Hydrogen production by thermochemical water-splitting IS process utilizing heat from high-temperature reactor HTTR

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1 Hydrogen production by thermochemical water-splitting IS process utilizing heat from high-temperature reactor HR Nariaki SAKABA a,b, Seiji KASAHARA b, Hirofumi OHAS a, Hiroyuki SAO a, Shinji KUBO b, Atsuhiko ERADA b, etsuo NISHARA b, Kaoru ONUKI b, Kazuhiko KUNIOI a a HR Cogeneration Design and Assessment roup, Nuclear Science and Engineering Directorate (Japan Atomic Energy Agency (JAEA), Oarai, Higashiibaraki, Ibaraki, , Japan, sakaba.nariaki@jaea.go.jp) b IS rocess echnology roup, Nuclear Science and Engineering Directorate, JAEA ABSRAC: High-temperature reactors (HRs) are particularly attractive due to their wide industrial application from electricity generation to hydrogen production. he Japan Atomic Energy Agency s (JAEA s) HR, which is the first HR in Japan, attained its maximum reactor-outlet coolant temperature and successfully delivered 950 C coolant helium outside its reactor vessel. A hydrogen production system based on the thermochemical water-splitting iodine sulphur (IS) process is planned to be connected to the HR in the near future. his will establish the hydrogen production technology with an HR, including the system integration technology for connection of hydrogen production system to HRs. It will probably be the world s first demonstration of hydrogen production directly using heat supplied from an HR. he HR-IS system design was launched from a conceptual design in his paper shows the summary of the HR, plan for developing the IS process in JAEA, thermal efficiency evaluation for the HR-IS system, etc. he verification of the hydrogen production by the HR-IS system by using heat from a nuclear reactor is greatly expected to contribute to the commercialization of nuclear hydrogen in coming hydrogen society. KEYWORDS : Nuclear hydrogen, IS process, VHR, HR, HR. 1. Introduction High emperature Reactors (HRs) are particularly attractive due to those inherent safety, economic viability, high efficiency, very high burnup, and wide industrial application (from electricity generation to hydrogen production). hey are expected to play a dominant role in the future hydrogen society. he Japan Atomic Energy Agency s (JAEA s) High emperature Engineering est Reactor (HR), which is the first HR in Japan, attained its maximum reactor-outlet coolant temperature and successfully delivered 950 C coolant helium outside its reactor vessel [1]. he rector-outlet coolant temperature of 950 C makes it possible to extend HR use beyond the field of electric power. Also, highly effective power generation with a hightemperature gas turbine becomes possible, as does hydrogen production from water. his paper describes the summary of the HR, R&D on the thermochemical water-splitting iodine sulphur (IS) process as well as a preliminary project plan and conceptual design of the HR-IS system. 2. Summary of the HR-IS system 2.1 Summary of the HR As the HR is the first HR in Japan and a test reactor, it has following purposes: Establishment of basic HR technologies, Demonstration of HR safety operations and inherent safety characteristics, Demonstration of nuclear process heat utilization, Irradiation of HR fuels and materials in an HR core condition, and, rovision of testing equipment for basic advanced studies. In order to demonstrate the nuclear process heat utilization, the intermediate heat exchanger (IHX) is equipped in the cooling system to supply high-temperature helium gas to a process heat application system 1/11

2 being coupled to the HR in the future. he detailed HR design was already reported [2] and the main cooling system is described in this chapter. As shown in Fig. 1, the cooling system of the HR consists of a main cooling system operating at normal operations; and an auxiliary cooling system and a vessel cooling system, the engineered safety features, operating after a reactor scram to remove residual heat from the core. he main cooling system, which consists of a primary cooling system, a secondary helium cooling system, and a pressurised water cooling system, removes heat generated in the core and dissipates it to the atmosphere by a pressurised water air cooler. he primary cooling system consists of an IHX, a primary pressurised water cooler (WC), a primary concentric hot-gas-duct, etc. rimary coolant of helium gas from the reactor at 950 C maximum flows inside the inner-pipe of the primary concentric hot-gas-duct