Analysis of water production costs of a nuclear desalination plant with a nuclear heating reactor coupled with MED processes

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1 Desalination 190 (2006) Analysis of water production costs of a nuclear desalination plant with a nuclear heating reactor coupled with MED processes Shaorong Wu Institute of Nuclear Energy Technology, Tsinghua University, Beijing, China Tel. +86 (10) ; Fax +86 (10) ; srwu@mail.tsinghua.edu.cn Received 20 June 2005; accepted 23 August 2005 Abstract A nuclear heating reactor (NHR) was designed with the required inherent safety and simplified design features. Power capacity of the NHR-200 (200 MW(th), with steam production of 380 t/h) is compatible with reasonably sized desalination plants. Thermal-hydraulic parameters of the produced steam (2.4 bar and 124EC) are suitable for coupling with distillation processes. Economic competitiveness of the NHR desalination plant is the key point to which the public and decision-makers are paying good deal of attention. Coupling of the NHR with selected MED processes and design parameters of an integrated desalination plant are described. Results of analyses of water production costs are presented as well. Based on the economic evaluation, the average energy cost of the nuclear plant may reach 5.44 $/t of steam, and the provided water production cost may reach 0.72 $/m 3 and 0.76 $/m 3 for coupling with HT VTE MED and LT HTE MED processes, respectively. Keywords: Nuclear desalination plant; Nuclear heating reactor (NHR); Multi-effect distillation process (MED); Economic analysis; Water production cost 1. Introduction Some coastal locations and islands in China where both fresh water and energy sources are severely lacking show a strong interest in potable water production by seawater desalination. For these cases, small- or medium-size seawater desalination plants using nuclear energy could be a suitable solution. A nuclear heating reactor (NHR), developed by the Institute of Nuclear Energy Technology, Tsinghua University, China, was designed with inherent safety and simplified design features. Power capacity of the NHR-200 (200 MW(th)) with steam production of 380 t/h is compatible with reasonably sized desalination plants and thermal-hydraulic parameters of the produced steam (2.4 bar and 124EC) are suitable for coupling with distillation processes. The integrated nuclear desalination plant couples two proven technologies: the NHR and /06/$ See front matter 2006 Elsevier B.V. All rights reserved

2 288 S. Wu / Desalination 190 (2006) the MED process. A secondary loop and a steam loop were incorporated between the nuclear reactor and the MED process as a safety barrier. The integrated desalination plant could provide 120,000 to 160,000 m 3 /d of potable water. The economical competitiveness of the NHR desalination plant is the key point to which the public and decision-makers are paying a good deal of attention. 2. Design parameters of the nuclear heating reactor The reactor structure of the NHR-200 is shown in Fig. 1. The NHR-200 is a vessel-type light-water reactor with an integrated arrangement, natural circulation of the primary coolant, Table 1 Main design parameters of the NHR-200 Operation mode Heat only Reactor power, MWt 200 Core outlet temperature, EC 212 Core inlet temperature, EC 155 Pressure at the primary circuit, MPa 2.5 Outlet temperature of the secondary circuit, EC 165 Inlet temperature of the secondary circuit, EC 135 Pressure at the secondary circuit, MPa 3.0 Outlet steam temperature of the motive 126 steam generator, EC Outlet steam pressure of the motive 0.24 steam generator, MPa Flow rate of motive steam supplied from 328 NHR to the MED process, t/h self-pressurized performance and dual-vessel structure. The core is located at the bottom of the reactor pressure vessel (RPV). Primary heat exchangers are arranged on the periphery in the upper part of the RPV. The system pressure is maintained by inert gas and steam. The containment vessel fits tightly around the RPV so that the core will not become uncovered under any postulated leakage at the reactor coolant pressure boundary. The reactor primary coolant circulates due to density differences between hot and cold regions in the RPV. There is a long riser on the core outlet to increase the natural circulation capacity. The main thermal hydraulic parameters of the NHR-200 are listed in Table 1. Fig. 1. Structure of the NHR-200 reactor. 3. Design parameters of the selected desalination process Two types of desalination processes were selected for comparative analysis. Their design parameters are listed in Table 2.

