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Thermo, Volume 1, Issue 2 (September 2021) – 10 articles

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Review
Thermodynamically Informed Nuclear Fuel Codes—A Review and Perspectives
Thermo 2021, 1(2), 262-285; https://0-doi-org.brum.beds.ac.uk/10.3390/thermo1020018 - 09 Sep 2021
Viewed by 355
Abstract
A number of codes are used to predict various aspects of nuclear fuel performance and safety, ranging from conventional fuel performance codes to simulate normal operating conditions to integral engineering codes to simulate severe accident behaviour. There has been a number of reportings [...] Read more.
A number of codes are used to predict various aspects of nuclear fuel performance and safety, ranging from conventional fuel performance codes to simulate normal operating conditions to integral engineering codes to simulate severe accident behaviour. There has been a number of reportings in the open literature of nuclear fuel codes being informed by thermodynamic calculations, ranging from the use of simple thermodynamic correlations to direct coupling of equilibrium thermodynamic software. Progress in expanding predictive capabilities have been reported, which also includes advances in thermodynamic database development to better capture irradiated fuel. However, this progress has been accompanied by several challenges, including effective coupling of different types of physical phenomena in a practical manner and doing so with a reasonable increase in computational expense. This review paper will summarize previous experiences reported in the open literature in coupling thermodynamic calculations with nuclear fuel codes and applications, identify current challenges and limitations, and offer some perspectives for the community to consider moving forward. Full article
(This article belongs to the Special Issue Thermodynamics and Nuclear Materials)
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Article
Thermochemistry of Polonium Evaporation from LBE
Thermo 2021, 1(2), 251-261; https://0-doi-org.brum.beds.ac.uk/10.3390/thermo1020017 - 08 Sep 2021
Viewed by 287
Abstract
Polonium is formed in relatively large quantities in lead-bismuth eutectic (LBE) cooled nuclear systems. Because of its radiotoxicity and volatility, a good understanding of the chemical equilibria governing polonium release from LBE is required. In this work, a set of thermochemical data is [...] Read more.
Polonium is formed in relatively large quantities in lead-bismuth eutectic (LBE) cooled nuclear systems. Because of its radiotoxicity and volatility, a good understanding of the chemical equilibria governing polonium release from LBE is required. In this work, a set of thermochemical data is derived for the chemical species involved in the equilibrium between a solution of polonium in LBE and its vapor in inert conditions. The data were obtained by matching thermochemical models with experimental vapor pressure measurements and ab initio results. The dilute-limit activity coefficient of dissolved polonium in LBE is estimated, as well as the solubility of solid lead polonide in LBE. The results indicate that polonium evaporates from LBE according to the experimentally determined Henry’s law, up to dissolved polonium concentrations well above that expected in LBE cooled nuclear systems. Full article
(This article belongs to the Special Issue Thermodynamics and Nuclear Materials)
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Article
Thermodynamic Assessment of the NaF-KF-UF4 System
Thermo 2021, 1(2), 232-250; https://0-doi-org.brum.beds.ac.uk/10.3390/thermo1020016 - 27 Aug 2021
Viewed by 508
Abstract
In the Molten Salt Reactor (MSR) concept, metal fluorides are key components of possible fuel and coolant salts. The fast reactor option opens the possibility for alternatives to the Li based matrix salts, avoiding the costly 7Li enrichment and the tritium production [...] Read more.
In the Molten Salt Reactor (MSR) concept, metal fluorides are key components of possible fuel and coolant salts. The fast reactor option opens the possibility for alternatives to the Li based matrix salts, avoiding the costly 7Li enrichment and the tritium production from residual 6Li. Such alternatives can be based on NaF and KF as matrix components. In this study, two pseudo-binary phase diagrams of NaF-UF4 and KF-UF4, and the NaF-KF-UF4 pseudo-ternary system were experimentally investigated using Differential Scanning Calorimetry (DSC). The obtained data were used to perform a full thermodynamic assessment of the NaF-KF-UF4 system. The calculated pseudo-ternary eutectic was found at 807 K and a 68.9-7.6-23.5 mol% NaF-KF-UF4 composition. The comprehensive experimental and modelling data obtained in this work provide further extension of the JRCMSD thermodynamic database describing thermodynamic properties of key fuel and coolant salts for the MSR technology. Full article
(This article belongs to the Special Issue Thermodynamics and Nuclear Materials)
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Review
Dynamic Character of Thermal Analysis Where Thermal Inertia Is a Real and Not Negligible Effect Influencing the Evaluation of Non-Isothermal Kinetics: A Review
Thermo 2021, 1(2), 220-231; https://0-doi-org.brum.beds.ac.uk/10.3390/thermo1020015 - 24 Aug 2021
Viewed by 348
Abstract
The development of instrumentation has allowed thermal analysis to become a widely used method not only in calorimetry but also in the field of non-isothermal kinetics that, however, provides a simplified philosophy of measurements. From the beginning, a methodology is used describing the [...] Read more.
