Structural and Fuel Materials for the Fuel Elements of Thermionic Nuclear Power Systems

Gontar, A. S.; Nelidov, M. V.; Nikolaev, Yu.V.; Rakitskaya, E. M.; Fedik, I. I.; Yastrebkov, A. A.

doi:10.1007/s10512-006-0019-2

Cited by 5 publications

(4 citation statements)

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“…The admissible deformation of the emitter shell over a service life of 5-10 years is limited to 2%, i.e., the admissible average rate of radial deformation of the shell must not exceed (2-4)·10 -5 %/h [4]. It is known that in order to satisfy these requirements the emitter shell material is chosen on the basis of the test results for creep in the candidate materials.…”

Section: Materials Propertiesmentioning

confidence: 99%

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Optimization and Long-Life Validation Methods for EGC

et al. 2014

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The methods and results of accelerated tests performed on fuel and structural materials, individual units and an entire EGC for computational and experimental validation of service-life-power characteristics are examined for long-life (≥7 yr) EGC operating regimes. The results of such studies provide the requisite initial data for the KIM software system used to model the service-life behavior of EGC taking account of the interaction of the main service-life-determining processes. It is shown on the basis of complex computational and experimental studies that the time required for reactor tests of EGC in order to validate a long service life, including for dual-regime operation as part of an NPP, can be reduced.Computational modeling of the behavior of an electricity generating channel (EGC) performed at the Luch Research Institute and Scientific Industrial Association (NII NPO Luch) is being done using the KIM software system, which makes it possible to investigate the thermoelectric characteristics of EGC, mass transfer in fuel elements and the deformation state of fuel elements [1]. The following are determined from the computational results:• electric potential distribution, current density and temperature of the electrodes, voltage and electric power of the EGC; • temperature distribution in the interior of a fuel kernel comprised of uranium dioxide as well as along gas-venting setups with protective perforated screens; • fuel configuration in a fuel element during radial and axial mass transfer; • heat removal through the gas-venting setup; • restructuring of the initial kernel structure; • rate of swelling of the fuel; • deformation of the emitter by a swelling kernel; and • variation of the interelectrode gap width along the EGC. Intra-and extra-reactor tests of materials, individual units and an entire EGC show that the processes enumerated above are service-life-determining for regular operating regimes. The results obtained provide the requisite initial data for KIM and at the same time direct experimental confirmation of the energy and service-life characteristics of EGC according to the aggregate of all the processes studied within the time frame of the tests (Fig. 1).The information value of the experimental data used in the calculations increases considerably if they reflect the specific nature of the long-time service life. This served as a basis for the development and implementation of the methods examined in the present article for performing accelerated tests of materials and individual units of an EGC.The methodological direction of development of methods for performing accelerated tests consisted of determining the accelerating factors and their subsequent mutual effect using a complex computer program.

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Section: Materials Propertiesmentioning

confidence: 99%

“…The effect of burnup on creep was also investigated under extra-reactor conditions using a model dioxide containing fission product simulators according to the prescribed burnup [4,8].…”

Section: Materials Propertiesmentioning

confidence: 99%

Optimization and Long-Life Validation Methods for EGC

et al. 2014

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“…A ventilated fuel element of a thermionic converter reactor with single-element electricity-generating channels based on uranium dioxide with mostly open porosity with ten-micron pores stabilized to thermal sintering is examined [6].…”

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“…Thus, the inequality d 2 (p/√ ⎯T)/dρ 2 > 0 is equivalent to Multiplying the last inequality by the positive quantity R 2 gives inequality (6). Neglecting the small, as compared with the change of the equilibrium vapor pressure, change of T 1/2 in the operating range of the fuel temperature, the condition for elongation of a spherical pore in the direction of motion at a point with the coordinate ρ along the radius of the fuel kernel can be written in the form d 2 p/dρ 2 > 0.…”

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Shape change of process pores in kernels of high-temperature uranium dioxide based fuel elements

Gontar¹,

Sotnikov²

2011

At Energy

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A computational method and results for calculating the shape change of an initially spherical vacuum pore with migration in uranium dioxide fuel during operation of a high-temperature fuel element are presented. The conditions for a spherical fuel element to be elongated and flattened in the direction of the temperature gradient, i.e., its transformation into prolate and lenticular, are determined. It is shown that the sign of the second derivative of the saturated vapor pressure of uranium dioxide with respect to the radius of the fuel kernel is decisive. It is established that the region of formation of the prolate pores is located at the periphery of the cross section of a fuel kernel and that of lenticular pores at the center. As the thermal neutron fraction in the reactor spectrum increases, the formation region becomes narrower for prolate pores and wider for lenticular pores.The initial process porosity of uranium dioxide strongly affects the evolution of the structure, strength properties, and radiation characteristics. For this reason, the shape change of the pores as they migrate in a temperature gradient field is of great interest [1][2][3][4]. Large pores which initially are approximately the same size as a grain become prolate as they migrate in the direction of a temperature gradient right up to the formation of cylindrical channels. The observed migration of lenticular pores forms a columnar structure of uranium dioxide grains. The sources of such pores are rounded microcracks in uranium dioxide, which arise in the starting-stopping regimes of a reactor [3]. Lenticular pores can also form during migration of grain boundaries oriented perpendicular to the direction of a temperature gradient with pores arranged on the boundaries and acquiring the shape of a lens as the curvature of the grain boundary increases as it migrates together with the pore [5].As a supplement to the indicated mechanism, the present work examines the effect of the character of the radial temperature distribution and temperature gradient in a high-temperature fuel element on the shape change of the technological pores distributed in the volume of a fuel pellet. A ventilated fuel element of a thermionic converter reactor with single-element electricity-generating channels based on uranium dioxide with mostly open porosity with ten-micron pores stabilized to thermal sintering is examined [6].Computational estimates show that vacuum pores with the indicated sizes at the operating temperature migrate as a result of the transfer of uranium dioxide vapors in the pore volume in the free-molecular regime. In this case, the migration rate and pore shape are most sensitive to the local values of the temperature and the temperature gradient in the fuel-element kernel which vary in the migration process. The effect of these factors on the porosity of a uranium dioxide kernel was studied in the present work.Mass transfer in a vacuum spherical pore with an arbitrary temperature distribution on its surface was investigated in [7]. The intensi...

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