Weon-Ju Kim

FABRICATION AND MATERIAL ISSUES FOR THE APPLICATION OF SiC COMPOSITES TO LWR FUEL CLADDING

The fabrication methods and requirements of the fiber, interphase, and matrix of nuclear grade SiCf/SiC composites are briefly reviewed. A CVI-processed SiCf/SiC composite with a PyC or (PyC.SiC)n interphase utilizing Hi-Nicalon Type S or Tyranno SA3 fiber is currently the best combination in terms of the irradiation performance. We also describe important material issues for the application of SiC composites to LWR fuel cladding. The kinetics of the SiC corrosion under LWR conditions needs to be clarified to confirm the possibility of a burn-up extension and the cost-benefit effect of the SiC composite cladding. In addition, the development of end-plug joining technology and fission products retention capability of the ceramic composite tube would be key challenges for the successful application of SiC composite cladding.

Fabrication and Ion Irradiation Characteristics of SiC-Based Ceramics for Advanced Nuclear Energy Systems

SiC-based ceramics are considered as candidate materials for the advanced nuclear energy systems such as the generation IV reactors and the fusion reactors due to their excellent high-temperature strength and irradiation resistance. The advanced nuclear energy systems and their main components adopting ceramic composites were briefly reviewed. A novel fabrication method of SiC f /SiC composites by introducing SiC whiskers was also described. In addition, the charged-particle irradiation (Si 2+ and H + ion) into CVD SiC was carried out to simulate the severe environments of the advanced nuclear reactors. SiC whiskers grown in the fiber preform increased the matrix infiltration rate by more than 60% compared to the conventional CVI process. The highly crystalline and pure SiC showed little degradation in hardness and elastic modulus up to a damage level of 10 dpa at 1000℃.

Two-step sintering of a TiB2-Ni cermet

The effect of atmosphere control on the sintering behaviour of TiB2-20 wt% Ni ceramics was investigated. Sintering was performed at 1700 °C for 1h with commercial TiB2 powders produced by the earbothermic reaction. Under a fixed single atmosphere such as vacuum or Ar, densification was limited and large pores remained. However, a sintered density above 99% of theoretical could be achieved by a two-step sintering procedure in which the atmosphere was changed from vacuum to Ar at 1600 °C during the heat-up with subsequent isothermal sintering being performed at 1700 °C for 1h. Qualitative considerations about these phenomena are discussed.

Mechanical Properties of Chemical-Vapor-Deposited Silicon Carbide using a Nanoindentation Technique

The mechanical properties of silicon carbide deposited by chemical vapor deposition process onto a graphite substrate are studied using nanoindentation techniques. The silicon carbide coating was fabricated in a chemical vapor deposition process with different microstructures and thicknesses. A nanoindentation technique is preferred because it provides a reliable means to measure the mechanical properties with continuous load-displacement recording. Thus, a detailed nanoindentation study of silicon carbide coatings on graphite structures was conducted using a specialized specimen preparation technique. The mechanical properties of the modulus, hardness and toughness were characterized. Silicon carbide deposited at 1300℃ has the following values: E=316 GPa, H=29 GPa, and K c =9.8MPa m 1/2 ; additionally, silicon carbide deposited at 1350℃ shows E=283 GPa, H=23 GPa, and K c =6.1MPa m 1/2 . The mechanical properties of two grades of SiC coating with different microstructures and thicknesses are discussed.

Development of Materials for a High Temperature Gas Cooled Reactor in Korea

The very high temperature reactor (VHTR) materials R&D started as an objective of the development of key technologies for a nuclear hydrogen production funded by the Korea government in 2006. We are performing materials R&D for 5 components: a reactor pressure vessel (RPV), a reactor/process intermediate heat exchanger (IHX) and hot gas duct, a control rods component, a reflector and support structures in the core region and reactor materials for the sulfur-iodine (SI) process. The scopes of our works are focused on a material screening/selection and qualification, codifications of a high temperature structural design to a very high temperature region, and to support the licensing of a system design, material characterizations and database establishments. Current target materials are modified 9Cr-1Mo, alloy 617, graphite, ceramic fiber reinforced composite, Fe-Si and SiC.Copyright

Effect of soft substrate on the indentation damage in silicon carbide deposited on graphite

Indentation-induced damage is investigated in silicon carbide (SiC) deposited on graphite substrate. The SiC films have been grown by LPCVD (Low Pressure Chemical Vapor Deposition) method using MTS (CH3SiCl3) as a source gas and H2 as a diluent gas to provide highly dense deposited layer and strong interfacial bonding. The elastic-plastic mismatch is very high to induce distinctive damages in the coating and the substrate layer. The specimens with various coating thicknesses are prepared by changing CVD condition or mechanical polishing. Indentation damages with different sizes are introduced by controlling indentation load in Nanoindentation, Vickers indentation and Hertzian indentation test. Basic mechanical properties such as hardness, toughness, elastic modulus are evaluated against coating thickness. Mechanical properties are sensitive to the indentation load and coating thickness. The results indicate that coating thickness has a vital importance on the design of hard coating/soft substrate system because the soft substrate affects on the mechanical properties.

Microstructure of Al2O3-ZrO2 nanocomposites prepared by combustion process

Abstracts are not published in this journal

Effect of Deposition Temperature on the Property of Pyrolytic SiC Fabricated by the FBCVD Method

【Silicon carbide(SiC) layer is particularly important tri-isotropic (TRISO) coating layers because it acts as a miniature pressure vessel and a diffusion barrier to gaseous and metallic fission products in the TRISO coated particle. The high temperature deposition of SiC layer normally performed at

Whisker Growing Assisted 화학침착 공정으로 제조된 SiC f /SiC 복합체의 파괴거동과 기계강도 평가

1500-1650^{\circ}C

Corrosive Degradation of MgO/Al 2 O 3 -Added Si 3 N 4 Ceramics under a Hydrothermal Condition

has a negative effect on the property of IPyC layer by increasing its anisotropy. To investigate the feasibility of lower temperature SiC deposition, the influence of deposition temperature on the property of SiC layer are examined in this study. While the SiC layer coated at