·
Tt The 2011 Srihoku earthquake (epicenter approximately 72 kilometers(45 mi ) east of the Oshika Peninsula of Shihoku, Japan. The nearest major city to the quake was Sendai, Honshu, and Japan 130 Km (81 mi) away. The tsunami was 9.0- magnitude undersea mega thrust earthquake off the coast of Japan that occurred on Friday 11 March 2011. The epicenter was approximately 72 kilometers east of the Oshika Peninsula of Shihoku, with the hypocenter at an underwater depth of approximately 32 km. The earthquake triggered extremely destructive tsunami waves of up to 23.6 m that struck Japan minutes after the quake, in some cases travelling up to 10 km inland, with smaller waves reaching many other countries after several hours. Tsunami warnings were issued and evacuations ordered along Japan’s Pacific coast and at least 20 other countries, including the entire Pacific coast of North America and South America. The earthquake and tsunami caused extensive and severe structural damage in Japan, including heavy damage to roads and railways as well as fires in many areas, and a dam collapse. Estimates of the Shihoku earthquake’s magnitude make it the most powerful known earthquake to have hit Japan and one of the five most powerful earthquakes in the world overall since modern record-keeping began in 1900.
· The Fukushima I, Fukushima II, Onagawa Nuclear Power Plant and Shukai nuclear power stations, consisting of a total eleven reactors, were automatically shut down following the earthquake. Japan declared a state of emergency following the failure of the cooling system at
Fukushima I & II Nuclear Power Plant, resulting in the evacuation of nearby residents. The Fujinuma irrigation dam in Sukagawa ruptured, causing flooding and washing away homes.
· One of Indonesia’s most active volcanoes has erupted, sending lava and searing gas clouds tumbling down its slopes, the world’s largest archipelago, is located on the so called Pacific
“Ring of Fire”, an arc of volcanoes and fault lines encircling the Pacific Basin. The eruption hours after a massive earthquake in Japan that triggered a Pacific wide tsunami.
| Radiation Sickness |
· A European bone marrow transplant group on Wednesday offered to treat Japanese emergency workers who may be exposed to dangerous radiation from the crippled nuclear reactors. Radiation typically kills many bone marrow cells, which can lead to a compromised immune system in patients, leaving them vulnerable to infections and other health problems. European doctors were not offering to perform bone marrow transplants, but to treat Japanese patients with supportive care like antibiotics until a transplant was possible.
· The background radiation levels were of the order of 0.07 microSv/hr; it rose to a few tens of microSv/hr and later to tens of milliSv/hr in the vicinity of the plant. Iodine-131, caesium-134, caesium-137, radioisotopes of xenon, krypton and other radionuclides released from the stricken nuclear reactors can cause exposure to the individuals. Among these, iodine-131 is very important during the early phase of the accident. Authorities distribute stable iodine tablets to the public if there is a possibility of exposure. Generally, counter measures include sheltering, ad hoc respiratory protection, administration of stable iodine, evacuation, relocation, control of access, control of food and water and use of stored animal feed and decontamination of affected areas and buildings. Stable iodine if present in the thyroid will prevent absorption of radioiodine by that organ. The dose reduction of 100 per cent is possible if stable iodine is administered before exposure. With administration one hour after exposure, the dose reduction will be 80 per cent if consumed after six hours of exposure stable iodine helps to lower dose to 50 per cent a day after it does not protect at all.
· Impact on India: Health physicists in every Indian nuclear power station routinely measure iodine -131 in goats' thyroid. Traces of iodine-131 may be deposited over grass in due course. Thyroid takes up the isotope. Extremely small amounts of radio iodine can thus be measured. Indian scientists have measured iodine-131 on a few occasions over the past several decades. They detected the iodine-131 fallout from the Chinese and French atmospheric weapons testing and from the accident at the Chernobyl nuclear power station. In all these cases the doses to people were trivial and a negligible fraction of the dose due to background radiation.
