Graphite Components Research Articles

Influence of Oxygen and Hydrogen Milling Atmospheres on the Electrochemical Properties of Ballmilled Graphite

The effect of the grinding oxygen or hydrogen atmosphere on the physical/electrochemical properties of ballmilled graphite was studied. These properties strongly depend on the atmosphere and pressure of the milling container of the oxygen and the hydrogen contents of the samples. For instance, grinding under a 10 bars of atmosphere leads to a highly disordered carbon, while 10 bars under gives a heterogeneous carbon having a well and poorly crystallized graphite component. In both cases, the reversible and irreversible capacities and the double-layer capacitance increase with milling time. The graphite ground 10 h under a strongly differs from the other samples. We ascribed such behavior to the presence of a large amount of oxygenated functional groups in relation with the formation of nanoporosity and/or the predominance of edge carbon upon grinding. In contrast, under or the variation of the Brunauer-Emmett-Teller (BET) surface area with milling time is correlated with the irreversible capacity. Differences in the voltage composition curves are also noticed with a low oxygen pressure strongly reducing the polarization of the charge/discharge cycling curve while leading to Li for Finally, 10 h of milling under were shown to produce a carbon with an Li and Li for while 80 h under led to a carbon having a double-layer capacitance of 57 F/g in © 2001 The Electrochemical Society. All rights reserved.

Acceptance Test of Graphite Components in Nuclear Reactor

The HTTR is the first high temperature gas-cooled reactor in Japan. It is a test reactor with thermal power of 30 MW and coolant outlet temperature of 950°C at maximum. To achieve high temperature coolant core internals were made of graphite and carbon materials due to their excellent thermal resistivity. After fabrication of graphite and carbon components at works they were installed in the HTTR, and now it is in the power up testing stage. Concerning the inspection standard of the graphite and carbon components, no domestic standard exists as main components in the nuclear reactor. It is necessary, therefore, to prescribe the inspection standards for the HTTR graphite components. Many research and developments in relation to the inspection standard, e.g. in the research field of nondestructive examination of the graphite material, had been performed, and then the JAERI established the inspection standard. The acceptance test of the graphite and carbon components was carried out based on the inspection standard. This paper prescribes the outline of the established inspection standard.

Ultrasonic signal characteristics by pulse-echo technique and mechanical strength of graphite materials with porous structure

Ultrasonic testing (UT) is an important non-destructive method to detect internal flaws and is widely applied to product control in industrial fields. In an investigation on ultrasonic signal characteristics in porous ceramics, the present authors developed an ultrasonic wave propagation model for the pulse-echo technique by improving an existing one for the transmission technique. A wave-pore reflection process was taken into account in the improvement. In the developed model, both diffusion and scattering losses can be treated as important factors of ultrasonic wave attenuation. The model was demonstrated by experimental data on ultrasonic signal characteristics of nuclear grade graphite. As an application of the model, the authors proposed a new approach combined UT signal with fracture mechanics to evaluate the mechanical strength of porous ceramics from UT signal. The combined approach was tried to apply to the acceptance test and the in-service inspection conditions of graphite components in the High Temperature Engineering Test Reactor (HTTR) as an example. This paper presents the developed propagation model for the pulse-echo technique as well as the combined approach. Moreover, both acceptance test and in-service inspection techniques of graphite components in high temperature gas-cooled reactors (HTGRs) using the combined approach was also proposed in this paper.

DLC films formed by hybrid pulse plasma coating (HPPC) system

A new coating system was developed which consists fundamentally of plasma CVD (chemical vapor deposition) and ion-mixing. The system employs pulsed-gas introduction, pulsed-plasma generation and plasma base ion implantation (PBII). In this paper the formation of DLC films by the HPPC system is reported. The plasma densities were measured using a Langmuir probe and a 10-GHz microwave interferometer. DLC films were formed on the surface of workpieces using hydrocarbon gases by the HPPC system, with monitoring plasma density during the coating process. Raman spectra of DLC films by the HPPC system are similar in shape to those by ion-plating, and the fractions of amorphous and graphite components in Raman spectrum gained by segregated four peaks decreased with the decrease of CH 4/C 7H 8 partial pressure ratios. The reason is considered that the larger the deposition rates of films become, the smaller the ion-mixing effects are. Furthermore, as the CH 4/C 7H 8 ratio becomes as low as 1, this phenomenon becomes more apparent. For the further study, the plasma density as well as the change in gas pressure in the chamber must be monitored for the formation of uniform DLC films.

