JPS58223092A - Bwr type reactor core - 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 invention] The present invention relates to an initial loading reactor for a boiling water nuclear reactor.

[Technical background of the invention and its problems]

In general, in a boiling water reactor, the core configuration at the time of initial operation, the so-called initial loading core, was composed of one type of fuel assembly with the same average enrichment of uranium-235. by the way,
The average enrichment of uranium-235 in the fuel assembly is 3 to 4 reactors/[7
It is set so that it can be burned in 2018. therefore,
Refueling at the end of the first cycle and the second cycle resulted in the removal of fuel assemblies containing a high proportion of uranium-235 from the reactor core, which had not yet undergone sufficient combustion, which was uneconomical.

[Purpose of the invention]

The present invention has been made based on the above circumstances, and its purpose is to prevent fuel assemblies whose combustion has not progressed sufficiently during the first few cycles from being removed from the furnace nozzle. The objective is to obtain a boiling water reactor core that can effectively utilize nuclear fuel.

[Summary of the invention]

The present invention divides the fuel assemblies loaded into the reactor core into a plurality of groups, 1st to nth groups, and calculates the average uranium-235 enrichment of the fuel assemblies in each group in order from the 1st group to the nth group. , and the number of fuel assemblies in any first group up to n-1 groups excluding the last n group was made to be approximately equal to the number of fuel assemblies to be replaced at the end of the first cycle. It is something. So, if we take out the fuel assemblies from one group in turn in each cycle, the number of fuel assemblies taken out from the reactor core 7 at the end of the first cycle is one reactor! Although it has only been burned for 20 years, the fuel assemblies removed in this first cycle have the lowest average enrichment of uranium-235, so the proportion of uranium-235 will be sufficiently reduced when removed from the core. ing. In addition, although the fuel assemblies removed in the second cycle have only been burned for two core years, the average enrichment of uranium-235 is the second lowest, so when the fuel assemblies are removed from the reactor, the uranium-2350 ratio is similarly sufficiently low. taken out in good condition. Therefore, a fuel assembly with a low uranium-235 content is not removed from the reactor core, and nuclear fuel can be used effectively.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. 1. FIG. 1 is a schematic plan view of a 1/4 reactor core.
1..., Ib... are control rods. Four fuel assemblies 21L..., 2b..., 2c... are loaded around these control rods 1a..., 7b...
One control rod 1a..., Ib... and four surrounding fuel assemblies 2a..., 2b...1, 2C... constitute a unit cell, and these unit cells are further They are arranged in a structure to form the reactor core. And the control rod 1a...
・, Ib... are at normal speed due to their functions. □Safety rods 1a... are pulled out at the time of i turn and inserted into the reactor core only during shutdown, and safety rods 1a... are inserted into the reactor nozzle during normal operation and inserted into the reactor core. and an adjustment rod 1b for controlling the reactivity of the reactor.

In addition, the fuel assemblies 2a..., 2b..., 2c...
... are bluntly divided into a plurality of groups, for example, three groups, and the first group of fuel assemblies 2a... has an average enrichment of uranium-235 of 1.4, and the number of fuel assemblies 2a is 164. Moreover, the fuel assembly 2b... belonging to the second group has its uranium 235
The average concentration of XF is 2.2%, and the number of bodies is 244. In addition, the fuel assemblies 2c... belonging to the third group have an average enrichment of uranium-235 of 30% and a number of fuel assemblies of 356.
It is the body. The total number of fuel assemblies 2a..., 2b-..., 2c... loaded in this core is 76.
There are four of them. In addition, in FIG. 1, the fuel assemblies 2a..., 2
b...

The number placed inside the square indicating 2C... is the number of the group to which the fuel assembly belongs. And the above uranium 2
35 First group fuel assembly 2a with the lowest average enrichment...
・ is loaded around the adjustment rod 1b... The remaining fuel assemblies 2a of the first group that were not fully loaded around the adjustment rods 1b are loaded in the center of the reactor core. Further, two fuel assemblies 2b of the second group and two fuel assemblies 2C of the third group are loaded around the safety rods 1a. The remaining third group of fuel assemblies 2e... are loaded around the core.

The number of fuel assemblies 2a of the first group is the first
The number is set equal to the number of fuel assemblies to be replaced at the end of the cycle, and the number of fuel assemblies 2b of the second group...
The number of fuel assemblies is set equal to the number of fuel assemblies to be replaced at the end of the second cycle. Note that the number of fuel assemblies 2c in the third group is the remaining number.

