The half-life of fuel for these reactors is very long - over 100,000 years. So for all practical biological effects they are basically stable. If it exploded before it was activated (far into space), it would be about the same danger to people and the environment as the rest of the exploding metal the rocket was made of.
Yeah, but this subthread is about protest reasons :) The reactor in the article (and the half-life of it's fuel) can't be the reason people are protesting.
