In my past coverage of engineering and construction firm Shaw Group (NYSE:SHAW), I've tended to focus on new reactor orders from utilities like Progress Energy (NYSE:PGN) and Southern (NYSE:SO) as the driver of Shaw's nuclear business. That's only part of the story, however.

The nuclear construction boom peaked about 25 years ago, yet U.S. nuclear generation continues to rise. In 1990, nuclear plants generated around 577 billion kilowatt-hours. That figure jumped 40% by 2008. We weren't exactly cranking out new reactors in that period, either. In fact, the number of reactors peaked in 1990 at 112, and is now down to 104.

So where did all that extra juice come from? The key is in the capacity factor of the nuclear fleet, which has risen from 66% to 92% in that time period. Reduced outage time is a major component of this change in utilization. Refueling outages can't be eliminated altogether, so we're beginning to push up against technical limits to higher utilization of the nuclear fleet.

Fortunately, there's another avenue to increased generation, short of building a new plant or adding new reactors to an existing site, as NRG Energy (NYSE:NRG) is attempting to do in Texas. In the field of nuclear generation, there's something known as a power uprate. This generally involves burning more fuel, hotter, and pushing higher flows of steam through the turbine generator. Uprates can add 5% to 20% to a reactor's capacity.

More than 5,700 megawatts in uprates have been approved by regulators since 1977. That has added the equivalent of five or six additional reactors to U.S. capacity. Shaw Group says that these uprates "are able to produce electricity at a lower than market rate of building any other type of electricity." There are a lot more to come.

How much is a lot? Shaw Group said on this week's conference call that it's "chasing" 60 or 70 such projects, worth $250 million to $500 million each. Given that the company already has fleetwide maintenance contracts with the likes of Exelon (NYSE:EXC) and Entergy (NYSE:ETR), Shaw Group has a real shot at winning a significant portion (say, $5 billion to $8 billion) of these bids. That's yet another reason to remain enthusiastic about Shaw Group's nuclear prospects.