The development of instrumentation has allowed thermal analysis to become a widely used method not only in calorimetry but also in the field of non-isothermal kinetics that, however, provides a simplified philosophy of measurements. From the beginning, a methodology is used describing the course of reaction in a simplified temperature regime measured in an inert sample. In a most common case of DTA, the degree of reaction is subtracted from the partial areas of the as-cast peak in the unified mode of the peak linear background. Usually, the effect of thermal inertia, resulting from the reality of heat transfer and changing the peak background to a non-linear s-shaped form, is not incorporated. Therefore, the question of whether or not to include this effect of thermal inertia has become a current underlying problem of thermo-analytical kinetics. The analysis of the rectangular input heat pulses and their DTA responding fundamentally point to the need to include it thus becoming essential and not negligible. In the case of parallel evaluations, the effect of inertia can be partially compensated for each other such as in the Kissinger evaluation method. The study presents a broad overview of the thermo-analytical methodology used and points to the often-neglected literature. However, standard mainstream kinetics procedures need be fixed, and an improved solution found to account for the effect of heat transfer and dissipation, which is becoming the focus of thermal analysis methods of future and also the intention of this review. Full article
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Article
Thermodynamic Assessment of the AF–CrF3 (A = Li, Na, K) and CrF2–CrF3 Systems
Thermo 2021, 1(2), 205-219; https://0-doi-org.brum.beds.ac.uk/10.3390/thermo1020014 - 18 Aug 2021
Viewed by 270
Abstract
Understanding the corrosion mechanisms and the effect of corrosion products on the basic properties of the salt (e.g., melting point, heat capacity) is fundamental for the safety assessment and durability of molten salt reactor technology. This work focused on the thermodynamic assessment of [...] Read more.
Understanding the corrosion mechanisms and the effect of corrosion products on the basic properties of the salt (e.g., melting point, heat capacity) is fundamental for the safety assessment and durability of molten salt reactor technology. This work focused on the thermodynamic assessment of the CrF2−CrF3 system and the binary systems of chromium trifluoride CrF3 with alkali fluorides (LiF, NaF, KF) using the CALPHAD (computer coupling of phase diagrams and thermochemistry) method. In this work, the modified quasi-chemical model in the quadruplet approximation was used to develop new thermodynamic modelling assessments of the binary solutions, which are highly relevant in assessing the corrosion process in molten salt reactors. The agreement between these assessments and the phase equilibrium data available in the literature is generally good. The excess properties (mixing enthalpies, entropies and Gibbs energies) calculated in this work are consistent with the expected behaviour of decreasing enthalpy and Gibbs energy of mixing with the increasing ionic radius of the alkali cations. Full article
(This article belongs to the Special Issue Thermodynamics and Nuclear Materials)
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Review
Corium Experimental Thermodynamics: A Review and Some Perspectives
Thermo 2021, 1(2), 179-204; https://0-doi-org.brum.beds.ac.uk/10.3390/thermo1020013 - 11 Aug 2021
Viewed by 392
Abstract
More than 30 years ago a specialist meeting was held at Joint Research Center Ispra (Italy) from 15 to 17 January 1990 to review the current understanding of chemistry during severe accidents in light water reactors (LWR). Let us consider that, at the [...] Read more.
More than 30 years ago a specialist meeting was held at Joint Research Center Ispra (Italy) from 15 to 17 January 1990 to review the current understanding of chemistry during severe accidents in light water reactors (LWR). Let us consider that, at the end of the 1980s, thermodynamics introduced in the severe accident codes was really poor. Only some equilibrium constants for a few simple reactions between stoichiometric compounds were used as well as some simple correlations giving estimates of solidus and liquidus temperatures. In the same time, the CALPHAD method was developed and was full of promise to approximate the thermodynamic properties of a complex thermochemical system by the way of a critical assessment of experimental data, a definition of a simple physical model and an optimisation procedure to define the values of the model parameters. It was evident that a nuclear thermodynamic database had to be developed with that new technique to obtain quite rapidly prominent progress in the knowledge of thermochemistry in the severe accident research area. Discussions focused on the important chemical phenomena that could occur across the wide range of conditions of a damaged nuclear plant. The most pressing need for improved chemical models is identified with condensed phase mixtures to model the corium progression. This paper reviews more than 30 years of experimental data production in the field of corium thermodynamics. This work has been conducted through multiple international programs (EURATOM, ISTC, OECD) as well as through more specific studies conducted at the national scale. This research has been capitalised in specific databases such as NUCLEA and TAF-ID, databases developed at IRSN and at CEA, respectively, and are now used in degradation models of the severe accident simulation codes. This research is presented in this paper. In the conclusion, we outline the research perspectives that need to be considered in order to address today’s and tomorrow’s issues. Full article
(This article belongs to the Special Issue Thermodynamics and Nuclear Materials)
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Article
Developing Practical Models of Complex Salts for Molten Salt Reactors
Thermo 2021, 1(2), 168-178; https://0-doi-org.brum.beds.ac.uk/10.3390/thermo1020012 - 28 Jul 2021
Viewed by 505
Abstract
Molten salt reactors (MSRs) utilize salts as coolant or as the fuel and coolant together with fissile isotopes dissolved in the salt. It is necessary to therefore understand the behavior of the salts to effectively design, operate, and regulate such reactors, and thus [...] Read more.
