Vented fuel element of a nuclear reactor
(57) Abstract:The invention relates to nuclear energy and space technology, may be used to create high-temperature fuel elements, in particular thermionic fuel elements for reactors converters for space power plants. The inventive vented fuel element of a nuclear reactor on the surface of gas Central cavity formed porous layer of refractory material introduction into the fuel material fine powder. The particle size of the powder is selected commensurate with the particulate fuel material in the amount of 1 - 5 vol.%. The result: better ventilation of a fuel rod. 1 C.p. f-crystals, 2 Il. The invention relates to nuclear energy, and more specifically to the development of a vented fuel elements (Fe) of a nuclear reactor designed to convert the energy division of nuclear fuel into thermal energy or directly into electricity, in particular for thermionic reactor Converter (TRD).Known vented fuel rods, which contain the fuel material (TM), a shell enclosing a fuel cell material, the venting device (GAO), shall roducti division from gas Central cavity outside of TVEL [1, 2]. Similar designs are implemented for high-temperature fuel elements with long service life, in which TM, as a rule, does not contain additives, inert diluent (for example, refractory metals). Therefore, TM, primarily refers to uranium dioxide has a higher temperature and has a large radial temperature gradient, contributing to the growth of the columnar grains whose boundaries are effective sinks GPA in the Central gas passage formed by precondensation and seal TM.As a rule, go with GPA face of volatile fission products and pairs of TM, which can disrupt the operation of a fuel rod and TRD mainly for the reasons:
1) unacceptably large number of TM released from thermal emission of a fuel rod violates the heat balance of the fuel and thus reduces the amount of electrical energy conversion (in the case of thermionic fuel elements);
2) out of TVEL TM condenses on the relatively cooler structural elements of the reactor and can bring them down;
3) TM, passing through the GOU may condense inside the tube Gow and thus clogging it, resulting in upsets you is low with a long service life.To reduce output TM through Gow and prevent condensation TM inside the tube GOU known vented fuel element of a nuclear reactor, comprising a fuel material and gas Central cavity, a tube which penetrates the fuel material and has two open end, one end of the tube, with the tip of the capillary channel is located in the Central gas cavity and the other end comes out of the fuel cladding in order to take volatile and gaseous fission products from the fuel material  . The presence of TVEL go with the capillary tip can reduce the vapor outlet TM from gas Central cavity.However, this design vented fuel elements, use go with the capillary tip, reduces the reliability of a fuel rod, because it increases the likelihood of unforeseen disturbances bandwidth Gow. The main disadvantage of this fuel - low reliability due to possible clogging of the capillary channel material of the emitter or vent tubes during condensation and reduction reaction of the capillary volatile oxides of metals (molybdenum, tungsten), made from the shell of a fuel rod and go. the existing UO2+xyou may receive a phase oxides of tungsten by oxygen from UO2+x. These oxides contribute to the formation of low-melting eutectics in the "W - U - O", which accelerates the penetration of uranium in tungsten. Thermodynamic analysis shows an increasing penetration of uranium due to the emergence of phase WO3followed by the formation of low-melting eutectics in the "W - U - O" and the creation of conditions of capillary condensation WO3.The technical result of the proposed solutions is to improve the ventilation of a fuel rod due to the increased reliability go, because the lower output of the TM and volatile fission products from the fuel elements and prevent condensation TM in the tube Gow can be obtained without using the design GOU unreliable the tip of the capillary channel.The invention consists in that in a vented fuel element of a nuclear reactor containing a shell enclosing the fuel material and gas Central cavity, a tube which penetrates the fuel material and has two open end, one end of this tube is gas Central cavity and its other end out of the fuel cladding, fuel is the fuel material in the amount of 1-5%. As the refractory material is tungsten, molybdenum and alloys based on them.In Fig. 1 shows a vented fuel element in the initial state. In Fig. 2 after the process of precondensation, restructuring of the TM and education has gas Central cavity, covered with a porous layer of refractory material.Vented fuel elements of nuclear reactor comprises a shell 1 enclosing TM 2 with fine powder of refractory material of tungsten, molybdenum or alloys with particle size, commensurate with the particulate fuel material in the amount of 1-5 vol.%, gas Central cavity 3, the venting device in the form of a tube 4.The introduction of a fine powder of refractory material in the TM based on the experimental fact that the redistribution of insoluble fission products to the microsections of irradiated fuel, observed as inclusions of the second phase with a characteristic metallic sheen . And most of the inclusions has a rounded shape, is located predominantly at the grain boundaries and is associated with pores. The size of the inclusions increases as we move from the periphery to the centre of the sample, i.e., from less hot to hotter parts of the sample.Small additive fine powder of refractory material, practically does not affect the processes of precondensation and restructuring of the fuel core of a fuel rod, which is especially important when forming the final structure of the fuel core with gas Central cavity from which go through out the GPA and volatile fission products.Settlement analysis of changes in thermal conductivity of two-phase compositions made according to the formula of Telescope  for a static structure, showed insignificant changes of thermal conductivity. So calculation example for the composition of the TM - UO2and additive fine powder of W 2 and 5 vol.