- Email: [email protected]
Software development for the simulation and design of the cryogenic distillation cascade used for hydrogen isotope separation
G Model
ARTICLE IN PRESS
FUSION-8484; No. of Pages 4
Fusion Engineering and Design xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Software development for the simulation and design of the cryogenic distillation cascade used for hydrogen isotope separation Mirela Mihaela Draghia ∗ , Gheorghe Pasca, Florina Porcariu SC I.S.TECH SRL, Timocului Street, No. 21, 300107 Timisoara, Romania
h i g h l i g h t s • Software for designing and simulation of a cryogenic distillation cascade. • The simulation provides the distribution of all the molecular species involved along each cryogenic distillation column and also the temperature profile along the columns.
• Useful information that are relevant for ITER Isotope Separation System.
a r t i c l e
i n f o
Article history: Received 22 August 2015 Received in revised form 7 January 2016 Accepted 21 January 2016 Available online xxx Keywords: Hydrogen isotopes separation Tritium Cryogenic distillation Simulation software
a b s t r a c t The hydrogen isotope separation system (ISS) based on cryogenic distillation is one of the key systems of the fuel cycle of a fusion reactor. Similar with ITER ISS in a Water Detritiation Facility for a CANDU reactor, one of the main systems is cryogenic distillation. The developments on the CANDU water detritiation systems have shown that a cascade of four cryogenic distillation columns is required in order to achieve the required decontamination factor of the heavy water and a tritium enrichment up to 99.9%. This paper aims to present the results of the design and simulation activities in support to the development of the Cernavoda Tritium Removal Facility (CTRF). Beside the main features of software developed “in house”, an introduction to the main relevant issues of a CANDU tritium removal facility for the ITER ISS is provided as well. Based on the input data (e.g. the flow rates, the composition of the gas supplied into the cryogenic distillation cascade, pressure drop along the column, liquid inventory) the simulation provides the distribution of all the molecular species involved along each cryogenic distillation column and also the temperature profile along the columns. The approach for the static and dynamic simulation of a cryogenic distillation process is based on theoretical plates model and the calculations are performed incrementally plate by plate. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Cryogenic distillation is preferred to other methods of gas separation at industrial scale because it has the advantage of high separation factors, the possibility to process large amounts of gas while obtaining high purity gases [1,2]. Similar with the conventional distillation processes, separation by cryogenic distillation is carried out by mass and heat transfer between vapour and liquid phases that flow in countercurrent. The cryogenic distillation column comprises a boiler that produces the
∗ Corresponding author. Tel.: +40 771218101; fax: +40 356173660. E-mail address: [email protected] (M.M. Draghia).
necessary amount of vapours along the column, plates or package where the isotopic transfer between the vapours and liquid take place and a condenser that provides the liquid reflux along the cryogenic distillation column. In the case of multi-component gas mixtures, determining the transport of the molecular species between the two phases is difficult due to the dependence of the physical-chemical properties of each mixture component. The transport of the molecular species is strongly influenced by the hydrodynamics of the two phases, closely connected with the size of the exchange interface. The vapoliquid interface depends on the constructive characteristics of the separation medium: plates or package. In addition, in the case of hydrogen isotopes mixtures, the problem is complicated by the non-idealities in the thermodynamic properties near the saturation curve at low temperatures [3–6].
http://dx.doi.org/10.1016/j.fusengdes.2016.01.044 0920-3796/© 2016 Elsevier B.V. All rights reserved.
