The reason for having many reactors is because you can produce more electrical energy from them. Also Japan use BWR type reactors(Boiling Water Reactor) which are not as efficent as a more commonly used PWR reactor(Pressurized Water Reactor).
No, Hawaii is currently not in danger of radiation from the incidents involving the nuclear reactors in Japan.
Before the Fukushima Daiichi Disaster, there were 54 operational nuclear reactors in Japan. Three of those melted down, and one had problems that rendered it inoperable. The government has decided the other two reactors at Fukushima Daiichi cannot be restarted. Also, as other reactors have been shut down for maintenance or refueling, they have not been restarted, with the result that now, in early December 2011, only eight Japanese reactors remain in operation.
The tsunami destroyed many buildings and damaged nuclear reactors
There are 59 nuclear reactors in France.
Well, as nuclear reactors are nuclear reactors, nuclear reactors are not used inside nuclear reactors.
There are over 400 nuclear reactors around the world.
As of 2010, India has 20 Nuclear Reactors.
the cause of the melt down of the reactors in japan is the water that is needed to cool down the reactors
Most nuclear reactors are thermal-neutron reactors. A few fast breeder reactors have been built, but not many.
Though Fukushima has lost 4 of its Nuclear Reactors, There are many more Nuclear Reactos running in Japan, Secondly Japan is mostly using Coal and Gas to compesate for fukushima.
Sweden currently has 3 active nuclear power plants with 10 reactors.
Radioisotopes for many uses (e.g. medical, industrial, scientific) are produced in nuclear reactors.