DE1571451A1 - HX-30 graphite object and method for its manufacture - Google Patents

Description

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PATENT Attorney DIPL.-ING. RICHARD MOLLER-BÖRNER PATENTANWALT DIPL.-ING. HANS-HEINRICH WEY BERLIN-DAHLEM · PODBIELSKIALLEE 68 MÖNCHEN 22 · WIDENMAYERSTRASSE 49 TELEPHONE: 76 29 07 - TELEGRAMS: PROPINDUS TELEPHONE: 22 55 83 TELEGRAMS: PROPINDUS

17 429 Berlin, June 9, 1966

European Atomic Energy Community (EURATOM), Brussels (Belgium)

HX-50 graphite object and method for its division

The invention relates generally to graphite and its Manufacture and it relates in particular to graphites suitable for use in nuclear reactors »

In nuclear reactors known as gas-cooled high-temperature reactors the fuel material is a carbide of a.nuclear Metal, for example uranium carbide, which is dispersed in a graphite matrix “It was recognized that some of the fission products is lost from the fuel material and these fission products diffuse fairly quickly through the graphite matrix, so there is a risk of contamination of the gaseous Coolant with radioactive fission products existed. In order to reduce this contamination, it was proposed to avoid the the matrix containing the fuel around a graphite fuel - Provide pipe and through the space between the fuel pipe and direct a stream of cleaning coolant through the fuel element The main coolant flow moves around the outside of the fuel pipe. It has been found

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that the graphite of the fuel pipe, insofar as it is v / ineffective intended to prevent the diffusion of fission products from the cleaning stream through the fuel tube into the main coolant reduce it to a minimum, must meet certain criteria »

Numerous graphites have been tested for nuclear purposes, but not all of them have been satisfactory a fuel pipe under the intended operating conditions of the aforementioned reactor type established criteria »

The object on which the invention is based is therefore to create a novel or improved graphite as well as a process for its production »

According to the invention, a graphite object is proposed in which a large proportion of the volume of the open pores consists of pores with a size of 5 W to 10 μm,

while the remaining open pores are essentially micropores with a size of less than 0.1 μm »

In general, there are about 50 of the open pores of pore fi having a size of 5 to 10yum, while the remaining 50 i> of the open pores are smaller than 0.1 / um and a few pores in the order of magnitude of 0.1 to 5 / um available"

It should be noted that a large proportion of the total volume

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of the open pores from a small number relatively large pores results, and it has been found that a graphite with such a pore structure has diffusion properties, those for fuel pipes in a gas-cooled high-temperature reactor are ideally suited «.

It has been found that such graphite can be produced by using a graphite starting material in which essentially all of the particles are larger than about 50 / um »

Thus, according to the invention, there is also a method for production brought a graphite object in proposal that thereby is characterized in that one starts from a graphite powder or milled material, in which all particles have a size of more than about 50 yum, and one that powder with mixing a binder to form a raw mixture, whereupon the mixture is processed to form a raw article, the article fired, the fired article impregnated with a pitch impregnant, the impregnated article fired and the fired impregnated object is heated up to a graphitization temperature «,

The graphite powder used as the starting material preferably contains particles which are essentially within the size range from about 50 µm to about 425 µm, although a little less Proportion, for example 7 percent by weight, particles with

IAD ORKMNAL Q ₀₉₈₅₀ / τ ₆₆₂

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Large sizes above or below each of these limits are allowed is.

Preferred graphite starting ground material is composed by weight of 0 to 2 <fc '- "-' particles with a size of over 422 μm, 43 to 48 # particles with a size between 422 μm and 251 μm, 27 to 28 ° C particles with a Big 251-124 yum, 15 to 17 $ particles having a Gpösse 124-70 / um, 5 to 7 $ particles of a size from 70 to 53 / um and 0 to 7 fo particles having a size of less than 53yum together O

The preferred binder is a pitch based on coal tar with a softening point of 90 G _0. The proportion of pitch used is in the range from 27 to 30 percent by weight of the raw mixture »

The raw mix can be processed using any suitable technique, such as rolling, but is done processing zv / square-wise by means of extrusion, whereby the mixture is preferably extruded twice · with twice In extrusion molding, the binder content is preferably 27.5 percent by weight.

