JPS5829480B2 - Kakunenryoutaba - Google Patents

Description

[Detailed description of the invention] The present invention relates to nuclear fuel bundles.

Some known types of nuclear reactors have non-homogeneous cores.

In that case, a plurality of fuel assemblies or bundles are vertically arranged at regular intervals to form a core capable of sustaining a nuclear fission reaction.

Such a core is housed in a pressure vessel, where it is submerged in a medium (eg, light water) that acts as both a coolant and a neutron moderator.

A plurality of control rods containing neutron absorbers can be selectively inserted between the fuel bundles to control the reactivity of the reactor.

Such a nuclear reactor system is described, for example, in U.S. Pat. No. 338
It is explained in more detail in the specification of No. 2153.

Each fuel bundle consists of a tubular channel containing a group of elongated clad fuel elements or fuel rods supported between upper and lower tie plates.

The fuel bundle is supported within the pressure vessel between an upper core grid and a lower core support plate.

The lower coupling plate of each fuel bundle is equipped with a pointed head that fits into a hole in the core support plate.

The point has an opening through which pressurized coolant flows upwardly through the fuel bundle to remove heat from the fuel element.

A typical fuel bundle of this type is, for example, U.S. Pat. No. 3,431
No. 170.

However, due to the water gap between the fuel bundles, the distribution and location of the control rods, and other factors, the neutron flux and therefore the power density in a non-homogeneous core is not uniform.

This also applies to the interior of individual fuel bundles.

In practice, the power output of a nuclear reactor is limited by the temperature limit of the fuel rods at the point of maximum power within the reactor core.

Therefore, in order to maximize the power of the core (and therefore each fuel bundle), it is desirable to minimize the ratio between the maximum power and the average power, that is, to "flatten" the fluctuations in power density.

(This problem is discussed in more detail, for example, in U.S. Pat. No. 3,147,191.

) Up to now, several means have been proposed to achieve power flattening in a fuel bundle.

One known method is to suitably vary the initial fuel enrichment in the fuel bundle.

In practice, the above objective is achieved by loading each fuel rod with fuel pellets having an enrichment appropriate to its location in the fuel bundle.

By the way, the operation of known power reactors is based on the concept of an operating cycle.

That is, in order to restore the required reactivity, the operation of the nuclear reactor is periodically interrupted and reloaded with fuel.

From the point of view of loading or reloading the core with fuel, the removable fuel bundle is the basic replaceable unit of the core.

According to known reloading schemes, only a small portion (eg, 20-30%) of the fuel bundle is replaced during each reload.

As a result, at any point in time, the core will contain fuel bundles exhibiting varying degrees of fuel depletion.

The degree of fuel depletion of each fuel bundle depends on its residence time.

The required enrichment of the reload fuel therefore depends not only on the planned location of the fuel bundle within the core, but also on the total enrichment that needs to be added to the core to restore the desired excess reactivity. It is.

Ideally, reloading fuel is desirably designed based on core operation data up to the time of reactor shutdown for reloading.

However, in reality, this is not possible due to the lead time required to produce the fuel bundles and the need to keep the outage for reloading as short as possible.

Therefore, it is important to reduce the lead time for fuel bundle production and also to provide flexibility in the selection of fuel rod enrichment in order to better match the nuclear properties of the reloaded fuel to the core requirements. This is extremely desirable.

On the other hand, in order to prevent misplacement of high-enrichment fuel rods in a fuel bundle, means are provided to prevent high-enrichment fuel rods from being inserted into positions of low-enrichment fuel rods in a fuel bundle. It is provided.

According to the known method, the shanks of the end plugs of high-enrichment fuel rods have a large diameter, so that the corresponding support holes in the fuel bundle coupling plates also have a large diameter.

As a result, insertion of high enrichment fuel rods into small diameter support holes at the location of low enrichment fuel rods is prevented.

However, the provision of supporting holes in the coupling plates of fuel bundles according to a specific arrangement is useful both for the purpose of shortening the lead time for fuel bundle production and for selecting the enrichment of the individual fuel rods as closely as possible. This proved to be a significant impediment to the objective of achieving flexibility, ultimately impeding the availability of assembled fuel bundles during reactor shutdowns for reloading.

The improvement of the present invention is now achieved by providing all of the fuel rod support holes in the tie plate with a single predetermined diameter.

In assembling the fuel bundle, a sleeve having a selected inner diameter is fitted into the support hole in accordance with an arrangement compatible with the desired enrichment specification.

