Tuesday, March 29, 2011
Wednesday, March 23, 2011
Monday, March 21, 2011
Fukushima(France)
The seriousness of the accident which occured at Fukushima is somewhere between that of three Mile Isle and Chernobyl.
«In the worst-case scenario, one has to be prepared for an impact worse than that of Chernobyl», declared Wednesday François Baroin, government spokesperson, about the events which have unfolded since Saturday at the Fukushima Nuclear Central. In the view of experts, the situation has little in common with the catastrophe which unfolded at Chernobyl in 1986.
The Soviet reactor was in full operation when it exploded, and the deflagration ripped it apart.The explosion was accompanied by a fire fed by he presence of graphite at the interior of the core. This explosive coktail projected enormous quantities of radioactive particules to near 10 kilometers of altitude. Nothing of all that in the Japanese situation. «There are two major kinds of nuclear accidents, points out Olivier Gupta, assistant director to the Autorité de sûreté nucléaire (ASN). Those due to a poor control of the core, which leads to a chain reaction, such as Chernobyl. And cooling accidents, as in the current case at Fukushima.» This is what happened at Three Mile Island (United States) in 1979 with a reactor which had melted, but whose core had not been breached.
Cooling
But, in the Japanese reactor, we are dealing with a cooling accident of extraordinary dimension. The tsunami and, to a lesser extent the earthquaque devastated the region, destroyed the electrically-controlled water system as well as the pumps and all of the reactor cooling systems. Such a scenario was never foreseen by nuclear industrialists. Three reactors started to melt, and the used fuel rods of reactor number 4, not in service during the earthquake, are no longer covered by water and are going up in temperature. Tepco is down to pumping in sea water. And the high radioactiviy at the site makes intervention more difficult.
In this chaotic situation, what are the key elements which will determine the gravity of the accident? Fusion of the reactors, due to a fault in cooling, can have effects whose gravity is often not mentionned. «Two elements are to be considered», claims Olivier Gupta.
For one, the confinement of the inner area (a metallic skin covered with asphalt) in which is kept the reactor basin. In the case of total fusion, this could provoke a breach; this is the catastrophe scenario, which we have yet to experience in the entire history of nuclear, not even at three Mile Island. Radioactive gases such as xanon can then disperse in the atmosphere. Inhaled, they are rapidly eliminated by the organism.
In the case of total fusion (with breach or without), forms within the basin what is called corium, a magma very heavy in metals and radioactive materials which sinks to the bottom. This scenario does not involve dispersion of radioactive particles in the environment, according to Olivier Gupta. But it is an enormous management problem for the industrialist in the long run. Second key element, the containers in which is emprisonned the atomic fuel (big pencils). The more these are damaged by the heat, the more there will be radioactivity in the basin and thus pollution during voluntary emissions, meant to reduce pressure. «We know nothing of how severely damaged these containers may be», says Olivier Gupta.
The case of the pool where the used fuels from reactor number 4 are starting to heat up is also a first. The outcome is more difficult to predict as are the consequences. This case has already revealed a shortcoming, namely that at Fukushima as is the case with all nuclear reactors in the world the storage pools have no protected inner area.
Tepco is waging this battle by trying to buy time. Already, the rate of iodine 131 responsible for thyroïde cancers at Chernobyl has considerably diminished within the reactors.
«In the worst-case scenario, one has to be prepared for an impact worse than that of Chernobyl», declared Wednesday François Baroin, government spokesperson, about the events which have unfolded since Saturday at the Fukushima Nuclear Central. In the view of experts, the situation has little in common with the catastrophe which unfolded at Chernobyl in 1986.
The Soviet reactor was in full operation when it exploded, and the deflagration ripped it apart.The explosion was accompanied by a fire fed by he presence of graphite at the interior of the core. This explosive coktail projected enormous quantities of radioactive particules to near 10 kilometers of altitude. Nothing of all that in the Japanese situation. «There are two major kinds of nuclear accidents, points out Olivier Gupta, assistant director to the Autorité de sûreté nucléaire (ASN). Those due to a poor control of the core, which leads to a chain reaction, such as Chernobyl. And cooling accidents, as in the current case at Fukushima.» This is what happened at Three Mile Island (United States) in 1979 with a reactor which had melted, but whose core had not been breached.
Cooling
But, in the Japanese reactor, we are dealing with a cooling accident of extraordinary dimension. The tsunami and, to a lesser extent the earthquaque devastated the region, destroyed the electrically-controlled water system as well as the pumps and all of the reactor cooling systems. Such a scenario was never foreseen by nuclear industrialists. Three reactors started to melt, and the used fuel rods of reactor number 4, not in service during the earthquake, are no longer covered by water and are going up in temperature. Tepco is down to pumping in sea water. And the high radioactiviy at the site makes intervention more difficult.
In this chaotic situation, what are the key elements which will determine the gravity of the accident? Fusion of the reactors, due to a fault in cooling, can have effects whose gravity is often not mentionned. «Two elements are to be considered», claims Olivier Gupta.
For one, the confinement of the inner area (a metallic skin covered with asphalt) in which is kept the reactor basin. In the case of total fusion, this could provoke a breach; this is the catastrophe scenario, which we have yet to experience in the entire history of nuclear, not even at three Mile Island. Radioactive gases such as xanon can then disperse in the atmosphere. Inhaled, they are rapidly eliminated by the organism.
In the case of total fusion (with breach or without), forms within the basin what is called corium, a magma very heavy in metals and radioactive materials which sinks to the bottom. This scenario does not involve dispersion of radioactive particles in the environment, according to Olivier Gupta. But it is an enormous management problem for the industrialist in the long run. Second key element, the containers in which is emprisonned the atomic fuel (big pencils). The more these are damaged by the heat, the more there will be radioactivity in the basin and thus pollution during voluntary emissions, meant to reduce pressure. «We know nothing of how severely damaged these containers may be», says Olivier Gupta.
The case of the pool where the used fuels from reactor number 4 are starting to heat up is also a first. The outcome is more difficult to predict as are the consequences. This case has already revealed a shortcoming, namely that at Fukushima as is the case with all nuclear reactors in the world the storage pools have no protected inner area.
Tepco is waging this battle by trying to buy time. Already, the rate of iodine 131 responsible for thyroïde cancers at Chernobyl has considerably diminished within the reactors.
Tuesday, March 15, 2011
Friday, March 11, 2011
Wednesday, March 2, 2011
Tuesday, March 1, 2011
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