Patent ID: 7864913

Claim:
A fast reactor having a reflector control system, comprising: a reactor vessel which is filled with a liquid metal coolant; a reactor core including a fuel assembly, which is placed at a central position of the reactor vessel; and a neutron reflector including a region, which is placed at an upper side thereof, and at which a neutron absorber or a neutron transmitting material having a neutron reflection ability lower than that of the liquid metal coolant is placed and a reflection region which is placed at a lower side thereof and provided outside the reactor core so as to be moved in a vertical direction in an installed state of the fast reactor for adjusting leakage of neutrons from the reactor core so as to control a reactivity thereof, wherein said neutron reflector is moved in an upward direction in accordance with a change in reactivity caused by burn-up of a fuel, and wherein said fuel assembly includes a fuel pin bundle having fuel pins filled with a fissile fuel and a non-fissile fuel placed in a wrapper tube and having an outermost fuel pin adjacent to the neutron reflector and another fuel pin placed at a farther distance away from the neutron reflector, and wherein, prior to neutron exposure in the reactor, the ratio of the fissile fuel amount in the outermost fuel pin to total amount of the fissile fuel and the non-fissile fuel in the outermost fuel pin is made smaller than the ratio of the fissile fuel amount in the another fuel pin to the total amount of the fissile fuel and the non-fissile fuel in another fuel pin.