Tablet of nuclear fuel

 

(57) Abstract:

Purpose: in nuclear engineering, in particular in the construction of nuclear fuel tablets for channel uranium-graphite reactors. The tablet contains a powder mixture of uranium dioxide with the addition of oxide of erbium (Er2O3). The content of the oxide of erbium in nuclear fuel is from 0.46 to 0.64 wt.% the erbium conditional mass fraction U-235 in nuclear fuel from 2.6 to 2.8 wt.%. Moreover, the open porosity of the pressed and sintered mixture of uranium dioxide (UO2with the addition of erbium oxide does not exceed 1%. The result is improved fuel burnup, reduced consumption of fuel assemblies per unit of produced energy and reduces the volume of spent nuclear fuel, decreases the magnitude of the steam reactivity coefficient and the non-uniform energy deposition, decreases the maximum linear load on the fuel elements. 3 C. p. F.-ly.

The invention relates to nuclear engineering, in particular to designs of fuel assemblies channel uranium-graphite reactors (LWGR (reactor high power channel), in which used nuclear fuel based on uranium dioxide with the addition of oxide of erbium (Er2O3).

adsteam led deficiencies in the design of the control rods and suboptimal uranium-graphite ratio. In the steam reactivity coefficient was (4 - 5) . After the accident at all units with RBMK-type reactors have been carried out to improve reactor safety. At the first stage steam reactivity coefficient was reduced to 1 due to the load (52 - 54) additional absorbers (DP) in RBMK - 1500 and about 80 DP in RBMK-1000 and increase operational reactivity margin to 55 rods in RBMK-1500 and 45 of the rods in the RBMK-1000. This method has been practically eliminated in an uncontrolled increase of the reactor power on prompt neutrons in case of possible dehydration of the active zone when the accident loss of coolant.

The increase in the number of additional absorbers in the core led to a significant decrease in burnup fuel and, as a consequence, the deterioration of the economic characteristics of the fuel cycle. Burn-paged fuel decreased by about 25%. In addition to the direct economic losses due to neovagina fuel exacerbated the problem of fuel because the growth rate of the overloads of fuel has led to accelerated filling of pools of spent fuel.

In the second stage of the RBMK reactors was launched on fuel with enrichment is cast cycle.

Simultaneously, research was performed to search for more cost-effective way of reducing the steam reactivity coefficient instead of using additional absorbers.

It is known that the active zone of water-cooled reactors can be formed from fuel assemblies containing fuel of different composition with the addition of burnable absorber that allows you to compensate for reactivity to align the energy liberated by the volume of the active zone and to maintain the temperature coefficient of reactivity at a given level. As burnable absorbers are used rare earth elements and their oxides, in particular erbium (WO 95/04994 A1,1995).

Erbium when it is used as a burnable absorber, unlike other rare earth elements, is introduced into nuclear fuel in much smaller concentrations, which positively affects the physical, mechanical and technological properties of the fuel. In particular, adding fuel erbium has little impact on such factors as thermal conductivity of the fuel.

Known fuel Assembly channel of a nuclear reactor containing the fuel elements with toplease time on the RBMK is a series of events aimed at further improvement of the active zone. In particular, the transition to the new control rods with tape link, starts operation of the fuel assemblies with spacer grids made of zirconium alloy instead of stainless steel, examined the possibility of reducing the operating reactivity margin. Alternative to save DP in the active zone is the increase in the concentration of erbium in the fuel. In order to increase the erbium content of the additive in the fuel is not led to losses in fuel burnup, it is necessary to increase fuel enrichment.

The introduction of erbium in the fuel channel of a nuclear reactor (RBMK) allows you to reduce the amount of steam reactivity coefficient.

The presence of erbium in the RBMK fuel allows to replace in the active zone, at least part of the additional absorbers (PD) for working fuel assemblies, which increases the depth of the burn-up fuel.

