Nuclear power is as close to magic as we’ve come when it comes to economically viable energy production, but it’s also controversial. A lot of the opposition is from the older generation who remember back to events like Chernobyl and Three Mile Island. Will the ongoing nuclear scare in Japan create a new generation of people opposed to nuclear power?

We’re witnessing the cost of a nuclear meltdown right now. Hopefully this is the worst things will get, but it’s already scary enough for me.

People don’t place bets if losing the bet carries too high a cost. And any engineering system is a bet. The output of a nuclear power plant isn’t actually Electricity + Waste as we typically think of it, the output is coarsely:

- Success with probability p
- Failure with probability (1-p)

Presumably, success has some positive value to society, Failure has some negative value, and p is very close to 1.

How do we, as a society, evaluate the output of the plant? As the expected return, Success*p + Failure*(1-p)? This is how the auto industry works, for example: they design with a tolerable expected deaths per vehicle-mile (like 0.0000000something).

The problem is expected return doesn’t work so well if failure is catastrophic. The reason is that whatever mathematical model we use estimate a value for p is inherently flawed, as all models are. Models don’t reflect the world, they are just rough approximations of it.

So the real probabilities are

- Success with probability p-epsilon
- Failure with probability (1-p+epsilon)

Where epsilon is some probability mass that represents the un-modeled failure situations – Donald Rumsfeld’s “unknown unknowns”. The problem with this term is that we don’t know how big it is. If we have catastrophic failure with probability (1-p+epsilon) and we don’t know how big epsilon is, that’s pretty scary.

The failure in Japan right now is happening somewhere in the probability mass covered by this epsilon term:

When Fukushima was built, TEPCO rated and tested reactors 1 & 2 to tremors equivalent of a 7.9 earthquake – the highest they thought was possible for the region. No need to test for an 8.9er – not factored into their risk model.

An 8.9 quake is the strongest in recorded history for Japan – 10 times worse than the 7.9 Fukushima was rated for (logarithmic scale). And it wasn’t just the quake that caused the reactor problems. Engineers spend a lot of time planning for shit to hit the fan. And when you look at catastrophic failures – the (1-p+epsilon) scenarios – it’s often a perfect storm of cascading failures that cause all of the checks and balances to fail.

In the case of this reactor, it was:

- Earthquake hits, shuts down nuclear reactor, power goes out
- Tsunami floods, takes out diesel backup generators that keep cooling system running
- Backup batteries run out because the above national infrastructure is too torn up to replace them
- Plant infrastructure (pipes, outer containers) crumble and burn, further damaging cooling system

That’s pretty complicated. And low probability.

The worst failure condition for a nuclear reactor doesn’t just kill people, it curses the earth for kilometers and decades. And that’s the scary thing: that there are unknown unknowns not factored into the risk assessments of engineering systems with potentially catastrophic results.

I think a whole new generation of people will grow up thinking that any power solution that places a nonzero – and worse, inherently unknowable – probability mass on nuclear fallout is unacceptable.

There’s an easy solution to this, of course: don’t build systems whose cost of failure is catastrophic. Will that be the policy mandate for years to come, or will we give in to the economic pressures created by scarce energy?