O. Beneš

Predicting material release during a nuclear reactor accident

In the aftermath of a nuclear reactor accident, understanding the release of fission products from the fuel is key.

Excess heat capacity in liquid binary alkali-fluoride mixtures

Using drop calorimetry, we measured enthalpy increments of the LiF-KF, LiF-RbF, and LiF-CsF binary systems at temperatures above the melting point. Ten samples with different compositions (four compositions for LiF-KF, one composition for LiF-RbF, and five compositions for LiF-CsF) were prepared and measured between 884 K and 1382 K. To protect the calorimeter from corrosive fluoride vapor at high temperature, an encapsulating technique developed for this purpose was used. The samples were filled in nickel containers that were sealed by laser welding and afterward used for the measurements. From the obtained results, we derived the molar heat capacity functions of the respective samples. The heat capacities of the samples, having different compositions of the same binary system, were compared with the values for ideal behavior and the excess heat capacity function was determined for the entire composition range of the liquid solution. It was found that the excess heat capacities clearly depend on the cation radius and increase in the following order: LiF-NaF < LiF-KF < LiF-RbF < LiF-CsF.

Determination of the thermodynamic activities of LiF and ThF4 in the LixTh1-xF4-3x liquid solution by Knudsen Effusion Mass Spectrometry

Knudsen effusion mass spectrometry (KEMS) has been used to investigate the vapour pressure over the molten LiF-ThF4 salt and determine the thermodynamic activity of LiF and ThF4 in the liquid solution. As part of the study, the vaporization of pure LiF and pure ThF4 was examined and the results were compared with the literature values finding a good agreement. Next, the vapour pressure of the LixTh1-xF4-3x liquid solution was investigated by measuring four samples having different compositions (XLiF∼ 0.2, 0.4, 0.6, 0.8 mol%). In order to determine the thermodynamic activities, the vapour pressure of LiF and ThF4 species over the liquid solution, as calculated from our results, were compared with the vapour pressure over the pure LiF(l) and pure ThF4(l) systems. A strong deviation from the Raoults law was observed, more evident in case of LiF species, in agreement with the predictions by our thermodynamic model.

The Actinides Elements: Properties and Characteristics

In this chapter, the properties of the actinide (5f) elements are discussed. These elements are unstable and undergo radioactive decay. Because handling them is complex and their availability is limited, it is difficult to experimentally investigate their (bulk) properties and most of the data presented here are given for the major actinides, uranium and plutonium, which have been studied extensively because they are fissile and are used as fuel in nuclear reactors.