![[schematic of the RPV for a GE BWR-3 or BWR-4, the two models that melted down at Fukushima]](http://upload.wikimedia.org/wikipedia/commons/thumb/a/a1/Bwr-rpv.svg/600px-Bwr-rpv.svg.png)
(See this previous lecture for an introduction to radioactivity and nuclear power.)
A few Sieverts of radiation dose will kill, and no medical countermeasures are available. By far the most people were killed this way in Japan in the Hiroshima and Nagasaki nuclear bombings carried out by the USA near the end of World War II. Chernobyl first responders fighting fires were working in the face of huge doses on the order of tens of Sieverts per hour. (Over 5000 metric tons of sand, lead, clay, and neutron-absorbing boron were also dropped by helicopters onto the burning reactor; the fire burned for days.) There were also the Slotin, Daghlian, and Goiania incidents [Monreal] in which doses of several Sieverts led to death. The Fukushima Fifty
who stayed behind to stabilize the reactor after the Tohoku earthquake and tsunami that claimed over 15,000 lives sustained smaller but still-dangerous dosages.
There were no fatalities linked to radiation due to the Fukushima Dai-ichi nuclear accident, according to an International Atomic Energy Agency (IAEA). According to Frank von Hippel's report from the IAEA expert fact-finding mission on Fukushima published in the Bulletin of the Atomic Scientists 67(5) 27-36 (2011), (a) the release of radioactivity (Cs-137 and I-131) into the atmosphere was about one-tenth of that from Chernobyl; (b) the estimated number of extra cancer deaths in the area long-term will probably be a few hundred to a thousand; (c) the long-term psychological damage could be even greater. You can read about the health impacts of the bigger Chernobyl nuclear accident in this World Health Organization report. Only a few tens of people died directly from the Chernobyl accident; there will probably be on the order of ten thousand extra cases of cancer in the long term. This is on top of the baseline rate of cancer in the general population which kills a lot more people.
[Note: the material in this subsection is partly based on a public lecture on the Fukushima accident impact by Ben Monreal of UCSB first mentioned in the previous chapter.]
Here is a simplified schematic of the BWR design in use at Fukushima when the accident happened in 2011.
For our discussion here, there is no need to get into any of the design details. We can imagine a healthy [BWR] reactor in terms of four basic components: (1) fuel pellets encased in super-tough stuff called zircalloy, (2) the cooling water around the fuel rods, (3) steam, and (4) the physical containment mechanisms --which have names like RPV
(reactor pressure vessel) and PCV
(primary containment vessel) for BWR reactors. Other reactors have broadly similar features, with the primary differences being in the substances used (a) to moderate (control) the chain reaction and (b) to exchange heat with the electricity generating mechanisms. For instance, MSR reactors use molten salt for heat exchange, not water.
[Note: the material in this subsection is partly based on a public lecture on the Fukushima accident impact by Ben Monreal of UCSB first mentioned in the previous chapter.]
What are the key features of radioactivity? The first is that each atom in a radioactive sample of a given chemical element has a constant probability of undergoing nuclear fission per second. You cannot tell which particular atom is going to decay radioactively at any moment; it is up to purely random quantum mechanical chance whether or not it does. Another important aspect of radioactivity is that radioactive versions of different chemical elements decay at different rates. Physicists characterize how fast radioactive decay happens by the half-life, which is the amount of time it takes for a radioactive substance to decay to half of its former activity.
Now let us imagine comparing two different radioactive samples, say Iodine-131 and Plutonium-239. Which would you rather stand next to: a box of a zillion I-131 atoms, half of which will radioactively decay in the next eight days, or a box of a zillion Pu-239 atoms, half of which will decay in the next twenty-four thousand years? If you guessed the plutonium, you were correct. When samples of two radioactive sources contain the same number of atoms, the sample with the shorter half-life is the more dangerous one and the sample with the longer half-life is the less dangerous one. Something with an infinitely long half-life is harmless: it never decays radioactively at all.
If the samples do not have the same number of atoms as each other, the answer to the question of which is the most dangerous will shift. Suppose instead that we adjust two samples to start out with the same number of radioactive decays per second, i.e. they register the same number of clicks on a Geiger counter. In this case, the activity of the sample with the longer half-life will decay more slowly over time than the sample with the shorter half-life, because it has a longer half-life. This is why people often speak of Plutonium-239 as evil: it decays away reeeeeeally slowly, taking over twenty-four thousand years before the Geiger counter reading will drop by a factor of two.
It is important to recognize that we also need to know other things about our source of radioactivity than just its half-life to calculate its overall danger to humans over time -- and this is where the biology gets really important. The mechanism of exposure, the biology of the element, whether the radiation is of alpha beta or gamma type, and the radiochemical behaviour of the decay daughters all come into the equation. This is why being a radiologist takes a lot of training.
Humans have very particular risks for radionuclides tied to our biochemistry. For instance, strontium-90 is absorbed readily into our bones and other structures because it is in the same chemical group in the periodic table as calcium (Group 2). Iodine-131 is also a dangerous radionuclide because it absorbs readily into our thyroids, which is a particular risk for children. This effect can be blocked by simply giving everyone plenty of ordinary non-radioactive iodine, eg in pills, so that the later-arriving radioactive iodine does not get absorbed very much (error: thyroid already full
). This was done broadly in the danger zone for Fukushima but not for Chernobyl. If you live within 50km of a nuclear power plant in Ontario, such as Darlington or Pickering, you can get KI (Potassium Iodide) pills in case of a nuclear emergency for free here.
