France, on the other hand, used "Francs". Conveniently, the exchange rate was 1:1. I'd be surprised if they went and changed everything to Euro's now, but I haven't heard anything firsthand from French nuclear engineers.

In the nuclear field, like in any highly skilled engineering field, the costs will come first from the salary of your employees. In fact, it will be cheaper in Europe, because in Europe, highly skilled engineers tend to work for less money because they have 6 weeks holidays (which you can take), 3 month sick days, very good health insurance and a 40h week. When you start to build stuff, the BOM is the same in the US or in Europe.

This is from my experience in the oil & gas and pharmaceutical industries (my field as process & chemical engineer).