Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21C—NUCLEAR REACTORS
  • G21C3/00—Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
  • G21C3/30—Assemblies of a number of fuel elements in the form of a rigid unit
  • G21C3/32—Bundles of parallel pin-, rod-, or tube-shaped fuel elements
  • G21C3/326—Bundles of parallel pin-, rod-, or tube-shaped fuel elements comprising fuel elements of different composition; comprising, in addition to the fuel elements, other pin-, rod-, or tube-shaped elements, e.g. control rods, grid support rods, fertile rods, poison rods or dummy rods
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21C—NUCLEAR REACTORS
  • G21C3/00—Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E30/00—Energy generation of nuclear origin
  • Y02E30/30—Nuclear fission reactors

Definitions

• the invention relates to a fuel assembly which can be used in pressurized water reactors, boiling water reactors, heavy water reactors and gas-cooled or sodium-cooled reactors.
• the reactor core of such reactors consists of a predetermined number of fuel elements, each of which is formed by a bundle of fuel rods, which are combined by spacers. Each fuel rod contains a column of fuel pills in a tube.
• the reactor core is located in a pressure vessel and a coolant flows through it from bottom to top.
• the nuclear fission is controlled by neutron-absorbing control elements, with boric acid also being added to the coolant in the case of water-cooled reactors. A large amount of excess reactivity of the reactor core can be bound by the boric acid.
• the object of the invention is to improve the corrosion resistance of the shell of fuel rods with the spacers and the fuel element structure unchanged.
• a fuel assembly in which fuel rods are combined into a bundle by means of spacers and at least two axial regions with different fuel enrichment are provided between two successive spacers in the fuel rods in such a way that in the flow direction of the Coolant seen the area with the highest fuel enrichment begins at the height of a spacer.
• the fuel rods of which contain fuel with the same enrichment between the spacers the service life and thus the erosion as well as the safety can be considerably increased, since the corrosion peaks can be flattened in predetermined axial positions of the fuel elements.
• the area with the highest fuel enrichment begins at a height given by the front edge of the spacer, since a lower oxide layer thickness usually occurs in the area of the axial spacer.
• the area with the highest fuel enrichment can also start at a height given by the upper edge of the spacer.
• fuel assemblies with fuel rods in which only three areas with different fuel enrichment are provided between two spacers. Since fuel tablets with three different fuel enrichments are usually used in fuel element production, fuel tablets of this type can be used in the fuel rods in a simple manner without incurring any expense for special production. The economic advantage which results from a high maximum achievable fuel consumption is considerable.
• FIG. 1 shows an oblique view of a fuel element for a pressurized water reactor in an exploded view
• FIG. 2 shows a fuel rod of the fuel element according to FIG. 1
• FIG Area of the same fuel enrichment curve E with two axial areas of different fuel enrichment
• 4 shows a further embodiment for fuel rods
• FIG. 5 curve D: oxide layer thickness of the cladding tube with fuel rods of the same fuel enrichment
• Curve E oxide layer thickness of the cladding tube with three areas of different fuel enrichment between the spacers
• FIG. 6 shows a third exemplary embodiment of a fuel rod with a continuously increasing enrichment gradation
• FIG. 7 shows the associated courses of the oxide layer thickness.
• a fuel assembly 1 which is constructed from fuel rods 2 in a square grid arrangement.
• a predetermined number of the same fuel elements are provided, which are arranged in a reactor pressure vessel and through which a coolant flows in the direction of arrow K from bottom to top.
• the fuel rods 2 of each fuel element are held in a supporting structure, which consist of a fuel element head 3 and a fuel element base 4 and intermediate guide tubes 5 for control rods, not shown.
• Spacers 6 to 11 are fastened to the guide tubes 5, which combine the fuel rods 2 into a bundle and hold them in such a way that they can expand freely and have the same cooling cross sections.
• the open design of the fuel elements at the side enables cross-mixing of the coolant and its warming up is evened out.
• each fuel rod 2 contains in a cladding tube 12, e.g. made of Zircaloy, a column of fuel tablets 13, 14, preferably made of uranium dioxide.
• a characteristic axial course D of the oxide layer thickness is plotted, which arises on the outside of the cladding tube of a fuel rod at the end of the permissible period of use, if the fuel rod contains fuel with the same enrichment over the entire axial area.
• the axial length of the fuel rod and the positions of the spacers 6 to 11 are plotted on the ordinate, and the oxide layer thickness is plotted on the abscissa.
• the oxide layer thickness between two spacers increases in each case in the flow direction of the coolant and drops steeply directly at the spacer. An area with the largest peaks of the oxide layer thickness occurs in the upper half of the fuel assembly.
• two axial areas A, B with different fuel enrichment are provided in the fuel rods 2 between the two successive spacers 9 and 10 (FIG. 2) in such a way that area A.
• Viewed in the flow direction of the coolant begins with the highest fuel enrichment at the level of a spacer 9. It is advantageous if the region A begins with the highest fuel enrichment at a height given by the front edge of the spacer 9.
• the area A preferably has a length of 1/3 of the distance between the two spacers 9 and 10. In this case, the highest fuel concentration is expediently also provided at the height of the spacer 9.
• FIG. 4 shows an example in which three axial regions A, B, C with different fuel enrichment are provided between all spacers 6 to 11 in the fuel rods 2.
• the oxide layer thickness is shown as a function of the axial position, a lower oxide layer thickness is uniformly achieved via the axial course of the fuel rods 13, 14, 15 of the fuel assembly.
• the areas A, B, C here each extend about 1/3 of the length of the distance between two spacers.
• FIGS. 6 and 7 show the conditions when a continuous axial enrichment gradation of the fuel 16 has been carried out between the individual spacers in the fuel rods.
• D of the oxide layer thickness there is in principle a uniform course E.

Landscapes

• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Monitoring And Testing Of Nuclear Reactors (AREA)
• Devices And Processes Conducted In The Presence Of Fluids And Solid Particles (AREA)
• Liquid Carbonaceous Fuels (AREA)

Applications Claiming Priority (1)

Publications (1)

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ID=6819707

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• 1988
  • 1988-09-14 WO PCT/DE1988/000572 patent/WO1990003035A1/de not_active Application Discontinuation
  • 1988-09-14 KR KR1019900701000A patent/KR900702536A/ko not_active Application Discontinuation
  • 1988-09-14 JP JP63507779A patent/JPH04500722A/ja active Pending
  • 1988-09-14 EP EP88908137A patent/EP0400008A1/de not_active Withdrawn
• 1989
  • 1989-09-14 ES ES8903126A patent/ES2019488A6/es not_active Expired - Fee Related

Non-Patent Citations (1)

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