Merits of the refractory metals single crystals in application to the TFE [thermionic fuel element]

Gontar, A. S.; Kucherov, R.Ya.; Nikolaev, Yu.V.; Nelidov, M. V.

doi:10.1109/iecec.1996.553827

IECEC 96. Proceedings of the 31st Intersociety Energy Conversion Engineering Conference

DOI: 10.1109/iecec.1996.553827

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Merits of the refractory metals single crystals in application to the TFE [thermionic fuel element]

A. S. Gontar¹,

R.Ya. Kucherov²,

Yu.V. Nikolaev³

et al.

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“…Experimental (---) and computed (--) rates of evaporation of tungsten in a gaseous medium on UO 2.005 (1, 2), UO 2.000(3,4), and UO 1.995(5), in vacuum…”

mentioning

confidence: 99%

“…, tungsten (4), single-crystal alloys of molybdenum (5) and tungsten (6) with niobium at 1700°C. the optimal content of alloying components have a higher creep resistance than one of the best polycrystalline alloys W-4Re-0.33HfC [2].…”

mentioning

confidence: 99%

“…Single-crystal tungsten was chosen as the emission coating, since the diffusion interaction of the materials of bimetallic cladding in the case of polycrystalline coatings results in the formation of pores at the interface and a large nonradiation deformation of the cladding (Fig. 2) [4,5]. The crystallographic direction <111> of a single-crystal substrate is oriented along the longitudinal axis of the cladding; in this case, predominantly the close-packed face (110) with maximum vacuum work function and, correspondingly, higher power and efficiency of the thermionic converter, emerges on the emission surface [6].…”

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

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The characteristic properties of hardened single-crystal alloys (Mo-Nb, W-Nb, W-Ta) and UO 2-x with open thermally stabilized porosity are presented. The combination of the indicated materials makes thermionic fuel elements very stable with a long service life. It is shown that the use of porous uranium dioxide under temperature conditions resulting in restructuring makes it possible to decrease the size of the columnar grains and increase the creep rate of the dioxide with optimal porosity and pore size. A model oxide fuel, which has been developed, with fission-product simulators for rapid determination under extra-reactor conditions of the properties of uranium with deep burnup and for performing accelerated reactor tests is described.Two distinguishing features of the fuel elements in thermionic nuclear power systems operating on thermal and fast neutrons is the high working temperature of the cladding (1500-1800°C) and the substantial yield of gaseous fission products from uranium dioxide. For this reason, the structural scheme of a ventilated fuel element is generally used. Then main service life limiting factor is the deformation of the cladding under the action of the swelling fuel kernel. Conceptually, the deformation is decreased by using strengthened cladding, fuel with a lower rate of swelling, and a high creep rate, all of which acting together redistributes the volume of the swelling fuel in the interior free volume of a fuel element. Strengthened single-crystal alloys based on molybdenum, tungsten, and a uranium dioxide modification that is optimized with respect to structure and composition have been developed to support this concept.Single Crystal Alloys Based on Molybdenum and Tungsten. To achieve and maintain high output electric parameters of the electricity-generating channel (EGC) during the service life, stringent, including also contradictory, requirements are imposed on the cladding material of a fuel element together with a high resistance to creep:• high vacuum work function;• compatibility with fuel and cesium vapor;• low diffusion penetration of the fuel components and fission products;• radiation resistance in a fast-neutron flux;• small cross section for the absorption of thermal neutrons. A compromise solution for satisfying these requirements was the development of bimetallic claddings with a strengthened substrate ~1 mm thick and an effective emission coating ~0.15 mm thick. Single crystal alloys Mo-Nb, W-Nb, and W-Ta have been developed for the substrate. The creep rate of these alloys is approximately 1000 times lower than the corresponding single-crystal metals (Fig. 1). In addition, the creep stage with high deformation rate, which is characteristic for metals at the nonsteady stage, is absent in these alloys [1]. The alloy Mo-Nb was used in the fuel element of a single-ele-

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“…Experimental (---) and computed (--) rates of evaporation of tungsten in a gaseous medium on UO 2.005 (1, 2), UO 2.000(3,4), and UO 1.995(5), in vacuum…”

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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

et al. 2005

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Merits of the refractory metals single crystals in application to the TFE [thermionic fuel element]

Cited by 1 publication

References 2 publications

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

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

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