Never before in the history of the world have we had both a nuclear disaster AND the ability for every Tom, Dick, and Harry to offer their opinions on the event.  Now you can add the Tin Hat Ranch to the list.  I’ve been asked repeatedly for months about the dangers we face from Fukushima.  To be very honest there is so much misinformation surrounding the accident it is very hard to make heads or tails of what is really going on.  The amount of bogus news about the Fukushima disaster rivals that of UFO’s and Bigfoot.  So after being asked for the umpteenth time I decided to take a crack at it.

Everyone knows the disaster occurred on the 11^th of March 2011 following an unfathomable tsunami.  In a nutshell here is what happened to the reactor complex. 

All nuclear reactors are built to survive what is called a “design basis accident”.  Before any work begins on any reactor teams of regulators, engineers, and scientists agree on the threats that might face the facility, be it natural or manmade.  Once all of the threats are identified they then decide how the facility should be designed to withstand a certain level of threat.  Some threats are so unlikely that they are discarded from the design.  For example, on the security side of things an identified threat might be invasion from a foreign army with heavy weapons.  Is it possible?  Sure, but unlikely.  A more realistic threat might be an organized band of terrorists with small arms with intent to steal special nuclear materials.  Protecting a plant from a foreign army with an onsite staff would be nearly impossible and too costly, but protecting against a terrorist attack is more realistic and attainable.  Security measures are designed around the terrorist threat.  The same goes for natural disasters.  A 7.0 earthquake and a 20 foot Tsunami are likely to happen every 100 years, whereas an 8.9 earthquake with a 46 foot Tsunami might be a 1 in 1000 year event.  Building a plant to withstand such an unlikely natural event would be too costly, but a 100 year event might encompass the lifespan of the reactor.  Engineers at Fukushima placed their bets on protecting against the more common event.   Unfortunately Fukushima Daiichi experienced the latter.  A 46 foot Tsunami rushed over the 33 foot seawall setting of the chain of events we are now discussing.

A nuclear power plant uses heat from a fission reaction to convert water into steam.  This steam is then used to turn a steam turbine which in turn spins a generator creating electricity.  Fission creates heat  and this water that is used to create steam also serves an important function, it cools the fuel in the reactor.  Maintaining enough steam to generate electricity and cool the reactor is a careful balance which is maintained in hundreds of reactors across the world every day.

When the ground started shaking at Fukushima the reactors immediately SCRAM’ed, just like they were designed to do.   When a reactor is SCRAM’ed control rods are inserted into the reactor to absorb neutrons to stop the nuclear fission.  Even though fission is stopped, the nuclear fuel still decays, creating heat for a long period of time.  Even with fission stopped water is normally circulated around the fuel to remove this heat, a process that must be maintained for 10 or more years.  For safety, a nuclear reactor has to have a number of methods to keep this process going indefinitely.  In the case of Fukushima these methods were as follows:

• Offsite Power- All nuclear reactors are fed power from other offsite power plants.  This power is conducted via high tension wires.  When the earthquake occurred the transmission lines were severed and this method failed immediately.
• Diesel Generators-  As a back up to the off-site power diesel generators are kept onsite to keep the water circulating.  For the first 50 minutes after the earthquake the generators took over the duties of cooling the reactor.  When the Tsunami arrived and overwhelmed the seawall the generators were flooded and stopped functioning.
• Batteries- As a last resort there was enough battery power to operate the emergency pumps for about 8 hours.  As soon as the Tsunami struck the batteries began powering the emergency water pumps.  At this point a race began to restore offsite power, a race which was lost.

When the batteries failed and the water stopped circulating the decay heat began building up.  Even with the reaction stopped the fuel in the reactor is highly radioactive.  A byproduct of radioactivity is heat, and in the case of a freshly shut down nuclear reactor, a lot of it.  This is when all hell broke loose.  One important thing to note is Nuclear fuel is housed in tubes made of Zircaloy.  When temperatures inside the reactor began to exceed normal limits the cladding around the fuel began to melt.  Hydrogen gas is created during this process.  This gas is what built up and resulted in explosions in buildings housing reactors 1-4.

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