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In order to progress in the development of Lead-cooled Fast Reactors, from the safety point of view it is essential to understand the chemical compatibility between liquid lead and uranium oxide. In the present work, entropy and heat capacity of Pb3U11O36, a possible ternary compound coming from fuel-coolant chemical interaction, were determined for the first time. Entropy at 298.15 K was obtained from low temperature heat capacity measurements using the Physical Property Measurement System (PPMS) in the temperature range 2–300 K, while the high temperature heat capacity has been measured by a drop calorimeter from 373 K to 1200 K. The experimental thermodynamic properties were compared with the values computed by means of DFT-GGA simulations, obtaining a very good agreement.

The low-temperature heat capacity of (U 1-y ,Am y )O 2− x solid solution with y = 0.0811 and 0.2005 and x = 0.01–0.03 was determined from a minimum of 12.52 K up to 297.1 K and from 9.77 K up to 302.3 K, respectively, using hybrid adiabatic relaxation calorimtry. The low temperature heat capacity results of the investigated system revealed the absence of the magnetic transition specific for UO 2 in the temperature region of 30 K. Since there are no experimental data available for AmO 2 in this temperature region, the results obtained for the intermediate compositions are validated based on the experimental data of UO 2 end-member and the low-temperature heat capacity computation of AmO 2 . In the measured temperature interval, excess heat capacity was observed for the two investigated intermediate compositions, which is concluded to be dominated by self-radiation effects at very low temperature.

PuF3 was synthetized by hydro-fluorination of PuO2 and subsequent reduction of the product by hydrogenation. The obtained PuF3 was analysed by X-Ray Diffraction (XRD) and found phase-pure. High purity was also confirmed by the melting point analysis using Differential Scanning Calorimetry (DSC). PuF3 was then used for thermodynamic assessment of the PuF3-LiF system. Phase equilibrium points and enthalpy of fusion of the eutectic composition were measured by DSC. XRD analyses of selected samples after DSC measurement confirm that after solidification from the liquid, the system returns to a mixture of LiF and PuF3.

The authors regret to inform that the thermodynamic data [Formula presented] of the pure compound CsI(l) was not reported correctly in Table 3. The corresponding enthalpy of formation should read: [Formula presented]

A thermodynamic model for the Na-O system was developed for the first time using the CALPHAD method after review of the structural, thermodynamic, and phase diagram data available on this system. Differential Scanning Calorimetry measurements were moreover performed to assess the phase equilibria and liquidus temperature in the Na2O-Na2O2 composition range. A CALPHAD model for the Na-U-O system was furthermore developed on the basis of both reviewed experimental data, and thermodynamic functions of the sodium uranates derived by combining ab initio calculations and a quasi-harmonic statistical model. The phase equilibria in this ternary system are particularly relevant for the safety assessment of the nuclear fuel-sodium coolant interaction in Sodium-cooled Fast reactors (SFRs). The model predicts the stability of the ternary phase field UO2-Na3UO4-Na4UO5, which is consistent with the most recent literature data. Further optimization was moreover performed to fit the sodium partial pressures measured experimentally in the NaUO3-Na2U2O7-UO2 and NaUO3-Na2UO4-Na2U2O7 phase fields, yielding an overall consistent description. Finally, the oxygen content required to form pentavalent Na3UO4 and hexavalent Na4UO5 in liquid sodium at 900 K were calculated to be 0.7 and 1.5 wppm, respectively, which are levels typically encountered in SFRs.

In this study we present a comprehensive thermodynamic description of the binary CsF-ThF4 system. The phase equilibria of several intermediate compositions in this system have been determined using the DSC technique combined with a post-analysis using powder X-ray diffraction. Considering all the novel experimental data, a thermodynamic model for the CsF-ThF4 system has been developed for the first time using the Calphad approach. The present model reproduces very well the measurements performed. Knudsen effusion mass spectrometry (KEMS) has further been used to investigate the vapour pressure over the molten CsF-ThF4 salt and to determine the thermodynamic activities of CsF and ThF4 in the liquid solution. As part of this study, the vaporization of pure CsF was examined and the results were compared with the literature showing a good agreement. Next, the vapour pressure of CsF-ThF4 in the liquid solution was investigated by measuring three samples with compositions X ThF4 = (0.4, 0.6, 0.8) mol/mol. A strong negative deviation from Raoult’s law was observed for both species, more evident in case of CsF, and a good agreement with the predictions of our thermodynamic model was found. This article is a pre-requisite for the assessment of the ternary LiF-CsF-ThF4 system.