Years after Chernobyl |
The Chernobyl disaster was a well-known nuclear accident of catastrophic proportions that occurred on 26 April 1986, at the Chernobyl Nuclear Power Plant in Ukraine (then in the Ukrainian Soviet Socialist Republic, part of the Soviet Union). It is considered the worst nuclear power plant accident in history and is the only level 7 event on the International Nuclear Event Scale.
Chornobyl, abandoned city, N Ukraine, near the Belarus border, on the Pripyat River. Ten miles (16 km) to the north, in the town of Pripyat, is the Chernobyl nuclear power station, site of the worst nuclear reactor disaster in history. On Apr. 25, 1986, during an unauthorized test of one of the plant's four reactors, engineers initiated an uncontrolled chain reaction in the core of the reactor after disabling emergency backup systems. On Apr. 26, an explosion ripped the top off the containment building, expelling radioactive material into the atmosphere; more was released in the subsequent fire. Only after Swedish instruments detected fallout from the explosion did Soviet authorities admit that an accident had occurred. The reactor core was sealed off by air-dropping a cement mixture, but not before eight tons of radioactive material had escaped.
Twenty firefighters died immediately from overexposure to radioactivity, while hundreds suffered from severe radiation sickness. Pripyat, Chernobyl, and nearby towns were evacuated. People who lived near the plant in Ukraine and Belarus at the time have seen a greatly increased incidence of thyroid cancer, and genetic mutations have been discovered in children later born to exposed parents. Nearly all thyroid cancer cases, however, were successfully treated. Ukraine has estimated that some 4,400 people died as a result of the accident and during its cleanup, but a 2005 report prepared by several UN agencies and regional governments indicated that some 50 deaths were directly attributable to radiation from the disaster and an estimated 4,000 deaths might ultimately result from it, mainly due to higher cancer rates. That prediction was challenged the following year by a Greenpeace report that said more than 90,000 deaths might result, roughly half of which would be due to conditions other than cancer. The agricultural economies of E and N Europe were temporarily devastated, as farm products were contaminated by fallout. One Chernobyl reactor remained in operation until Dec., 2000, when the complex was shut down.
In the absence of reliable methods to quantify the impact of the Chernobyl disaster on public health, supporters and opponents of nuclear energy have proposed different investigation methods adapted to their respective beliefs and political agendas. In its assessment of the catastrophe, the Soviet Union considered that only deaths caused by acute radiation poisoning within the first three months following the accident can be linked to the explosion of the reactor. Today, Ukraine, Russia and Belarus are still providing assessments of the catastrophe largely based on figures from the Soviet era, and limit their communication about non-lethal diseases caused by radiation exposure to a strict minimum. While the figures presented by local authorities and nuclear supporters tend to underestimate the number of casualties from the Chernobyl disaster, the figures presented by anti-nuclear organisations are equally misleading. In some instances, ecologist organisations have been accused of keeping record of all casualties among emergency workers and rescuers on the accident site, even including every individual dying of natural causes unrelated to radiation. Among neighboring populations, premature deaths were also systematically attributed to Chernobyl, regardless of other environmental factors, such as smoking, alcoholism, or professional diseases among miners and industrial workers.
As a result of these specific surveys, both supporters and opponents of nuclear energy have presented rather absurd assessments of the Chernobyl disaster. During the 1990s, supporters of nuclear energy claimed that only 31 deaths could be directly attributed to the Chernobyl disaster – including two helicopter pilots who died in a crash on their way to the rescue operation. In a recent report, a scientific committee of the United Nations could only identify 64 deaths related to the nuclear accident, but acknowledged the possibility of 4,000 extra deaths due to the long-term effects of radiation poisoning. In contrast, Greenpeace believes that more than 200,000 people died directly from various causes related to the Chernobyl accident. Other ecologist organizations claim a staggering one million victims, including a questionable 170,000 deaths in North America.
