Conductivity Of Pebble Beds Research Articles

Repeatable experimental measurements of effective thermal diffusivity and conductivity of pebble bed under vacuum and helium conditions

Effective thermal diffusivity and conductivity are two crucial parameters to determine inherent safety in porous pebble bed of High Temperature Gas-cooled Reactor. A full-radius-scale heat test facility has been developed to measure these thermal properties at high temperature. Two vacuum tests and two atmospheric-pressure helium tests up to 1200 °C have been conducted to determine the temperature-dependent parameters by the inverse method. Repeatable results are validated by both tests with different heating processes. Furthermore, the primary experimental errors from installation positions of thermocouples as well as random packing effect are reduced by retrieving positions in the inverse method. Sensitivity and uncertainty analyses are carried out in respective tests to give the reasonable descriptions of the results of effective thermal diffusivity and conductivity in these tests.

Method and Validation for Measurement of Effective Thermal Diffusivity and Conductivity of Pebble Bed in High Temperature Gas-Cooled Reactors

The effective thermal diffusivity and conductivity of pebble bed in the high temperature gas-cooled reactor (HTGR) are two vital parameters to determine the operating temperature and power in varisized reactors with the restriction of inherent safety. A high-temperature heat transfer test facility and its inverse method for processing experimental data are presented in this work. The effective thermal diffusivity as well as conductivity of pebble bed will be measured at temperature up to 1600 °C in the under-construction facility with the full-scale in radius. The inverse method gives a global optimal relationship between thermal diffusivity and temperature through those thermocouple values in the pebble bed facility, and the conductivity is obtained by conversion from diffusivity. Furthermore, the robustness and uncertainty analyses are also set forth here to illustrate the validity of the algorithm and the corresponding experiment. A brief experimental result of preliminary low-temperature test is also presented in this work.

Measurement on effective thermal diffusivity and conductivity of pebble bed under vacuum condition in High Temperature Gas-cooled Reactor

A full-radius-scale heat test facility has been developed by the Institute of Nuclear and New Energy Technology (INET) of Tsinghua University in China to measure the effective thermal diffusivity and conductivity of pebble bed in High Temperature Gas-cooled Reactor (HTGR). In present test, a separate-effect transient experiment under vacuum condition is conducted successfully up to 1200 °C. Through inverse method and experimental temperature data, this paper presents the process of determining these thermal parameters and compares the results with previous researches, which reveals that the results are comparable in low-temperature region and valid in high-temperature region. In addition, it also studies the experimental errors and the results' uncertainties in this test. The correct knowledge on effective thermal diffusivity and conductivity of pebble bed inside the reactor core is significant to ensure the valid design and inherent safety, which will give a better balance between safety and economic competitiveness.

A Measurement Platform Scheme and Data Post-processing Method for Thermal Conductivity of Li4SiO4 Pebble Bed

The effective thermal conductivity of tritium breeder pebble bed is an important thermal parameter and must be known for the thermo-mechanical design of solid tritium breeder blankets. In order to obtain the parameter, experimental measurement is an effective method. A measurement platform was designed by University of Science and Technology of China for CFETR solid blanket scheme to measure the immediate thermal conductivity data and study the effect of pebble bed temperature, the purge gas pressure and pebble deformation on the thermal conductivity of pebble bed. Measurements were performed based on about 1 mm diameter Li4SiO4 pebbles in the temperature range between 100 and 800 °C, with purge gas pressure ranging from 0.1 to 0.3 MPa. This paper described a measurement platform scheme by thermal probe method. On the other hand, for the sake of increasing the precision of thermal conductivity data transformed from temperature data, some improvements for the data post-processing using Monte Carlo inversion method were made in this paper too.

Experimental Investigation on Anisotropic Effective Thermal Conductivity of Pebble Bed

The thermal properties of the pebble beds have a significant impact on the temperature profile of the Helium Cooled Pebble Bed blanket and the extraction of heat from the pebble beds to the coolant. The effective thermal conductivity of pebble bed has been modeled as the isotropic one. However, the isotropic thermal conductivity inherently can be achieved only the case with perfectly isotropic arrangement which is difficult to realized in the actual blanket device. In this paper, the relation between effective thermal conductivity tensor and fabric tensor in 2D pebble bed is investigated experimentally. It is cleared that the effective thermal conductivity tensor is proportional to the structural anisotropic tensor. And, the anisotropic feature is quite different between core region and near wall region, so that it is suggested that modeling of the effective thermal conductivity tensor of the pebble bed should be separately carried out at least in above two regions.

Heat Transfer Issues in Finite Element Analysis of Bounding Accidents in PPCS Models

Modelling of temperature excursions in structures of conceptual power plants during hypothetical worst-case accidents has been performed within the European Power Plant Conceptual Study (PPCS). A new, 3D finite elements (FE) based tool, coupling the different calculations to the same tokamak geometry, has been extensively used to conduct the neutron transport, activation and thermal analyses for all PPCS plant models. During a total loss of cooling, the usual assumption for the bounding accident, passive removal of the decay heat from activated materials depends on conduction and radiation heat exchange between components. This paper presents and discusses results obtained during the PPCS bounding accident thermal analyses, examining the following issues: (a) radiation heat exchange between the inner surfaces of the tokamak, (b) the presence of air within the cryostat volume, and the heat flow arising from the circulation pattern provided by temperature differences between various parts, and (c) the thermal conductivity of pebble beds, and its degradation due to exposure to neutron irradiation, affecting the heat transfer capability and thermal response of a blanket based on these components.

Effective Thermal Conductivity of a Li2TiO3 Pebble Bed for a DEMO Blanket

ABSTRACTIn development of the ceramic breeder blanket, the effective thermal conductivity of pebble beds is an important design parameter. For thermo-mechanical design of blanket, pebble beds were investigated used for Li2TiO3 that was a candidate for tritium breeder. Li2TiO3 pebble beds, whose size was 0.28-1.91 mm diameter, were measured on load under no neutron irradiation. The effective thermal conductivity was increased with load increasing was obtained.

Effective Thermal Conductivity Measurement of the Candidate Ceramic Breeder Pebble Beds by the Hot Wire Method

The effective thermal conductivity of the pebble beds is one the most important design parameters for pebble bed solid breeder blanket. In the framework of IEA Implementing Agreement on Solid Breeder Subtask Group, measurement of pebble bed thermal conductivity by the hot wire method were defined as one of tasks to provide comparative information on the effective thermal conductivity of candidate ceramic pebble beds for DEMO blanket designs and ITER breeding blanket design. The authors previously reported the preliminary result of the pebble bed thermal conductivity for Li2O, Be and Al2O3. This paper presents the result of Li2TiO3, Li2ZrO3 (1 mm diameter) from CEA, and Li4SiO4 (0.25 - 0.63 mm diameter) from FZK.Observation was compared to the correlations, SZB model and HM model. Contact area fraction was obtained by correlation fitting, of which the value is 4.9×10−3 for Li2TiO3, Li2ZrO3 (the same value as Li2O) and 1×10−6 for and Li4SiO4.