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Operating experience of the experimental industrial plant for reprocessing of tritiated water wastes
Fusion Engineering and Design 58 – 59 (2001) 439– 443 www.elsevier.com/locate/fusengdes
Operating experience of the experimental industrial plant for reprocessing 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, Russia b JSC ‘DOL’, Moscow, Russia
Abstract The results of 5-year operation of the experimental industrial plant for hydrogen isotope separation using combined electrolysis and catalytic exchange (CECE) process are presented. The plant is used for large-scale studies of CECE process and for reprocessing tritiated heavy water wastes. The main parts of the plant are a 100-mm diameter exchange column of 6.9 m overall height, alkaline electrolytic cells and catalytic burners. The separation performance of the column was determined. The computer code makes it possible to carry out the calculation over a wide range of 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 and allows regarding CECE process as a considerable promise for the industrial use, in particular, for water purification from tritium. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Tritiated water wastes; Hydrogen isotope separation; Combined electrolysis and catalytic exchange
1. Introduction The problem of high purification of heavy water and light water wastes from tritium has remained unsolved because of the lack of the convenient processing technology. The combined electrolysis catalytic exchange (CECE) process utilizing wetproofed catalyst is the most attractive one for extracting tritium from water due to its high separation factors and near-ambient operat* Corresponding author. Tel./Fax: + 7-812-7131-985. E-mail address: [email protected] (I.A. Alekseev).
ing conditions. This process is regarded as an alternative for detritiation in comparison to conventional water distillation (DW) and vapour phase catalytic exchange (VPCE) processes in the ITER isotope separation system [1,2]. The tests of a pilot plant operating at various modes can adduce evidence of practical applicability of this method for tritium recovery. An experimental industrial plant for hydrogen isotope separation using CECE process has been built in Petersburg Nuclear Physics Institute in co-operation with JSC ‘DOL’ and D. Mendeleyev University of Chemical Technology of Russia [2–
0920-3796/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 0 - 3 7 9 6 ( 0 1 ) 0 0 4 8 6 - 0
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I.A. Aleksee6 et al. / Fusion Engineering and Design 58–59 (2001) 439–443
4]. The plant is designed for carrying out largescale studies of the CECE process in a wide range of parameters, for producing commercial heavy water from heavy water wastes, and for recovery of tritium from water. The paper presents the results of 5-year operating experience of the plant.
2. Design data and principle of operation The schematic flow diagram of the plant is presented in Fig. 1. The chemical exchange column of 6.9 m overall height and an inner diameter of 100 mm is filled with alternating layers of wetproofed catalyst and stainless steel spiral-prismatic packing. The column consists of three separation sections connected through a distributor of liquid. Each section is provided with a heating water jacket for maintaining the column temperature within 300– 360 K. The operating pressure is 0.13– 0.4 MPa. The sections of the column are bolted together. This enables an easy replacement of catalyst and packing to improve the inner structure of the sections. The feed points (FP) and sample points (SP) are located between the separation sections, at the top and at the bottom of the column. The overall
separation height of the column is 5.2 m. The wetproofed catalyst used has been developed by the D. Mendeleyev University of Chemical Technology of Russia. It consists of 0.8 wt.% platinum deposited on porous polysorb (styrene–divinylbenzene copolymer) [2]. The plant uses alkaline electrolytic cells as a lower reflux device and hydrogen catalytic burners as an upper reflux device. The hydrogen output of electrolytic cells is 5 m3/h. All equipment of the plant was manufactured in Russia. The schematic diagram of the plant is presented in detail in Ref. [3]. The risks of explosion and radioactive contamination formed the basic criteria for the design, construction and operation of the plant. The main equipment of the plant is located in the room specially provided for the operation under hydrogen and tritium conditions. The main results were obtained at the steadystate mode of operation of the plant during processing diluted heavy water. The feed flow containing about 47% deuterium and 108 Bq/kg tritium is injected into the column feed point FP3. Heavy water concentrated up to 99.85– 99.995 is withdrawn from the bottom as a liquid. The top product containing less than 1% deuterium is withdrawn as liquid when the catalytic burners are operated, or as hydrogen when natural water is fed to the top of the column as reflux. The tritium concentration in the top product is less than 105 Bq/kg. The separation performance of the column was determined by accurately measuring the deuterium and tritium concentration in water and gas from different sample points. The samples of heavy water were analysed by the IR-spectrophotometer, and gas samples by gas chromatography. Tritium was measured by the liquid scintillation method.
