The estimate for the two reactors involves 3500 on-site construction workers [1] with a completion date of 2016 or 2017 [2]. This means 1750 construction workers employed for 4-5 years at each reactor. The average annual wage for a construction laborer is 34,040 [3]. So we're looking at labor costs of about 0.3 billion / reactor. Even if the US workers get paid double the average, and the Chinese close to nothing, labor costs only explain about 10% of the price difference.
Regarding components, anything that's not built on the spot (including pipe) can and will be shipped internationally from the cheapest supplier (particularly if it's expensive). Again, we're looking at price differentials of around 10% rather than 2500%.
Presumably nuclear reactor construction requires more skill than building houses or whatever. And this is for people with absolutely zero prior experience, so not counting experienced people, not counting management, not counting various overhead (payroll taxes, HR, etc., which is often significant).
I would not be surprised if components had a similar story to the workers: nuclear means extremely specialized, and that means the normal rules for commodity resources may not apply. For such a political project, it also would not surprise me if certain things were required to be purchased from US suppliers even if they aren't the lowest bidders.
I don't know exactly where all of the difference comes from, but the situation seems more complicated than simply hiring standard construction workers at average salary and buying commodity components from international suppliers.
Also, you probably want to double the salary figure to get an idea of the total compensation cost to the company doing the hiring. A $70k worker can easily have a compensation package that costs $140k to the company doing the hiring, depending on the exact benefits and what sort of discounts the employer can wring from insurance companies, if most employees have families, if there's relocation assistance, etc. Since there aren't a lot of qualified people to work in the nuclear industry I'd expect the packages to be pretty decent.
The wage of construction workers is $34,000, but what is the cost of employing a construction worker? I'm surprised if it does not double the total cost per worker. That said, your point is still taken that it does not explain the full price difference.
Regarding components, anything that's not built on the spot (including pipe) can and will be shipped internationally from the cheapest supplier (particularly if it's expensive). Again, we're looking at price differentials of around 10% rather than 2500%.
[1]http://www.whitehouse.gov/the-press-office/obama-administrat...
[2]http://www.huffingtonpost.com/2012/02/09/federal-regulators-...
[3]http://www.bls.gov/iag/tgs/iag23.htm#earnings