Becker, E.W.

Bier, W.

Ehrfeld, W.

Schubert, K.

Schuette, R.

Seidel, D.

English

Becker, E. W.

KITopen

November 1975Institut für I<ernverfahrenstechnikI<FI< 2235E.W. Becker, W. Bier, W. Ehrfeld1<. Schubert, R. Schütte, D. SeidelGESELLSCHAFTF.ÜRKERNFORSCHUNG M.B.H.KARLSRUHEAls Manuskript vervielfältigtFür diesen Bericht behalten wir uns alle Rechte vorGESELLSCHAFT FÜR KERNFORSCHUNG M. B. H.KARLSRUHEKERNFORSCHUNGSZENTRUM KARLSRUHEKFK 2235Institut für KernverfahrenstechnikURANIUM ENRICHMENT BY THE SEPARATIONNOZZLE PROCESS +)byE.W. Becker, W. Bier, W. Ehrfeld, K. Schubert,R. Schütte, and D. SeidelGesellschaft für Kernforschung mbH, Karlsruhe+) Paper presented by E.W. Becker at the AmericanNuclear Society Meeting, San Francisco,November 1975.The separation nozzle process for the enrichment of thelight uranium isotope U-235 has been developed at theKarlsruhe Nuclear Research Center as an alternative to thegaseous diffusion and centrifuge processes. Since 1970 theSTEAG company, Essen, has been involved in the comrnercialimplementation of the nozzle process.A first separation nozzle demonstration plant with aseparative capacity of 180 t SWU/a shall be erected in Brazilwith the participation of the Brazilian company NUCLEBRASand the German companies STEAG and INTERATOM. Methods forthe mass production cf separation elements were developedby industry and extensive performance tests were carriedout on commercially fabricated separation elements. Twoprototype separative stages were successfully tested inKarlsruhe. Besides further plant components, a prototypeof a UF 6 recycle facility was developed which serves thepurpose of stripping the UF 6 from the light auxiliary gasto be recycled in aseparation nozzle cascade.The performance level achieved to date character~zes theseparation nozzle process as reliable and feasibleeconomically. Therefore, the erection of aseparationnozzle demonstration plant can be recognized as theimplementation of an enrichment process which combinesa reliable and comparatively simple technology with ahigh potential for further improvements.ZusammenfassungDas Trenndüsenverfahren zur Anreicherung des leichten Uran-isotops U-235 wird am Kernforschungszentrum Karlsruhe alsAlternative zum Gasdiffusions- und zum Zentrifugenverfahrenentwickelt. Seit 1970 beteiligt sich die STEAG AG, Essen,an der technischen Weiterentwicklung des Verfahrens.Im Rahmen der Entwicklung der Anlagentechnik wurden in Zu-sammenarbeit mit der Industrie Verfahren zur Massenfertigungvon Trennelernenten ausgearbeitet. Die technischen Trennele-mente zeichnen sich durch eine hohe Trennleistung und einehervorr~gende Dauerstandsfestigkeit aus, was durch ausführ-liche Testreihen unter Verfahrensbedingungen demonstriertwerden konnte. Bereits 1970 wurde eine Prototyp-Trennstufein Karlsruhe errichtet und erfolgreich erprobt. Eine zweitefortgeschrittene Prototyp-Trennstufe, deren Konstruktionbesonders auf die Serienfertigung der Stufenkomponentenausgerichtet ~ar, ist seit Ende 1973 in Betrieb. Mit einerUFS-Abscheidungsanlage, die für die Abtrennung des UF S vornleichten Zusatzgas in einer Trenndüsen-Kaskade notwendigist, konnte der geforderte hohe Abscheidungsgrad problemloserreicht werden.Eine erste Trenndüsen-Demonstrationsanlage mit einer Trenn-leistung von 180 t UTA/Jahr soll unter Beteiligung derbrasilianischen Gesellschaft NUCLEBRAS und der deutschenFirmen STEAG und INTERATOM in Brasilien errichtet werden.Dies stellt einen wichtigen Schritt in der industriellenAnwendung des Trenndüsenverfahrens dar, das sich durch eineeinfache Technik und ein hohes Entwicklungspotential aus-zeichnet.- 1 -1. IntroductionThe separation nozzle process for the enrichment of U-235has been developed at the Karlsruhe Nuclear ResearchCenter as an alternative to the gaseous diffusion andcentrifuge processes (Refs. 1-5). Isotope separation iseffected by the same basic mechanism as in the centrifugemethode However, the serious mechanical problems of highlystressed rotating machines are avoided, since theseparating centrifugal forces are generated in the nozzlemethod by deflection of a high speed jet consisting ofuranium hexafluoride and a light auxiliary gas.Since 1970 the German company STEAG has been involved inthe technological development and commercial implementationof the nozzle process (Ref. 6). In June 1975, the Braziliancompany NUCLEBRAS and the STEAG company signed agreementsby which they intend to cooperate in the field of uraniumenrichment using the separation nozzle process. As a firststep in the Brazilian/German cooperation, aseparationnozzle demonstration plant with a capacity of 180 t SWU/ashall be erected in Brazil. For the erection and operationof the demonstration plant a Brazilian/German company willbe founded with the participation of the German companiesSTEAG and INTERATOM.2. Separation ElementsFig. 