Please cite this article in press as: M.M. Draghia, et al., Software development for the simulation and design of the cryogenic distillation cascade used for hydrogen isotope separation, Fusion Eng. Des. (2016), http://dx.doi.org/10.1016/j.fusengdes.2016.01.044
G Model FUSION-8484; No. of Pages 4 2
ARTICLE IN PRESS M.M. Draghia et al. / Fusion Engineering and Design xxx (2016) xxx–xxx
The model presented in this paper can be used for the design of a cryogenic distillation facility and is based on a traditional analysis model of the exchange process, but is applied to the low temperatures range which is specific to hydrogen and its isotopes. The software developed based on this model is designed for a water detritiation facility employing isotopic catalytic exchange and cryogenic distillation. 2. The model for a cryogenic distillation column The software was developed for simulation and design of a cryogenic distillation cascade for hydrogen isotopes separation. The usual approach for dynamic simulation of a packed column is to adopt the theoretical plate model and carry out stage-by-stage calculations [8,9]. The model equations are based on mass, species and energy balances around each stage. A schematic representation of three general stages in series is shown in Fig. 1. Each stage is a theoretical plate where stage 1 is a condenser and stage N is the reboiler. The “n ” and “ln ” in Fig. 1 are the vapour and liquid flow rates leaving stage n. There are assumed to be species. (For hydrogen isotope distillation, the species are H2 , HD, HT, D2 , DT and T2 .) The vapour flows to the previous stage n − 1 and the liquid flows to the next stage n + 1. - “l dn,i ” and “v dn,i ” are the extraction flow rates for the component i, for vapours, respectively, liquid; f f - “l n,i ” and “v n,i ” are the supply flow rates for the component i, for vapours, respectively, liquid. Following additional simplifying assumptions have been considered: 1. the pressure drop across the column is negligible; 2. the column is adiabatic;
3. the molar holdup in each stage is constant throughout a given time interval; The overall mass balance and heat balance equations are described as follows: f
f
n+1 − ln = −ln−1 + n − ln − n + lnd + nd vap Hn+1 n+1
liq − Hn ln
f,liq f ln
− Hn
=
liq −Hn−1 ln−1
f,vap f n
− Hn
(1)
vap + Hn n
liq
vap
+ Hn lnd + Hn nd
(2)
ˇ
− En − En
ˇ
where Hn is the total enthalpy in stage n, En is the radioactive decay heating rate in stage n and En is the cooling/heating power in the condenser/reboiler. For the dynamic simulation, component material balance equations are developed by performing a component flow rate balance around each stage n. For the general stage, the component mass balance is:
∂qn,i = n+1,i + ln−1,i − n,i − ln,i ∂t f
(3)
f
d − d + ln,i + n,i − ln,i n,i
where qn,i is the holdup of component i in stage n. The heat balance for the general stage in terms of material flows, heating or cooling, and tritium decay heat effects is:
∂Hn liq liq = Hn−1 ln−1 − Hn ln + lnd ∂t vap
− Hn
f,vap f n
+ Hn
vap
f,liq f ln
n + nd + Hn+1 n+1 + Hn
(4)
ˇ
+ En + En
Equations of energy mass balance and calculation of the flow rates begin with the condenser, and continue with the next plates down to the bottom of the column. For each plate the equations of energy and mass balance are considered. The reboiler duty is calculated using the heat exchange equation for the last plate. 3. Cryogenic distillation cascade design
Fig. 1. Schematic representation of three distillation column stages.
Depending of the input data (e.g. the flow rate and the composition of the gas supplied into the cryogenic distillation cascade) the simulation provides the temperature and concentrations profiles along the columns. Using the simulation results as input data, a cryogenic distillation cascade of four columns for the Cernavoda Tritium Removal Facility was designed. The cascade configuration and the supply and withdrawn streams for each column can be seen in Fig. 2. The cryogenic distillation cascade is designed for the separation and enrichment of tritium from the tritiated deuterium supplied from the Liquid Phase Catalytic Exchange (LPCE) system, and to transfer the enriched tritium to the Tritium Gas Handling and Storage System (TGHSS). The first cryogenic distillation column is the largest column due to the separation requirements and has the largest feeding flow rate. Due to this reason the condenser of the first column shall provide the higher cooling capacity of the cascade. In order to reduce operating costs, the reboiler of the first column is designed to operate as a heat pump. For the other three distillation columns, electrical heaters can be implemented as reboilers. In order to produce tritium concentration of 99% T/(H + D + T) in the bottom of the fourth column it is necessary to generate T2
Please cite this article in press as: M.M. Draghia, et al., Software development for the simulation and design of the cryogenic distillation cascade used for hydrogen isotope separation, Fusion Eng. Des. (2016), http://dx.doi.org/10.1016/j.fusengdes.2016.01.044
G Model
ARTICLE IN PRESS
FUSION-8484; No. of Pages 4
M.M. Draghia et al. / Fusion Engineering and Design xxx (2016) xxx–xxx
3
Fig. 2. Cryogenic distillation cascade diagram.
