Many advocates of nuclear power would deny this. During the 25th anniversary last week of the Chernobyl disaster, some commentators asserted that few people died in the aftermath, and that there have been relatively few genetic abnormalities in survivors’ offspring. It’s an easy leap from there to arguments about the safety of nuclear energy compared to alternatives like coal, and optimistic predictions about the health of the people living near Fukushima.
But this is dangerously ill informed and short-sighted; if anyone knows better, it’s doctors like me. There’s great debate about the number of fatalities following Chernobyl; the International Atomic Energy Agency has predicted that there will be only about 4,000 deaths from cancer, but a 2009 report published by the New York Academy of Sciences says that almost one million people have already perished from cancer and other diseases. The high doses of radiation caused so many miscarriages that we will never know the number of genetically damaged fetuses that did not come to term. (And both Belarus and Ukraine have group homes full of deformed children.)
Nuclear accidents never cease. We’re decades if not generations away from seeing the full effects of the radioactive emissions from Chernobyl.
As we know from Hiroshima and Nagasaki, it takes years to get cancer. Leukemia takes only 5 to 10 years to emerge, but solid cancers take 15 to 60. Furthermore, most radiation-induced mutations are recessive; it can take many generations for two recessive genes to combine to form a child with a particular disease, like my specialty, cystic fibrosis. We can’t possibly imagine how many cancers and other diseases will be caused in the far future by the radioactive isotopes emitted by Chernobyl and Fukushima.
Doctors understand these dangers. We work hard to try to save the life of a child dying of leukemia. We work hard to try to save the life of a woman dying of metastatic breast cancer. And yet the medical dictum says that for incurable diseases, the only recourse is prevention. There’s no group better prepared than doctors to stand up to the physicists of the nuclear industry.
Still, physicists talk convincingly about “permissible doses” of radiation. They consistently ignore internal emitters — radioactive elements from nuclear power plants or weapons tests that are ingested or inhaled into the body, giving very high doses to small volumes of cells. They focus instead on generally less harmful external radiation from sources outside the body, whether from isotopes emitted from nuclear power plants, medical X-rays, cosmic radiation or background radiation that is naturally present in our environment.
However, doctors know that there is no such thing as a safe dose of radiation, and that radiation is cumulative. The mutations caused in cells by this radiation are generally deleterious. We all carry several hundred genes for disease: cystic fibrosis, diabetes, phenylketonuria, muscular dystrophy. There are now more than 2,600 genetic diseases on record, any one of which may be caused by a radiation-induced mutation, and many of which we’re bound to see more of, because we are artificially increasing background levels of radiation.
For many years now, physicists employed by the nuclear industry have been outperforming doctors, at least in politics and the news media. Since the Manhattan Project in the 1940s, physicists have had easy access to Congress. They had harnessed the energy inside the center of the sun, and later physicists, whether lobbying for nuclear weapons or nuclear energy, had the same power. They walk into Congress and Congress virtually prostrates itself. Their technological advancements are there for all to see; the harm will become apparent only decades later.
Doctors, by contrast, have fewer dates with Congress, and much less access on nuclear issues. We don’t typically go around discussing the latent period of carcinogenesis and the amazing advances made in understanding radiobiology. But as a result, we do an inadequate job of explaining the long-term dangers of radiation to policymakers and the public.
When patients come to us with cancer, we deem it rude to inquire if they lived downwind of Three Mile Island in the 1980s or might have eaten Hershey’s chocolate made with milk from cows that grazed in irradiated pastures nearby. We tend to treat the disaster after the fact, instead of fighting to stop it from happening in the first place. Doctors need to confront the nuclear industry.
Nuclear power is neither clean, nor sustainable, nor an alternative to fossil fuels — in fact, it adds substantially to global warming. Solar power, wind energy and geothermal energy, along with conservation, can meet our energy needs.
At the beginning, we had no sense that radiation induced cancer. Marie Curie and her daughter didn’t know that the radioactive materials they handled would kill them. But it didn’t take long for the early nuclear physicists in the Manhattan Project to recognize the toxicity of radioactive elements. I knew many of them quite well. They had hoped that peaceful nuclear energy would absolve their guilt over Hiroshima and Nagasaki, but it has only extended it.
