Becker, E.W.

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Becker, E. W.

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Juni 1969Institut für KernverfahrenstechnikThe Separation Nozz1e Process for Uraniu:m Enrich:mentE. W. BeckerKFK 1002B. H.Juni 1969KERNFORSCHUNGS ZENTRUM KARLSRUHEKFK 1002Institut für KernverfahrenstechnikThe Separation Nozzle Pro~ess forUranium EnrichmentbyE.Ttl. BeckerGesellschaft für Kernforschung m.b.H., KarlsruheVortrag auf Einladung des Nieder-ländischen Atomforums am 30.5.1969in BunnikThe Separation Nozzle Process forUranium EnrichmentE.W. BeckerInstitut für Kernverfahrenstechnik der Universitätund des Kernforschungszentrums KarlsruheIn recent years we have developed a method for U235 enrichmentcalled the separation nozzle process (1). It is based on pressurediffusion in a gaseous mixture of UF 6 and an additional light gasflowing at high speed along curved walls. At the Turin meetingon Isotope Separation held in October of last year, we have pre-sented papers on the Principles and Economic Aspects of the Sepa-ration Nozzle Process (2) and on the Operation of a 10-stage Sepa-rationNozzle Pilot-Plant (3). In our opinion the published figureshave shown that the separation nozzle process holds considerablepromise to become an alternative to the classical diffusion process.The main purpose of today's presentation is to give some infor-mation about the progress we have made in the last 8 months. Aswe cannot expect that everybody is acquainted with the separationnozzle process we shall also give an account of the principles andthe results formerly obtained.Fig. 1 shows a cut through the separation nozzle system. A mixtureof about 5 mole% UFS and 95 mole% He is expanded through a slit-shaped nozzle. The jet flows along a curved wall and is subsequent-ly divided into two fractions which are pumped off separately. Thedeflection of the jet by the curved wall results in a partial spatialseparation of the components, the gas moving close to the deflectingwall becoming enriched in the heavy isotope, while the light oneaccumulates in the remaining fraction. The helium admixture increasesthe velocity of UFS' thereby improving the separation effect.- 2 -In practical application the elementary effect, as in the otherseparation processes, must be multiplied in a cascade arrangement.In coupling together the individual separating elements we haveadjusted the UF6 cut at such a level that the separative workfor the demixing of the uranium isotopes is conserved whereasthe separative work for the demixing of He and UF6 is largely lost.The residual helium transported to the cascade head is separatedthere from the UF6 and is returned to the foot of the cascade.For the experimental demonstration of the gas-dynamic stabilityof aseparation nozzle cascade working with a He-UF6 mixture, a10-stage pilot plant was built in Karlsruhe; it began operatingat full capacity in November 1967 (3). Fig. 2 shows this instal-lation as seen from the control desk. As the arrangement is U-shaped-,only half of the separation stages can be seen. Fig. 3 shows thevariation along the cascade of the enrichment factor which refersto one end of the cascade. The overall enrichment factor agreeswithin the limits of error with the value calculated on the basisof the separation factor of the individual stage. At present thepilot-plant is used to check the feasibility of a computer programfor calculating the behavior of technical cascades.After the successful implementation of the pilot plant, developmentand design work was started on a separating stage to be constructedon an industrial scale. In the separation nozzle process the optimalinlet pressure of the feed gas is inversely proportional to thecharacteristic dimensions of the slit-shaped separation nozzlesystem. Since, for economic reasens, high inlet pressures are de-sirable, separation nozzle systems with particularly small charac-teristic dimensions were built and were tested experimentally.In Turinowe have presented results obtained with laboratory-typeseparation nozzle systems. In the meantime, in cooperation withindustry, a method for inexpensive mass-production of separation- 3 -nozzle-systems with optimum inlet pressure of 600 mm mercuryhas been developed. Prototype",:,elements of that kind were testedsuccessftl!J;Y.Fig. 4 shows sehematically the design of the tube-shaped sepa-rating elementsto be used in the industrial-scale separatingstage. Ten slit-shaped separation nozzle systems are arrangedon the circumference of an aluminium tube of 2 m in leng~h withan external diameter of about 10 cm. The inside of the tube issubdivided by means of partition walls into 10 channels. Five oftheses channels are used for the inlet of the feed gas and fivefor leading off the heavy fraction. The light fraction flows ra-diallY outwards into a tank encasing the separating elements.Fig. 5 shows the entire separating stage. The tank contains 100of the separating tubes described above. It forms, together witha twö-stage radial compressor, a self-contained structural unitwhich can be tested and, if necessary, exchanged as a whole. Theexpected separating capacity is 1700 kgSW/year under full loadwhen a mixture of He and UF6 is used; this is about one-thirdof the separating capacity of the largest American diffusion stages.One such separating stage is now being constructed by industry.Fig. 6 shows a drawing of the building which will contain the stageand its accessories. In the basement you may recognize the frequencyconverter, which