molecular specie along the fourth cryogenic distillation column. Therefore, the dynamic simulation model was use to design the fourth column and to establish the location of the chemical equilibrator which generate T2 molecular species out of reaction: 2DT ↔ D2 + T2 In addition, a detailed investigation has been carry-out aiming to minimize the tritium inventory in the fourth column. 4. Dynamic simulation of the column with the highest tritium concentration The most important activities for the design of the entire cryogenic distillation cascade are concerning the minimization of explosion hazard and consequently reducing the hydrogen inventory in the cascade. Based on the calculation using the dynamic simulation model, an optimization of the cryogenic distillation cascade has been carry-out, and the hydrogen and tritium inventory have been minimized. In Table 1 the distribution of the tritium and hydrogen inventories of the cryogenic distillation columns of the cascade is shown. The percentages of each column are relative to the total inventory of cascade in normal operating conditions. The reduction of hydrogen inventory is primarily an issue for the design of the heat pump since the reflux ration has not significant impact on the inventory. The tritium inventory in the cascade depends mostly by the diameter of the last column and the design of the boiler. Therefore, the tritium inventory was minimized considering the cooling capacity as parameter and calculating the
Table 1 Tritium and hydrogen inventories in the cryogenic distillation columns. Columns
Hydrogen inventory [%]
Tritium inventory [%]
Column 1 Column 2 Column 3 Column 4
95.23 4.34 0.33 0.1
7.80 1.75 2.87 87.58
inventory dependence upon the length of the column needed to achieve the 99% tritium concentration in the bottom of the column. The dynamic simulation software has been also used to estimate the time required to reach steady state into the entire cryogenic distillation cascade and in particular to find out when tritium concentration reach more than 99% T/(H + D + T) in the bottom of the fourth column. The dynamic simulation software provides time variation of all parameters/concentrations along the cascade. In Fig. 3 the concentration profiles along the column 4 at steady state are shown. The main hazard of the CTRF is related to the deuterium explosion due to the large amount of deuterium in the first column. In the heat pump from the boiler of the first column it is envisaged that more than 50 l of liquid deuterium will be collected and quite the same amount in the liquid redistributors and the packing along the column. As far as tritium hazard is concerned, the column four contains most of the inventory and therefore the design shall include provision for tritium recovery in any events that may lead to tritium release. In order to quantify the tritium inventory in the cascade columns, on-line measurements of tritium concentration in the deuterium streams circulated between the cryogenic distillation columns are foreseen. Due to the major inventory from the fourth column, for this column many measurements were foreseen: - monitoring of the tritium concentration in the deuterium tritiated flow extracted from the fourth column to the equilibration loop and returned back to the fourth column; - monitoring the tritium concentration in the flow extracted from the fourth column to the Tritium Gas Handling and Storage System (TGHSS); - monitoring of the tritium concentration in the flow extracted from the fourth column to the high tritium expansion tank. It is proposed to use a Laser-Raman spectrometer that allows the required type of accuracy. The dynamic of tritium separation and accumulation in the fourth column of a tritium removal facility for a CANDU reactor is slow in comparison with the tritium behaviour in the cryogenic
Please cite this article in press as: M.M. Draghia, et al., Software development for the simulation and design of the cryogenic distillation cascade used for hydrogen isotope separation, Fusion Eng. Des. (2016), http://dx.doi.org/10.1016/j.fusengdes.2016.01.044
G Model FUSION-8484; No. of Pages 4
ARTICLE IN PRESS M.M. Draghia et al. / Fusion Engineering and Design xxx (2016) xxx–xxx
4
Fig. 3. Dynamic of the hydrogen species in the column 4.
