GB798282A - Improvements in or relating to fuel elements for nuclear reactors - Google Patents

Abstract

798,282. Nuclear reactors. UNITED KING- DOM ATOMIC ENERGY AUTHORITY. April 4, 1957 [April 19, 1956], No. 12026/56. Class 39(4). A fuel element for a nuclear reactor comprises a fuel member enclosed in a protective sheath arranged to have parts of the sheath in inferior heat transfer relation with the fuel member and the remaining parts in superior heat transfer relation with the fuel member so that those parts in inferior heat transfer relation can be swept by inflowing coolant and sustain the stresses due to the weight of the fuel element and those parts in superior heat transfer relation can be swept by outflowing coolant and be relatively unstressed. In the Figure the uranium 1 is enclosed between inner and outer zirconium sheaths 2, 3 sealed together by a flexible end cap 4 and a rigid end cap 5. The sheath 2 is pressurized tight on to the uranium so as to be in good heat transfer relationship with it whilst the sheath 3 is spaced from the uranium so that the heat transfer to it is poor. The sheath 3 is joined to a support ring 6 having a flange for resting in a header plate 8. The fuel element is located in a channel formed in a graphite moderator 10 lined with zirconium 11 and is cooled by sodium which flows downwards along sheath 3 and then upwards along sheath 2. Thus the sheath 3 which carries the weight of the fuel element is kept moderately cool by the incoming sodium and heat transfer to the sodium takes place mainly over sheath 2. The sheath 2 may be of zircalloy or niobium for higher temperature working. The space between sheath 3 and the fuel 1 may be maintained as an air gap or may contain a poor heat conducting material such as magnesia.