I don't believe there are any sources. The symptoms of the sick crew (not the tank carrying one, the one in the OP) as reported seem consistent with radiation poisoning. If the pirates opened a hold with nuclear material, they probably weren't prepared (and it's unlikely the freight had the usual radiation warning placards if this is supposed to be a secret shipment) and got a good dose of REMs.

I'm sure there are frogmen in subs right now with geiger counters waiting for the go signal.