3. Methods of separation performance estimation
Fig. 1. The schematic flow diagram of the plant.
The separation performance of the exchange column was determined by two different methods. The first method considers the separation process in the column as a counter-current exchange process between liquid water and hydrogen–water
I.A. Aleksee6 et al. / Fusion Engineering and Design 58–59 (2001) 439–443
vapour mixture. The values of height equivalent to a theoretical plate (HETP) were determined at a steady-state mode under various conditions. The dependence of separation factors on temperature and deuterium concentration was taken into account. Another way of looking at this process is proposed also. Simulation code ‘EVIO-3’ (one of descendants of the code ‘KIO’ [5]) deals with three streams (liquid water, water vapour and hydrogen gas) and with six components. Dependency of temperature and concentration on separation factors is incorporated. The Murphree-type factors are introduced in the code to consider the efficiency of both scrubbing and catalyst layers. Two constants which define each of the factors for catalyst and scrubbing layers are reverse reaction velocity constants of hydrogen/vapour catalytic exchange and water/vapour phase exchange, respectively. The code provides stable and relatively rapid computation of a concentration profile if values of both constants are known. However, some uncertainties have not allowed so far to solve the inverse problem that is, unique determination of these constants if the concentration profile is experimentally known. This fact is the only reason why values of the constants are not presented here. Nevertheless, ‘EVIO-3’ allows now correct forecasting a concentration profile within the column operated under conditions (temperature, pressure, values of water and gas flow rates) different from those under which these two constants are ‘measured’. And what is more, the numerical analysis on the base of the code ‘EVIO-3’ agrees with experimental data over a wide range of conditions.
4. Start-up of the plant and operational experience The first tests of the plant as a whole began in November 1995. The tests of the separation column were carried out at various operation modes. The temperature, pressure, gas flow rate, manner of a column filling were varied. The hydraulic and separation characteristics of the isotope exchange column have been investigated.
441
Fig. 2. Effect of the temperature on the HETP.
During the initial tests, satisfactory separation and hydraulic performance was not achieved. It was found that the manner how the column was filled affected significantly the limiting hydrogen flow rate. The change of the column filling allowed increasing the gas flow velocity up to 0.18 m/s without flooding. A strong dependence of the separation efficiency on the column pre-treatment procedure was found. The developed pre-treatment procedure allows reducing HETP about three times. Some experimental data are presented in Ref. [4]. The values of HETP were usually determined at the gas flow rate close to the flooding. Thanks to sample points between the separation sections, one can calculate the efficiency of each section. It is interesting to note that, although the packing of the separation section was identical, the efficiency of the lower section was higher than that of the upper section. Perhaps, it is due to continuous activation of catalytic beds in the lower section by oxygen admixture in hydrogen from electrolytic cell during the plant operation. Fig. 2 presents the effect of the temperature on HETP. HETP reduces as the temperature is increased. It should be noted that the values of HETP determined in our work are nearly the same as in the 28-mm diameter column [2] and much lower than that obtained in 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 observed during 2700 h of the plant operation. Then deterioration in performance was found. Separation efficiency was recovered to the initial one by reactivation of the catalyst. The reactivation procedure consists of feeding dry nitrogen with approximately 0.1% oxygen and then dry hydrogen with about 0.01% oxygen to the column during 100 h. The plant operation is semiautomatic. Personnel are required to carry out various adjustments and analyses. Two persons ensure operation. The automatic control system of the plant has been developed. Besides monitoring of the parameters, the system provides automatic maintenance of the feed liquid flow discharge to the isotope exchange column with accuracy not worse than 1%. Real work of the computerized process control system is shown in Fig. 3. Relative deviations from rated values of process parameters are within 0.4% over a period of 2 h. At present, operation of the plant is continuous. The total operation time of the plant is more than 12000 h, and several tons of heavy water and considerable quantity of deuterium have been produced.