Radionuclides that are watched like a hawk in a nuclear accident with emergency venting include the following [Monreal]:-
When there is a reactor fire, there is also soot to deal with. This is of worst concern to first responders and can be moved around (by tens of km) by weather. This is what stay indoors
advisories are for: to prevent you from getting exposed by getting soot on your clothes and skin. Soot can be cleaned from buildings and streets, but for agriculture you either have to wait it out or remove the top 10cm of the soil and find somewhere to store it safely as it decays. Massive land and waterway remediations are still under way in post-Tohoku-quake Japan, but even despite their best efforts and billions of dollars, radioactive water is still leaking into the ocean, producing a negative impact on fisheries.
Radionuclides to watch for in soot include the following [Monreal]:-
You may not be aware that it was actually not the earthquake on 11th March 2011 that damaged the Fukushima Dai-ichi reactors 1-3; workers scrammed them properly. It was the 15-metre-high tsunami that followed that cut off power to the cooling water pumps and their backup generators that caused the reactors to overheat and melt down. Seawater was used as an emergency coolant, but this contains many impurities compared to plain water and wrecks the reactors irrevocably. The accident was rated 7 out of 7 on the INES scale, due to high radioactive venting releases in the first few days. After about two weeks, units 1-3 were stable with water addition but had no proper heat sink for removal of decay heat from fuel. By July they were being cooled with recycled water from a new treatment plant. The reactor temperatures had fallen to below 80C at end of October, and official cold shutdown condition
was announced in mid December. Apart from cooling, the basic ongoing task is to prevent release of radioactive materials, particularly in contaminated water leaked from the three units and the storage tanks for contaminated water. This process will probably take decades to complete. The overall cleanup operation has been extremely expensive: it will cost over a hundred billion US dollars and take thirty to forty years.
Why are people so afraid of ionizing radiation? Mostly for a very simple reason: because they cannot see it, hear it, smell it, taste it, or touch it. The cure for this fear is science -- to understand what radiation is and how it behaves, and to know that it can be measured, e.g. by Geiger counters.
The worst radiation hazards from Fukushima were local and mitigatable because of early evacuations and controls on iodine in food. The global risk from radiation hazard is, realistically speaking, nil, even though knee-jerk anti-nuclear people keep breathlessly reporting discovery of tiny amounts of radionuclides that have travelled to other countries across the ocean. Again, their mistake is to think in binary terms. Radiation is not a binary hazard -- you measure it in milliSieverts.
Fear was Japan's biggest public health problem after the Fukushima Dai-ichi nuclear accident. There were huge communication and education failures by the utility TEPCO and the Japanese government. The public, especially those in and around the evacuation zone, were under enormous duress from psychological stress and fear. Similar problems occurred for Chernobyl victims and survivors, although the affected people in Europe did not have the same historical trauma from nuclear bombing as the Japanese.
The tsunami from the Tohoku quake drowned several times more people than will ever die from the nuclear accident, even though the latter will take decades more to remediate. The only people who took a really major health risk around the Dai-ichi emergency were the Fukushima Fifty -- the few plant workers who refused to flee and instead used their expertise to bring the meltdowns under control. After the accident began, the psychological impact of the Fukushima disaster was partly avoidable; the Fifty's sacrifice was not.
The most important source of worldwide radiation that we should go after among electric utilities is actually coal -- you get a significant amount of radioactive rubbish in the fly ash that coal plants emit. As was indicated in the previous seminar's numbers on radiation doses: for living near a nuclear power station you get a radiation dose of 0.0001–0.01 mSv/year while living near a coal-fired power station you get 0.0003 mSv/year. As we saw last lecture, neither is risky compared to eating bananas, having granite under your bed, or sleeping next to another human being every night.
Failures in nuclear design originated in lack of imagination of the engineers. As each nuclear accident has occurred in world history, lessons have been learned that inform the designs of more modern reactors. Ideally, from a technical engineering perspective there would be much more modern reactor designs in operation in countries like Japan and the USA than 1970s BWRs like the faulty Fukushima Dai-ichi design. The reason this has not happened is both technical and political: regulation of nuclear power plants has to be extremely tight technically, because of the sheer raw power of nuclear fission, which in turn makes the process of approving new plants extremely expensive and prone to delays.
In practice, what hamstrings the nuclear industry in rich industrialized countries is political cowardice. One way to see this is to look into how long the USA has been delaying constructing a long-term repository for high-level nuclear waste -- or, as John Oliver so succinctly put it in August 2017, America's nuclear toilet
. The fear politicians have of voters reacting badly to new nuclear power plants and the nuclear waste repository paralyzes policymaking. There is also a continuing tendency of governments on this continent to dump hazardous waste on the territory of Indigenous nations, along with other ugly undercurrents. In Japan there is even less political will to allow nuclear plant operation or new construction because the country was the only one in history to have nuclear bombs dropped on it by another country as an act of war. France poisoned parts of countries it colonized with nuclear testing, and bombed a Greenpeace ship in a port in New Zealand in an act of state-sponsored terrorism when I was a kid, because its crew was trying to stop French nuclear testing in the Pacific. If their nuclear testing was so safe, why didn't they do it under the Champs Élysée in central Paris?
It is physically possible for humanity to conserve energy by changing our consumption habits so that we can wean ourselves off nuclear power and fossil fuels in future. That time, however, is a minimum of several decades away politically. Your average first-world citizen is unwilling to change their energy consumption habits in significant ways -- like giving up a car or setting the thermostat a few degrees lower in winter and a few degrees higher in summer, necessitating wardrobe adjustments. Your average first-world citizen is also typically unwilling to face the currents of environmental racism running through a lot of green energy advocacy. Imagine if the environmental impacts of energy production affected wealthy Torontonians living in Rosedale too! Personally, I think the ethical thing to do is to advocate for energy policy that incorporates physics knowledge to improve environmental sustainability while at the same time ensuring human sustainability.
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