% showed a change in the conductivity of the composition by 5.9% and 16% respectively (thermal conductivity of UO2and W were taken 2.5 and 100 W/(mgrad), respectively). Additive fine powder up to 10% vol. increases thermal conductivity of the composition already 37.6%, which leads to a significant change in the process of heat transfer in the fuel core of a fuel rod and time formitalia the manufacture of products made of uranium dioxide powder and surface area gas Central cavity, formed in the process of precondensation and restructuring of the TM. Computational studies have shown that to ensure long and reliable operation of the GOU volume of gas Central cavity should be about 30% of the volume of the fuel core. Resulting characteristic configuration of the surface gas Central cavity discussed in detail in . Characteristics of uranium dioxide powder, depending on the technology of production is the average particle size, which can vary from 0.08 to 0.44 μm  up to 40 µm  . We believe that in the process of precondensation and redistribution of the concentration of TM and additive fine powder on the surface of gas Central cavity formed by the powder layer with a minimum thickness corresponding to the characteristic particle size (particle size adopted 40 μm). Knowing the characteristic volume (about 30%) and surface area gas Central cavity , it is easy to calculate the limiting case of the minimum additive fine powder component of the order of 1%, while on the surface of the Central gas cavity is formed by a layer of refractory powder thickness of at least one particle. At least the addition of refractory material (less than 1%) in powder, that can dramatically reduce the efficiency of vented fuel element. In addition, the static structure of the fuel composition, forming a homogeneous mixture with the above amount of additive with a particle size approximately equal to the particle TM, obviously, at the initial stage of operation of a fuel rod will prevent the formation of a continuous matrix structure of the material of the additive fine powder. Obviously, at the subsequent operation of a fuel rod, taking into account the redistribution of TM and fine additive, the additive fine powder of refractory material in the direction of the temperature gradients will increase from the periphery of the fuel rod to its Central part, with a maximum at the boundary gas Central cavity, seeking over time to the isothermal surface. Over time, with increasing concentration of the fine powder of refractory material, on the border gas Central cavity thus formed porous layer of refractory material.Vented fuel elements of a nuclear reactor works as follows. In the operation of the reactor at high temperature fuel rod is nuclear fission TM 2: the transformation of the energy division in the ATA which is a reorganization of the structure and reconcretion TM 2 with the formation of gas Central cavity 3, where flock GPA, which is formed in the fission process TM 2. Resulting from neutron irradiation observed changes in the structure and physico-mechanical properties of TM 2, in particular in the direction of the temperature gradient in the fuel is a redistribution of the concentration of TM 2 and put fine powder of refractory material and insoluble fission products. Moreover, the concentration of the refractory powder and insoluble fission products by temperature gradients increases from the periphery to the center of the fuel rod. Resulting in surface gas Central cavity 3 is formed of a porous layer of refractory material 5, which reduces the free surface evaporation and creates an additional diffusion resistance TM.The use of the proposed vented fuel elements in a nuclear reactor in comparison with the prototype provides the following benefits:
1) decreases the likelihood of unforeseen disturbances bandwidth GOU;
2) the ability to control valid output TM of the fuel rod by varying the number and size of powder particles of refractory material;
3) allows to exclude from design GOU unreliable tip with capillarylike. French patent N 2151007 class H 01 J 45/00 for 19732. Vented fuel element of a nuclear reactor. U.S. patent N 4163689 class G 21 C 3/02 priority from 03.12.1965,, N 512823.3. The method of calculation of temperature fields of heterogeneous fuel core thermal emission electricity generating element. Nuclear energy, I. 49, vol. 6, S. 393 - 394, 1980.4. Olander D. R. Fundamental Aspects of Nuclear Reactor Fuel Elements. - U. S. Departament of Energy, 1976. - 610 p.5. High temperature nuclear fuel. /R. B. Kotelnikov, S. N. Bashlykov, A. I. Chestnuts, T. S. Menshikova): Atomizdat, 1978, S. 117.6. High temperature nuclear fuel /R. B. Kotelnikov, S. N. Bashlykov, A. I. Chestnuts, T. S. Menshikova): Atomizdat, 1969, S. 7.7. Modeling of heat and mass transfer in the core thermionic fuel elements. Nuclear energy, I. 53, vol. 2, S. 74 - 76, 1982.8. The processes of heat and mass transfer in high-temperature fuel elements, thermoemission electricity generating channels. /Sat.: CT. Ser. XII//RSC "Energia", Korolev, 1996. Vol. 2 - 3. Calculation, design, construction and testing of space systems. S. 99 - 112.9. C. S. Emelianov, A. I. Evstyuhin. Metallurgy of nuclear fuel. - M.: Atomizdat, 1968, S. 122.10. . S. 90.
FIELD: nuclear power engineering; fuel rods for water-moderated water-cooled reactors.
SUBSTANCE: proposed fuel rod designed for use in water-cooled water-moderated power reactors such as type VVER-1000 reactor has fuel core disposed in cylindrical can. Outer diameter of fuel rod is chosen between 7.00 . 10-3 and 8.79 . 10-3m and fuel core diameter is between 5.82 . 10-3 and 7.32 . 10-3m and mass, between 0.93 and 1.52 kg, fuel core to fuel rod length ratio being between 0.9145 and 0.9483.
EFFECT: reduced linear heat loads and fuel rod depressurization probability, enlarged variation range of reactor power, optimal fuel utilization.
7 cl, 3 dwg
FIELD: nuclear power engineering; tubular dispersed-core three-layer fuel elements.
SUBSTANCE: proposed method includes production of powder mixture, powder mixing in plasticizer environment, cold molding in core billet with plasticizer, thermal sintering, hot molding-calibration of fuel core, core placing in can made in the form of sleeve with annular slot, calibration, hot molding through die, and drawing; inner surface of external can of sleeve is provided with longitudinal bulges and outer surface bears bulge location marks; fuel core is provided with longitudinal flats and placed in sleeve taking care to align bulges of the latter with core flats; in the course of drawing marks are aligned on arbor ribs.
EFFECT: enhanced stability of active layer and can thickness in shaping polyhedral fuel elements.
1 cl, 4 dwg