In addition, the erbium as a neutron absorber, fade is not as intensive as, for example, gadolinium or boron, and retains its impact on the steam reactivity coefficient the greater part of the campaign. At the same time adding erbium in topline closest to the technical essence and the achieved result to the described invention is a tablet of nuclear fuel, containing compacted and sintered powder mixture of uranium dioxide (UO2with the addition of oxide of erbium (Er2O3(see Mezhuev C. A. and other aspects of design and manufacturing technology FA power reactors with increased service life and increased reliability, Nuclear power, I. 84, vol. 2, February 1998, S. 126, 127).

In the famous tablet of nuclear fuel for the channel of a nuclear reactor uranium enrichment is from 2.4% to 2.6%, and the concentration of erbium in the fuel (uranium dioxide) is 0,41% by weight. Adding fuel oxide erbium allows replacement of additional absorbers on regular fuel assemblies, which improves the parameters of the active zone. The use of nuclear fuel with the addition of erbium and increased uranium enrichment can significantly increase the burnup of nuclear fuel.

It is obvious that increasing the number of output additional absorbers from the active zone and their replacement fuel assemblies with uranium-erbium fuel, respectively, to increase the percentage of erbium supplements. Moreover, increasing the number of output sinks should be compensated for their lack of increase in the content of erbium fuel.

However, for an arbitrary choice of the ratio between elevated values for fuel enrichment and additive concentration of erbium may be a situation where it is established, for example, by calculation, that of the active zone, you cannot remove the required number of APS. Indeed, without the consent of the correlation between the enrichment and the fuel content of the additive erbium and unloading the required number of APS possibly a sharp decrease in burnup. Especially negative factors will occur with small values of enrichment fuel and material content of erbium in the fuel.

The essence of the invention.

The present invention is the development and creation of tablets nuclear fuel with improved economic performance.

The solution of this problem can be obtained new technical results, namely, that increased fuel burnup decreases the consumption of nuclear fuel per unit of produced energy and reduces the volume of spent nuclear fuel, decreases the magnitude of the steam reactivity coefficient and the non-uniformity of energy deposition in the active zone, reduces the maximum linear load on the fuel is Rasa pressed and sintered powder mixture of uranium dioxide (UO2with the addition of oxide of erbium (Er2O3), the content of the oxide of erbium in the fuel is from 0.46% weight. to 0.64 wt%. the erbium conditional mass fraction U-235 from 2.6% to 2.8 wt%, and the open porosity of the compacted and sintered mixture of uranium dioxide (UO2with the addition of erbium oxide does not exceed 1%.

The distinctive feature of this invention consists in the following. Adding erbium fuel can significantly reduce the steam reactivity coefficient in RBMK, because the isotope167Er, the concentration of which was 22.9%, has a strong resonance at neutron energy of 0.47 eV. Decreasing the density of the fluid shift neutron spectrum in the direction of resonance and the absorption of neutrons in erbie. This is because the reduced speed slowing down of neutrons, because of the slowdown on the water is not happening, and in the formation of the spectrum increases the role of graphite, has an operating temperature (200 - 250)oC higher than water. Although the resonance167Er is far from the maximum of the spectrum of the Maxwell, the neutron flux falling on the region of the resonance, when the dehydration is considerably increased. Thus, the spectrum shift to higher energy leads to an increase in the POG is aktivnosti. More than erbium in the fuel, the less steam reactivity coefficient and higher operating safety of the RBMK.

However, high concentrations of erbium in the fuel reduces fuel burnup, because it increases the parasitic absorption of neutrons. Therefore, high concentrations of erbium has to be offset by a corresponding enrichment of nuclear fuel. This is a clear relation between the enrichment and the fuel content of erbium in it.

It was found that when the content of erbium in the active fuel zone from 0.46% weight. to 0.64 wt%. the erbium, conditional mass fraction of U-235 in nuclear fuel active zone should be from 2.6 % to 2.8 wt%. When the open porosity of the pressed and sintered mixture of uranium dioxide (UO2with the addition of erbium oxide should not exceed 1%, since only in this case, the serviceability of this tablet.

Otherwise, the above technical results can not be implemented due to the lack of a certain correspondence between the content of erbium in nuclear fuel and enrichment.

