> Maybe "the largest + 200%" is a better place to start? Of course, it costs more money. Consider two possibilities. One: design the reactor so that a magnitu

> Maybe "the largest + 200%" is a better place to start? Of course, it costs more money. Consider two possibilities. One: design the reactor so that a magnitude-9 quake leaves it completely undamaged. Let's say that makes it cost $4B instead of $2B. Two: design the reactor so that a magnitude-8.2 quake leaves it completely undamaged and a magnitude-9 quake (which might affect it, let's say, once per 200 years on average) makes it fail in a way that takes 100 lives and requires it to be completely rebuilt (to the same spec, let's say) at a cost of $2B. Cost of option 1: $4B now. Nothing more. Cost of option 2: $2B now. $2B and 100 lives in another 200 years. Suppose your discount parameter is 0.5% per year (much, much lower than just about any real person or institution uses). Then $2B + 100 lives in 200 years = $740M + 37 lives now. Can you save 37 lives for $260M? Why yes, you can. Far more than 37 lives, in fact. If you do anything reasonable with $260M you may well save more than 37 lives just by (say) making everyone a little better off. (Wealth correlates with health.) Therefore, option 2 is probably better. Turning from hypothetical examples to the real world: $2B/$4B is probably an underestimate (in which case, the advantage of option 2 over option 1 is greater) and 100 lives is probably an overestimate (in which case, again the advantage of option 2 is greater). On the other hand, the earthquake happened improbably early in the life of the plant. It is not an error to do things that work out well in almost all cases but badly when you get unlucky, when the alternative is something that works out (relatively) badly most of the time but well when you get unlucky.