feeds the stage with a current of 300 cycles. Theroof supports the cooling tower. The separating stage is expectedto be ready for testing at the end of this year.Fig. 7 shows the building site as of May 1969.In Turino we presented a detailed cost analysis on the basisof the state of development at that time (2). The calculation wascarried out for a so-called demonstration plant with a net outputof 600 000 kg SW/year. The specific investment, exclusive of thepower plant, turned out to be 123 Z/(kg SW/year). Within the marginof error this value corresponds to the figure published for the- 4 -American diffusion plants which are ten times larger. The specificenergy consumption, however, was expected at that time to be higherby a factor of 2.2 as compared to the corresponding published fi-gure Lor the American plants operating under full load.In an attempt to overcome the drawback of the relatively highenergy consumption we first concentrated on the possibility ofusing hydrogen instead of helium as the accelerating gas. In anearlier paper (1), we have already stated that more favorable re-sults can be obtained with hydrogen. Our Turino cost analysis wasnevertheless based on helium since, at that time, we did not havesufficient knowledge about the chemical properties of hydrogen-UF6mixtures. In the meantime aseries of experiments and a carefulanalysis of published data have shown that no difficulties at allare to be expected when working with hydrogen under the conditionsprojected. We therefore base our present calculation on the useof a UF6-hydrogen mixture with 5 mole% of UF 6 • By switching fromhelium to hydrogen we have sa~ed 30% both with regard to specificenergy consumption and specific investment cost.Our next point was to find the cheapest way of energy supply. Inour former calculations a separate power station with a 300 cyclegenerator and 90% on-line time was anticipated. It turned out, how-ever, that this solution would not derive full benefit from the factthat aseparation nozzle plant has a very short equilibrium time andcan be stopped and restarted without appreciable technical difficultyor economic loss. We now proceed on the assumption that comparativelysmall plants will be integrated within a large electrical grid system.Their power supply could be shut off in the unlikely case that thegrid system is in danger of being overloaded. Under these restrie-tions an electricity price of 4 mills/kWh appears conservative, evenunder European conditions. On the other hand, we have to consideradditional investment costs and additional power consumption forthe frequency conversion.- 5 -The following cost estimate. appeC1J.:!s~,I!e4s<:>nable in the presentstate of development:Tab. 1: Expected Separative Work Costs in Z/kg~Wof a Separation Nozzle Plantwith a Net Outputof 700 000 kgSW/year.Electricity (4 mills/kWh)Depreciation (25 years)Interest (7.5%)Additional CostsTotal22.05.25.02.835.0Basis of Calculati9n:90% on line time. Total investment, incl.energy distribution and frequency conversion,91 million Z. Total power needed,500 MW. Specificpower consumption,5500 kWh/kgSW. Specific investment,130 Z/(kgSW/year).The price of a separative work unit turns out to be 35.0 Z.This is still 35 % more than the guaranteed U.S. price. Whenjudging this result, however, one must bear in mind that theseparation nozzle process is a comparatively new one.ln additionto our technical development work we are continuing an extensiveprogram of basic research. We are convinced that a deeper under-standing of the separation mechanism will result in further eco-nomic improvements.- 6 -References:1) See e.g. E.W. Becker, K. Bier, W. Bier, R. Schütte, D. Seidel,Angew. Chemie, Internat. Edition in English, 6, 507-518 (1967).2) E.W. Becker, W. Bier, R. SchüttePrinciples and Economic Aspects of the Separation NozzleProcess, KFK 853 (October 1968); see also E.W. Becker, W. Bier,G. Frey, R. Schütte, atomwirtschaft 14, 249-251 (1969).3) E.W. Becker, G. Frey, R. Schütte, D. Seidel,Operation of a 10-Stage Separation Nozzle Pilot-Plant,KFK 854 (October 1968); see also: atomwirtschaft, 13,359-3~2 (1~68).- 7 -Figure CaptionsFig. 1:Fig. 2:Fig. 3:Fig. 4:Fig. 5:-Fig. 6:Fig. 7:Cut through the separation nozzle system with aschematic representation of the streamlines.10 stage separation nozzle pilot plant.Experimental enrichment factor A of u235 , relative tothe heavy fraction of stage 1:D = Nozzle feed, M and K = light and heavy fraction atstages 1 - 10.TUbe-shaped separatirtg element to be used in thefull-scale separating stage.Full-scale separating stage now being constructedby industry.Drawing of the building which will contain the fullscale separating stage and its accessories.Building site as of May 1969.I~"""-n.::):t~....0o0'Q)(1)-.....-.....o0EElC)lC)0)89Fig.2Fig.710a""-~L...Q.)R..QEC):::Jc::0)QJC)Dl0.......,COCI)C)1:Jc::0~C).......,c::0.......Qt5Q...........~~0L...1:J..c::.......,'t~C)L01tLJIr~I~""-C)""-I~aCO~'t~C)0)""-C)C)C)C)0)",,-"'\""-"'\.--"\""-"\",,-"'""-"'\o-LL~~1112Heavy fraet ion---Jf-_from a higher stageHeavyfractionTank Separating elementsFeedgasIntermediateseetionCompressorFig.5=-+t-II- --1'-1-1----/.-_RecompressedgasCooling system1m13--------~-__t_ooooooooooooooliD'I1101'01111110110'I'-t!----!110I1I'0I:11i====1"'Id0I,IinIII~==II,II'.........I,10."",_-.oooo

The separation nozzle process for uranium enrichment

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The separation nozzle process for uranium enrichment

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