JP2005083966A - Metal fuel fast reactor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a coolant void reactivity by reducing a coolant volume ratio in an inner region of a core. <P>SOLUTION: Metal fuel is used and the core 10 is partitioned in a plurality of regions for flattening power distribution. For the metal fuel, TRU-Zr ternary alloy with U-Pu or Pu as a main composition is used. All fuel pins have a uniform Pu enrichment in the fuel and the same pin diameter. A Zr content in metal fuel slug in inner core fuel pins 22 has larger value than that of outer fuel pins 24. Fuel assemblies have a structure installed with a multitude of fuel pins in a wrapper tube with the same array. Individual fuel pins are kept at a constant interval by wire type spacers. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention uses TRU (super uranium) mainly composed of U, Pu or Pu as a metal fuel, and a ternary alloy composed of Zr, with a single Pu enrichment and a pin diameter, and a metal fuel slag. This relates to a metal fuel fast reactor that is divided into a plurality of core regions according to the difference in the Zr content of each of them and the power distribution is flattened.

  Currently, U-Pu mixed oxides are the mainstream of nuclear fuel materials used in fast reactors, but in recent years, the development of alloys that can achieve high burn-up is also progressing for metal fuels. A typical example is U-Pu-Zr ternary alloy. This alloy has excellent properties in terms of swelling and relaxation of eutectic reaction with the cladding tube, and steady irradiation and in-furnace transient tests have been conducted, and a lot of information on irradiation behavior and failure behavior has been prepared. ing.

  By the way, when metal fuel is used as the fuel for the fast reactor, it is necessary to prevent liquid phase formation at the contact portion between the fuel and the cladding tube. It is necessary to suppress the temperature. As a result, the reactor outlet temperature also decreases, and a decrease in thermal efficiency is observed. As a measure to strengthen the weak point, it is proposed to adopt a fuel assembly of grid type with a single Pu enrichment of fuel, using several types of fuel pins with different pin diameters to flatten the core power distribution. As a result, the coolant flow distribution can be rationalized, and the prospect of achieving an outlet temperature equivalent to that of an oxide fuel core is obtained.

  However, in such a specification, a fuel pin having a relatively small diameter is used in the inner core region, so that the gap between the fuel pins becomes large in that region. As a result, the coolant volume ratio increases and the coolant void reactivity, which is important for core safety, tends to increase. Moreover, since there is almost no track record in a fast reactor about a grid type spacer system, it is necessary to solve the technical problem for engineering feasibility.

  The problem to be solved by the present invention is that the coolant volume ratio increases in the inner core region and the coolant void reactivity increases.

  The present invention uses a metallic fuel, a fast reactor that is divided into a plurality of core regions for flattening the power distribution, and is composed of TRU mainly composed of U, Pu, or Pu as metallic fuel, and Zr. The alloy is used, and all fuel pins have a single Pu enrichment and the same pin diameter, and are divided into regions by changing the Zr content of the metal fuel slag. A metal fuel fast reactor characterized by

  Further, the present invention uses a TRU mainly composed of U, Pu or Pu as a metal fuel in a two-zone fast reactor that uses a metal fuel and is divided into an inner core region and an outer core region in order to flatten the power distribution. , And Zr, and all the fuel pins have a single fuel Pu enrichment and the same pin diameter, and the inner core fuel pin is better than the outer core fuel pin. The metal fuel fast reactor is characterized in that the Zr content of the metal fuel slag is set to a large value.

  Furthermore, the present invention uses U, Pu or Pu as a metal fuel in a three-zone type fast reactor that uses a metal fuel and is divided into an inner core region, an intermediate core region, and an outer core region for leveling the power distribution. All the fuel pins have the same Pu enrichment and the same pin diameter, and the intermediate core fuel pins are on the outer side. The Zr content rate of the metal fuel slag is set to a larger value than the core fuel pin, and the Zr content rate of the metal fuel slag is set to a larger value than the intermediate core fuel pin. It is a featured metal fuel fast reactor.

  In these, all fuel assemblies loaded in the core region have a structure in which a large number of fuel pins are loaded in a trumpet tube in the same arrangement, and each fuel pin is maintained at a constant interval by a wire type spacer. Is preferable.

  The metal fuel fast reactor core according to the present invention has a single Pu enrichment and a single pin diameter, and the core power distribution is flattened by changing the Zr content of the metal fuel slag. Since the gap between the fuel pins is reduced, the coolant volume ratio is reduced, and the coolant void reactivity can be reduced. Furthermore, since it is possible to apply a wire-type spacer that has been used in the fast reactor, development problems are greatly reduced, and the feasibility of the concept is dramatically improved. Further, since there is only one type of fuel cladding tube, the fuel manufacturing process can be simplified.

  The present invention is a metal fuel fast reactor that is divided into two or three core regions in order to flatten the power distribution. As the metal fuel, ternary alloy composed of TRU mainly composed of U, Pu or Pu and Zr is used. All fuel pins have a single fuel Pu enrichment and the same pin diameter, and the inner core fuel pin has a higher Zr content of metal fuel slag than the outer core fuel pin. Is set to All the fuel assemblies loaded in the core region have a structure in which a number of fuel pins are loaded in the same arrangement in a trumpet tube, and each fuel pin is maintained at a constant interval by a wire type spacer.

