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Journal Articles

Applicability study of nuclear graphite material IG-430 to VHTR

Osaki, Hirotaka; Shimazaki, Yosuke; Sumita, Junya; Shibata, Taiju; Konishi, Takashi; Ishihara, Masahiro

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 8 Pages, 2015/05

For the design on the VHTR graphite components, it is desirable to employ graphite material with higher strength. IG-430 graphite has been developed as an advanced candidate for VHTR. However, the new developed IG-430 does not have enough databases for the design of HTGR. In this paper, the compressive strength (Cs) of IG-430, one of important strengths for design data, is statistically evaluated. The component reliability is evaluated based on the safety factors defined by the graphite design code, and the applicability as the VHTR graphite material is discussed. It was found that IG-430 has higher strength (about 11%) and lower standard deviation (about 27%) than IG-110 which is one of traditional graphites used for HTGR, because the crack in IG-430 would not easy to propagate rather than IG-110. Since fracture probability for IG-430 is low, the higher reliability of core-component will be achieved using IG-430. It is expected that IG-430 is applicable for VHTR graphite material.

Journal Articles

Development of evaluation method with X-ray tomography for material property of IG-430 graphite for VHTR/HTGR

Sumita, Junya; Shibata, Taiju; Fujita, Ichiro*; Kunimoto, Eiji*; Yamaji, Masatoshi*; Eto, Motokuni*; Konishi, Takashi*; Sawa, Kazuhiro

Nuclear Engineering and Design, 271, p.314 - 317, 2014/05

 Times Cited Count:6 Percentile:46.09(Nuclear Science & Technology)

In this study, in order to develop evaluation method for material properties and to evaluate the irradiation-induced property changes under higher neutron doses for IG-430, the oxidation and densification effects on elastic modulus of IG-430 were investigated. Moreover, the correlation of the microstructure based on the X-ray tomography images and the material properties was discussed. It was shown that the elastic modulus of the densified graphite depends on only the closed pores and it is possible to evaluate the material properties of graphite by using X-ray tomography method. However, it is necessary to take into account of the change in the number and shape of closed pores in the grain to simulate the elastic modulus of the highly oxidized and irradiated materials by the homogenization analysis.

JAEA Reports

Evaluation of oxidation characteristics of fine-grained graphites (IG-110 and IG-430) for very high temperature reactor; Changes in density distribution and compressive strength caused by air-oxidation

Fujita, Ichiro*; Eto, Motokuni*; Osaki, Hirotaka; Shibata, Taiju; Sumita, Junya; Konishi, Takashi; Yamaji, Masatoshi; Kunimoto, Eiji

JAEA-Research 2013-004, 20 Pages, 2013/07

JAEA-Research-2013-004.pdf:2.4MB

Graphite components in HTGR and VHTR may be oxidized by impurities in coolant helium-gas even at normal operation, as well as by air at air-ingress accident. In this study, by air-oxidation test at 520-900$$^{circ}$$C, oxidation characteristics of IG-110 and IG-430 graphites, and associated decrease in compressive strength were examined. The following results were obtained. (1) The activation energy of the air-oxidation for IG-430 is 176 kJ/mol being almost same as for IG-110, though the oxidation rate for IG-430 is less than a half of that for IG-110. (2) There are correlations between density change and decrease in compressive strength. Decrease in strength is the largest in case that the oxidation temperature is lower than 600 $$^{circ}$$C where the homogenous oxidation occurs. (3) In the process of oxidation, amorphous binder regions are predominantly oxidized. It suggests that peeling-off of cokes grains is necessary to be considered for oxidation weight loss, as well as gasification.

