9 things you probably don’t know about Nuclear Power

As some of the readers here will know, academically speaking I am a Nuclear Engineer, although I never practiced it, since I went into computers and later communications straight after University.

This meant that – like anybody who possesses a “weird” body of knowledge compared to the people around him/her – I have been time and again asked to explain this or this other thing about these arcane pieces of marvelous engineering.

Notice that I carefully avoid the discussion on the politics around Nuclear Power, because I find that they are usually between people who are equally uninformed and biased.

So – in light of the proposal by my good friend Stuart Bruce we should talk about this subject at some juncture – I thought of giving him some heads up with my list of

Things most people do not know about Nuclear Power

1. Nuclear fuel is VERY cheap; so cheap, in fact, that the cost of nuclear-generated energy is essentially the cost of amortization and maintenance of the plant itself.
2. Nuclear fuel consumption is very low when compared to traditional power plants; depending on the design, a 1,000 MW plant consumes less than a hundred tons of fuel per year – by comparison, generating the same amount of energy consumes 4 million tons of coal, 2.6 billion liters of oil or 1.9 billion cubic meters of gas.
3. A consequence of the above is that a traditional plant requires a constant flow of fuel to operate; turn off the tap and the plant stops in a few hours. Not so for a Nuclear Plant: stopping the supply does nothing because the core already contains all its fuel.
4. Another consequence of the above is that the Nuclear Power plant is essentially NEVER turned off: it can be put in a state where energy output is zero, but this state is the equivalent of a car engine in neutral: the car does not move, but the engine is running: touch it and you’ll burn yourself.
5. Yet another consequence of the above is that a NPP MUST have electricity. At all times, even when it’s in idle; that is why next to every NPP you find big diesels. The reason is that (#4) the core cannot be turned off but only idled, and to do so, the core must be crammed with moderator, a substance (water, molten salt, liquid sodium, graphite…) which will absorb neutrons, thereby slowing / stopping the chain reaction. No power = no moderator = no stopping of core. In reality reactors are designed with a “dead man switch” logic in mind, i.e. power failure triggers a moderator flood, but in practice there are so many things that require power (remember humans can only survive for a few minutes in the vicinity of the core) that a total power failure is tantamount to catastrophe.
6. Physically speaking, NPPs are small, orders of magnitude smaller than equivalent plants burning gas, oil or coal. This is a major design flaw of plants put in operation in the 60s and 70s (the majority), as in case of accident, the entire plant area quickly becomes unsuitable for human operation. If the same plants were designed today, probably the big backup diesels would be miles away to ensure that a disaster (such as a tsunami) would not cut power, but in those days the big worry was a terrorist attack and the ensuing need for military-grade security, much easier to achieve with a smaller plant footprint. So Fukushima’s diesels were meters away from the reactor; when the tsunami struck the reactor building weathered the hit without problems, but the diesels didn’t, power went off and BAM!
7. The catastrophic scenario of a NPP diverges, while that of a traditional power plant converges: accidents typically involve faulty valves or lines, leading to leakages and/or fluid pressure losses. Temperature rises, steam pressure builds and in the worst case, an explosion may occur. This typically self-destroys a traditional plant, while in a NPP it leads to the loss of control of the core which continues to burn albeit not in the highly ordered chain reaction: look at Chernobyl whose now ceramized corium lava is still happily burning 28 years after the accident.
8. The history of nuclear power generation is marred by the fact it was initially funded by the military who were interested in the well-being of humanity, but also <*ahem*> in the Pu239 (plutonium) by-product with which they built the most destructive (and luckily least used) weapons arsenal in the history of humankind. Were this not the case, research could arguably have explored the alternative Thorium cycle: Th232 is much more abundant, cheaper and better distributed. While its cycle is not without problems, it produces far less plutonium and actinides making it almost worthless for military purposes.
9. Unlike traditional power plants, an NPP cannot be installed just anywhere: it needs water (LOTS of water: a water-cooled reactor needs 50 to 80,000 tons of water PER HOUR), seismically stable flat land and as little population as possible living within a 30 kilometers radius from the plant. Unfortunately the water abundance and people scarcity are usually at odds with each other; that does not mean these conditions are not met anywhere, but it means there’s plenty of locations (entire countries in some cases) where a NPP does not make any sense at all.