Mixed uranium and americium dioxides (U, Am)O 2±x are candidates as possible transmutation targets for generation IV reactors. In this work, the enthalpy increments of this solid solution were measured in the 470–1750 K temperature range by drop calorimetry for Am/(Am + U) ratios equal to 0.32, 0.39, 0.49, 0.58 and 0.68. Then, the heat capacity functions were obtained by derivation of the enthalpy data. The results of this work were compared to the heat capacity and enthalpy functions reported in the literature for the UO 2 [1] and AmO 2 [2] binary oxides and for the U 0.9 Am 0.1 O 2±x , U 0.8 Am 0.2 O 2±x mixed oxides [3]. From the obtained trend, it was found out that an excess contribution to the enthalpy increment appears for T > 1100 K in the compositions with Am/(Am + U)≥0.4 and a possible explanation attributing this effect to oxygen hypostoichiometry is provided. Finally, to verify the hypothesis, thermodynamic computations based on the CALPHAD method were performed for AmO 2-x under air and the results confirmed that the source of the excess contribution is the formation of oxygen vacancies.

Four fluoride fuel salt samples (78LiF-22ThF4) in graphite crucibles were irradiated in the HFR Petten for a duration of 508 Full Power Days under the name SALIENT-01 (SALt Irradiation ExperimeNT). Goal of the experiment was to gain experience with the design of liquid salt experiments and the handling of the salts before and after irradiation. Specific research goals for SALIENT-01 are (i) to confirm claims of good fission product retention in the salt, (ii) to obtain size distributions for noble metal particles using Transmission Electron Microscopy and (iii) to assess possible interactions between fuel salt and fine-grained nuclear graphite, as well as possible uptake of fission products by the graphite. Here the design and irradiation history of the experiment are discussed together with plans for post-irradiation examinations. Limitations in representativeness of this experiment and capsule irradiations in general are discussed as well as follow-up actions to improve the quality of future irradiations.

Investigations on the phase relation in the Pb-U-O ternary system have shown the formation of three lead uranium(VI) oxides: PbUO 4 , Pb 3 UO 6 , and Pb 3 U 11 O 36 . We present here the synthesis, thermal expansion, low- and high-temperature heat capacity, and thermal diffusivity of two representative phases (PbUO 4 and Pb 3 UO 6 uranates). Combining these results, a value for their thermal conductivity was derived and reported here for the first time.

Quantum chemical calculations of the molecular properties of the UO 2 (OH) 2 molecule are presented. From the results the thermodynamic properties of this gaseous species have been calculated, and these have been used to re-evaluate the existing literature study on the volatilization of U 3 O 8 in steam, allowing to derive the enthalpy of formation of the UO 2 (OH) 2 molecule.

A thermodynamic assessment of the KF-ThF4 binary system using the CALPHAD method is presented, where the liquid solution is described by the modified quasichemical formalism in the quadruplet approximation. The optimization of the phase diagram is based on experimental data reported in the literature and newly measured X-ray diffraction and differential scanning calorimetry data, which have allowed to solve discrepancies between past assessments. The low temperature heat capacity of α-K2ThF6 has also been measured using thermal relaxation calorimetry; from these data the heat capacity and standard entropy values have been derived at 298.15 K: Cp,mo(K2ThF6,cr,298.15K)=(193.2±3.9) J·K-1·mol-1 and Smo(K2ThF6,cr,298.15K)=(256.9±4.8) J·K-1·mol-1. Taking existing assessments of the relevant binaries, the new optimization is extrapolated to the ternary systems LiF-KF-ThF4 and NaF-KF-ThF4 using an asymmetric Kohler/Toop formalism. The standard enthalpy of formation and standard entropy of KNaThF6 are re-calculated from published e.m.f data, and included in the assessment of the ternary system. A calculated projection of the NaF-KF-ThF4 system at 300 K and the optimized liquidus projections of both systems are compared to published phase equilibrium data at room temperature and along the LiF-LiThF5 and NaF-KThF5 pseudobinaries, with good agreement.