to the IHX and WC. he primary helium is cooled to about 400 C by the IHX and WC and returns to the reactor flowing through the annulus between the inner- and outer-pipes of the primary concentric hot-gas-duct. he HR has two operation modes. One is the single-loaded operation mode using only the WC for the primary heat exchange. Almost all the basic performance of the HR system has been confirmed by the single-loaded operation mode. he other is the parallel-loaded operation mode using the WC and IHX. In a single-loaded operation mode the WC removes 30W of heat and in a parallel-loaded operation mode the WC and IHX remove 20W and 10W, respectively. It is planned to utilize the secondary helium gas of the IHX for the thermochemical water-splitting IS process and the secondary pressurised water cooler (SWC) will be replaced to the main components, e.g. SO 3 decomposer, decomposer, of the IS process. Reactor containment vessel Vessel cooling system C SWC SC IHX : Intermediate heat exchanger WC : rimary pressurized water cooler C : rimary gas circulator SWC : Secondary pressurized water cooler SC : Secondary gas circulator AHX : Auxiliary heat exchanger AC : Auxiliary gas circulator Auxiliary water air cooler AHX AC Reactor IHX WC C ( 3) ressurized water pump ressurized water air cooler Auxiliary water pump Auxiliary cooling system ain cooling system Fig. 1 Schematic diagram of the reactor cooling systems of the HR 2.2 R&D on the IS rocess hermochemical water-splitting is the method of obtaining hydrogen from water that consists of several reactions. he concept was first proposed in 1960s with the thermodynamic study [3], and since then, various processes have been proposed. he IS process [4] is one of the processes that have been researched intensively. he IS process consists of the following chemical reactions: I 2 + SO (the Bunsen reaction) (1) + SO O 2 (2) 2 H 2 + I 2 (3) he thermodynamically optimum temperature for decomposition of ideal gas of SO 3 made by vaporization of, which is the highest temperature reaction, is 779 C [5]. he optimum temperature in actual process condition is considered to be near of that. herefore the IS process is a candidate process of utilization of the HR heat. able 1 shows the overview of the R&D on the IS process in JAEA. he R&D started in the middle of 1980s. he main goal of the lab stage study was to show feasibility of the continuous hydrogen production. he initial stage was completed by the demonstration of the continuous and stochiometric hydrogen production of 1 NL/h for 48 hours [6]. 2/11

3 Duration WHEC 16 / June 2006 Lyon France able 1 Overview of the R&D on the IS process in JAEA Hydrogen production rate [Nm 3 /h] Lab stage middle of 1980s ~ 1997 Bench stage Heat supply Electric Electric aterial of apparatus lass lass ilot stage (entative) HR-IS stage (entative) 1998 ~ ~ ~ 2014 ~ ~ 0.05 ~ 30 ~ 1000 Helium heated electrically Helium heated by HR Industrial Industrial materials materials rocess pressure Atmospheric Atmospheric High pressure High pressure In the bench-scale study, the second stage, the following research fields were investigated: o control the process for long-time stable hydrogen production, o process decomposition procedure using membrane technologies, and, o screen corrosion resistant materials for the construction of the process. In achieving long-term stable hydrogen production, automated reaction control methods of the Bunsen reaction and devices were proposed. A bench-scale test apparatus was constructed for the verification of the methods and devices. Fig. 2 shows the simplified flowsheet of the test apparatus [7]. he IS process was split into three procedures; Bunsen reaction procedure (Bunsen ROC), decomposition procedure ( ROC) and decomposition procedure ( ROC). solution and x solution (solution of, I 2 and ) obtained in the Bunsen reactor are separated. Each of the solution is concentrated, vaporised and decomposed in ROC and ROC, respectively. H 2 and O 2 are obtained as products and other compounds return into the Bunsen reactor. he control methods and devices were tested in the demonstration experiment with the hydrogen production rate of 31 NL/h for 175 hours [2][7]. he results verified the effectiveness of the devised control method for long-term stable operation. Efficient separation of from the x solution and enhancement of the conversion ratio are effective to improve thermal efficiency. As for the former requirement, x solution was successfully concentrated to over the pseudo-azeotropic composition by the