no
No. There is no possibility whatsoever of a nuclear power plant having a nuclear explosion. It is not physically, or even theoretically, possible for the core to be brought into a super-prompt critical geometry and held there long enough to consume enough fuel to "go nuclear".
nuclear plant explosion
The nuclear plant explosion of 1986
hibaku jumoku
First and foremost, it is impossible for a nuclear power plant to explode. i.e. to go nuclear, because it is impossible for it to stay in prompt critical geometry long enough to consume the fuel for a runaway reaction to occur. Period. Not possible. Even if a terrorist organization infiltrated the facility and blew it up, that would be a chemical explosion, not a nuclear explosion. Yes, there would be release of radioactive materials to the environment, but it would not be a nuclear detonation as from a nuclear bomb. Get your heads straight around that. Its just not possible. The geometry is all wrong.
lots
No, but there would be more release of radioactivity because the reactor itself would probably be melted in the explosion.
Yes, the explosion happened in Japan. It was very tragic.
radiological not toxicological
A powerful explosion which leads to the complete destruction of the plant would be considered a major explosion. Since fertilizer is highly explosive, it is possible that any minor explosion will lead to a much greater explosion.
no it was caused by the tectonic plates the nuclear plant disaster happened because of the earthquake
A nuclear power plant uses a slow, controlled nuclear chain reaction to heat water and generate electricity. A nuclear bomb uses a very rapid uncontrolled nuclear chain reaction in order to generate a massive explosion.