The firing of the molded article can be done either under pneumatic or at atmospheric pressure »The object can be impregnated more than once and after each impregnation process to be burned

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It has been found that objects manufactured according to the method according to the invention have a low permeability constant for viscous substances as well as a low transmission coefficient and they are superior to the other tested materials in this respect. " Using the method according to the invention, it has been found possible to produce approximately 2.5 m long rods with a diameter of 82.55 mm (3 1/4 inches) which meet the requirements for graphite for use as fuel pipes The experiment with gas-cooled high-temperature reactors, known as the Dragon project, suffices ₀

For a better understanding of the invention, some examples of the production of graphite according to the invention are described in detail below.

example 1

The Ausgangsmahlgut was a technique known as nuclear graphite "A" graphite powder for nuclear purposes with the following weight moderate composition: 48 $ particles of a size between 422 / um and 251 / um, 28 $ particles of a size between 251 / um and 124 / um, 17 $ particles between 124 / um and 70 Am and 7 i> particles of a size between 70 / um and 53 / um _o this Graphitmahlgut were gewichtamässig 27.5 # a pitch powder Kohlenteerbaais having a softening point of 90 ° G and a Teilchengröase of less than about 350> um added »

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The millbase and binder were then placed at room temperature chilled in a double cone maker for half an hour and then continue for 45 minutes at a temperature of about 160 C in a Pfleiderer kneader (sigma-bladed dough mixer) warm mixed

The hot mixture was then introduced into an extruder, in which it was heated for 45 minutes at a temperature of 110.degree standliesa · Then the mixture was during an application period « It was extruded at a speed of 76 cm per minute, whereupon it was allowed to cool down. The extruded material was there often in poor condition, showing a rough and / or brittle surface »which is at this stage of the procedure but was irrelevant

The material hardened as it cooled to room temperature, whereupon it is ground to a suitable particle size of less than 6.35 mm (1/4 inch) and put back into the hot kneader was introduced, in which it was further mixed for a period of 45 minutes

After renewed mixing and kneading, the v / lean mixture was returned to the extruder, in which it was before the second extrusion at least 45 minutes with one A temperature of 115 G was left. The second extrusion process took place at an application speed of 22 to 30 cm / in and resulted in a raw rod

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The individual raw bars obtained in this way were each placed centrally in one Flux steel sleeve open at its ends with an inner diameter arranged by about 95 mm (3 3/4 inches) * the annular The seam between the rod and the sleeve was then covered with a coke breeze filled in with a particle size of 124 to 4-22 µm » whereupon the individual pods were surrounded by a pack of ordinary coarse coke "

The firing plan was set up as follows? Warming up from room temperature up to 150 ° C at 20 ° 0 per hour, from 150 ° G to 200 ° C at 6 ° G per hour, from 200 ° C to3 550 ° G at 3 ° G per hour, from 550 ° G to 700 ° G at 6 ° C per hour and from 700 ° G bia 850 ° G at 20 ° G per hour The maximum final temperature of 850 ° G was then held for four hours, after which the oven was allowed to cool to room temperature, which took about four days in Claimed <> During the performed at atmospheric pressure During the firing process, a neutral atmosphere, for example nitrogen, was used

The individual rods were removed from the sleeves by held the sleeve in a tight-fitting jig and the rod using a 10 ton pressure cylinder squeezed out

The ends of the rods were found to have flared and were brittle internally over a distance of approximately 3 "(76.2 mm) from each end, but after removing these ends, the remaining rod was found to be homogeneous» ■ · -. · ■■ BAD OFUQlNAL 009850/1662