  FIG. 1 is an explanatory view showing an embodiment of a metal fuel fast reactor according to the present invention, schematically showing a core structure and a cross section of a fuel assembly. The core 10 of this fast reactor uses a ternary alloy made of U, Pu, and Zr as a metal fuel. A TRU mainly composed of Pu may be used instead of Pu. This is because MA (minor actinide) is also accompanied when recovering Pu from spent fuel. The core 10 is divided into two regions, an inner core region and an outer core region, for the purpose of flattening the power distribution. The inner core fuel assembly 12 is provided in the inner core region, and the outer core fuel is provided in the outer core region. Each of the aggregates 14 is loaded. Both the inner core fuel assembly 12 and the outer core fuel assembly 14 have a structure in which a large number of fuel pins are loaded in a hexagonal tubular trumpet tube 16, and all of these fuel pins have a Pu enrichment of fuel. It is single and has the same pin diameter (one type). Accordingly, all the fuel assemblies loaded in the core region have a structure in which fuel pins are loaded in the same arrangement in the trumpet tube (that is, the inner core fuel assembly 12 and the outer core fuel assembly 14 are shaped in shape. Are the same). Here, in the fuel assembly, the fuel pins are kept at regular intervals by a wire-type spacer (not shown), and the coolant channel 18 is formed between them.

  In the present invention, the Zr content in the U-Pu-Zr ternary alloy in the inner core fuel pin 22 is larger than the Zr content in the U-Pu-Zr ternary alloy in the outer core fuel pin 24. Is set to The relationship between the Zr content in the U-Pu-Zr ternary alloy in the inner core fuel pin 22 and the outer core fuel pin 24 is shown by a pie chart in FIG. A is the inner core fuel and B is the outer core fuel.

  As shown in FIG. 2, by changing the Zr content of the metal fuel slag, the core power distribution can be flattened even if a fuel assembly having a structure in which a number of fuel pins are loaded in the same arrangement in the trumpet tube is used. As a result, the gap between the fuel pins in the inner core fuel assembly can be reduced compared with the case where two types of fuel pins having different pin diameters are used, so that the coolant volume ratio is reduced and the coolant voids are reduced. Reactivity can be reduced. In addition, since it is possible to apply wire type spacers that have been used in fast breeder reactors, development issues are greatly reduced, and the feasibility of the concept is dramatically improved. Furthermore, since only one type of fuel cladding tube is required, the fuel production process can be simplified.

  An example of specific fuel specifications, core specifications, and nuclear characteristic evaluation results for a medium-sized inner / outer two-region core to which the present invention is applied is shown below. Table 1 shows the fuel specifications. The required core characteristics as shown in Table 2 were obtained by analysis based on this specification. The power distribution was sufficiently flattened, and the prospect of setting the reactor inlet / outlet temperature to the level of an oxide fuel core was obtained.

  In the present invention, the Pu enrichment depends on the core size, and the Pu enrichment decreases as the core becomes larger, but is approximately 10 to 15 wt%. In the medium-scale core shown in Table 1-2, it is about 12 wt%.

  In the present invention, it is desirable to keep the Zr content as low as possible in order to improve the neutron economy and improve the nuclear characteristics. However, in order for the TRU-Zr ternary alloy mainly composed of U-Pu or Pu to have sufficient strength as a fuel, the Zr content needs to be 10 wt% or more. Therefore, in the fuel specifications shown in Table 1, the Zr content of the outer core fuel is 10 wt%, and the Zr content of the inner core fuel is adjusted so that the power distribution is appropriate. Here, the Zr content of the inner core fuel is set to 14.4 wt%.

  The above embodiment is a case of the two-region type, but it may be a three-region type including an inner core region, an intermediate core region, and an outer core region. In that case, the Zr content of the metal fuel slag in the intermediate core fuel pin (the Zr content in the U-Pu-Zr ternary alloy) is larger than the Zr content of the metal fuel slag in the outer core fuel pin. The Zr content of the metal fuel slag in the inner core fuel pin is set to a value larger than the Zr content of the metal fuel slag in the intermediate core fuel pin.

  In the above embodiment, wire type spacers are used, and since there are abundant use results in fast reactors, development problems are greatly reduced and the concept is dramatically improved, but in some cases grid type It is also possible to use spacers.

Explanatory drawing which shows one Example of the metal fuel fast reactor which concerns on this invention. The graph which shows the Zr content rate of an inner / outer core fuel.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Core of fast reactor 12 Inner core fuel assembly 14 Outer core fuel assembly 16 Trumpet pipe 18 Coolant flow path 22 Inner core fuel pin 24 Outer core fuel pin

Claims (4)

In a fast reactor that uses metal fuel and is divided into a plurality of core regions for flattening power distribution, TRU mainly composed of U, Pu or Pu, and ternary alloy consisting of Zr are used as the metal fuel. All fuel pins have a single Pu enrichment and the same pin diameter, and are characterized by changing the Zr content of the metal fuel slag. Metal fuel fast reactor. In a two-zone type fast reactor that uses metal fuel and is divided into an inner core region and an outer core region for flattening the power distribution, it consists of TRU and Zr mainly composed of U, Pu or Pu as the metal fuel Using ternary alloys, all fuel pins have a single fuel Pu enrichment and the same pin diameter, and the inner core fuel pin has a higher Zr of metal fuel slug than the outer core fuel pin. Metal fuel fast reactor characterized in that the content is set to a large value. In a three-zone fast reactor that uses metallic fuel and is divided into an inner core region, an intermediate core region, and an outer core region for leveling the power distribution, TRU mainly composed of U, Pu, or Pu as the metallic fuel , And Zr, and all the fuel pins have a single fuel Pu enrichment and the same pin diameter, and the intermediate core fuel pin is better than the outer core fuel pin. A metal fuel characterized in that the Zr content of the metal fuel slag is set to a larger value, and the inner core fuel pin is set to a larger value of the Zr content of the metal fuel slag than the intermediate core fuel pin. Fast reactor. All the fuel assemblies loaded in the core region have a structure in which a large number of fuel pins are loaded in a trumpet tube in the same arrangement, and each fuel pin is maintained at a constant interval by a wire type spacer. 3. The metal fuel fast reactor according to 3.

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