18
Probably not unless they somehow scored a direct hit into the reactor itself. And even then, the fuel rods are typically under several meters of water while in use, which would probably absorb a lot of the blast.
Depending on how the reactor was designed, there is a chance that the damage could somehow lead to a runaway fission reaction a la Chernobyl. But imo, the more likely worst case scenario of a direct hit (or even near miss) to the reactor is probably that the foundation gets cracked and radioactive water starts leaking into the soil, which would obviously be pretty bad if a significant amount of that can find its way into a nearby aquifer.
I doubt the controls for launching nukes are at Dimona tbh. It's main function seems to be research and the production of nuclear warheads (also maybe power generation, but I couldn't find anything saying that it's being used as a power plant).
In terms of groundwater though, the facility does seem to be sitting right on top of the southern tip of the Mountain Aquifer. The silver lining is that the groundwater seems to flow into the area rather than out of it, so the contamination would likely be at least somewhat contained to the southern end of Israel, which is largely desert and thus doesn't have many people living in it.