Physicists had the knowledge to begin the nuclear age. Physicians have the knowledge, credibility and legitimacy to end it.
By Helen Caldicott, founder of Physicians for Social Responsibility, author of “Nuclear Power Is Not the Answer.”
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Fukushima I nuclear accidents
The Fukushima I nuclear accidents are a series of ongoing equipment failures and releases of radioactive materials at the Fukushima I Nuclear Power Plant, following the 9.0 magnitude Tôhoku earthquake and tsunami on March 11 2011. The plant comprises six separate boiling water reactors maintained by the Tokyo Electric Power Company (TEPCO). This accident is the largest of the 2011 Japanese nuclear accidents arising from the Tôhoku earthquake and tsunami, and experts consider it to be the second largest nuclear accident after the Chernobyl disaster, but more complex as all reactors are involved.
At the time of the quake, reactor 4 had been de-fueled while 5 and 6 were in cold shutdown for planned maintenance. The remaining reactors shut down automatically after the earthquake, with emergency generators starting up to run the control electronics and water pumps needed to cool reactors. The plant was protected by a seawall designed to withstand a 5.7 m (19 ft) tsunami but not the 14 m (46 ft) maximum wave which arrived 41–60 minutes after the earthquake. The entire plant was flooded, including low-lying generators and electrical switchgear in reactor basements and external pumps for supplying cooling seawater. The connection to the electrical grid was broken. All power for cooling was lost and reactors started to overheat, due to natural decay of the fission products created before shutdown. The flooding and earthquake damage hindered external assistance.
Evidence soon arose of partial core meltdown in reactors 1, 2, and 3; hydrogen explosions destroyed the upper cladding of the buildings housing reactors 1, 3, and 4; an explosion damaged the containment inside reactor 2; multiple fires broke out at reactor 4. Despite being initially shutdown, reactors 5 and 6 began to overheat. Fuel rods stored in pools in each reactor building began to overheat as water levels in the pools dropped. Fears of radiation leaks led to a 20 km (12 mi) radius evacuation around the plant while workers suffered radiation exposure and were temporarily evacuated at various times. One generator at unit 6 was restarted on 17 March allowing some cooling at units 5 and 6 which were least damaged. Grid power was restored to parts of the plant on 20 March, but machinery for reactors 1 through 4, damaged by floods, fires and explosions, remained inoperable. Flooding with radioactive water through the basements of units 1–4 continues to prevent access to carry out repairs.
Measurements taken by the Japanese science ministry and education ministry in areas of northern Japan 30–50 km from the plant showed radioactive caesium levels high enough to cause concern. Food grown in the area was banned from sale. It was suggested that worldwide measurements of iodine-131 and caesium-137 indicate that the releases from Fukushima are of the same order of magnitude as the releases of those isotopes from the Chernobyl disaster in 1986; Tokyo officials temporarily recommended that tap water should not be used to prepare food for infants. Plutonium contamination has been detected in the soil at two sites in the plant. Two workers hospitalized as a precaution on 25 March had been exposed to between 2000 and 6000 mSv of radiation at their ankles when standing in water in unit 3.
Japanese officials initially assessed the accident as level 4 on the International Nuclear Event Scale (INES) despite the views of other international agencies that it should be higher. The INES level was eventually raised successively to 5 and then the maximum 7. The Japanese government and TEPCO have been criticized for poor communication with the public and improvised cleanup efforts. Experts have said that a workforce in the hundreds or even thousands would take years or decades to clean up the area. On 20 March, the Chief Cabinet Secretary Yukio Edano announced that the plant would be decommissioned once the crisis was over.
The Fukushima I Nuclear Power Plant consists of six light water, boiling water reactors (BWR) designed by General Electric driving electrical generators with a combined power of 4.7 gigawatts, making Fukushima I one of the 25 largest nuclear power stations in the world. Fukushima I was the first nuclear plant to be constructed and run entirely by the Tokyo Electric Power Company (TEPCO).