The fired rod was then lifted about 0.635 (0.025 inches) from the surface and heated to about 150 ° C and held at this temperature for half an hour at a pressure of about 5 torr before being in a 160 G oil-based pitch impregnating agent with an extension Spunk t of about 90 ° C were immersed · Above the impregnating agent nitrogen was up to a pressure of 28 kg / cm (400 psi) were introduced, whereupon this pressure was maintained for 3 hours «

The rods were made _t the impregnating away, were what the impregnated rods on a similar plan, as it was used when burning the Rohstäbe, post-baked. " The maximum temperature reached was 850 C in all cases, but in some cases the minimum heating rate was now 6 ° G per hour instead of 3 ° C per hour.

The refired rods were then placed in a graphitizing furnace and placed in an argon atmosphere for a period of time from 8 hours to a graphitization temperature of Heated 2 700 ° C · The graphitization temperature was maintained for half an hour, after which the furnace was opened Let cool down to room temperature

Possible changes to this process include bringing in of the hot rod from the first extrusion process directly into the hot kneader, in order to heat it up again

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and mixing, instead of letting the extrusion cool down, firing or post-firing under pneumatic pressure, both

for example "using 7 kg / cm (100 psi) compressed Nitrogen, except for at least 550 ° G and carrying out more than one impregnation and machinability process

Examples 2 to 10

The procedure detailed in Example 1 was followed Made on some of the minor changes indicated in Table I *

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Table I.

CD O CD OO cn ο

cn cn to

example Binary
medium-
salary
(Wt. ^) Type of
Burning number of
Impregnation
struggles Type of
Burning graphite
density
O / cm ⁵ ) - ^B o (cm) _D : ■■■ m ² /lake) CVl 27 ¹ A U . 2 U 1.76 4.2 χ ΙΟ " ¹¹ 3 .8th X ΙΟ " ¹² 3 27 ¹ A U 3 U 1.81 5.3 X 10 ~ ¹² 1 .8th X ίο " ¹⁰ 4th 27 ¹ A ü 2 P. 1.80 6.6 χ ΙΟ " ¹² 1 .0 X ίο " ¹² 5 27 ¹ A P. 1 U 1.77 7.4 χ ΙΟ " ¹¹ 1 .5 X ίο " ¹⁶ 6th 27 ¹ A P. 2 U 1.80 2.5 χ ΙΟ " ¹¹ 4th .5 X 10 " ¹⁵ 7th 28 P. 2 U 1.83 2.3 χ ΙΟ " ¹¹ 1 .1 X ίο " ¹² 8th 27 P. 3 U . 1.83 4.0 χ ΙΟ " ¹² 1 .9 X ΙΟ " ⁹ 9 27 ¹ A P. 1 P. 1.79 " 2.5 χ ΙΟ " ¹¹ 2 .1 X ίο " ¹⁰ 10 27 ¹ A P. 2 P. 1.82 4.1 χ ΙΟ " ¹² 2 .1 X ίο " ⁸

O I.

tn

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In Table I, U means that the burning process takes place at atmospheric Pressure and P, that the burning process was carried out under pressure, while B is the permeability constant viscous substances and D the degree of permeability to fission product gases is that as

1 ^ D ¹ = -

is defined, wherej

j is the flow of fission product gases through graphite of thickness L; and c is the concentration on the graphite side. is while the concentration on the other side is zero

It was determined that in the fuel tube of a gas-cooled high temperature reactor (for the Dragon Prodakt) to use graphite to achieve satisfactory gas flow rates into the space between the fuel element and the fuel tube and to maintain a sufficiently low fission product concentration in the main coolant B and D less than 3 x 10 "cm or« 10 * "cm / ae-c must be ₀ In all cases it can be stated that the value D is satisfactory, but that in Examples 2 and 5 the value of B is above the specified maximum value © However, it is clear from Examples 3 and 6 that the value of B can be reduced to a satisfactory Y / ert by means of a suitable number of impregnations and that the products after a single additional impregnation

