JPH04198891A - Manufacture of fuel assembly, and fuel assembly - Google Patents

Abstract

PURPOSE:To flatten outputs of fuel rods by considering a composition of each isotope by taking a composition ratio of each isotope into consideration about uranium and plutonium of the fuel rod containing plutonium when a degree of enriching the plutonium is set for the fuel rod. CONSTITUTION:In production lines 21a and 21b, PuO2 -UO2 mixed powders 22a and 22c an UO2 powders 22b and 22d are supplied to composition ratio analysis means 23a-23d are supplied and isotopes are analyzed to determine a composition ratio. The results of the analysis is inputted into a degree of enriching fuel rod plutonium calculator 13, with which 13 a degree of enriching plutonium to satisfy a target fissile value and target local output peaking coefficient and the results are inputted into a degree of enriching plutonium setting means 24a and 24b, by which 25a and 25b a mixing ratio of the powders 22a-22d is determined based on a degree of enriching plutonium set value to mix. The mixed fuel powder is formed 26a and 26b to pellets and the pellets are loaded 27a and 27b into a cover pipe to produce a fuel assembly by a fuel assembly producing means 28.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a nuclear reactor fuel assembly using a fuel material containing plutonium and a method for manufacturing the same, and in particular to a method for manufacturing the same, and particularly to The present invention relates to a fuel assembly adjusted to a value that satisfies both target reactivity (burnup) and target local peaking coefficient, and a method for manufacturing the same.

[Prior Art] Conventionally, the plutonium enrichment of the fuel material to be filled into each fuel rod constituting a fuel assembly has been determined according to Dynamic Fuel Technical Report No. 70. pp
77-81 (June 1989) [Plutonium enrichment management using the equivalent fit-sile method J], the composition data (uranium isotope composition ratio, plutonium isotope composition ratio, etc.) of only the fuel material is was determined by applying the equivalent Fitzsail method. The amount of plutonium in the fuel assembly was then adjusted in accordance with the determined plutonium enrichment. In other words, in this equivalent fit-sile method, the nuclear value of each isotope of uranium and plutonium is evaluated in advance using reactivity (burnup) as an objective function, and based on this and the composition data of the fuel material, the fuel material is The nuclear value of plutonium is determined, and based on this the plutonium enrichment is adjusted to achieve the target reactivity (burnup).

[Problem to be solved by the invention 1 By the way, in a plutonium fuel assembly in a thermal neutron reactor such as a light water reactor such as a BWR or a PWR or a new converter reactor such as an ATR, it is necessary to flatten the output of each fuel rod in the fuel assembly. The plutonium enrichment of the fuel material in the outer fuel rod group, which has a high heat generation density, is lower than that of the fuel material in the center fuel rod group, which has a lower heat generation density.

However, in thermal neutron reactors, the local power peaking coefficient (hereinafter referred to as LP), which is an index of power flattening within the fuel assembly,
F) is highly dependent on the plutonium enrichment distribution among the fuel rods in the fuel assembly, so changing the plutonium enrichment of the outer or central fuel rods will significantly increase the LPF. It will change. This LPF directly affects important parameters in core characteristics such as maximum linear power density and minimum power limit ratio, so LPF
It is important to suppress changes in PF.

In this regard, in the conventional technology described above, the plutonium enrichment of each fuel rod is adjusted independently for each fuel rod based on the composition data of only the fuel material of the fuel rod itself. Because fuel assemblies were manufactured by combining fuel rods, even though the target reactivity (fuel rods) could be achieved, no consideration was given to plutonium enrichment distribution within the fuel assemblies. , there is a problem that the LPF may vary greatly from the target value.

An object of the present invention is to provide a method for manufacturing a fuel assembly for a nuclear reactor, and a fuel assembly that satisfies target values for both reactivity and LPF.

[Means for Solving the Problem] In order to achieve the above object, the present invention provides a method for producing a fuel assembly that is composed of a plurality of fuel rods, in which some or all of the constituent fuel rods are made of a fuel material containing plutonium. In the method, the fuel assembly is divided into a plurality of concentric fuel rod groups, the composition ratio of each isotope of the fuel material for each concentric fuel rod group is analyzed, and the composition ratio of each isotope is analyzed based on the composition ratio of each isotope. find the correlation between the average equivalent fitsize amount of the fuel assembly and the plutonium enrichment, and extract the first distribution combination relationship of the plutonium enrichment between the fuel rod groups that satisfies the target equivalent fitsize amount according to this correlation. , Further, based on the correlation between the local power peaking coefficient determined in advance and the plutonium enrichment between the fuel rod groups, the plutonium enrichment between the fuel rod groups that satisfies the target local peaking coefficient is determined. extracting the second combination relationship, setting the plutonium enrichment of each fuel rod group according to the distribution combination common to the first and second distribution combination relationships, and adjusting the plutonium amount of each fuel rod based on this setting. It is characterized by

In addition, in the above, the isotope analysis is performed on plutonium, uranium, and americium contained in the fuel material, and the composition ratio of each isotope is analyzed, and the average equivalent fit amount of the fuel assembly is analyzed. The correlation between plutonium enrichment and plutonium enrichment is determined based on the composition ratio of each analyzed isotope and a predetermined equivalent fitting coefficient of each isotope.