Unit 1 is a 439 MWe type (BWR3) reactor constructed in July 1967. It commenced commercial electrical production on 26 March 1971. It was designed for a peak ground acceleration of 0.18 g (1.74 m/s2) and a response spectrum based on the 1952 Kern County earthquake. Units 2 and 3 are both 784 MWe type BWR-4 reactors, unit 2 commenced operating in July 1974 and unit 3 in March 1976. The design basis for all units ranged from 0.42 g (4.12 m/s2) to 0.46 g (4.52 m/s2). All units were inspected after the 1978 Miyagi earthquake when the ground acceleration was 0.125 g (1.22 m/s2) for 30 seconds, but no damage to the critical parts of the reactor was discovered.
Units 1–5 have a Mark 1 type (light bulb torus) containment structure, unit 6 has Mark 2 type (over/under) containment structure. From September 2010, unit 3 has been fueled by mixed-oxide (MOX) fuel.
Cooling requirements
Cooling is needed to remove decay heat from the reactor core even when a plant has been shut down. Nuclear fuel releases a small quantity of heat under all conditions, but the chain reaction when a reactor is operating creates short lived fission products which continue to release heat despite shutdown. Immediately after shutdown, this decay heat amounts to approximately 6% of full thermal heat production of the reactor. The decay heat in the reactor core decreases over several days before reaching cold shutdown levels Nuclear fuel rods that have reached cold shutdown temperatures typically require another several years of water cooling in a spent fuel pool before decay heat production reduces to the point that they can be safely transferred to dry storage casks.
In order to safely remove this decay heat, reactor operators must continue to circulate cooling water over fuel rods in the reactor core and spent fuel pond. In the reactor core, circulation is accomplished by use of high pressure systems that pump water through the reactor pressure vessel and into heat exchangers. These systems transfer heat to a secondary heat exchanger via the essential service water system, taking away the heat which is pumped out to the sea or site cooling towers.
To ensure that cooling water can continue to be circulated, reactors typically have redundant electrical supplies to operate pumps when the reactor is shut down, including electric generators, electrical supplies from the grid, and batteries. In addition, boiling water reactors have steam-turbine driven emergency core cooling systems that can be directly operated by steam still being produced after a reactor shutdown, which can inject water directly into the reactor. Steam turbines results in less dependence on emergency generators, but steam turbines only operate so long as the reactor is producing steam, and some electrical power is still needed to operate the valves and monitoring systems.
If the water in the unit 4 spent fuel pool had been heated to boiling temperature, the decay heat has the capacity to boil off about 70 tonnes of water per day (12 gallons per minute), which puts the requirement for cooling water in context. On 16 April 2011, TEPCO declared that reactors 1–4’s cooling systems were beyond repair and would have to be replaced.
Cooling problems at unit 1 and first radioactivity release
Unit 1 before the explosion. The join can be seen between the lower concrete building and upper lighter cladding which was blown away in the explosion. The trees and lamp posts indicate its size.
On 11 March at 14:46 JST, unit 1 scrammed successfully in response to the earthquake though evacuated workers reported violent shaking and burst pipes within the reactor building. All generated electrical power was lost following the tsunami leaving only emergency batteries, able to run some of the monitoring and control systems. At 15:42, TEPCO declared a "Nuclear Emergency Situation" for units 1 and 2 because "reactor water coolant injection could not be confirmed for the emergency core cooling systems." The alert was temporarily cleared when water level monitoring was restored for unit 1 but it was reinstated at 17:07 JST. Potentially radioactive steam was released from the primary circuit into the secondary containment area to reduce mounting pressure.