Journal Articles

Development of evaluation method with X-ray tomography for material property of IG-430 graphite for VHTR/HTGR

Sumita, Junya; Shibata, Taiju; Fujita, Ichiro*; Kunimoto, Eiji*; Yamaji, Masatoshi*; Eto, Motokuni*; Konishi, Takashi*; Sawa, Kazuhiro

Proceedings of 6th International Topical Meeting on High Temperature Reactor Technology (HTR 2012) (USB Flash Drive), 6 Pages, 2012/10

In this study, in order to develop evaluation method for material properties and to evaluate the irradiation-induced property changes under higher neutron doses for IG-430, the oxidation and densification effects on elastic modulus of IG-430 were investigated. Moreover, the correlation of the microstructure based on the X-ray tomography images and the material properties was discussed. It was shown that the elastic modulus of the densified graphite depends on only the closed pores and it is possible to evaluate the material properties of graphite by using X-ray tomography method. However, it is necessary to take into account of the change in the number and shape of closed pores in the grain to simulate the elastic modulus of the highly oxidized and irradiated materials by the homogenization analysis.

Journal Articles

Correlation of microstructure and compressive strength of C/C composite using X-ray tomography

Sumita, Junya; Shibata, Taiju; Kunimoto, Eiji*; Yamaji, Masatoshi*; Konishi, Takashi*; Sawa, Kazuhiro

IOP Conference Series; Materials Science and Engineering, 18(16), p.162012_1 - 162012_4, 2011/09

 Times Cited Count:1 Percentile:39.71

For control rod element of Very High Temperature Reactor, carbon fiber reinforced carbon matrix composite (C/C composite) is one of the major candidate materials for its high strength and thermal stability. The development of a property prediction model of the two-dimensional (2D)-C/C composite is one of the most important subjects for the design methodology for control rod. Since the property of the 2D-C/C composite is strongly dependent on its microstructure, fiber/matrix, it would be possible to evaluate the properties of the 2D-C/C composite from its microstructure. In this study, in order to develop the property prediction model of the 2D-C/C composite base on its microstructure, pore distribution was investigated by using the X-ray computed tomography (X-ray CT) images and developed image based voxcel model. The compressive strength of the 2D-C/C composite was measured and evaluated by the voxcel model. This study shows that the pore distribution in the 2D-C/C composite can be confirmed visually and the volume and shape of the pores can be estimated from X-ray CT images. It is also shown that evaluation of the compressive strength by using the voxel model is useful to simulate the trend of the stress distribution of the 2D-C/C composite. However, it is necessary to characterize the property of the 2D-C/C composite and to set up the appropriate mesh to simulate the absolute stress value precisely.

Journal Articles

Investigation of microstructural change by X-ray tomography and anisotropic effect on thermal property of thermally oxidized 2D-C/C composite for Very High Temperature Reactor

Sumita, Junya; Shibata, Taiju; Kunimoto, Eiji*; Yamaji, Masatoshi*; Konishi, Takashi*; Sawa, Kazuhiro

Journal of Nuclear Science and Technology, 47(4), p.411 - 420, 2010/04

 Times Cited Count:4 Percentile:65.73(Nuclear Science & Technology)

Two dimensional carbon fiber reinforced carbon composite (2D-C/C composite) is one of the candidate materials for a reactor internals, e.g. control rod element, of Very High Temperature Reactor (VHTR) because of its high strength at high temperature and thermal stability. From the viewpoint of its application to the reactor internals of VHTR, it is important to investigate the anisotropy effect on its properties for the design and safety analysis of VHTR. Moreover, the property of 2D-C/C composite is strongly related to its microstructure, therefore, it is necessary to observe the internal microstructure to investigate the relationship between the microstructural change and the property change. This study has shown that the X-ray tomography could be applied to observe the microstructural change of thermally 2D-C/C composite. The relationship between the thermal conductivity and the coefficient of thermal expansion (CTE) change and burn-off of thermally oxidized 2D-C/C composite could be expressed by the empirical exponential decay formula in both directions perpendicular and parallel to lamina. It could be explained the direction of hexagonal graphite crystal structure from carbon atoms and microstructural change of 2D-C/C composite.

