KR20010029512A - Nuclear fuel sintered body, process for producing a nuclear fuel sintered body and fuel rod with a cladding tube - Google Patents

Abstract

The present invention relates to a fuel rod having a nuclear fuel sintered body, a method of manufacturing the same, and a cladding tube. The fuel sintered body, which optimally slightly stresses the cladding tube of the fuel rod by combustion, comprising a chemical compound of hydrogen and at least one element of uranium and plutonium, has a first micrograph (in the polished section of the Ceramo graphic). 1) and a second micrograph 2, which can be arranged on the sintered granules. In relation to the plane of each micrograph, the first micrograph 1 has a first pore size distribution I and the second micrograph 2 has a second pore size distribution II. The sum III of the two pore size distributions has a first maximum value M1 and a second maximum value M2. There is also provided a method of producing a fuel sintered body of the above manner, and a fuel rod having a cladding tube and the fuel sintered body.

Description

NUCLEAR FUEL SINTERED BODY, PROCESS FOR PRODUCING A NUCLEAR FUEL SINTERED BODY AND FUEL ROD WITH A CLADDING TUBE}

Nuclear fuel sinters composed of hydrogen and chemical compounds of at least one element of uranium and plutonium are commonly used in nuclear reactors. In the reactor, the fuel sintered body is first subjected to shrinkage and then expanded by subsequent combustion.

A number of nuclear fuel sinters of this type are cylindrical bodies in the column in the reactor, with layers layered up and down in a cladding tube made of, for example, zirconium alloy of the combustion rod of the reactor combustion element. Due to the high pressure of the coolant in the reactor, the cladding tube extends to the fuel sinter along the outer side of the cladding tube. However, when the fuel sinter begins to expand, the cladding tube expands again. The cladding tube forms a barrier to the fission product, especially in gaseous form, exposed from the fuel sinter due to combustion. Therefore, it is important that the cladding tube is not overstressed with the fuel sinter in the reactor for the lifetime of the fuel rods.

The present invention relates to a fuel rod having a nuclear fuel sintered body, a method of manufacturing the same, and a cladding tube.

1 is a polished section of a Ceramo graphic with a high magnification of a longitudinal section of a cylindrical fuel sintered body according to the invention,

FIG. 2 shows the sum of the pore size distribution and the pore size distribution of the two sintered granule micrographs in FIG. 1,

3 is a partial cross-sectional view of a fuel rod side for a reactor combustion element.

It is an object of the present invention to form a nuclear fuel sintered compact so that the stress of the cladding tube of a fuel rod containing the nuclear fuel sintered compact of the above-described method by the nuclear fuel sintered compact due to combustion in the reactor is small. Also provided is a method for producing a nuclear fuel sintered body. Correspondingly formed fuel rods may also be provided.

The object of the invention first mentioned is achieved by the formation of a nuclear fuel sinter according to the invention according to claim 1. The formation of the fuel sinter starts with the expansion of the fuel sinter to the required volume in the reactor again by the fission product, which is in most gaseous form produced during nuclear fission. Nuclear fuel sinters with locally different pore size distributions also have very different dimensional change characteristics locally in the reactor. The dimensional change of the fuel sintered body by combustion in the reactor is set by the selection of a pore size distribution that is locally correspondingly overall and is preferably kept relatively small.

The object of the present invention mentioned first is achieved by a second formation according to the invention of a nuclear fuel sintered body according to claim 2. The second formation of the fuel sinter starts with the fact that locally different dimensional change characteristics in the reactor cause locally differently high fissable isotope concentrations within the fuel sinter, the concentration being fuel sinter in the reactor. Causes locally different strong combustion in the interior.

The object of the present invention mentioned first is achieved by a third formation according to the invention of a nuclear fuel sintered body according to claim 5. The third formation of the fuel sintered body is that isotopes, which may be raw materials for fissile material, become nuclear fissionable isotopes in the fuel sintered body with a time delay in the reactor, and correspondingly local in the fuel sintered body with a time delay. Starting from causing different strong combustion, this can be important for the precise setting of fuel sinter dimension changes in the reactor.

