The Molten Salt Reactor (MSR) is one of the six nuclear reactor concepts considered in the Generation IV initiative. In the MSR concept, the fissile material is dissolved in a molten salt mixture, which serves as both fuel and coolant. The main task of this work was to study thermodynamic properties of molten salts systems, in order to determine the safety limit for the molten salt fuel. The investigations were carried out entirely on fluoride salts, which are currently the most relevant salts considered as potential fuel for MSR. In the present work, two techniques - Differential Scanning Calorimetry (DSC) and drop calorimetry - were employed to measure the thermodynamic properties (heat capacity, phase diagram equilibrium points, fusion enthalpy and mixing enthalpy) of some fluoride systems. A challenging task was the measurement of the mixing enthalpy of binary systems, which required the development of a new method compatible with the used DSC technique. In order to verify the possibility to measure the mixing enthalpy using this calorimeter, the well-known LiF-KF system was adopted as reference and studied. Based on the good results obtained, the technique was applied for the LiF-ThF4 system, important for Molten Salt Fast Reactor (MSFR), and its enthalpy of mixing has never been measured before. Moreover, the phase diagram equilibrium points were measured for both systems using the same technique, confirming the existence of LiThF5 phase. The Li3ThF7 compound was synthesized and its fusion enthalpy was determined. All the experimental data collected were used to assess the phase diagrams, using the CALPHAD method. Experimental determination of heat capacity were carried out using drop calorimeter on the following fluoride systems: CsF in the solid phase, (Li0.5Rb0.5)F in the liquid phase and ThF4 in the solid phase. While the data on ThF4 are not yet finalized and only preliminary results are shown in this thesis, the study of the other two systems has been concluded. The study of LiF-RbF liquid solution confirmed a trend of the excess heat capacity behaviour in the LiF-AlkF (Alk=Na,K,Rb,Cs) system.
Il reattore a sali fusi (MSR-Molten Salt Reactor) è uno dei sei concetti di reattori che costituiscono la Generazione IV. In questo reattore, il materiale fissile è disciolto in una miscela di sali fusi che svolge la duplice funzione di combustibile e fluido termovettore. L'obiettivo principale di questo lavoro di tesi è stato lo studio delle proprietà termodinamiche dei sistemi di sali fusi, utile a stabilire i limiti di sicurezza delle miscele. Le misure sono state svolte sulla classe dei fluoruri, i cui sali sono i principali candidati come combustibile per il reattore a sali fusi. Le proprietà termodinamiche (calore specifico, punti del diagramma di fase, entalpia di fusione ed entalpia di miscelamento) sono state misurate utilizzando la calorimetria differenziale a scansione e la calorimetria a caduta. Un compito importante è stato la misura dell'entalpia di miscelamento dei sistemi binari, che ha richiesto lo sviluppo di un nuovo metodo di misura compatibile con il calorimetro a scansione differenziale. Per confermare la possibilità di misurare l'entalpia di miscelamento con questo metodo, è stato scelto come riferimento il sistema LiF-KF, ben noto in letteratura. Grazie ai buoni risultati ottenuti, il metodo è stato applicato al sistema LiF-ThF4, fondamentale per il reattore veloce a sali fusi (MSFR-Molten Salt Fast Reactor), ed è stata misurata l'entalpia di miscelamento per la prima volta. Inoltre, sono stati misurati i punti del diagramma di fase, confermando l'esistenza della fase LiThF5, ed è stato sintetizzato il composto Li3ThF7, misurandone l'entalpia di fusione. Tutti i dati sperimentali ottenuti sono stati combinati per la modellazione del diagramma di fase, utilizzando l'approccio CALPHAD. Utilizzando il calorimetro a caduta, sono state eseguite misure di calore specifico su tre sistemi di fluoruri: CsF e ThF4 in fase solida e (Li0.5Rb0.5)F in fase liquida. Mentre i risultati sul ThF4 sono preliminari, lo studio degli altri due sistemi è da ritenersi concluso. L'analisi del sistema LiF-RbF ha confermato una tendenza del calore specifico in eccesso nel sistema LiF-AlkF (Alk=Na,K,Rb,Cs).
Thermodynamic characterization of salt components for molten salt reactor fuel
CAPELLI, ELISA
2010/2011
Abstract
The Molten Salt Reactor (MSR) is one of the six nuclear reactor concepts considered in the Generation IV initiative. In the MSR concept, the fissile material is dissolved in a molten salt mixture, which serves as both fuel and coolant. The main task of this work was to study thermodynamic properties of molten salts systems, in order to determine the safety limit for the molten salt fuel. The investigations were carried out entirely on fluoride salts, which are currently the most relevant salts considered as potential fuel for MSR. In the present work, two techniques - Differential Scanning Calorimetry (DSC) and drop calorimetry - were employed to measure the thermodynamic properties (heat capacity, phase diagram equilibrium points, fusion enthalpy and mixing enthalpy) of some fluoride systems. A challenging task was the measurement of the mixing enthalpy of binary systems, which required the development of a new method compatible with the used DSC technique. In order to verify the possibility to measure the mixing enthalpy using this calorimeter, the well-known LiF-KF system was adopted as reference and studied. Based on the good results obtained, the technique was applied for the LiF-ThF4 system, important for Molten Salt Fast Reactor (MSFR), and its enthalpy of mixing has never been measured before. Moreover, the phase diagram equilibrium points were measured for both systems using the same technique, confirming the existence of LiThF5 phase. The Li3ThF7 compound was synthesized and its fusion enthalpy was determined. All the experimental data collected were used to assess the phase diagrams, using the CALPHAD method. Experimental determination of heat capacity were carried out using drop calorimeter on the following fluoride systems: CsF in the solid phase, (Li0.5Rb0.5)F in the liquid phase and ThF4 in the solid phase. While the data on ThF4 are not yet finalized and only preliminary results are shown in this thesis, the study of the other two systems has been concluded. The study of LiF-RbF liquid solution confirmed a trend of the excess heat capacity behaviour in the LiF-AlkF (Alk=Na,K,Rb,Cs) system.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/47702