Da un articolo di Giuseppe Onufrio su Cado in piedi .
Il terremoto che ha colpito il Giappone è di sismicità spropositata, è un evento molto raro. Tuttavia questo evento spiega esattamente la natura del rischio nucleare. I reattori nucleari in Giappone erano progettati fino al 1995 per resistere a un terremoto di scala 6,5. Nel 95, dopo il terremoto di Kobe che arrivò a 7,2, sono stati progressivamente ristretti e resi molto più stringenti gli standard sismici. Ma è importante tener presente che la tecnologia può cercare di ridurre la probabilità che una certa catena di eventi accada, non la può eliminare del tutto. E allora what is the problem? The problem is that the new reactors, the EPR, which are constructed in a manner better than those who are jumping in the air in Japan, have a size twice the unit 3 of Fukushima are reactors that are almost four times the size in terms of power and then in terms of material and ability to contain the radioactivity.
The nuclear risk has two elements: the probability that certain things happen and the extent of possible consequences. You can work on probability, but until now the magnitude of the consequences in reality has been increasing and that none of the technologies we offer today is inherently safe. Che vuole dire intrinsecamente sicura? Vuole dire che se succede un guasto, il reattore in maniera passiva si mette in una posizione di sicurezza: no. Qui siamo sempre con la necessità di una vigilanza attiva e di sistemi attivi di controllo.
Che cosa è successo a Fukushima? A Fukushima è successa una situazione simile, più che a Chernobyl, a Three Miles Island e cioè il problema è stato causato dal terremoto. Un terremoto produce due tipi di effetti sul reattori: uno sono gli effetti strutturali, ossia si possono rompere le condutture, c'è una perdita di liquido di raffreddamento, il reattore si surriscalda e rischia di scoppiare. La seconda cosa è che, anche se la struttura ha tenuto, cosa che è successo nel caso di Fukushima 1, lo tsunami ha messo fuori gioco i generatori diesel di emergenza, conseguentemente il reattore è rimasto senza elettricità e, senza elettricità, il sistema delle pompe non ha funzionato. In particolare per quel tipo di reattore il sistema delle pompe era azionato in corrente continua ed è successo che il reattore ha cominciato a surriscaldarsi.
Che cosa accade quando un reattore si surriscalda? Quando un reattore si surriscalda succede questo: dobbiamo pensare a un bollitore con delle barre lunghe quattro metri che hanno una camicia di zirconio - lo zirconio è un metallo particolare - una lega di zirconio che si usa perché lo zirconio è abbastanza trasparente ai neutroni che vengono sparati dalla reazione and uranium in particular. Overheating causes the merger, may cause the opening of the shirt, these shirts are in the pads of nuclear fuel began to leak and then the child elements of fission, cesium 137 and iodine 131. Zirconium also has a problem: it is used because it is very useful from the point of view, nuclear engineer, since it is virtually transparent to neutrons, but reacts with water and creates hydrogen from water, hydrogen, being lighter , salt, and then we have these pots. In the case of the Fukushima internal pressure was double or more than double the project, then what have they done? They vented the steam which also contained hydrogen as a gas, hydrogen goes to the roof and at one point it expands and explodes, then started the first third of the building, it seems, without damaging the pot, the so-called vessel.
Now, in case of meltdown, what happens? That these shirts are opened and the tablets of fuel began to circulate inside the reactor, which is why the risk? The risk is that they go into the bottom of the reactor and become uncontrollable. ll reactor is controlled by rods made with boron which are put inside the reactor to absorb neutrons, but if these pills end up at the bottom should continue while pumping water to cool and, in addition, boric acid is put into circulation, which is always a compound of boron, which has the same effect to absorb neutrons, otherwise it happens that we are moving towards a condition in which the core melts. The reaction, so out of control and there may be a significant release of radioactivity.
