Power costs calculations will be principally made with the CEA code system, SEMER. Desalination related costs will be determined by the IAEA code, DEEP/V2.
Apresentação oral Publicado na acta da conferência:
FISA-2001 - EU Research in Reactor Safety 11-14 de Novembro 2001, Luxemburgo
Applications of Innovative Nuclear Reactor Concepts for Sea-water Desalination in Southern Europe; The EURODESAL project Simon NISAN¹, Olga ASUAR ALONSO², Bogdan BIELAK³, Gianfranco CARUSO4, Luciano CINOTTI5, J. Roger HUMPHRIES6, Nelson MARTINS7, Antonio NAVIGLIO4, and Linda VOLPI¹
1) CEA, CEN Cadarache, DER/SERI (France) 2) EMPRESARIOS AGRUPADOS INTERNACIONAL, SA (Spain) 3) FRAMATOME ANP (France) 4) DINCE, Universita di Roma « La Sapienza » (Italy) 5) ANSALDO Nucleare (Italy) 6) CANDESAL Technologies (Canada) 7) IRRADIARE (Portugal)
SUMMARY Conservative estimates already indicate that, for the Mediterranean region alone, there would be a water shortage of about 10 million m3/day in 2020. World potable water requirements would be more than double this figure. Sea-water desalination is an attractive and economic solution to meet this demand. However, over the long term, desalination with fossil energy sources would neither be practical nor desirable: fossil fuels reserves are finite and must be conserved for other essential uses whereas demands for desalted water would continue to increase; furthermore, the combustion of fossil fuels would produce large amounts of greenhouse gases and toxic emissions. A sustainable solution could thus only be provided by nuclear energy and, to a certain extent, by renewable energy systems. In this context, EURODESAL basically aims to investigate the technical and economic feasibility of sea-water desalination with innovative nuclear reactors, (e.g. the GT-MHR and the AP-600), presenting enhanced safety features and cost advantages. Major goals of the project are: Coherent demonstration of the technical feasibility of nuclear desalination through the development of technical principles for optimum cogeneration of electricity and water and by exploring the unique capabilities of the innovative nuclear reactors and desalination technologies
2 Objective assessment of the competitiveness and sustainability of proposed solutions through comparison with fossil and renewable energy based solutions. Enlargement of the role of nuclear energy and its increased public acceptance by meeting a fundamental human need, water. Maintaining the competitive position of EU industrials in the world market through the exportation of viable integrated nuclear desalination systems Partial results obtained so far seem to be quite encouraging as regards the technical feasibility of nuclear desalination. It is expected that, at the end of the project, sufficient technical data and economical motivation will be available in a coherent form to lay the foundations of a more detailed nuclear desalination project for the South of Europe and, eventually, for other regions of the world.
A - Background and Motivation Around the time horizon 2010-2030, the shortage of water supply for drinking and irrigation purposes would be a major problem in many countries of the European Union such as Greece, Italy (Southern regions and islands), Portugal (Alentejo and Algarve regions and islands such as Porto Santo, Corvo etc.) and Spain (Southern and Eastern regions and Islands). Other states in the Mediterranean region, such as Malta and Cyprus, as well as the North African states (e.g. Algeria, Egypt, Morocco, Tunisia) would also suffer from acute water shortages. For the entire Mediterranean region, conservative estimates indicate a shortage of water of about 10 million m3/day in 2020. In this context, sea water (or to a lesser extent, polluted and brackish water) desalination could be a very attractive and sustainable alternative for the solution of the water shortage problem. However, desalination is an energy intensive process that brings with it a demand for an additional energy generation capacity. The general public in the EU has become increasingly sensitive to the long term environmental costs of technological solutions and in particular to their medium and long term sustainability. A future desalination strategy based solely on the use of fossil fuels would therefore be neither practical nor desirable: reserves of fossil fuels are limited where as demands for desalted water would continue to increase as population grows and standards of living improve. Conservation measures such as recycling, minimisation of leakage in the distribution networks and more efficient utilisation of water would limit this demand to a certain extent, but in no way they will allow to avoid a dissemination of new desalination plants and, consequently, also of new plants for their energy supply. The combustion of fossil fuels for the operation of such plants would emit large amounts of greenhouse or toxic gases, contributing to global warming or producing adverse effects on public health. Assuming an increase in the daily water production of 10 million m3 up to the year 2020, using nuclear instead of fossil powered energy production and using innovative desalination technologies, it can be shown that emissions of about: 20 000 000 t/year of CO 2, 200 000 t/year of SO2, 60 000 t/year of NOx and 16 000 t/year of other hydrocarbons can be avoided in the Mediterranean region alone. The potential world wide reduction in these emissions would be more than double these figures. Nuclear energy may thus be the only industrially proven, non-polluting and non-fossil energy source for sea-water desalination.
