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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:7 Percentile:46.7(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

Study on fracture behavior of 2D-C/C composite for application to control rod of very high temperature reactor

Sumita, Junya; Fujita, Ichiro; Shibata, Taiju; Makita, Taiyo*; Takagi, Takashi*; Kunimoto, Eiji*; Sawa, Kazuhiro; Kim, W. J.*; Park, J. Y.*

IOP Conference Series; Materials Science and Engineering, 18(16), p.162010_1 - 162010_4, 2011/09

 Times Cited Count:1 Percentile:40.02

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. Since the crack propagation of the C/C composite is complicated, the fracture behavior is one of the most important subjects of the design methodology for the control rod with the C/C composite. In this study, in order to assess the Mode-II fracture behavior of the two-dimensional (2D-) C/C composite which has the layer structure of laminas composed of fibers and matrix, bending test with oxidized end notched flexure specimen was carried out. The interlaminar fracture toughness decreased with increasing the oxidation for the 2D-C/C composite. The oxidized matrix causes reduction of fracture toughness and the reduction ratio is dependent on the matrix type. The crack initiates at the boundary between fiber bundles and grows along them without breaking the fiber. It is thought that the cracks which were initiated at the interface between matrix and fiber were gathered into the voids in the boundary between fiber bundles, and then the crack grows up in the matrix.

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:40.02

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

Interpolation and Extrapolation method to analyze irradiation-induced dimensional change data of graphite for design of core components in Very High Temperature Reactor (VHTR)

Shibata, Taiju; Kunimoto, Eiji*; Eto, Motokuni*; Shiozawa, Shusaku; Sawa, Kazuhiro; Oku, Tatsuo*; Maruyama, Tadashi*

Journal of Nuclear Science and Technology, 47(7), p.591 - 598, 2010/07

 Times Cited Count:8 Percentile:45.28(Nuclear Science & Technology)

no abstracts in English

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:65.91(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.

Journal Articles

Characterization of 2D-C/C composite for application of very high temperature reactor

Shibata, Taiju; Sumita, Junya; Makita, Taiyo*; Takagi, Takashi*; Kunimoto, Eiji*; Sawa, Kazuhiro; Kim, W. J.*; Jung, C. H.*; Park, J. Y.*

Nippon Kikai Gakkai Rombunshu, A, 76(764), p.383 - 385, 2010/04

no abstracts in English

JAEA Reports

Draft of standard for graphite core components in High Temperature Gas-cooled Reactor

Shibata, Taiju; Eto, Motokuni*; Kunimoto, Eiji*; Shiozawa, Shusaku; Sawa, Kazuhiro; Oku, Tatsuo*; Maruyama, Tadashi*

JAEA-Research 2009-042, 119 Pages, 2010/01

JAEA-Research-2009-042.pdf:26.28MB

For the design of the graphite components in the High Temperature Engineering Test Reactor (HTTR), the graphite structural design code for the HTTR etc. were applied. However, general standard systems for the High Temperature Gas-cooled Reactor (HTGR) have not been established yet. The authors had studied on the technical issues which is necessary for the establishment of a general standard system for the graphite components in the HTGR. The results of the study were documented and discussed at a "Special committee on research on preparation for codes for graphite components in HTGR" at Atomic Energy Society of Japan (AESJ). As a result, "Draft of Standard for Graphite Core Components in High Temperature Gas-cooled Reactor" was established. In this draft standard, the graphite components are classified three categories (A, B and C) in the standpoints of safety functions and possibility of replacement. For the components in the each class, design standard, material and product standards, and in-service inspection and maintenance standard are determined. This draft standard is the first standard in the world which shows the concept of standard for the graphite core components in HTGR.

Journal Articles

The Development of a microstructural model to evaluate the irradiation-induced property changes in IG-110 graphite using X-ray tomography

Sumita, Junya; Shibata, Taiju; Kunimoto, Eiji; Hall, G.*; Marsden, B. J.*; Sawa, Kazuhiro

Securing the Safe Performance of Graphite Reactor Cores, p.163 - 170, 2009/12

In order to develop a microstructural / property change model of fine-grained IG-110 graphite, one of candidates for core components for VHTR, the relationship between changes in the bulk properties and the microstructure of IG-110 graphite are being investigated. In this study, a microstructure of IG-110 graphite was changed by thermal oxidation and the change of it was measured by electrical resistivity. Then, the applicability of X-ray tomography, which has been thought to be difficult to apply to IG-110 graphite due to limit of resolution of apparatus, was investigated. The following results were obtained. (1) IG-110 graphite samples were oxidized uniformly in atmosphere at 500 $$^{circ}$$C and we got the relationship between electrical conductivity and burn-off (porosity) of IG-110 graphite. (2) Three-dimensional images based on the high resolution X-ray tomography can be used to describe the microstructure change of IG-110 graphite. It is expected this method can be used to predict the changes in the bulk properties of irradiated IG-110 graphite.

Journal Articles

Research and developments on C/C composite for Very High Temperature Reactor (VHTR) application

Shibata, Taiju; Sumita, Junya; Makita, Taiyo*; Takagi, Takashi*; Kunimoto, Eiji; Sawa, Kazuhiro

Ceramics in Nuclear Applications, Vol.30, Issue 10, p.19 - 32, 2009/11

Japan Atomic Energy Agency (JAEA) carries out R&Ds for Very High Temperature Reactor (VHTR). Since the core components in VHTR will be used at severer condition than in the High Temperature Engineering Test Reactor (HTTR), it is important to develop heat-resistant ceramic composite. C/C and SiC/SiC composites are major candidates substitute for metallic control rod. JAEA studies on the application of the composite materials for the VHTR control rod following the scheme; (1) Database establishment, (2) Design and (3) Demonstration test by HTTR. In this paper, the development plan was explained. It was expressed that the irradiation effects on graphitized C/C composite showed similar trend with that of graphite. It is possible to evaluate the irradiation effects based on the existing graphite irradiation database. The HTTR can irradiate large component. It is possible to demonstrate the structural integrity of the mock-up of the composite control rod being necessary for the final phase.

