013. |↩
17. 19. Geoff Brumfiel and Ichiko Fuyuno. “Japan's nuclear crisis: Fukushima's legacy of fear” Nature 07 March 2012. |↩
20. David Ropeik. “Fear vs. Radiation: The Mismatch” The New York Times 21 October 2013. |↩
2. 21. Wikipedia contributors. "Fukushima Daiichi nuclear disaster." Wikipedia. |↩
22. Carol J. Williams. “With nuclear plants idled, Japan launches pioneering wind project” Los Angeles Times 11 November 2013. |↩