For a 500 MWe plant, the construction labor would be about 340,000 man-hours, of this roughly 136,000-170,000 man-hours would be boilermaker activity.
Some of the hours are made up by fixing machines. 
mnli hypothesis: Some of the hours are made up by fixing machines.  premise: For a 500 MWe plant, the construction labor would be about 340,000 man-hours, of this roughly 136,000-170,000 man-hours would be boilermaker activity.