beaker size experiment of electro-electrodialysis (EED) [8]. he result shows highly concentrated can be obtained in the following distillation by application of the cell. As for the latter, a hydrogen permselective membrane reactor (HR) achieved to improve the one-pass conversion ratio to over equilibrium ratio by extracting hydrogen from reaction field [9]. Corrosion resistant materials are necessary because corrosive compounds are used at high temperatures in the IS process. Selection of the materials by corrosion tests has been carried out [10]. rototypes of heat exchanging blocks for the vaporiser [11] and SO 3 decomposer [12] were fabricated by using SiC ceramics, which show corrosion resistance in liquid phase environments. Structural integrity of these blocks was confirmed by thermal stress analysis as well as leakage tests of the block for vaporiser under horizontal loading were performed [11]. cooler, separator 0.5O2 H 2 SO 3 decomposer (SO 3 SO O 2 ) Bunsen reactor (I 2 + SO ) Reflux drum recovery ( SO 3 + ) solution x solution decomposer (2 H 2 + I 2 ) distillation H 2 SO 4 concentrator purifier x Liquid-liquid purifier separator ROC Bunsen ROC ROC Fig. 2 Simplified flowsheet of the bench-scale test apparatus [7] 3/11

4 he pilot stage is to follow the bench stage. Objectives of the pilot stage study are described as follows [10]: Construction of a pilot test plant made of industrial materials and completion of hydrogen production test utilizing electrically-heated helium gas as the process heat supplier, Development of analytical code system for the HR-IS system safety case review, Component tests to assist the hydrogen production test and to improve the process performance for the commercial plant, and, Design study of the HR-IS system. Heat from electrically heated helium is supplied to components such as SO 3 decomposer, vaporiser and decomposer. Verification of developed control procedure, obtaining operation data useful for verification of analytical codes, verification of integrity of apparatuses for corrosive environments, and feasibility of newly added apparatuses are expected through the hydrogen production tests. Computational codes were selected and an analytical code system was constructed based on the CAD/CAE [13]. his analytical code system is to be developed in the pilot stage for the design of the HR-IS system. he code will be utilized in the evaluations of the total process, materials, mechanical strength, thermal hydraulics, and safety case analysis. Component test apparatuses were constructed and experiments utilizing them have been carried out in order to improve the process performances. For instance, thermal-hydraulic test loops and a catalyst test apparatus for SO 3 decomposition were fabricated with corrosion resistant materials [14]. Data of, for example, performance and integrity of components, visualisation of boiling, and performance of catalysts for SO 3 decomposition is expected. Important data for scaling-up and for the improvement of concentration efficiency are expected to be taken by larger scale EED cells [13]. Corrosion rates of some structural materials were evaluated in Bunsen reaction environment as a part of the component test [15]. Design study of the HR-IS system where the HR and the IS process will be connected by the IHX are carried out during the pilot stage period. In the HR-IS stage, the integration of the HR and IS process will be conducted. he preliminary conceptual design of the HR-IS system has launched in 2005 in order to complete its design by the Conceptual design of the HR-IS system A hydrogen production system based on the IS process is planned to be connected to the actual hightemperature reactor HR in the near future. his will establish the hydrogen production technology with an HR including the system integration technology for connection of hydrogen production system to HRs. It will probably be the world s first demonstration of hydrogen production directly using heat supplied from a nuclear system. he HR-IS system aims to: Establish procedures on safety design and evaluation, Establish the technology on key high-temperature components, such as high-temperature valves, high-temperature bellows, Establish the control technology for both of the IS process and reactor, Add to experience of construction, operation, and maintenance, and, Show the roadmap towards the commercialisation of nuclear hydrogen production systems by the IS process including cost evaluation of the produced hydrogen by the VHR (Very High