I did google "Cassini Kerry" and this is what was to be found:

"Sen. John Kerry (D-MA) has also come out for postponement of Cassini for Congressional investigation."

This doesn't seem particularly bright of him, but not a condemnation of nukes or an anti-nuke stanch exactly. He wanted to know if what Michio Kaku was saying was truth.

I've heard Kaku speak on this subject and he is persuasive and sincere if a bit nuts.

BTW, there was other stuff by the anti-nuke folks trying to make Kerry sound in support of a ban on nukes in space, but no actual info from Kerry on the subject of a ban of anykind.