The low-temperature heat capacity of the (Th1−y,Puy)O2 solid solution with y=0.03, 0.08, 0.30, 0.54 and 0.85 was determined from 4 K up to about 300 K with a PPMS instrument using the hybrid adiabatic relaxation method. In addition, the heat capacity of 239PuO2 end member was also measured and compared with available literature data for 242PuO2, observing an indistinguishable match. The obtained heat capacity values of the intermediate compositions are greater than the data obtained from Neumann–Kopp's molar additivity rule based on the ThO2 and PuO2 end-members, and a substantial excess capacity is observed for all intermediate compositions, particularly at the lowest temperatures.

The chemistry of cesium and iodine is of main importance to quantify the radioactive release in case of a nuclear reactor accident, or sabotage involving irradiated nuclear materials. We studied the interaction of CsI with different metallic fission products such as Mo and Ru. These elements can be released from nuclear fuel when exposed to oxidising conditions, as in the case of contact of overheated nuclear fuel with air (e.g. in a spent fuel cask sabotage, uncovering of a spent fuel pond, or air ingress accidents). Experiments were performed by vaporizing mixtures of the compounds in air, and analysing the produced aerosols in view of a possible gas–gas and gas–aerosol reactions between the compounds. These results were compared with the gaseous species predicted by thermochemical equilibrium calculations and experimental equilibrium vaporization tests using Knudsen Effusion Mass Spectrometry.

This study presents an original approach of oxygen stoichiometry determination during high temperature (>2000 K) measurements of vapour pressure using the Knudsen effusion mass spectrometry technique. The method has been developed taking into account the vapour pressure measurements of series of (U1-x,Pux)O2-δU1-x,Pux)O2-δ samples with x(Pu) = 0.25, 0.5, 0.75 together with pure UO2-δUO2-δ and PuO2-δPuO2-δ end-members coupled with equilibrium calculations based on thermodynamic assessment of the U–Pu–O system. The presented method consists of two steps; in the first step the oxygen potential of the oxide phase is determined based on the measured partial vapour pressures of UO(g), UO2(g), PuO(g) and PuO2(g) gaseous species and during the second step the thus determined oxygen potential is linked with the matching oxygen stoichiometry of the sample. From the obtained results it has been demonstrated that it is possible to accurately estimate the oxygen stoichiometry of the mixed oxide fuel samples knowing the description of the oxygen potential of the corresponding end-members only.

The work presents the measured heat capacity of the (Li1−xCax)F1+x liquid solution. Four samples with different compositions have been prepared and measured using a Differential Scanning Calorimeter. Since this technique was newly adopted for measuring encapsulated fluoride samples, some modifications were introduced in the standard configuration of the instrument and they are described in this work as well. For comparison one of the analysed composition (xCaF2 = 0.5) was also measured using drop calorimetry, which has been previously used for similar studies. The reliability of the results obtained was confirmed by the good agreement between the two techniques. Moreover, the excess heat capacity of the (Li1−xCax)F1+x liquid solution was derived and a strong deviation from the ideal behaviour was observed.

The enthalpy increments of ( U 1 - y , Am y ) O 2 - x mixed oxides with y = 0.0877 and 0.1895 and x = 0.01–0.03 were measured using drop calorimetry in the temperature range 425–1790 K and the heat capacity was obtained as differential of the obtained enthalpy increments with respect to temperature. The thermal diffusivity was measured using the laser flash technique from 500 to 1550 K. The thermal conductivity was calculated from the measured thermal diffusivity, density and heat capacity. Measured enthalpy increments of the ( U 1 - y , Am y ) O 2 - x solid solutions are very close to the end members, indicating no excess contribution. The derived heat capacities for the two intermediate compositions are slightly higher than that of UO2 and in a good agreement with literature data of AmO2 up to 1100 K. For the thermal conductivity of (U, Am)O2−x mixed oxides a correlation using the classical phonon transport model in crystal structures is proposed.

