DE8904627U1 - Core element base with adjustable throttling - Google Patents

Description

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Intexatom GmbH 89 G 6 7 0 8 OE D-5060 Bergisch Gladbach 1 Core element base with adjustable throttling

The present invention relates to a core element base with adjustable throttling for box-shaped fuel, breeder, reflector or absorber elements of a particularly liquid metal cooled nuclear reactor. The various types of core elements are normally located in corresponding openings of a grid plate with the same external shape and lateral inflow openings and are flowed through by a cooling medium from bottom to top during normal operation of the reactor.

If an equilibrium temperature of the cooling medium is reached at the upper end of these different core elements, which is desired, for example, with regard to efficiency or to avoid thermal cycling stresses on the adjacent components, core elements with different heat outputs should be flowed through by different throughputs of the cooling medium. There are such significant differences between the core elements with the highest and lowest heat outputs that it is normally not possible to achieve the pressure loss in a core element with the lowest output with just one single throttling point. This would involve the risk that cavitation would occur there due to the very high flow velocity in some places, which could lead to the destruction of the directly affected components and also interfere with the acoustic monitoring systems used in nuclear reactors of this type. Therefore, several throttling points connected in series are often necessary. Up to now, such multiple throttling points have been formed by stacking perforated disks, sieves or grids on top of one another. However, the pressure loss of such stacks is, according to the

Assembly can only be changed by removing or adding

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additional throttle elements. This involves considerable effort. The problems in the manufacture and assembly of these core element feet are described in detail in EP-B-O 122 191.

In German patent 15 64 140, the applicant proposed a liquid-cooled nuclear reactor with fuel elements through which coolant flows and which are provided with an adjustable orifice for changing the inflow cross-section. This shows a throttle body which can be adjusted in the axial direction and which forms a variable ring cross-section with a fixed shoulder in the core element base. This ring cross-section can even be reduced during reactor operation by means of a helical spring arranged in the fuel element base and a long, flexible device leading out of the reactor vessel. In the meantime, however, it has been recognized that changing the throttling of core elements in nuclear reactors of this type during operation is not necessary and the effort associated with remote-controlled adjustment is also not desirable.

The object of the present invention is a particularly cavitation-free core element base with adjustable throttling for externally identical but different core elements in terms of their thermal output of a nuclear reactor, in particular one cooled by liquid agmetal. A change in the throttling should be possible as the last step in the finished core element.

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To solve this problem, a core element base according to the first claim is proposed. This throttle body is inserted into the core element base after the completion of the complete core element and is centered there in a corresponding hole. The shoulder is significantly larger than this hole, so that the throttle body cannot under any circumstances protrude upwards from the

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j ·..· ..· 896 670 8DE core element base could be pushed out. This could lead to a significant disruption of the core element cooling. The free ring cross-section between the throttle body and one or more fixed shoulders in the core element base can be changed as required using the height-adjustable and lockable shoulder.

According to the second claim, the height of the throttle body shoulder is adjustable using an adjusting sleeve between the throttle body and the core element foot, the height of which can be changed shortly before assembly. Sleeves of this type can also be manufactured with graduated heights and kept in stock so that only a suitable sleeve is selected when required.

According to the third claim, the locking nut has one or more wrench openings accessible from below, for example a hexagon socket or several holes or radial slots distributed around the circumference into which a suitably shaped wrench tool can be inserted.

In the fourth claim, an alternative for the height adjustability of the throttle body is proposed.

In claim 5, a possibility for securing the throttle body is specified that matches claim 4. The locking nut proposed in this case needs a sufficiently large opening to access the key openings in the throttle body.

According to claim 6, all of the previously mentioned core element feet can be closed at the lower end with a preferably conical part so that the core element with its core element foot can be better inserted into a grid plate from above. The concentric hole should be there in the finished

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core element to enable the height of the throttle body to be measured with a gauge. This hole can also be made large enough in diameter to allow the passage of a key tool for the throttle body and/or

Locking nut is sufficient. Then you can adjust the height of the

throttle body relative to the core element base without having to remove the conical part.

According to claim 7, the throttle body has several throttle points arranged one above the other opposite the core element base, so that the pressure difference to be reduced as a whole does not have to be dealt with by a single throttle point, which can lead to undesirable cavitations,

According to claim 8, the free ring cross-sections of the throttling points should increase from bottom to top, because the risk of cavitation increases with decreasing local pressure.

According to claim 9, the throttle body is centered and supported not only at its lower end but also at its upper end in order to avoid any vibrations in the horizontal direction. This particularly applies to the designs according to claims 7 and 8,

Figures 1 and 2 show two different embodiments of the invention, each based on a vertical longitudinal section through a core element base for a liquid metal-cooled breeder reactor, each with three identical throttle points arranged one above the other.