According to the above manufacturing method, a plurality of fuel rods are arranged to form a plurality of concentric fuel rod groups, and in a fuel assembly in which some or all of the fuel rods are made of a fuel material containing plutonium, each of the above-mentioned fuel rods is arranged. The distribution relationship of the plutonium enrichment of the fuel rods containing plutonium between the fuel rod groups is such that the distribution follows the correlation between the average equivalent fitsize amount of the fuel assembly and the plutonium enrichment, and satisfies the target equivalent fitsize amount, and According to the correlation between the local power peaking coefficient and the plutonium enrichment between the fuel rod groups, a fuel assembly with an allocation that satisfies the target local peaking coefficient is obtained.

[Function] With this configuration, according to the present invention, the above object is achieved by the following function.

In other words, when setting the plutonium enrichment of each fuel rod, the composition of each isotope of uranium and plutonium, which is not only the fuel material of the fuel rod in question, but also the fuel material of most other fuel rods containing plutonium, is determined. Since the ratio etc. are also taken into account, plutonium enrichment settings for other fuel rods can also be set in relation to each other. This makes it possible to simultaneously adjust the average plutonium enrichment of the fuel assembly as seen from the target reactivity (burnup) and adjust the plutonium enrichment distribution within the fuel assembly as seen from the target LPF.
It becomes possible to set the plutonium enrichment of each fuel rod that satisfies both the target reactivity (burnup) and target LPF.

Further, according to the fuel assembly of the present invention, the correlation between the plutonium enrichment of each fuel rod is the target reactivity (burnup) and the target L
Since the relationship is set to satisfy both PF, the output of each fuel rod in the fuel assembly is flattened, and core characteristics such as maximum linear power density and minimum power limit ratio are improved.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a flowchart showing the procedure for setting the fuel rod plutonium enrichment, which is the main part of the method for manufacturing a fuel assembly according to an embodiment of the present invention. This applies to cases in which products are manufactured.

As shown in Fig. 2, the second fuel assembly has a plurality of fuel rods arranged concentrically, including 18 outer layer fuel rods (group) 31 and 12 middle layer fuel rods (group) 32. , and six inner layer fuel rods (groups) 33, a total of 36 fuel rods, and an assembly support rod 34. Each fuel rod is composed of a cladding tube 35 and a fuel substance 36, 37, 38 filled therein.

The fuel material of each fuel rod in this example is a mixed oxide of plutonium and natural uranium (MOX fuel), and the fuel material of the inner layer and intermediate layer on the center side of the fuel assembly with low heat generation density is high in plutonium. The fuel material in the outer layer outside the assembly with high enrichment of MOX and high heat generation density is made to be MOX with low plutonium enrichment. Note that some of the fuel rods may include fuel material that does not contain plutonium.

Next, a procedure for manufacturing a fuel assembly having the above configuration will be explained with reference to FIG. In this embodiment, it is assumed that the same raw material is used as the fuel material for the inner layer fuel rods 32 and the intermediate layer fuel rods 33.

(1) First, in steps 5a and 5b, the compositions of the fuel materials for the inner/middle layer fuel rods and the outer layer fuel rods are analyzed, respectively. The analysis determines the composition ratio α, which is the content ratio of each isotope of plutonium and americium to the total plutonium, and the composition ratio β, which is the content ratio of each isotope of uranium to the total uranium.

■Next, in steps 6a and 6b, the following formula (1
) and the equivalent fitzile amount E and plutonium enrichment ε shown in
Find the relationship between

Note that the clonic term is a general formula of the equivalent fitting method. Further, k is a symbol for distinguishing between the inner/middle layer fuel rods and the outer layer fuel rods, and in FIG. 1, the inner/middle layer fuel rods are expressed as 1=1, and the outer layer fuel rods are expressed as 2=2.

E = f (ε) = ε Σ α, η, +(l−ε
) Σβ, 77°...(1) Two trowels.

