PRODUCTION Nuclear Fuel: Chemical Product Chemical processing is important part of Britain's latest experimental atomic pow&r station C HEMICAL PROCESSING plays
a
big
part in Britain's new experimental atomic power station under construction at Dounreay, Scotland (see page 62). Two plants process irradiated fuel elements—from the fast reactor and the materials testing reactor—separating uranium and plutonium from waste fission products. A third plant prepares uranium metal from the nitrate. In addition, there is an evaporation plant which concentrates highly radioactive wastes from the separation plants. In the fast reactor chemical plant, irradiated fuel elements are mechanically stripped of their niobium or stainless steel cans and then dissolved in nitric acid. The dissolver is continuous and is heated by steam. Solution from the dissolver is adjusted to the proper pH and is then passed through a sludge remover. A constant volume feeder feeds it to a pulsed mixer-setder extraction unit, in which a counter current stream of tributyl phosphate extracts plutonium and uranium, leaving most of the fission products. The fission products stream goes to the waste evaporation plant. The rich solvent is backwashed with nitric acid to remove the uranium and plutonium. The backwash solution then goes through a second cycle similar to the first to remove the last of the fission products. A third solvent extraction cycle separates plutonium from uranium. Uranyl nitrate solution then goes to the adjacent metal plant. The plutonium solution is further purified, concentrated by evaporation, and shipped to another U. K. Atomic Energy Authority plant, Windscale, for processing to metal. ^ The materials testing reactor chemical plant is similar. Irradiated fuel elements are received in shielded coffins and dumped into a pond of water. Sides are milled off under water. The plates are then coiled and dissolved batchwise. A solvent extraction process follows—similar to the one in the other plant but with fewer stages. In a plant handling solutions of fissionable material, there is always the 86
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danger that -a critical mass—resulting in a nuclear chain reaction—can be formed. This could happen if a solution of the right concentration was contained in a vessel of the right size and shape. The fast reactor chemical plant is "eversafe" in this respect. That is, it is dimension&Hy safe for any mass or concentration of fissionable material. The other plant, for the material testing reactor, is operated on a batch basis rather than continuously. Only one fuel element sat a time is dissolved and processed, so it is much easier to keep track of concentrations and avoid forming a critical mass. Initial stages of the chemical separation process a.re carried out inside fourfoot thick concrete shields for protection of personnel. • Uranium Metal. The uranyl nitrate
solutions from both chemical separation lines are processed in the same uranium metal plant. However, materials from the two plants are kept separate. Batches of solution are enriched or blended to the correct ratio of U 2 3 s and U23;v Metal production consists of precipitating a uranium compound, drying it, and reducing it with another metal in a bomb-type reactor. The uranium billet from the bomb is then sent to fuel element fabrication. Slag and other side streams go through recovery processes to save the uranium. Most chemical processing in the uranium plant is done in very large, laboratory-type glassware. Feed solution is free of gross beta activity, so alpha rays are the only radiation to be guarded against. Generally, each unit operation is enclosed in one "dry box." The backs of these boxes face onto a series of corridors separate from the operating faces. If a unit must be replaced, the work is done from the back. Entrance to the back corridors is only through a special sub-change room where workers leave their contaminated clothing. • Waste Evaporation. Solution containing fission products is highly radioactive, so it cannot b e disposed of by ordinary means. Instead, it will be stored for many years in stainless steel tanks. Liquor from the fast reactor tanks is concentrated by evaporation to save space. Some of the materials
Construction is well along on Britain's latest atomic power station at Dounreay, Scotland. Its fast neutron reactor is scheduled to go critical next April, feeding some 15 megawatts of electricity to the national grid. In this photo, the huge hole in the foreground is excavation for storage of radioactive wastes. Building houses evaporators; dome at right contains the reactor itself
BlililM ο WITH N E W G O R R O S I O N - F R E E CÎRAINÂ6E
ÔYSTEM
Industry develops new easy-to-install (low cost drainage pipes and fittings of PVC based on ΕΧΟΝ 402-A . . . another use iyp/ca/ of the Pin-Pointed Properties in Exon Vinyl resins T u b e Turn Plastics, Inc., timed a journey m a n p l u m b e r as h e made a bell and spigot joint in a 2 " Schedule 40 alloy cast iron line. It took 3 minutes, 45 seconds. T h e n h e joined a l e n g t h of n e w 2 " Schedule 4 0 PVC pipe to a newly devel oped PVC socket type solvent welding drainage fitting. Complete time: 56 sec onds . . . α labor saving of 75%. This is o n e reason it is more economical to dispose of corrosive industrial liquid wastes with drainage systems of P V C based on Exon 402-A resin. Installation requires less labor per j o i n t . . . fewer tools
and materials . . . a n d fewer joints. The n e w socket type drainage fitting eliminates troublesome corrosion pockets and gives you u n i m p e d e d flow conditions. It is unaffected b y ground conditions, acid or alkaline, wet or dry. I t is not subject to galvanic or electrolytic action. Exon 402-A is just one resin in indus try's most complete line of versatile vinyls. No wonder industry looks to Firestone for engineered answers to its needs. For resin properties pin-pointed to t h e best answer to your own plant or product problems, check with Firestone. For complete information and technical service, call or write:
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testing reactor solutions contain con siderable aluminum (not completely stripped from "the fuel elements before dissolving) . These are not evaporated because of t h e possibility that alu m i n u m nitrate might settle out. Highly active liquor is sent batch wise to a. constant volume feeder. F r o m there it flows t o a steam stripping column w'hicli removes t h e tributyl phosphate and kerosine. T h e solution is then evaporated i n continuous equip ment. Condensate is monitored before being discharged into t h e sea. Processing equipment for the evap oration plant is set u p inside a concrete shield. Opera-tion is remote. No me chanical p u m p s a r e used—to avoid maintenance work in t h e sealed area behind t h e shield. Vacuum lifting through steam ejectors is used through out. The steam ejectors a r e set out side the shielding f o r easy maintenance. In the futuLre even more chemical processing facilities may be installed at Dounreay. Waste liquors contain iso topes of value t o industry a n d medicine —such as cesiu.rn-137 a n d strontium-90. Some day a plant may be p u t up to extract these from stored liquor.
Irradiate Wastes Army Chemical Corps workers at Fort Detrick, MUL, liave found that they can sterilize sewage or waste by irradia tion. They conclude that, with a nu clear reactor a s a source of radiation, ultimate cost could be as low as a quar ter cent p e r gallon of waste. T h e re actor would supply heat or electricity; waste would h e used as a secondary coolant, going: between the reactor and thermal shielding rather than through the reacto>r core. These conclusions a r e based on ex periments with a suspension of a virus and one o f bacterial spores irradiated from isotopes. Another result: About 2 0 0 0 times more radiation is needed to kill a bacterial spore than to kill a person.
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minerals
• Process for molding Teflon into ar ticles of thin cross-section ( V i e t h inch or less) h a s heen patented by Sparta Mfg., Dover, Ohio. Articles made this w a y are uniform a n d free of cracks, and h a v e the effects of plastic memory mini mized, t h e company claims. • More than ΊΟ.Τ' million trucks are rolling 011 American highways this year, according to "the Automobile Manufac turers' Association. This is double the truck registration o f only 12 years ago, the association says. Trucking employs about 7 million people, some 6 million of them drivers.