1 shows a cross section of the nozzle systemused in the commercial implementation of the process. Gaseousuranium hexafluoride mixed with hydrogen expands along acurved fixed wall. At the end of deflection the flow issplit up into a lighter and a heavier fraction by means ofNHeavyFract ionDepletedin U235and H2LightFractionEnrichedin U235and H2'~Ililt,::~~fmrrr~~Feed Gas5% UF695 OJo H2Fig. 1. Cross-section of the separation nozzle system used in thecommercial implementation of the separation nozzle process.- 3 -a skimmer. The light auxiliary gas which is present in alarge molar excess increases the flow velocity of the UF6and, hence, it increases the centrifugal force determiningthe separation. In addition, the auxiliary gas enhancesisotope separation by delaying the sedimentation of the UF6in the centrifugal field of the curved flow (Ref. 7).According to the gas-kinetic scaling relations, the optimumoperating pressure of the nozzle system is inverselyproportional to its characteristic dimensions. Thus, aseparation nozzle with the smallest practical dimensionsis the most attractive,economically,due to the savings inequipment sizes associated with a high operating pressure.Fig. 2 illustrates the design of a commercial separationelement manufactured by the MESSERSCHMITT-BÖLKOW-BLOHMcompany, Munich. An extruded aluminium tube, which isshown schematically in the lower part of Fig. 2, servesas the basic unit of the commercial separation element.This tube is subdivided by partition walls into sector-shaped chambers marked by the letters Fand H, respectively.It carries 10 slit-shaped nozzle systems on its periphery.As shown in detail in .the upper part of Fig. 2, the separationnozzle system proper consists of the deflection groovemachined in the tube and alu~inium strips, the edges ofwhich are designed as the skimmer and the nozzle wall,respectively. The aluminium strips are fixed in the dovetailgrooves of the tube and held in place by balls forced inbetween the strips. The deflection groove of the nozzlesystem normally has a radius of curvature of 1/10 mm.The feed gas for the nozzle systems is introduced at oneend of the tube into the channels marked F; the heavyfraction is withdrawn at the opposite end of the tube fromthe channels marked H. The light fraction is pumped offfrom the space around the tube.- 4 -HEAVVFRACTIONLIGHT FRACTION~J-------,t ..-------\.FEED GASFig. 2. Schematic representation of acommercial separation element tubemanufactured by the MESSERSCHMITT-BöLKOW-BLOHM company,Munich.U~6 /He -MIX IUKtIU~6/H2-MIXIUKt()() () (~()~()()..... .... - -.. - - ...... -. ()() ()()111'••--. -- ... . 0 "c.n35000300002500015000 20000HOURS OF OPERATION1000050002<l:W==.....<[=<[a....Lo..Jcn 0o.....c..JLo..JLI-LI-Lo..J""=.-Fig. 3. Endurance test of a commercially produced separation nozzleelement, carried out with He/UFS- and H2/UFS-mixtures.- 6 -Fig. 3 represents the results of endurance tests performedon a section of a commercial separation element underprocess conditions with He/UF6- and H2/UF 6-mixtures,respectively. Obviously, the performance of this separationelement has not changed within the error limits over aperiod of more than 4 years.It is evident, that the compactness of the separationelements influences the equipment size and the costincident to it. Therefore, the SIEMENS company, Munich,has developed another method for the commercial productionof separation elements for further possible reductionsln the equipment size. The method is based on the stackingof photo-etched metal foils.Fig. 4 shows aseparation nozzle structure produced by theetching technique. Considering that the radius of curvatureof the deflection wall is only 1/10 mm, the picturedemonstrates the accuracy of the fabrication method.Fig. 5 illustrates the assembly of a photo-etched separationelement. On the left side', a section of a metal foil stripis shown. A large number of separation nozzle structurestogether with the ducts for the feed gas and the heavyfraction, are photo-etched at the edges of the foil strip.As shown in the middle of the picture, approximately 100such metal foil strips are stacked one above the other,covered with cover plates and clamped together. In thisway, a compact separation nozzle chip is produced. The feedgas is introduced through the holes of the upper coverplate and the heavy fraction is removed through the holesof the lower cover plate; the light fraction leaves thechip at both sides. About 100 such chips are arranged ina tube as shown on the right side of the picture. The two- 7 -Fig. 4. Separation nozzle structure produced bymeans of photo-etching techniques(SIEMENS company, Munieh).I IlmmCHIP............10mmTUBE50mmcoFig. 