This is the second blog response to a blog entry made by The King of the country Lagom. The previous entry dealt with his claims that opinions are sacred and how one must not speak up against them. This entry will deal with the purely factual errors of his claims about nuclear power.
The King of Lagom claims that an incident that took place in 2006 at the Forsmark nuclear power plant could have escalated into a Chernobyl-type accident. Well… first he says that, and then he says it could have become something entirely different. If this sounds confusing it is because the King of Lagom probably doesn’t quite know what he’s talking about but rather builds this statement on misconceptions about what actually happened at Chernobyl and Forsmark respectively. So let’s examine the incidents and compare.
The 1986 Chernobyl accident
April 26, 1986. The night shift at reactor 4 at the V.I Lenin Nuclear power plant, 20 km north west of the town of Chernobyl, Ukraine, has been ordered to do a test. Due to operator error, they accidentally poison the RBMK-type reactor which makes it almost grind to a halt. They don’t know why the reactor is giving so little power though because they were mostly coal plant workers, inexperienced with nuclear power, and oblivious to things such as nuclear poisoning. The shift boss, determined to finish the test, gives orders to proceed, telling the operators to perform actions that go against several operating rules of the reactor. This puts the reactor in an unstable state.
When the test is finished and they shut down the reactor, a fatal flaw in the reactor’s control system causes the reactivity to spiral out of control, making it output between ten to onehundred times normal thermal effect. The water in the reactor flash boils and the enormous steam pressure blows the building apart. A few seconds later a chemical explosion, when water that has been split into hydrogen and oxygen burns, rocks the complex again. The reactor is on fire for ten days, resulting in a large plume of radioactive fallout.
There are several factors that allowed this accident to happen.
First it was operated by poorly educated personnel, in a political system where safety came second. In the Soviet Union, you did not rise to attractive jobs like this one by being good at your craft but by kissing up to the communist party. Also you did not stay at jobs like this by speaking up against safety issues, because such things made the party look bad. For instance this particular test was supposed to have been run years ago when the plant was commissioned. But since it failed back then, it had to be done again, this time in secret from the Soviet nuclear regulatory authorities.
This shouldn’t have been a problem. But the second reason the accident could take place was the deliberate violations of the operating rules of the reactor. The test was to have taken place when the reactor was outputting at least 700 MW; they started when it was at 200 MW. They were not allowed to withdraw more than a certain number of control rods; they withdrew almost all of them. They were not allowed to increase water flow in the reactor past a certain amount when operating at low power; they did. They were not allowed to disengage the safety systems that would have shut down the reactor when they did any of the aforementioned; but they did indeed disable them.
All of this made reactor come into an unstable state that let its most critical design flaw come into play: the positive void coefficient. The void coefficient is a quality in a nuclear reactor that tells us what happens when it gets too hot. When coolant boils in a reactor that has a positive void coefficient, the nuclear reaction increases. This makes the reactor hotter, which makes more water boil. This speeds up the reaction more, making it even hotter… and so forth. And not only was the void coefficient in the RBMK-reactors of the Chernobyl plant positive, it was also dangerously high.
Finally, because the reactor had no real core vessel, nor any concrete containment, the force of the explosion wrecked the building completely. A fire started in the hundreds of tons of graphite that was in the reactor. Also the building itself that was supposed to have been made from fireproof material, was not, and the debris caught fire as well.
This is what is known as a criticality accident, when the nuclear reaction goes out of control. In this case it produced so much heat that the entire reactor blew up from all the thermal energy. This accident was not a nuclear meltdown.
The 2006 Forsmark incident
July 27, 2006. At the switch-yard for Forsmark-1, an electrical arc causes a short circuit which leads to the unit being disconnected from the power grid. This is serious as the plant relies on power to keep all pumps going.
If a nuclear reactor does not have working pumps, eventually the cooling water in the reactor will boil away. If that starts to happen you must engage the emergency core cooling, reserves of water kept for this very purpose. If this too fails and the reactor boils dry, the heat can be such that the reactor core becomes damaged, popularly called a meltdown. This can happen even when the nuclear reaction has been stopped because decay heat continues to be produced a few hours after a reactor is shut down as very short-lived nuclear waste falls apart. This is what happened at Three Mile Island in 1979.
So when a nuclear plant becomes disconnected from the power grid, the reactor is shut down and on-site diesel generators start to provide power for the pumps to deal with the decay heat, and this was what happened at Forsmark 1. However in this case, two out of the four diesel generators did not start, disabling two safety trains out off four. But the two remaining diesel generators were more than enough to drive the pumps. Hence the reactor was cooled and emergency core cooling was not necessary. The reactor shutdown proceded normally.
No, there are no similarities between these two incidents. The Chernobyl disaster was the case of a criticality accident that caused an extremely violent explosion that completely wrecked the reactor core; the building it operated in; burned for days. The Forsmark incident was the case of slight degradation of safety features while the reactor and its cooling operated normally. The cooling system was operational the whole time; the emergency cooling did not need to be engaged; the reactor core was not damaged; the reactor tank was in no way threatened; the over one meter thick reactor contaiment remained perfectly safe. And fire? Naw… there is no graphite in Forsmark-1. Water handles that job instead.
