WAEC - Physics (2008 - No. 44)
Nuclear fission is preffered to nuclear fusion in the generation of energy because
very high temperature are required for fusion
the raw materials for fusion are easily obtained
energy obtained from fusion is relatively small
the by-products of fusion is very dangerous
Explication
Elevated temperatures are necessary to initiate fusion but not fission reactions because, In a fission reaction, the positively charged nucleus and neutrally charged neutrons clash to start the fission process. The procedure can be carried out at lower temperatures since it has a low activation barrier.
NOTE: fusion creates less radioactive material than fission.