Thermodynamic assessments of the Th–U and Th–Pu binary systems are performed in this study according to CALPHAD method and together with the data on the U–Pu system, which has been already published in the literature, the Th–U–Pu ternary system is determined. All available experimental data from the literature were used for the binary system assessments and based on them the Gibbs energy properties of the unknown phases have been optimized. For the excess Gibbs energy of the liquid phase the ionic liquid model has been used, whereas for solid solutions the Redlich–Kister description was selected. In case of the Th–U and Th–Pu binary systems a very good agreement between the assessment and the experimental equilibrium data has been achieved, with 80% of equilibrium data reproduced within ±20K.

The enthalpy increments of the (Th1-y, Puy)O2 solid solution with y= 0.03, 0.08, 0.30, 0.54 and 0.85 and the PuO2 and ThO2 end-members were measured using drop calorimetry in the temperature range 476-1790 K. The heat capacity was obtained by derivation of the obtained enthalpy data with respect to temperature. The presented results for PuO2 and ThO2 are compared with the available literature data whereas the results obtained for (Th1-y, Puy)O2 solid solutions were compared with the Neumann-Kopp's molar additivity rule to search for possible non-ideal behaviour. This paper presents the first heat capacity data obtained for this system., JRC.E.3-Materials research

Samples of irradiated MOX of 44 GWd/tHM mean burn-up were prepared by core drilling at three different radial positions of a fuel pellet. They were subsequently heated in a Knudsen effusion mass spectrometry system up to complete vaporization of the sample (~2600 K) and the release of fission gas (krypton and xenon) and helium was measured. Scanning electron microscopy was used in parallel to investigate the evolution of the microstructure of a sample heated in the same condition up to given key temperatures as determined from the gas release profiles. A clear difference for fission gas release and microstructure was observed as a function of the radial position of the samples and therefore of irradiation temperature. A good correlation between the microstructure evolution and the gas release could be established as a function of the temperature of irradiation and (laboratory) heating., JRC.E.3-Materials research

We report a design for accelerator-driven subcritical fission in a molten salt core (ADSMS) that utilizes a fuel salt composed of NaCl and transuranic (TRU) chlorides. The ADSMS core is designed for fast neutronics (28% of neutrons >1 MeV) to optimize TRU destruction. The choice of a NaCl-based salt offers benefits for corrosion, operating temperature, and actinide solubility as compared with LiF-based fuel salts. Molecular dynamics (MD) codes have been used to estimate properties of the molten salt system that are important for ADSMS design but have never been measured experimentally.Results from the MD studies are reported. Experimental measurements of fuel salt properties and studies of corrosion and radiation damage on candidate metals for the core vessel are anticipated., JRC.E.3-Materials research

The work herein presents the first high temperature Knudsen effusion mass spectrometric measurements carried out on the sodium neptunate α-Na2NpO4. The material’s vaporization behaviour was investigated under vacuum conditions, in a tungsten metal cell up to T = 2700 K, and in an alumina cell up to T = 1900 K. Gaseous and condensed phases are in equilibrium under Knudsen conditions. The equilibrium decomposition reaction of α-Na2NpO4 to neptunium oxide, sodium oxide, and oxygen was established in the temperature range 1030 K to 1206 K. The enthalpy of formation of α-Na2NpO4 at 298.15 K was furthermore estimated at (−1761.0 ± 7.7) kJ·mol−1 using a second law analysis in the interval 1030 K to 1115 K, in good agreement with the value reported by Goudiakas et al. [25] (−1763.9 ± 7) kJ·mol−1, who used solution calorimetry. In the interval 1115 K to 1206 K, where the vaporization of sodium oxide formed by decomposition of α-Na2NpO4 is considered, the analysis yielded at 298.15 K (−1761.9 ± 20.4) kJ·mol−1 and (−1758.8 ± 22.3) kJ·mol−1 taking into account two different sodium oxide sublimation mechanisms suggested by Hildenbrand and Lau [56] and Steinberg and Schofield [37] respectively. Finally, the detection of the masses 253 and 292 in the temperature range 1350 to 1620 K suggests a probable sublimation of the high temperature tetragonal phase of the Na2NpO4 compound in parallel with the decomposition. The method developed in the present paper holds promise for the thermodynamic investigation of other sodium neptunates and plutonates phases.

