JPS60181682A - Fuel aggregate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to fuel-rich combinations used in boiling water nuclear reactors.

[Technical background of the invention and its problems] A fuel assembly is loaded in the core of a boiling water nuclear reactor. This fuel assembly is shown in longitudinal section in FIG. In this fuel assembly 1, a large number of fuel rods 3 and water rods 4 are arranged in a matrix (for example, 8×8 rods) in a rectangular cylindrical channel box 2, and the upper ends of the fuel rods 3 and water rods 4 are The mutual spacing of the fuel rods 3 is controlled by supporting the upper tie plate 5 and the lower tie plate 6, respectively, and by supporting multiple locations between the upper tie plate 5 and the lower tie plate 6 with the smears 7. The configuration is such that it is held constant.

Here, a vertical cross-sectional view of the fuel rod is shown in FIG. As shown in the figure, in the fuel rod 3, a large number of cylindrical fuel pellets 9 are filled in an elongated circular plow-shaped fuel tube 8, and the upper and lower ends of the fuel tube 8 are an upper end, a The end plug 11 is fixed by welding and has six holes for sealing. A Blenheim spring 13 is attached to the upper plenum 12 in the fuel barrel tube 8, and applies appropriate pressing force to the fuel pellets 9 stacked in the axial direction of the fuel pellets 1-1 to elastically support them.

As shown in FIG. 3, which is a cross-sectional view of the fuel assembly, the fuel rods 3 are arranged in a square arrangement of 8 rows and 8 columns with equal spacing between each other in a column perpendicular to the longitudinal direction of the fuel assembly 1. has been done. Also, the gap between the fuel rods 3 on the inner and outer peripheries of the fuel assembly 1 and the channel box 2 is called a water gap, but this water gap is also equal to the distance between the fuel rods 3, which is I″f. .For such a combination, four units are further arranged in a square array, and tttll it N 14 is placed in the center, σ, to form one unit cell of the shape J2'Z 1..And-
C. Two water rods 4 (indicated by reference number W in FIG. 1) are installed approximately in the center of the fuel assembly 1 in order to average the output within the cross section of the id fuel assembly 1.

As shown in Table 1 (2), the fuel rod 3 is made of 54-I class I momme (Yonkalin 3 is manufactured) in which the uranium-235 (hereinafter referred to as U235) shoulder content is changed to, for example, 4 steps μ&. .

(i person'T: total 6) Table 1: Five types of fuel rods 311-1: According to the thermal neutron flux distribution in the cross section of the fuel assembly 1, each fuel rod The rods 3 are arranged so as to equalize the power distribution. In other words, the fuel rods at the four corners of the square array, where the thermal neutron flux level is highest, have a low U285 base content.
Therefore, fuel rods with high U285 content are arranged.

Water, which is a coolant, passing through fuel assembly 1 becomes a two-phase flow of water and steam and goes to the top? Li8 is rising. Here, FIG. 4 shows a characteristic distribution diagram of the fuel assembly, with the vertical axis representing the height direction of the fuel assembly and the horizontal axis representing the steam ratio in the channel box and the output distribution. As shown in steam distribution curve A in FIG. 4, the proportion of steam increases from the bottom to the top of the fuel mixture 1. Water, which is this intoxicant, also has the property iQ as a moderator, and the slow neutrons (thermal neutrons) are 11. Since the neutrons are generated by water, which is an M fast material, slow neutrons are supplied not only from outside the channel box 2 but also from the coolant inside the channel box 2 . Since the steam increases as it goes to the upper part of the 7'c fuel assembly 1, the supply of the slow-speed medium insulator from inside the iron box 2 decreases as it goes to the upper part.

If the degree of contraction of the fuel rod 3 is one in the height direction, the rate of nuclear fission σ solvent ~ row < lr: a decreases at the top of the splitting body 1, and the output (() decreases as it goes to the top. In addition, since force neutrons fan out from the upper i%i and lower part of the fuel assembly 1, respectively, the resultant force is Therefore, the power distribution in the height direction of the fuel assembly 1 is like the power distribution curve HI3 in Fig. 4, and the average power distribution in the vicinity of the lower end of the fuel assembly 1 is approximately It increased by about 50%, and the *+a+ direction output peak kinda (ratio between the maximum value and the average value of the output of the fuel assembly in the height direction) became @11.5.