Effects of O2 Gas Addition on Diamond-Like Carbon Film Deposition

ABSTRACTThe role of 02 gas addition on the deposition of Diamond-like Carbon (DLC) film was studied for hard disk drive (HDD) media application. The influence of 02 gas mixing ratio on DLC film quality was investigated using the dc magnetron sputtering method with a solid graphite target and Ar, CH4 and 02 mixing gases. The 02 mixing ratio was varied between 0% and 50%. Film quality was evaluated using Raman spectroscopy and XPS. When 02 gas mixing ratio increased the peak in Raman spectra shifted gradually to higher wavenumbers and its bandwidth became narrower. This indicates graphite component increased in the DLC film. In addition, the lubricant coverage on oxygen-containing DLC was improved. Because adding oxygen increases the terminations of carbonyl group on DLC surface, this result suggests that the polar surface causes higher affinity for the lubricant

Deuterium trapping by carbon materials for tokamak plasma-facing components

The experiments on large tokamaks on measuring the hydrogen isotope pressure in the near-wall or divertor plasma are briefly described. Based on the analysis of exchange fluxes between the plasma and the wall it is stated that the plasma action, with respect to hydrogen sorption by graphite components of the tokamak first wall, is identical to materials exposure in the atmosphere of molecular hydrogen at pressures of 1–10 3 Pa and temperatures of 1200–1700 K. Within these ranges of pressures and temperatures RG-Ti-91 and USB-15 graphites are shown to be impermeable to molecular hydrogen in contrast to easily permeable POCO-AXF-5Q. Sorption capacity of well-treated dense graphites is about 10 2 appm. Sorption capacity of materials is increased to (1–3)×10 4 appm with defects like unsaturated carbon bonds, introduced into the above materials by mechanical treatment, ion irradiation, graphite gasification (exposure at 1200 K, 133 Pa during 1 h). At the same time permeability of graphites is increased to molecular hydrogen. Graphite modification by boron retards the rise of sorption capacity. The hydrogen sorption process is described as the filling of two sets of traps, i.e. weak traps arranged over the boundaries of carbon materials and deep traps arranged in the volume of separate crystallises. Russian-made graphites RG-Ti-91 and USB-15 can be used in large tokamaks as divertor and first wall tiles, respectively.

Carbon Composite for A Pem Fuel Cell Bipolar Plate

ABSTRACTThe current major cost component for proton exchange membrane fuel cells is the bipolar plate. An option being explored for replacing the current, nominal machined graphite component is a molded carbon fiber material. One face and the volume of the component will be left porous, while the opposite surface and sides are hermetically sealed via chemical vapor infiltration of carbon. This paper will address initial work on the concept.

5476679 Methods for making a graphite component covered with a layer of glassy carbon: Lewis Irwin C;Pirro Terrence;Miller Douglas Strongsville,OH, United States assigned to UCAR Carbon Technology Corporation

5476679 Methods for making a graphite component covered with a layer of glassy carbon: Lewis Irwin C;Pirro Terrence;Miller Douglas Strongsville,OH, United States assigned to UCAR Carbon Technology Corporation

Evaluation of aseismic integrity in the HTTR core-bottom structure V. On the static and dynamic behavior of graphitic HTTR key-keyway structures

The graphite components in high temperature gas-cooled reactors are connected to each other through a key-keyway structure that has gaps between the key and the keyway to accomodate thermal expansion. Because a dynamic load concentrates on the key-keyway structure during earthquakes, it is considered to be a crucial element for assessing the integrity of the graphite components. A combination of experiments and analyses was employed to investigate the dynamic behavior of the key-keyway structure, i.e. the equivalent stiffness associated with vibrational characteristics of the graphite components and the stress distribution under dynamic loading. The experiments were performed using a graphite scale model and a dynamic photo-elastic method. The analysis was carried out using the finite element method (FEM) code Abaqus, taking account of the contact between the key and the keyway. The following conclusions were derived. (1) The equivalent stiffness of the key-keyway structure shows nonlinearity, owing to the contact deformation. (2) The equivalent stiffness evaluated by the FEM analysis, taking account of the non-inear contact deformation, is applicable for predicting the vibrational characteristics of ky-keyway structure. (3) The stress concentration under dynamic loading is lower than or nearly equal to that under static loading. The maximum stress concentration of the seismic load can be sufficiently evaluated under static loading conditions.

Development of a Method for Measuring Residual Strain Based on Small Deformation Characteristics of Graphite Materials.