5. The assembly of a commercial separation element manufacturedby means of photo-etching (SIEMENS company, Munieh).Fig. 6. Section of the automatie produetion line for manufaeturingphoto-etehed separation nozzle elements: The setup formetal foil eoating with a photo-sensitive resist. (SIEMENSeompany, Munieh).c.D- 10 -tube halves serve to introduee the feed gas and to remavethe heavy fraetion. The light fraetion leaves the separationelement tube between the two halves.An automatie produetion line for manufaeturing photo-etehedseparation elements was installed by the SIEMENS eompany lnMunich.As an exampleof the produetion line equipment)Fig. 6 shows the setup for metal foil eoating with a photo-sensitive resist.3. Separative StagesA large number of eommereial separation elements have beentested in two prototype separative stages. Fig. 7 shows thefirst prototype stage installed in Karlsruhe in 1970. Thestage is eonstrueted as an integrated unit. It eonsistsof a tank eontaining the separation elements, agasdistribution system, a gas cooler, and a eentrifugaleompressor. The separation experiments performed with thisstage were sueeessful from the outset. No failuresoeeurred in the major eomponents of the stage, althoughthey were put under a severe stress by more than 400 startsand by testing the limits of maximum load and stableoperation.On the basis of the operating experienee gained with thefirst prototype stage, an advaneed version of a separativestage has been developed by the STEAG eompany. Fig. 8 showsthe insertion of the separation elements into this stage.The separation elements are arranged as a eompaet unit toallow easy installation. All major eomponents of the STEAGstage were designed with a view to the requirements ofmass produetion.- 11 -Fig. 7. View of the first prototypeseparative stage installedin 1970.- 12 -Fig. 8. Insertion of the separation elementunit into the separative stagedeveloped by the STEAG company,Essen.~w'-'SEPARATION EFFECT EAUF6- CUT -5-u~ ~ " '" ~ - ~0.40.2-5-uIiH1.2EA .1021.00.80.640o0 20 60 80 100--- HOURS OF OPERATION120Fig. 9. Results of the acceptance test of the STEAG separative stage.- 14 -Fig. 9 represents the results of the acceptance test ofthat stage. The separation experiments were performed withan H2/UF6-mixture. The stable operation of the separativestage is demonstrated by the constant separation effectand UF 6-cut.4. Cascade DesignFig. 10 represents a side view of the projected stagearrangement for the industrial-scale utilization of theseparation nozzle process. Groups of stages are each mountedin a concrete plate and supported by a base plate carryingthe electric motors. In the right group of Fig. 10 anintermediate state of assembly is illustrated.Fig. 11 shows a schematic representation of an industrialseparation nozzle cascade using two types of separativestages. A total of about 500 separative stages must beconnected in series in separation nozzle cascades in orderto produce enriched uranium containing 3 % U-235 and tostrip to some 0.3 % the U-235 content in the waste uranium.Furthermore, Fig. 11 illustrates the transport of the lightauxiliary gas in aseparation nozzle cascade. The netupward flow of the auxiliary gas must be recycled from thetop to the bottom of the cascade sections. This operationis performed by means of so-called UF 6 recycle facilities.Such a facility comprises a special separation nozzle stagewhich partially stripsthe UF 6 from the auxiliary gasthereby limiting the UF 6-holdup of the system. The remainingUF 6 content of the gas stream is then frozen out in a lowtemperature heat exchanger system which is run in cyclicoperation.~ ~GROUP 1~ ~SEPARATIONELEMENTSTANK,~ ~GROUP 23m0"~U1Fig. 10. Side view of the stage arrangement planned for aseparationnozzle demonstration plant.