emperature Reactor) which is one of the eneration IV reactor candidates. he requirements of users, such as efficiency, amount and cost of produced hydrogen, safety scenario of the connection between a nuclear reactor and chemical plant, should be satisfied or should be shown its way to commercial reactors by the HR-IS system development. Since the secondary helium of the HR will be utilized in this system, the possibility of utilization of a non-nuclear class IS system as a chemical plant is investigated. Hydrogen explosion, tritium transfer, etc. will be evaluated in order to separate IS process from nuclear facilities by high-temperature valves. Development of the HR-IS system started from a conceptual design. Available structure of the system and its heat mass balance is evaluated initially. Basic design will be performed from design of apparatuses, kinetic analysis, and design of instrumentation and control systems in Safety case studies, detailed design, cost evaluation, and risk evaluation will be carried out in he safety analysis codes will be validated by using the component tests data and IS pilot plant operation data. he know-how of the pilot plant tests will be applied to the HR-IS system design. In 2009, safety assessment will be started. he 4/11

5 assessment will possibly need about two years, while some studies for the higher efficiency of the HR-IS system continues. he design of the HR-IS system will be completed until Separation technology of hydrogen will also be expected to be applied. he development schedule of the HR-IS system is shown in able 2. able 2 Development schedule of the HR-IS system Design Stage Detail Conceptual Design System Flow Evaluation Determination of Number of ain Component Heat ass Balance Abnormal Event Study (HAZO) (IS process) Basic Design Cost Evaluation Determination of Flowsheet lot lanning Apparatus Design Abnormal Event Study (Reactor) Failure Rate Data Collection Representative Abnormal Event Detailed Design, Cost Evaluation, Rationalization Design Design of Instrumentation & Control System Detailed Apparatus Design Code Development (Coupling with Reactor & IS process) Seismic Design Component Design ( Rationalization Design ) Code Validation by Indivisual Component ests Safety Analysis Code Validation by ilot lant est Fablication Design Fablication Design Safety Case Review by overnment rior to the abnormal event study, the number of main apparatuses in the IS process should be decided. he most severe event will be selected as a representative event in the HR-IS system. hen the event will be compared with the abnormal transient of the HR secondary system which was already evaluated during the HR design stage [2]. he IS process is designed conceptually using results of the component tests performed from 2005 and the concept of the HR-300H [16] which is the Japanese future HR designed by JAEA. In order to achieve higher efficiency in the HR-IS system, for instance, concentration of hydrogen iodide will be studied. he verification of the hydrogen production by the HR-IS system by using heat from a nuclear reactor is greatly expected to contribute to the commercialisation of nuclear hydrogen in coming hydrogen society. Fig. 3 shows the schematic diagram of a candidate HR-IS system [17]. Heat produced by the HR core is transferred to the secondary helium gas at the IHX. he secondary helium flows through the inner-pipe of the concentric hot-gas-duct and a high-temperature valve, and supplies heat to the components of the IS process such as SO 3 decomposer, vaporiser and decomposer. Finally, after cooled by the steam generator and a helium cooler, the secondary helium is pressurised by the helium gas circulator. Secondary helium returns to the IHX through the outer-pipe of the concentric hot-gas-duct IHX (Legend) Reactor containment vessel (inside) (outside) ressure [a (gauge)] emperature [ O C] Flow rate [t/h] Secondary helium purification system Diverter valve F 3.94 SO decomposer decomposer 875 Cooling water F By-pass diverter valve F Secondary helium gas circulator Cooling water Steam generator Helium gas cooler F Secondary helium purification system Cooling water Cooling water Fig. 3 Schematic diagram of a candidate HR-IS system [17] 5/11