distillation cascade of a fusion device. Nevertheless, useful information can be collected concerning the dynamic of a cryogenic distillation process when more than two molecular species are involved. Comparison between the predicted evolution of the D2 , DT and T2 along the fourth cryogenic distillation column and the experimental data will be used for the enhancement and eventually validation of the dynamic software used for the design of the Cernavoda Tritium Removal Facility [7]. The accuracy of the Laser Raman spectrometer is high enough as far as dynamic of the cryogenic distillation process of the fourth column is concerned. The dynamic simulation showed that the accumulation of almost the entire tritium inventory in the fourth column requires about 280 h. 5. Conclusions Dynamic simulation software has been developed and used for the design of the cryogenic distillation cascade of the Tritium Removal Facility for the Cernavoda NPP. The tritium accumulation in the fourth column of the cascade and the time behaviour of the D2 , DT and DT molecular species may give useful information as far as dynamic separation of the multicomponent mixtures that are relevant for ITER Isotope Separation System. Measuring the isotopic concentrations at the sampling points of the last cryogenic distillation column will provide better understanding concerning
the time behaviour of the separation process. The measured compositions will be compared with the predicted values provided by the simulation software that will allow calibration of the software and provide support for the software enhancement, if necessary identified. References [1] D. Murdoch, I. Cristescu, C. Day, M. Glugla, R. Laesser, A. Mack, EU Fuel cycle development priorities for ITER, Fusion Eng. Des. 82 (2007) 2158–2163. [2] I. Cristescu, I.R. Cristescu, L. Dörr, G. Hellriegel, R. Michling, D. Murdoch, P. Schaefer, S. Welte, W. Wurster, Experiments on water detritiation and cryogenic distillation at TLK; Impact on ITER fuel cycle subsystems interfaces, Fusion Sci. Technol. 54 (2008) 440–445. [3] P.C. Souers, Cryogenic hydrogen data pertinent to magnetic fusion energy, in: UCRL-52628, 1979. [4] P.C. Souers, Hydrogen Properties for Fusion Energy, University of California Press, Oakland, 1986. [5] I. Prigogine, The Molecular Theory of Solutions, North-Holland Publishing Company, Amsterdam, 1957. [6] A. Farkas, Ortohydrogen, Parahydrogen and Heavy Hydrogen, Cambridge University Press, Oxford, 1935. [7] I. Cristescu, D. Demange, R. Michling, Design and R&D activities of TriPla-CA consortium in support of ITER Tritium Plant development, Fusion Eng. Des. 89 (2014) 1524–1528. [8] T. Yamanishi, K. Okuno, Mass transfer in cryogenic distillation column separating hydrogen isotopes, J. Nucl. Sci. Technol. 31 (6) (1994) 562–571. [9] M. Kinoshita, Y. Naruse, Separation characteristics of cryogenic distillation column with a feedback stream for separation of protium tritium systems and tritium, J. Nucl. Sci. Technol. 2 (1982) 410–425.
Please cite this article in press as: M.M. Draghia, et al., Software development for the simulation and design of the cryogenic distillation cascade used for hydrogen isotope separation, Fusion Eng. Des. (2016), http://dx.doi.org/10.1016/j.fusengdes.2016.01.044
ARTICLE IN PRESS
FUSION-8484; No. of Pages 4
Fusion Engineering and Design xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Software development for the simulation and design of the cryogenic distillation cascade used for hydrogen isotope separation Mirela Mihaela Draghia ∗ , Gheorghe Pasca, Florina Porcariu SC I.S.TECH SRL, Timocului Street, No. 21, 300107 Timisoara, Romania
h i g h l i g h t s • Software for designing and simulation of a cryogenic distillation cascade. • The simulation provides the distribution of all the molecular species involved along each cryogenic distillation column and also the temperature profile along the columns.
• Useful information that are relevant for ITER Isotope Separation System.
a r t i c l e
i n f o
Article history: Received 22 August 2015 Received in revised form 7 January 2016 Accepted 21 January 2016 Available online xxx Keywords: Hydrogen isotopes separation Tritium Cryogenic distillation Simulation software
a b s t r a c t The hydrogen isotope separation system (ISS) based on cryogenic distillation is one of the key systems of the fuel cycle of a fusion reactor. Similar with ITER ISS in a Water Detritiation Facility for a CANDU reactor, one of the main systems is cryogenic distillation. The developments on the CANDU water detritiation systems have shown that a cascade of four cryogenic distillation columns is required in order to achieve the required decontamination factor of the heavy water and a tritium enrichment up to 99.9%. This paper aims to present the results of the design and simulation activities in support to the development of the Cernavoda Tritium Removal Facility (CTRF). Beside the main features of software developed “in house”, an introduction to the main relevant issues of a CANDU tritium removal facility for the ITER ISS is provided as well. Based on the input data (e.g. the flow rates, the composition of the gas supplied into the cryogenic distillation cascade, pressure drop along the column, liquid inventory) the simulation provides the distribution of all the molecular species involved along each cryogenic distillation column and also the temperature profile along the columns. The approach for the static and dynamic simulation of a cryogenic distillation process is based on theoretical plates model and the calculations are performed incrementally plate by plate. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Cryogenic distillation is preferred to other methods of gas separation at industrial scale because it has the advantage of high separation factors, the possibility to process large amounts of gas while obtaining high purity gases [1,2]. Similar with the conventional distillation processes, separation by cryogenic distillation is carried out by mass and heat transfer between vapour and liquid phases that flow in countercurrent. The cryogenic distillation column comprises a boiler that produces the
∗ Corresponding author. Tel.: +40 771218101; fax: +40 356173660. E-mail address: [email protected] (M.M. Draghia).
