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 thermionic fuel elements. The inventive fuel element has a venting device made in the form of a Central tube with an axisymmetric tip with the capillary channel inside. The tip is made concentric with the capillary channel, the cavity filled with nuclear fuel. This reduces the likelihood of overlapping capillary channel volatile fission products and condensate. 1 C. p. F.-ly, 1 Il.

The invention relates to the nuclear industry, more specifically to the development of a vented fuel elements (Fe) of a nuclear reactor, in particular for thermionic reactor Converter (TRD), intended for direct energy conversion fission of nuclear fuel into electrical energy.

Known fuel rods with the withdrawal of gaseous fission products (GPA) and volatile fission products from the fuel elements, which contain the fuel material (TM), a shell enclosing a fuel cell material, the venting device (GOU), made in the form of a tube is m life, where TM, as a rule, does not contain fuel additives inert diluent (for example, refractory metals). So TM 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 following reasons:

1) unacceptably large number of TM released from thermionic fuel elements, violates the heat balance of the fuel and thus reduces the amount of electrical energy conversion;

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 a broken normal output GPA of TVEL.

It is especially important to organize reliable conclusion GPA of TM for high-temperature fuel elements with long service life.

castac tube GOU, located in the Central zone of the gas cavity, are in the form of the tip of the capillary channel.

Closest to the technical essence is the design of a vented fuel element with an output gap of the TM through the SEI. GOU made in the form of a tube of refractory metal and axisymmetric tip of the capillary channel, located in the Central gas cavity vel [3].

However, the efficiency of such fuel design depends on the temperature of operation of a fuel rod, the geometric dimensions of the fuel elements and GOU used TM and material Gow. There are areas of the above parameters under which this design GOU may not be acceptable because TM overlaps condensate capillary channel tip Gow. As shown by computational research [3] and the practice of creating high-temperature thermionic fuel elements, in the reactor at rated power, there is a time period, characterized by an intense process of condensation TM at the capillary tip GOU, leading to a temporary failure of the system output GPA. Moreover, this period can be quite long. That is, as a result, precedences the control of the operation of a fuel rod or unstable his work.

Instability can be caused by a temporary overlap of the capillary channel, explained as follows. After closing condensate TM capillary channel in a gas Central cavity pressure rises through the newly formed gap and thus increases the diffusion resistance to the flow of molecules TM to the tip, i.e. the flow at the tip is reduced, and the flow TM of the capillary channel to the outside of a fuel rod remains the same or even increases due to the pressure drop inside the path of the output gap. The differences flows TM tip and flow TM out in the condensate layer on the tip forms a channel that connects with a capillary channel tip, which leads to the discharge pressure in the Central gas cavity and increase the flow of TM on the tip, which again leads to an overlap of the capillary channel and the above situation is repeated.

The technical result of the proposed solutions is to prevent failure or unstable operation of the fuel rod due to potential overlapping of the capillary tip, SEI condensate TM and volatile fission products, stabilization of the output mode GPA and stock enhancement in the reactivity of the reactor.

holding the shell, containing the fuel material, the venting device in the form of a Central tube with an axisymmetric tip with the capillary channel inside, located in the Central gas cavity, the tip is made concentric with the capillary channel cavity, which is filled with nuclear fuel and is supplied mounted on the tip cover. As used nuclear fuel uranium compounds UO2, UC, UN, US or compositions based on them.

The proposed design allows you to raise the temperature of the tip of the GOU and evaporate the condensate TM from the tip by increasing the internal heat dissipation and reduce the effective thermal conductivity of the plot go.

The following drawing shows a General view of a fuel rod with the conclusion of the GPA and volatile fission products through a special device.

The fuel element includes a shell 1 enclosing TM 2, the gas passage 3, the venting device in the form of a tube 4 with axisymmetric tip 5 with the capillary channel 6. Inside tip 5 is made of the cavity 7 is filled with nuclear fuel 8 and closed by a cover 9. The cover 9 is welded to the tip 5 of the SEI and is made of the same material as the SEI.

Ventilated TVEL nuclear R the RNA fission TM 2: the transformation of the energy division in the heat. TM 2 experiences in this complex radiation, temperature and mechanical impact, resulting in the restructuring and reconcretion TM 2 with the formation of gas Central cavity 3, which accumulate GPA, which is formed in the fission process TM 2. In the process of restructuring of the fuel core condensation occurs TM 2 on the tube 4 and tip 5 with the capillary channel 6. In the result of the division of nuclear fuel 8 located in the cavity 7 tip 5 go (as of this fuel can be used, for example, uranium dioxide, having a relatively low thermal conductivity) thermal energy is released, resulting in overheating of the tip 5 of the SEI. This circumstance leads to the evaporation TM 2 with tip 5 go's and does not allow to block the capillary channel 6, thus ensuring the smooth conclusion of the GPA from gas Central cavity 3.

The use of nuclear fuel inside the tip of the GOU distinguishes offer a vented fuel element from the specified prototype, because:

1) prevents failure or erratic operation GOU due to potential overlapping of the capillary channel condensate TM;

2) stabilizes mode

3) increases the reactivity margin of the reactor due to the replacement of metal parts handpiece go nuclear fuel.

Sources of information:

1. French Patent N 2151007, H 01 J 45/00, 1973.

2. U.S. patent N 4163689, G 21 C 3/02, 1965.

3. Kornilov C. A. and other transport Processes fuel cathode node EGK. Abstracts of the conference on thermionic method of converting thermal energy into electrical energy. IPPE. - Obninsk: 1979, S. 24-26.

4. Kornilov C. A. and other Method of calculation of temperature fields of heterogeneous fuel core thermal emission electricity generating element. Atomic energy. - T. 49, vol. 6, S. 393-394, 1980.

1. Vented fuel element of a nuclear reactor containing a shell enclosing the fuel material, the venting device in the form of a Central tube with an axisymmetric tip with the capillary channel inside, located in the Central gas cavity, wherein the tip is made concentric with the capillary channel cavity, which is filled with nuclear fuel and is supplied mounted on the tip of the lid.

2. Item under item 1, characterized in that as used nuclear fuel uranium compounds UO

 

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