raw snow also is not allowed
why would you put that in a nuclear reactor ?
ice compressed from single snowball, lava used for reactor heating, water bukets allowed.
Well that's somewhat of a point there, although I'd rather just let it run without cooling than put lava in it.
But maybe water cells don't work because they are a bit too easy to make in large amounts. Buckets are harder since you gotta fill all of them and snowballs, well can you even automate that?
Yeah I guess water cells don't work on purpose. If they would you could just make water cell farms with BC and pump these into the reactor = unlimited cooling way more powerful than normal means. (let aside the constant tin consumtion)
ICe and Waterbuckets were choosen because they are not trivially avaible material. (first one because you need to compress snowballs, second one because it isn't stackable)