Effect of the composition of radiation on the radiation damage to graphite

Nikolaenko, V. A.; Karpukhin, V. I.; Kuznetsov, V. N.; Platonov, P. A.; Алексеев, В. М.; Chugunov, O. K.; Shtrombakh, Ya. I.; Baldin, V. D.; Rodchenkov, B. S.; Smirnov, Yu. I.; Subbotin, A. V.; Khandomirov, Yu. É.; Lebedev, I. G.

doi:10.1007/bf02673205

Cited by 8 publications

(3 citation statements)

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“…In this process, the material almost completely loses its inherent physical and mechanical properties. In [2] it is shown that when GR-280 graphite, which is used to fabricate the bearing blocks of the core and reflector in RBMK reactors, is irradiated at 500°C the critical neutron fluence also decreases appreciably with decreasing radiation composition factor. The γ radiation probably stimulates diffusion processes and thereby accelerates the transformation of the defect structure, approaching the onset of degradation of the material [2].…”

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confidence: 97%

“…Radiation γ annealing, which introduces substantial corrections in the understanding of radiation damage to materials and was first observed for diamonds [1], has been found to be significant also for important materials such as reactor graphite [2] and vessel steel [3]. The γ rays which give rise to this phenomena act on matter, primarily, because of Compton electrons, which interact with the atoms of the irradiated material and not directly with the material itself.…”

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Radiation ? annealing of Silicon Carbide irradiated in a BOR-60 reactor

Nikolaenko

Subbotin

2004

At Energy

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The results of irradiating at 400-800°C silicon carbide, having the β-SiC cubic modification, in different channels of the BOR-60 reactor, where the radiation composition factor was varied over the range 2.3-6.5, are discussed. The expansion of the crystal lattice of β-SiC in the saturation stage is taken as the measure of damage. Data on isochronous annealing are used to investigate the energy spectrum for activation of annealing of defects -the smearing at high and low energy under the influence of γ radiation. The results are compared with data from similar irradiation of silicon carbide in MR and BR-10 and with data on the influence of γ radiation on other materials and their properties.Radiation γ annealing, which introduces substantial corrections in the understanding of radiation damage to materials and was first observed for diamonds [1], has been found to be significant also for important materials such as reactor graphite [2] and vessel steel [3]. The γ rays which give rise to this phenomena act on matter, primarily, because of Compton electrons, which interact with the atoms of the irradiated material and not directly with the material itself.The defects produced by neutron irradiation are bound with the crystal lattice more weakly than with the regular lattice atoms. For example, to produce a Frenkel pair, i.e., remove an atom from a lattice site and form an interstice and a vacancy for a regular atom, tens of electron volts must be transferred, and the migration activation energy for vacancies and interstices is several electron volts or even tenths of an electron volt. Consequently, the electrons which appear as a result of γ radiation are ordinarily ineffective in producing new defects, but actively interact with defects which have already been produced. It is believed that one possible mechanism of radiation γ annealing is that under the influence of γ radiation the spectrum of the activation energy for annealing of defects which have already been produced by neutrons is transformed, becoming diffuse at high and low energies. In the process, the defects with the lowest activation energy are annealed at the irradiation temperature (this is the radiation γ annealing effect), and the more stable defects remain up to a higher annealing temperature.In studying radiation γ annealing, it is convenient to introduce the concept of the radiation composition factor, which is the ratio of the neutron and γ-ray flux densities at 0.2 MeV and characterizes the combined action of these radiations on the material. For example, for a low value of the factor when the γ-ray flux is relatively high, the action of the flux becomes more intense and the radiation γ-annealing efficiency increases.Irradiation and Annealing of Silicon Carbide. In the present work, the results of irradiation of silicon carbidehaving the cubic modification β-SiC, in a reactor are analyzed from the standpoint of the radiation composition factor. This material was prepared artificially at the A. A. Baikov Institute of Metallurgy by condensation...

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Radiation ? annealing of Silicon Carbide irradiated in a BOR-60 reactor

Nikolaenko

Subbotin

2004

At Energy

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“…The investigations showed that the expansion of the diamond lattice in the uppermost containers is much smaller than for the other containers. This effect is reminiscent of radiation γ annealing observed in diamond [2], found in graphite [3], and probably influencing the properties of vessel steel [4]. There are no reliable data on the intensity of γ radiation at the level of the top container.…”

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Influence of the neutron flux density on the radiation embrittlement of VVér-440/213 vessel materials

et al. 2004

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In work on minisamples of the fifth complex of the No. 3 unit of the Kola nuclear power plant it is shown that for neutron fluence 4·10 23 m -2 (operation for approximately 10 yr), neutron flux density 3·10 15 sec -1 ·m -2 and copper content 0.03% and 0.09% in the metal the shifts of the cold-brittleness temperature are 50 and 120°C, respectively. Under the same irradiation conditions but with neutron flux density 3·10 16 sec -1 ·m -2 , this shift for standard samples is 50°C. These results attest to the state of the vessel material at a given moment in time.Guaranteed safe operation of VVÉR reactors for their entire operational life is largely determined by the vessel materials. Investigations performed in the 1960s showed that vessel materials become brittle under neutron irradiation. This resulted in more stringent requirements not only for the quality of structural materials, including their radiation resistance, but also the development and implementation of tracking programs, among other things, control samples for monitoring the change in the properties of vessel steel and the weld seams in every vessel.To determine the mechanical properties of the main metal and the metal in the weld connections, control samples placed in a reactor in accordance with the requirements of the design documentation are tested. The degree of embrittlement of the materials is determined after set periods of time as the radiation life is expended. The control samples are placed inside the vessel in special irradiation setups (strings). It is important to note that since the material of the control samples is damaged before the inner surface of a vessel, the strings are placed between the vessel and the shaft, i.e., closer to the core.Programs for the control samples are being developed on the basis of the results of theoretical and experimental investigations of the strength of vessel components taking account of the experience gained in fabricating and operating them. Control samples are used to monitor the mechanical properties (yield point, ultimate resistance to rupture, relative elongation, relative contraction) and the characteristics of the resistance to brittle fracture (critical temperature of embrittlement, fracture toughness).The main goal of the program for control samples is to confirm the conservativeness of the dependences adopted for the change in the properties of the materials for substantiating the service life set for the reactor vessel. The implementation of this program makes it possible to obtain experimental information about radiation embrittlement of materials and is the basis for determining more accurate normative relations for estimating radiation damage to reactor vessel materials.Two VVÉR-440 units equipped with control samples -the Nos. 3 and 4 units at the Kola nuclear power plant -are now operating in our country. The core-shell material -the main metal, the weld-seam metal connecting the shell, and the metal in the thermal influence zone -are monitored according to these programs.Before operati...

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Irradiation Creep in Materials

Onimus

Jourdan

et al. 2020

Comprehensive Nuclear Materials

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Effect of the composition of radiation on the radiation damage to graphite

Cited by 8 publications

References 3 publications

Radiation ? annealing of Silicon Carbide irradiated in a BOR-60 reactor

Radiation ? annealing of Silicon Carbide irradiated in a BOR-60 reactor

Influence of the neutron flux density on the radiation embrittlement of VVér-440/213 vessel materials

Irradiation Creep in Materials

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