| 摘要 |
923,343. Nuclear fuel elements. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. Aug. 9, 1960 [Aug. 17, 1959], No. 28021/59. Class 39 (4). A fast reactor fuel element has a cylindrical protective sheath with an outer diameter of 0.1 to 0.4 inch and of metal of high creep strength, which sheath has a wall thickness of at least 1/10 of the outer diameter and capable of withstanding an internal pressure of at least 10,000 p.s.i. at a temperature of 600‹ C., and nuclear fuel enclosed within the sheath having a cross-sectional shape to provide intimate contact of the fuel with the sheath over at least a major portion of the periphery of such shape, there being left unoccupied by the fuel between 10 and 30% of the interior of the sheath to serve as expansion spaces for the fuel and also space for accommodation of fission products on irradiation of the fuel. The nuclear fuel is uranium or plutonium metal without any alloying additions of non-fissile material and not of oxide or carbide form. The 10 to 30% unoccupied volume may be obtained by providing the fuel with an axial cavity, enclosing a number of fuel discs within the sheath and spacing them apart by interposed pins, or by a combination as shown in Fig. 3 of an axial cavity 9 and discs 7 spaced apart by pins 7a. Alternatively, the discs may be recessed on opposite faces to provide voids in which case interposed pins are not required, the fuel may have longitudinally extending radial slots of narrow width around its surface, or a porous fuel may be used. In Fig. 7, a fuel element capsule 28 is shown comprising two tubular fuel members 23 enclosed within a sheath 24 formed from two halves welded together at line 25. The fuel has axial voids 26 and the two members 23 are spaced apart by pins 23a to provide an intermediate void 27. Fig. 8 shows an assembly of such capsules 28 in an open-ended flat can 29. A specimen fuel element is shown in its entirety in Fig. 10, four pellets 1 with axial voids 3 being enclosed within a cylindrical sheath 2 closed by cavitied plugs 37, 38 of the same material as the sheath. The plugs have rounded ends and the sheath is swaged over these ends for the relief during operation of stresses imposed on joins effected by spot welding between the plugs and the sheath. Helium or argon gas fills the unoccupied space within the element. The sheaths and end plugs may be of Ni-Cr, Ni-Cr-Co or Ni-Cr-Fe type alloys. These alloys are suitable for use in liquid sodium at 400‹ to 600‹ C. when used in conjunction with a refractory interlayer of niobium, vanadium, molybdenum or tantalum provided as a coating on the inside of the sheath, the outside of the fuel, or both. The sheath may alternatively be of molybdenum, no interlayer then being required. |
