HTGR fuel and fuel elements

Chernikov, A. S.

doi:10.1016/0360-5442(91)90105-u

Cited by 5 publications

(4 citation statements)

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“…3b, c). As the irradiation dose accumulates, the average size (>100 nm) of pores, which appear in the form of etch pits in an oxygen plasma of a glow discharge gradually decreases, likewise attesting to a smaller role for the nongraphite component in the pyrocarbon layer with initial density about 1 g/cm 3 .…”

Section: Of Htgr Fuel Elementsmentioning

confidence: 97%

“…Thus, buffer layer thicknesses less than 20 µm are too small to extinguish the kinetic energy of the recoil nuclei; the result is an unfavorable over-irradiation of the inner surface of the pyrocarbon layer, giving rise to anisotropic radiation-induced size changes in it [16]. In most requirements for HTGR fuel, it is assumed that the density of the pyrocarbon buffer layer must be ≤1.1 g/cm 3 [3][4][5][6]. Other requirements are not imposed.…”

Section: Of Htgr Fuel Elementsmentioning

confidence: 99%

“…The specifications for the microsphere fuel for HTGR take account of the following essential characteristics: thickness, density, anisotropy of the pyrocarbon coating, contamination of the coatings by fissile materials, defects in the silicon carbide layer, and others [2][3][4][5][6].…”

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confidence: 99%

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Formation of multifunctional barriers to increase the radiochemical resistance of the protective coatings of HTGR fuel elements

Kurbakov

2009

At Energy

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The radiation-size changes of pyrocarbon protective coatings on HTGR microfuel elements are analyzed. It is shown that there is a relationship between the microstructural inner pyrolytic layers and the formation of cracks in these layers as the irradiation dose accumulates. The effect of cracks in the inner pyrocarbon layers on the damage to the silicon carbide layer is examined. It is determined that incorporating into the inner pyrocarbon layer or forming on the inner pyrocarbon-silicon carbide interface compositions, for example, silicon carbide-carbon, Ti 3 SiC 2 , ZrC, TiC, and nitrides of Zr, Ti, and Al creates an obstacle to interior cracks, increasing the radiation-chemical resistance of the carbide layer and the microfuel as a whole.The structure of the microfuel of high-temperature gas-cooled reactors has evolved from particles with a single-layer protective coating consisting of pyrocarbon with a laminar structure through a bilayer pyrocarbon coating with different density to a fuel microsphere with three layers made of, respectively, inner high-density isotropic pyrocarbon and silicon carbide and an outer layer of high-density isotropic pyrocarbon ( Fig. 1) [1].The specifications for the microsphere fuel for HTGR take account of the following essential characteristics: thickness, density, anisotropy of the pyrocarbon coating, contamination of the coatings by fissile materials, defects in the silicon carbide layer, and others [2-6].The operational parameters (temperature, degree of fuel burnup, fluence of fast neutrons, and others) which have been obtained on the experimental stand satisfied the technical requirements for uranium dioxide microspherical fuel based on multilayer coatings (see Fig. 1, position I) and even exceeded the requirements in individual cases (see Fig. 1, positions II and III).In connection with new problems arising in the development of fourth-generation nuclear-energy systems, the requirements for the operational parameters (nuclear fuel burnup, irradiation temperature, hast-neutron fluence, energy release from a fuel microsphere, and others) are increasing substantially. Probably the biggest problem will be due to the realization of deep burnup of fuel at high irradiation temperature -up to 20% h.a. and higher than 1100°C under stationary operating conditions of a very-high-temperature gas-cooled reactor (VHTR, Japan).One of the variants under consideration variant for improving the performance of multilayer coatings is replacing the silicon carbide load-bearing layer by a zirconium carbide layer. However, such a replacement will make it necessary to solve a multitude of materials-engineering problems, develop methods for monitoring the properties of carbide-zirconium coatings and rejecting microfuel based on them, and determine the capability of zirconium carbide to confine solid fission products at elevated irradiation temperatures taking account of the high neutron fluence for VHTR and GFR (see Fig. 1, positions IV, V).Laboratory investigations performed in the USA on micros...

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Section: Of Htgr Fuel Elementsmentioning

confidence: 97%

Section: Of Htgr Fuel Elementsmentioning

confidence: 99%

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Formation of multifunctional barriers to increase the radiochemical resistance of the protective coatings of HTGR fuel elements

Kurbakov

2009

At Energy

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“…Chernikov [20] obtained the main characteristics of materials and components of spherical pebble fuel. His study included microspheres of uranium dioxide, pyrocarbon and silicon carbide protective layers, coated fuel particles, and matrix graphite.…”

Section: Introductionmentioning

confidence: 99%

Pyrocarbon Coating on Granular Al2O3 for HTGR-Type Power Reactor

Sklabinskyi,

Pitel,

Skydanenko

et al. 2023

Coatings

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Fourth-generation nuclear power systems are based on high-temperature gas-cooled reactors, in which the pebble fuel is the primary energy carrier. In this regard, applying protective pyrocarbon coatings on granulated fuel is an essential problem in ensuring the reliability of nuclear power plants. The article’s main idea is to research rational technological parameters of forming a pyrocarbon protective coating on the granules of a nuclear fuel model. For this purpose, granulated Al2O3 with the protective pyrocarbone coating was applied as a fuel model. The article’s aim is to study the effect of thermophysical parameters on applying a protective pyrocarbon coating on granulated Al2O3. During the experimental studies, thermal imaging of the pyrolysis process was used. The scientific novelty of the work is the equilibrium curves for the systems Al2O3:CH4, Al2O3:CH4:N2, and Al2O3:CH4:Ar. Their analysis allowed for evaluating rational thermochemical parameters of the pyrolysis process. As a result, rational thermophysical parameters of coating granulated Al2O3 with a pyrocarbon layer were evaluated, and the practical possibility of applying the pyrocarbon coating to granulated Al2O3 in the electrothermal fluidized bed was experimentally proven. It was shown that nitrogen does not significantly affect the target reaction product under a temperature of less than 1500 K. Also, the rational conditions for the pyrocarbon coating at a pressure of 0.1 MPa were realized at a temperature of 900–1500 K and using argon. Moreover, pyrocarbon was precipitated from hydrocarbon at 1073–1273 K. Overall, the need to add an inert gas for reducing the carbon black formation was proven to prevent a reduction of natural gas efficiency.

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