Molten salt reactors (MSRs) utilize salts as coolant or as the fuel and coolant together with fissile isotopes dissolved in the salt. It is necessary to therefore understand the behavior of the salts to effectively design, operate, and regulate such reactors, and thus there is a need for thermodynamic models for the salt systems. Molten salts, however, are difficult to represent as they exhibit short-range order that is dependent on both composition and temperature. A widely useful approach is the modified quasichemical model in the quadruplet approximation that provides for consideration of first- and second-nearest-neighbor coordination and interactions. Its use in the CALPHAD approach to system modeling requires fitting parameters using standard thermodynamic data such as phase equilibria, heat capacity, and others. A shortcoming of the model is its inability to directly vary coordination numbers with composition or temperature. Another issue is the difficulty in fitting model parameters using regression methods without already having very good initial values. The proposed paper will discuss these issues and note some practical methods for the effective generation of useful models. Full article
(This article belongs to the Special Issue Thermodynamics and Nuclear Materials)
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Review
Steam Oxidation of Silicon Carbide at High Temperatures for the Application as Accident Tolerant Fuel Cladding, an Overview
Thermo 2021, 1(2), 151-167; https://0-doi-org.brum.beds.ac.uk/10.3390/thermo1020011 - 27 Jul 2021
Viewed by 531
Abstract
Since the nuclear accident at Fukushima Daiichi Nuclear Power Station in 2011, a considerable number of studies have been conducted to develop accident tolerant fuel (ATF) claddings for safety enhancement of light water reactors. Among many potential ATF claddings, silicon carbide is one [...] Read more.
Since the nuclear accident at Fukushima Daiichi Nuclear Power Station in 2011, a considerable number of studies have been conducted to develop accident tolerant fuel (ATF) claddings for safety enhancement of light water reactors. Among many potential ATF claddings, silicon carbide is one of the most promising candidates with many superior features suitable for nuclear applications. In spite of many potential benefits of SiC cladding, there are some concerns over the oxidation/corrosion resistance of the cladding, especially at extreme temperatures (up to 2000 °C) in severe accidents. However, the study of SiC steam oxidation in conventional test facilities in water vapor atmospheres at temperatures above 1600 °C is very challenging. In recent years, several efforts have been made to modify existing or to develop new advanced test facilities to perform material oxidation tests in steam environments typical of severe accident conditions. In this article, the authors outline the features of SiC oxidation/corrosion at high temperatures, as well as the developments of advanced test facilities in their laboratories, and, finally, give some of the current advances in understanding based on recent data obtained from those advanced test facilities. Full article
(This article belongs to the Special Issue Thermodynamics and Nuclear Materials)
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Review
Hybrid Electric Vehicles: A Review of Existing Configurations and Thermodynamic Cycles
Thermo 2021, 1(2), 134-150; https://0-doi-org.brum.beds.ac.uk/10.3390/thermo1020010 - 22 Jul 2021
Cited by 1 | Viewed by 704
Abstract
The mobility industry has experienced a fast evolution towards electric-based transport in recent years. Recently, hybrid electric vehicles, which combine electric and conventional combustion systems, have become the most popular alternative by far. This is due to longer autonomy and more extended refueling [...] Read more.
The mobility industry has experienced a fast evolution towards electric-based transport in recent years. Recently, hybrid electric vehicles, which combine electric and conventional combustion systems, have become the most popular alternative by far. This is due to longer autonomy and more extended refueling networks in comparison with the recharging points system, which is still quite limited in some countries. This paper aims to conduct a literature review on thermodynamic models of heat engines used in hybrid electric vehicles and their respective configurations for series, parallel and mixed powertrain. It will discuss the most important models of thermal energy in combustion engines such as the Otto, Atkinson and Miller cycles which are widely used in commercial hybrid electric vehicle models. In short, this work aims at serving as an illustrative but descriptive document, which may be valuable for multiple research and academic purposes. Full article
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Article
Thermodynamic Description of the ACl-ThCl4 (A = Li, Na, K) Systems
Thermo 2021, 1(2), 122-133; https://0-doi-org.brum.beds.ac.uk/10.3390/thermo1020009 - 16 Jul 2021
Viewed by 540
Abstract
The ACl-ThCl4 (A = Li, Na, K) systems could be of relevance to the nuclear industry in the near future. A thermodynamic investigation of the three binary systems is presented herein. The excess Gibbs energy of the liquid solutions is described using [...] Read more.
The ACl-ThCl4 (A = Li, Na, K) systems could be of relevance to the nuclear industry in the near future. A thermodynamic investigation of the three binary systems is presented herein. The excess Gibbs energy of the liquid solutions is described using the quasi-chemical formalism in the quadruplet approximation. The phase diagram optimisations are based on the experimental data available in the literature. The thermodynamic stability of the liquid solutions increases in the order Li < Na < K, in agreement with idealised interactions and structural models. Full article
(This article belongs to the Special Issue Thermodynamics and Nuclear Materials)
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