The invention will be described in detail below in conjunction with the accompanying drawings.

According to known core configurations of nuclear reactors (as described in more detail in U.S. Pat. Four replaceable fuel bundles form a cell.

A reactor core is constructed by arranging a large number of such cells in a substantially regular cylindrical shape.

A typical cell constituting such a core consists of four fuel bundles 20 surrounding a control rod 11, as shown in FIG.

In that case, the fuel bundle 20 is arranged so that the heel 12 is adjacent to the control rod 11 .

A typical fuel bundle 20 is shown in elevation in FIG.

The fuel bundle 20 is comprised of a plurality of fuel elements or fuel rods 21 supported between a skeletonized upper tie plate 22 and lower tie plate 23.

The fuel rods 21 pass through a plurality of fuel rod spacers 24, which serve as intermediate supports to maintain the spacing of the elongated fuel rods and prevent lateral vibrations.

Each fuel rod 21 consists of an elongated tube containing fissile material and other materials (e.g., fuel parent material, burnable poisons, inert materials, etc.) and sealed by upper and lower end plugs 26, 27. .

The lower end plug 27 is equipped with an extension or shank 28 for alignment and connection of the fuel rods to support holes 29 provided in the lower coupling plate 23.

The upper end plug 26 is also equipped with an extension or shank 30 for alignment and connection of the fuel rods to support holes 31 provided in the upper coupling plate 22.

According to the invention, each support hole 31 in the upper coupling plate 22 is (
(Excluding the case of water pipes described below), all of them are provided to have a predetermined excessive standard diameter.

Each support hole 31 is then fitted with a sleeve 32 having an inner diameter corresponding to the diameter of the shank 30 of a fuel rod containing fuel of an enrichment appropriate for that location (as will be explained in more detail below). .

To add to the moderation effect in the center of the fuel bundle, the illustrated fuel bundle 20 uses water tubes 41 in place of centrally located fuel rods.

Such water tube 41 has an end plug and fuel rod 21
are installed in the fuel bundle in a similar manner, except that they contain no fuel and are perforated to allow the flow of coolant and moderator water. .

Additionally, water tube 41 is also equipped with ears 45 or other spacer capture means to prevent fuel rod spacer 24 from moving axially.

Incidentally, the structure of such a water pipe is disclosed in U.S. Patent No. 380299.
It is described in more detail in the specification of No. 5.

Some of the support holes 29 (e.g. two along each side) in the lower coupling plate 23 have threaded lower shanks 2B.
' is threaded to receive a fuel rod with a '.

The upper shank 30' of the same fuel rod extends through a support hole in the upper coupling plate 22 and has threads for receiving a retaining nut 33.

A coil spring 34 is installed on the shank 30 of each fuel rod, extending from the upper end of the fuel rod to the lower surface of the upper coupling plate 220.

In this way, the upper and lower coupling plates and the fuel rods are integrally constructed.

Fuel bundle 20 also contains thin walled tubular channels 35 having a substantially square cross section.

Its dimensions are such that it achieves a sliding fit with the upper and lower coupling plates 22, 23 and the fuel rod spacers 24, so that the channel 35 can be easily installed and removed.

A tab 36 is fixed to the top end of the channel 35.

Thereby, the channel 35 along with the spring-stop assembly 37 is secured to the strut 38 of the upper coupling plate 22 with bolts 39.

The upper coupling plate 22 also includes a handle 4 for handling the fuel bundle.
2 is also fixed.

Core support plate in the reactor pressure vessel (not shown, not included)
The lower coupling plate 23 is equipped with a pointed head 43 for supporting the fuel bundle 20 in the socket of the fuel bundle 20 .

The distal end of the point is provided with an aperture 44 so that pressurized coolant entering through the aperture flows upwardly between the fuel rods 21.

FIG. 3 is an elevational view (partly a vertical sectional view) of the upper coupling plate 22 to clearly illustrate the support hole 31 and the sleeve 32.
It is.

Figure 4A is the cut plane 4 A - 4A K Tr in Figure 3.
FIG. 4B is a cross-sectional view of the top bonding plate 22, while FIG.
2 is a chart showing the diameter of 0 and the inner diameter of the sleeve 32.

The corner of the upper coupling plate adjacent control rod 11 (FIG. 1) is designated by reference numeral 12.

As previously mentioned, the neutron flux distribution along the transverse direction of the fuel bundle depends on the width of the flow path between the control rods and the fuel bundle.