The refinement according to claim 8 starts from that locally different high aluminum concentrations in the fuel sinter lead to locally different shrinkage rates of the fuel sinter in the reactor. The different shrinkage rates of the fuel sinter thus open up the possibility for precise dimensional changes of the fuel sinter in the reactor. The first concentration mentioned in claim 8 may be zero.

An improvement according to claim 9, wherein the lanthanum group and tantalum group are nuclear poisons and thus the lanthanum group and tantalum group have locally different concentrations in the fuel sintered body and cause locally differently strong combustion, As a result, it is used to produce severely different dimensional changes in the reactor. This is also useful for precise setting of dimensional changes in fuel sintered bodies in a reactor. The first concentration mentioned in claim 9 may be zero.

The second object of the invention is achieved by the measures described in claims 10, 11, 12, 13 and 14 according to the invention. The nuclear fuel sintered body according to claim 1 may be manufactured by the method according to claim 10, the nuclear fuel sintered body according to claim 2 may be manufactured by the method according to claim 11, and the method according to claim 12. A nuclear fuel sintered body according to claim 5 can be produced. The process according to claim 13 forms a nuclear fuel sinter with particularly high mechanical stability, and the press body obtained in the process according to claim 14 is continuously free of cracks and hence the sinter obtained from the press body has a good surface quality. Has

The refinement of the method according to claim 15 results in a nuclear fuel sintered body from the press body which is not only continuously cracked but also has high sealing properties and whose surface does not fall off.

With the refinement of the method according to claim 16, a nuclear fuel sintered body is obtained from the press body, not only having a high sintering concentration but also having a large particle size. In large particles, the fission product in the form of gas is suppressed, and relatively strong combustion is obtained by the nuclear fuel sintered body in the reactor.

The starting powder for the type 1 granules and the type 2 granules in the method according to claim 10 consists of at least one powder of uranium oxide powder, plutonium powder and uranium-plutonium-compatible oxide powder described above.

Two or more types of granules may be used for producing the press body. Correspondingly, micrographs of more different sintered granules are present in the cerramographic polished sections of the fuel sintered body according to the invention.

According to the invention, fuel rods having at least one fuel sintered body and having a cladding tube are advantageously corresponding to any one of claims 1 to 9.

Looking at the embodiment of the present invention in detail with reference to the accompanying drawings as follows.

The nuclear fuel sintered body with the polished section of the Ceramo graphic according to FIG. 1 consists of a single-phase uniform UO ₂ with a CaF ₂ -type crystal structure. It is also possible to grasp micrographs of a number of sintered granules bounded by at least closed boundary walls 3 made of relatively large pores.

In the diagram according to FIG. 2, the abscissa of the pore diameter is in μm and the ordinate represents the percent of different porosity in relation to the total volume of the fuel sintered body. The progress curve (I) shown by the dotted line is a different volume of the sintered granules (1) micrograph (1) of the pores of FIG. 1 and the progress curve (II) shown by the dotted line is the other graph of the sintered granules (2) of FIG. Of different pore volume. The pore size distribution of the micrographs 1 and 2 is related to the face of the micrograph 1 or 2 and is proportional to the different corresponding pore volumes. The numbering and evaluation of the pores is made according to "Stereometrische Metallographie" by Leipzip 1974, Saltykov of VEB Deutscher Verlag fuer Grundstoffindustrie, in particular Chapters 7.7 and 8 and 9. The pores of the boundary wall 3 forming the boundary of each micrograph do not add up. The summation curve III of the progress curves I and II of FIG. 2 has two maximum values M1 and M2.

In addition, the micrograph (1) and corresponding sintered granules of FIG. 1 have a first concentration of fissable uranium isotope 235, and the micrograph (2) and corresponding sintered granules are second to nuclear fissable uranium isotope 235 Has a concentration. The two concentrations differ by at least 0.5 absolute weight%, preferably at least 0.7 absolute weight% or at least 0.9 absolute weight%. The concentration of the fissile isotope can be determined by the test from the sintered granules as a mass spectrum or as a gamma spectrum for the test.

Also, the micrograph 1 and corresponding sintered granules of FIG. 1 may have a first concentration of thorium isotope, which may be a raw material of fissile material, and the second micrograph 2 and corresponding sintered granules may be Has a second concentration of thorium isotope, which can be a source of fissile material. The second concentration of thorium isotope, which can be a source of fissile material, differs from the first concentration of 1 thorium isotope, which can be a source of fissile material, at least 0.5 absolute weight%. The two concentrations preferably differ by 0.7 absolute weight%, or 0.9 absolute weight%. The first concentration may be zero.