- 16 -_1lil!II!I!III.PRODUCT3.0 wt % U-235UF6- RECVCLE FACILITIESIILIGHT FRACTION------I ! RECYCLEDOF TOP STAGES~~I.I~ H21UF6 -MIXTUREPURE HYDROGENr---- ....--------r-IIIIIIIIIIIIIIIII IL----./f'--------..JIIL ~-..,IIIIIIIIINORMAL FEED0.71 wt % U-235IIIIII IL -lTAILS0.3 wt % U-235Fig. 11. Schematic representation of aseparationnozzle cascade with UF 6-recycle facilities.Fig. 12. View of the low-temperature freeze-out system of aUF6-recycle facility manufactured by the LINDEcompany, Munieh.~--...J- 18 -A prototype of such a freeze-out system was built by theLINDE company, Munich. It consists of a heat exchangerunit with an associated cooling system. Fig. 12 gives aview of the arrangement. The experiments performed withUF 6/H 2-mixtures under process conditions have demonstratedthat an extremely low UF 6-content in the light gas processedcan be achieved without difficulty. Accordingly, onlynegligible losses of separative work are associated withthe recirculation of the light gas from the top to thebottom of the cascade sections.5. ConclusionsThe development of reliable manufacturing methods forcommercial separation elements, the successful operation ofseparative stages, and extensive tests performed on plantcompohents and auxiliary systems provide the basis for theconstruction of aseparation nozzle demonstration plant.The performance level achieved to date characterizes theprocess as reliable and economically feasible. In particular,it is generally accepted that comparatively low investmentand maintenance costs are to be expected for the separationnozzle process.On the other hand, the nozzle process appears to have thedis advantage of a comparatively high specific powerconsumption. This situation, however, by no means shouldbe regarded as a static one, as evidently demonstrated byFig. 13. The curve shown in this diagram represents thereduction in the specific power consumption of the separationnozzle process since 1968. The data refer to an industrial-scale plant, i.e. the compressor efficiency, the cascadeefficiency, the power consumption of the auxiliary systems,- 19 -800019761970 1972 1974CAlENDAR VEAR\\ SEPARATION NOZZLE\1\~EXISTING PLANTS ~------------------DIFFUSION--PROJEci'EDPLANTS---I I I I I Io1968..::a::c::::::':)..............CL.:::E==Cf)~ 4000a:::......3:c::::::':)CL.c:..,).......LA-.......~ 2000CL.Cf)Fig. 13. The reduction in the specific powerconsumption of the separation nozzleprocess since 1968. The data werecalculated for an industrial-scaleseparation nozzle plant and includethe cascade efficiency, the compressorefficiency, the power consumption ofthe auxiliary systems, and the pressurelosses in the piping of the cascade.- 20 -and the press ure los ses in the piping were taken intoaccount. At the present state of development, the powerconsumption of the separation nozzle process is still slightlyhigher than that of the existing U.s. gaseous diffusionplants. However, considering the slope of the powerconsumption curve, there is no doubt that a furthersignificant reduction of the specific power consumptionis to be expected.In conclusion, it can be stated that the erection of aseparation nozzle demonstration plant in Brazil can berecognized as the implementation of an enrichment processwhich combines a reliable and comparatively simpletechnology with a high potential for further improvements.- 21 -References11J E.W. Becker, K. Bier, W. Bier, R. Schütte, D. SeidelAngew. Chemie, Intern.Edit. (in English) 6,507 (1967).This paper includes a list of previous pUblicationson the nozzle process.12J E.W. Becker, W. Bier, P. Bley, U. Ehrfeld, W. Ehrfeld,G. EisenbeißAtomwirtschaft ~, 524 (1973).13J E.W. Becker, W. Berkhahn, P. Bley, U. Ehrfeld,W. Ehrfeld, U. KnappInternational Conference on Uranium Isotope Separation,London (1975).[4J E.W. Becker, W. Bier, W. Fritz, P. Happe, D. Plesch,K. Schubert, R. Schütte, D. SeidelInternational Conference on Uranium Isotope Separation,London (1975).15J E.W.Becker, W. Bier, W. Ehrfeld, K. Schubert, R. Schütte,D. SeidelEuropean Nuclear Conference, Paris (1975).[6] H. Geppert, P. Schuhmann, U. Sieber, H. Stermann,H. Völcker, G. WeinholdInternational Conference on Uranium Isotope Separation,London (1975).17J E.W. Becker, W. Bier, W. Ehrfeld, G. EisenbeißZ. Naturforsch. 26a, 1377 (1971).

Uranium Enrichment by the Separation Nozzle Process

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Uranium Enrichment by the Separation Nozzle Process

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