[UPSC CSE 1989] Nuclear Physics (Q215, 60M)

Given a rough sketch showing the variation of binding energy per nucleon with mass number of nuclei and hence explain how an enormous amount of energy is emitted in uranium fission. How it is that two blocks containing uranium of mass number 235 may remain quiet when separated but may explode when brought together into a single block? Explain the function of a moderator in a nuclear reactor.