They need all that sea water (or lake water) for the cooling system, which is why they are near large bodies of water. When I was in high school (1973-77) they were building the "Seabrook Station" which is a Nuke Plant in Seabrook, NH, just 3 miles down the road from where I grew up.

Lots of kids dropped out of high school to go work construction there as they were paying about $10/hr. for unskilled labor, pouring cement, tieing up re-bar, etc. At that time I think I was making about $1.85/hr. as a bus boy in a local steak house.

Anyway, there were always large protest marches against the site, as it was built right on the south NH shore, with huge (10' diameter) cooling tunnels which ran underground for about 3 miles out to the sea floor, intake and outflow tunnels. Everyone was worried about what might happen if they ever had a "Meltdown" and all that sea water became contaminated, flowing right out into the prime fishing and lobster grounds. The fish loved the warmer water coming out of the tunnel, and that soon became a prime fishing spot!

The cold seawater goes into the plant and through a heat exchanger, radiator type system, then right back into the ocean.

All the protests caused many construction shutdowns, the plant ended up being finished years late of schedule and billions over budget. So much so that the NH Power company had to SELL the electricity to all the other New England states just to try to recover the losses!

One thing I've been wondering about ever since way back in high school, why don't they just build the reactor UNDER GROUND?!

I mean, if there's going to be a Meltdown and/or explosion, with a radio active cloud, wouldn't it be better if the entire reactor vessel was already 20' underground? How hard is it to dig a deep hole first, build it, then cover it up?

More about Seabrook Station:

http://www.hampton.lib.nh.us/hampton/history/randall/chap18/randall18_4.htm