In addition, the micrograph and corresponding sintered granules of FIG. 1 may have a first concentration of aluminum, and the micrograph 2 and corresponding sintered granules may have a second concentration of aluminum. The second concentration is at least 30 ppm to 2000 ppm different from the first concentration. The first concentration of aluminum may be zero.

In addition, the micrograph 1 and corresponding sintered granules of FIG. 1 may have a first concentration of at least one element among lanthanum and tantalum elements, and the micrograph 2 and corresponding sintered granules described above It may have a second concentration of at least one of the elements consisting of elements of one lanthanum group and tantalum group, the second concentration having a difference of at least 0.5 absolute weight% from the first concentration. The first concentration may be zero.

In order to produce a nuclear fuel sinter having a polished section of the Ceramo graphic corresponding to FIG. 1, a press body consisting of a mixture consisting of first type granules and second type granules is sintered. The two types of granules are each formed by separate granulation of a starting powder consisting of one powder of uranium oxide powder (UO ₂ ), plutonium oxide powder (PuO ₂ ) and uranium plutonium oxide powder (UO ₂ + PuO ₂ ) Can be. The amount of each of the two types of granules and granules of the press body is selected so that it has a different pore size distribution in the sintered state in the nuclear fuel sintered body.

The first type granules are obtained by atomizing the uranium oxide powder obtained from uranyl fluoride, for example, by dry conversion of UF 6 in the presence of intermediate product, water vapor, hydrogen and nitrogen. For the second type granules, uranium oxide prepared from the intermediate product obtained by wet conversion from UF 6 is separately atomized. The intermediate product is aluminum uranyl carbonate (AUC) in the AUC method and aluminum diuranate (ADU) in the ADU method (1981, "Gmelin Handbuch der Anorganischen Chemie U Uran, Ergaenzungsband A3, Technologie, Verwendung" , In particular, see sections 2.1.4.1, 2.1.4.2 and 2.1.6). Uranium oxide powders prepared by calcination can be granulated from AUC for first type granules and from ADU for second type granules.

The first and second type granules, however, are obtained by separating and granulating two batches of uranium oxide powder obtained by calcining the aforementioned intermediate product, uranil fluoride, AUC and ADU in UO ₂ . At least one of the calcination parameters for the first batch is different from the calcination parameter for the second batch. As the calcining parameter, for example, the calcining temperature, the calcining time and amount and the ratio of the calcining gas, hydrogen and water vapor amount are used.

The first and second type granules can also be obtained by different granulation of uranium oxide powder. Different granulation means separate granulation of two powder batches, wherein at least one of the granulation parameters for the powder batch is different from the granulation parameters for the other powder batch. Granulation parameters are for example milling time during prepress of uranium oxide powder before granulation, fineness of milling, press pressure and thus concentration of obtained granules, size of granules obtained from granulation and granulation Amount and type of additive previously added to the uranium oxide powder. The additives include lubricants such as zinc stearate, aluminum stearates such as polyvinyl alcohol, plasticizers, pore-forming agents such as U ₃ O ₈ and azodicarbonacid dimid and oxalic Oxalicaciddiamide. The polishing cutting machine used for polishing the fuel sinter composed of UO ₂ may also be an additional additive.

In addition, by test, two types composed of at least one powder of UO ₂ powder, PuO ₂ powder and (U, Pu) O ₂ powder (ie, uranium oxide powder, plutonium oxide powder and uranium-plutonium-mixed oxide powder) It can continue to be determined in which way the granules of can be produced, whereby the granules have different pore size distribution in the sintered state after sintering of the press body made from the powder in the nuclear fuel sintered body.

Uranyl fluoride is prepared from UF 6 by dry conversion to 550 ° C. to obtain a first batch of UO ₂ -powder and calcined at a calcination temperature of 650 ° C. U ₃ O ₈ -powder and zinc stearate are added to the UO ₂ -powder to contain 30 wt% U ₃ O ₈ -powder and 0.3 wt% zinc stearate. The first batch is granulated so that the obtained first type granule has a concentration of 5 g / cm ³ . The granules have an average diameter of 0.65 mm.

