Patent GB-857959-A (GB)
Title: Power breeder reactor
IPC: G21C19/32
Filed: 1958-10-16
Abstract: 857,959. Nuclear reactors. UNITED STATES ATOMIC ENERGY COMMISSION. Oct. 16, 1958 [Nov. 18, 1957], No. 33024/58. Class 39(4). In a fast neutron reactor, the effect of temperature upon reactivity is reduced by restricting the core distortion caused by bowing of the fuel and reflector tubes. Heating of the central section of each tube normally tends to produce bowing towards the reactor central axis which reduces the core diameter, increases reactivity and hence introduces instability. In the invention the mounting of each tube is arranged so that with increasing temperature the bowing produces first a decrease and then an increase in core diameter, thus reducing the reactivity. The reactor core is housed in a neutron flux attenuating shield and immersed in a liquid coolant within a tank. Fuel handling and control is effected vertically through the tank upper cover. The heat developed produces steam for a turbine generator. The fuel core is completely enclosed in reflector zones; the control elements are located at the core perimeter ; the safety elements pass through the core and in an emergency are moved downwards from the core by gravity. The fuel and reflector elements are housed in hexagonal tubes mounted vertically. Each fuel tube carries the fuel in its middle section and the reflector material in the sections immediately above and below which the elements forming the inner and outer reflector zones surrounding the fuel core contain reflector material only. The control and safety elements are slidable vertically in stainless steel tubes and contain a middle fuel section a reflector section above and below. Coolant, which flows vertically through the reactor elements, is at high pressure through the central core and low pressure through the reflectors. The flow into the control core passes through ports which direct the highest flow rate along the central axis. The reactor and cooling system are contained in a double walled tank, the interwall space being filled with an inert gas, minitored to detect leakage. The tank is surrounded by air-cooled blast and biological shields. As shown, Figs. 6, 7, 8, the fuel tube 70 consists of upper and lower reflector sections 58, 60 and fuel section 56 mounted in the hexagonal tube 76. The fuel elements 78, in 56, are supported at their lower ends and spaced apart by the helical ribs 80 wound round the sheath. The reflector sections are formed of elements 100, mounted in tube 104 and held in place by the spring 108. Each fuel tube 70 is supported near its lower end on the spherical shoulder 270 about which a limited rotation is permitted, but no lateral movement. Coolant flows into the tubes 70 through adapter 128 and upwards round elements 78 and 100 to the outlet 124. upon inward bowing of tubes 70, and rotation round 270, contact between adjacent tubes is made at raised points 126 on each external surface. A further temperature rise produces a radial thermal expansion owing to the contact at 126 with a consequential increase in core diameter. The materials employed are ; fuel, 49% enriched uranium, the thermal bond between the fuel and sheath being sodium; fuel sheath, stainless steel; reflector, depleted uranium; control rod reflector, steel; tank, stainless steel ; blast shield, layers of steel and glass wool ; biological shield, concrete ; coolant, sodium. Specification 721,108 and U.S.A. Specifications 2,841,545, 2,942,483 are referred to.