So when the King of Lagom says that the Forsmark incident could have become another Chernobyl, he is wrong. There is no way that Forsmark-1 or any of the other Swedish nuclear reactor could undergo the process that led to the explosion in Ukraine in 1986. And this is not just because we employ people that know what they are doing; care about safety first; follow procedure; don’t do things behind the back of the nuclear regulatory authorities. No, the most important reason why a Chernobyl-type criticality accident cannot happen in Sweden is the reactors themselves. Because unlike the RBMK-reactors of the Soviet Union, our boiler- and pressurized water reactors do not have a positive void coefficient. We did it the opposite way, so that when water starts boiling in the reactor, the nuclear reaction slows down because of inescapable laws of physics. It’s nature’s own choke collar on nuclear reactions.
The RBMK-type of reactor was employed only in the Soviet Union. The international community is working hard to get the twelve RBMK’s that are still in operation closed. Even though I’m a nuclear friend I’m not an idiot, and as such I am very glad that one of the remaining RBMK’s. Ignalina-2, will be shut down in 2009, meaning that Lithuania no longer operates them. Now we just need to get Russia to shut down theirs and we’ll finally be rid of this blight.
When discussing nuclear safety, anyone that uses Chernobyl as an example of what could go wrong in nuclear reactors is ignoring reality. The BWR/PWR reactors of the world hold about as much in common with the RBMK-design of the Soviet Union as does slavery to common work; as does forced child soldiers to commissioned adults. There just is no comparing them as they operate differently down to subatomic level.
The Forsmark incident was not, and could not have become, another Chernobyl. This is not an opinion, it is physical reality.
ADDENDUM: As I posted a link to this entry in his blog, and called him on his Ad hominem attacks, he first approved the entry, then he cencored it and claimed that I was violating his right to have “free opinions”, i.e. he doesn’t want anyone telling him he’s wrong.2 Comments
(kd) gör en rimlig bedömning av kärnkraftens framtidPublished by Michael on January 30, 2009
Göran Hägglund (kd) skriver på DN Debatt:
Detta är nog första gången som vi ser att en svensk politiker verkligen sätter fingret på grundproblemet i den svenska kärnkraftsfrågan: kärnkraft kan inte ersättas med förnybart, för vi har inga garantier att förnybart kommer att räcka till.
Motståndare till kärnkraft hävdar att förnybara kraftkällor, i Sverige då i första hand vind och vattenkraft, kommer att kunna ersätta kärnkraften. Men detta är osäkra kort. Vattenkraften är fullt utbyggd och finns det någon fråga som är heligare i Sverige än kärnkraften så är det älvarna. Det är inte rimligt att anta att vi kommer att kunna bryta exploateringsförbudet av älvarna.
Vindkraft är då ett alternativ. Men vind, om än ungefär lika miljösnål per producerad kilowatt-timme som kärnkraft, har ett inneboende problem: när det inte blåser har man ingen kraft.
Bilden ovan är hämtad från vindstat.nu, och motsvarar originalet i skrivande stund. Som mest kan man idag av svensk vindkraft få 16 800 MWh per dygn (bilden går upp till 14 000 MWh). I går låg produktionen på ca 4% av max; dagarna innan det ännu lägre. Vi vet inte från dag till dag vad vindkraften kommer att producera. Vi vet inte ens från timme till timme. Detta är uttryckligen vad Göran Hägglund skriver: “vi har inga garantier att det kommer räcka till”.
En energikälla som när den själv känner för det levererar så lågt som 3% av installerad effekt är inte pålitlig, och ingeting vi kan bygga ett helt lands kraftförsörjning på.
Och detta är inte vindkraftens enda nackdel heller. Som vi har skrivit om tidigare är vindkraft en mardröm för kraftnäten därför att den är lynnig till sin natur, vilket gör styrning svårt och riskerar att kollapsa elnäten med mycket stora strömavbrott som följd. För att klara av att basera vår kraftförsörjning på vindkraft måste vi i princip slänga ut hela elnätet och bygga nytt. Och hur dyrt kommer det att bli? Med tanke de bökiga miljökrav som gäller att få bygga nya kraftledningar så är det frågan om detta ens är möjligt med mindre än att kraftbolagen nästan ges fritt spelrum att köra över lokalbefolkningen vid ledningsdragning. Om inte enklare regler och förkortad tillståndsprocess kommer till stånd kan kraftbolagen aldrig ta på sig den kostnad som det innebär att förnya elnätet.
Vi kan alla önska oss en framtid där vi inte behöver kärnkraftverk, eller klarar oss utan vattendammar som riskerar att kollapsa och dränka hela städer. Men vi måste också vara realistiska och börja räkna på saker och ting för att se om de räcker till eller inte. (kd) har nu gjort det. Och siffrorna ljuger inte: förnybart har inga garantier för att klara vår kraftförsörjning. Alltså måste vi inkludera ett alternativ som klarar av att leverera, samt lever upp till miljökraven: kärnkraft.
Sålunda välkomnar vi detta beslut av (kd). Kärntekniklagen 5§ måste ändras. Förbudet att bygga nya reaktorer i Sverige skall tas bort, för att säkra vår energiförsörjning.
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