E; Equivalent amount of fittings in the fuel rod ε: Plutonium enrichment in the fuel rod α1; Composition ratio of plutonium in the fuel rod and "' Am isotope ('°" Am is also considered as an isotope of plutonium) β, : Uranium isotope composition ratio η of fuel fuel, (1);
From the definition formula for the average equivalent fit size E of a fuel assembly shown in 2), the relationship between the average equivalent fit size E shown in the following equation (3) and the plutonium enrichment ε of each fuel rod group is determined.

E-ΣEXN/ΣN...(2) Here,
E; aggregate average equivalent fittile amount E, fittile amount to fuel rod N; number of fuel rods, Σf(ε)XN E=g (ε',...ε)=□−ΣN... ...(3) In this equation (3), if the average equivalent fit size E is determined, the relationship between the plutonium enrichment of the inner/middle layer fuel rod group and the outer layer fuel rod group is as shown in Figure 3. Become. In addition,
The figure shows an example where E=2.7wt%. Further, this value of E corresponds to a case where the burnup is 30 Gwd/l.

■Next, in step 9, the target average equivalent fitting amount E ([lJ standard) and the target L are obtained from the setting value file 10.
PF (target) and further data file 11
Based on the known correlation (distribution dependence) between the LPF calculated in advance and the plutonium enrichment between the fuel assembly groups, the plutonium enrichment between the fuel assembly groups that satisfies the target LPF is determined. Extract the allocation correlation of An example of this allocation correlation is shown in FIG. In the example shown in the figure, LPF=1. ]. Then, the distribution combinations of plutonium enrichment among the fuel assembly groups that satisfy the target average equivalent fit size E (target) shown in Figure 3 are determined using equation (3), and among these combinations, the combinations shown in Figure 3 are calculated. A search is made for one that simultaneously satisfies the plutonium enrichment distribution relationship of the target LPF shown. The plutonium enrichment between the fuel groups that satisfies this simultaneously is expressed as the plutonium enrichment of the inner/middle layer fuel rods and the outer layer fuel rods ε' (=a) and ε' (=b
). In the example of Fig. 3, the values on the vertical and horizontal axes corresponding to the point where the two curves intersect (4.2W°C% and 1.2W°C%).
4wt%) is the desired plutonium enrichment.

■Plutonium enrichment of inner/middle layer fuel rods and outer layer fuel rods determined in this way ε' (-a), ε' (=b)
is output to a fuel mixing means of a fuel rod manufacturing apparatus (not shown) in steps 12a and 12b. As a result, a fuel assembly is formed with a plutonium enrichment level that satisfies the desired burnup and desired LPF at the same time.

FIG. 4 shows an embodiment of a fuel assembly manufacturing apparatus for carrying out the above-described fuel manufacturing method.

The production lines 21a and 21b of this embodiment are respectively manufactured by the above-mentioned Kinen Giho (No. 70, pp. 77-81 (1989).
It is basically the same as the fuel rod production line disclosed in June 2013). The difference is that two production lines are used to manufacture the inner/middle layer fuel rods and the outer layer fuel rods in parallel, and the plutonium enrichment of each is outputted from the fuel rod plutonium enrichment calculation device 13. The purpose is to make adjustments based on the set values. The fuel rod plutonium enrichment calculation device 13 is
The functions from steps 6a and 6b in FIG. 1 are realized by a computer.

Here, the manufacturing line of this embodiment will be explained. Note that since both production lines 21a and 21b have the same configuration,
The explanation will be based on the production line 21a for middle/intermediate layer fuel rods. Plutonium-containing uranium Pu○, -UO as fuel raw material
, mixed powder 22a.

The uranium UO2 powders 22b are supplied separately. The composition ratio analysis means 23a and 23b respectively sample the fuels and analyze each isotope to determine the composition ratios α and β. This analysis result 5a is input to the fuel rod plutonium enrichment calculation device 13. Based on this, the fuel rod plutonium enrichment calculation device 13 calculates the target fitting amount and the target L according to the procedure explained in FIG.
The plutonium enrichment setting means 24
Enter a. The mixing means 26a determines the mixing ratio of the PuO, -UO, mixed powder 22a and the UO, powder 22b based on the given plutonium enrichment set value, and mixes the two in accordance with this.

Next, the pellet manufacturing means 26a forms the mixed fuel powder into pellets of a predetermined shape, and sends the pellets to the inner/intermediate layer fuel rod manufacturing means 27a. The inner/middle layer fuel rod manufacturing means 27a manufactures individual fuel rods by loading the sent pellets into a cladding tube, and sends them to the fuel assembly manufacturing means 28. The fuel assembly manufacturing means 28 uses this and the outer layer fuel rods delivered from the outer layer fuel rod manufacturing line 21b to manufacture a fuel assembly as shown in FIG.

