One commonly overlooked source of uranium is the world's oceans in which there are approximately 4 billion tons.  In 1998 Japanese research revealed that the extraction of uranium from the oceans would cost approximately $100/kg. The ocean source of uranium is sufficient enough to supply a population of 2000 light water reactors for 5000 years. [Richard L Garmin, Georges Charpak, Megawatts and Mega tons, A Turning Point in The Nuclear Age.? Toronto: Random House of Canada Limited, 2001)