3 Table 2 Design parameters of the selected desalination processes S. Wu / Desalination 190 (2006) Type of desalination process Inlet steam temperature in MED process, EC Top brine temperature, EC Installed unit capacity of MED process, m 3 /d Unit number Number of effects GOR HT VTE MED , LT HTE MED 125/ , , with heat pump Coupling of NHR with desalination process Two coupling schemes were selected for the comparative analysis: C NHR-200 coupled with LT HTE MED (low temperature multi-effect distillation with horizontal tube evaporators), shown in Fig. 2. C NHR-200 coupled with HT VTE MED (high temperature, multi-effect distillation with vertical tube evaporators), shown in Fig. 3. For both cases, the design parameters of the NHR with heat-only mode are the same for these two coupling schemes. In Fig. 2 it can be seen that the saturated steam with higher temperature (125EC) generated in the steam generator of the NHR-200 was directly conducted to the inlet of the heat pump (a steam ejector) as its motive steam. Some amount of steam with lower pressure is drawn out from a middle effect of the LT HTE MED process and blended with the motive steam in the mixing chamber of the ejector. At the exit of the heat pump, the mixed steam reaches a temperature of 73EC. This mixed steam is conducted to the first effect of the LT HTE MED desalination process as its motive steam. Part of the condensate from the first effect was pumped back to the motive steam generator of the heating reactor as its feed water. Meanwhile, another part of the condensate from the first effect must be conducted to the produced water line to keep the total mass balance of the system. The total water production of the NHR+LT HTE MED coupling scheme was 118,080 m 3 /d, which is lower than that of the NHR+HT VTE MED coupling scheme due to the lower temperature of its motive steam (73EC) and therefore a lower GOR (15). In Fig. 3 it can be seen that the saturated steam with a temperature of 125EC, generated in the steam generator is directly conducted to the first effect of the HT VTE MED process and the condensate from the first effect was pumped back to the steam generator as its feed water. Therefore, the motive steam circuit also works as an additional barrier between the nuclear reactor and the desalination process. The NHR-200+HT VTE MED coupling scheme has a higher efficiency (GOR 21.5) due to the higher top brine temperature (120EC) and therefore a higher useful total temperature difference. 5. Calculations of water cost by using DEEP DEEP software [1 4] was selected for the calculation of water production costs. By using the collected technical and economical data as the input data into the DEEP program, the water costs for both HT VTE MED and LT HTE MED processes were calculated. The main assumptions are listed in Table 3. The power cost calculation

4 290 S. Wu / Desalination 190 (2006) Fig. 2. Coupling scheme of the NHR-200 with the LT HT MED desalination process.

5 S. Wu / Desalination 190 (2006) Fig. 3. Coupling scheme of the NHR-200 with the HT VTE MED desalination process.

6 292 S. Wu / Desalination 190 (2006) Table 3 Main assumptions Desalination plant type HT VTE MED LT HTE MED Installed capacity of distillation part, m 3 /d 170, ,000 Distillation plant design cooling water temperature, EC Seawater total dissolved solids (TDS), ppm 31,500 31,500 Distillation plant product water TDS, ppm Distillation plant optional unit size, 3 /d 85,000 30,000 Maximum brine temperature, EC Water plant specific power use, kw(e)h/m Yearly discount rate: 5.85% Yyearly interest rate: 5.85% Plant economic life: 30 y Purchased electricity cost: 0.06 $kw(e)/h Table 4 NHR-200 power cost calculations Total specific construction cost, W/kW(t) Total construction cost, M$ 58 Interest during construction (IDC), M$ 6 Total plant investment, M$ 64 Specific investment cost, $/kw(t) 321 Levelized fixed charge rate, % 7.15 Annual levelized capital cost, M$ 4.5 Annual fuel cost, M$ 4.2 Annual O&M cost, M$ 4.1 Annual electric power cost 0.94 (heat only plants), M$ Annual levelized decommissioning cost, M$ 0.53 Total annual required revenue of power 14.3 plant, M$ Average energy cost, $/t, steam 5.44 results are given in Table 4. The results of water production cost calculations for both HT VTE MED and LT HTE MED processes are jointly listed in Table 5, shown in order for a convenient comparative review. Table 5 Water production cost calculation results Distillation process HT VTE MED LT THE MED Installed water production 170, ,000 capacity, m 3 /d Annual average water 55,239,999 39,766,594 production, m 3 Total construction cost, M$ Interest during construction, M$ Total investment, M$ Specific investment cost, $/(m 3 /d) Annual water plant fixed charge, M$ Annual water plant heat cost 14.3 (heat plant), M$ 14.3 Annual purchased electric power cost, M$ Annual water plant O&M cost, M$ Total annual required revenue, M$ Total water cost, $/m

