RU2532083C2 - Method of fitting of fuel element cores with rod fuel cells - Google Patents

Abstract

FIELD: physics, nuclear.

SUBSTANCE: invention relates to fabrication of nuclear reactor fuel elements. The method of fitting of fuel element cores with rod fuel cells is offered, when from the batch of fuel cells with the average length L₀ randomly the poles with the amount of elements n is selected. If the pole length D falls within (nL_o-d; nL₀+d), where d=min[h-(H-nL₀), h+(H-nL₀)], h - half of the core length tolerance field, H - rated length of the core, they are used for core fitting. From the remained rods of the batch again randomly the poles are selected and then the operations are iterated.

EFFECT: practically complete utilisation of the batch of rods for core fitting and possibility for considerable simplification of the automated lines for fabrication of fuel elements.

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Description

Description of the invention

1. The technical field to which the invention relates.

The invention relates to the field of nuclear energy, in particular to the technology of cermet fuel elements of the active zones of low-power nuclear reactors, and may find application in automated and automatic lines at fuel rod manufacturing enterprises.

2. The level of technology

One of the areas in nuclear energy is the use of fuel rods in which fuel cores are drawn from fuel cells in the form of cermet rods (see, for example, Gavrilin S.S., Deniskin V.P. et al., A New Generation of Microfuel-Based Fuel Rods for VVER, Nuclear Energy. - 2004. - No. 96, issue 4. - p. 280; Pat. 2313142, Russia, IPC G21C 3/64, Kermet fuel element of a water-water nuclear reactor / Gavrilin SS, Deniskin V.P. . and others - No. 2006109585/06; Application. March 28, 2006; Publish. December 20, 2007. Bull. No. 35).

Unlike fuel rods, in which the cores are drawn from fuel cells in the form of compressed tablets of relatively short length, the cermet rods are a cylindrical zirconium capsule about 50 mm long with nuclear fuel and matrix material enclosed in it (see; e.g., Pat.2371789, Russia, IPC G21C 3/00, A method of manufacturing a cermet rod for the fuel core of a fuel element of a nuclear reactor / Gavrilin S.S., Deniskin V.P. et al. - No. 2008117710/06; Application. 04.05.2008; Publish. 10.27.2009 Bull. No. 30). The consequence of the increased length of the fuel element of the cores of such fuel rods is a fixed number of rods in all the cores of the reactor fuel rods, which complicates the selection of rods, the total length of which lies within the limits specified on the core.

There is a method of equipping a core of a fuel rod with rod fuel cells, based on the manual selection of a column of elements with their multiple visual selection to obtain a given core length (see, for example, US Patent No. 3925965 of 12.16.1975). Such a solution is obviously characterized by low productivity and is unacceptable in conditions of mass production.

There is also a method of equipping the core of a fuel rod with rod fuel elements, in which fuel elements were equipped with some excess of a given column length (see, for example, RF Patent No. 2070740 of 05.17.1994). For fuel rods where the cores are composed of relatively short length tablets, this solution may be satisfactory. In the case of cermet rods, the length of which is significant (about 50 mm), such an excess in a number of applications, for example, for small-sized reactors, becomes unacceptable due to an increase in the heterogeneity of energy release along the length of the active zone.

There is a method of equipping a core of a fuel rod with rod fuel cells (see, for example, Afanasyev V.L., Rozhkov V.V. et al. Method and device for equipping tablets with shells of rod fuel elements, RF Patent No. 2156508 of 08.12.1998, publ. 20.09 .2000), which consists in the fact that:

- from a batch of elements with known statistical characteristics in the first position of the equipment, the main column is drawn from randomly selected elements, and the length of this column is obviously less than the required;

- at the second position of the equipment (the position of the equipment) for a certain number of elements randomly selected from the batch, the lengths of these elements and their spatial location with the message of these parameters to the data bank of an electronic computer (computer) are determined;

- the measured deficit of the length of the main column of elements is reported to the computer, which determines the spatial coordinates of those elements of the position of the additional equipment, the addition of which to the main column will form a column whose length is within the specified limits;

- certain computer elements are added to the main column, the length of the obtained column is measured, and if the measured length of the column lies within specified limits, it is sent to the core equipment;

- of the remaining batch elements, the following columns are collected using the same algorithm and the cycle is repeated.

The disadvantage of this method is the complexity of the hardware implementation, and, as applied to small-sized reactors, fuel rod cores of which are drawn from a fixed number of cermet rods, there is a high probability of non-assembled core of a given length and, as a result, the appearance of unclaimed rods, which makes production more expensive.

With the proposed method, the latter method coincides with the following essential features:

- from a batch of fuel cells with known statistical characteristics, columns are randomly collected;

- measure the length of the posts;

- direct the poles to the equipment of the cores, if their lengths lie within specified limits;

- from the remaining elements of the party, poles are again randomly collected and then the cycle is repeated.

