Never a nuclear reactor is used in airplanes. However, it is used in submarines.
Never ever
The #4 reactor is the reactor at the Chernobyl Nuclear Power Plant (Pripyat, Ukraine) that exploded on April 26, 1986. It is still the worst nuclear accident to ever take place anywhere.
The first ever reactor was in 1942, but not power producing. The first electric power producing reactor was in the UK in 1956
Three Mile Island
No, but the reactor at Three Mile Island in Pennsylvania had a near melt-down. Nuclear plants don't explore. They have meltdowns.
The main one is disbursal of its radioactive contents into the environment. The fallout from this has the potential to be much worse than the fallout from nuclear weapons, as the amount of material inside the reactor that can be disbursed is far larger than the fallout that can be generated by any nuclear weapon ever deployed.
one of the largest earthquakes ever recorded followed by a tsunami that disabled the backup diesel generators.
Because of the size of the sun, there is not enough chemicals on earth to compare to what the sun holds, besides no one has ever gone to the sun to do research on it.
All current nuclear reactors are fission reactors, tritium has no function in a fission reactor, in standard water moderated reactors deuterium also has no function, in heavy water moderated reactors deuterium is the moderator. If we are ever able to make a fusion reactor, deuterium/tritium mix will be used as fuel.
Once the nuclear power plant has been built and put into service, nuclear power is very reliable, it is only dependent on how reliable the plant's equipment is, things like pumps, instruments, turbines, and so on. The reactor itself hardly ever fails.
The RBMK reactors at Chernobyl were probably the most unsafe reactors ever designed and built. They should never have been built.
The worst damaged reactor would require complete demolition and rebuilding to repair it and the levels of radiological contamination in the area are unsafe for such work and of a nature as to make cleanup impractical. The best course of action at this time is encapsulation of the reactor to prevent further contamination of the surrounding area (much like at Chernobyl).