Why we should say YES to
nuclear power

4. Because nuclear power is the safest energy option

Nuclear safety and serious accidents

Safety is the most common fear about nuclear power, yet the nuclear power industry has an excellent operational safety record.

A study of 4,290 energy-related accidents by the European Commission’s ExternE research project14 examined the number of deaths per terawatt hour of energy for each of various technologies. It found:

• oil kills 36 workers a terawatt hour

• coal kills 25

• gas kills 4

• hydro, wind, solar and, yes, nuclear, all kill less than 0.2

(These figures ignore deaths from pollution and global warming.)

Even so, there have been notable nuclear accidents in the past, such as Three Mile Island in 1979 in the US. It started with a valve getting stuck, and was escalated by staff misreading instruments and taking inappropriate actions. It ended with the cooling water draining from the reactor, causing the nuclear fuel to partially melt (a “meltdown”). However, the concrete and reinforced steel containment dome remained secure, so the damage was held within the reactor building.

Still, the core was destroyed and the accident cost the private utility that owned the plant billions of dollars. And although no one was killed, Three Mile Island seriously undermined public confidence in nuclear power.

A much worse incident occurred in 1986 at Chernobyl in the Ukraine. During a poorly planned experiment with the safety systems deliberately disabled, a massive power surge caused the reactor water to vaporise (a steam explosion). This started a fire in the reactor’s graphite moderator, and, because this cheap Soviet design lacked a containment dome, fission products became airborne. A radioactive cloud drifted over the western Soviet Union and across Europe. More than 50 emergency workers were killed and up to 4,000 extra premature cancer deaths may eventually result.15

In a nuclear-powered future, could such incidents happen again?

Passive safety systems – banking on the laws of physics

There are two key ways to avoid such problems. The first is to build reactors that can’t result in massive, self-reinforcing power surges. The Chernobyl reactor ran out of control because it used graphite as a moderator; when the coolant water flow was accidentally stymied, the nuclear reaction ran out of control. In any non-Russian reactor, if the coolant cannot shed heat, the water expands and moderation is reduced. The upshot is that the reactor shuts down. The laws of physics allow for no other eventuality. Comparing the flawed Chernobyl design to today’s reactors is like saying modern aviation is too dangerous because the Hindenburg airship exploded in 1937.

The second way is to design passive (or “inherent”) safety systems. These rely on natural, universal processes, as opposed to active, engineered systems or operator actions (such as hitting a button to activate a safety measure).

A good example of a passive safety system is the core cooling tank in the existing Westinghouse AP-1000 design­, an enhanced, third-generation nuclear power plant. In an emergency, valves held shut by electric power open, and water is channelled into the reactor core by gravity, rather than by electric pumps.

These improvements make a big difference. Risk assessment puts the probability of core damage at one in 20,000 reactor years for a reactor designed in the 1970s.16 However, for the AP-1000, it is one in 24 million.17 So, even if there were 10,000 AP-1000 reactors in the world (instead of the present 440 older reactors) there would be an incident of the severity of Three Mile Island only once every 2,400 years. A Chernobyl-like accident simply could not occur, at least without breaking the laws of physics.

Inherent safety features of fast reactors and liquid fluoride thorium reactors

Moving towards fast reactors and liquid fluoride thorium reactors over the next few decades will also enhance inherent safety. Consider two examples:

In the liquid fluoride thorium reactor design, the coolant is a molten fluoride salt, with uranium and thorium dissolved in it (in other words, a liquid fuel). If the reactor starts to overheat, the molten salt expands. The uranium particles in it move away from each other, just as dots on the surface of a balloon spread apart as it inflates. This heat-expansion feedback, in turn, causes the nuclear reaction to slow down, and allows the reactor to cool. It is a self-regulating control.

Integral fast reactors are fuelled by a metal alloy (of uranium, plutonium and other heavier elements), not a ceramic oxide as in today’s reactors. Because metals are superb heat conductors, there is not much heat stored in the fuel pins that would need to be dissipated if the coolant stops flowing and the reactor shuts down. Integral fast reactors are designed so the core expands if the reactor overheats and then the fuel rods move apart. As with the liquid fluoride thorium reactor, this causes the reaction to slow or shut down. Then natural convection currents in the sodium coolant take heat away from the core without needing active pumps.18

These stunning safety features are not just theory – they have been proven in experiments at US Government research laboratories. This makes these two “next generation” nuclear power designs more than 100 times safer than the already incredibly safe AP-1000, with an incident like Three Mile Island likely only once every 430 million reactor years. That’s safe.

Radiation exposure from nuclear power plants

The health effects of radiation exposure have been studied intensely over many decades. The consensus expert view is that while high levels of ionising radiation can be medically dangerous, the effects of low-level exposure are very difficult to detect. There is also consensus that radiation levels up to five (or even more) times the average background rate are harmless and may even be beneficial.19 (This idea is called “radiation hormesis”.) Even so, this book must consider the additional radiation risk nuclear power might create.

The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) says the additional radiation exposure of living in the vicinity of nuclear power plants is no more than 1/10,000 of the normal background radiation most people live with day-to-day.20 Natural radiation is due to everything from cosmic rays, to radon gas emissions from the ground, to eating a single banana. (A banana gives you more radiation than a year’s worth of living near a nuclear power plant.)

So it works out that about 0.007 per cent of your total yearly dosage of radiation would come from nuclear electricity generation. By comparison, living near a coal-fired power station would give you 10 to 300 times more radiation exposure from the fly ash,21 and even that is trivial and not the reason coal burning is damaging to health.

The fearsome reactor meltdown or terrorist act: what is the worst case scenario?

There is no limit to what the imagination can come up with regarding industrial accidents.

Imagine if a fire broke out in a natural gas refinery on the outskirts of a city. High winds then carried the hot embers aloft, setting ablaze nearby suburbs and the surrounding forest. What if this triggered explosions in adjacent chemical plants? This chain of events might ultimately lead to a city-wide conflagration that killed hundreds of thousands of people. Such a scenario is exceedingly unlikely, but not impossible. In the end, it is the probability that matters.

There is, for instance, some risk that a terrorist could hijack an aircraft, hit a reactor with pinpoint accuracy, breach containment, and cause the release of nuclear material. However, it is an incredibly low risk that all of these things will occur together. For instance, it has been estimated that only about one in every 1,000 direct aircraft strikes might crack a steel-reinforced concrete containment dome.22