For a nuclear reactor in which the fission rate is constant, which one of the following statements is correct?
A There is a critical mass of fuel in the reactor.
B For every fission event, there is, on average, one further fission event.
C A single neutron is released in every fission event.
D No neutrons escape from the reactor.
Can someone pleas explain why the answer is B and also why the other options are wrong please?