Thermal diffusivity of ATF cladding materials using laser flash technique

A new method to determine the thermal diffusivity of polymer film by flash radiometry is presented. The transient infrared radiation from the sample surface was measured after the sample film was heated by a short-duration pulsed light. The thermal diffusivity was determined by fitting the transient infrared signal to the theoretical curve of a one-dimensional heat diffusion model. The transient infrared signal of polymethylmethacrylate (PMMA) film could be well fitted by the theoretical curve using appropriate thermal diffusivity in the wide temperature range between 100 K and near the softening point of PMMA. The temperature dependence of thermal diffusivity of PMMA film showed that the thermal diffusivity sensitively reflects the molecular motion of polymer chain.

Since the 2011 Fukushima accident, significant research has been devoted to developing accident-tolerant fuel (ATF) cladding materials. These investigations have mostly focused on the ability to resist runaway steam oxidation and retain mechanical strength and structural integrity under thermal shocks. However, much remains unknown about the materials’ thermal-hydraulic behavior, particularly under light-water reactor (LWR) operating conditions. Two phenomena that determine safety margins in both normal and off-normal operating conditions - i.e., the critical heat flux (CHF) and Leidenfrost point (LFP) temperature - have not been investigated thoroughly for ATF materials. Surface properties, such as wettability and roughness, are known to influence pool and flow boiling CHF, as well as the LFP temperature. However, little is known about the surface wettability of ATF materials, particularly at LWR pressure and temperature. Little has been done on flow-boiling CHF and quenching heat transfer, especially for droplet quenching. Nonetheless, it is known that CHF in transient conditions, e.g., an exponentially escalating power transient, can be significantly different from that expected in steady-state operation. Very few studies have investigated transient CHF, either on ATF materials or under LWR pressure and temperature. The thorough understanding of transient CHF under prototypical reactor conditions will benefit not only the deployment of ATF but also the upcoming national efforts to study transient ATF behavior in the Transient Reactor Test Facility (TREAT) at Idaho National Laboratory. In summary, as a part of ATF development efforts, there is an urgent need to understand how and how much these materials may affect two-phase heat transfer phenomena in nuclear reactor conditions.

Critical processes and parameters in the development of accident tolerant fuels drop-in capsule irradiation tests

Thermophysical and structural investigation OP Eu 2O 3 - Mo system

Development Status of Accident-tolerant Fuel for Light Water Reactors in Korea

Accident-tolerant fuels (ATF) represent a crucial advancement in nuclear reactor safety and efficiency. These cladding materials and coatings were developed to enhance the integrity and safety of nuclear fuel elements under accident scenarios, particularly during high-temperature transients. This article details the oxidation testing methodologies used to evaluate the performance of uncoated and chromium-coated cladding materials in simulated severe accident conditions with air ingress. The results of the oxidation in high temperature steam and air are presented, and the examination of microstructure of the oxide layer and the molten metals are examined and illustrated. Additionally, separate effect testing methods are described that are used to determine the mechanical properties of the cladding samples under various loads: ring compression, and ring tensile tests, ballooning and burst tests, and mandrel ductility tests simulating pellet-cladding mechanical interaction.

Study of change in thermal diffusivity of amorphous polymers during glass transition

Preliminary safety analysis of the PWR with accident-tolerant fuels during severe accident conditions

Thermal diffusivity is an important material thermophysical property. The most widely used method for measuring thermal diffusivity is the laser flash technique. In this technique, a sample is placed within a controlled atmosphere furnace and subjected to a finite impulse of radiant energy on its front surface, through the use of a laser. The transport of heat through the sample, as a result of the laser impulse, causes a transient temperature rise on the rear surface of the specimen. This temperature rise is measured by an IR detector placed above the rear sample surface. The net result is a “thermogram” which is a plot of the rear‐face temperature versus time. Assuming a proper set‐up and careful experimentation, the transfer of heat under these conditions approximates one‐dimensional heat flow. Comparing the experimental data with one‐dimensional heat flow theoretical predictions, allows an estimation of thermal diffusivity. There are several methods available to determine thermal diffusivity based on experimental and theoretical comparisons. The simplest method is to determine the “half‐rise time,” t 0.5, which is the time at which the experimentally measured rear‐face temperature reaches half of its maximum value. More accurate methods use sophisticated analysis algorithms to model and fit the entire experimental thermogram curve to an ideal theoretical curve by means of a nonlinear least‐squares procedure. These approaches can include corrections that account for the fact that the experimental measurements only approximate one‐dimensional heat flow conditions. Using the thermogram curve fitting techniques, the measurement of thermal diffusivity of a range of material types including solid thermal insulators and conductors is possible. It is also possible to measure the apparent diffusivity of inhomogeneous samples such as composites and porous materials. Using two‐ and three‐layer analysis methods allows the measurement of thermal diffusivity of liquids. The layer methods can be extended to a determination of the thermal contact resistance of interfaces encountered in coated or bonded materials.

A new transient measuring method of thermal diffusivity by continuous heating of a slab-like specimen to obtain the temperature dependence of thermal diffusivity covering a wide temperature range in a short time, is investigated. The principle is based on the solution of equation of linear heat conduction and the thermal diffusivity is determined from the temperature response at the center face of the specimen heated continuously from both surfaces. The measuring conditions are determined by theoretical analysis. By comparing the linear solutions of the measuring principle with the non-linear solutions of the measurement obtained analytically or numerically, the heating conditions of the specimens under which the linear principle is satisfied within required accuracies are determined. Results of testing polyethylene up to the softening temperature with an apparatus based on the above conditions are shown.

The impacts of various ATF (accident tolerant fuel) claddings on neutronic performances of pressurized water reactor fuel assembly and soluble‐boron‐free small modular reactor autonomous transportable on‐demand reactor module (ATOM) are investigated. There are two ATF cladding concepts which are evaluated here: (a) Coating Zircaloy‐4 cladding with thin layer of Cr or Cr alloys; (b) High‐strength and oxidation‐resistant claddings: SS‐304 and FeCrAl. A minor modification of burnable absorber loading in the ATOM core is proposed to adopt the selected ATF cladding and maintain the core performances.

(Y1-xNdx)3Zr5O14.5 solid solutions as inert matrices: Phase evolution, order-disorder dynamics and thermophysical behavior

Thermophysical properties of BaThO3

This work presents the thermal properties of ytterbium‐doped yttrium aluminium garnet (Yb:YAG) transparent ceramics at elevated temperatures in dependence on the dopant concentration and on temperature. Transparent polycrystalline Yb:YAG ceramics were prepared by solid‐state reaction of oxide powders sintered under high vacuum. The dopant amount varied from 0 to 20 at.% of Yb. Thermal diffusivity of the sintered samples was measured by the laser and xenon flash methods at temperatures ranging from room temperature to 900°C. Both the thermal diffusivity and thermal conductivity values decreased with increasing dopant content, and until 500°C a decrease was observed also with increasing temperature. When available, the measured values were compared to data published in literature, and were found to be in good agreement. Based on the measured values, empirical relations in the form of shifted power laws are proposed for the temperature dependence of thermal diffusivity.

The influence of temperature-dependent thermal diffusivity on the conductive cooling rates of plutons and temperature-time paths in contact aureoles