In Figure 1, the lower end of a known core element 1 is shown at the top, which widens further up outside the figure to form a hexagonal casing box, which in a known manner contains numerous long, thin combustion, breeding,

reflector or absorber elements. The end includes

a core element foot 2, is connected to it by bolts 3

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and ends at a piston ring seal 4, which is known per se and is attached to the core element base 2 with smaller bolts 5. A perforated plate 6 serves as an upper guide and centering for a throttle body 7. In the present case, this throttle body has three curved, conical parts 8, which form a variable ring cross-section relative to fixed shoulders 9 in the core element base 2. Further down, the fuel element base 2 has several elongated inflow openings 10 evenly distributed around the circumference and, below this, a concentric bore as a lower guide and centering for the throttle body 7, which at this point must be slightly larger in diameter than its conical parts 6, because this throttle body must be inserted from below. Further down, the throttle body 7 has a shoulder 11, which must be so large in diameter that it cannot be pushed through the above-mentioned bore in the core element base 2. Between the core element base 2 and the shoulder 11 there is an adjusting sleeve 12, the height of which determines the height of the throttle body 7 relative to the core element base 2. Below the shoulder 11 the core element base 2 has an internal thread into which a locking nut 13 with an external thread fits, with which the throttle body 7 is pressed against the core element base 2 via the adjusting sleeve 12. At the lower end the core element base 2 has a conically shaped part 1* for insertion into a grid plate (not shown) and also a sealing ring seal 15, which is held in place with bolts 16. Part 14 has a through hole 17 on the one hand so that the liquid metal that has penetrated there can drain off and on the other hand so that the set height of the throttle body 7 can be measured from the outside. Locking nut 13 and part 14 are secured against twisting in a conventional manner.

Figure 2 shows an alternative with the same numbers as in Figure 1, whereby the parts that differ from Figure 1 are each marked with a. In this case, paragraph 11a of the

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1 throttle body 7a has an external thread and can be

The height of the core element base 2a can be adjusted by turning the key opening 18 using the corresponding internal thread of the core element base 2a. The locking nut 13a must have a sufficiently large key opening 19 so that, for example, a hexagon socket wrench can access the key opening and, in addition, the bore 17a in the conical part 14a must be large enough for another wrench to access the key opening 19. The alternative shown in Figure 2 has the advantage that the throttle body 7a can be adjusted from the outside without having to remove the conical part 14a. There is a channel between the recess 11 and the core element base 2s from which liquid metal can flow out via bores 20 and 21.
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Instead of the piston rings 4 and 5 shown in Figures 1 and 2, known labyrinth seals can also be used.

The proposed designs allow the

To complete core elements using nuclear technology without the core element base and without subsequent welding work.

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Claims (9)

Protection claims 89 6 6 7 O 8 DE 1. Core element base for core elements arranged in a grid plate of a nuclear reactor, in particular a nuclear reactor cooled by liquid metal; this core element base has lateral inflow openings and a throttle body that can be adjusted in the axial direction and that forms a variable ring cross-section with a fixed shoulder in the core element base, characterized in that the throttle body (7) can be inserted from below with a cylindrical part into a corresponding bore in the core element base (2) and has a shoulder (II) that is adjustable in height and can be locked. 2. Core element base according to claim 1, characterized in that the shoulder (11) of the throttle body (7) is pressed against a shoulder in the core element base (2) via a concentric adjusting sleeve (12) and is secured by a concentric locking nut (13) with an external thread in the Core element foot (2) is attached. 3. Core element base according to claim 2, characterized in that the locking nut (13) has one or more key openings accessible from below, 4. Core element base according to claim 1, characterized in that a shoulder (11a) of the throttle body (7a) has an external thread and the core element base (2a) has a corresponding internal thread and the throttle body (7a) has one or more key openings accessible from below. 5. Core element base according to claim 4, characterized in that the throttle body (7a) is fixed with a concentric locking nut (13a) which 02 01 I) · · f ·· ti MIl III«» 4 If I ······ »Iff I I &bull; · I &Ogr; J J » &bull; U <>·· t · * · f · I uJL * 89 G 6 7 0 8 EN also has one or more key openings accessible from below, as well as a concentric opening as access to the key openings (18) of the throttle body (7a). 6. Core element base according to one of the preceding claims, characterized in that the core element base (2) is closed at the lower end with a preferably conical part (14) which contains a concentric bore. 10 7. Core element foot according to claim 1» dsdurc h ge k e &eegr;'&eegr;&zgr; eich &eegr; e t that the di^osselkrper forms two circular, superimposed throttle points at the base of the core element. 15 8. Core element foot according to claim 7, characterized in that ula ring cross sections of the upper throttle points are larger than those of the lower ones. 9. Core element base according to one of the preceding claims, characterized in that the throttle body (7) carries a concentric pin at its upper end, which is centered with a perforated plate (6) in the core element base (2). 02