WO2002061761A1

WO2002061761A1 - Reflector block for a high temperature reactor

Info

Publication number: WO2002061761A1
Application number: PCT/DE2002/000068
Authority: WO
Inventors: Heiko Barnert; Jasbir Singh
Original assignee: Forschungszentrum Jülich GmbH
Priority date: 2001-02-01
Filing date: 2002-01-11
Publication date: 2002-08-08
Also published as: ZA200306759B; DE10104404C1

Abstract

The invention relates to a reflector block for a high temperature pebble-bed reactor, comprising at least one vertical groove (10) that receives a tongue (11) and at least one horizontal groove (15, 17) that extends on the upper and/or lower base face. It was found that the use of a tongue and groove system in all horizontal joints of the inner and outer ring wall of the side reflector reduces leakages. The inventive blocks with horizontal joints and the respective exactly fitting tongues give a so-called anti-gape sealing system. Due to its advantageous form gaps that occur can be geometrically closed, the leakage can be restricted to an admissible extent by suitable fitting tolerances, and the gap can be easily closed when the normal operating temperature gradients disappear. A suitable fitting tolerance for fulfilling the two above-mentioned requirements is for example the fitting tolerance class mobility with ample play .

Description

Reflector block for high temperature reactor

The invention relates to a high-temperature reactor (HTR), in particular the side reflector of such an HTR, comprising individual reflector blocks.

State of the art:

In "Construction of the HTTR In-Core Components", JAERI Conference, 1996, a high temperature test reactor (HTTR) is described. This high-temperature reactor, constructed by the Japan Atomic Energy Research Institute (JAERI), comprises several hexagonal graphite blocks (in-core components), so-called fuel assemblies and interchangeable reflector blocks. These are surrounded by permanent reflector blocks (PRBs) that are held together by an encompassing system.

The reflector blocks surrounding the in-core components are geometrically adapted to the hexagonal graphite blocks. Eight individual permanent reflector blocks are arranged in vertical columns, the entire circumference being formed by 12 columns. Horizontal and vertical springs on the outside of the permanent reflector blocks serve to position the individual blocks against each other. Furthermore, the permanent reflector blocks have horizontal and vertical sealing elements on the outside, which serve to limit leakage flows.

Project information 4, March 1973, entitled: 300 MW THTR Nuclear Power Plant Uentrop, published by the THTR consortium, discloses a high temperature pebble-bed reactor (HTR) which, in addition to the actual pebble stack, has ceramic internals made of graphite and coal stone. These ceramic internals include the side reflector, comprising an inner and an outer reflector ring wall. These consist of individual basic elements (reflector blocks) made of ceramic material, e.g. As graphite or coal stone, and usually have the shape of a prism with a base surface that corresponds to a symmetrical trapezoid. Several reflector blocks placed flush on top of one another and held in mutual positioning by dowels in the base areas form a column. Several columns placed side by side form the ring walls of the side reflector. For the inner ring wall there are 72 columns, for the outer 24. The individual reflector blocks of the columns of the inner ring wall are connected to one another by so-called wedges, of the same height as the reflector blocks. The function of these wedges are tongues and grooves. The inner ring wall is mainly used for the reflection of neutrons, the outer one is mainly used for thermal insulation. The mechanical forces from the filling with spherical fuel elements are transferred directly from the pillars to a metal circumferential wall (called a thermal shield for the THTR). The columns are regularly set up in such a way that a gap, also called a column gap, remains between every two columns in all operating states. According to the prior art, the column gaps are closed by wedges in the groove system, as a result of which the leakage current through the column gaps is limited to an admissible level. The leakage flow through the horizontal joints between the layers of the reflector blocks is limited to a permissible level by the joints of the reflector blocks standing on top of one another according to the prior art.

However, a disadvantage in this construction of a HTR is that an unexpected decrease in temperature by measuring comparable ^■> different temperatures was found in the individual holes of the side reflector in the commissioning phase of the THTR. As an explanation for this temperature drop, three bypass mass flows of a total of 7% of the cooling mass flow at the core outlet are regarded as justification, as in the dissertation: Jürgen Hoffmann, "Plant simulation of the THTR-300 using the example of recorded start-up attempts", RWTH Aachen, day of the oral Test: May 11, 1990. The test result can be explained by the fact that some horizontal joints between the layers of corresponding reflector blocks become gaping due to the conditions of normal operation and thus permit these bypass currents understand that temperature gradients in the ring walls of the side reflector mean different thermal expansions of the inside of each column from the outside would lead to bending outwards if the columns were freely installed, but is regularly prevented by a metallic peripheral wall that serves to absorb the force. The columns are kept straight through the metallic circumferential wall regularly all around, but not uniformly over the entire height of the side reflector, so that horizontal gaps become disadvantageous in some places. A special characteristic of these Klaff columns is that they do not appear in all positions of the ceramic internals (inner and outer side reflector), but only indefinitely in some places. The temperature measurements of the THTR indicated only three altitudes, in which a horizontal gap gap occurred. This indeterminacy is based on the fact that the individual reflector blocks of each column are not individually guided, but are mainly lying on top of one another due to their mass and fixed by dowels.