5. Conclusion The tests of the plant have shown a high efficiency of isotope separation. At a temperature within 330–350 K and a pressure of 0.128–0.166 MPa, the values of HETP are within a range of 20–30 cm. The maximum permissible gas linear velocity in the column is 0.18 m/sec. The operating experience allows considering the CECE process as a significant promise for the industrial use, in particular, for processing of tritiated water wastes with a high degree of purification from tritium. The CECE process will be used at the Detritiation Plant being developed at Petersburg Nuclear Physics Institute for tritium and protium extraction from heavy water of PIK reactor. This process can find an application at the ITER fusion facility.
References [1] D. Spagnolo, A.I. Miller, The CECE alternative for upgrading/detritiation in heavy water nuclear reactors and for tritium recovery in fusion reactors, Fusion Technology 28 (1995) 748 – 754.
I.A. Aleksee6 et al. / Fusion Engineering and Design 58–59 (2001) 439–443 [2] B.M. Andreev, Y.A. Sakharovsky, et al., Installation for separation of hydrogen isotopes by the method of chemical isotopic exchange in the ‘water–hydrogen’ system, Fusion Technology 28 (1995) 515 –518. [3] V.D. Trenin et al., Experimental industrial plant for the studies and development of reprocessing technology of tritiated water wastes, in: Proceedings of 20th SOFT, Marseilles, Fusion Technology, 1998, pp. 963 – 966. [4] I.A. Alekseev et al., The study of CECE process at the experimental industrial plant, in: Proceedings of the 20th
443
Symposium on Fusion Technology, Marseilles, Fusion Technology, 1998, pp. 959 – 962. [5] O.A. Fedorchenko, et al., Computer simulation of the water and hydrogen distillation and CECE process and its experimental verification, Fusion Technology 28 (1995) 1485 – 1490. [6] S.K. Malhotra, M.S. Krishnan, H.K. Sadhukhan, Combined electrolysis and catalytic exchange: operation of a single stage, in: Proceedings of National Symposium on Heavy Water Technology, Bhabha Atomic Research Centre, 1989, pp. PD6.
Operating experience of the experimental industrial plant for reprocessing 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, Russia b JSC ‘DOL’, Moscow, Russia
Abstract The results of 5-year operation of the experimental industrial plant for hydrogen isotope separation using combined electrolysis and catalytic exchange (CECE) process are presented. The plant is used for large-scale studies of CECE process and for reprocessing tritiated heavy water wastes. The main parts of the plant are a 100-mm diameter exchange column of 6.9 m overall height, alkaline electrolytic cells and catalytic burners. The separation performance of the column was determined. The computer code makes it possible to carry out the calculation over a wide range of 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 and allows regarding CECE process as a considerable promise for the industrial use, in particular, for water purification from tritium. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Tritiated water wastes; Hydrogen isotope separation; Combined electrolysis and catalytic exchange
1. Introduction The problem of high purification of heavy water and light water wastes from tritium has remained unsolved because of the lack of the convenient processing technology. The combined electrolysis catalytic exchange (CECE) process utilizing wetproofed catalyst is the most attractive one for extracting tritium from water due to its high separation factors and near-ambient operat* Corresponding author. Tel./Fax: + 7-812-7131-985. E-mail address: [email protected] (I.A. Alekseev).
ing conditions. This process is regarded as an alternative for detritiation in comparison to conventional water distillation (DW) and vapour phase catalytic exchange (VPCE) processes in the ITER isotope separation system [1,2]. The tests of a pilot plant operating at various modes can adduce evidence of practical applicability of this method for tritium recovery. An experimental industrial plant for hydrogen isotope separation using CECE process has been built in Petersburg Nuclear Physics Institute in co-operation with JSC ‘DOL’ and D. Mendeleyev University of Chemical Technology of Russia [2–
0920-3796/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 0 - 3 7 9 6 ( 0 1 ) 0 0 4 8 6 - 0
440
I.A. Aleksee6 et al. / Fusion Engineering and Design 58–59 (2001) 439–443
4]. The plant is designed for carrying out largescale studies of the CECE process in a wide range of parameters, for producing commercial heavy water from heavy water wastes, and for recovery of tritium from water. The paper presents the results of 5-year operating experience of the plant.
