I thought not many people knew I am Nuclear Engineer by background, but evidently they are enough to have a few of them asking what is my opinion about the situation in Japan. And knowing how complex such plants are, and to avoid showing disrespect for a wonderful nation hit by such a cruel catastrophe by treating these matters superficially, I will refrain from any analysis of a technical nature.
I will instead state four simple and – I believe – objective facts, all of which I learned in my university years.
Fact 1 – Nuclear Power Stations are small.
MUCH smaller than other power stations. A 1000 MW nuclear station is maybe 250k square meters; a photovoltaic plant of similar output would be around 400 square KILOMETERS ! This is good news (little land usage, securing is less expensive) but is also inherently more dangerous: should a catastrophe occur, it is likely to hit a nevralgic point.
UPDATE 22/3: especially when you build six reactors within walking distance from each other
Fact 2 – Nuclear plants contain all their fuel.
If a gas powered station blows up or is kidnapped by terrorists, all you have to do (in theory) is walk 5 kilometers upstream and close a valve for the plant to become inert (this is an approximation, as most power stations do have local fuel storage, but you get my point).
This is impossible in a Nuclear station, as the fuel rods are IN the plant at all times, enough to keep it going for a long time.
UPDATE 22/3: on my flight back yesterday someone was (rather loudly) saying: “Thanks God, the explosions in Fukushima were chemical, not nuclear like in Chernobyl”. Not so: all explosions in a nuclear accident are chemical, typically when release hydrogen oxydizes (Fukushima) or when moderating graphite burns (Chernobyl). These explosions happen in an environment contaminated by radioactivity and therefore carry it out, but no core ever becomes a bomb, although it reaches a temperature so high it melts destroying containment systems, (which in the case of Chernobyl were not so performing to start with) therefore polluting the surroundings with radioactivity.
Fact 3 – Removing fuel makes things worse.
In a gas, coal or oil furnace no fuel = no fire. Simple as that. In a Nuclear Power Station, pulling out the rods from the moderating medium makes them burn faster and uncontrollably. The nuclear fission reaction in fact is so furious that the only way to make it manageable is to have fuel immersed in a moderating medium that slows it down; in some reactors this moderating medium is pressurized water, in some is liquid sodium or graphite. Move the bars, leak some moderating fluid and the reactor immediately heats up.
UPDATE 15/3: While press reports speak of reactors being “automatically turned off” as soon as the quake hit, this is not technically what happens. The procedure, called SCRAM, quickly inserts more than a hundred neutron absorbing rods in the fissile core, stopping the chain reaction. The fuel rods are still active, however; if this were a car, it would be like putting the shift in neutral and applying the brake: the engine still runs, but the car does not move.
Fact 4 – Those catastrophes you cannot prepare for, you must avoid.
My university professor of Nuclear Plant Design used to say that, given all the above three facts, you must minimize the chances of a catastrophic event that you cannot prepare for (like a magnitude 9 earthquake followed by a 10 meter tsunami) by carefully selecting the location which, ideally, must have:
- plenty of water
- stable soil
- nobody (or as little people as possible) living in a 30 kilometers radius
At the end of the day, nobody would place a hydro power station in the desert, right ?