1.  Explain nuclear fission.        2.  Explain chain reaction.                                                  3.  Fill in the missing words:             The most common fuel used in a nuclear power station is           .                                    is controlled by the use of control rods.             The                        from nuclear power stations remain active for thousands of years.              A            takes heat away from the nuclear reactor to a boiler where            is made.        4. Complete the following table about the disposal of different types of nuclear waste: Low level Intermediate level High level