A thermodynamic description of the LiF-CeF3-ThF4 system is made in this study using a two-sublattice model for the description of the solid solution and a quasi-chemical model based on quadruplet approximation for the liquid phase. New calorimetric experimental data of the binary LiF-CeF3, CeF3-ThF4 and ternary LiF-CeF3-ThF4 systems have been obtained in this work justifying the calculated phase diagrams. Using the obtained thermodynamic assessment the concentration of PuF3 in the LiF-ThF4 melt was estimated based on the similarities with CeF3 and the melting behaviour of the initial molten salt fast reactor fuel was discussed., JRC.E.3-Materials research

A thermodynamic investigation of the LiF–ThF 4 system is presented in this study. The enthalpy of mixing of the (Li,Th)F x liquid solution was measured for the first time using a method designed for conventional DSC technique. To verify the possibility to measure the mixing enthalpy with the used calorimeter, the known LiF–KF system was first investigated and compared to the literature data. After the successful test, this technique was applied to investigate the LiF–ThF 4 system and obtained novel results are presented in this study. Furthermore, using the DSC technique, new equilibrium data of the LiF–ThF 4 phase diagram were measured, confirming the stability of the LiThF 5 phase. The intermediate compound Li 3 ThF 7 was synthesized and its enthalpy of fusion was determined. Considering the new experimental data, the LiF–ThF 4 system was re-optimized using a quasi chemical model for the description of excess Gibbs parameters of the liquid solution.

In this study, we present new experimental heat capacity data of solid and liquid phase of CsF covering the temperature range from 5 K to 1400 K. The low temperature data were obtained by adiabatic calorimetry and compared with the theoretical heat capacity computed from ab initio harmonic crystal approximation. The absolute entropy at T = 298.15 K determined based on the presented results is 93.60 J · K - 1 · mol - 1 . The high temperature heat capacity was measured using a drop calorimeter and the data for the solid phase revealed significant excess properties. The data for the liquid phase were correlated with the molecular dynamic simulation obtaining a good agreement. The recommended molar heat capacity of the CsF solid phase is: C p , m ( J · K - 1 · mol - 1 ) = 24.291 + 6.4607 · 10 - 2 · ( T / K ) + 589981 · ( T / K ) - 2 J · K - 1 · mol - 1 and the one of the liquid phase was determined as: C p , m = 70.56 J · K - 1 · mol - 1 . From the calorimetric results the enthalpy of fusion of CsF was determined as: △ fus H = 22.1 ± 2.0 kJ · mol - 1 .

In this article new thermodynamic descriptions of the (LiF + UF3) and the (NaF + UF3) systems based on new calorimetric data are presented. The experimental investigations were carried out using differential scanning calorimetry (DSC) to obtain phase transition temperatures between (0 and 60) mol% of UF3. On the basis of these measurements a thermodynamic assessment of the ( Li x U 1 - x ) F 3 - 2 x and ( Na x U 1 - x ) F 3 - 2 x liquid solutions, using the quasi-chemical model was achieved. UF3 undergoes a disproportionation at higher temperatures to UF4 and U metal which had a significant impact on the transition temperatures in the (LiF + UF3) system. For this reason the influence of the presence of up to 15 mol% of UF4 in this system was calculated and compared to the experimental results. The final thermodynamic description was corrected for the pure binary system.