Object of the invention

The object of the invention is to provide a simpler structure for a side reflector of a high-temperature reactor (HTR) than is known from the prior art, which also largely prevents leakage currents. Furthermore, it is the object of the invention to meet special conditions from the application for a helium turbine process with regard to loads from larger pressure differences and pressure transients The object is achieved by a side reflector with individual reflector blocks, a single reflector block comprising the entirety of the features according to claim 1. Advantageous embodiments of the reflector block according to the invention result from the related claims.

Subject of the invention

The reflector block for a high temperature reactor according to claim 1 comprises at least one vertical groove

Picking up a spring. A groove is to be understood as an elongated recess in the surface for receiving additional construction parts by counterparts corresponding to the groove, such as wedges or springs (tongue and groove system). In particular, it is a recess with a rectangular profile, which is formed over the entire height of the side surfaces (vertical end face) of the reflector block.

The reflector block according to the invention also has at least one further horizontal groove.

This horizontal groove is advantageously formed over the entire width (horizontal face) of the reflector block.

In particular, the reflector block has a horizontal groove on the upper and lower end faces.

A further advantageous embodiment according to claim 4 provides that the vertical groove, or the vertical grooves, and the horizontal groove, or grooves lie in one plane. Especially for a block where two side faces (vertical end faces) and grooves are formed on the two base faces (horizontal end faces), this configuration advantageously leads to a circumferential notch.

A further special embodiment according to claim 5 provides for the dimensions of the vertical and horizontal grooves to be dimensioned similarly.

It was found within the scope of the invention that a tongue and groove system in all horizontal joints of the inner and the outer ring wall of the side reflector contributes to the solution of the task. The blocks according to the invention with horizontal joints and precisely fitting springs result in a so-called anti-gap sealing system.

Due to its expedient shape, the Klaff gaps that form are geometrically closed, the leakage flow is limited to an acceptable level by means of appropriate fit tolerances, and the closure of the Klaff gaps is allowed without hindrance when the normal operating temperature gradients disappear. A suitable fit tolerance to meet the two aforementioned requirements is, for example, the fit tolerance class "mobility with plenty of play".

From the point of view of closing gaps, the tongue and groove system in the horizontal joints is similar to the tongue and groove system in the column gaps known from the prior art. The difference, however, is in the first mentioned system in the mecha- nik the formation and closure of the gap gap, which requires a fit with a larger game than the latter. The boundary condition applies that the functions of both systems do not interfere with each other. This is achieved through appropriate shaping.

Special description part

The invention is explained in more detail below by figures and three exemplary embodiments. Show it:

Figure 1: Inner side reflector of a high temperature reactor (HTR) with a vertical tongue and groove system according to the prior art (the arrangement of the dowels has been omitted) Figure 2: Formation of gaping horizontal gaps

(Gaping gaps) due to normal operating temperature gradients when kept straight through a lateral peripheral wall

Figure 3: Inner side reflector of a high-temperature reactor (HTR) with an additional horizontal

Tongue and groove system (anti-gap seal)

Figure 4: Embodiment of an anti-gap seal in different sectional representations

Figure 5: Embodiment of an anti-gap seal in different sectional representations

Figure 6: Embodiment 1: Inner side reflector of an HTR Figure 7: Embodiment 2: outer side reflector of an HTR

FIG. 8: Embodiment 3: inner side reflector of an HTR. FIG. 1 shows part of the inner ring wall of a side reflector for a high-temperature reactor, comprising four reflector blocks 1 a, 1 b, 2 a, 2 b. Blocks la and 2a, like blocks lb and 2b, are arranged as a column, the individual blocks being fixed flush with one another by dowels (not shown in FIG. 1). Due to the design, there is a column 9 between the columns. This gap takes into account the fact that the reflector blocks expand when the temperature rises. This effect is partially absorbed by the gap 9.

