Thermal and Mechanical Characterization of Carbides for High Temperature Nuclear Applications

Abstract

In the facilities for the production of Radioactive Ion Beams (RIBs) according to the Isotope Separation On-Line (ISOL) technique, a production target is typically impinged by a high-power primary beam, generating radioactive isotopes for basic research and technological applications. With the aim to guarantee an efficient extraction of the aforementioned isotopes, the production target must work in a high vacuum environment, at temperatures that are usually between 1600 °C and 2200 °C. Its main components are often characterized by intense temperature gradients and consequently by severe thermal stresses. Carbides are widely used for target manufacturing, and in this work a specific method for their thermal and mechanical characterization is presented and discussed. It is based on the comparison between experimental measurements and numerical simulations, with the introduction of the novel Virtual Thermoelastic Parameters approach for the structural verification procedure. High-performance silicon carbides (SiC) are taken as a reference to describe the method. Measured emissivity and thermal conductivity data are presented and discussed, together with the experimental estimation of material limitations for both temperature and stress fields. The aforementioned results can be promptly used for the design process of high-power ISOL targets.

Thermal and Structural Characterization of a Titanium Carbide/Carbon Composite for Nuclear Applications

“…The 1 μm spectral emissivity data collected for all three samples exhibited a consistent quasi-constant behavior between 0.7 and 0.8. This range is typical for this kind of carbide and was observed in previous works for similar materials [ 18 ]. Furthermore, the consistency of the data collected for the three different samples confirmed the repeatability of the production technique.…”

“…For the estimation of ε and k at a high temperature, two specific experimental procedures were developed in previous works based on a dedicated experimental setup ( Figure 1 ) [ 18 , 24 ]. This device consisted of a vacuum chamber, capable of operating at vacuum levels around 10 −6 mbar, containing a graphite Ohmic heater.…”

“…The same experimental test bench used for the thermal characterization could be used to perform fracture tests by thermal stresses on the sample disks. This procedure, described in detail in previous works [ 18 ], involved the gradual intensification of such stresses by slowly increasing the heating current on the graphite heater up to the fracture of the sample. In the case of ceramic samples, a brittle fracture was expected.…”

“…This extreme working condition entails thermal stresses within the target disks that could eventually lead to their failure if their stress limit is reached. As a result, the characterization of the target material’s thermostructural behavior is a crucial aspect for both target design and the safe operation of the facility [ 18 ].…”

“…In this work, taking the strategy adopted for the thermal and mechanical characterization of a commercial dense SiC as reference, the production procedure of custom porous composite TiC/C disks is described with the experimental measurement of their spectral emissivity and the estimation of their thermal conductivity. The stress limit of this custom material was estimated according to the virtual thermoelastic parameter (VTP) approach that was theorized in previous works [ 18 ]. This method allows the evaluation of the target’s structural design, even if thermoelastic material properties, such as Poisson’s ratio, Young’s modulus, and the coefficient of thermal expansion, are unknown.…”