6 Chemical impurity in the secondary helium will be removed by the secondary helium purification system. In order to construct the IS process by utilizing the non-nuclear standard, tritium permeation is one of the most important key parameters. he secondary helium purification system will be re-designed and will be replaced by using the newly developed chemistry control method [18]. he secondary pressure should be controlled to be higher than that of the primary in order to avoid the graphite-core oxidation as does in the HR. he pressure is kept below 1.1 times of the maximum design pressure by releasing gas from relief valves in a case of abnormal pressure increase. he process pressure of the IS process will be kept lower than that of secondary helium in order to avoid corrosions of the secondary pipes and equipment by entering the process gas or liquid, e.g. to the secondary system. During the loss of heat transfer from secondary helium to the IS process components, the steam generator and the helium cooler remove all of the secondary heat of 10Wt. At the same time, the by-pass diverter valve will open and the IS process components will be isolated by closing the diverter valves which will be installed at the entrance and exit of the IS process. In the commercial high-temperature gas-cooled reactors, the gas-turbine will be able to play its role of the steam generator adapting at the HR-IS system. he conceptual layout of the HR-IS system is shown in Fig. 4. Concerning the hydrogen explosion [19] which will be an assumed accident event in the hydrogen production system, the position of the section which includes hydrogen in its system should be set appropriate distance from the reactor facility. In addition, considering the effect of missile phenomenon, any equipment should not locate between the reactor and decomposer. From the viewpoint of the diffusion prevention such as the noxious fumes, the equipment utilized in some of the section and some of the section is stored in buildings. he results of conceptual layout design shows that it is possible that the IS process can construct compactly within 30m 103m. On the other hand, since our final target of IS produced hydrogen cost is 15JY (about 0.1euro or 0.125USD)/m 3, it is necessary for economic evaluation to reduce the IS process area in the commercial IS process (VHR-IS system, e.g. HR300-IS system). Some R&D is in progress for reducing the quantity or number of apparatus, for instance, grouping and packaging of some of main equipment, designing all-inone type heat exchanger, passive safety function to prevent entering liquid to some vapour section, etc. Detailed layout design will be determined based on both of the apparatus design and safety design in HR decomposer Concentric hot gas duct section SO 3 decomposer section Steam generator Bunsen reaction section Secondary helium loop IS process control room 30m Fig.4 Conceptual layout of the HR-IS system 6/11

7 Dynamic simulation code is necessary not only for the process simulation of the HR-IS system but also its safety case analysis. Since there was no needs of the coupling dynamic simulation code for a nuclear system and a chemical plant in the past, we are developing a code for the HR-IS system which can analyse plant dynamics and thermal hydraulics, and transient simulations for both of the HR and the IS process. he analytical code Conan-HR based on RELA5/OD3 was successfully developed by JAEA and applied to heat transfer calculations of the HR for its verification [20]. For the steam generator an analytical code was successfully developed based on the RELA5/OD2 and OD3 and it was verified by mock-up test facility of the steam reformer hydrogen production system [21]. For the IS process dynamic simulation code development is now underway within the IS pilot plant project. he IS process dynamic simulation code and Conan-HR code will be coupled in the FY2006. he coupling code will be verified by IS process apparatus test results and pilot plant tests, and it will be utilized for the safety case studies as transients simulation for reactor start-up and shut-down, reactor emergency shut-down, abnormal transients triggered by some IS process apparatus breakdown e.g. pump trip, etc., accident simulation by rupture of secondary helium system, etc. he results will be utilized for the safety case review for the government. he current accident simulation of the HR [2], the most severe accident of the secondary helium cooling system is rupture of the concentric hot-gas-duct. Even after replacing the secondary helium cooling system to the IS process, the most severe accident is assumed to be rupture of concentric hot-gas-duct besides hydrogen explosion [19]. he detailed analysis will be performed from the FY2007 to FY2009. Since attaining the higher thermal efficiency is not a purpose