The letter's here, with the operative sentence "As climate and energy scientists concerned with global climate change, we are writing to urge you to advocate the development and deployment of safer nuclear energy systems." I would change the ending of that sentence to safer nuclear energy systems if fiscally prudent.
I personally couldn't support the letter as written just as I couldn't support the reverse, a letter urging unqualified opposition to nuclear energy. The reverse may be somewhat worse in the real world, because I think much of the opposition to nuclear energy isn't empirically based but tiered off of Cold War era ideological battles. Still, I don't see a whole lot of empiricism going on here. Why not urge advocacy and deployment of carbon capture and sequestration? CCS certainly has economic issues but adding 40% to the cost of coal might still keep it cheaper than nuclear, and CCS of biomass power is a carbon negative solution, one of the very few available. I'm not saying we must do CCS - maybe it doesn't pencil out - but then the same flexibility should apply to nuclear.
Just adding those three magic words may not be enough. We might need to finish the sentence as safer nuclear energy systems if fiscally prudent and if nuclear proliferation issues are addressed. Nuclear power won't be a large solution to the climate change problem unless it spreads to many countries where it doesn't currently exist, maybe virtually all medium-sized and larger countries. Al Gore used to be a national security guy before he went green, and I think proliferation is one of the reasons for his nuclear skepticism.
Finally the sentence might need to read if fiscally prudent and if nuclear proliferation and terrorism issues are addressed. Terrorists causing catastrophic radioactive releases or getting their scheming hands on some radioactive material from these thousands of new nuclear plants around the world could be problematic. I'd concede this one isn't as important as the other two, but it's there.
The letter writers are right that accidents and nuclear waste, the issues most opponents emphasize, are way overblown, but they take a big step from that point to saying nuclear is therefore a good idea.
I'll stay a nuclear waffler for now.