Never a nuclear reactor is used in airplanes. However, it is used in submarines.
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
No, a nuclear reactor would not explode solely due to the absence of people. Reactor safety systems are designed to shut down automatically in case of any abnormal conditions, such as the reactor overheating or losing cooling. The presence or absence of people would not impact the reactor's physical safety mechanisms.
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.
The only nuclear reactor meltdown in the US occurred at Three Mile Island in Pennsylvania in 1979. It was a partial meltdown caused by a combination of equipment failure and human error.
one of the largest earthquakes ever recorded followed by a tsunami that disabled the backup diesel generators.
Yes, the Three Mile Island nuclear power plant in Pennsylvania experienced a partial core meltdown in 1979, which resulted in the most serious accident in the history of the US commercial nuclear power generating industry. However, the reactor did not explode like a nuclear bomb.
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).
At this point, there are no known nuclear powered jet engines.Anyone, of course, with better information, is welcome to refine this answer.Both prototype nuclear powered jet engines ever built are stored in the EBR-1 site parking lot in Idaho and can be seen by anyone when they tour the EBR-1 reactor historical monument and museum.
The first one ever was in 1942