The enrichment distribution is then selected to flatten the neutron flux and thus minimize power peaking in the fuel bundle.

In the example shown in Figures 4A and 4B, four enrichment levels are used.

In this case, the diameter of the shank 30 varies from the maximum value for the fuel rod with the highest enrichment (position A) to the diameter of the fuel rod with the lowest enrichment (position D).
) to the minimum value.

As a result of such a configuration, the insertion of high enrichment fuel rods into the position of low enrichment fuel rods is prevented, thus eliminating the possibility of excessive power peaking due to misplacement of such fuel rods. .

(In such a configuration, insertion of a low enrichment fuel rod in the position of a high enrichment fuel rod is not prevented.

However, this is not a serious problem.

This is because such a misplacement of the low enrichment fuel rods merely reduces the output of the fuel bundle.

) Note that for the water tube location W, no sleeve is required.

This is because the position of the water tube in the fuel bundle can be standardized.

The support hole 31 can be fitted with various types of sleeves 32 as shown in FIGS. 5A to 50.

In the case of FIG. 5A, the annular sleeve 321
11 so as to contact a shoulder 51 formed therein.

To retain the sleeve 321 in the support hole 311,
For example, a non-interference press fit, tack welding as shown at 52, or upsetting techniques (such as with a punch) may be used.

Note that the lower edge of the support hole 311 is adjacent to the (preferably chamfered) lower outer edge of the sleeve 321 as shown at 53.

In the case of FIG. 5B, the sleeve 322 and the support hole 31
2 have mutually corresponding threads.

In FIG. 5C, a sleeve with a shoulder 54 is fitted into a support hole 313 of constant diameter.

Such sleeve 323 may be held by tight fitting or tack welding.

(After assembling the fuel bundle, coil spring 3 in Fig.
Note that the sleeve 32 is prevented from falling out due to the pressure exerted by 4.

) Described herein is a fuel bundle that includes a sleeved tie plate that indicates enrichment.

If this is adopted, it becomes possible to manufacture and stockpile the coupling plates with holes drilled in advance and to stockpile various relatively inexpensive sleeves, thereby shortening the lead time for manufacturing the fuel bundle.

As a result, a newer reactor transport system 11E' [based on reports,
It becomes possible to select the fuel enrichment to better match the requirements of the core to be loaded with fuel.

[Brief explanation of drawings]

Figure 1 is a schematic plan view of a core cell containing four fuel bundles;
Fig. 2 is an elevational view (in some cases, a longitudinal sectional view) of the fuel bundle, Fig. 3 is an elevational view (in some cases, a longitudinal sectional view) of the upper coupling plate of the fuel bundle in Fig. 2, and Fig. 4A is an elevational view (in some cases, a longitudinal sectional view) of the fuel bundle. A cross-sectional view of the upper coupling plate taken along section 4A-4A in Figure 3; Figure 4B shows the enrichment distribution in a typical fuel bundle and the diameter of the fuel rod shank indicating the enrichment; Figures 5A, 5B, and 50 are perspective views of support holes and sleeves fitted into the corresponding coupling plate sleeves having various configurations. In the figure, 11 is a strut rod, 20 is a fuel bundle, 21 is a fuel rod, 2
2 is an upper coupling plate, 23 is a lower coupling plate, 24 is a spacer, 26 and 27 are terminal plugs, 28 and 30 are shanks, 29 and 31 are support holes, 32 is a sleeve, 35
41 represents a channel, and 45 represents a spacer capturing means.

Claims (1)

[Claims] 1 A plurality of elongated fuel rods are supported between spaced apart upper and lower binding plates, the binding plates having fuel rod support means to which the fuel rods are mounted in a regularly spaced array. The upper end of each fuel rod is adapted to hold the fuel rods, the upper end of each fuel rod being formed with a long shank, the diameter of which is smaller than the diameter of the fuel rod to be attached to the fuel rod support means of the upper coupling plate; The fuel rod support means of the upper coupling plate is comprised of support holes having the same inner diameter, and each support hole is fitted with a sleeve for reducing the inner diameter, corresponding to the enrichment of the fuel contained in the fuel rod. The inner diameter of each sleeve is selected to receive each shank of a matching diameter, thus providing an enrichment indication corresponding to the desired enrichment distribution of the fuel rods within the fuel bundle. A fuel bundle used in large numbers in the core of a nuclear reactor.