necessary amount of vapours along the column, plates or package where the isotopic transfer between the vapours and liquid take place and a condenser that provides the liquid reflux along the cryogenic distillation column. In the case of multi-component gas mixtures, determining the transport of the molecular species between the two phases is difficult due to the dependence of the physical-chemical properties of each mixture component. The transport of the molecular species is strongly influenced by the hydrodynamics of the two phases, closely connected with the size of the exchange interface. The vapoliquid interface depends on the constructive characteristics of the separation medium: plates or package. In addition, in the case of hydrogen isotopes mixtures, the problem is complicated by the non-idealities in the thermodynamic properties near the saturation curve at low temperatures [3–6].
http://dx.doi.org/10.1016/j.fusengdes.2016.01.044 0920-3796/© 2016 Elsevier B.V. All rights reserved.
Please cite this article in press as: M.M. Draghia, et al., Software development for the simulation and design of the cryogenic distillation cascade used for hydrogen isotope separation, Fusion Eng. Des. (2016), http://dx.doi.org/10.1016/j.fusengdes.2016.01.044
G Model FUSION-8484; No. of Pages 4 2
ARTICLE IN PRESS M.M. Draghia et al. / Fusion Engineering and Design xxx (2016) xxx–xxx
The model presented in this paper can be used for the design of a cryogenic distillation facility and is based on a traditional analysis model of the exchange process, but is applied to the low temperatures range which is specific to hydrogen and its isotopes. The software developed based on this model is designed for a water detritiation facility employing isotopic catalytic exchange and cryogenic distillation. 2. The model for a cryogenic distillation column The software was developed for simulation and design of a cryogenic distillation cascade for hydrogen isotopes separation. The usual approach for dynamic simulation of a packed column is to adopt the theoretical plate model and carry out stage-by-stage calculations [8,9]. The model equations are based on mass, species and energy balances around each stage. A schematic representation of three general stages in series is shown in Fig. 1. Each stage is a theoretical plate where stage 1 is a condenser and stage N is the reboiler. The “n ” and “ln ” in Fig. 1 are the vapour and liquid flow rates leaving stage n. There are assumed to be species. (For hydrogen isotope distillation, the species are H2 , HD, HT, D2 , DT and T2 .) The vapour flows to the previous stage n − 1 and the liquid flows to the next stage n + 1. - “l dn,i ” and “v dn,i ” are the extraction flow rates for the component i, for vapours, respectively, liquid; f f - “l n,i ” and “v n,i ” are the supply flow rates for the component i, for vapours, respectively, liquid. Following additional simplifying assumptions have been considered: 1. the pressure drop across the column is negligible; 2. the column is adiabatic;
3. the molar holdup in each stage is constant throughout a given time interval; The overall mass balance and heat balance equations are described as follows: f
f
n+1 − ln = −ln−1 + n − ln − n + lnd + nd vap Hn+1 n+1
liq − Hn ln
f,liq f ln
− Hn
=
liq −Hn−1 ln−1
f,vap f n
− Hn
(1)
vap + Hn n
liq
vap
+ Hn lnd + Hn nd
(2)
ˇ
− En − En
ˇ
where Hn is the total enthalpy in stage n, En is the radioactive decay heating rate in stage n and En is the cooling/heating power in the condenser/reboiler. For the dynamic simulation, component material balance equations are developed by performing a component flow rate balance around each stage n. For the general stage, the component mass balance is:
∂qn,i = n+1,i + ln−1,i − n,i − ln,i ∂t f
(3)
f
d − d + ln,i + n,i − ln,i n,i
where qn,i is the holdup of component i in stage n. The heat balance for the general stage in terms of material flows, heating or cooling, and tritium decay heat effects is:
∂Hn liq liq = Hn−1 ln−1 − Hn ln + lnd ∂t vap
− Hn
f,vap f n
+ Hn
vap
f,liq f ln
n + nd + Hn+1 n+1 + Hn
(4)
ˇ
+ En + En
Equations of energy mass balance and calculation of the flow rates begin with the condenser, and continue with the next plates down to the bottom of the column. For each plate the equations of energy and mass balance are considered. The reboiler duty is calculated using the heat exchange equation for the last plate. 3. Cryogenic distillation cascade design
Fig. 1. Schematic representation of three distillation column stages.
