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It looks like you're using an Ad Blocker. Please white-list or disable AboveTopSecret.com in your ad-blocking tool. Thank you. Some features of ATS will be disabled while you continue to use an ad-blocker. Originally posted by THEDUDE86 This is a load of speculation and crap... I work for an emergency management agency in a state with many nuclear facilities. Our facility was federally funded after sept 11 and has several different emergency related agencies including military... I cant say exact amount nuclear plants,because then you could find out where I work. We have a command center that is for the nuclear power plants located in my building. This facility has devices throughout the state and country that can detect radioactive particles in the atmosphere. Now, I am allowed in this area, but friday the area was on full lock down and they brought in security and nuclear commission people. Now this facility would only be activated given a threat to the united states of a radiological event. There is also a secure room that was I am never allowed in was also busy. This room has secure phone lines to Washington. My building is one of the safest buildings in the Midwest. It is protected from gamma radiation with a metal mesh around the building. I'm not trying to stir up something here but the only time I see this room activated is for training exercises and they train on nuclear winter, nuclear meltdown that results in releases, and even strong solar flare activity. All this seems interesting to me that things were activated he because of japan. That much I do know because one of my coworkers who is a earthquake expert was called in to the area to talk about the type of quake Originally posted by BobbyTarass You should rename you thread as "OMG ! STUNNING NEWS, NUCLEAR FALSE FLAG, THE SHOCKING LIE ! JOURNALIST CONSPIRACY". Then you'll get something like 100+ S&F and people would read your paper. When you're posting on ATS, quit trying to be reasonnable, people here only listen to fearmongers, they'll tell you that they do not want the worse to happen and thus try to prevent it by acting like it's already happening but don't fall for it, those guys have a hard-on everytime the earth cough. Originally posted by THEDUDE86 This is a load of speculation and crap... I work for an emergency management agency in a state with many nuclear facilities. Our facility was federally funded after sept 11 and has several different emergency related agencies including military... I cant say exact amount nuclear plants,because then you could find out where I work. We have a command center that is for the nuclear power plants located in my building. This facility has devices throughout the state and country that can detect radioactive particles in the atmosphere. Now, I am allowed in this area, but friday the area was on full lock down and they brought in security and nuclear commission people. Now this facility would only be activated given a threat to the united states of a radiological event. There is also a secure room that was I am never allowed in was also busy. This room has secure phone lines to Washington. My building is one of the safest buildings in the Midwest. It is protected from gamma radiation with a metal mesh around the building. I'm not trying to stir up something here but the only time I see this room activated is for training exercises and they train on nuclear winter, nuclear meltdown that results in releases, and even strong solar flare activity. All this seems interesting to me that things were activated he because of japan. That much I do know because one of my coworkers who is a earthquake expert was called in to the area to talk about the type of quake I repeat, there was and will *not* be any significant release of radioactivity from the damaged Japanese reactors. By "significant" I mean a level of radiation of more than what you would receive on - say - a long distance flight, or drinking a glass of beer that comes from certain areas with high levels of natural background radiation. What happened at Fukushima I will try to summarize the main facts. The earthquake that hit Japan was 7 times more powerful than the worst earthquake the nuclear power plant was built for (the Richter scale works logarithmically; the difference between the 8.2 that the plants were built for and the 8.9 that happened is 7 times, not 0.7). So