| How The Nuclear Plant Crisis Happened |
· The crisis at the three Fukushima Daiichi nuclear power stations came not from the buildings collapsing after the March 11 earthquake of magnitude 9 and the tsunami that followed the quake. The tsunami knocked out the generations that produced the power. Lack of power in turn caused the cooling systems of the reactors to fail. The Fukushima nuclear reactor 1 went critical on March 1971 and is 460 MW reactors. Unite-2 and Unit-3 are 784 MW each and went critical in July 1974 and March 1976 respectively. All the three are Boiling Water Reactors (BWR) and use demineralised water for cooling the nuclear fuel. The fuel in the form of pellets is filled inside a metal rod called cladding. The cladding is made of zirconium alloy, and it completely seals the fuel. Fuel pins in the form bundles are kept in the reactor core. Several hundred fuel pins that are assembled in the core starts the chain reaction through fission process and heat is generated. The fuel bundles have gaps through which the coolant flows. The coolant never comes in direct contact with the fuel as it is kept sealed inside the zirconium alloy cladding. The coolant changes into steam as it cools the hot fuel. It is this steam that generates electricity by driving the turbines. All the heat that is produced by nuclear fission is not used for producing electricity. The efficiency of power plant, including nuclear, is not 100 per cent. In the case of nuclear power plant the efficiency is 30-35 per cent. “About 3 MW thermal energy is required to produce 1 MW of electrical energy. Hence for the 460 MW Unit-1, 1,380 MW thermal energy is produced.” “This heat has to be removed continuously.”
· In the case of Fukushima units, demineralised water is used as a coolant. Uranium-235 is used as fuel in Unit-1 and Unit-2 and Plutonium-239 is used as fuel in Unit-3.
| Coolant Flow |
· Since very high amount of heat is generated, the flow of the coolant should never be disrupted. But on March 11, pumping of the coolant failed as even the diesel generator failed after an hour’s operation. Though the power producing fission process was stopped by using control rods that absorb the neutrons immediately after the quake, the fuel still contains fission products such as iodine-131 and caesium-137 and activation products such as plutonium-239.
| Decay Heat |
· These radionuclides decay at different timescales, and they continue to produce heat during the decay period. The heat produced by radioactive decay of the fission products is called “decay heat. Just prior to shut down of the reactor the decay heat is 7 per cent. It reduces exponentially, about 2 per cent in the first hour. After one day, the decay heat is 1 per cent. Then it reduces very slowly. While the uranium fission process can be stopped and heat generation can be halted, there is no way of stopping the radioactive decay of the fission products. Apart from the original heat as well as the heat produced continuously by the fission products, including iodine, and cesium, has to be removed even after the uranium fission process has been stopped.
· Inability to remove this heat led to a rise in coolant temperature. According the Nature journal, when temperature reached around 1,000 degree C, the zirconium alloy that encases the fuel (cladding) probably began to melt or split apart. “In the process it reacted with the steam and created hydrogen gas, which is highly volatile,” Nature notes. Though the pressure created by hydrogen gas was reduced by controlled release, the massive build-up of hydrogen led to the explosion that blew the roof of the fuel hall in Unit-1 [and subsequently Unit-3]. The reactor core is present inside the primary containment. But the real danger arises from fuel melting. This would happen following the rupture of the zirconium casing. “If the heat is not removed, the zirconium cladding along with the fuel would melt and become liquid.” the government has said that the fuel rods in Unit-3 were likely already damaged.
Why the Fukushima disaster is worse than Chernobyl
This nation has recovered from worse natural – and manmade – catastrophes. But it is the triple meltdown and its aftermath at the Fukushima nuclear power plant 40km down the coast from Soma that has elevated Japan into unknown, and unknowable, terrain. Across the northeast, millions of people are living with its consequences and searching for a consensus on a safe radiation level that does not exist. Experts give bewilderingly different assessments of its dangers.
Some scientists say Fukushima is worse than the 1986 Chernobyl accident, with which it shares a maximum level-7 rating on the sliding scale of nuclear disasters. One of the most prominent of them is Dr Helen Caldicott, an Australian physician and long time anti-nuclear activist who warns of "horrors to come" in Fukushima.