3 It is for this reason that the EURODESAL project is being carried out by a consortium comprising: EU and Canadian industrials: ANSALDO (Italy), CANDESAL Technologies (Canada), EMPRESARIOS AGRUPADOS (Spain), FRAMATOME ANP (France), IRRADIARE (Portugal), and R&D Organizations: CEA (Project Coordinator, France) and DINCE, The University of Rome (Italy).
The combined knowledge and experience of these organizations, both in nuclear reactor development and desalination technologies, exceeds by far the individual competence. This knowledge will be used in the project to ensure that the best available technologies and the state of the art R&D are integrated to produce the most competitive product with the highest level of Safety.
A.1
Major Objectives
The basic objective of EURODESAL is to provide a choice of options and technical specifications for a future common European sea-water desalination system, using principally nuclear energy. This could be a demonstration plant or a full fledged integrated system based on one or two nuclear reactors coupled to a desalination process. In fact, the Project Work Plan (§B) is designed to achieve this objective through: Consistent and quantitative estimates of achievable water and power costs with innovative reactors (eg the GT-MHR and the AP-600), and with an existing reference reactor such as the French PWR 900 MWe, all operating in the cogeneration mode (simultaneous production of electricity and water). The use of selected desalination technologies such as the Multiple Effect Distillation (MED), the Reverse Osmosis Process (RO) and an innovative RO with preheating of the feed water. «System Optimisation» of the above desalination technologies coupled to the nuclear reactors
B. Work Programme B.1- Technical Approach The project comprises 4 technical work packages (WPs), designed to show the technical and economical feasibility of sea water desalination by selected nuclear reactor concepts, currently under study or development in Europe and the USA. The fifth WP deals with the Administrative and co-ordination aspects of the project. The technical approach to be implemented in the project is essentially based on the employment of two innovative reactors: the GT-MHR, and the AP600. To compare the integrated system performances, an operating 900 MWe French PWR is also being studied as a reference base case.
4 These reactors will be coupled to two competing and currently the most promising and economic desalination technologies: the Multiple Effect Distillation Processes (MED) and the Reverse Osmosis (RO) membrane process. This is illustrated in Figure 3, with a GT-MHR.
Figure 1: Co-generation using the two competing desalination technologies (MED and RO, with or without preheating). A minimal electrical power is required for MED pumps etc. Integrated systems, using these technologies, are substantially different in their design and optimisation objectives. In the distillation system, the objective is to deliver the reject heat at the highest possible temperature without noticeable impact on the power production level. In the case of the GT-MHR, heat is available at 105°C, compared to ~ 35°C (in normal operation) at the turbine outlet for PWRs. Emphasis will therefore be placed on distillation concepts, coupled to the GT-MHR, which effectively use higher temperatures to increase the Gain Output Ratio, GOR, (amount of water produced per unit thermal energy). In the RO system, the objective will be to minimise the electric power utilisation. As the maximum membrane temperatures are much less, reject heat in the RO preheating configurations can be directly used through the condenser of PWRs. The GT-MHR can also be configured to minimise power costs at a fixed reject heat temperature most suited to RO.
B.2
Work Packages
Concomitant with this technical approach, the project includes the following work packages (WPs):
WP1-Nuclear Reactor and Desalination System Coupling and Optimisation This WP will first be concerned with the determination/establishment of selection criteria for available or innovative desalination technologies from international studies. These criteria will include the economy of energy use, number of barriers presented against contamination, plant availability, reliability and efficiency, feed back of experience etc. The results obtained will be applied to elaborate the design and process flow diagrams of coupling schemes. An analysis of the advantages and disadvantages of different alternatives will be made in order to optimise the coupling scheme most suitable for a given reactor. A detailed study, using the ECOSIMPRO multidisciplinary tool, will be made to verify the above coupling schemes with the calculation of heat and mass balances. These will help understand the advantages or inconveniences of the energy transfer mechanisms from the
5 nuclear reactor to the desalination plant e.g. use of steam from the steam cycle, the use of electricity, combination of the two, use of exhaust water from the power plant to preheat feedwater in RO, use of steam for ejectors. No such detailed calculations have been so far reported in the literature.
