I studied the incident at Chernobyl at length. I reviewed many documents and interviews. I even went as far as studied the whole scheme of this particular reactor type (RBMK-100). It blew out due to negligence of personnel, not due to some technical malfunction.
The operators have deliberately turned off all safety mechanisms and run it in a mode it had not been designed for. This accident can be put in a textbook named 'A complete idiot's guide to blowing a nuclear reactor. Seven practical steps' (There were SEVEN fatal mistakes that operators made on 26.04.1986 in order to blow it).
The reactor resisted till the last moment but they blew it nevertheless.

Well, we don't need Al-Quaeda if them at power plants will do this now and then.