Additionally, the content of the oxide of erbium, it is advisable to select equal 0,50,04% weight. or 0,60,04% weight. on erbium. Dust and increased the ratio of fuel consumption.

It is preferable to choose the size of the grains of the powder mixture of uranium dioxide with the addition of oxide of erbium from 10 μm to 20 μm.

Tablet of nuclear fuel may have a Central hole.

Information confirming the possibility of use of the invention.

Manufacturing technology of nuclear fuel tablets are almost identical to standard manufacturing techniques tablets without burnable absorber. An important aspect of development of the technology of manufacturing of tablets nuclear ceramic uranium-erbium fuel was to provide high quality mixing powders of uranium dioxide and erbium oxide. Some technical difficulties in the operation of mixing powders are related to the fact that the amount of added oxide of erbium relatively small. You can use a two-stage scheme mixing with the preparation of the first stage ligatures - mixtures with a high content of erbium. The content of the oxide of erbium in nuclear fuel is from 0.46% weight. to 0.64 wt%. the erbium conditional mass fraction U-235 in nuclear fuel from 2.6% to 2.8 wt%. Calculations showed, when using such fuel is reduction in the steam reactivity coefficient. Despite the increase in enrichment from 2.6% to the Orok with lower levels of erbium.

This tablet nuclear fuel is produced in a known manner by conventional means on the standard equipment. The fuel must have a certain phase composition, average grain size, the maximum size of unreacted particles and other standard options.

Manufacturing technology of nuclear fuel tablets is the following. In the mixer, in particular a vane type, is preparing a two-component mixture of uranium dioxide with conventional mass fractions of U-235 in nuclear fuel from 2.6% to 2.8 wt%. and erbium oxide. Moreover, in the nuclear fuel add this amount of erbium oxide to its content in nuclear fuel was 0,50,04% weight. or 0,60,04% weight. on erbium. Next, the mixture is subjected to mixing with a standard plasticizer. Then produce granulation mixture with plasticizer, with subsequent grinding of granules and sieving at the preparation stage press powder. After drying, press powder carry out the pressing of tablets and their sintering. The obtained tablets equip fuel elements included in the fuel assemblies.

Example. You must obtain tablets of nuclear fuel with the additive oxide of erbium. Given the content of additives on pastem mixer parties, consisting of 7,0 kg of uranium dioxide and 40,23 g of erbium oxide. The mixing time is 10 minutes. Before mixing manually prepared a ligature, consisting of all of erbium oxide and 40-50 grams of uranium dioxide. From each batch produced samples for the determination of erbium in a two-component mixture. Then was carried out by mixing a two-component mixture with a standard plasticizer in the same mixer for 5 minutes. The mixture with plasticizer is subjected to double granulation by extrusion hydraulic press. The obtained granulate is subjected to grinding and sieving using vibrating screens with grid cell size is 0.63 mm, and after drying in a rotary kiln received press powder, which is using a rotary press machine pressed into the "raw" tablets, "raw" tablet is sintered at a temperature of 1720oC for 4 hours and subjected to regular development and control operations. You get a tablet with an open porosity of less than 0.51% of average grain size of 11.8 microns.

At all stages of manufacturing tablets produce control parameters. Controlling the content of erbium in the nuclear fuel may be effected by various methods, such as roentgenoradiometric dioxide (UO2with the addition of oxide of erbium (Er2O3), characterized in that the oxide content of erbium in the fuel is from 0.46 to 0.64 wt.% the erbium conditional mass fraction U - 235 from 2.6 to 2.8 wt.%, and the open porosity of the compacted and sintered mixture of uranium dioxide (UO2with the addition of erbium oxide does not exceed 1%.

2. Tablet of nuclear fuel under item 1, characterized in that the oxide content of erbium is or 0,6 0,5 0,04 0,04 wt.% on erbium.

3. Tablet of nuclear fuel under item 1 or 2, characterized in that the grain size of the powder mixture of uranium dioxide with the addition of erbium oxide is from 10 to 20 microns.

4. Tablet of nuclear fuel under item 1, or 2, or 3, characterized in that it has a Central hole.

 

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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.

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7 cl, 3 dwg

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