the first hooray for Japanese engineering, everything held up. When the earthquake hit with 8.9, the nuclear reactors all went into automatic shutdown. Within seconds after the earthquake started, the moderator rods had been inserted into the core and nuclear chain reaction of the uranium stopped. Now, the cooling system has to carry away the residual heat. The residual heat load is about 3% of the heat load under normal operating conditions. The earthquake destroyed the external power supply of the nuclear reactor. That is one of the most serious accidents for a nuclear power plant, and accordingly, a “plant black out” receives a lot of attention when designing backup systems. The power is needed to keep the coolant pumps working. Since the power plant had been shut down, it cannot produce any electricity by itself any more. Things were going well for an hour. One set of multiple sets of emergency Diesel power generators kicked in and provided the electricity that was needed. Then the Tsunami came, much bigger than people had expected when building the power plant (see above, factor 7). The tsunami took out all multiple sets of backup Diesel generators. When designing a nuclear power plant, engineers follow a philosophy called “Defense of Depth”. That means that you first build everything to withstand the worst catastrophe you can imagine, and then design the plant in such a way that it can still handle one system failure (that you thought could never happen) after the other. A tsunami taking out all backup power in one swift strike is such a scenario. The last line of defense is putting everything into the third containment (see above), that will keep everything, whatever the mess, moderator rods in our out, core molten or not, inside the reactor. When the diesel generators were gone, the reactor operators switched to emergency battery power. The batteries were designed as one of the backups to the backups, to provide power for cooling the core for 8 hours. And they did. Within the 8 hours, another power source had to be found and connected to the power plant. The power grid was down due to the earthquake. The diesel generators were destroyed by the tsunami. So mobile diesel generators were trucked in. This is where things started to go seriously wrong. The external power generators could not be connected to the power plant (the plugs did not fit). So after the batteries ran out, the residual heat could not be carried away any more. At this point the plant operators begin to follow emergency procedures that are in place for a “loss of cooling event”. It is again a step along the “Depth of Defense” lines. The power to the cooling systems should never have failed completely, but it did, so they “retreat” to the next line of defense. All of this, however shocking it seems to us, is part of the day-to-day training you go through as an operator, right through to managing a core meltdown. It was at this stage that people started to talk about core meltdown. Because at the end of the day, if cooling cannot be restored, the core will eventually melt (after hours or days), and the last line of defense, the core catcher and third containment, would come into play. But the goal at this stage was to manage the core while it was heating up, and ensure that the first containment (the Zircaloy tubes that contains the nuclear fuel), as well as the second containment (our pressure cooker) remain intact and operational for as long as possible, to give the engineers time to fix the cooling systems. Because cooling the core is such a big deal, the reactor has a number of cooling systems, each in multiple versions (the reactor water cleanup system, the decay heat removal, the reactor core isolating cooling, the standby liquid cooling system, and the emergency core cooling system). Which one failed when or did not fail is not clear at this point in time. So imagine our pressure cooker on the stove, heat on low, but on. The operators use whatever cooling system capacity they have to get rid of as much heat as possible, but the pressure starts building up. The priority now is to maintain integrity of the first containment (keep temperature of the fuel rods below 2200°C), as well as the second containment, the pressure cooker. In order to maintain integrity of the pressure cooker (the second containment), the pressure has to be released from time to time. Because the ability to do that in an emergency is