[en] The sulfur-iodine (SI) thermochemical cycle is one of the main candidate methods to produce hydrogen from non-fossil sources like nuclear (GEN IV reactor) or solar thermal power. A major issue for the successful implementation of the SI cycle is the selection of technically viable and economic materials for construction of process components, particularly heat exchangers. Challenging conditions are encountered in each of the three sections of the SI cycle due to the corrosive chemicals present, including sulfuric acid, iodine, hydroiodic acid, sulfur dioxide, hydrogen, oxygen, and others. In Section I, aqueous, non-aqueous (liquid iodine), and gaseous multi-component phases are present at about 120 ^oC and 0.7 MPa. Section II involves gaseous and aqueous phases of sulfuric acid, sulfur dioxide, and oxygen at up to about 830 ^oC and 3.6 MPa. In Section III , aqueous, non-aqueous, and gaseous phases, at up to 310 ^oC and 2.2 MPa, containing iodine, hydroiodic acid, hydrogen, and others are present. Numerous materials have been suggested for use in structural applications for the SI cycle. They can be divided into the following generic categories: refractory metals, reactive metals, superalloys, glassy metals, ceramics, cermets, polymers, composites, and coatings. A capsule method has been developed to rapidly quantify the decomposition rate of the candidate materials under the target conditions of temperature, pressure, and fluid composition of Section I and Section III. This paper describes experimental results obtained to date. Recommendations and rationale for the material selections for the measurements are given (also applicable to copper-chlorine cycle). (author)

[en] Although it has been recognised that SMA materials have a significant potential for deployment actuators, the number of applications of SMA-based actuators to the present day is still quite small, since a deeper understanding of the thermomechanical behaviour of SMA and how it might be exploited in the design of working actuators is necessary. In order to get a complete picture of the thermomechanical behaviour of Nitinol, one type of SMA, two kinds of experiment, purely thermal tests and thermomechanical tests, were carried out on Nitinol wires with diameters of 1 mm and 0.5 mm, and on Nitinol bars with diameter of 6.5 mm. In the purely thermal tests, a Differential Scanning Calorimeter was used to determine the phase transformation/ temperature relation of Nitinol wire with diameter of 1 mm and Nitinol bar. The thermomechanical tests, including tension tests at different temperatures, tension tests under different strain rates, response to suddenly applied loads, thermal cycling under different loads and thermal cycling with fixed length were carried out on Nitinol wire. Torsional tests, thermal cycling under different torques, and normal tension and thermal cycling tests were carried out on Nitinol bars with diameter of 6.5 mm. We have developed a thermo-micromechanical model based on complementary free energy and micromechanical transformation system to investigate the behaviour of shape memory under uniaxial load cycling and thermal cycling. Experimentally observed phenomena, such as V-shape of critical stress, non-symmetrical behaviour in tension and compression, transformation front behaviour, and multiphase transformation, were explained by this model. We present a phenomenological model which is based on the tension test, carried out at different constant temperatures, and a thermal cycling test under different constant loads. We have shown that our model can reproduce accurately the stress-strain-temperature relationship for all the quasi-static tests we have carried out on Nitinol wires. This model has no difficulty in dealing with incomplete loading or thermal cycling. This model has been used to simulate thermal cycling behaviour with fixed length, strain rate effects, and phase transformation front behaviour. Three Nitinol wire-based rotatory actuators, a one-way actuator, a biased actuator, and a two-way actuator, have been designed and tested. The behaviour of these actuators has been simulated by using the phenomenological model that we have developed. The power consumption to operate all actuators was measured. Two simple approaches were proposed to estimate the average power requirements. A preliminary study of a torsional actuator has been made. The general design procedure for Nitinol-based actuators is summarised. The broad aim of this dissertation is also to provide a user's guide to the design of SMA-based actuators. (author)

[en] A capsule method was employed to screen a number of materials for degradation under selected conditions of the sulphur-iodine (SI) and the copper-chlorine (Cu-Cl) thermochemical cycles. A summary of the results of an experimental investigation is given. The recommendations for the selection of the materials required for the construction of the electrolyser subsystem of the copper chlorine hybrid cycle are presented and discussed with the associated rationale. Some remaining uncertainties are illustrated on the basis of the experimental evidence gathered. (author)

[en] The key data for thermochemical calculations involving plutonium compounds are discussed. The problems involved in determining reliable standard entropies for plutonium compounds are emphasized, and it is suggested that much more use will have to be made of accurate measurements of equilibria involving the gaseous plutonium species whose standard entropies are known (namely Pu(g) and PuF₆ (g)) to obtain entropies of condensed phases. A number of equilibria which could be of use for this purpose are discussed. The data for the plutonium carbides have been critically assessed. (author)