A second batch of UO ₂ -powder is obtained by dry converting UF 6 to uranil fluoride at a conversion temperature of 650 ° C. and then calcining the uranil fluoride to a calcination temperature of 700 ° C. The UO ₂ -powder does not contain U ₃ O ₈ and zinc stearate but contains 200 ppm of aluminum. Granulation of the UO ₂ -powder yields a second type granule having a concentration of 3.8 g / cm ³ . The granules have an average diameter of 0.85 mm.

The first type and second type granules prepared from two batches of UO ₂ -powder are mixed in equal proportions and the mixture is pressed into a press body having a concentration of 6 g / cm ³ . The press body is finally sintered to the nuclear fuel sintered body. The sintering temperature at oxygen partial pressure in a hydrogen sintering atmosphere during sintering to 10 ⁻¹² atm and upon cooling at room temperature of 10 ⁻²⁰ atm is 1680 ° C.

The nuclear fuel sinter thus obtained has a concentration of 10.51 g / cm ³ and an average particle size of 12 μm. After burning to 40000 MWd / tU, the volume of the fuel sinter increased by 2.8%.

In comparison, a sintered fuel body obtained from a press body having a concentration of 6 g / cm ³ by sintering under the same sintering conditions described above, and used only for first type granules, has an average particle size of only 7.8 μm. The volume of the fuel sintered body also increased by 3.8% after burning to 40000 MWd / tU.

The fuel rods shown in FIG. 3 comprise a cladding tube 5 made of a zirconium alloy which is determined for a reactor combustion element. In the cladding tube 5 there is a cylindrical nuclear fuel sintered body 7 arranged in accordance with the invention and arranged such that the cylinder axis is the transverse axis of the cladding tube 5. The cladding tube 5 consists of a zirconium alloy, respectively, at the two tube ends, and is closed by a gas seal soldered stopper 6 by the cladding tube 5.

According to the present invention, a method for producing a low-stressed fuel sintered body and a fuel sintered body by the fuel sintered body, the fuel rod cladding tube containing the fuel sintered body of the above-described method, and the corresponding method formed by combustion in the reactor Fuel rods are provided.

Claims (19)