The individual blocks have vertical grooves 10 on each of two opposite side faces (vertical end faces). The grooves are arranged in such a way that the grooves complement one another in a type of guide in the case of two adjacent blocks. A geometrically coordinated spring 11, which is also called a wedge, fits into this guide. This tongue and groove system serves in particular to seal the gaps 9 between the individual blocks of a reflector wall. This design corresponds to the state of the art for both the inner and the outer side reflector wall of a high-temperature reactor.

FIG. 2 explains the effect that individual gaping gaps arise in a few layers of blocks of the reflector wall. In Figure 2a is a reflector column with the Blocks 1 to 7 shown in section, namely in the installed state, or for conditions of constant temperature. The blocks are mutually fixed and positioned vertically by dowels. The vertical tongue and groove system is used for sealing. FIG. 2b shows the same reflector column under normal operating conditions. Inside, ie towards the ball core, the temperatures are higher. This applies both to the outer reflector wall, the function of which is the insulation, and to the inner reflector wall. The higher temperature leads to greater thermal expansions on the inside of the reflector wall compared to the outside. This would lead to a bending of the reflector column to the outside if it were installed freely. However, this is prevented piece by piece by keeping the surrounding wall straight in that a few horizontal joints become gaping to compensate for the height of the thermal expansion difference, that is, so-called gap gaps are formed. The number of gap gaps and their position is determined by tolerances and the load transfer to the outside. If the difference in thermal expansion of the blocks of the columns were to be distributed evenly over all layers, this would require considerable construction effort. FIG. 2 b shows the formation of a gap gap 12 between the blocks 4 and 5 in a greatly exaggerated manner. As a result, they lie edge-on-edge and are arranged slightly tilted relative to the tilting edge 13. Such gap gaps regularly result in large leakage currents, which have a disadvantageous effect on the operation of the reactor. This should definitely be avoided. From the experimental results of the commissioning of the THTR, it can now be concluded that gap conditions arise due to the conditions of operation, namely by gaping in the outer area with edge-to-edge standing in the inner area, here referred to as tilting edge. To close these gap gaps, a further tongue and groove system is introduced according to the invention, as is illustrated in FIG. 3.

3 shows, similarly to FIG. 1, part of a side reflector for a high-temperature reactor, comprising four reflector blocks 1 a, 1 b, 2 a, 2 b. Furthermore, the column gap 9 between two reflector columns and a vertical spring (wedge) 11 are shown. According to the invention, the reflector blocks now additionally have horizontal grooves 15 and 17, respectively. The geometrically precisely fitting horizontal springs 14 serve as a seal for the grooves 15 and 17. They form the tongue and groove system in the horizontal joints. With the tongue and groove system, it is arranged in a functionally coordinated manner in the column columns.

The gap gap 12 is closed by springs 14 which lie in the grooves 15 (in reflector block 1a) and 16 (in reflector block 1b) and 17 (in reflector block 2a) and 18 (in reflector block 2b).

This tongue and groove system is advantageously arranged in the horizontal joints so that it lies in the same plane as the tongue and groove system in the column gaps. This results in a circumferential groove in the individual reflector blocks. Appropriate dimensions of the two tongue and groove systems ensure that the mating surfaces, which function here as sealing surfaces yaw, the two systems merge. The arrangement ensures that columns are closed to a maximum.

Figures 4 and 5 show advantageous arrangements of the two tongue and groove systems based on different sectional drawings.

Figure 4:

By appropriately selecting the tolerances of the grooves and the springs in both systems, the required qualities of the fit clearance, namely a relatively large clearance for the tongue and groove system in the horizontal joints 15, 16, 17 and 18 with tongue 14, are at relative small play for the tongue and groove system in the vertical grooves 10 with the tongue 11 can be achieved.

It can make sense in terms of production technology to ensure that the grooves of the two systems, because they merge into one another, also with the same tolerance, e.g. B. H7, and to adjust the different games by corresponding tolerances of the springs of the two systems, z. B. H7 / g7 and H7 / e7.

FIG. 4 shows an arrangement with a "continuous" spring 14, ie the spring 14 covers the column gap 9 in that it lies in the grooves of two columns a and b. This arrangement is advantageous because the greatest geometric coverage of possible gap gaps is achieved and the possible displacement of the spring 11 for each spring 11 is prevented individually by the spring 14 by positive locking. Figure 5:

In contrast, FIG. 5 shows an arrangement with a “non-continuous” spring 14, which also achieves the object on which the invention is based and which fulfills the requirements set therein.