so important, the reactor has 11 pressure release valves. The operators now started venting steam from time to time to control the pressure. The temperature at this stage was about 550°C. This is when the reports about “radiation leakage” starting coming in. I believe I explained above why venting the steam is theoretically the same as releasing radiation into the environment, but why it was and is not dangerous. The radioactive nitrogen as well as the noble gases do not pose a threat to human health. At some stage during this venting, the explosion occurred. The explosion took place outside of the third containment (our “last line of defense”), and the reactor building. Remember that the reactor building has no function in keeping the radioactivity contained. It is not entirely clear yet what has happened, but this is the likely scenario: The operators decided to vent the steam from the pressure vessel not directly into the environment, but into the space between the third containment and the reactor building (to give the radioactivity in the steam more time to subside). The problem is that at the high temperatures that the core had reached at this stage, water molecules can “disassociate” into oxygen and hydrogen – an explosive mixture. And it did explode, outside the third containment, damaging the reactor building around. It was that sort of explosion, but inside the pressure vessel (because it was badly designed and not managed properly by the operators) that lead to the explosion of Chernobyl. This was never a risk at Fukushima. The problem of hydrogen-oxygen formation is one of the biggies when you design a power plant (if you are not Soviet, that is), so the reactor is build and operated in a way it cannot happen inside the containment. It happened outside, which was not intended but a possible scenario and OK, because it did not pose a risk for the containment. So the pressure was under control, as steam was vented. Now, if you keep boiling your pot, the problem is that the water level will keep falling and falling. The core is covered by several meters of water in order to allow for some time to pass (hours, days) before it gets exposed. Once the rods start to be exposed at the top, the exposed parts will reach the critical temperature of 2200 °C after about 45 minutes. This is when the first containment, the Zircaloy tube, would fail. And this started to happen. The cooling could not be restored before there was some (very limited, but still) damage to the casing of some of the fuel. The nuclear material itself was still intact, but the surrounding Zircaloy shell had started melting. What happened now is that some of the byproducts of the uranium decay - radioactive Cesium and Iodine - started to mix with the steam. The big problem, uranium, was still under control, because the uranium oxide rods were good until 3000 °C. It is confirmed that a very small amount of Cesium and Iodine was measured in the steam that was released into the atmosphere. It seems this was the “go signal” for a major plan B. The small amounts of Cesium that were measured told the operators that the first containment on one of the rods somewhere was about to give. The Plan A had been to restore one of the regular cooling systems to the core. Why that failed is unclear. One plausible explanation is that the tsunami also took away / polluted all the clean water needed for the regular cooling systems. The water used in the cooling system is very clean, demineralized (like distilled) water. The reason to use pure water is the above mentioned activation by the neutrons from the Uranium: Pure water does not get activated much, so stays practically radioactive-free. Dirt or salt in the water will absorb the neutrons quicker, becoming more radioactive. This has no effect whatsoever on the core - it does not care what it is cooled by. But it makes life more difficult for the operators and mechanics when they have to deal with activated (i.e. slightly radioactive) water. But Plan A had failed - cooling systems down or additional clean water unavailable - so Plan B came into effect. This is what it looks like happened: In order to prevent a core meltdown, the operators started to use sea water to cool the core. I am not quite sure if they flooded our pressure cooker with it (the second containment), or if they flooded the third containment, immersing the pressure cooker. But that is not relevant for us. The