Development of a method for measuring the residual strain in graphite components in the gas-cooled nuclear reactors which is nondestructive is a major research aim. In order to measure the residual strain in graphite components, the applicability of a micro indentation method was investigated using a micro hardness testing machine. In the test indentation load to depth characteristics and micro hardness were determined at several levels of tensile residual strain in the graphite material. We describe the experimental results and discusses the applicability of the micro indentation method to residual strain measurement for graphite components.

ＨＴＴＲ炉床部構造物の耐震強度，（ＶＩ）応力集中を有する黒鉛構造物の衝撃強度特性

In order to clarify the dynamic strength characteristics of a graphite component under stress concentration condition, the static and dynamic fracture tests were performed using scale-model specimens of the component. The strain rate applied to the specimens was around 10-5l/s in the static test and 1 to 5l/s in the dynamic test. As a result of the experiment, it was found that the ratio of the dynamic strength to the static one depends on the stress gradient in the specimen; the specimen with higher stress gradient shows a higher value of the strength. Moreover, it was also found that there is a critical stress gradient at which the strength ratio reaches almost a constant value even if the stress gradient increases in the specimens.

B 4CSiC reaction-sintered coatings on graphite for plasma facing components

Boron carbide plus silicon carbide (B 4CSiC) reaction-sintered coatings for use on graphite plasma-facing components were developed. Such coatings are of interest in TEXTOR tokamak limiter-plasma interactions as a means of reducing carbon erosion, of providing a preferred release of boron for oxygen gettering, and of investigating silicon's effect on radiative edge phenomena. Specimens evaluated had (a) either Ringsdorfwerke EK 98 graphite or Le Carbone Lorraine felt-type AEROLOR A05 CFC substrates; (b) multiphase coatings, comprised of B 4C, SiC, and graphite; (c) nominal coating compositions of 69 wt% B 4C + 31 wt% SiC; and (d) nominal coating thicknesses between 250 and 775 μm. Coated coupons were evaluated by high heat flux experiments in the JUDITH (electron beam) test facility at KFA. Simulated disruptions, with energy densities up to 10 MJ m −2, and normal operation simulations, with power densities up to 12 MW m −2, were conducted. The coatings remained adherent; at the highest levels tested, minor changes occurred, including localized remelting, modification of the crystallographic phases, occasional microcracking, and erosion.

Evaluation of aseismic integrity in the HTTR core-bottom structure IV. Structural integrity of connecting elements between graphite components

Former investigation on the aseismic test for core-bottom structure in the high temperature engineering test reactor (HTTR) clarified the response of acceleration, strain, impact load etc. Following this investigation the component test of connecting elements between graphite components was carried out to evaluate their fracture load and fracture mode. The stress analysis was also performed to estimate the stress profile by the analytical approach. The seismic design load is also estimated by considering the load concentration factor. In this paper the experimental and analytical results are compared and the structural integrity of these connecting elements is discussed under the severest earthquake condition postulated in the HTTR structural design.

Solution to level 3 dismantling of gas-cooled reactors: the graphite incineration

This paper presents an approach developed to solve the specific decommissioning problems of the G2 and G3 gas-cooled reactors at Marcoule, and the strategy applied with emphasis on incinerating the graphite core components, using a fluidized-bed incinerator developed jointly between the French Atomic Energy Commission (CEA), Electricité de France and FRAMATOME. The incineration option was selected over subsurface storage for technical and economic reasons. Environmental studies have shown that gaseous incineration releases are environmentally acceptable. By using a pilot plant of a fluidized-bed incinerator (30–50 kg h −1), it has been demonstrated that it is possible to incinerate moderator blocks or other graphite components of gas-cooled power reactors, and to reduce significantly the residual amount of waste to be stored after incineration. More than 20 tons of nuclear-grade graphite was incinerated in a fluidized-bed incinerator pilot plant located at the FRAMATOME research centre. The volume of secondary waste after incineration is about 1%–2% of the original mass, and the combustion efficiency is very high at more than 99.8%.

95/00436 Numerical study on the turbulence structures in closely spaced rod bundle subchannels

