| 摘要 |
1,219,264. Fuel elements. UNITED KING- DOM ATOMIC ENERGY AUTHORITY. 27 March, 1968 [12 April, 1967], No. 16875/67. Heading G6C. A fuel pin for a fuel element for a fast breeder nuclear reactor comprises an external metallic sheath containing ceramic nuclear fuel material, characterized in that the sheath has a multiplicity of longitudinally spaced regions of reduced diameter along its length, each such region having a uniform reduction of diameter over a length of the sheath at least equal to the overall unreduced diameter of the sheath, the ceramic nuclear fuel material at least in the regions of reduced diameter of the sheath being of vibrocompacted ceramic nuclear fuel powder, whereby that fuel material in register with the regions of reduced diameter of the sheath has a decreased heat rating with a less tendency to melt on occurrence of a temperature excursion of the reactor, thus providing barriers against reorientation of the fuel within the pin. Such a fuel pin may consist of a stainless steel sheath 2 containing both fissile fuel 3 and fertile fuel 4, the former consisting of UO 2 /PuO 2 powder vibrocompacted to 80% theoretical density and the latter providing upper and lower axial breeder regions and consisting of solid pellets 5 and annular pellets 6, respectively. The fissile fuel 3 is separated from the pellets 5 by a solid stainless steel spacer 7 and from the pellets 6 by an annular stainless steel spacer 8 containing a fine filter 9 of stainless steel wool. A spacer 10 similar to the spacer 8 but containing a coarser filter 11 separates the breeder pellets 6 from a chamber 12 for the collection of gaseous fission products. The end regions of the sheath 2 are provided with inner sleeves 13, 14 and are swaged down and sealed with end welds 15, 16. Prior to the loading of the fuel, three spaced diameter reductions 19 are formed in the sheath 2 by cold rotary butt swaging, cold planetary swaging, or the use of high energy shock waves and employing within the sheath a mandrel of suitable profile. In an alternative construction, a stack of fissile fuel pellets is loaded into the sheath over a portion only of the fuelled length of the pin, the sheath is subjected to local swaging just above the top of the stack of pellets to effect a reduction of diameter, fissile fuel in powder form is loaded into the sheath in the region of diameter reduction and vibrocompacted, another stack of fuel pellets is loaded above the compacted powder, and the operations of diameter reduction, powder loading, powder compaction, and pellet loading are repeated until the fuelled length of the pin is fully occupied. |