"Fukushima is still boiling its radionuclides all over Japan,"
"Chernobyl went up in one go. So Fukushima is worse."
On the other side of the nuclear fence are the industry friendly scientists who insist that the crisis is under control and radiation levels are mostly safe. “The government and Tokyo Electric Power [Tepco, the plant's operator] are doing their best," Mr Sekimura initially advised residents near the plant that a radioactive disaster was "unlikely" and that they should stay calm"
Slowly, steadily, and often well behind the curve, the government has worsened its prognosis of the disaster. Last Friday, scientists affiliated with the Nuclear and Industrial Safety Agency said the plant had released 15,000 terabecquerels of cancer-causing Cesium, equivalent to about 168 times the 1945 atomic bombing of Hiroshima, the event that ushered in the nuclear age. (Professor Busby says the release is at least 72,000 times worse than Hiroshima).
Caught in a blizzard of often conflicting information, many Japanese instinctively grope for the beacons they know.
That's a mistake, say skeptics, who note a consistent pattern of official lying, foot-dragging and concealment. Last week, officials finally admitted something long argued by its critics: that thousands of people with homes near the crippled nuclear plant may not be able to return for a generation or more. "We can't rule out the possibility that there will be some areas where it will be hard for residents to return to their homes for a long time," said Yukio Edano, the government's top government spokesman. "We are very sorry."
Last Friday, hundreds of former residents from Futaba and Okuma, the towns nearest the plant, were allowed to visit their homes – perhaps for the last time – to pick up belongings. Wearing masks and radiation suits, they drove through the 20km contaminated zone around the plant, where hundreds of animals have died and rotted in the sun, to find kitchens and living rooms partly reclaimed by nature. "It's hard to believe we ever lived here," one former resident told NHK.
Several other areas northwest of the plant have become atomic ghost towns after being ordered to evacuate – too late, say many residents, who believe they absorbed dangerous quantities of radiation in the weeks after the accident. "We've no idea when we can come back," says Katsuzo Shoji, who farmed rice and cabbages and kept a small herd of cattle near Iitate, a picturesque village about 40km from the plant.
Although it is outside the exclusion zone, the village's mountainous topography meant radiation, carried by wind and rain, lingered, poisoning crops, water and school playgrounds.
The young, the wealthy, mothers and pregnant women left for Tokyo or elsewhere. Most of the remaining 6000 people have since evacuated, after the government accepted that safe radiation limits had been exceeded.
Mr Shoji, 75, went from shock to rage, then despair when the government told him he would have to destroy his vegetables, kill his six cows and move with his wife Fumi, 73, to an apartment in Koriyama, about 20km away. "We've heard five, maybe 10 years but some say that's far too optimistic," he says, crying. "Maybe I'll be able to come home to die." He was given initial compensation of one million yen (£7,900) by Tepco, topped up with 350,000 yen from the government.
It is the fate of people outside the evacuation zones, however, that causes the most bitter controversy. Parents in Fukushima City, 63km from the plant, have banded together to demand that the government do more to protect about 100,000 children. Schools have banned soccer and other outdoor sports. Windows are kept closed. "We've just been left to fend for ourselves," says Machiko Sato, a grandmother who lives in the city. "It makes me so angry."
Many parents have already sent their children to live with relatives or friends hundreds of kilometers away. Some want the government to evacuate the entire two million population of Fukushima Prefecture. "They're demanding the right to be able to evacuate," says anti-nuclear activist Aileen Mioko Smith, who works with the parents. "In other words, if they evacuate they want the government to support them."
So far, at least, the authorities say that is not necessary. The official line is that the accident at the plant is winding down and radiation levels outside of the exclusion zone and designated "hot spots" are safe.