The enthalpy increments of PuPO 4 have been measured using drop calorimetry in the temperature range from 530 K to 1386 K. The heat capacity was derived from the obtained data and compared with heat capacity data obtained directly from differential scanning calorimeter measured in this study from 400 K to 1400 K. The recommended heat capacity of PuPO 4 was determined based on both techniques as: C p 0 ( J K - 1 mol - 1 ) = 126.600 + 32.999 × 10 - 3 ( T / K ) - 1.9503 × 10 6 ( T / K ) - 2 .

In this work a thermodynamic assessment of the (LiF + NaF + CaF 2 + LaF 3 ) system is reported. For the thermodynamic modeling of the liquid phase, the classical polynomial model, and the modified quasi-chemical model were used in parallel and compared. The extrapolation to higher order systems was done according to the Toop mathematical formalism. Furthermore, differential-scanning calorimetry data of the ternary (LiF + CaF 2 + LaF 3 ), (NaF + CaF 2 + LaF 3 ), and the quaternary (LiF + NaF + CaF 2 + LaF 3 ) mixtures are presented. Good agreement between the experimental data and the thermodynamic assessment was obtained.

The α – β phase transition of a zirconium alloy doped with 1 mol% of niobium (E110 alloy) is investigated using differential scanning calorimetry. The onset and endpoints of the transition are identified from the measured heat flow signal and from the integration of the observed peak the extent of the α – β phase change is calculated as a function of temperature. The experiment has been performed at different heating rates and a shift of the onset temperature with increasing heating rate was observed. From the dataset the equilibrium transition curve has been extrapolated and compared with other types of zirconium-based cladding materials.

The enthalpy increments of pure NpO2 have been measured using drop calorimetry in the temperature range from (376 to 1770) K. The heat capacity was derived using the obtained data constrained to 66.20 J · K−1 · mol−1 at 298.15 K taken from published low temperature measurements. The heat capacity of NpO2 determined in this study is given by the following equation: C p ,m 0 / ( J · K - 1 · mol - 1 ) = 71.608 + 0.015845 · ( T / K ) - 900648 · ( T / K ) - 2 .

The present study describes the full thermodynamic assessment of the LiF–NaF–BeF 2 –ThF 4 –UF 4 system which is one of the key systems considered for a molten salt reactor fuel. The work is an extension of the previously assessed LiF–NaF–ThF 4 –UF 4 system with addition of BeF 2 which is characterized by very low neutron capture cross section and a relatively low melting point. To extend the database the binary BeF 2 –ThF 4 and BeF 2 –UF 4 systems were optimized and the novel data were used for the thermodynamic assessment of BeF 2 containing ternary systems for which experimental data exist in the literature. The obtained database is used to optimize the molten salt reactor fuel composition and to assess its properties with the emphasis on the melting behaviour.

An innovative encapsulation technique designed for the DSC high temperature measurements of the volatile samples is presented in this study. Stainless steel crucibles with a screwed bolt were developed for this purpose. The technique was demonstrated on the phase diagram measurement of the NaNO3–KNO3 system and the obtained results are presented in this study. Up to date two thermodynamic assessments of the NaNO3–KNO3 phase diagram have been made, one characterized by a single eutectic point with limited solubilities in the solid state in both NaNO3 and KNO3 rich corners, whereas the other version prefers a continuous solid solubility with minimum on the liquidus line. Based on our results we confirm limited solubilities in the solid state.

The enthalpy increments of four liquid solutions Li 0.8 Na 0.2 F, Li 0.6 Na 0.4 F , Li 0.4 Na 0.6 F , and Li 0.2 Na 0.8 F were measured in the temperature range (1230 to 1470) K by drop calorimetry. The liquid phases of the LiF and NaF end-members were also measured, in the temperature range (1230 to 1470) K and (1320 to 1540) K, respectively. From the obtained results the molar heat capacity was derived and the data for pure LiF and NaF were correlated with the literature. In order to overcome problems related with the corrosive nature of alkali metal fluoride vapours at high temperature, a novel encapsulation technique is presented in this study. Small nickel crucibles were developed for this purpose which are sealed by laser welding.

