To reduce storage control cost of abandoned plutonium resulting from repeated reprocessing of a plutonium fuel and having an increased content of plutonium 242 hardly undergoing nuclear fission and strongly capturing a neutron and americium separated as a residue in reprocessing.

A nuclear fuel rod 131 with a neutron source is constituted by loading neutron source pellets 146 on the top end and the bottom end of a conventional nuclear fuel rod 31 and loading a stainless steel wool 147 on the bottom end. The neutron source pellet is made by interposing a low melting point metal 152 such as bismuth between an americium oxide disc 151 having a thickness of about 0.1 mm and a beryllium oxide disc 153 having a thickness of about 0.1 mm and compressing them to form a laminate. The fuel rods with the the neutron source are bundled to constitute a nuclear fuel assembly with the neutron source. The low melting point metal is melted down to the stainless steel wool due to high temperature during operation. Thus, the americium oxide and the beryllium oxide are brought into direct contact with each other, and beryllium is irradiated with an α ray of americium to emit a fast neutron to cause the plutonium 242 to undergo nuclear fission in the same level that plutonium 239 does.