[en] The iodine sulphur thermochemical cycle appears to be one of the most promising candidate for the massive production of hydrogen using nuclear energy. The key step in this cycle is the HI distillation section which must be optimized to get a good efficiency of the overall cycle. The concept of reactive versus extractive distillation of HI has been proposed because of its potentiality. The design and the optimization of the reactive distillation column requires the knowledge of the liquid vapour equilibrium over the ternary HI-I₂-H₂O mixtures up to 300 C and 100 bars. A general methodology based on three experimental devices imposed by the very corrosive and concentrated media will be described: 1) I1 for the total pressure measurement versus different ternary compositions. 2) I2 for the partial and total pressure measurements around 130 C and 2 bars to validate the choice of the analytical optical 'online' techniques we have proposed. 3) I3 for the partial and total pressures measurements in the process domain. The results obtained on pure samples, binary mixtures HI-H₂O and ternary mixtures using an experimental design analysis in the experimental device I2 will be discussed. (authors)

[en] The objective of this paper is to provide an overview of the copper-chloride thermochemical cycle and to discuss, in some detail, recent improvements in the hydrolysis reaction. The rationale behind the development of the Cu-Cl thermochemical cycle has been to offer a moderate temperature (< 550C) option for hydrogen production. If successfully developed, this chemical process could be coupled with several types of Gen IV nuclear reactors, e.g., the super critical water reactor or the Na-cooled fast reactor, or with a solar heat source such as the solar power tower with molten salt heat storage. The use of these lower temperature heating sources is expected to place less demand on materials of construction

[en] Full text of publication follows: While oxalate precipitation is a key operation leading to the first solid phase, the thermal transition of Pu(IV) oxalate into oxide plays a significant role in ensuring important properties of the oxide powder: open/closed porosity, specific area, residual carbon concentration. The overall control of these properties is relatively well achieved by suitable choice of the maximal heating temperature. The specific surface area of plutonium oxide, for example, depends directly on the maximum temperature reached during the heating step of the conversion. Conversely, the first steps of the decomposition imposed by the thermal program have often been neglected even though they can significantly affect the total carbon departure from the solid phase, the creation of porosity, and even the potential formation of fine solid fractions when the solid particles burst from thermal stress. The reaction mechanism of the thermal conversion of Pu^IV(C₂O₄)₂,6H₂O to oxide in air or argon was thoroughly investigated recently by TG analysis and structural analysis of the solid intermediates. Distinct reaction paths were established depending on the atmosphere used. The identity of some intermediates was assessed comparatively with previous studies and uncertainties about the Pu(III) intermediates formed, either under air or argon, were clarified. The discussion focuses on the main differences observed between air and Ar calcination, which could explain distinct properties of the final oxide product. (authors)

[en] A capsule method was employed to screen a number of materials for degradation under selected conditions of the sulphur-iodine (SI) and the copper-chlorine (Cu-Cl) thermochemical cycles. A summary of the results of an experimental investigation is given. The recommendations for the selection of the materials required for the construction of the electrolyser subsystem of the copper chlorine hybrid cycle are presented and discussed with the associated rationale. Some remaining uncertainties are illustrated on the basis of the experimental evidence gathered. (author)

[en] This paper examines the relevant thermophysical properties of compounds of chlorine and copper that are found in thermochemical water splitting cycles. There are four variants of such Cu-Cl cycles that use heat and electricity to split the water molecule and produce H₂ and O₂. Since the energy input is mainly in the form of thermal energy, the Cu-Cl water splitting cycle is much more efficient than water electrolysis, if the electricity generation efficiency for electrolysis is taken into account. A number of copper compounds (Cu₂OCl₂, CuO, CuCl₂, CuCl) and other chemicals (Cu, HCl) are recycled within the plant, while the overall effect is splitting of the water molecule. The system includes a number of chemical reactors, heat exchangers, spray dryer and electrochemical cell. This paper identifies the available experimental data for properties of copper compounds relevant to the Cu-Cl cycle analysis and design. It also develops new regression formulas to correlate the properties, which include: specific heat, enthalpy, entropy, Gibbs free energy, density, formation enthalpy and free energy. No past literature data is available for the viscosity and thermal conductivity of molten CuCl, so estimates are provided. The properties are evaluated at 1 bar and a range of temperatures from ambient to 675-1000K, which are consistent with the operating conditions of the cycle. Updated calculations of chemical exergies are provided as follows: 21.08, 6.268, 82.474, and 75.0 kJ/mol for Cu₂OCl₂, CuO, CuCl₂ and CuCl, respectively. For molten CuCl, the estimated viscosity varies from 2.6 to 1.7mPa.s. (author)

[en] 'Full text': The Nuclear Hydrogen Initiative requires a sophisticated understanding of the operation of a nuclear reactor as a high temperature heat source for hydrogen production. Accurate prediction of the behavior of a nuclear reactor coupled to a thermo-chemical cycle is essential to the safe operation of a nuclear reactor in steady state, off-normal, and accident conditions. A simplified transient model of the Sulfur-Iodine (SI) and Hybrid Sulfur (HyS) thermo-chemical cycles is developed. A control volume approach is used in analysis of the production schemes, and a study based on several reaction chamber assumptions is presented. Steady-state solutions of the control volume approach are extended to a fully transient model of both cycles. Transient results for simple initiating events are presented for both cycles. Concepts for continuing future work are suggested. (author)