Abstract:Research on the behaviour of polycrystalline graphite exposed to neutrons from nuclear fission reactions began around the year 1942. Up to today, many serious questions concerning properties and structural changes have been answered and in many countries graphite became a standard material for the core of gas-cooled reactors. However, the basis for that is a broad knowledge about manufacturing and a huge amount of numerical data from irradiation testing. After many years of successful use of graphite, new prob… Show more
“…In the damage area from surface to ∼500 nm displacement, the hardness and Young’s modulus of C/C composites after irradiation show an obvious enhancement with increasing of the irradiation fluence, whereas in the much deeper region the growth rate of both physical quantities begin to decrease and gradually keep unchanged with increase of displacement. Moreover, all of the hardness and Young’s modulus of C/C composites after irradiation increased significantly compared with the original value, indicating an obvious irradiation-hardening phenomenon, which is well consistent with the results obtained from the proton or neutron irradiation reports. ,, Similar to the founds reported by Kelly, the hardness increase in C/C should be ascribed to pinning effect caused by irradiation-induced point defects and defect clusters, meanwhile the elastic modulus enhancement attributed to point defects via pin dislocations caused by irradiation . Notably, the maximum increase amplitude of the average hardness (400–900 nm) in the matrix is ∼3.5 times (from ∼0.63 to ∼2.22 GPa) after irradiation in Figure b and that of elastic modulus in matrix is ∼2.4 times (from ∼12.20 to ∼29.25 GPa) in Figure d, which showed more significant increase than the changes in fiber as shown in Figure a and c, indicating that the matrix is more sensitive to irradiation effect.…”
To
optimize the performance of the carbon fiber reinforced carbon
matrix (C/C) composites by controlling the microstructure for more
reliable and safety application in thorium molten salt reactor (hereafter,
TMSR), we have investigated the irradiation effects of fiber, matrix,
and their interfaces in C/C composite induced by He+ ions
and further reveal their corresponding micromechanism. Compared with
fibers, an obviously fragmented surface morphology in matrix appears
and then gradually becomes widespread around the surface of C/C composite
with increasing dose of irradiation. This found is attributed to the
breakage of crystallites observed by synchrotron-based grazing incidence
X-ray diffraction (GIXRD) and the increase of defect state density
revealed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy,
respectively. Three different microstructure evolutions in fiber,
matrix and fiber-matrix interface induced by irradiation damage have
been further revealed in detail by transmission electron microscopy
(TEM) and high-resolution TEM (HRTEM). It is found that the layered
structure gradually loses its initial ordering and the nanostructural
degradation in carbon matrix is much more serious than that of the
fiber, resulting in breaks and bends in the lattice with increasing
dose. Observed by nanoindentation experiment, the enhancement of the
hardness and modulus of the matrix is more significant than that in
fiber, which can be attributed to the more obviously pinning of basal
plane dislocations in the matrix due to lattice defects induced by
He+ irradiation. These discoveries are properly contribute
to improve the performance of the C/C composites by regulatory microstructure
composition, such as fiber and matrix.
“…In the damage area from surface to ∼500 nm displacement, the hardness and Young’s modulus of C/C composites after irradiation show an obvious enhancement with increasing of the irradiation fluence, whereas in the much deeper region the growth rate of both physical quantities begin to decrease and gradually keep unchanged with increase of displacement. Moreover, all of the hardness and Young’s modulus of C/C composites after irradiation increased significantly compared with the original value, indicating an obvious irradiation-hardening phenomenon, which is well consistent with the results obtained from the proton or neutron irradiation reports. ,, Similar to the founds reported by Kelly, the hardness increase in C/C should be ascribed to pinning effect caused by irradiation-induced point defects and defect clusters, meanwhile the elastic modulus enhancement attributed to point defects via pin dislocations caused by irradiation . Notably, the maximum increase amplitude of the average hardness (400–900 nm) in the matrix is ∼3.5 times (from ∼0.63 to ∼2.22 GPa) after irradiation in Figure b and that of elastic modulus in matrix is ∼2.4 times (from ∼12.20 to ∼29.25 GPa) in Figure d, which showed more significant increase than the changes in fiber as shown in Figure a and c, indicating that the matrix is more sensitive to irradiation effect.…”
To
optimize the performance of the carbon fiber reinforced carbon
matrix (C/C) composites by controlling the microstructure for more
reliable and safety application in thorium molten salt reactor (hereafter,
TMSR), we have investigated the irradiation effects of fiber, matrix,
and their interfaces in C/C composite induced by He+ ions
and further reveal their corresponding micromechanism. Compared with
fibers, an obviously fragmented surface morphology in matrix appears
and then gradually becomes widespread around the surface of C/C composite
with increasing dose of irradiation. This found is attributed to the
breakage of crystallites observed by synchrotron-based grazing incidence
X-ray diffraction (GIXRD) and the increase of defect state density
revealed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy,
respectively. Three different microstructure evolutions in fiber,
matrix and fiber-matrix interface induced by irradiation damage have
been further revealed in detail by transmission electron microscopy
(TEM) and high-resolution TEM (HRTEM). It is found that the layered
structure gradually loses its initial ordering and the nanostructural
degradation in carbon matrix is much more serious than that of the
fiber, resulting in breaks and bends in the lattice with increasing
dose. Observed by nanoindentation experiment, the enhancement of the
hardness and modulus of the matrix is more significant than that in
fiber, which can be attributed to the more obviously pinning of basal
plane dislocations in the matrix due to lattice defects induced by
He+ irradiation. These discoveries are properly contribute
to improve the performance of the C/C composites by regulatory microstructure
composition, such as fiber and matrix.