As a way to reduce @1 side + LJ output cubby king,
There is a method of making the enrichment of U285 in the fuel rod 3 lower in the lower part than in the upper part. For example, as described in Japanese Unexamined Patent Publication No. 53-40188, some fuel rods 15 are divided into upper and lower regions, and a fuel pellet 2F45 is loaded onto the upper part of the fuel rod 15. An improved version VI is shown that is higher than the fuel pellet. This improved example is shown in No. 51y, which is a cross-sectional view of the fuel assembly 16.
This will be explained with reference to 1.

As shown in Table 2, the fuel rods 15 have six sleeves with different U235 heat exchange rates.

Table 2 These hexavalent fuel rods 15 are arranged so as to equalize the power distribution of each fuel rod 15 according to the thermal neutron flux distribution in the cross section of the fuel assembly 16 as shown in FIG. has been done. However, in this embodiment, fuel rod 1 is
The local power peaking (hereinafter referred to as P and F) is the output of the maximum θ1 output fuel right when the enrichment distribution to 5 is set to 1 in the lower region and the average output of all fuel rods in the fuel assembly is 1.
If it is made so that it becomes small, the glue in the upper region, P,
F is a quotient, and the upper average 69 degree of shrinkage of the 0-sensitivity bar is 2.11%, and the lower average daughter contractility is 1.94%, 1-1.
As a result, the axial output distribution is flattened, but L,
There were problems such as the fact that the weighted output of the fuel rods did not decrease due to the increase in P and F19.

[Objective of the Invention] The object of the present invention is to "reduce the local output caving by flattening the power distribution, and to reduce the axial output caving by flattening the vertical output (J) within the fuel assembly. The aim is to obtain a fuel assembly that can be made smaller and have better soundness.

[Summary of the Invention] The present invention divides a fuel assembly in the p-axis direction into two regions, an upper region and a lower region, and determines the average enrichment of uranium-235 UB in the upper region and uranium-235 in the lower region. The average concentration L1 is 1. E (Uranium in the lower region of the i-sparrow fuel rod housed in the fuel assembly, having the relationship UE)
The fuel assembly is characterized in that the enrichment level LEi of 235 uranium-235 has the following relationship with the enrichment level uni of uranium-235 in the upper region of the i-th fuel rod.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIGS. 6 and 7. Here, FIG. 86 shows a cross-sectional view of a fuel assembly according to the present invention. As shown in the figure, fuel rods 21 are arranged at equal intervals of 10 J in the fuel assembly 20;
It is arranged in a square array with 8 rows and 8 columns. The gap between the fuel rods 21 on the outermost periphery of the fuel assembly 20 and the channel box 22 is called a water gap, and this water gap is also set to be approximately equal to the spacing between the niJ fuel rods 21. Such a fuel assembly 20 further has four rods arranged in a square array and a control rod 23 arranged in the center to form one unit cell. Two water rods 24 are installed in the center of the fuel assembly 20 in order to average the output within the cross section of the fuel assembly 20.

For example, the rod 21 is divided into two regions in the axial direction as shown in No. 3, and the concentration in the upper region is higher than that in the 9th region of 13, and the enriched layers are different. In addition, a fuel tank 23 with a 5-ratio and 1-power ratio is manufactured in which the fuel concentration ratio between the lower region and the lower region is constant, and the U285 content rate is varied in four stages.

Table 3 Here, FIG. 7 shows a power distribution diagram in the stomach direction of the fuel assembly of FIG. 6. As shown in the same figure, the height of the conventional one! The output distribution curve C of a roasted material assembly with a uniform concentration has an axial output peaking of 1.5, whereas the output distribution of a fuel assembly that divides the taste direction into two regions. The bright one-direction output cubby king on a curved line is 1.3, indicating that the output distribution on the curved line is flattened. Therefore,
According to the present invention, the local power peaking can be reduced and the axial power peaking can be reduced in the same way as in the conventional improvement example. As a result, the maximum output of the fuel rods becomes lower than before, and the integrity of the fuel assembly can be improved.

