Nuclear Weapons used for peaceful pruposes are called Peaceful Nuclear Explosions or PNEs. In June 1996, Scientific American ran an extensive article on the subject, which you can read here. The real problem with PNEs is political. It conflicts with the stated goals of a Comprehensive Test Ban Treaty and irritates the anti-nuke/environmentalists. The engineers and scientists have worked out the the technical problems involved, so civil engineering with PNEs is feasible. Possible peaceful purposes* include:
Diverting Rivers - Chinese engineers have proposed diverting the Brahmaputra River to bring fresh water to the Gobi desert which is half of China’s landmass, but only contains 7% of its water.
Increase oil and gas production - The Plowshare program involved 27 actual detonations in Nevada, Alaska, New Mexico, Colorado and other states. Although the tests did increase production, they had problems with fallout and the fuel produced was sometimes too radioactive to use. The program lasted from 1950-1973. We’ve learned a lot in 28 years, I suspect that the efficient use of smaller tactical weapons would solve these problems.
Harbor improvement and canal building - The Plowshare program again. The former Soviets have also done the same as was mentioned earlier. In the past, they led the way with 124 PNEs.
Earth moving and excavation - During the Plowshare tests, the US created the world’s largest man-made crater at the Nevada test site (12 million tons of Earth). The former Soviets had similar projects to move large quantities of earth and rock.
Fire fighting - again the soviets to combat oil and gas fires (no details)
Geology - PNEs combined with seismic equipment allow scientists to investigate the properties of geologic formations.
Waste Storage - ironically, one of the better uses of PNEs is as a means of creating underground storage areas for toxic or nuclear waste.
Electricity generation - Chinese engineers have propsed creating underground chambers lined with steel tubes which would conduct steam to turbines on the surface during controlled blasts. US scientists looked at this idea in the 1970’s but dismissed it. It’s economically impractical.
Asteroid deflector - a popular idea - you’ve all heard about it.
Propulsion - the Orion project, et al.
[sub]* satisfying my daily alliteration requirement.[/sub]