What was the incentive to adequately estimate the fallout vs. underestimate it?
There's no real incentive to estimate accurately because it's in Algeria, which the French did not care much for.
Wasn’t it more in the south pacific?
There was a need to underestimate radiation doses so as to undercut our opposition.
When we made the fuss those in power in France took the time to send a military team to bomb a Greenpeace ship in Auckland, killing someone. They followed up with economic sanctions when we caught their amateur operatives, and later gave the soldiers medals for the murder they committed.
Who needs enemies with friends like these?