Development of Three-Dimensional Distribution Visualization Technology for Boron Using Energy Resolved Neutron-Imaging System (RADEN)

Boron carbide is used as a neutron-absorbing material in Fukushima-Daiichi Nuclear Power Station (1F), producing borides that are twice as hard as oxides (such as UO2 and ZrO2). The high neutron absorption of boron affects the evaluation of re-criticality during the process of debris retrieval. Therefore, it is important not only to determine the presence of boron but also to investigate the distribution of boron inside the material in a non-destructive manner during decommissioning. To address the uncertainties in the core material relocation behavior of boiling water reactor (BWR) during a severe accident (SA), solidified melt specimens of a simulated fuel assembly were prepared by plasma heating. If core material melting and relocation (CMMR) specimens can be used to estimate the B distribution in 1F Unit-3, that will provide valuable information in the decommissioning of 1F. To address this, the authors focused on the energy-resolved neutron-imaging system, RADEN, which utilizes a wide energy range, from meV to keV. This is an innovative three-dimensional analysis technology for boride distribution that affects the evaluation of hardness and re-criticality. In the calibration standard samples (ZrxB1-x and FexB1-x), there was a good correlation between boron concentration and the energy-dependence of the cross sections of cold and epithermal neutrons. In the CMMR specimens, boron distribution was confirmed from the contrast difference between cold and epithermal neutrons. In the future, the results of calibration standard samples will be applied to the results of CMMR specimens. With this method, three-dimensional boron distribution will be measured, and the understanding of boride distribution 1F Unit-3 will be improved, which may be reflected in an improved SA code.

МОДЕЛИРОВАНИЕ МЕЛКОЗАЛЕГАЮЩИХ ЛЕГИРОВАННЫХ СЛОЕВ P-ТИПА

В настоящей работе исследовано формирование мелкозалегающих легированных слоев p-типа. Работа охватывает теоретическое и практическое рассмотрение реализации мелкозалегающего p-n-перехода. Проведен анализ дефектов, возникающих в процессе ионной имплантации (с особым вниманием к протяженным EOR-дефектам), а также рассмотрено их влияние на профиль распределения бора. The paper studies the formation of shallow p-type doped layers, as well as theoretical and practical implementation of shallow p-n junction. The analysis of defects arising in the process of ion implantation (with special attention to extended EOR-defects) has been carried out, and their influence on the profile of boron distribution has been considered.

Boron Characterization, Distribution in Particle-Size Fractions, and Its Adsorption-Desorption Process in a Semiarid Tunisian Soil

Boron is essential for crop growth but needed in very small amounts. The range between boron deficiency and toxicity for plants is quite narrow. These stress conditions gravely reduce yield and quality of many crop species. Therefore, understanding the factors and the reactions affecting boron availability in soil is necessary. Against this framework, our research aims to determine the available boron status in a semiarid soil of Dour Ismail irrigated perimeter (North Tunisia). The objectives are also to investigate boron distribution in different particle-size fractions throughout the soil profile and to understand boron adsorption-desorption mechanisms according to some soil properties. For this purpose, one soil profile was dug in the field plot that had not received any previous boron fertilization. Soil samples were gathered from the different horizons of the profile and analyzed for the main physicochemical properties. Our results showed that the studied soil is Stagnic Fluvisol (clayic). The highest boron amounts were recorded in deep horizons and were greatly affected by soil salinity, organic matter, and clay contents. However, the increase in the pH level and the high percentage of total lime significantly diminished the available boron amounts in surface layers. The investigation of depth boron distribution in the different particle-size fractions indicated a considerable contribution of the silt (2–50 µm) fraction (52% of the soil total available boron), while the coarse (>50 µm) and clay (<2 µm) fractions seem to play a less important role. The adsorption data were fitted to Freundlich adsorption isotherm. It revealed that adsorption of boron increased with the increase of boron concentrations in soil solution. Desorption isotherm denotes that the accumulated boron in soil was not easily released. Adsorption and desorption of boron in soil were greatly affected by soil properties, such as pH, salinity, sand content, clay content, total organic carbon, total nitrogen, and cation exchange capacity.