Eeveryone is crab, because they evolved to crabs due to radiation.

 Hire worker crabs and make them work at reactor, hire defender crabs and make them defend the plant from mutants! But remember to fire crabs that are turning green, otherwise you will get a lot of green crabs (they are radioactive)...

Your main goal is NOT to survive as long as possible, BUT to get as much money as possible! If you have 200$ and mutants are breaking your reactor, it might be better to let them do it instead of throwing costly defenders at them.