There is one nuclear power plant (NPP) in Lithuania – the Ignalina NPP – which is under decommissioning now. The Ignalina NPP has two units with RBMK-1500 reactors, which are the most powerful and the most advanced versions of RBMK-type reactor design. Unit 1 of the Ignalina NPP was shut down at the end of 2004 and Unit 2 was shut down at the end of 2009. RBMK is a water-cooled graphite-moderated channel-type power reactor and the decommissioning of these reactors faces specific challenges for proper characterisation and disposal of irradiated reactor graphite.Apart from radiological inventory, the spatial distribution of radionuclides in the reactor graphite is also very important because it could indicate the possibilities for decontamination/treatment of the irradiated graphite. This is important for consideration of the near surface disposal option for irradiated graphite, as without treatment it usually does not meet the waste acceptance criteria.Based on that, the work presented in this paper is focused on the modelling of the induced activity spatial distribution in the Ignalina NPP RBMK-1500 reactor graphite components: blocks and rings/sleeves. The modelling was performed with MCNP and SCALE computer codes and consisted of two mains stages: modelling of the neutron flux in the reactor graphite components, and then modelling of the neutron activation in them using the already modelled neutron flux. In such a way, the spatial induced activity distribution in the analysed reactor components was obtained. Modelling results show that the thermal neutron flux is more intensive in the outer radial regions of the graphite components and this, in general, results in higher induced activities there.

The prospects of using carbon-graphite materials as construction elements of the microwave plasma diagnostic in a fusion reactor

The comparative study of working characteristics of some graphite and metallic components of SHF diagnostics, such as several kinds of antennae, plane reflectors and cylindrical waveguides are presented. To simulate the consequence of a plasma disruption in large tokamaks on graphite-made antenna, we tested two antennae (MPG and ARV kinds of graphite) on the influence of power plasma flow: W ≥ 1.10 MJ/m 2 with the time duration Δ t ≈ 0.1 ms. All results show that the prospects to use graphite elements in a reactor-scale fusion device are rather promising.

Evaluation of aseismic integrity in HTTR core-bottom structure. I. Aseismic test for core-bottom structure

Abstract The aseismic tests were carried out using 1 5 - scale and 1 3 - scale models of the core-bottom structure of the HTTR to quantitatively evaluate the response of acceleration, strain, impact load etc. The following conclusions are obtained. 1. (i) The frequency response of the keyway strain is correlative with that of the impact acceleration on the hot plenum block. 2. (ii) It was confirmed through 1 5 - scale and 1 3 - scale model tests that the applied similarity law is valid to evaluate the seismic response characteristics of the core-bottom structure. 3. (ii) The stress of graphite components estimated from the scale model test using S2-earthquake excitation was sufficiently lower than the allowable stress used as the design criterion.

Evaluation of aseismic integrity in HTTR core-bottom structure II. Vibrational characteristics of keyed graphite components

The assembly system consisting of keyed graphite components, which is employed in the core bottom structure of a high temperature engineering test reactor (HTTR), has a nonlinear vibrational characteristic. The vibrational test was carried out to grasp the vibrational characteristics using the element model of the key-keyway structure. The analytical code was developed based on the experimental results. The main conclusions are summarized as follows: (i) the stress distribution around the keyway is independent of whether it is induced under a dynamic or a static state; (ii) the stiffness of the key-keyway structure has the nonlinear characteristics due to contact behavior. The stiffness can be evaluated by contact analysis, taking account of the relative slip and the deformation on the contact surface between key and keyway; (iii) the analytical code employing a nonlinear spring for the key-keyway structure is available to predict the vibrational characteristic of the keyed graphite components.

Model for deuteron retention and reemission in graphites in a wide range of temperatures and energies

Abstract The experimental data available on hydrogen isotope trapping and release in graphite irradiated with deuterium ions under various conditions (energies 0.05–20 keV, temperatures 300–1300 K) are discussed. A new model of radiation-induced sequential reactions for hydrogen trapping and molecules reemission is proposed. The principal difference of our model from earlier models derives from the proposal that hydrogen retention occurs in two systems of traps (CD and CD2 complexes) that are formed locally and consequently in the irradiated area, and the molecular reemission takes place as a result of interaction between incoming ions and the already filled CD and CD2 traps. In our model the temperature dependence of retention and reemission is based on the assumption of the increase, at different rates, of reaction volumes with the irradiation temperature rising. Numerical simulations of hydrogen isotopes retention and reemission through the model equations agree well enough with the accumulated existing experimental data. The model could be used for the analysis of hydrogen isotopes behavior in graphite plasma-facing components.

Cooling performance of helium-gas/water coolers in HENDEL

The helium engineering demonstration loop (HENDEL) has four helium-gas/water coolers where the cooling water flows in the tubes and helium gas on the shell side. Their cooling performance was studied using the operational data from 1982 to 1991. The heat transfer of helium gas on the shell was obtained for segmental and step-up baffle type coolers. Also, the change with operation time was investigated. The cooling performance was lowered by the graphite powder released from the graphite components for several thousand hours and thereafter recovered because the graphite powder from the components was reduced and the powder in the cooler shell was blown off during the operation.