7 6. Analysis of the calculated energy and water costs 6.1. Analysis on the calculated energy cost According to the above results for the nominal design condition, the energy cost breakdown of the NHR-200 is shown in Fig. 4. S. Wu / Desalination 190 (2006) Fig. 4. Energy cost breakdown of the NHR Levelized capital cost, US$/t of steam: (31.5%). 2 Nuclear fuel cost, US$/t of steam: (29.4%). 3 O&M cost, US$/t of steam: (28.7%). 4 Consumed electric power cost (for heat only plants), US$/t of steam: (6.57%). 5 Decommissioning cost, US$/t of steam: (3.83%). Total energy cost, US$/t of steam: 5.44 (100%). Fig. 6. Components of water cost for the LT HTE MED process. 1 Heat plant levelized capital cost, US$: (15%). 2 Nuclear fuel cost, US$: (14%). 3 Heat plant O&M cost, US$: (14%). 4 Heat plant consumed electric power cost, US$: (3%). 5 Decommissioning cost, US$ : (2%). 6 Water plant fixed charge, US$: (26%). 7 Water plant electric power cost, US$: (16%). 8 Water plant O&M cost, US$: (10%). Total water cost, US$/m 3 : 0.76 (100%) Comparison of energy and water costs produced by both a nuclear heating plant and a fossil fuel power plant As an example, the cost of steam with pressure of about 3 4 bar, produced by an oil-fired plant at a city in northeast China and the expected water production costs are given in Table 6 and are compared with that of the NHR-200. Fig. 5. Components of water cost for the HT VTE MED process. 1 Heat plant levelized capital cost: US$ (11%). 2 Nuclear fuel cost: US$ (11%). 3 Heat plant O&M cost: US$ (10%). 4 Heat plant consumed electric power cost: US$ (2%). 5 Decommissioning cost: US$ (1%). 6 Water plant fixed charge: US$ (29%). 7 Water plant electric power cost: US$ (23%). 8 Water plant O&M cost: US$ (13%). Total water cost: US$/m (100%). Table 6 Comparison of energy and water costs produced by both NHR-200 and fossil fuel power plants Plant type Steam cost a, US$/t Oil-fired plant NHR Water cost b, US$/m 3 a With an assumption of oil price of 100 US$/t. b Coupled with HT VHE MED process and with all the same assumptions and input parameters for both plants.

8 294 S. Wu / Desalination 190 (2006) Analysis of the calculated water cost The calculated components of water cost for the HT VTE MED and LT HTE MED processes are shown in Figs. 5 and 6, respectively. 7. Conclusions Under the conditions in China, the energy and water production costs of an oil-fired plant (for an oil price of 100 US$/t, and coupled with the HT VTE MED process), are about 1.6 times and 1.2 times higher than that of the NHR-200 plant, respectively. Water costs produced by an integrated NHR desalination plant coupled with HT VTE MED or LT HTE MED can be about 0.72 US$/m 3 and 0.76 US$/m 3, respectively. Considering the high quality of the product water, these costs are acceptable. The base unit construction cost and electricity consumption cost have a leading effect on further reduction in the water production cost of a desalination plant using a NHR reactor coupled to the MED process. It is proposed to continue the research with a view further to decrease water production costs and improve economic competitiveness. Acknowledgement The investigation presented in this paper was supported by a CRP project of the International Atomic Energy Agency. References [1] Desalination Economic Evaluation Program, User s Manual, Computer Manual Series No. 14, IAEA, Vienna, Austria, [2] Methodology for the Economic Evaluation of Cogeneration/Desalination Options: A User s Manual, Computer Manual Series No. 12, IAEA, Vienna, Austria, [3] Examining the Economics of Seawater Desalination Using the DEEP Code, IAEA-TECDOC-1186, [4] Publications and Studies Using the IAEA Software, Desalination Economic Evaluation Program DEEP, Working Material, IAEA 622-I3, 2000.