WP2- Preliminary Safety Assessment of Coupled Nuclear Reactor-Desalination Systems This work package will address the specific safety problems raised by the coupling of desalination plant to nuclear reactor in both normal operation and transient conditions. Analyses of different normal and accidental situations will be made with well known and qualified codes, e.g. CATHARE, RELAP etc. In the case of a nuclear reactor coupled to a RO plant with preheating, there is a limited thermal coupling but the possibility of interaction effects has to be examined. In the case of MED plants, the coupling is primarily thermal. Operational transients in either the nuclear plant or desalination plant could have a direct effect on the operation of the other system with safety implications which must be assessed. Scenarios involving failure mechanisms in materials, systems or components that could lead to carry over of radioactive materials to product water will therefore be given particular attention and actions will be taken in order to limit the levels of risk so that these satisfy the most stringent safety criteria. In this context, the addition of intermediate loops, maintained at sufficiently high pressures to prevent the transfer of contamination to product water, will be examined. In the case of a dual purpose plant, the nuclear plant has to simultaneously satisfy the requirements of both the generation of electricity and the water production through the coupled desalination system. Safety implications of balancing the energy needs of both plants shall therefore be assessed in the base load operation as well as in eventual load follow configurations involving fluctuations in demand for either or both products. Similarly, the potential safety impacts of the shutdown of either one or both plants shall also be studied. Accidental scenario studies will include transients such as Loss of Heat Sink, Loss of Load (especially with RO couplings) and Steam Line Break .
WP3- Fossil and Renewable Energy Systems This WP will involve comparison studies of fossil and renewable energy systems and, where possible, hybrid fossil-renewable energy systems. The work will involve selection of the BAT (Best Available Technologies) based on the use of renewable and fossil energy sources for desalination purposes. Technical and economical evaluation of the selected technologies will then be undertaken and compared with the performances of integrated nuclear desalination systems. Evaluation of the economic and technical potential of hybrid (fossil-renewable) desalination systems will also be made.
6 WP4- Economic and Sustainability Evaluation of Integrated Nuclear Desalination Systems The construction of integrated nuclear desalination systems may involve relatively high capital costs but low fuel and operating costs. It is indeed necessary that decision makers have at their disposal all information and tools to determine relevant factors effecting costs in order to ensure the selection of the best possible technical and economical plant configuration. With the other Work packages as input, this task will, therefore, study a matrix of key parameters allowing to minimise the total energy costs and water costs of the selected concepts and processes, taking into account the specific conditions of selected types of users of interest for EU and the potential for providing long term solutions. Comparisons between different energy sources and desalination systems will be based on criteria related to the sustainable development, environmental friendliness, safety of installations and protection of personnel and population. Power costs calculations will be principally made with the CEA code system, SEMER. Desalination related costs will be determined by the IAEA code, DEEP/V2
C. Progress Made and Associated Innovations C.1
General Summary
EURODESAL started on February, 4, 2001 (kick-off Meeting) as a Thematic Network project of the EC (Contract N°FIKI-Ct-2000-20078) as part of the 5th EURATOM Framework Programme. [1] A second technical meeting was held in Madrid from May 4 to 5, 2001. [2] In this short time, significant progress has already been realised, especially in WP1 and WP4. Some results from WP2 and WP3 will be discussed in the oral presentation. The general physical and economical hypotheses, and the calculational procedures to be used, have also been defined [2]. Thus the partners have agreed on the common data to be used by all, where relevant. These are principally concerned with the types of nuclear power plants (GT-MHR, AP600 and PWR900) and their characteristics, the MED and RO desalination plant specifications, sea-water and product water qualities and product water capacities, general site characteristics and various economic hypotheses. (See [2] for details).
The General Safety Approach The general safety objectives would be the same as those already being implemented for next generation reactors (adequacy in meeting the EUR, for example). All or most of the safety issues concerning the PWR900, the AP600 and the GT-MHR have already been dealt with and analysed in the context of the design and certification of these reactors. It is for this reason, and in view of the available limited funding, that the study will mainly concentrate on the possible or hypothetical interaction of the desalination system on the reactor operation, or vice versa, in normal, incidental or accidental situations.