Unlike Chernobyl reactor does not contain this type of graphite: graphite is as the lead of our pencils, is used in reactors like Chernobyl to slow down the neutrons, while here we use the water, which has the dual function to cool and slow down neutrons to increase the likelihood that the nuclear fission reaction is sustained. We are faced with a technology that essentially is inherently insecure We in Europe, near the gates of Italy, a reactor, to Krusk, in Slovenia, which is exactly on an earthquake fault. I think there the reactor has been designed to withstand a Richter scale of Grade 5, we must keep in mind that the Richter scale is a logarithmic scale, and then between 5 and 6 there are thirty levels of more power, more or less.
What does it mean? It means that nuclear power is a big risk and we do not need. Today in Europe the debate on a scenario in 2050 is entirely based on renewable sources has been discussed at the technical level and also in economic terms, renewables still cost a bit 'more, but do not cost more than nuclear power. When they tell us that nuclear must be done because it saves on phone bills tell a falsehood, because the costs of nuclear plants have been growing in all these decades and today the new facilities have costs that are at least double compared to what we said Enel in Italy. With nuclear
we face a risk that can not be eliminated, despite these new third-generation reactors, the EPR.
Meanwhile we have to tell those who listen to us that these EPR reactors there is not even in an office at the time, there are two sites in Europe, one in Finland and one in France, there is a shipyard in China, these EPR reactors are new and have many problems in the sense that the projects are still under examined from the standpoint of security. For one thing, the security agencies of France, the United States, England and Finland have not yet adopted the system drive the system in case of emergency. We say that the EPR, at least looking at the project, it is more robust than those that are skipped in Japan, but remember that in the Finnish shipyard were observed at least 3,000 violations of safety and there have been major problems in the welds of the primary circuit. It was discovered only a year after the French company that was working on the concrete structure of the reactor had made out the welding standard, which for years has worked without the security officer on site and were given a series problems with contracts and subcontracts, with works made out of standard. Some of these things are rectified, but we do not know to what extent are correct: the project is one thing and one thing is what is done on site.
When you say that in 50 years may not be enough fossil fuels than they tell you the truth, but a lie from the point of view of nuclear power, because it is not that uranium, on which this technology is still based, is exhausted after gas or, even worse, after coal. For more what I mean is that nuclear produces only electricity, so it's not that we get rid of uranium from oil: a large part of oil products is used in transport, uranium produces electricity and is the same thing that makes solar, or photovoltaic that can produce biomass and wind energy. Today the country has to choose and we see that on the one hand the government is destroying the market for renewable energy in Italy and the other began to speak of nonsense: nonsense like that, for example, to reassure the public about what is happening in Japan.
All the while the French and the Americans, who know the nuclear much better than we have told their citizens to leave. E 'yesterday's news that the U.S. Seventh Fleet which was offshore, 160 km off after the accident at sea, are turning away because they're reporting radioactivity in the air. We have this government that has exceeded the limits of idiocy, starting from the Chairman of the Nuclear Safety, Professor Veronesi, that nonsense has fired more than one: one, that we attacked more macroscopic, is to say that he could sleep with nuclear waste at home, if this happened in Italy if the Italians would follow his example, having to sleep on the night of the nuclear waste would take a collective dose that would result in a year, an increase of 250,000 cases of cancer .
We are in the hands of a government that makes jokes, we know that the prime minister is known to be a big joke in the nuclear field would be better not to make jokes e non dire idiozie come dice il professor Rigotti, sempre dell'Agenzia Nucleare del Politecnico di Milano, che dice delle idiozie cercando di dire che non è successo niente, senza avere nessuna contezza di quello che capita. Credo che dobbiamo tutti pensare che ci sarà un referendum sul nucleare, non è facile portare la gente a votare, perché sappiamo che il referendum è uno strumento visto in maniera un po' scettica. Ritengo però che quest'occasione del referendum sia importante. Proprio per il referendum stiamo raccogliendo le firme per accorpare la data con quella delle amministrative di maggio.
Tratto da www.marcoabrate.blogspot.com 
