GB963791A - Nuclear reactors - Google Patents

Abstract

963,791. Nuclear reactors. SOC. ANGLOBELGE VULCAIN S.A. Dec. 10, 1962 [Jan. 11, 1962], No. 1047/62. Heading G6C. A nuclear reactor core comprises a central stationary fuel unit 11 assembled as a neutron multiplying region and surrounded by a plurality of rotary fuel units 12-17 having three sectors 18, 21, 19 assembled respectively as neutron multiplying, neutron moderating and neutron absorbing regions and being rotatable to afford control of the core reactivity. The fuel units 11-17 are in the form of cylindrical drums with the central drum 11 containing enriched uranium aggregated in rod form and assembled together with graphite according to a uniformly spaced lattice configuration or systematically repeating pattern so as to have an infinite multiplication factor greater than unity. Coolant fluid is circulated through the lattice. Similarly the sectors 18 of the fuel drums 12-17 are assembled as neutron multiplying regions while the sectors 19, 21 are assembled from boron-containing material and graphite, respectively, so as to constitute neutron absorbing and moderating regions. A stationary reflector 22, e.g. of graphite bricks, embraces the core and fills the outer interstitial spaces between the drums. Alternatively, fertile material such as natural or depleted uranium can be used to fill these spaces. The inner interstitial spaces afford location for the insertion of further neutron moderating material, or conventional control rods 23 for supplementary control. Initially, the neutron absorbing sectors 19 are positioned adjacent the central drum 11 and the core is subcritical. Criticality is brought about by rotating the drums 12-17 clockwise to move the multiplying sectors 18 inwards towards the central drum 11 to the position shown. In this initial critical state the core is under-moderated and criticality is accompanied by absorption of excess neutrons in fertile material in the core to convert this material into fissile material. As the core is burnt up the initial excess reactivity of the core is reduced and criticality of the core is maintained by further clockwise rotation of the drums 12-17 so that the moderating sectors 21 are gradually moved inwards towards the central drum 11. Modifications to the above include the use of peripheral arcuate sectors for the different regions of the fuel units and the use of a star-shaped central unit with the encircling drums rotating between the arms of the star. The invention is described as having particular advantages for marine propulsion. Specification 922,498 is referred to.