Uranium is non-renewable in current methods of nuclear power generation, and there is only enough in the proven crust resources for a few hundred years. This is a serious problem, but it can be overcome by several methods.
Thorium is more plentiful than U235, and it can be used in a reactor. Modern ideas for thorium reactors are associated with Carlo Rubbia. Thorium breeds U233 from thorium, and U233 is fissile.
One can alternatively use thermonuclear weapons explosions to generate power. The fission component of these bombs are plutonium, which can be bred from regular Uranium using neutrons, which are produced during the fusion process. So thermonuclear power can make plutonium for triggers, and can add neutrons to thorium to make U233, which is also fissile. The fusion fuel itself is essentially infinite deuterium, and the neutron breeder can produce new fissile elements in sufficient amounts to make the whole thing self sustaning.
This approach to nuclear power is politically untenable nowadays, because of the risk of proliferation and theft associated to H-bombs. It is also an untried method, and will require deep underground cavities which are made hugely radioactive scattered throughout the world. Nevertheless, this is a complete solution to the problem of renewable energy. It is discussed in these questions: How much of the energy from 1 megaton H Bomb explosion could we capture to do useful work? , Why was PACER abandoned? . It is an engineeringwise very practical way to achieve fusion power.