After the loss of site power, unit 1 initially continued cooling using the isolation condenser system; by midnight water levels in the reactor were falling and TEPCO gave warnings of the possibility of radioactive releases. In the early hours of 12 March, TEPCO reported that radiation levels were rising in the turbine building for unit 1 and that it was considering venting some of the mounting pressure into the atmosphere, which could result in the release of some radioactivity. Chief Cabinet Secretary Yukio Edano stated later in the morning the amount of potential radiation would be small and that the prevailing winds were blowing out to sea. At 02:00 JST, the pressure inside the reactor containment was reported to be 600 kPa (6 bar or 87 psi), 200 kPa higher than under normal conditions. At 05:30 JST, the pressure inside reactor 1 was reported to be 2.1 times the "design capacity", 820 kPa. Isolation cooling ceased to operate between midnight and 11:00 JST 12 March, at which point TEPCO started relieving pressure and injecting water. One employee working inside unit 1 at this time received a radiation dose of 106 mSv and was later sent to a hospital to have his condition assessed.
Rising heat within the containment area led to increasing pressure. Electricity was needed for both the cooling water pumps and ventilation fans used to drive gases through heat exchangers within the containment. Releasing gases from the reactor is necessary if pressure becomes too high and has the benefit of cooling the reactor as water boils off but this also means cooling water is being lost and must be replaced. If there was no damage to the fuel elements, water inside the reactor should be only slightly radioactive.
In a press release at 07:00 JST 12 March, TEPCO stated, "Measurement of radioactive material (iodine, etc.) by monitoring car indicates increasing value compared to normal level. One of the monitoring posts is also indicating higher than normal level." Dose rates recorded on the main gate rose from 69 nGy/h (for gamma radiation, equivalent to 69 nSv/h) at 04:00 JST, 12 March, to 866 nGy/h 40 minutes later, before hitting a peak of 0.3855 mSv/h at 10:30 JST. At 13:30 JST, workers detected radioactive caesium-137 and iodine-131 near reactor 1, which indicated some of the core’s fuel had been damaged. Cooling water levels had fallen so much that parts of the nuclear fuel rods were exposed and partial melting might have occurred. Radiation levels at the site boundary exceeded the regulatory limits.
On 14 March, radiation levels had continued to increase on the premises, measuring at 02:20 an intensity of 0.751 mSv/h on one location and at 02:40 an intensity of 0.650 mSv/h at another location on the premises. On 16 March, the maximum readings peaked at 10.850 mSv/h.
Explosion of reactor 1 building
At 15:36 JST on 12 March, there was an explosion in the reactor building at unit 1. The side walls of the upper level were blown away, leaving in place only the vertical steel framed gridworks. The roof collapsed covering the floor and some machinery on the south side. The walls were relatively intact compared to later explosions at units 3 and 4.[85][86] A video of the explosion shows that it was primarily directed sideways.
The roof of the building was designed to provide ordinary weather protection for the areas inside, not to withstand the high pressure of an explosion or to act as containment for the reactor. In the Fukushima I reactors the primary containment consists of "drywell" and "wetwell" concrete structures below the top level, immediately surrounding the reactor pressure vessel. The top floor has water filled pools for storing fuel either ready to be craned into the reactor or used fuel which is left to cool before being transferred elsewhere.
Experts soon agreed the cause was a hydrogen explosion.[88][89][90] Almost certainly the hydrogen was formed inside the reactor vessel[88] because of falling water levels, and this hydrogen then leaked into the containment building.[88] Exposed zircaloy clad fuel rods became very hot and reacted with steam, oxidising the alloy, and releasing hydrogen. Safety devices normally burn the venting hydrogen before it reaches explosive concentrations. These systems failed, possibly due to the shortage of electrical power.
Officials indicated reactor containment had remained intact and there had been no large leaks of radioactive material, although an increase in radiation levels was confirmed following the explosion. The Fukushima prefectural government reported radiation dose rates at the plant reaching 1.015 mSv/h. The IAEA stated on 13 March that four workers had been injured by the explosion at the unit 1 reactor, and that three injuries were reported in other incidents at the site. They also reported one worker was exposed to higher-than-normal radiation levels but the level fell below their guidance for emergency situations.
Two independent nuclear experts cited design differences between the Chernobyl Nuclear Power Plant and the Fukushima I Nuclear Power Plant, one of them saying he did not believe that a Chernobyl-style disaster would occur.
en.wikipedia.org/wiki/Fukushima_I_nuclear_accidents