As described above, according to this embodiment, it is possible to form a fuel assembly whose plutonium enrichment is adjusted to satisfy a desired burnup and a desired LPF at the same time.

Although each of the above embodiments has been described assuming that the fuel assembly shown in FIG. 2 is manufactured, the plutonium enrichment setting method of the present invention is universal, so A similar effect can be obtained when applied to the plutonium fuel assembly of a light water-fueled neutron reactor.

[Effects of the Invention] As explained above, according to the present invention, when setting the plutonium enrichment level of each fuel rod, not only the fuel material of the fuel rod but also most other fuel rods containing plutonium are determined. Since the composition ratio of each isotope for uranium and plutonium, which are fuel materials, is also taken into account, the plu/tonium enrichment setting of other fuel rods can also be related, and the It can also respond to changes in americium content, etc. This makes it possible to simultaneously adjust the average plutonium enrichment of the fuel assembly as seen from the target reactivity (burnup) and adjust the plutonium enrichment distribution within the fuel assembly as seen from the target LPF. This makes it possible to set the plutonium enrichment of each fuel rod that satisfies both the target reactivity (burnup) and the target LPF.

Furthermore, according to the fuel assembly of the present invention, it is possible to determine whether the plutonium enrichment of each fuel rod is correlated with the target reactivity (burnup) and the target L
Since the relationship is set to satisfy both PF, the output of each fuel rod in the fuel assembly is flattened, and power peaking parameters such as the maximum linear power density of the core and core characteristics such as the core operating cycle interval are However, it is possible to satisfy the predetermined conditions without being affected by the composition of the fuel substance.

The effect is particularly noticeable when applied to plutonium fuel assemblies for thermal neutron reactors.

[Brief explanation of the drawing]

Fig. 1 is a flowchart showing an example of the plutonium enrichment setting procedure which is the main part of the fuel assembly manufacturing method of the present invention, Fig. 2 is a cross-sectional view of an example of a fuel assembly, and Fig. 3 is an average FIG. 4 is a diagram showing the relationship between the equivalent fit size and the distribution of plutonium enrichment and the relationship between the LPF and the distribution of plutonium enrichment. FIG. 4 is a block diagram of an example of a fuel assembly manufacturing apparatus. 7.1 data file, 10...setting value file,
31... Outer layer fuel rod, 32... Middle layer fuel rod, 33...
- Inner layer fuel rod, 36... Outer layer fuel material, 37... Middle layer fuel material, 38... Inner layer fuel material, 13... Fuel rod plutonium enrichment calculation device.

Claims (1)

[Scope of Claims] 1. A method for manufacturing a fuel assembly composed of a plurality of fuel rods, in which part or all of the constituent fuel rods are made of a fuel material containing plutonium, in which the fuel assembly is arranged in a plurality of concentric circles. The composition ratio of each isotope in the fuel material for each concentric fuel rod group is analyzed, and the average equivalent fissile amount and plutonium enrichment of the fuel assembly are calculated based on the composition ratio of each isotope. A first distribution combination of the plutonium enrichment among the fuel rod groups that satisfies the target equivalent fissile amount is extracted according to this correlation, and a predetermined local power peaking coefficient is obtained. extracting a second combination relationship of the plutonium enrichment between the fuel rod groups that satisfies the target local peaking coefficient based on the correlation between the plutonium enrichment between the fuel rod groups and the first and Production of a fuel assembly characterized in that the plutonium enrichment of each fuel rod group is set according to a common allocation combination in the second allocation combination relationship, and the plutonium amount of each fuel rod is adjusted based on this setting. Method. 2. In claim 1, the isotope analysis is performed on plutonium, uranium, and americium contained in the fuel material, and the composition ratio of each isotope is analyzed, and the average equivalent of the fuel assembly is A fuel assembly characterized in that the correlation between the amount of fissile and the plutonium enrichment is determined based on the composition ratio of each analyzed isotope and the equivalent fissile coefficient of each isotope determined in advance. Production method. 3. In a fuel assembly in which a plurality of fuel rods are arranged to form a plurality of concentric fuel rod groups, and some or all of the fuel rods are made of a fuel material containing plutonium, The distribution relationship of the plutonium enrichment of the fuel rods containing plutonium between them follows the correlation between the average equivalent fissile amount of the fuel assembly and the plutonium enrichment, and satisfies the target equivalent fissile amount, and the local power peaking coefficient and the plutonium enrichment between the fuel rod groups, and the distribution satisfies a target local peaking coefficient.