In the aggregate of essential features, the latter method is closest to the proposed one and is selected as a prototype.

3. Disclosure of invention

The proposed method for equipping fuel rods cores with rod fuel elements consists in randomly picking up poles from a batch of fuel cells with known statistical characteristics, measuring their lengths and, if their lengths are within specified limits, sending poles to the core equipment, and from the remaining batch elements again randomly pick up the columns and then repeat the cycle.

From prototype inventive method is characterized in that the number of fuel elements in all columns and pillars equally directed to cores gear when the condition nL -d≤D≤nL _{0 0} + d,

where D is the length of the column;

L ₀ - the average length of the fuel cells in the party;

n is the number of fuel cells in the core;

d is the smaller of two values: h- (Н-nL ₀ ), h + (Н-nL ₀ );

h - half of the tolerance field for the core length;

N is the nominal length of the core.

The meaning of the imposed condition is that the column is sent to the core equipment if the deviation of its length from the average length of the fuel element multiplied by the number of elements in the core lies in the tolerance field symmetrical with respect to this product, and this field does not go beyond the specified tolerance field for the core length.

The consequence of this difference is that under this condition, the removal of elements from the batch that left the equipment of the cores is not associated with a change in the normal distribution of elements in the batch, there is practically no drift in the distribution maximum, leading to the appearance of unclaimed elements.

In addition, the implementation of the proposed method eliminates the need to create a position of additional equipment and related processes and means of search and individual selection of the necessary elements, which greatly simplifies the task of automating the technology of equipment of the core of fuel rods.

4. Information confirming the possibility of implementing the invention.

As an example of the implementation of the proposed method, consider the process of equipping cores from a batch of fuel cells in the form of rods in the amount of 10,000 pcs. The batch of rods is characterized by the normal law of the distribution of rods along the lengths with an average value of 50 mm and a standard deviation of 0.3 mm. We take the number of rods in the core equal to 24 pcs. Then the average column length of 24 rods will be 1200 mm with a standard deviation of 0.3 · 24 ^0.5 = 1.47 mm. Let the core length specified by the design documentation be 1204.0 ± 4.4 mm, i.e. the average value of the dial length is included in the specified tolerance field. In accordance with the condition of the present invention, a set of 24 rods is sent to the core equipment only with its length ranging from 1199.6 mm to 1200.4 mm.

The stream of rods from the finishing section is fed to a sorting machine, which groups the rods into columns of 24 pcs. in each, measures the length of the column and, if the length of the column is within the above limits, directs the column to the core equipment, otherwise the rods of the column are sent to the drive. After the entire batch of rods has passed through the sorting machine, the rods are fed into it from the accumulator and the process is repeated until the seizure of suitable sets of rods in one sorting cycle becomes negligible compared to the total number of equipped cores.

Mathematical modeling of the process of equipment of the cores in the conditions of the considered example showed the following.

Figure 1 explains the relative position of the curve 1 of the distribution density of the lengths of columns of 24 rods specified in the documentation of the tolerance field for the core length - 2 and the selection field of the columns sent to the core equipment - 3.

Figure 2 is a diagram showing the increase in the number of columns sent to the core equipment for the first five sorting cycles, and Figure 3 is a diagram for 100 cycles.

The diagram of figure 3 shows the ultimate capabilities of the proposed method is the almost complete use of manufactured rods (more than 99%). It should be noted that during successive cycles, the nature of the distribution curve of the rods remaining after each cycle is not violated, which guarantees their full use not only as the number of cycles grows, but also simply when replenishing a batch.

Figure 4 shows the corresponding curves for the initial distribution - 4 and after the first five cycles (5-9).

Figure 5 shows a diagram of the selection of suitable columns from the condition of finding their lengths in the tolerance field specified by the documentation, for five sorting cycles, figure 6 - for a hundred cycles. It is seen that in the initial sorting cycles, the selection of suitable posts is faster than in the case illustrated in figure 2, however, due to the preferential selection of the rods, the length of which is longer than the average value in the batch, the maximum distribution of the rods to the left drifts (Fig. 7, where 10 - initial distribution, 11 - distribution after 20 cycles), which leads to the lack of demand for the rods - under the conditions of the considered example, their number will be about 1300 pcs.

Claims (1)

A method of equipping fuel rod cores with rod fuel elements, which consists in randomly collecting poles from a batch of fuel cells with known statistical characteristics, measuring their lengths and, if their lengths are within specified limits, sending poles to the core equipment, and from the remaining batch elements again randomly recruited poles and then the cycle is repeated, characterized in that the poles directed to the cores gear when the condition nL -d≤D≤nL _{0 0} + d, where
D is the length of the column;
L ₀ - the average length of the fuel cells in the party;
n is the number of fuel cells in the core;
d is the smaller of the two values: h- (H-nL ₀ ), h + (H-nL ₀ );
h - half of the tolerance field for the core length;
H is the nominal core length.

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