Oral presentation

R&Ds for application of IG-110 graphite to VHTR in-core components

Shibata, Taiju; Kunimoto, Eiji; Sumita, Junya; Yamaji, Masatoshi*; Konishi, Takashi*; Sawa, Kazuhiro

no journal, , 

Fine-grained isotropic graphite IG-110 (Toyo Tanso Co.) is used for the core components in the HTTR. It is a proven graphite and a major candidate for in-core components of the VHTR. Japanese graphite code and standard for the HTTR show the criteria of IG-110 for the application to the in-core components. They include IG-110 property data, oxidation effect, irradiation effect and so on. They are established on the basis of IG-110 component test results. It is thought that the code and standard for the IG-110 would be applicable to the VHTR with some adjustments. For this purpose, establishment of the IG-110 design data for the VHTR condition is one of the key subjects. The development of interpolation and extrapolation for the irradiation data would help the design data establishment. The R&D subjects on the IG-110 for the in-core VHTR components will be summarized and presented in this study.

Oral presentation

Evaluation of material properties for IG-110 and IG-430 by using X-ray tomography

Sumita, Junya; Shibata, Taiju; Fujita, Ichiro; Kunimoto, Eiji; Yamaji, Masatoshi; Eto, Motokuni*; Konishi, Takashi; Sawa, Kazuhiro

no journal, , 

no abstracts in English

Oral presentation

Evaluation of oxidation effect on 2D-C/C composite (CX-270G) for the application to stress analysis of control rod element of VHTR

Sumita, Junya; Shibata, Taiju; Fujita, Ichiro; Yamaji, Masatoshi; Eto, Motokuni*; Konishi, Takashi; Sawa, Kazuhiro

no journal, , 

no abstracts in English

Oral presentation

Upgrading and expansion of IG-110 graphite data for component design and development of high performance graphites for HTGR

Kunimoto, Eiji; Konishi, Takashi; Eto, Motokuni*; Fujita, Ichiro; Shibata, Taiju; Sawa, Kazuhiro; Kato, Yutai*

no journal, , 

no abstracts in English

Oral presentation

Pre-irradiation sample size validation on the compressive strength of nuclear graphite for HTGRs

Kunimoto, Eiji; Konishi, Takashi; Eto, Motokuni*; Sumita, Junya; Shibata, Taiju; Sawa, Kazuhiro; Kuroda, Masatoshi*; Kato, Yutai*

no journal, , 

no abstracts in English

Oral presentation

Evaluation of material properties of IG-110 and IG-430 from their microstructure

Sumita, Junya; Shibata, Taiju; Osaki, Hiroki*; Eto, Motokuni*; Konishi, Takashi*

no journal, , 

Graphite materials are used for the in-core components of High Temperature Gas-cooled Reactor (HTGR). The HTGR is particularly attractive due to its passive and inherent safety features. The Very High Temperature Reactor (VHTR) is one of the most promising candidates as the Generation-IV nuclear reactor systems. IG-110 graphite having high strength and resistance to oxidation is used in the HTTR of JAEA and HTR-PM in China. IG-110 graphite is also a major candidate for the in-core graphite components of VHTR, too. IG-430 graphite having the higher strength and resistance to oxidation than IG-110 is an advanced candidate for the VHTR. In this study, the elastic modulus and coefficient of thermal expansion of these graphites were measured and correlation of compressive strength and microstructure was evaluated. Moreover, the densification effects on the material properties were discussed from the standpoint of microstructure using X-ray tomography method.

Oral presentation

Evaluation on irradiation effects of graphite for HTGR

Shibata, Taiju; Sumita, Junya; Ueta, Shohei; Osaki, Hirotaka; Kunimoto, Eiji; Eto, Motokuni*; Konishi, Takashi

no journal, , 

no abstracts in English

Oral presentation

Collaboration with Republic of Kazakhstan regarding development of HTGR, 3; Collaboration of development of oxidation-resistant graphite material for HTGR

Shibata, Taiju; Sumita, Junya; Nagata, Hiroshi; Saito, Takashi; Tsuchiya, Kunihiko; Sakaba, Nariaki; Osaki, Hiroki*; Kato, Hideki*; Fujitsuka, Kunihiro*; Muto, Takenori*; et al.

