IIRC Aeroplane Monthly published an in-depth article on the B-36 a few months back, which included coverage of the NB-36H. I don't think the engines were actually powered by the reactor, rather it was powered up in flight to assess the practicalities... but I may well be wrong!
The crew stations were rather well shielded as I recall...
Strewth, an accident would have been more than slightly embarrasing!