7 C.2
WP1-Nuclear Reactor and Desalination System Coupling and Optimisation
The schemes for the coupling of MED and RO have been elaborated and are being optimised over the entire integrated system (reactor plus MED, or reactor plus RO). For PWRs such as the PWR900 or the AP600, coupling to MED is normally realised by steam extraction from the back-pressure turbine (see Figure-2). Turbine P= 56 bar
Steam
To Desalination Plant
Steam Extraction Intermediate Heat Exchanger
Brine Heater
Steam T = 34.75°C P = 0.055 bar
Generator
T= 219°C
Tout = 32.75°C
Brine
From Desalination Plant
Tin= 20°C Condenser
Feedwater pump
Figure 2: Conventional Coupling of a PWR to MED plant Framatome ANP has also studied and optimised the GT-MHR/MED coupled system, shown in the Figure-3 below:
C.3 WP4- Economic and Sustainability Evaluation of Integrated Nuclear Desalination Systems CEA undertook the economic evaluation of the AP-600 based on the data available in the literature and further verified by ANSALDO. Results, obtained with the help of CEA economic evaluation code SEMER, have so far been extremely encouraging. When compared with the accepted project evaluations, using similar hypotheses (1994 US$, 8% discount and interest rate, 12% contingencies) it appeared that the differences, on selected plant cost items evaluated by CEA and those by the Vendor, did not exceed few percents. Having thus « qualified » the SEMER code, CEA then evaluated the desalination costs. These are summarized in Tables 1 and 2, below.
8
Figure-3: Coupling of the GT-MHR to an MED plant
Table 1: AP-600 coupled to MED Average daily water production [1000 X m /d]
43.04
GOR = 17.7 53.80 107.60 215.20
Specific Investment Cost [$/(m3/d)]
1312
1298
1179
1175
1138
Net saleable Power [MW]
618
616
602
577
522
Water Cost [$/m3]
1.02
0.97
0.88
0.79
0.79
3
430.40
Table 2: AP-600 coupled to RO(without preheating) Recovery Ratio = 0.5* Average daily water production [1000 X m3/d]
54.6
65.51
131.03
240.22
458.60
Specific Investment Cost [$/(m3/d)]
933
916
826
808
787
Net saleable Power [MW]
618
616
604
582
540
Water Cost [$/m3]
0.66
0.64
0.59
0.57
0.55
* Recovery Ratio is the permeate flow rate divided by the total feed-water flow rate
9 C.4
Innovations made
An important feature of EURODESAL is the degree of innovation that the partners of are endeavouring to bring into the project, notwithstanding the current low funding. Two specific innovative coupling schemes deserve a special attention. The first is concerned with the coupling of PWRs to MED through the condenser, proposed by CEA. A direct consequence of the conventional coupling shown in figure-2 above is the very significant loss of electric power ( 20% for the PWR900) since this type of coupling scheme requires steam bleeding from the turbine stages. This effect is shown in the following table.
Table-3: Net saleable power for nuclear and coal fired plants coupled to MED and RO Desalted water produced (m3/d)
Power option MWe PWR
Coal
MED
RO
Net Power consumed (MWe)
Net Saleable Power (MWe)
MED
RO
MED
RO
619
530 000 546 000
91* +42 = 133
108
486
511
928
795 000 808 000
136* + 61= 197
160
731
768
617
530 000 546 000
103* + 37 = 140
108
477
509
925
795 000 808 000
154* + 54 = 208
160
717
765
* Power lost because of steam extraction from the turbine
The innovative scheme being studied in EURODESAL is based on the utilisation of nearly twothirds of the total heat energy that is normally lost to the heat sink via the condenser. As is shown in Figure -2, in normal operation, the output temperature of the water from the condenser, connected to the turbine at the last stage, is too low (33°C, for PWR900) to be meaningfully connected to an MED system. In such conditions, the pressure in the condenser is about 55 mbar in the PWR900. The innovation resides in raising this pressure (> 100 mbar) so that the output water temperature is of the order of 60 or 70°C. With this temperature, and an intermediate flash tank where water is vaporised for the MED process, very large quantities of sea-water (> 500 000 m3/day) can be desalted. The operation of condensers at such high pressures does not appear to be a problem for the safety and operation of the PWR secondary system. The advantage is that there is negligible (nearly 5% at 47°C) loss of the saleable electric power. This is shown in Table 4. To avoid a large table, only values up to 105 mbar are presented.
