It's pretty compact, the whole reactor is about the size of a large house IIRC. Putting the whole core in a container and shipping it off is pointless, though- it's designed to operate for many decades and uses a continuous refueling process. They're also designed to be able to get really high utilization of fuel and not produce much waste. This design is very different from current commercial plant designs.

Operating costs are also not the problem for nuclear plants, they are dirt cheap to run relative to their energy production. It's the upfront capital cost of building a large plant that makes them uneconomical currently, which is why smaller-scale designs like this one are appealing.

Edit: http://www.world-nuclear.org/information-library/economic-as... is informative regarding the economics.

The commercial versions of these are bigger than that. Economies of scale are still very much at play in nuclear due to the unique regulatory and supply chain issues, as well as how much not-highly-enriched fuel you need to go critical. But some folks working on nuclear farms (fields of small nukes with one security force) are dreaming of interesting new options.

Regarding economics, there are lots of reactors in the USA that have their capital cost completely paid off but they're still expensive because of high Operation and Maintenance costs. A lot of this is expensive retrofits and added security costs post 9/11. More of it is that cheap natural gas in deregulated markets has brought electricity prices way down and therefore electricity sales revenue way down. This is why some nuclear plants in the US are shutting down early before their lifetime is up. It's a great tragedy because these plants are massive carbon-free baseload electricity sources. Nukes in the US make 60%+ of the carbon-free energy of the country.

Size wise I think even the commercial units they are planning have the core and associated support machinery at about that size, not including things like turbines etc that would be needed for a proper plant. It's been a while since I've seen any technical presentations about TerraPower though so maybe that's out of date.

The cost of retrofits is a good point, especially given that our nuclear fleet is getting pretty old. I am also worried about the glut of cheap natural gas and its tendency to stifle other technologies. It's almost unbeatable right now price wise, but I'm a bit concerned about what will happen when that changes. Renewables are great, but base-load power is still a problem.