Next, the operation of the above embodiment will be explained. First, when the first cycle of combustion is completed, the first group of fuel assemblies 2a...1
64 bodies will be removed from the core and replaced with new fuel assemblies with an average enrichment of uranium-235 of 3.0%. In this case, the fuel assembly is shuffled if necessary. Next, when the second cycle of combustion is completed, the second group of fuel assemblies 2b...244 are removed from the reactor, and new fuel assemblies with an average enrichment of uranium-235 of 30 inches are loaded in their place. Furthermore, at the end of the vL3 cycle, from 356 fuel assemblies 2c of the third group, approximately 1 of the total number of fuel assemblies of all fuel groups i is combined.
,4-. A quarter of the fuel assemblies will be removed from the core and replaced with new fuel assemblies with an average enrichment of uranium-235 of 3.0%.

1-1 The above-mentioned first group of fuel assemblies 2a... are taken out from the core after only one core year of combustion.・
... is uranium 2: (5 average enrichment is low, so when it is taken out from the core), uranium 2' (50 ratio is taken out in a sufficiently low f state. 2b... is also removed from the core after only two core years of combustion, but this second edition fuel assembly 2b...1.The average enrichment of uranium-235 is relatively low at 2.2%. Therefore, the proportion of it-old K tit uranium-235 taken out from the core has decreased sufficiently. = 1+, the third group fuel assembly 2c... has an average enrichment of uranium-235 of 30
%, but this number: (Group of fuel 44i combination 2C...
//'J: Since the core is burned for three core years, the proportion of uranium-235 is sufficiently reduced when it is ejected from the core. Therefore, in a reactor core configured in this way, all the fuel assemblies removed in each cycle have a reduced proportion of uranium-235, and it is unlikely that a fuel assembly with a lower proportion of uranium-235 will be removed. Therefore, fuel can be used effectively.

In addition, the first group and the 21st T fuel assembly 2a...
The average degree of uranium-235 shrinkage and the number of uranium-235 of .
is set to remain at a fixed value. The relationship between this average enrichment of uranium-235 and the number of bodies in each group will be explained below.

First, the number of fuel assemblies in the first group is \Nl, the number of fuel assemblies in the second group is 82 + the number of fuel assemblies in the third group is Nl.
Set it to 3. Furthermore, if the average infinite multiplication factor at the end of the core cycle is 1 (ao), the moving area is B2, and the effective buckling is 132, then the effective multiplication factor of the core is Keff.
is Keff=-mu1 ・・・・・・(1) 1,000M
It is given by 2・B2. In addition, K■ is the infinite multiplication factor K for each group based on the average enrichment of uranium-235 in each group. oi (,t=1・
...3) can be found by . Moreover, the combustion change of Kc,)i becomes as follows, if the influence of burnable poisons is ignored: Kooi=ai')i・Ei --(3). However, ai'bi is a constant.

First, W, the length of one cycle is the burnup, ΔEl,
If the length of the second cycle is ΔE21 and the length of the third cycle is ΔE3, the first -tt cycle is Kcoi =
IJ blΔEt − (4).

Also, normally, Keff at the end of the cycle is set to be 1.0, but in the first cycle, some margin is left in the reactivity by 1-7 and Keff = 1.0 + C, so = t, O + C... ...(5) becomes.

Also, in the second cycle, the fuel assemblies of the first group are replaced with new fuel assemblies (i=4), so at the end of the second cycle, I′1Kool becomes KOO2”” B2
B2 (ΔF, +ΔE2) =
−<69K(K)3 = as ba (ΔE,
+ΔE2) −=-<6″) Kco4 = a4
b4 ・ΔE2. ．． . . . (6/#) Then, in this second cycle, if Koff at the end of the cycle is 1.0, then = 10 (7).

Furthermore, in the third cycle, a new fuel assembly (i=5) is loaded in place of the second group of fuel assemblies, and assuming that Keff at the end of the cycle is 1.0, =1.0... ...(8) becomes. If the total number of fuel assemblies is Nj, then N H + N 2 + N 3. = Nt・
Old...(9).

