| 摘要 |
976, 366. Nuclear fuel elements. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. May 27, 1963 [June 13, 1962], No. 22801/62. Heading G6C. A nuclear fuel element comprises a plurality of fuel pellets, each of truncated conical form, arranged end to end in a column and enclosed in a protective sheath 2. The sheath 2 is of stainless steel and, prior to loading of the pellets, is of cylindrical form. The pellets are loaded into the sheath to which end closures (not shown) are applied and welded in position, and the sheath is deformed into intimate contact with the pellets by external pressurisation. The pellets in a preferred form, and as shown, have chamferred corners 4 at the major diameter but may also be formed with rectangular, curved or sharp corners. Accordingly, the external contours of the sheath after pressurising comprise either a series of round edged or a series of sharper edged annular corrugations, depending on the shape of the pellets employed. The sharper edged corrugations are considered preferable from the point of view of optimum heat transfer between sheath and coolant. The direction of coolant flow over the fuel element is preferably in the direction of the arrow 5. The pellets 1 have a thickness to major diameter ratio in the range 1: 4 to 1: 2 and a difference between major and minor diameters in the range 0. 01 to 0. 04 inch. Suitable dimensions are major diameter 0. 38 inch., minor diameter 0. 36 inch. and thickness 0.1 inch., the sheath 2 having a wall thickness of 0. 01 inch. Specifications 873, 073 and 889, 536 are referred to. |
