In the field of high-temperature thermal energy storage, the use of reacting systems that reversibly decompose and regenerate, absorbing and releasing heat on demand, is becoming more and more attractive. It is essential in the perspective of achieving high thermal energy density storage, appearing potentially suitable for long-term applications too. Thermochemical Systems (TCS) can contribute to increasing the dispatchability of thermal storage, potentially even on a seasonal timescale. So far, most of this field's scientific works have focused on the conventional concept of fixed-bed reactors.To improve the heat transport phenomena involved in TCS storage, a fluidized bed solution was considered in this article. At this aim, a manganese aluminium spinel, which is a low toxic, low pollutant and very cost-effective is proposed for this application. It was synthesized in the form of properly sized (150-200 mu m of diameter) particles to be effectively adopted for fluidizing beds. The present work deals with the sizing of the reactor and its coupling with a Concentrating Solar Thermal (CST) system using the Solar Central Receiver (SCR) technology with air as Heat Transfer Fluid (HTF). Imposing realistic boundaries, an optimal configuration was established, with an operating HTF pressure of 4 bar and a thermal discharging power of about 16 MWth. A volumetric energy density of 170 kWhth/m3 was achieved and, despite a relatively low TES reaction enthalpy, the resulting specific cost of 33 euro/kWh demonstrates the suitability of this configuration even for the current thermal storage commercial solution, and shows the high potentiality of this type of storage systems.

ThermoChemical Storage systems (TCS) are gaining attention for long term-thermal energy storage applications. Those systems can successfully increase the electricity generation flexibility in CSP (Concentrated Solar Power) plants or optimize the heat recovery and storage in energy-intensive industries (EII) as well. CaO/CaCO3 based systems are currently broadly investigated for thermochemical storage, either natural or synthetic materials. Among these, CaO/Mayenite (Ca12Al14O33) sorbents are considered very promising. CaO/Mayenite (Ca12Al14O33) based material was developed according to two different synthesis methods. The first one con-sisted in a one-step sol-gel method where aluminium precursor and pure CaO are weighted to obtain the exact weight ratio of 75/25 (CaO/Ca12Al14O33). In the second one, a two-step method was adopted: pure Mayenite was preliminarily synthetized by one step sol-gel method and CaO/Mayenite was obtained by direct wet mixing with pure CaO. Samples obtained were characterized by XRD, SEM, TGA, nitrogen physisorption, Raman spectroscopy and thermal stability was tested over 40 charging/discharging cycles in TGA. Raman spectra revealed free ox-ygen O2 � presence in the structure of Mayenite and in CaO-Mayenite samples as well, lying at 1128 cm-1. Thermal properties such as thermal conductivity, heat capacity and volumetric energy density storage have been deter-mined. The thermal conductivity found were 0.377 & PLUSMN; 0.004 (W/mK) for A; 0.101 & PLUSMN; 0.006 (W/mK) for B and for Mayenite 1.16 & PLUSMN; 2.7 10-4 (W/mK). It was found that two step method led to a better performing material in terms of carbonation reaction reactivity, and hence thermal storage. This material showed 50 % carbonation reaction conversion value at 40th cycle, corresponding to 0.250 g CO2/g dry sample, which is 4 times higher than CaO conversion. At 40th cycle, moderate sintering effect is remarked, with 2.3 % conversion drop, indicating that Mayenite insertion effectively acts as spacer. Volumetric storage energy density Sd has been determined for both samples and compared to CaO at increasing cycle number. Sample B storage density was effectively even at 40th cycle with 0.69 GJ/m3, thus about 3.5 times higher than CaO.

Parabolic trough concentrated solar power (CSP) plants are particularly promising renewable sources of energy, whose easy integration with thermal energy storage (TES) systems allows to mitigate the intermittency of electricity generation. Currently, molten nitrates, with two tanks arrangement, are mainly used for sensible heat accumulation. To reduce costs and make the CSP storage systems more manageable, single tank configurations have been proposed, where the cold and hot fluids are stored in the same container and separated because of their density difference. The aim of the present work is to study the storage performances presented by two novel ternary and quaternary mixtures, proposed within the European project IN POWER. An experimental campaign was preliminarily performed to investigate the fluids thermo-physical properties, and the obtained values were utilized as input data to model the discharge phase in a thermocline tank. The simulation results were compared with the ones acquired considering two commercial materials, namely, solar salt and Hitec XL (R). Overall, considering same temperature ranges, higher discharging times are obtained for the quaternary and ternary mixtures, with the ternary presenting a smaller thermocline thickness than the solar salt while this parameter is the same considering the quaternary and Hitec XL (R).

Thermal oils are nowadays largely employed as heat transfer fluids or cooling media in industrial and energy production plants. However, despite their widespread use, very few data are currently available about their chemical stability and possible composition changes in function of the operating temperatures, which are of crucial importance to evaluate the lifetime of these materials in real conditions. In the present work, a commercial terphenyl-based oil was investigated with respect to its thermal stability, performing ageing tests followed by a complete post-characterization analysis. To this purpose, a dedicated experimental set-up was designed and constructed to study the degradation processes, with a qualitatively and quantitatively analysis of the released gases and condensable products, together with a post-ageing characterization of the oil thermo-physical properties. The results show that the main decomposition mechanism involves the loss of hydrogen atoms, followed by partial polymerization processes, which explain the increase in dynamic viscosity and the decrease in volatility observed for the thermally stressed materials. Finally, the decomposition kinetic constants were estimated, obtaining a value of about 100 kJ/mol for the activation energy, which is in good agreement with the data available in the scientific literature.

The global need for energy in the world is constantly increasing. Critical fission reactors have proved great efficiency in the energy production, but the fear of nuclear wastes and accidents due to an uncontrolled chain reaction makes these unpleasant to public. More safe fusion reactors, on the opposite, have low efficiency. Hybrid reactors capable of using the advantages of both are studied, but not yet developed. In this paper, a simple fusion–fission pilot experiment model has been developed. A Tokamak with the same characteristics of DTT (Divertor Tokamak Test facility) has been considered as a reference machine for the fusion component. The fusion system has been coupled with a relatively simple low-power fission blanket configured into three different modes by using different fuels and materials. This model could be useful in order to investigate the properties of the fusion–fission hybrid coupling from a neutronic point of view.