Looks like it won't be happening now, so I might as well come clean.  Revel's plan was to coax the Immortal into letting him discharge a massive amount of electricity point-blank into his brain, disrupting his higher mental functions or at least giving him a whopping case of amnesia.  It wouldn't damage the brain, but short-circuit it enough to silence the Immortal's mental anguish.

...Oh, and does setting off a grenade this close to a reactor have negative effects on said reactor?  Like exploding?