Depending of the input data (e.g. the flow rate and the composition of the gas supplied into the cryogenic distillation cascade) the simulation provides the temperature and concentrations profiles along the columns. Using the simulation results as input data, a cryogenic distillation cascade of four columns for the Cernavoda Tritium Removal Facility was designed. The cascade configuration and the supply and withdrawn streams for each column can be seen in Fig. 2. The cryogenic distillation cascade is designed for the separation and enrichment of tritium from the tritiated deuterium supplied from the Liquid Phase Catalytic Exchange (LPCE) system, and to transfer the enriched tritium to the Tritium Gas Handling and Storage System (TGHSS). The first cryogenic distillation column is the largest column due to the separation requirements and has the largest feeding flow rate. Due to this reason the condenser of the first column shall provide the higher cooling capacity of the cascade. In order to reduce operating costs, the reboiler of the first column is designed to operate as a heat pump. For the other three distillation columns, electrical heaters can be implemented as reboilers. In order to produce tritium concentration of 99% T/(H + D + T) in the bottom of the fourth column it is necessary to generate T2
Please cite this article in press as: M.M. Draghia, et al., Software development for the simulation and design of the cryogenic distillation cascade used for hydrogen isotope separation, Fusion Eng. Des. (2016), http://dx.doi.org/10.1016/j.fusengdes.2016.01.044
G Model
ARTICLE IN PRESS
FUSION-8484; No. of Pages 4
M.M. Draghia et al. / Fusion Engineering and Design xxx (2016) xxx–xxx
3
Fig. 2. Cryogenic distillation cascade diagram.
molecular specie along the fourth cryogenic distillation column. Therefore, the dynamic simulation model was use to design the fourth column and to establish the location of the chemical equilibrator which generate T2 molecular species out of reaction: 2DT ↔ D2 + T2 In addition, a detailed investigation has been carry-out aiming to minimize the tritium inventory in the fourth column. 4. Dynamic simulation of the column with the highest tritium concentration The most important activities for the design of the entire cryogenic distillation cascade are concerning the minimization of explosion hazard and consequently reducing the hydrogen inventory in the cascade. Based on the calculation using the dynamic simulation model, an optimization of the cryogenic distillation cascade has been carry-out, and the hydrogen and tritium inventory have been minimized. In Table 1 the distribution of the tritium and hydrogen inventories of the cryogenic distillation columns of the cascade is shown. The percentages of each column are relative to the total inventory of cascade in normal operating conditions. The reduction of hydrogen inventory is primarily an issue for the design of the heat pump since the reflux ration has not significant impact on the inventory. The tritium inventory in the cascade depends mostly by the diameter of the last column and the design of the boiler. Therefore, the tritium inventory was minimized considering the cooling capacity as parameter and calculating the
Table 1 Tritium and hydrogen inventories in the cryogenic distillation columns. Columns
Hydrogen inventory [%]
Tritium inventory [%]
Column 1 Column 2 Column 3 Column 4
95.23 4.34 0.33 0.1
7.80 1.75 2.87 87.58
inventory dependence upon the length of the column needed to achieve the 99% tritium concentration in the bottom of the column. The dynamic simulation software has been also used to estimate the time required to reach steady state into the entire cryogenic distillation cascade and in particular to find out when tritium concentration reach more than 99% T/(H + D + T) in the bottom of the fourth column. The dynamic simulation software provides time variation of all parameters/concentrations along the cascade. In Fig. 3 the concentration profiles along the column 4 at steady state are shown. The main hazard of the CTRF is related to the deuterium explosion due to the large amount of deuterium in the first column. In the heat pump from the boiler of the first column it is envisaged that more than 50 l of liquid deuterium will be collected and quite the same amount in the liquid redistributors and the packing along the column. As far as tritium hazard is concerned, the column four contains most of the inventory and therefore the design shall include provision for tritium recovery in any events that may lead to tritium release. In order to quantify the tritium inventory in the cascade columns, on-line measurements of tritium concentration in the deuterium streams circulated between the cryogenic distillation columns are foreseen. Due to the major inventory from the fourth column, for this column many measurements were foreseen: - monitoring of the tritium concentration in the deuterium tritiated flow extracted from the fourth column to the equilibration loop and returned back to the fourth column; - monitoring the tritium concentration in the flow extracted from the fourth column to the Tritium Gas Handling and Storage System (TGHSS); - monitoring of the tritium concentration in the flow extracted from the fourth column to the high tritium expansion tank. It is proposed to use a Laser-Raman spectrometer that allows the required type of accuracy. The dynamic of tritium separation and accumulation in the fourth column of a tritium removal facility for a CANDU reactor is slow in comparison with the tritium behaviour in the cryogenic
Please cite this article in press as: M.M. Draghia, et al., Software development for the simulation and design of the cryogenic distillation cascade used for hydrogen isotope separation, Fusion Eng. Des. (2016), http://dx.doi.org/10.1016/j.fusengdes.2016.01.044
G Model FUSION-8484; No. of Pages 4
ARTICLE IN PRESS M.M. Draghia et al. / Fusion Engineering and Design xxx (2016) xxx–xxx
4
Fig. 3. Dynamic of the hydrogen species in the column 4.
