GB688821A - Improvements relating to the production of energy from radio-active materials - Google Patents

Abstract

688,821. Nuclear reactors. IMPERIAL TRUST FOR THE ENCOURAGEMENT OF SCIENTIFIC AND INDUSTRIAL RESEARCH. Dec. 10, 1941 [April 2, 1941], No. 4426/41. Class 39(iv) U<SP>233</SP> or PU<SP>239</SP> is produced in a nuclear reactor (breeder) by transmuting Th<SP>232</SP> or U<SP>238</SP> respectively. A single-medium reactor producing Pu<SP>239</SP> comprises about 10 kg. of U<SP>235</SP> or U<SP>235</SP> diluted with U<SP>238</SP>, (this U<SP>235</SP> being concentrated as described in Specification 685,360), and mixed with natural uranium and water to give a total mass of a few tons. The ratio of enriched U<SP>235</SP> to the U<SP>235</SP> present in natural uranium is 0.4 to 1 and it is stated that a theoretical minimum of 0.2 to 1 for a homogeneous reactor or 0.15 to 1 for a heterogeneous reactor would require infinite total mass. In this reactor the H to U<SP>238</SP> ratio is 6-8 atoms to 1 atom, and the ratio PU<SP>239</SP> produced to U<SP>235</SP> consumed is 4 to 1.2. A reactor producing U<SP>233</SP> comprises U<SP>235</SP>, H 2 O and Th in the weight ratio 1:10:50, and yields 1 gram U<SP>233</SP> per gram U<SP>235</SP>. A less efficient (two-medium) reactor, requiring a lesser amount of enriched U<SP>235</SP> comprises a neutron-producing mass surrounded by a neutronreceiving mass. A neutron-producing mass comprises more than 30 litres of pure U<SP>235</SP> and H 2 O in proportions 1:23 by weight, cooling being assisted by preserving a suitable surface/volume ratio, by forming the mass as a flattened shape, as a hollow sphere, or as a string of 30-litre spheres, or by setting a part of the mass in motion, as described in Specification 688,822. Similar reactors are described comprising (a) 116 kg. of benzene and 3.5 kg. of U<SP>235</SP>; (b) 240 litres of H 2 O containing U<SP>235</SP> in the ratio 61:1 by weight; (c) D 2 O+ H 2 O+ U<SP>235</SP>; (d) several hundred litres of D 2 O + U<SP>235</SP> in the ratio 1200: 1 by weight; (e) highdensity deuteroparaffin of approximate formula CD 2 + U<SP>235</SP>; (f) graphite plus several kgs. of U<SP>235</SP> cooled by CO 2 or intermittently by H 2 O or molten metal; and these reactors give better cooling, or require less U<SP>235</SP>. The neutron-receiving mass or envelope may comprise natural uranium, thorium, or U<SP>238</SP> and is of the order of one or a few decimeters thick. 2 to 6 atoms H (in H 2 O) per atom U or Th are needed as moderators in the case of U<SP>238</SP> or Th. With an envelope containing natural uranium, convergent fission chains are produced therein. This uranium is mixed homogeneously or heterogeneously with H 2 O or other suitable hydrogen compound (e.g. paraffin wax). A homogeneous mixture of uranium oxide with water (3 atoms H per atom U) surrounding a core emitting 1.5 neutrons per fission yields 5 atoms Pu per fission. A similar core surrounded by a heterogeneous mixture of U with paraffin wax (3 to 4 atoms H per atom U) yields 15 atoms P'u per fission. These reactors are of the order 10 to 100 tons. Thorium in the envelope may be arranged heterogeneously with respect to the uranium to avoid dilution of U<SP>233</SP> with the natural uranium. The accumulation of Pu<SP>239</SP> or U<SP>233</SP> in any of these reactors continues until it becomes practicable (a) to extract U<SP>233</SP> or Pu<SP>239</SP> chemically, leaving enough fissile material for the reactor to continue functioning, or (b) to add 50 per cent to 100 per cent to the water content of the core as the concentration of Pu<SP>239</SP> or U<SP>233</SP> in the envelope makes it energyproducing, independent of the core; or (c) singlemedium systems become workable in smaller sizes as Pu<SP>239</SP> or U<SP>233</SP> accumulates, so that such a system may form a core for a two-medium system.