“…26 along with fits to data for two creep control ATR-2E specimens irradiated at ∼500°C in HFR Petten. 7 The F function for Gilsocarbon at 600°C tends to zero at zero fluence, whereas the Gilsocarbon 430°C specimen at zero fluence has a finite value, indicating that c -axis crystal swelling needs to be accounted for at the lower temperature. Figure 26 Influence functions ‘ F ’ for Gilsocarbon specimens irradiated at 430°C and 600°C 80 and ATR-2E 7 creep control specimens irradiated to 500°C…”
Section: Analysis Of Irradiation-induced Dimensional Changementioning
confidence: 99%
“…The reason for including the ATR-2E data in this review is that it is later used to explore the creep behaviour in nuclear graphite. Figure 5 Irradiation creep in loaded and unloaded ATR-2E Graphite, irradiated at 550°C. 7 a Compression loading (5MPa). b Tension loading (5MPa).…”
Section: Empirical Materials Test Reactor Datamentioning
confidence: 99%
“…Irradiation creep in loaded and unloaded ATR-2E Graphite, irradiated at 550°C. 7 a Compression loading (5MPa). b Tension loading (5MPa).…”
Section: Empirical Materials Test Reactor Datamentioning
confidence: 99%
“…In this section the microstructure of PGA and Gilsocarbon are discussed in some detail. In the case of ATR-2E some limited information on manufacture is given by Haag, 7 but unfortunately the authors are not aware of any microstructural images or detailed microstructural studies of ATR-2E graphite. This is unfortunate as the ATR-2E dataset is the only reasonable source of graphite irradiation creep data irradiated to a high fluence.…”
Section: Nuclear Graphite Manufacture and Microstructurementioning
Since the start of the 'nuclear age' graphite has been employed as a moderator in around 100 nuclear reactors, and today there are still some 30 graphite-moderated reactors operating and there are plans for new Generation IV high-temperature reactors. Many of the graphite moderator reactors now producing power are operating beyond their original design life. Therefore in some cases, to aid the reactor operators and designers, the existing graphite irradiation databases need to be extended either to a higher temperature or higher neutron fluence. Furthermore, data are needed for the different grades of graphite that are available at present. This can either be achieved by expensive, time consuming irradiation programmes or by improving the understanding of the mechanisms and processes which lead to irradiationinduced dimensional and property changes in the graphite core components. This review looks at three of the most important graphite properties which change with exposure to irradiation, namely dimensional change, irradiation creep and thermal expansion. The behaviour of UK AGR, Magnox and an experimental grade of German reactor graphite are explored in some detail. First graphite reactor core design is briefly discussed, giving examples of typical graphite components and core arrangements. Issues related to aging graphite component and core behaviour are illustrated through examples of component internal and thermal stress generation, and issues related to whole core behaviour are also outlined. Second the manufacture and microstructure of different nuclear graphite grades are discussed, highlighting how the choice of raw materials and manufacturing technique influences the graphite properties. Third the coefficient of thermal expansion, dimensional change and irradiation creep are analysed using microstructural and averaging methods which are used to relate crystal to bulk properties by accounting for graphite crystal orientation and porosity. These techniques, which were first applied to nuclear graphite in the 1960s, are extended and discussed with the aim of trying to lend some understanding to the role the microstructural crystallite and porosity distributions play in defining the dimensional stability and properties of virgin graphite, irradiated graphite and stressed graphite.
Nuclear graphite has been used as a moderator material in nuclear reactor designs dating back to the first reactor to reach criticality, Chicago Pile 1, in 1942. In addition, it is anticipated to be used in the conceptual Generation four (GenIV) Molten-salt reactors (MSRs) and the High-temperature gas-cooled reactors (HTRs). The macroscopic dimensional change observed in irradiated nuclear graphite is a property change of significant importance. Largely, volumetric change provides valuable insight into the in-service lifetime of graphite components used in nuclear reactors. The dimensional change behavior varies amongst each grade of nuclear graphite due to processing techniques and the resulting microstructure. In this work, historic data for nuclear graphite H-451 is revisited. A semi-empirical methodology is proposed to describe the dimensional change behavior as a function of temperature for nuclear graphite H-451. The turnaround dose, or when there is a reversal of the dimensional change from contraction to expansion, is proposed to be a thermally activated process and thus can be described by an Arrhenius model. On the atomic scale, H-451 is sp2-bonded carbon atoms with some degree of disorder regardless of orientation. Towards that end, the activation energy is assumed to be a constant irrespective of orientation.
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