of the bench stage, the thermal efficiency of hydrogen production by the bench-scale IS process is calculated as 6.4 % by using components used in the bench-scale apparatus [2]. In the HR-IS system, higher thermal efficiency of about 40 % is expected to contribute to the commercialisation of water-splitting nuclear hydrogen production systems. able 3 ain properties of the IS process used in efficiency calculation he process using components in the bench-scale apparatus [2] 7/11 he process using components in the benchscale apparatus [2] HR-IS plant (using using a HR for separation of H 2 in decomposer) rocedure Apparatus Operation parameter Unit Bunsen ROC Bunsen reactor concentration in light phase mol% concentration in heavy phase mol% I 2 concentration in heavy phase mol% purifier, I 2 removal ratio mol% x purifier removal ratio mol% ROC Direct contact heat exchanger recovery ratio mol% concentration at the inlet of the decomposer mol% decomposition ratio mol% SO 3 decomposer SO 3 decomposition ratio * mol% Heat exchanger minimum temperature difference ** K ROC EED cell apparent transport number of proton of the CE *** mol/mol-e apparent electroosmosis coefficient of the CE *** mol/mol-e voltage V concentration of at cell exit mol% RO membrane selectivity - - infinite concentration of at exit mol% , I 2 recovery, I 2 recovery ratio mol% distillation pressure in the a decomposer one-pass conversion ratio mol% Heat exchanger minimum temperature difference **** K - 7 * SO 3 decomposition ratio = [outlet SO 2 ]/([inlet ] + [inlet SO 3 ]) 100 ** liquid phase / gas phase *** CE: Cation exchange membrane **** liquid phase / liquid phase Fig. 5(a) illustrates a tentative schematic flowsheet of the HR-IS system. here are several differences from bench-scale test apparatus. A three stage multiple-effect vaporiser is used as concentrator. A direct contact heat exchanger at upper stream of the vaporiser is adapted in order to recover unreacted in the SO 3 decomposer and exchange heat efficiently. An EED cell and a reverse osmosis (RO) membrane are added in order to increase the concentration of the x solution to over pseudoazeotropic one. When the concentrated x solution is fed to the distillation, -rich vapour is

8 obtained from the top. I 2 is removed from the reaction field by reaction with cobalt (Co) in decomposition reactor. One pass conversion ratio is expected to be improved by the shift of reaction equilibrium by the removal of I 2 [22]. Fifteen heat exchangers are attached for its heat recovery in this process. roperties of the components in the HR-IS process are compared with those of the bench-scale components in able 3. For the hydrogen production rate and thermal efficiency evaluation, mass balance in the process was determined at first as standardization of the 1 mol/s of hydrogen production rate. Heat balance was calculated based on the mass balance. In the heat balance calculation, following assumptions were applied: he calculation covered part of the IS process, he process is operated adiabatically, and, Electricity generation efficiency is 40 %. Hydrogen production rate depends upon the available amount of heat supplied from secondary helium gas. he flow of 880 C helium gas is supplied at the rate of approximately 2.5 kg/s. Heat of the helium is utilized in the IS process components and temperature of the gas is decreased. he amount of heat transfer is limited because the IS process components require certain temperatures. Hydrogen production rate was calculated from the heat balance of 1 mol/s of hydrogen production rate and the heat supply from the secondary helium gas. hermal efficiency of the IS process (η) was calculated by the following equation (4): Higherheatingvalueof hydrogen(285.8kj/mol) η = 100 H + H heat elec. (4) Here, H heat denotes the net heat demand and H elec. denotes the heat required to produce the net electricity demand. Details of the method of the thermal efficiency calculation are reported elsewhere [23]. Hydrogen production rate of the process of Fig. 4(a) can be calculated about 850 Nm 3 /h and its efficiency was about 43 % [17]. Fig. 6(a) shows the heat and temperature demands of the IS process and the heat supply from the secondary helium. Recovery of Co requires heat of C and the amount of heat transferred from helium is limited by the lower limit temperature (circle in Fig. 6(a)). Decrease of required temperature for decomposition is an important key to increase hydrogen production rate. One method for decrease the temperature is to add the