The ;9r1 family aggregate according to the present invention described above can be produced as follows. If the enriched layer of U285 in the upper region of the fuel assembly 20 is UH, and the degree of reduction of U2135 in the lower region is LE, then LE
< Set as uπ. If the degree of U285 shrinkage in the upper region of each yuzu fuel rod is uEi, and the enrichment degree of U285 in the lower region is LEi (r, B; /u
E1) = (LH/UE), the enrichment ratio of 285 in the upper region and lower region of each type of fuel rod is kept constant, and furthermore, URN <...(uBi+1 (
Set uBi <...< UEI. Said, ■≦ni≦
N, (IEk+1≦bEi (uP!'), and the degree of U2O5 in natural uranium is UEN+ll L
Set BN+1. The uranium dioxide powder with a U2O5 enrichment of Lgi used for the production of the lower IS region of the i-th fuel rod, the uranium dioxide powder with a U2O5 enrichment of UEk (hereinafter referred to as UO2 powder) and the powder with υoz of uEk+1 When manufacturing by mixing U2O5 with
UO2 powder whose v'A11f degree is UEk't' is (LEi-uEk+1)/(uEk-Ugk+1)
(As the ratio of υ, the reef shrinkage of s U2115 is uEk+1
UO2 powder is 1-((LEl-UEk+1)/(t+16-UW)
k+1 ) ) (mixed in a ratio of 2+ to produce U02 powder with a U2O5 stripe degree of LEi. Then, this UO2 powder is processed into a fuel pellet and loaded into the lower area of the No. 1 Q, N fuel rod. be done.

For example, when producing UO2 powder to be used in the lower region of fuel rod X, 1 is the UO2 powder used in the upper region of fuel rod X.
22,2) powder and the UO2 powder used on the upper part of the fuel rod may be mixed in the ratio of formula (1) and formula 121.

Here, the U of 1j02 powder used in the lower region of H44X is
The enrichment bei of 2O5 is 153 when the enrichment ratio between the upper region and the lower region is set to 0.9. [U2O5 of JO2 powder used in the upper region of fuel rod
ek is 17, and the force used in the upper region of the fuel rod cutting is 0285 g1 shrinkage uek+1 of UO2 powder is 1.3. As a result, Uek+1≦L”i<Vek
ir, i p'i)) standing chi, (1) 2 and (2)
From the formula, the fuel used in the upper region of Nu
By mixing 57.5% of the powder and 42.5% of the U02 powder used in the upper region of Fuel No. J,
Degree of indentation 1 of U2O5 used in the lower region of fuel rod X
．． 53 UO2 powder can be used for 8 times.

In addition, other manufacturing methods include U02 powder wood with the highest concentration KuM used in boiling water reactors with U02 powder with a U2O5 concentration of 5 as the upper limit, and UO2 powder wood with natural gun shrinkage NulE 8. It is also possible to produce UO2 powder of the required concentration xE from 1-. This method uses UO2 powder of highest concentration UE and UO28 of natural concentration NVE.
The final mixture of 91" Tani is the highest enrichment UE uranium dioxide powder as CXH-NVE)/(uE-NVE) +81, and the natural 6 fine NvE as 1-((XE-NVE)/(VB- NVE) ) (4
), it is necessary to produce UO2 powder of (fineness xE).

[Young fruit of the invention] According to this book or three, there are 72 areas in the axial direction of the fuel fruit assembly:
”+N, the fuel compression ratio in the upper region is made higher than the 3ta N bHxlii degree in the lower region, and the fuel a compression degree ratio in the lower @j′I region is made one foot, so that the local Pl[ By flattening the power distribution, local power peaking is reduced, and by flattening the axial power distribution of the fuel assembly, axial power peaking is reduced and the integrity of the fuel assembly is increased. I can do it.

[Brief explanation of the drawing]

is a cross-sectional view of the fuel assembly shown in Figure 1, Figure 4 is a performance diagram of the fuel assembly shown in Figure 1, Figure 5 is a cross-sectional view of the fuel assembly showing a conventional improvement example, and Figure 6 is a cross-sectional view of the fuel assembly shown in Figure 1. The figure is a (continuous i1i) diagram of the fuel assembly according to the present invention, and Fig. 7 is a power distribution diagram comparing the conventional vIJ and this @mei. 2υ...Fuel assembly 21...Fuel rod 22...
Channel Box 23...i,il u Park 24
・Water rod

Claims (1)

[Claims] (1) The axial direction of the fuel assembly is divided into two regions: an upper region and a lower region.
Divide into regions, and calculate the average concentration v degree υE of uranium-235 in the upper region and the average linear shrinkage degree L of uranium-235 in the lower region.
H is in the relationship LE<UB, and LEi is 9 degrees LEi of uranium-235 in the lower region of the i-th fuel rod housed in the fuel assembly.
A fuel assembly having the following relationship with respect to the enrichment uH+.