point is that the nuclear fuel has now been cooled down. Because the chain reaction has been stopped a long time ago, there is only very little residual heat being produced now. The large amount of cooling water that has been used is sufficient to take up that heat. Because it is a lot of water, the core does not produce sufficient heat any more to produce any significant pressure. Also, boric acid has been added to the seawater. Boric acid is "liquid control rod". Whatever decay is still going on, the Boron will capture the neutrons and further speed up the cooling down of the core. The plant came close to a core meltdown. Here is the worst-case scenario that was avoided: If the seawater could not have been used for treatment, the operators would have continued to vent the water steam to avoid pressure buildup. The third containment would then have been completely sealed to allow the core meltdown to happen without releasing radioactive material. After the meltdown, there would have been a waiting period for the intermediate radioactive materials to decay inside the reactor, and all radioactive particles to settle on a surface inside the containment. The cooling system would have been restored eventually, and the molten core cooled to a manageable temperature. The containment would have been cleaned up on the inside. Then a messy job of removing the molten core from the containment would have begun, packing the (now solid again) fuel bit by bit into transportation containers to be shipped to processing plants. Depending on the damage, the block of the plant would then either be repaired or dismantled. ***UPDATE – 3/14 8:15 pm EST*** Units 1 and 3 are currently in a stable condition according to TEPCO press releases, but the extent of the fuel damage is unknown. That said, radiation levels at the Fukushima plant have fallen to 231 micro sieverts (23.1 millirem) as of 2:30 pm March 14th (local time). ***UPDATE – 3/14 10:55 pm EST*** The details about what happened at the Unit 2 reactor are still being determined. The post on what is happening at the Unit 2 reactor contains more up-to-date information. Radiation levels have increased, but to what level remains unknown. Since the reactor’s cooling capability was limited, and the water inventory in the reactor was decreasing, engineers decided to inject sea water (mixed with boric acid – a neutron absorber) to ensure the rods remain covered with water. Although the reactor had been shut down, boric acid is added as a conservative measure to ensure the reactor stays shut down. Boric acid is also capable of trapping some of the remaining iodine in the water so that it cannot escape, however this trapping is not the primary function of the boric acid. The water used in the cooling system is purified, demineralized water. The reason to use pure water is to limit the corrosion potential of the coolant water during normal operation. Injecting seawater will require more cleanup after the event, but provided cooling at the time. This process decreased the temperature of the fuel rods to a non-damaging level. Because the reactor had been shut down a long time ago, the decay heat had decreased to a significantly lower level, so the pressure in the plant stabilized, and venting was no longer required. News Updates and Current Status of Facilities Posted on March 16, 2011 10:59 am UTC by mitnse Units 1 and 2: TEPCO has released estimates of the levels of core damage at these two reactors: 70% damage at Unit 1 and 33% at Unit 2. They have also stated that Unit 1 is being adequately cooled. Outlook: It is difficult to make conjectures at this point about the final disposition of the damaged fuel without further information. However, during our only operating experience with a partially melted and subsequently cooled core, Three Mile Island, the fuel mass was fully contained by the reactor vessel, resulting in minimal radiation release to the public. A decision is currently being made on how to best supply cooling water to Unit 2. Unit 3: At 8:34 AM JST, white smoke was seen billowing from the roof of Unit 3. The source of this smoke was not investigated because workers were evacuated due to radiation levels. These levels had been fluctuating during the early morning hours before rising to 300-400 millisievert/hr around the time that the smoke appeared. It was unclear at the time whether these rising levels were a result of some new event at Unit 3, or