Jim, nothing can instantaneously roll back the risks cited in the IPCC paper. Even if we develop a new industry that can produce small modular reactors in factories, the way Boeing produces airliners, it will take many decades to produce enough units to displace fossil fuel burning worldwide.
The waste heat of all thermal/electric power plants, including nuclear, is a necessary byproduct of the thermodynamics of the conversion of thermal energy to electricity. But that heat is small in comparison to the heating of the earth from the COw-caused imbalance of solar radiation onto and infra-red radiation from the earth. The OTEC wouldn't stop that, but it would, as you say, move the heat to the relative safety of the deep ocean. It will all get there eventually, though it might take centuries; it wouldn't stop the heat additions, however.