Fusion Engineering and Design 58–59 (2001) 439–443

Operating experience of the experimental industrial plant forreprocessing of tritiated water wastes

I.A. Alekseev a,*, S.D. Bondarenko a, O.A. Fedorchenko a, A.I. Grushko a,S.P. Karpov a, K.A. Konoplev a, V.D. Trenin a, E.A. Arkhipov b,

T.V. Vasyanina a, T.V. Voronina a, V.V. Uborsky b

a Petersburg Nuclear Physics Institute, 188300 Gatchina, Leningrad district, Russiab JSC ‘DOL’, Moscow, Russia

Abstract

The results of 5-year operation of the experimental industrial plant for hydrogen isotope separation using combinedelectrolysis and catalytic exchange (CECE) process are presented. The plant is used for large-scale studies of CECEprocess and for reprocessing tritiated heavy water wastes. The main parts of the plant are a 100-mm diameterexchange column of 6.9 m overall height, alkaline electrolytic cells and catalytic burners. The separation performanceof the column was determined. The computer code makes it possible to carry out the calculation over a wide rangeof conditions and to forecast a concentration profile within the column when the values of flow rates are changed.The experience gained during the plant operation shows a high efficiency of isotope separation by CECE process andallows regarding CECE process as a considerable promise for the industrial use, in particular, for water purificationfrom tritium. © 2001 Elsevier Science B.V. All rights reserved.

Keywords: Tritiated water wastes; Hydrogen isotope separation; Combined electrolysis and catalytic exchange

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1. Introduction

The problem of high purification of heavy wa-ter and light water wastes from tritium has re-mained unsolved because of the lack of theconvenient processing technology. The combinedelectrolysis catalytic exchange (CECE) processutilizing wetproofed catalyst is the most attractiveone for extracting tritium from water due to itshigh separation factors and near-ambient operat-

ing conditions. This process is regarded as analternative for detritiation in comparison to con-ventional water distillation (DW) and vapourphase catalytic exchange (VPCE) processes in theITER isotope separation system [1,2]. The tests ofa pilot plant operating at various modes canadduce evidence of practical applicability of thismethod for tritium recovery.

An experimental industrial plant for hydrogenisotope separation using CECE process has beenbuilt in Petersburg Nuclear Physics Institute inco-operation with JSC ‘DOL’ and D. MendeleyevUniversity of Chemical Technology of Russia [2–

* Corresponding author. Tel./Fax: +7-812-7131-985.E-mail address: aleksiv@pnpi.spb.ru (I.A. Alekseev).

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4]. The plant is designed for carrying out large-scale studies of the CECE process in a wide rangeof parameters, for producing commercial heavywater from heavy water wastes, and for recoveryof tritium from water. The paper presents theresults of 5-year operating experience of the plant.

2. Design data and principle of operation

The schematic flow diagram of the plant ispresented in Fig. 1. The chemical exchangecolumn of 6.9 m overall height and an innerdiameter of 100 mm is filled with alternatinglayers of wetproofed catalyst and stainless steelspiral-prismatic packing. The column consists ofthree separation sections connected through a dis-tributor of liquid. Each section is provided with aheating water jacket for maintaining the columntemperature within 300–360 K. The operatingpressure is 0.13–0.4 MPa. The sections of thecolumn are bolted together. This enables an easyreplacement of catalyst and packing to improvethe inner structure of the sections.

The feed points (FP) and sample points (SP)are located between the separation sections, at thetop and at the bottom of the column. The overall

separation height of the column is 5.2 m. Thewetproofed catalyst used has been developed bythe D. Mendeleyev University of Chemical Tech-nology of Russia. It consists of 0.8 wt.% platinumdeposited on porous polysorb (styrene–divinyl-benzene copolymer) [2]. The plant uses alkalineelectrolytic cells as a lower reflux device and hy-drogen catalytic burners as an upper reflux device.The hydrogen output of electrolytic cells is 5m3/h. All equipment of the plant was manufac-tured in Russia. The schematic diagram of theplant is presented in detail in Ref. [3].

The risks of explosion and radioactive contami-nation formed the basic criteria for the design,construction and operation of the plant. The mainequipment of the plant is located in the roomspecially provided for the operation under hydro-gen and tritium conditions.

The main results were obtained at the steady-state mode of operation of the plant during pro-cessing diluted heavy water. The feed flowcontaining about 47% deuterium and 108 Bq/kgtritium is injected into the column feed point FP3.Heavy water concentrated up to 99.85–99.995 iswithdrawn from the bottom as a liquid. The topproduct containing less than 1% deuterium iswithdrawn as liquid when the catalytic burnersare operated, or as hydrogen when natural wateris fed to the top of the column as reflux. Thetritium concentration in the top product is lessthan 105 Bq/kg.

The separation performance of the column wasdetermined by accurately measuring the deu-terium and tritium concentration in water and gasfrom different sample points. The samples ofheavy water were analysed by the IR-spectropho-tometer, and gas samples by gas chromatography.Tritium was measured by the liquid scintillationmethod.

3. Methods of separation performance estimation

The separation performance of the exchangecolumn was determined by two different methods.The first method considers the separation processin the column as a counter-current exchange pro-cess between liquid water and hydrogen–waterFig. 1. The schematic flow diagram of the plant.

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vapour mixture. The values of height equivalentto a theoretical plate (HETP) were determined ata steady-state mode under various conditions. Thedependence of separation factors on temperatureand deuterium concentration was taken intoaccount.