were lingering as a result of Unit 2’s recent troubles. Outlook: In order to provide some perspective on worker doses to this point, radiation sickness sets in at roughly 1000 millisieverts. A future post will deal further with the health effects of various amounts of radiation. Response to the smoke seen at Unit 3 appears to be in an information gathering phase at this point. Chief Cabinet Secretary Yukio Edano speculated that the smoke from Unit 3 might be the result of a similar wetwell explosion to that at Unit 2, but there is not enough information currently available to support or refute that statement. Units 4-6: Flames at Unit 4 were reported to be the result of a pump fire, which caused a small explosion that damaged the roof of Unit 4 (See TEPCO’s press release on the most recent fire at www.tepco.co.jp...) . Efforts at Units 4-6 are focused on supplying cooling water to the spent fuel storage pools. Temperatures in these pools began to rise in the days after the quake. At the time of the quake, only Unit 4’s core had been fully offloaded to the spent fuel pool for maintenance; roughly 1/3 of the cores of Units 5 and 6 had been offloaded. This explains in part why the temperature in Unit 4’s pool has risen faster than at the other reactors: it has a higher inventory, both in fuel volume and in heat load. Outlook: The fuel within these pools needs to remain covered with cooling water in order to prevent the low levels of decay heat present from causing it to melt, and also in order to provide shielding. Boiling of the water results in reduction of the water level in the pools, so if/when the pools get hot enough for boiling to begin, water needs to be added to replace what boils off. The staff of Unit 4 plan to begin pumping water to the spent fuel pool from ground level as soon as radiation levels from Unit 3 are low enough for them to return. This pumping operation should be relatively easier than injection of cooling water into the reactor vessels at Units 1-3 because the pools are at atmospheric pressure. Sources: TEPCO, World Nuclear News UPDATE (11:48 AM EST): A report by the Federation of Electric Power Companies of Japan indicates that radiation levels as a result of the Unit 4 fire were higher than those reported previously. Radiation levels early this morning at the outside of Unit 3 measured at 400 millisieverts/hr. At the present time however, radiation levels at the boundary of the facility are 1530 microsieverts/hour. We will continue to update as further reliable information is available.
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Nakon eksplozija i kvarova što su ih prošli tjedan u japanskim nuklearkama izazvali snažan potres i cunami, brojni su mediji upozorili kako postoji mogućnost da se ponovi nuklearna katastrofa černobilskog tipa Međutim, stručnjaci za nuklearnu energiju ističu da su uglavnom sve te vijesti, pa i one uglednih medijskih kuća poput CNN-a, obilovale dezinformacijama i pogreškama. Josef Oehmen znanstvenik s MIT-ja u Bostonu kaže da je situacija u Japanu ozbiljna, no ipak pod kontrolom te ističe kako je važno da to shvate i obični ljudi koji nemaju dovoljno znanja o nuklearkama. U uvodu svoje podulje analize Oehmen kaže da je objašnjenje zbivanja u japanskim nuklearkama teško sažeto predstaviti, međutim, ističe da će svatko tko ga uspije pročitati do kraja vjerojatno o nuklearnim elektranama znati više od svih novinara svijeta zajedno i shvatiti zašto u japanskom scenariju nije bilo niti će biti 'značajnijeg radioaktivnog zagađenja' opasnog po čovječanstvo. 'Pod značajnijim zagađenjem podrazumijevam razine zračenja više od onih što bismo ih primili tijekom dugog putovanja zrakoplovom ili ispijanjem čaše piva proizvedenog u dijelovima svijeta s visokim prirodnim zračenjem', kaže dr. Oehmen. Struktura nuklearne centrale Fukushima Nuklearka Fukushima spada u tzv. reaktore na vodenu paru koji su slični ekspres loncima. Nuklearno gorivo u njima zagrijava vodu, ona vrije i stvara paru, a para pokreće turbine koje proizvode struju. Para se potom hladi i ponovno pretvara u vodu koja se vraća u sustav. Ovaj ekspres lonac radi na temperaturi od oko 250 stupnjeva Celzijevih. Kao gorivo se koristi uranov oksid koji se topi na vrlo visokoj temperaturi od oko 3.000º C. Izrađuje se u obliku malenih valjaka veličine lego-kocke. Valjci se smještaju u duge cijevi cirkonijeve slitine s talištem na 2.200º C i nazivaju se šipkama goriva. Više takvih