But many experts warn that the crisis is just beginning. Professor Tim Mousseau, a biological scientist who has spent more than a decade researching the genetic impact of radiation around Chernobyl, says he worries that many people in Fukushima are "burying their heads in the sand." His Chernobyl research concluded that biodiversity and the numbers of insects and spiders had shrunk inside the irradiated zone, and the bird population showed evidence of genetic defects, including smaller brain sizes.
"The truth is that we don't have sufficient data to provide accurate information on the long-term impact," he says. "What we can say, though, is that there are very likely to be very significant long-term health impact from prolonged exposure."
In Soma, Mr Ichida says all the talk about radiation is confusing. "All we want to do is get back to work. There are many different ways to die, and having nothing to do is one of them."
Economic cost
Fukushima: Japan has estimated it will cost as much as £188bn to rebuild following the earthquake, tsunami and nuclear crisis.
Chernobyl There are a number of estimates of the economic impact, but thetotal cost is thought to be about £144bn.
Safety
Fukushima: workers are allowed to operate in the crippled plant up to a dose of 250mSv (millisieverts).
Chernobyl: People exposed to 350mSv were relocated. In most countries the maximum annual dosage for a worker is 20mSv. The allowed dose for someone living close to a nuclear plant is 1mSv a year.
Death toll
Fukushima: Two workers died inside the plant. Some scientists predict that one million lives will be lost to cancer.
Chernobyl: It is difficult to say how many people died on the day of the disaster because of state security, but Greenpeace estimates that 200,000 have died from radiation-linked cancers in the 25 years since the accident.
Exclusion zone
Fukushima: Tokyo initially ordered a 20km radius exclusion zone around the plant
Chernobyl: The initial radius of the Chernobyl zone was set at 30km – 25 years later it is still largely in place.
Compensation
Fukushima: Tepco's share price has collapsed since the disaster largely because of the amount it will need to pay out, about £10,000 a person
Chernobyl: Not a lot. It has been reported that Armenian victims of the disaster were offered about £6 each in 1986
Fukushima: The UN's Office for the Co-ordination of Humanitarian Affairs reported bilateral aid worth $95m
Chernobyl: 12 years after the disaster, the then Ukrainian president, Leonid Kuchma, complained that his country was still waiting for international help.
| Effect Of Melted Fuel |
· Melted fuel is called “corium.” Since melted fuel is at a very high temperature it can even “burn through the concrete containment vessel.” According to Nature, if enough melted fuel gathers outside the fuel assembly it can “restart the power-producing reactions, and in a completely uncontrolled way.” What may result is a “full-scale nuclear meltdown.”
· Pumping of sea-water is one way to reduce the heat and avoid such catastrophic consequences. The use of boronic acid, which is an excellent neutron absorber, would reduce the chances of nuclear reactions restarting even if the fuel is found loose inside the reactor core. Both these measures have been resorted to in Unit-1 and Unit-3. Despite these measures, the fuel rods were found exposed in Unit-2 on two occasions.
| Fate Of Reactor Core |
· While the use of sea-water can prevent fuel melt, it makes the reactor core completely useless as it results in corrosion. The case of unit -4 is different from the other three units. Unlike in the case of unit -1, 2 and 3, the Unit -4 is under maintenance and the core has been taken out, and the spent fuel rods are kept in the cooling pond. Whatever led to a decrease in water level, the storage pond caught fire on March 15 possibly due to hydrogen explosion. The radioactivity was released directly into the atmosphere.
| Spent Fuel Fate Unknown |
It is not known if the integrity of the cladding has been already affected and the fuel exposed. Since the core of a Boiling Water Reactor (BWR) is removed only once a year or so, the number of spent rods in the pond will be more. If the fuel is indeed exposed, the possibility of fuel melt is very likely. Though the fuel will be at a lower temperature than found inside a working reactor, there are chances of the fuel melting. ince it does not have any containment unlike the fuel found inside a reactor, the consequences of a fuel melt would be really bad. Radioactivity is released directly into the atmosphere. Radioactivity of about 400 milliSv/hour was reported at the site immediately after the fire.
Source: The Hindu