In a nuclear fuel sinter, the fuel sinter contains a chemical compound composed of hydrogen and at least one element of uranium and plutonium and displays a first (1) and a second (2) micrograph in the polished section of the Ceramo graphic. Element, and two micrographs can be placed on the sintered granules, in which the pores forming the boundary wall 3 of the two micrographs 1, 2 are not summed up, but the first micrograph ( 1) has a first pore size distribution I associated with the face of the first micrograph 1, and a second micrograph 2 has a second pore size distribution associated with the face of the second micrograph 2. II), in which the second pore size distribution (II) has a first maximum value M1 and a second maximum value M2 in which the sum of the two pore size distributions has a first pore size distribution ( Distinguished from I) Nuclear fuel sintered body made of gong. In a fuel sintered body, the fuel sintered body contains a compound composed of hydrogen and at least one element of uranium and plutonium and exhibits a first micrograph 1 and a second micrograph 2 in a polished section of the ceramograph. Having a basic element, two micrographs can each be placed on sintered granules, from which the first micrograph 1 has a first concentration of fissile isotopes, and the second micrograph 2 has fission A nuclear fuel sintered body having a second possible concentration of isotope, the second concentration being at least 0.5% by weight absolute difference from the first concentration. 3. The nuclear fuel sintered body according to claim 2, wherein the nuclear fuel sintered body has a second concentration of the fissable isotope which is at least 0.7 absolute weight% different from the first concentration. 4. A nuclear fuel sintered body according to claim 3 wherein the fuel sintered body has a second concentration of fissable isotope that is at least 0.9 absolute weight% different from the first concentration. In a fuel sintered body, the fuel sintered body contains oxygen and at least one element of uranium and plutonium and shows a first micrograph (1) and a second micrograph (2) in the polished section of the ceramo graphic. Micrographs can each be placed on the sintered granules, from which the first micrograph 1 has an isotope concentration which can be a source of fissile material, preferably a first concentration of thorium isotope, and a second micrograph The graph 2 has a second concentration of isotope, preferably thorium isotope, which can be a source of fissile material, the second concentration being at least 0.5 absolute weight% different from the first concentration. Sintered body. 6. The nuclear fuel sintered body according to claim 5, wherein the fuel sintered body has a second concentration of isotope which can be a raw material of fissile material, and the second concentration is at least 0.7 absolute weight% different from the first concentration. The fuel sintered body according to claim 6, wherein the fuel sintered body has a second concentration of isotope which can be a raw material of fissile material, and the second concentration is at least 0.9 absolute weight% different from the first concentration. 8. The method according to claim 1, wherein the first micrograph 1 has a first concentration of aluminum, the second micrograph 2 has a second concentration of aluminum, and the second concentration is 15. A nuclear fuel sintered body, the first concentration being at least 30 ppm to 2000 ppm different. The first micrograph (1) according to any one of the preceding claims, wherein the first micrograph (1) has a first concentration of at least one of the elements consisting of a lanthanum group and a tantalum group, and the second micrograph (2) has said A nuclear fuel sintered body having a second concentration of at least one of the elements consisting of a lanthanum group and a tantalum group, the second concentration being at least 0.5 absolute weight% different from the first concentration. A method of producing a nuclear fuel sintered body, the nuclear fuel sintered body comprising the first type granules produced by the separation granulation of a starting powder containing at least one powder of uranium oxide powder, plutonium oxide powder and uranium-plutonium-mixed oxide powder; Produced by sintering of a press body consisting of a mixture of second type granules, wherein the two types of granules are selected to have different pore size distributions in the sintered state of the nuclear fuel sintered body. 1. A method of producing a nuclear fuel sintered body, wherein the nuclear fuel sintered body is formed of a first type granule and a granule produced by separate granulation of a starting powder containing at least one powder of uranium oxide powder, plutonium oxide powder and uranium-plutonium-mixed oxide powder Prepared by sintering a press body consisting of a mixture of two type granules, characterized in that the first type granules have a concentration of fissile isotopes different from the second type granules. 1. A method of producing a nuclear fuel sintered body, wherein the nuclear fuel sintered body is formed of a first type granule and a granule produced by separate granulation of a starting powder containing at least one powder of uranium oxide powder, plutonium oxide powder and uranium-plutonium-mixed oxide powder It is produced by sintering of a press body consisting of a mixture of two type granules, characterized in that the first type granules have a concentration of isotopes, preferably thorium isotopes, which can be a source of fissile material different from the second type granules. How to. 1. A method of producing a nuclear fuel sintered body, wherein the nuclear fuel sintered body is formed of a first type granule and a granule produced by separate granulation of a starting powder containing at least one powder of uranium oxide powder, plutonium oxide powder and uranium-plutonium-mixed oxide powder Produced by sintering of a press body consisting of a mixture of two type granules, the first type granules having a first aluminum concentration, the second type granules having a second aluminum concentration, the second concentration being different from the first concentration How i characterized. 1. A method of producing a nuclear fuel sintered body, wherein the nuclear fuel sintered body is formed of a first type granule and a granule produced by separate granulation of a starting powder containing at least one powder of uranium oxide powder, plutonium oxide powder and uranium-plutonium-mixed oxide powder Prepared by sintering of a press body consisting of a mixture of two type granules, the first type granules having a first concentration of at least one of the elements composed of lanthanum groups and tantalum groups, and the second type granules being the lanthanum groups and tantalum And a second concentration of at least one of the elements consisting of groups, the second concentration being different from the first concentration. The method according to any one of claims 10 to 13, wherein the granules use a press body having an average diameter of 0.05 to 2 mm. The method according to any one of claims 10 to 13, characterized by using a press body which is prepared by pressing granules having a concentration of 1.9 to 5 g / cm ³ . The method according to claim 10, wherein a press body having a concentration of 5 to 6.7 g / cm ³ is used. 14. The press body according to any one of claims 10 to 13, wherein the press body is sintered at a sintering temperature of 1000 ° C to 1800 ° C in a sintering atmosphere having an oxygen partial pressure in the range of 10 ^-8 to 10 ^-28 atm. How to. 10. A fuel rod having a cladding tube (5), characterized in that at least one nuclear fuel sinter according to claims 1 to 9 is present in the fuel rod.