Fuel assembly

Details Fuel assembly Fuel assembly

2002-08-26

2004-05-11

Carone, Michael J. (Department: 3641)

Induced nuclear reactions: processes, systems, and elements

Fuel component structure

Plural fuel segments or elements

C376S434000, C376S444000, C376S419000

Reexamination Certificate

active

06735267

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel assembly and particularly to a fuel assembly suitable for a boiling water reactor and having a plurality of fuel rods arranged in 10 by 10.
2. Prior Art
In recent years, high burn-up of fuel assemblies are required from the viewpoints of effective use of the uranium resource and reduction of the generated amount of used fuel assemblies. In order to attain high burn-up, it is required to increase an average enrichment of the fissionable materials in the fuel assembly. However, because increase of the enrichment causes increase in reactivity change due to void change, an absolute value of void coefficient is increased to deteriorate reactor core stability. The reactor core stability can be improved by increasing the moderator ratio (the ratio of moderator to fuel) in the fuel assembly.
In order to effectively react the fissionable material and to maintain the nuclear-thermal-hydraulic stability of the boiling water reactor stable, it is necessary to increase the moderator ratio in the fuel assembly as the enrichment of the fissionable materials is increased.
A fuel assembly capable of attaining a burn-up of 45 GWd/t by arranging fuel rods in an array of 9 rows by 9 columns is disclosed in Japanese Patent Application Laid-Open No.7-234293. This fuel assembly comprises two large-diameter water rods arranged in a region capable of placing seven fuel rods in the central portion of cross section, and eight short-length fuel rods having an axial length shorter than that of the other fuel rods. These short-length fuel rods improve the void coefficient of the fuel assembly. Further, use of the short-length fuel rods decreases the pressure loss of the fuel assembly because the cooling water flow passage area is increased in the steam-water two-phase region in the upper portion of the fuel assembly. Most of fuel assemblies having a fuel rod array of above 9 rows by 9 columns comprise short-length fuel rods.
Further, a fuel assembly having a fuel rod array of 10 rows by 10 columns is disclosed in Japanese Patent Application Laid-Open No.5-232273. In this fuel assembly, short-length fuel rods are arranged adjacently to non-boiling region (a water rod, a gap water region) so as to accelerate the neutron slowing down effect to increase the improving effect of void coefficient.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a fuel assembly which is capable of attaining allowable core stability by further increasing burn-up and without increasing the pressure loss compared to a conventional fuel assembly.
A feature of a first invention capable of attaining the above object is a fuel assembly comprising a plurality of first fuel rods and a plurality of second fuel rods having a length shorter than a length of the first fuel rod, the first and the second fuel rods being arranged in a fuel rod array of 10 rows by 10 columns; and a plurality of water rods occupying regions capable of arranging 8 fuel rods, the second fuel rods being not arranged in the outermost tier of the fuel rod array, which satisfies the following conditions, that is,
B≧60  (Equation 1)
15
≦n
≦20(
n
: integer)  (Equation 2)
Awr/Ach
≦0.149  (Equation 3)
Lp/Lf
≧11/24  (Equation 4)
Awr/Ach
≧(3.00×10
−4
×n
2
+6.00×10
−4
×n
−1.2×10
−2
)×(
Lp/Lf
−1)+1.75×10
−1
  (Equation 5)
Awr/Ach
≦(8.63×10
−4
×n
2
−6.09×10
−2
×n
+1.33×10
−1
)×(
Lp/Lf
−8.32×10
−1
)  (Equation 6)
where Awr is a total sum of horizontal sectional areas of the water rods, Ach is a horizontal sectional area of a coolant flow passage in a bottom portion of the fuel assembly, Lf is an effective fuel length of the first fuel rod, n is number of the second fuel rods, Lp is an effective length of the second fuel rod, and B (GWd/t) is an average burn-up.
The present invention satisfying the above conditions can further increase burn-up, and can attain allowable core stability without increasing the pressure loss compared to a conventional fuel assembly.
A feature of a second invention capable of attaining the above object is a fuel assembly comprising a plurality of first fuel rods and a plurality of second fuel rods having a length shorter than a length of the first fuel rod, the first and the second fuel rods being arranged in a fuel rod array of 10 rows by 10 columns; and a plurality of water rods occupying regions capable of arranging 9 fuel rods, the second fuel rods being not arranged in the outermost tier of the fuel rod array, which satisfies the following conditions:
B
≧60  (Equation 1)
10
≦n
≦20(
n
: integer)  (Equation 7)
Awr/Ach
≦0.169  (Equation 8)
Lp/Lf
≧11/24  (Equation 4)
Awr/Ach
≧(2.65×10
−4
×n
2
+2.15×10
−3
×n
−1.96×10
−2
)×(
Lp/Lf
−1)+1.68×10
−1
  (Equation 9)
Awr/Ach
≦(7.41×10
−4
×n
2
−5.63×10
−2
×n
+8.84×10
−2
)×(
Lp/Lf
−8.52×10
−1
)  (Equation 10)
where Awr is a total sum of horizontal sectional areas of the water rods, Ach is a horizontal sectional area of a coolant flow passage in a bottom portion of the fuel assembly, Lf is an effective fuel length of the first fuel rod, n is number of the second fuel rods, Lp is an effective length of the second fuel rod, and B (GWd/t) is an average burn-up.
The second invention can also attain the same effects as those of the first invention.
A feature of a third invention capable of attaining the above object is a fuel assembly comprising a plurality of first fuel rods and a plurality of second fuel rods having a length shorter than a length of the first fuel rod, the first and the second fuel rods being arranged in a fuel rod array of 10 rows by 10 columns; and a plurality of water rods occupying regions capable of arranging 10 fuel rods, the second fuel rods being not arranged in the outermost tier of the fuel rod array, which satisfies the following conditions, that is,
B
≧60  (Equation 1)
9
≦n
≦20(
n
: integer)  (Equation 11)
Awr/Ach
≦0.190  (Equation 12)
Lp/Lf
≧11/24  (Equation 4)
Awr/Ach
≧(2.31×10
−4
×n
2
+3.69×10
−3
×n
−2.71×10
−2
)×(
Lp/Lf
−1)+1.60×10
−1
  (Equation 13)
Awr/Ach
≦(6.18×10
−4
×n
2
−5.18×10
−2
×n
+4.41×10
−2
)×(
Lp/Lf
−8.72×10
−1
)  (Equation 14)
where Awr is a total sum of horizontal sectional areas of the water rods, Ach is a horizontal sectional area of a coolant flow passage in a bottom portion of the fuel assembly, Lf is an effective fuel length of the first fuel rod, n is number of the second fuel rods, Lp is an effective length of the second fuel rod, and B (GWd/t) is an average burn-up.
The third invention can also attain the same effects as those of the first invention.
A feature of a fourth invention capable of attaining the above object is a fuel assembly comprising a plurality of first fuel rods and a plurality of second fuel rods having a length shorter than a length of the first fuel rod, the first and the second fuel rods being arranged in a fuel rod array of 10 rows by 10 columns; and a plurality of water rods occupying regions capable of arranging 8 fuel rods, the second fuel rods being arranged both at positions in the outermost tier of the fuel rod array and at positions adjacent to the water rods, or only at positions in the outermost tier of the fuel rod array, which satisfies the following conditions, that is,
B
≧60  (Equation 1)
9
≦n
≦20(
n
: integer)  (Equation 11)
Awr/Ach
≦0.

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