The correct answer is: D. It is ready to produce controlled energy.
A nuclear reactor is said to have become “critical” when the rate of nuclear fission in the reactor is self-sustaining. This means that the number of neutrons produced by fission is equal to the number of neutrons absorbed by the fuel. When a reactor is critical, it is producing a steady stream of heat, which can be used to generate electricity.
Option A is incorrect because a nuclear reactor does not stop due to malfunctioning when it becomes critical. In fact, the opposite is true: a nuclear reactor becomes critical when it is operating correctly.
Option B is incorrect because a nuclear reactor does not start emitting dangerous radioactive radiations when it becomes critical. In fact, the amount of radiation produced by a nuclear reactor is actually quite low when it is operating correctly.
Option C is incorrect because a nuclear reactor is not shut down to avoid explosion when it becomes critical. In fact, a nuclear reactor is only shut down if there is a problem with the reactor, such as a loss of coolant.
I hope this helps! Let me know if you have any other questions.