Embodiment 1, Figure 6:

Reflector block and tongue and groove systems in the horizontal joints for the inner wall of the side reflector.

In FIG. 6, the reflector blocks 1a and 2a represent a left column, reflector blocks 1b and 2b represent a right column (viewed from the inside). In between is the column gap 9. This is closed by springs 11, which lie in the associated grooves 10. The positioning of the reflector blocks in the columns and the columns in the base plate and in the cover plate takes place by means of the dowels 19, which together with the circular depressions in the base surfaces (the upper and lower) of the reflector blocks functionally designate a spring - Show grooves system. The bore 20 regularly receives a reflector rod sleeve and serves the function of switching off. Up to this point, this paragraph describes the state of the art.

When the high-temperature reactor is in operation, the gap gap 12 is formed by rotating individual blocks around the tilting edge 13. The corresponding layers, lower layer, represented by reflector blocks 1a and 1b and upper layer, represented by reflector blocks 2a and 2b, are after relative rotation around the tilting edge 13 Corner on corner. The gap gap 12 is closed by spring 14 concluded. The associated halves of the groove are marked with 15, 16, 17 and 18.

The functional dimensions and fit of the tongue and groove system in the horizontal joints 15-18 are e.g. B. 60 mm, H7 / e7 or e8, which sets a larger game than the tongue and groove system 11/10 in the column columns 9 with, for example, 60 mm, H7 / f7. The longitudinal dimension of the spring 14 is selected such that it advantageously spans two adjacent columns, with which a maximum gap closure is achieved.

Embodiment 2, Figure 7:

Reflector block and tongue and groove systems in the horizontal joints for the outer wall of the side reflector.

FIG. 7 shows a second exemplary embodiment, which is almost identical to exemplary embodiment 1. The difference lies in the spring 14, which is divided into two in this second exemplary embodiment (14a and 14b). The shape of the reflector block for the outer wall is correspondingly represented, represented by reflector block la. The associated horizontal grooves are angled. There is no hole 20 for switching off here; but instead the bore 21, which serves the function of supplying the cooling gas (prior art). The dowel 22 serves for the vertical positioning of the reflector blocks of the outer wall, similar to dowels 19 for those of the inner wall. Embodiment 3, Figure 8:

Inner wall with tongue and groove system in the horizontal joints in an interrupted arrangement, in contrast to the two previous embodiments with continuous arrangement.

The description corresponds to that of the first embodiment. The only difference is that the tongue and groove system in the horizontal joints is interrupted and the column columns are longer. In this arrangement, the gap gap 12 is not closed in the area between the end faces of the springs 11. However, this arrangement also does justice to the task.

Legend for the figures:

1,2,3,4,5,6,7 reflector blocks in different

Altitudes la, lb reflector blocks in a lower position

2a, 2b reflector blocks in an upper position

8 outer metallic conversion

9 vertical gap

10 vertical groove (half of the groove) 11 vertical tongue (key)

12 horizontal gap, gap gap

13 tipping edge

14 horizontal tongue 15,16,17,18 horizontal grooves (groove halves) 19 dowels for inner wall

20 Hole for switching off for reflector rod sleeves

21 Hole for the supply of the cooling gas

(Helium)

22 wall anchors

Claims

P a t e n t a n s r u c h e

Reflector block (1) for a high-temperature ball-heap reactor, comprising at least one vertical groove (10) for receiving a spring (11), characterized by, at least one horizontal groove (15, 16, 17, 18) on the top and / or the lower base side runs.

2. reflector block, according to the preceding claim, characterized in that the horizontal groove (15, 16, 17, 18) is formed over the entire width of the reflector block

3. reflector block, according to one of the preceding claims, characterized in that both the vertical grooves (10) and horizontal grooves (15, 16, 17, 18) lie in one plane.

4. reflector block, according to one of the preceding claims, characterized by the same profiles for the vertical groove (10) and the horizontal grooves (15, 16, 17, 18).

5. reflector column, comprising at least two reflector blocks (1, 2) according to one of the preceding claims, with at least one to the horizontal grooves (15, 16, 17, 18) corresponding geometrically corresponding spring (14).

6. reflector wall comprising at least two reflector columns according to the preceding claim 5.

7. reflector wall, according to the preceding claim with a spring 14 which spans two adjacent columns.

8. reflector ring wall, comprising radially arranged reflector columns according to claim 5 or reflector walls according to claims 6 to 7, characterized by at least one horizontally circumferential tongue and groove system (15, 16, 17, 18 and 14).