10 Turbine
Multi-Effect Distillation Flash Tank Steam
Flash Tank
Product Water
Seawater Intake
Pre-heated Water Makeup
Steam Brine Outfall
Generator Condenser
Flash Tank Blowdown Intermediate Recirculation Pump
Feedwater pump
Makeup Pump
Figure 4: MED coupling utilising waste heat from the condenser
Table-4: Estimation of the Power loss in a PWR900 MWe against condenser temperature/pressure (Figures in bold represent normal operating conditions) Pcond
mbar
44
55
62
81
105
Tcond
°C
30.79
34.75
37
42
47
r
0.380
0.375
0.372
0.365
0.358
r
0.335
0.330
0.327
0.321
0.315
Pe net
MWe
933
919
911
894
877
Pthcond
MWth
1.852
1.866
1.874
1.891
1.908
Here, Pcond, Tcond are the pressure and the corresponding saturation temperature in the condenser; r, r are respectively the Rankine and net efficiencies of the turbine; Pe net is the net saleable power from the system, and Pthcond, is the net thermal loss. A similar conclusion has been reached independently by ANSALDO for the AP-600. (Figure 5)
11
Turbine output Vs Condenser hot well temperature 680 T urbine output (MWe)
675 670 668 660 657 650 647 640
637
630
628
620 40.0
45.0
50.0
55.0
60.0
Condenser hot well temperature (°C)
Figure 5: AP600 coupling to MED via the condenser
The second important innovation is the coupling of nuclear reactors to RO with pre-heating of the feed-water (CANDESAL). The principle of the CANDESAL method is based on the observation that the permeability of RO membranes increases as the temperature (and pressure) of the feed water is increased. This then leads to an increased water production, reduced energy consumption and the consequent reduction in costs. Our studies to date show that by using a combination of non-traditional operating strategies/regimes, highly sophisticated design optimisation to establish system configuration and operating parameters, and advanced feed-water pre-treatment and energy recovery techniques, we can significantly reduce product water cost up to about 20%. below those that can be achieved in a plant designed in a more traditional manner. This is achieved using commercial off-the-shelf components and without violating any of the suppliers design specifications/limitations, so that the level of commercial risk is quite low even though there is significant improvement in operating and economic characteristics.(Figure 8).
12
Figure 6: Relative water production as a function of RO feed-water temperature and pressure
Figure 7: Energy consumption as a function of RO feed-water temperature and pressure
Figure 8: Reduction of the unit water production cost with RO preheating
13 D
Conclusion
EURODESAL is one of the rare on-going international project on desalination in the world. Although it is basically oriented towards the applications of innovative nuclear reactors (such as the GT-MHR and the AP600), comparison and analysis with other sources of energy, in particular renewable energies, is not excluded. At the time of preparing this paper, only few months have elapsed but the project has made considerable progress. Its specific innovations are the use of well qualified codes and methods and novel technologies and systems for the coupling of nuclear reactors to desalination processes such as the Multiple Effect Distillation Process (MED), using waste heat, and the Reverse Osmosis membrane process (RO), with pre-heating of the feed water. Results obtained so far are only preliminary and much verification still needs to be done, but analysis shows that they are highly encouraging both as regards the technical feasibility and economic competitiveness.
E
Future Activities
These include the ongoing detailed studies of PWR coupled to MED via the condenser (CEA, ANSALDO) and other reactors coupled to RO with preheating, (CANDESAL). The most important points which still remain to be verified in the former innovative coupling are the adjustment of the sea-water flow rate in the condenser to allow condenser pressures of the order of 110 mbar and the corrosion and scaling aspects in the condenser. Other remaining tasks are:coupling of fossil and renewable energy based systems to MED and RO, (IRRADIARE), setting up of the EcosimPro code for detailed heat and mass balances of the couples systems (EMPRESARIOS AGRUPADOS), safety related studies, (DINCE) and sensitivity studies of the heat performances of these systems (energy consumed/kg of distilled water) for different water production capacities (DINCE). After the first coherent feasibility study which is the main objective of the current project, the scope of the project will be extended to cover detailed site specific technical and economic studies. These will be proposed as part of the future EURODESAL DEMO project, to be carried out as a cost shared action in the context of EURATOM’s 6 th Framework programme. We believe that only thus we could contribute meaningfully towards the resolution of a basic human problem: that of the electricity needs and of the medium and long term acute water shortages in the South European countries and in other regions of the world. As such, the future project would not only provide economic solutions but would also effectively promote public acceptance of nuclear energy in the world. Because energy and water shortages are essentially world wide problems, integrated nuclear desalination systems, conceived, developed and tested as standardized, common EU products could position EU industrials as leaders in the important future world markets.
14
E
References
[1]
S. Nisan, Meeting Report, EURODESAL kick-off Meeting , Cadarache, (February 5-6, 2001)
[2]
S. Nisan, Meeting Report, EURODESAL First Technical Meeting, Madrid, (May 4-5, 2001)