distillation cascade of a fusion device. Nevertheless, useful information can be collected concerning the dynamic of a cryogenic distillation process when more than two molecular species are involved. Comparison between the predicted evolution of the D2 , DT and T2 along the fourth cryogenic distillation column and the experimental data will be used for the enhancement and eventually validation of the dynamic software used for the design of the Cernavoda Tritium Removal Facility [7]. The accuracy of the Laser Raman spectrometer is high enough as far as dynamic of the cryogenic distillation process of the fourth column is concerned. The dynamic simulation showed that the accumulation of almost the entire tritium inventory in the fourth column requires about 280 h. 5. Conclusions Dynamic simulation software has been developed and used for the design of the cryogenic distillation cascade of the Tritium Removal Facility for the Cernavoda NPP. The tritium accumulation in the fourth column of the cascade and the time behaviour of the D2 , DT and DT molecular species may give useful information as far as dynamic separation of the multicomponent mixtures that are relevant for ITER Isotope Separation System. Measuring the isotopic concentrations at the sampling points of the last cryogenic distillation column will provide better understanding concerning
the time behaviour of the separation process. The measured compositions will be compared with the predicted values provided by the simulation software that will allow calibration of the software and provide support for the software enhancement, if necessary identified. References [1] D. Murdoch, I. Cristescu, C. Day, M. Glugla, R. Laesser, A. Mack, EU Fuel cycle development priorities for ITER, Fusion Eng. Des. 82 (2007) 2158–2163. [2] I. Cristescu, I.R. Cristescu, L. Dörr, G. Hellriegel, R. Michling, D. Murdoch, P. Schaefer, S. Welte, W. Wurster, Experiments on water detritiation and cryogenic distillation at TLK; Impact on ITER fuel cycle subsystems interfaces, Fusion Sci. Technol. 54 (2008) 440–445. [3] P.C. Souers, Cryogenic hydrogen data pertinent to magnetic fusion energy, in: UCRL-52628, 1979. [4] P.C. Souers, Hydrogen Properties for Fusion Energy, University of California Press, Oakland, 1986. [5] I. Prigogine, The Molecular Theory of Solutions, North-Holland Publishing Company, Amsterdam, 1957. [6] A. Farkas, Ortohydrogen, Parahydrogen and Heavy Hydrogen, Cambridge University Press, Oxford, 1935. [7] I. Cristescu, D. Demange, R. Michling, Design and R&D activities of TriPla-CA consortium in support of ITER Tritium Plant development, Fusion Eng. Des. 89 (2014) 1524–1528. [8] T. Yamanishi, K. Okuno, Mass transfer in cryogenic distillation column separating hydrogen isotopes, J. Nucl. Sci. Technol. 31 (6) (1994) 562–571. [9] M. Kinoshita, Y. Naruse, Separation characteristics of cryogenic distillation column with a feedback stream for separation of protium tritium systems and tritium, J. Nucl. Sci. Technol. 2 (1982) 410–425.
Please cite this article in press as: M.M. Draghia, et al., Software development for the simulation and design of the cryogenic distillation cascade used for hydrogen isotope separation, Fusion Eng. Des. (2016), http://dx.doi.org/10.1016/j.fusengdes.2016.01.044