The enthalpy increments of UPd3 and ThPd3 have been measured using the drop calorimetry for temperature range (480 to 1290) K. The heat capacity curves have been derived using the simultaneous linear regression of our data and the low temperature heat capacity data from previous studies. Furthermore the Schottky contributions for UPd3 were determined by comparing the ThPd3 and UPd3 heat capacity functions and correlated with the theoretical values calculated from the crystal field energy levels.

Nitride compounds are currently considered as possible fuels for advanced nuclear reactors. Among the relevant properties to be investigated, thermophysical quantities such as heat capacity and thermal diffusivity/conductivity are key to ensure safe operation of the fuel in the reactor. Both physical and chemical phenomenological experimental activities are included in this effort. The experimental procedures were optimized to limit oxidation of materials in presence of even small quantities of oxygen and moisture, especially during the measurements at high temperature. Heat capacity and thermal diffusivity/conductivity were measured for ZrN and (Zr,Pu)N compounds. A consistent set of results was obtained from low- and high-temperature Cp measurements for both materials. The excess Cp of solution was estimated. Increasing trends with temperature were observed for the thermal diffusivity and conductivity of both materials in the temperature range considered, confirming the metallic behavior of this class of materials. The presence of Pu causes an almost constant decrease of the thermal conductivity compared to the pure ZrN matrix.

This work is a critical review of the chemical–physical properties of the fluoride salts of interest in the Molten Salt Reactor project. In total five salt compositions are discussed. Two of them are choices for coolant applications (based on LiF–BeF 2 and NaF–NaBF 4 systems) one is considered as a heat transfer salt (LiF–NaF–KF system) whereas the other two are the main candidates for the fuels in non-moderated breeder and thermal breeder reactors, respectively (LiF–ThF 4 and LiF–BeF 2 –ThF 4 systems). For all the systems the phase diagrams are presented with the emphasis on the melting behaviour and the vapour pressure. Heat capacity, density, viscosity and thermal conductivity, as well as the solubility for actinides in case of the fuels are presented also.

In previous studies a thermodynamic description of the LiF–NaF–KF–RbF–CsF–LaF 3 system was presented. In order to add PuF 3 to this system the assessments of LiF–PuF 3 , NaF–PuF 3 , KF–PuF 3 , RbF–PuF 3 , CsF–PuF 3 and LaF 3 –PuF 3 binary phase diagrams have been made. In case of the LiF–PuF 3 and NaF–PuF 3 the assessments have been based on known experimental data. The other binary systems have not been measured yet and the thermodynamic description has been made using the excess parameters from the previously assessed binaries containing LaF 3 , which is considered as a proxy compound for PuF 3 . The main aim of this study is to analyze potential compositions for a molten salt fast burner fuel.

A full thermodynamic description of the quaternary NaCl–MgCl 2 –UCl 3 –PuCl 3 system, a Molten Salt Fast Breeder Fuel, is presented. The binary phase diagrams have been assessed in this study and the data were used to extrapolate the higher order systems. To optimize the excess parameters of the liquid phase the modified quasi chemical model has been used, while for the solid solution the classical polynomial model has been applied. From the obtained results a possible fuel composition for the Molten Salt Reactor has been evaluated.

In this work the three binary phase diagrams LiF–ZrF 4 , BeF 2 –ZrF 4 and UF 4 –ZrF 4 were thermodynamically assessed. The three ternary phase diagrams LiF–BeF 2 –ZrF 4 , BeF 2 –ZrF 4 –UF 4 and LiF–ZrF 4 –UF 4 were approximated on the basis of binary data. A pseudo-ternary LiF–BeF 2 –ZrF 4 system with constant amount of UF 4 set to 0.83 mol% was calculated as well, typical for molten salt reactor fuel. Based on this diagram a suggestion for the composition of the fuel in this system was made.

The heat capacity of gadolinium pyrochlore ( Gd 2 Ti 2 O 7 ) was measured by enthalpy increment measurements in the range of (585 to 1485) K utilizing drop calorimetry on a synthetic Gd-pyrochlore and the high-temperature dependence of the heat capacity has been determined.