šipki u zajedničkom omotaču naziva se jezgrom. Omotač od cirkonijeve slitine smatra se prvim spremnikom koji radioaktivno gorivo odvaja od ostatka svijeta. Jezgra se polaže u tzv. tlačnu posudu koja je drugi spremnik. Tlačna posuda vrlo je čvrsto građena i može podnijeti zagrijavanje jezgre na više stotina stupnjeva Celzijevih. Njome je pokriven scenarij u kojem se hlađenje jezgre u nekom trenutku nakon kvara može ponovno uspostaviti. Cijeli hardver nuklearnog reaktora – tlačna posuda, sve cijevi, pumpe i spremnici vode za hlađenje potom se osiguravaju trećim spremnikom. Njegove stjenke od najkvalitetnijeg čelika vrlo su debele i hermetički zatvorene. Treći je spremnik dizajniran, izgrađen i testiran s jednom, jedinom svrhom – da na neograničeno vrijeme zadrži i podnese potpuno topljenje jezgre. Kako bi se to osiguralo, unutar trećeg spremnika drugi spremnik - tlačna posuda, polaže se u bazen od debelih stjenki betona ispunjen grafitom. Ovaj dio zove se hvatač jezgre. Ako se jezgra otopi i tlačna posuda eksplodira, on će uhvatiti otopljenu jezgru i sve ostale materijale. Izgrađen je tako da omogućuje širenje i time hlađenje nuklearnog goriva. Treći spremnik smješta se u zgradu reaktora koja je vanjski omotač i reaktor štiti od vremenskih uvjeta i nepogoda. U eksploziji u Japanu oštećena je ta zgrada. Osnove nuklearne reakcije Uranovo gorivo toplinu stvara procesom koji se zove nuklearna fisija. Veliki atomi urana raspadaju se na manje atome. U tom procesu dio mase pretvara se u energiju, a također nastaju slobodni neutroni (neutron je jedan od sastavnih dijelova jezgre atoma). Kada slobodni neutroni udare u druge atome urana, oni se također raspadaju, stvaraju nove neutrone i energiju, a cijeli se proces naziva nuklearnom lančanom reakcijom. Kada bi se šipke goriva smjestilo jedne pored drugih, one bi se brzo pregrijale, a nakon nekih 45 minuta i otopile. Treba istaknuti da gorivo u reaktoru nikada ne može eksplodirati poput nuklearne bombe. Izgradnja nuklearne bombe zapravo je vrlo zahtjevan posao. Havariju u Černobilu izazvali su prevelik tlak, eksplozija vodika i popuštanje svih spremnika nakon čega je rastopljena jezgra iscurila u okoliš – slučaj koji možemo nazvati 'prljavom bombom'. Nadalje ćemo pokušati objasniti zašto se to nije dogodilo i zašto se neće dogoditi u Japanu. Da bi mogli kontrolirati nuklearnu lančanu reakciju, stručnjaci u nuklearkama koriste tzv. kontrolne šipke. Ove šipke apsorbiraju neutrone i trenutno zaustavljaju reakciju. Reaktori su tako izgrađeni da se za normalnog rada vade sve kontrolne šipke. Voda hladi reaktor, pretvara se u paru i stvara struju istom brzinom kojom jezgra stvara toplinu. Na taj način ostaje dovoljno slobodnog manevarskog prostora oko radne temperature od 250º C. No problem je u tome što jezgra još neko vrijeme nastavlja stvarati toplinu čak i nakon što se ubace kontrolne šipke. Lančana reakcija urana se zaustavlja, međutim, u njoj je stvoren niz radioaktivnih elemenata poput izotopa cezija i joda koji će se s vremenom raspasti na manje atome i izgubiti radioaktivnost. Budući da je njihovo stvaranje u raspadu urana prestalo, količina im se s vremenom smanjuje te se jezgra kroz nekoliko dana ohladi. Ova toplina trenutačno stvara probleme stručnjacima. Dakle, prvu vrstu radioaktivnog materijala sačinjavaju uranove šipke i radioaktivni elementi nastali raspadom urana koji se također nalaze u šipkama. Izvan šipki stvara se i druga vrsta radioaktivnog materijala, međutim njegovo je vrijeme poluraspada vrlo kratko pa će se vrlo brzo - u nekoliko sekundi - raspasti i pretvoriti u neradioaktivne materijale. Ako ti materijali dospiju u okoliš, možemo reći da je iscurio radioaktivni materijal, međutim on je potpuno bezopasan. Naime, dok kažete 'nuklearni reaktor', oni će već biti bezopasni, jer će se raspasti na elemente koji ne zrače. Ti radioaktivni elementi su radioaktivni izotop dušika N-16 te plemeniti plinovi poput ksenona. Kako oni nastaju? Uran tijekom raspada oslobađa neutrone. Većina tih neutrona udarat će u druge atome urana i održavati lančanu reakciju. Međutim, neki će izaći iz šipki te udariti u molekule vode ili pak zraka u njoj. Elementi koji uhvate te neutrone postat će radioaktivni. No kroz nekoliko sekundi otpustit će ih i ponovno postati bezopasni. Ova druga vrsta zračenja vrlo je važna u priči o curenju radioaktivnosti u okoliš koju ćemo kasnije predstaviti. Što se dogodilo u Fukushimi? Uvećajte klikom Potres koji je pogodio