As the crisis continues, some reporters were noting that Hamas' new rockets have the potential to reach Israel's super-secret nuclear facility that is in Dimona.
Firstly, a secret nuclear facility that everyone knows about is an oxymoron.
More importantly, would it be possible for a Grad or Katyusha rocket to hit the nuclear facility and cause a nuclear meltdown. The answer as far as I can tell is no.
A couple things to remember is that the natural construction of a nuclear facility involves some form of radiation shielding (usually concrete) that would prevent a direct hit from causing serious damage. As an analogy, particle accelerators are usually built deep underground or are covered by large concrete blocks to prevent radiation from harming researchers. These would also protect the source from any missile strikes.
If somehow the missile were to strike an unprotected area it would not likely matter anyways, any nuclear facility has numerous redundancies and backups in case there is a failure in one. The reason Chernobyl occurred in the first place was because some researchers deliberately shut off all the backup and safety systems in order to perform a test (I somehow doubt that sort of experiment would clear the ethics board these days).
From a strategic standpoint it does not make much sense either, the ultimate goal of striking a nuclear facility would be to either destroy it or to cause some sort of nuclear disaster. Since destroying it is pretty much out of the question with the type of weapons available to Hamas that leaves only the other.
Even if somehow an unguided missile managed to strike some crucial part of the nuclear facility that paralyzed numerous backup systems and cause a nuclear accident the accident would be occurring dangerously close to Gaza and the West Bank, which would both be undoubtedly affected.
Is Hamas crazy enough to destroy their own people along with Israel? If you assume that Hamas as an organization with both pragmatists and idealists, then yes you might find some religious extremists who believe that god will protect them from the radiation poisoning and hence be willing to risk it. But finding religious extremists who are that far out there would be tough I think and few enough to be overwhelmed by the pragmatists who know better.