There’s no mistaking the fact that the events in Japan over the past few days will be remembered for a long time, in a matter of minutes entire cities vanished under a wave of black sludge and houses.
However the shock from the massive Earthquake and resulting Tsunami has been overshadowed by the events at the Fukushima nuclear facility. While reactors 4,5 & 6 were already shut down for inspection, reactors 1,2 &3 immediately shut down (known as SCRAM) when this happened power generation at the plant ceases. However because of the nature of nuclear power, even when shut down the reactor creates heat meaning the cooling system needs to be maintained. However the earthquake had knocked out the power grid so the reactors switched to emergency generators.
While I’m not going to go into the specifics of what happened since other sites do a better job. I am going to explain two very simple things that I think everyone should know.
Unfortunately the generators were in the path of the Tsunami, so when it hit, they were quickly flooded and went offline. The plant then switched to the emergency batteries but they have a life of around 8 hours, while this was happening new batteries and generators were being sent over but the area used to connect them was now underwater.
One thing that has been uttered countless times on the news in particular is that it is “like Chernobyl” except it isn’t. The design of the Chernobyl reactor is a text book example of how NOT to do it. In fact the best comparison I can find is this:
“The Chernobyl reactor was a copy of the Chicago reactor¹ whose main safety system was a man holding an Axe next to a rope with a control rod on” The moderator in the reactor was Graphite, a material that isn’t used in Japanese or even US plants because of the inherent safety flaws (See Windscale fire) Another problem was from Shutdown to the backup generators providing enough power to run the cooling system (The radioactive material still produces a large amount of heat that needs removing) there was a dangerous gap of upto 70-80 seconds (enough to cause serious problems)
Infact the whole reason the explosion happened was because they were testing a new way of avoiding dangerous build-ups. At around 1:30AM the reactor went into SCRAM (for reasons still not clear) What happened next is known as a positive feedback loop. Water pumped into the reactor turned to steam resulting in more power, meaning more water was pumped in, which in turn, converted into steam. Control rods automatically began to insert into the core in an attempt to control this. However one of the rods had a serious defect and the reactions in the core sped up.
Eventually the Core simply tore itself apart under the strain. The Graphite moderators ignited and the steam and pressure build up blew the core up.
The result is well known. Thousands died and fallout was recorded all over western Europe.
However the Fukishima plant is an entirely different design, there is no Graphite moderator. In fact the BBC said it best when they compared it to a kettle, but instead of a metal filament in the bottom it’s a rod of nuclear material. The other main difference is a pretty obvious one. The Russians didn’t build a containment structure around their reactor. Meaning once the explosion happened the radioactive material blew straight out into the atmosphere. Now the Fukishima plant has a pretty solid containment structure around it.
Now ignoring the Daily Mail Armageddon coverage The media have been highly irresponsible in the coverage of this. Experts have been saying “If X happens then Y happens then it’s bad” but the BBC especially have been omitting the “if” from their live updates. Infact this reminds me of the West Wing episode “Duck and Cover” in particular this quote
“I don’t like hearing the term ‘meltdown’ on cable news. Twelve things have not gone wrong yet. By my count we’re barely at six or seven.”
Meltdown for many conjures up images of Chernobyl, or a reactor melting its way to China. What has happened in the reactors in Japan is known as a “Partial fuel melt” meaning the fuel rods have partially melted (meaning the plant will very likely be offline permanently. So while there has been a meltdown of sorts, it’s not going to result in mass death.
In a light water reactor, water is used as both a coolant for the fuel core and as the moderator. If the moderator is removed the process can’t continue. An LWR design limits the damage caused by a meltdown, because if all of the coolant is boiled away, the fission reaction will not keep going, because the coolant is also the moderator. What would happen is the rods would continue to generate heat but it wouldn’t end up with “china syndrome”
The explosions were the result of the venting Hydrogen gas, normally this is ignited as it’s released to lessen the environmental impact, however in this case it built up in the space between the “outer structure” and the containment building, and like the hindenburg, it ignited. Any radiation reports come from this gas, while the phrase “exposed to a months worth of radiation” is scary this is still around 1/10th of the exposure you get in a dental X-ray.
The reactors are now being flooded with Sea water and Boron to stem the reactions. Hopefully this will be sufficient to keep a minor disaster at bay.
(0003 Mar15) During the time I was writing this there has been a 3rd explosion. Details are just coming in so I’ll update it as it develops
EPCO reported that they confirmed 8217 micro Sievert at the front gate of the Daiichi Fukushima Powerplant.
This is 3 times of what a person normally exposed to in a year in one hour.
Radiation levels have fallen at the plant following the explosion at reactor #2. There is an issue with a spent fuel pool in reactor #4