Japan bio je čak sedam puta snažniji od najgoreg potresa koji je bio predviđen tijekom gradnje nuklearne centrale. Naime, centrala je građena da podnese 8,2 stupnja, a kako Richterova skala funkcionira logaritamski, potres od 8,9 stupnjeva zapravo je sedam puta snažniji, a ne 0,7. U svakom slučaju japanski su inženjeri obavili dobar posao! Kada se tlo zatreslo, nuklearni su se reaktori automatski isključili. Već nekoliko sekundi od početka potresa u jezgru su ubačene kontrolne šipke i lančana je reakcija stala. Nakon toga rashladni je sustav trebao odvesti preostalu toplinu koje ima oko tri posto od ukupne topline što se stvara u normalnim radnim uvjetima. Međutim, potres je uništio izvanjsko napajanje reaktora, a budući da je centrala isključena, više nije stvarala električnu energiju. To je jedna od najtežih nezgoda koje se mogu dogoditi u nuklearki pa se tom problemu u izgradnji posvećuje velika pozornost i osiguravaju pomoćni sigurnosni sustavi. Prvih sat vremena stvari su se odvijale kako treba. Jedno od brojnih postrojenja benzinskih generatora struje uključilo se i opskrbljivalo sustav potrebnom energijom. No potom je stigao cunami, mnogo veći od onoga koji su konstruktori nuklearke predvidjeli prilikom gradnje, i isključio generatore. Prilikom gradnje elektrane slijedi se vrlo rigorozan sustav osiguranja u kojem se sve prvo projektira tako da može podnijeti najgoru katastrofu koju možete zamisliti, a potom se sustav konstruira tako da može podnijeti još niz dodatnih kvarova za koje ste mislili da se nikako ne mogu dogoditi. Takav scenarij bio je prodor cunamija koji je isključio sve pomoćne sustave napajanja. Posljednja linija obrane je smještanje svega u treći spremnik koji će sve probleme, uključujući i rastopljenu jezgru, zadržati unutar reaktora (pogledajte ilustraciju desno). Kada su benzinski generatori prestali raditi operateri su reaktor prebacili na baterijsko napajanje koje je zamišljeno kao zamjenski sustav za zamjenske sustave. One su konstruirane tako da osam sati daju struju potrebnu za hlađenje jezgre. U tih osam sati trebalo je centralu uključiti u novi izvor struje. Mrežu je uništio potres, a benzinske generatore cunami. Trebalo je stoga dopremiti mobilne generatore. No tu su stvari krenule krivim putem. Dopremljeni generatori nisu se mogli povezati s centralom jer utikači nisu odgovarali! Stoga se jezgra nastavila zagrijavati čim su se baterije potrošile. U tom trenutku operateri su počeli slijediti hitne procedure za slučaj gubitka rashladnog sustava. To je još jedna od standardnih procedura osiguranja. Potpuni prekid napajanja nikada se nije smio dogoditi, no ipak se dogodio. Iako nam se sve ovo može činiti šokantnim, zapravo je dio uobičajenog treninga kroz koji prolaze svi operateri. U tom trenutku počelo se govoriti o topljenju jezgre. Naime, ako se ne osigura hlađenje, jezgra će se nakon više sati ili dana konačno rastopiti te će ključnu ulogu imati treći spremnik. U ovoj fazi trebalo je nekako osigurati da prvi spremnici - cijevi od cirkonijeve slitine i drugi spremnik – tlačna posuda, ostanu što dulje funkcionalni sve dok inženjeri ne osiguraju rad rashladnog sustava. Budući da je hlađenje jezgre izuzetno važno, svi reaktori imaju više rashladnih sustava, a svaki od njih više verzija. U ovom trenutku (kada je pisan tekst) nije jasno koji je sustav otkazao. Zamislite, dakle, ekspres lonac na laganoj vatri. Operateri su uključili sve sustave hlađenja koji su im na raspolaganju kako bi izvukli što više topline, međutim, tlak ipak raste. Sada je prioritet održavanje integriteta prvog spremnika (održavanje temperature ispod 2.200º C), kao i drugog – tlačne posude. Kako bi ovaj drugi ostao u funkciji s vremena na vrijeme potrebno je ispustiti tlak. U tu svrhu reaktor je opremljen sa 11 ventila. Operateri su ih povremeno otvarali, a temperatura je bila oko 550º Celzijevih. Tada su krenule vijesti o curenju radijacije. Ranije smo objasnili zašto se ispuštanje ventila teorijski može nazvati puštanjem zračenja u okoliš, ali i zašto nije opasno. Radioaktivni dušik i plemeniti plinovi ne predstavljaju prijetnju ljudskom zdravlju. U nekom trenutku tijekom ispuštanja pritiska došlo je do eksplozije. Ona se dogodila izvan trećeg spremnika – posljednje linije obrane i zgrade reaktora. Podsjećamo da svrha zgrade nije zaustavljanje zračenja. Nije potpuno jasno što se dogodilo, međutim, operateri najvjerojatnije nisu htjeli ispustiti tlak u okoliš, već u prostor