2. Design data and principle of operation The schematic flow diagram of the plant is presented in Fig. 1. The chemical exchange column of 6.9 m overall height and an inner diameter of 100 mm is filled with alternating layers of wetproofed catalyst and stainless steel spiral-prismatic packing. The column consists of three separation sections connected through a distributor of liquid. Each section is provided with a heating water jacket for maintaining the column temperature within 300– 360 K. The operating pressure is 0.13– 0.4 MPa. The sections of the column are bolted together. This enables an easy replacement of catalyst and packing to improve the inner structure of the sections. The feed points (FP) and sample points (SP) are located between the separation sections, at the top and at the bottom of the column. The overall
separation height of the column is 5.2 m. The wetproofed catalyst used has been developed by the D. Mendeleyev University of Chemical Technology of Russia. It consists of 0.8 wt.% platinum deposited on porous polysorb (styrene–divinylbenzene copolymer) [2]. The plant uses alkaline electrolytic cells as a lower reflux device and hydrogen catalytic burners as an upper reflux device. The hydrogen output of electrolytic cells is 5 m3/h. All equipment of the plant was manufactured in Russia. The schematic diagram of the plant is presented in detail in Ref. [3]. The risks of explosion and radioactive contamination formed the basic criteria for the design, construction and operation of the plant. The main equipment of the plant is located in the room specially provided for the operation under hydrogen and tritium conditions. The main results were obtained at the steadystate mode of operation of the plant during processing diluted heavy water. The feed flow containing about 47% deuterium and 108 Bq/kg tritium is injected into the column feed point FP3. Heavy water concentrated up to 99.85– 99.995 is withdrawn from the bottom as a liquid. The top product containing less than 1% deuterium is withdrawn as liquid when the catalytic burners are operated, or as hydrogen when natural water is fed to the top of the column as reflux. The tritium concentration in the top product is less than 105 Bq/kg. The separation performance of the column was determined by accurately measuring the deuterium and tritium concentration in water and gas from different sample points. The samples of heavy water were analysed by the IR-spectrophotometer, and gas samples by gas chromatography. Tritium was measured by the liquid scintillation method.
3. Methods of separation performance estimation
Fig. 1. The schematic flow diagram of the plant.
The separation performance of the exchange column was determined by two different methods. The first method considers the separation process in the column as a counter-current exchange process between liquid water and hydrogen–water
I.A. Aleksee6 et al. / Fusion Engineering and Design 58–59 (2001) 439–443
vapour mixture. The values of height equivalent to a theoretical plate (HETP) were determined at a steady-state mode under various conditions. The dependence of separation factors on temperature and deuterium concentration was taken into account. Another way of looking at this process is proposed also. Simulation code ‘EVIO-3’ (one of descendants of the code ‘KIO’ [5]) deals with three streams (liquid water, water vapour and hydrogen gas) and with six components. Dependency of temperature and concentration on separation factors is incorporated. The Murphree-type factors are introduced in the code to consider the efficiency of both scrubbing and catalyst layers. Two constants which define each of the factors for catalyst and scrubbing layers are reverse reaction velocity constants of hydrogen/vapour catalytic exchange and water/vapour phase exchange, respectively. The code provides stable and relatively rapid computation of a concentration profile if values of both constants are known. However, some uncertainties have not allowed so far to solve the inverse problem that is, unique determination of these constants if the concentration profile is experimentally known. This fact is the only reason why values of the constants are not presented here. Nevertheless, ‘EVIO-3’ allows now correct forecasting a concentration profile within the column operated under conditions (temperature, pressure, values of water and gas flow rates) different from those under which these two constants are ‘measured’. And what is more, the numerical analysis on the base of the code ‘EVIO-3’ agrees with experimental data over a wide range of conditions.
4. Start-up of the plant and operational experience The first tests of the plant as a whole began in November 1995. The tests of the separation column were carried out at various operation modes. The temperature, pressure, gas flow rate, manner of a column filling were varied. The hydraulic and separation characteristics of the isotope exchange column have been investigated.
441
Fig. 2. Effect of the temperature on the HETP.