Another way of looking at this process is pro-posed also. Simulation code ‘EVIO-3’ (one ofdescendants of the code ‘KIO’ [5]) deals withthree streams (liquid water, water vapour andhydrogen gas) and with six components. Depen-dency of temperature and concentration on sepa-ration factors is incorporated. The Murphree-typefactors are introduced in the code to consider theefficiency of both scrubbing and catalyst layers.Two constants which define each of the factorsfor catalyst and scrubbing layers are reverse reac-tion velocity constants of hydrogen/vapour cata-lytic exchange and water/vapour phase exchange,respectively. The code provides stable and rela-tively rapid computation of a concentrationprofile if values of both constants are known.However, some uncertainties have not allowed sofar to solve the inverse problem that is, uniquedetermination of these constants if the concentra-tion profile is experimentally known. This fact isthe only reason why values of the constants arenot presented here.

Nevertheless, ‘EVIO-3’ allows now correct fore-casting a concentration profile within the columnoperated under conditions (temperature, pressure,values of water and gas flow rates) different fromthose under which these two constants are ‘mea-sured’. And what is more, the numerical analysison the base of the code ‘EVIO-3’ agrees withexperimental data over a wide range ofconditions.

4. Start-up of the plant and operationalexperience

The first tests of the plant as a whole began inNovember 1995. The tests of the separationcolumn were carried out at various operationmodes. The temperature, pressure, gas flow rate,manner of a column filling were varied. The hy-draulic and separation characteristics of the iso-tope exchange column have been investigated.

Fig. 2. Effect of the temperature on the HETP.

During the initial tests, satisfactory separationand hydraulic performance was not achieved. Itwas found that the manner how the column wasfilled affected significantly the limiting hydrogenflow rate. The change of the column filling al-lowed increasing the gas flow velocity up to 0.18m/s without flooding. A strong dependence of theseparation efficiency on the column pre-treatmentprocedure was found. The developed pre-treat-ment procedure allows reducing HETP aboutthree times. Some experimental data are presentedin Ref. [4].

The values of HETP were usually determined atthe gas flow rate close to the flooding. Thanks tosample points between the separation sections,one can calculate the efficiency of each section. Itis interesting to note that, although the packing ofthe separation section was identical, the efficiencyof the lower section was higher than that of theupper section. Perhaps, it is due to continuousactivation of catalytic beds in the lower section byoxygen admixture in hydrogen from electrolyticcell during the plant operation. Fig. 2 presents theeffect of the temperature on HETP. HETP re-duces as the temperature is increased. It should benoted that the values of HETP determined in ourwork are nearly the same as in the 28-mm diame-ter column [2] and much lower than that obtainedin 48-mm diameter column by Malhotra et al. [6].

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Fig. 3. System’s parameters relative deviations from face values.

No loss of separation efficiency was observedduring 2700 h of the plant operation. Then deteri-oration in performance was found. Separationefficiency was recovered to the initial one byreactivation of the catalyst. The reactivation pro-cedure consists of feeding dry nitrogen with ap-proximately 0.1% oxygen and then dry hydrogenwith about 0.01% oxygen to the column during100 h.

The plant operation is semiautomatic. Person-nel are required to carry out various adjustmentsand analyses. Two persons ensure operation. Theautomatic control system of the plant has beendeveloped. Besides monitoring of the parameters,the system provides automatic maintenance of thefeed liquid flow discharge to the isotope exchangecolumn with accuracy not worse than 1%. Realwork of the computerized process control systemis shown in Fig. 3. Relative deviations from ratedvalues of process parameters are within 0.4% overa period of 2 h.

At present, operation of the plant is continu-ous. The total operation time of the plant is morethan 12000 h, and several tons of heavy water andconsiderable quantity of deuterium have beenproduced.

5. Conclusion

The tests of the plant have shown a high effi-ciency of isotope separation. At a temperaturewithin 330–350 K and a pressure of 0.128–0.166MPa, the values of HETP are within a range of20–30 cm. The maximum permissible gas linearvelocity in the column is 0.18 m/sec. The operat-ing experience allows considering the CECE pro-cess as a significant promise for the industrial use,in particular, for processing of tritiated waterwastes with a high degree of purification fromtritium. The CECE process will be used at theDetritiation Plant being developed at PetersburgNuclear Physics Institute for tritium and protiumextraction from heavy water of PIK reactor. Thisprocess can find an application at the ITER fu-sion facility.

References

[1] D. Spagnolo, A.I. Miller, The CECE alternative for up-grading/detritiation in heavy water nuclear reactors andfor tritium recovery in fusion reactors, Fusion Technology28 (1995) 748–754.

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[2] B.M. Andreev, Y.A. Sakharovsky, et al., Installation forseparation of hydrogen isotopes by the method of chemi-cal isotopic exchange in the ‘water–hydrogen’ system,Fusion Technology 28 (1995) 515–518.

[3] V.D. Trenin et al., Experimental industrial plant forthe studies and development of reprocessing tech-nology of tritiated water wastes, in: Proceedings of 20thSOFT, Marseilles, Fusion Technology, 1998, pp. 963–966.

[4] I.A. Alekseev et al., The study of CECE process at theexperimental industrial plant, in: Proceedings of the 20th

Symposium on Fusion Technology, Marseilles, FusionTechnology, 1998, pp. 959–962.

[5] O.A. Fedorchenko, et al., Computer simulation of thewater and hydrogen distillation and CECE process andits experimental verification, Fusion Technology 28(1995) 1485–1490.

[6] S.K. Malhotra, M.S. Krishnan, H.K. Sadhukhan, Com-bined electrolysis and catalytic exchange: operation of asingle stage, in: Proceedings of National Symposium onHeavy Water Technology, Bhabha Atomic ResearchCentre, 1989, pp. PD6.