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Sumita, Junya; Shibata, Taiju; Sawa, Kazuhiro; Fujita, Ichiro; Ohashi, Jun*; Takizawa, Kentaro*; Kim, W.*; Park, J.*
Ceramic Materials for Energy Applications; Ceramic Engineering and Science Proceedings, Vol.32, No.9, p.1 - 12, 2011/11
Since the temperature condition in Very High Temperature Reactor (VHTR), one of the Generation-IV reactor systems, is severe, the application of heat-resistant carbon fiber reinforced carbon matrix composite (C/C composite) for control rod elements is one of the important subjects for the VHTR development. JAEA focuses on the application of two-dimensional (2D-) C/C composites for control rod. The 2D-C/C composite has an anisotropy in properties for parallel and perpendicular to lamina directions. Irradiation effects of the 2D-C/C composite also show anisotropic behavior. It is hence important to consider the anisotropy in control rod design. To investigate the irradiation effects of the 2D-C/C composite on properties, irradiation test and post irradiation examination (PIE) were carried out and the irradiation effects were evaluated for the both directions. Since the C/C composite is composed of fibers and matrix, this geometry should be considered to evaluate the crack propagation in the composite. To assess the fracture behavior with crack propagation, bending test was carried out assuming a crack in the control rod and cracks in specimens were observed. This paper describes the irradiation effects of the 2D-C/C composite based on the PIE results considering the anisotropy. The evaluation results on equivalent fracture toughness and fracture mechanism are also discussed.
Takizawa, Kentaro*; Kakehashi, Kazuyuki*; Fukuda, Toshiaki*; Kida, Toru*; Sawa, Kazuhiro; Sumita, Junya; Kato, Yutai*; Snead, L. L.*
Ceramic Materials for Energy Applications; Ceramic Engineering and Science Proceedings, Vol.32, No.9, p.13 - 19, 2011/11
Fine-grained isotropic graphite shows high strength making it a promising material for the graphite component of High Temperature Gas-cooled Reactor (HTGR) and Very High Temperature Reactor (VHTR). Service life of the graphite component is determined primarily by the residual strength after neutron irradiation in the reactor core. It is expected that development of a new nuclear grade graphite possessing higher strength will contribute toward added design margins and an extension of the service life of components, which likely improve the reactor economy very significantly. Tokai Carbon Co. LTD. has started the development of nuclear grade graphite for the graphite component of VHTR. G347S and G458S grades are fine-grained isotropic graphites having high tensile strength greater than 30 MPa. It is planned to carry out the neutron irradiation tests using High Flux Isotope Reactor at Oak Ridge National Laboratory up to the neutron fluence of 30 dpa and the irradiation temperatures of 300-900
C. The dimensional changes, elastic modulus, coefficient of thermal expansion, etc., will be studied. It is also planned to evaluate the non-irradiated mechanical/thermal properties and the irradiation effects in collaboration with Japan Atomic Energy Agency. This paper introduces our technical R&D plan for G347S and G458S. The initial results of the properties and the irradiation test plan are also shown.