no journal, , 

no abstracts in English

Oral presentation

Evaluation of material properties of IG-430 graphite for next generation High Temperature Gas-cooled Reactor; Compressive strength and Oxidation property

Osaki, Hirotaka; Konishi, Takashi*; Eto, Motokuni*; Shibata, Taiju; Sumita, Junya

no journal, , 

no abstracts in English

Oral presentation

Characterization of oxidation behavior of boron-doped graphite

Osaki, Hiroki*; Sumita, Junya; Shibata, Taiju; Konishi, Takashi*

no journal, , 

Boron-doped graphite is one of candidate materials for oxidation-resistant graphite. It was reported that B$$_{2}$$O$$_{3}$$, which was generated by oxidation of B$$_{4}$$C, prevented boron-doped graphite from oxidation. However, to apply boron-doped graphite to core support graphite structure of HTGR, it is necessary to measure the mechanical and thermal property of oxidized boron-doped graphite. This study reports results of oxidation test, bending strength test and surface observation using GB-210 fabricated by Toyo Tanso Co., Ltd. in order to measure the bending strength of oxidized boron-doped graphite.

Oral presentation

Characterization of oxidation behaviour of boron-doped graphite

Sumita, Junya; Osaki, Hiroki*; Kunimoto, Eiji*; Yamaji, Masatoshi*; Konishi, Takashi*

no journal, , 

Graphite materials are used for the in-core components of High Temperature Gas-cooled Reactor (HTGR) which is a graphite-moderated and helium gas-cooled reactor. The HTGR is particularly attractive due to capability of producing high temperature helium gas, and its passive and inherent safety features. It is required for core support graphite structure, which support the core, to have oxidation resistance in the case of air ingress accident in order to maintain the core arrangement and cool the core from a viewpoint of ensuring high safety of HTGR. Boron-doped graphite is one of candidate materials for oxidation-resistant graphite. It was reported that B$$_{2}$$O$$_{3}$$, which was generated by oxidation of B$$_{4}$$C, prevented boron-doped graphite from oxidation. To apply boron-doped graphite to core support graphite structure of HTGR, it is necessary to understand oxidation mechanism of boron-doped graphite. This study reports evaluation results of oxidation mechanism of boron-doped graphite on the basis of oxidation test, bending strength test and surface observation.

Oral presentation

Evaluation of material properties of IG-430 graphite for next generation high temperature gas-cooled reactor

Kunimoto, Eiji*; Sumita, Junya; Osaki, Takashi*; Osaki, Hiroki*; Yamaji, Masatoshi*; Konishi, Takashi*

no journal, , 

Graphite materials are used for the in-core components of High Temperature Gas-cooled Reactor (HTGR) which is a graphite-moderated and helium gas-cooled reactor. The major features of the HTGR are that the HTGR can take out the high-temperature helium gas at the reactor outlet and has inherent safety characteristics. The Very High Temperature Reactor (VHTR) is one of the most promising candidates as the Generation-IV nuclear reactor systems. IG-110 graphite having high strength and resistance to oxidation is used in the HTTR of JAEA and HTR-10 in China. Moreover, IG-110 graphite provides highly consistent quality and long-term stable supply. IG-110 graphite is a major candidate for the in-core graphite components of VHTR. IG-430 graphite having the higher strength and resistance to oxidation than IG-110 is an advanced candidate for the VHTR. However, a new material of IG-430 does not have enough databases for the design of HTGR. Therefore, preparation of the necessary database for the design, mechanical and thermal properties, irradiation effect on them, is underway. In this study, the tensile strength, compressive strength and fatigue strength of IG-430 were statistically evaluated and the applicability of IG-430 as HTGR graphite materials was discussed. Moreover, the Su value of tensile and compressive strength of IG-430 was evaluated and compared to that of IG-110. It was found that IG-430 has excellent properties.

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