Therefore, if the average uranium-235 enrichment of each group of fuel assemblies, Keff at the end of each cycle, etc. are set, N1 r N2 can be calculated using the above equations (5), (7), (8), and (9). +N, that is, the number of fuel assemblies in each group is determined. In addition, the number of fuel assemblies in each group in the above embodiment is such that the average enrichment of uranium-235 in the first group of fuel assemblies 2a is 1.4%, and the number of fuel assemblies in the second group is 1.4%. The average enrichment of uranium-235 is 2.2%, and the uranium-23 of fuel assembly 2c of the third group is 2.2%.
5 average enrichment of 3.0%, new fuel assembly uranium-23
5 Average concentration is 3.0%Each cycle length is ΔEl"' I OGwD/T ΔE2=ΔE 3 = 8.5 GWD/T, and the reactivity margin C at the end of the first cycle is C=0. ↑ in the case of 02.The relationship between such exchange/turn of the fuel assembly and the infinite multiplication factor ω is shown in Fig. 2.

Further, in this embodiment, the first group of fuel assemblies 2a... having a low average enrichment of uranium-235 are loaded around the adjustment rods 7h.... Therefore, during operation, these adjustment rods 1b
... is inserted or pulled out, and even if the reactivity of the surrounding area changes, the output of the first group of fuel assemblies 2a ... around this fuel assembly is low.
Therefore, the impact on its soundness is small.

In fact, because the fuel assemblies 2C of the third group are arranged in the periphery of the core where the reaction rate is low, the power distribution in the horizontal direction of the reactor knob B is made uniform.

Note that the present invention is not limited to the above-mentioned one example.

For example, the number of bright spots is not necessarily limited to three groups, but may be two groups or four or more groups.

Furthermore, the average enrichment of uranium-235 in each group of fuel assemblies is not limited to the above embodiment. However, it is preferable that the average enrichment of uranium-235 between each group is 0.05 or more.

Furthermore, the arrangement of the fuel assemblies in each group is not necessarily limited to the above embodiment.

〔Effect of the invention〕

As described above, the present invention divides the fuel assemblies loaded into the reactor 10 into a plurality of groups from 1st to nth groups, and calculates the average enrichment of uranium-235 for each group from 1st group to nth group. in the order of s'r;
< Also, the number of fuel assemblies in any first group up to n-1 groups excluding the last n group is approximately the number of fuel assemblies to be replaced at the end of the first cycle. I made it equal. It is something. Therefore, if fuel assemblies are taken out from the first group in order for each cycle, the fuel assemblies taken out from the reactor 1 at the end of the first cycle have been burned for only one core year, but in this first cycle The fuel assembly removed from the reactor has the lowest average enrichment of uranium-235, so when it is removed from the reactor core, the uranium-235
50 ratio has decreased sufficiently. In addition, although the fuel assembly to be taken out in the second cycle has only been burned for two core years, the average enrichment of uranium-235 is the second lowest, so when it is taken out from the core, the uranium-2350 ratio is also sufficiently low. It is taken out.

Therefore, fuel assemblies with a high proportion of uranium-235 are not removed from the reactor core, and nuclear fuel can be used effectively, which has great effects.

[Brief explanation of drawings]

The figures show one embodiment of the present invention, Fig. 1 is a schematic plan view of a 1/4 reactor nob, and Fig. 2 shows the relationship between the exchange gloss turn of each group of fuel assemblies and the infinite multiplication factor. ′ is a line diagram. 1a... Control rod (safety rod), 1b... Control rod (adjustment rod), 2a... Fuel assembly (first group), 2b... Fuel assembly (second group), 2C...・Burning effect, combination (3rd group)
.

Claims (3)

[Claims] (1) Divide the loaded fuel assemblies into multiple groups: 1st group, 2nd group, ... nth group, and uranium-235 of the fuel assemblies of each group.
The average enrichment is increased in the order of 1st group, 2nd group... nth group, and the number of fuel assemblies belonging to any 1st group up to n-1 group is determined at the end of the 1st cycle. A reactor core for a boiling water reactor, characterized in that the number of fuel assemblies to be replaced is set to be approximately equal to the number of fuel assemblies to be replaced. (2) A patented reactor core characterized in that the first group of fuel assemblies having the lowest uranium-235 enrichment are loaded around control rods used as adjustment rods. (3) The core of the boiling water nuclear reactor according to claim 1, wherein the n-th group of fuel assemblies having the highest uranium-235 enrichment are loaded at the outermost periphery of the core.