During the initial tests, satisfactory separation and hydraulic performance was not achieved. It was found that the manner how the column was filled affected significantly the limiting hydrogen flow rate. The change of the column filling allowed increasing the gas flow velocity up to 0.18 m/s without flooding. A strong dependence of the separation efficiency on the column pre-treatment procedure was found. The developed pre-treatment procedure allows reducing HETP about three times. Some experimental data are presented in Ref. [4]. The values of HETP were usually determined at the gas flow rate close to the flooding. Thanks to sample points between the separation sections, one can calculate the efficiency of each section. It is interesting to note that, although the packing of the separation section was identical, the efficiency of the lower section was higher than that of the upper section. Perhaps, it is due to continuous activation of catalytic beds in the lower section by oxygen admixture in hydrogen from electrolytic cell during the plant operation. Fig. 2 presents the effect of the temperature on HETP. HETP reduces as the temperature is increased. It should be noted that the values of HETP determined in our work are nearly the same as in the 28-mm diameter column [2] and much lower than that obtained in 48-mm diameter column by Malhotra et al. [6].
442
I.A. Aleksee6 et al. / Fusion Engineering and Design 58–59 (2001) 439–443
Fig. 3. System’s parameters relative deviations from face values.
No loss of separation efficiency was observed during 2700 h of the plant operation. Then deterioration in performance was found. Separation efficiency was recovered to the initial one by reactivation of the catalyst. The reactivation procedure consists of feeding dry nitrogen with approximately 0.1% oxygen and then dry hydrogen with about 0.01% oxygen to the column during 100 h. The plant operation is semiautomatic. Personnel are required to carry out various adjustments and analyses. Two persons ensure operation. The automatic control system of the plant has been developed. Besides monitoring of the parameters, the system provides automatic maintenance of the feed liquid flow discharge to the isotope exchange column with accuracy not worse than 1%. Real work of the computerized process control system is shown in Fig. 3. Relative deviations from rated values of process parameters are within 0.4% over a period of 2 h. At present, operation of the plant is continuous. The total operation time of the plant is more than 12000 h, and several tons of heavy water and considerable quantity of deuterium have been produced.
5. Conclusion The tests of the plant have shown a high efficiency of isotope separation. At a temperature within 330–350 K and a pressure of 0.128–0.166 MPa, the values of HETP are within a range of 20–30 cm. The maximum permissible gas linear velocity in the column is 0.18 m/sec. The operating experience allows considering the CECE process as a significant promise for the industrial use, in particular, for processing of tritiated water wastes with a high degree of purification from tritium. The CECE process will be used at the Detritiation Plant being developed at Petersburg Nuclear Physics Institute for tritium and protium extraction from heavy water of PIK reactor. This process can find an application at the ITER fusion facility.
References [1] D. Spagnolo, A.I. Miller, The CECE alternative for upgrading/detritiation in heavy water nuclear reactors and for tritium recovery in fusion reactors, Fusion Technology 28 (1995) 748 – 754.
I.A. Aleksee6 et al. / Fusion Engineering and Design 58–59 (2001) 439–443 [2] B.M. Andreev, Y.A. Sakharovsky, et al., Installation for separation of hydrogen isotopes by the method of chemical isotopic exchange in the ‘water–hydrogen’ system, Fusion Technology 28 (1995) 515 –518. [3] V.D. Trenin et al., Experimental industrial plant for the studies and development of reprocessing technology of tritiated water wastes, in: Proceedings of 20th SOFT, Marseilles, Fusion Technology, 1998, pp. 963 – 966. [4] I.A. Alekseev et al., The study of CECE process at the experimental industrial plant, in: Proceedings of the 20th
443
Symposium on Fusion Technology, Marseilles, Fusion Technology, 1998, pp. 959 – 962. [5] O.A. Fedorchenko, et al., Computer simulation of the water and hydrogen distillation and CECE process and its experimental verification, Fusion Technology 28 (1995) 1485 – 1490. [6] S.K. Malhotra, M.S. Krishnan, H.K. Sadhukhan, Combined electrolysis and catalytic exchange: operation of a single stage, in: Proceedings of National Symposium on Heavy Water Technology, Bhabha Atomic Research Centre, 1989, pp. PD6.