application of HRs. Fig. 5(b) shows the flowsheet adapted with HRs. When HRs are installed to the system, temperature can be expected to decrease to about C. A preliminary calculation of thermal efficiency and hydrogen production rate was carried out and the hydrogen production rate was calculated as 1,100 Nm 3 /h and its efficiency was about 44 %. Fig. 6(b) shows the detail of demands and supply of heat. Hydrogen production rate was improved because lower temperature range of helium could be utilized and thermal efficiency was increased by more efficient heat utilization. able 4 shows the heat demand per 1 mol of hydrogen and thermal efficiency of the benchscale apparatus and HR-IS system. hough electric energy is required for the usage of the EED cell in the HR-IS system, heat demand is significantly decreased comparing with the bench-scale apparatus because the newly applied components can concentrate or decompose and in the HR-IS system effectively. Bunsen ROC ROC SO 3 decomposer SO 3 SO O 2 Bunsen ROC ROC SO 3 decomposer SO 3 SO O 2,, I 2 SO 2, O 2 SO 3, SO 2, O 2,,, I 2 SO 2, O 2 SO 3, SO 2, O 2, O 2 O 2 purifier O 2 Bunsen reactor SO 2 +I Liquidliquid separator 3 stage concentrator ROC Direct contact heat exchanger SO 3 + B/L: O 2 O 2 purifier O 2 Bunsen reactor SO 2 +I Liquidliquid separator 3 stage concentrator ROC Direct contact heat exchanger SO 3 + B/L: SO 2, O 2 x purifier H 2 purifier H 2 SO 2, O 2 x purifier H 2 purifier H 2 H B/L:O 2 2 H B/L:O 2 2 Lean EED cell + RO membrane Rich, I 2 recovery EED cell, I 2 H 2 Lean Rich + RO recovery membrane H 2, I 2, H 2, I 2, I 2, distillation decomposer,i 2 absorber Co CoI 2 Co recovery, I 2, distillation decomposer, H 2 separator 2+Co H 2 +CoI 2 2 H 2 +I 2 Fig. 5(a) entative simplified flowsheet of the HR- IS plant (absorption of I 2 by Co in the decomposer) Fig. 5(b) entative simplified flowsheet of the HR- IS plant (utilizing a HR for separation of H 2 in the decomposer) 8/11

9 Heat supply [kw] distillation rocess flow Secondary Helium Co recovery SO 3 decomposer emperature [ ] Fig. 6(a) Q- diagram of HR-IS plant (absorption of I 2 by Co in the decomposer) Heat supply [kw] rocess flow Secondary Helium decomposer distillation SO 3 decomposer emperature [ ] Fig. 6(b) Q- diagram of HR-IS plant (utilizing a HR for separation of H 2 in the decomposer) able 4 Heat demands and thermal efficiency Unit he process using components in the bench-scale apparatus [2] HR-IS plant (using a HR for separation of H 2 in decomposer) HR300C-IS plant (using Co absorption of I 2 for separation of H 2 in decomposer) Heat demand kj/mol-h Heat for electricity kj/mol-h * otal kj/mol-h hermal efficiency (η) % * Not including the electricity for pump and utilities JAEA s design of the commercial reactor and its IS system, HR300-IS process plant, is almost same as that of the HR-IS system using I 2 absorption by Co in decomposition reactor [16]. Hydrogen production rate is calculated as about 26,000 Nm 3 /h by the application of the HR300C. 4. Concluding remarks Japan Atomic Energy Agency (JAEA) launched a preliminary design of the hydrogen production system by using heat from the Japan s first high-temperature gas-cooled reactor HR from he thermochemical water-splitting iodine sulphur (IS) process is the progressive candidate for the hydrogen production system. he conceptual design of the HR-IS system and its thermal efficiency for the hydrogen production are evaluated in this paper. Since the secondary helium of the HR will be utilized in this hydrogen production system, the possibility of utilization of a non-nuclear class IS process as a chemical plant is investigated and available structure of the HR-IS system with its approved heat mass balance is proposed. Hydrogen explosion, tritium transfer, etc. should be evaluated in order to separate IS process from nuclear facilities by high-temperature valves. he results of flowsheet evaluation show that the hydrogen production rate of about 1,100 Nm 3 /h and its thermal efficiency of 44 % can be achieved by the optimized HR-IS system. he design of the HR-IS system will finally be determined considering economy and efficiency. It is expected that the HR-IS system will be a world first water-splitting hydrogen production demonstration by using the direct heat from a high-temperature gas-cooled reactor and the verification of the hydrogen production by nuclear system is greatly expected to produce massive quantity of hydrogen in coming hydrogen society. 9/11

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