The major advantage to the light water design concept is that it is simple and similar to existing systems in many ways. It has one major disadvantage, however, which is that the water removes neutrons which lowers the reactor's overall neutron economy. This is enough of an effect that there are not enough neutrons of the right energy to maintain the chain reaction in natural uranium fuel. This requires such designs to use enriched uranium to offset this effect, which increases the price of fuel.