između trećeg spremnika i zgrade reaktora kako bi osigurali dovoljno vremena za slabljenje radioaktivnosti pare. No problem je u tome da se na visokim temperaturama, koje je u međuvremenu dosegla jezgra, molekule vode mogu raspasti na kisik i vodik, a ta je mješavina vrlo eksplozivna. Smjesa je eksplodirala i oštetila zgradu reaktora. Ovakva vrsta eksplozije dogodila se i u Černobilu, ali ne u zgradi, već unutar trećeg spremnika koji je bio loše dizajniran i slabo održavan. Opasnosti od takve eksplozije u Fukushimi ni u jednom trenutku nije bilo. Problem stvaranja mješavine kisika i vodika jedan je od najvažnijih o kojima se vodi računa pri konstrukciji centrale, pa su reaktori tako građeni da se ona nikako ne može dogoditi u njima. Eksplozija se dogodila izvan spremnika i ni u jednom ih trenutku nije ugrozila. Tlak je sada bio pod kontrolom jer je para ispuštena. Međutim, kada nastavite grijati lonac i ispuštati paru, razina vode postupno pada. Jezgra je prekrivena s nekoliko metara vode kako bi prošlo dovoljno vremena - više sati ili dana - prije nego što ostane na suhom. Kada šipke ostanu na suhom izloženi dijelovi kroz 45 minuta dostižu temperaturu od 2.200º C. Tada propada prvi sloj zaštite - cirkonijeve cijevi. Japanski stručnjaci nisu uspjeli osigurati hlađenje prije nego što se oštetio dio cijevi. U tom trenutku dio radioaktivnih tvari nastalih raspadom urana - cezija i joda - počeo se miješati s parom. No najveći problem – uran - i dalje je bio pod kontrolom jer se on topi tek na 3.000º C. Japanski su stručnjaci potvrdili da su u pari koja je ispuštena u atmosferu zabilježene male količine cezija i joda. Centrala u Fukushimi Tragovi ovih elemenata operaterima su bili znak da cijevi popuštaju te da treba preći na plan B. Plan A podrazumijevao je osposobljavanje redovnih sustava hlađenja jezgre. Zašto nije uspio još uvijek nije jasno. Moguće je da je cunami zagadio čistu vodu neophodnu za regularne sustave hlađenja. Ta je voda vrlo čista poput destilirane. Uran raspadom ne može jako aktivirati čistu vodu, međutim, nečistoće ili soli u vodi brže apsorbiraju neutrone i postaju radioaktivne. To za jezgru nije bitno - njoj je svejedno čime ćete je hladiti. Međutim, scenarij predstavlja problem za operatere i mehaničare koji trebaju rukovati, vodom koja je postala radioaktivna. Dakle, nakon što je propao plan A, pokrenut je plan B. Najvjerojatnije se dogodilo sljedeće: da spriječe topljenje jezgre operateri su je počeli hladiti morskom vodom. Nije sigurno jesu li njome zalijevali tlačnu posudu ili treći spremnik. No to i nije bitno. Najvažnije je da se nuklearno gorivo počelo hladiti. Budući da je nuklearna reakcija odavno prestala, u reaktoru se stvaralo još vrlo malo topline pa je prestao rasti tlak. Morskoj vodi dodana je borna kiselina koja se smatra tekućom kontrolnom šipkom jer upija neutrone i ubrzava hlađenje jezgre. Dakle, jezgra je u Fukushimi došla blizu točke topljenja te je izbjegnut najgori scenarij. Naime, da se za hlađenje nije mogla upotrijebiti morska voda, operateri bi morali otvarati ventile kako bi spriječili rast tlaka. Treći spremnik bi se tada potpuno zatvorio kako bi se jezgra u njemu mogla rastopiti, a da radioaktivni materijal ne iscuri. Nakon topljenja trebalo bi pričekati da se u reaktoru raspadnu izotopi te da se radioaktivne čestice u spremniku slegnu. Sustav hlađenja u nekom bi trenutku proradio, a jezgra bi se rashladila na potrebnu temperaturu. Potom bi spremnik trebalo očistiti iznutra. Konačno bi započeo prljav posao uklanjanja rastopljene jezgre i transport u centrale za procesuiranje. Ovisno o veličini štete centrala bi se popravila ili srušila. Kakva je situacija sada? Ukratko, centrala je sigurna, a tako će i ostati. Situacija je teška za kompaniju, ali nije opasna za ljude. Nešto zračenja iscurilo je tijekom ispuštanja ventila, međutim, ono je bezopasno. U more je isteklo tek vrlo malo radioaktivnog joda i cezija. U rashladnu vodu će isteći još malo izotopa, no oni će se moći pročistiti. Jezgru reaktora trebat će rastaviti i prevesti u postrojenja za obradu kao što se to redovno radi prilikom promjene goriva. Centralu će trebati temeljito provjeriti. Za to će biti potrebno četiri do pet godina. Sustavi osiguranja nakon ove katastrofe bit će unaprijeđeni tako da najmanje mogu podnijeti potres magnitude 9,0 i cunami. Najveći problem bit će nestašice struje. - Sviđa vam se članak? Preporučite ga prijateljima putem ovih servisa: Pošaljite mailom