JAEA Reports

Expansion of irradiation data by interpolation and extrapolation for design of graphite components in high temperature gas-cooled reactor; Evaluation on IG-110 graphite irradiation data for component design

Kunimoto, Eiji; Shibata, Taiju; Shimazaki, Yosuke; Eto, Motokuni*; Shiozawa, Shusaku; Sawa, Kazuhiro; Maruyama, Tadashi*; Oku, Tatsuo*

JAEA-Research 2009-008, 28 Pages, 2009/06

JAEA-Research-2009-008.pdf:4.6MB

The VHTR is being focused and developed internationally. In Japan, the HTTR of the JAEA is in operation, and research and development for the development of commercial HTGRs are carried out. Nuclear graphites are used for core components of the HTGRs and expansion of irradiation data is necessary when enough irradiation data are not established, because the graphite components in the HTGRs are used at severer condition than that in the HTTR. The necessary database can be established by expansion of existing irradiation data with appropriate interpolation and extrapolation methods. This paper shows the reasonable interpolation and extrapolation method for IG-110 graphite which is used for the HTTR and a major candidate for the VHTR. The interpolation and extrapolation method was developed so as to be general by using the irradiation data of the other graphites. As a result, irradiation properties of the IG-110 graphite were successfully expanded to the VHTR condition for the first time and the irradiation properties being necessary for the design could be developed.

JAEA Reports

Measurement on irradiation-induced property change of carbon composite material for Very High Temperature Reactor; Irradiation-induced dimensional change, coefficient of thermal expansion and elastic modulus

Takagi, Takashi*; Makita, Taiyo*; Kunimoto, Eiji; Shibata, Taiju; Sawa, Kazuhiro

JAEA-Technology 2008-094, 22 Pages, 2009/03

JAEA-Technology-2008-094.pdf:5.49MB

To advance the performance and safety of High Temperature Gas-cooled Reactors (HTGRs), it is expected to use heat-resistant materials substitute for metallic materials in the core internal structural components of HTGRs at higher temperature. Carbon fiber reinforced carbon-carbon composite (C/C composite) is one of candidates as heat-resistant materials, and investigations are under going to apply the core internal structural components such as the control rod for the Very High Temperature Reactor (VHTR). This report describes the experimental results of irradiation effects on dimensional change, coefficient of thermal expansion and elastic modulus obtained by PIE (Post-Irradiation Examinations) for C/C composite irradiated in 03M-47AS capsule at the Japan Materials Testing Reactor (JMTR).

Journal Articles

Characterization of 2D-C/C composite for application to in-core structure of Very High Temperature Reactor (VHTR)

Shibata, Taiju; Sumita, Junya; Kunimoto, Eiji; Sawa, Kazuhiro

Proceedings of 2008 International Conference on Carbon (Carbon 2008) (CD-ROM), 5 Pages, 2008/07

Very High Temperature Reactor (VHTR) is an advanced high temperature gas-cooled nuclear reactor to provide high temperature helium gas about 950 $$^{circ}$$C to the reactor outlet. To enhance its performance, it is important to develop heat-resistant ceramics composite material in the core so as to increase the operating temperature. For the application of the 2D-C/C composite (CX-270G), neutron irradiation effects on the dimension and thermal conductivity were studied. Neutron irradiation test was carried out by JMTR at 600 $$^{circ}$$C to the fluence of 8.2$$times$$10$$^{24}$$ n/m$$^{2}$$ (E$$>$$1.0MeV) corresponding to 1.2 dpa. It was shown that the irradiation-induced shrinkage of plain-woven CX-270G expressed the same trend of 2D- random fiber composite. The neutron irradiation decreased thermal conductivity of CX-270G and it seemed to be recovered to some extent above 1200 $$^{circ}$$C. It is thought that the annealing effect on irradiation-induced defects in fiber direction affects the recovery.

Oral presentation

R&D subjects on graphite and carbon materials for High Temperature Gas-cooled Reactor

Shibata, Taiju; Sumita, Junya; Kunimoto, Eiji; Sawa, Kazuhiro

no journal, , 

no abstracts in English

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

Characterization on C/C composites for VHTR application; Test condition selection

Shibata, Taiju; Makita, Taiyo*; Takagi, Takashi*; Kunimoto, Eiji; Sawa, Kazuhiro

no journal, , 

no abstracts in English

Oral presentation

Characterization of 2D-C/C composite for application of very high temperature reactor

Shibata, Taiju; Sumita, Junya; Makita, Taiyo*; Takagi, Takashi*; Kunimoto, Eiji; Sawa, Kazuhiro; Park, Y.*; Kim, W. J.*; Jung, C. H.*

no journal, , 

no abstracts in English

Oral presentation

Development of Japanese technical criteria for VHTR graphite components

Shibata, Taiju; Eto, Motokuni*; Kunimoto, Eiji*; Shiozawa, Shusaku; Sawa, Kazuhiro; Oku, Tatsuo*; Maruyama, Tadashi*

no journal, , 

no abstracts in English

Oral presentation

Expansion of irradiation data by interpolation and extrapolation for design of graphite components in high temperature gas-cooled reactor

Kunimoto, Eiji*; Shibata, Taiju; Shimazaki, Yosuke; Eto, Motokuni*; Shiozawa, Shusaku; Sawa, Kazuhiro; Oku, Tatsuo*; Maruyama, Tadashi*

no journal, , 

no abstracts in English

28 (Records 1-20 displayed on this page)