BATH ORIGINAL

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Examples 2 and 5 then meet the requirements (see examples 3 and 6) β It can also be concluded that a satisfactory Product is obtained more easily if at least some of the firing processes are carried out under pressure, and that at firing under pressure requires fewer impregnations, in order to obtain a product in which the values of B and D are below the specified limits (see example 9 »in which, after a complete firing under pressure, achieves a satisfactory product with just one impregnation treatment will) »Examples 7 and 8 show that a minor Modification of the pitch content is possible and you still get a product graphitized in a suitable form » It should be noted that a satisfactorily graphitized product

• 2

generally has a density of at least 1.80 g / cm, so that after it was found that the densities of the fired and graphitized products were very similar to each other is assumed that a fired product density of 1.80 g / cm2 indicates that when graphitizing such Body the end product is likely to have satisfactory properties »

Example 11

The starting graphite grist according to Example 1 was 28 percent by weight Tar added, extruded twice, at a pressure of 7 kg / cm (100 psi) up to 600 ° C and then at atmospheric Pressure fired up to 850 ° C, graphitized, impregnated once, fired under pressure and again graphitized die

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1 - »112-4 2«

Values of B and D were 4.1 χ 10 cm and »1.2 χ 10 cm / seo« respectively

This example showed that when using the specified Regrind can be achieved by means of one or more impregnations with pitch suitable products that these impregnations but must be done before the material is graphed *

Examples 12-17

The procedure of Example 1 was followed with minor modifications as in Examples 2 to 10 repeated using different starting material · The details, des the respective grist are given in Table II, while the results obtained using these grinds in the Table III lists · "'

Table II

Jiahlgut
& r Composition (Gewo $>) 251-422
/around 124-251
yum 70-124
/around 53-70
yum less than
53 / um 4th
6th
7th 17th
26th
50 19th
34
8th 12th
18th
12th 6th
7th
7th 46
15th
23

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It is found that the value of D is by no means satisfactory was, although the treatment used was such that one obtained a satisfactory one with the millbase according to Example 1 Product would have received (see in particular Examples 14 and 17)

Ea is assumed that the failure, with these starting grinds, to achieve satisfactory products, the high proportion of particles with a size of less than 53 / .mu.m, the they contain, is to be attributed, from which an unsuitable pore structure of the graphitized product results, so that so the pore structure seems to control the value of D »

ORIGINAL INSPECTED

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Table III

example Regrind number of
btrangpres-
sings Bindemit
tel salary
(Wt. ° / ₀ ) Type of
Burning number of
Impregnation
struggles Type of
Burning graphite
density B _{0 2} D ¹
(cm / see) 4th
4th 1
2 31
29 ¹ no 2 U
U CO CM U
U 1.80
1.81 CM CM
O- O
X X
co CM
• *
H Cv | 2.6 χ 10 ~ ⁵
1.0 χ 10 " ⁴ 4th 2 31 P. 1 P. 1.87 8.3 X 10 ^r13 6.5 χ io " ⁵ 6th 3 26V2 U 3 U 1.85 3.2 χ 10 " ¹³ 6.0 χ OK "" ⁵ 6th 3 26th P. 1 P. 1.85 4.2 x 10 " ¹³ 3.3 x OK " ⁵ 7th . 2 27 P. 1 P. 1.81 7.6 χ 10 ~ ¹³ 3.1 x OK " ⁵ 12th
13th 14th 15th 16 17th
ο
! ___

Examples 18-25

To the highest permissible proportion of particles with a size of less than 53 / in order to determine, further experiments were carried out. It is essential to determine that in the In economic practice, sieving below about 70 / µm is not possible * However, careful grinding procedures lead to one Proportion of particles with a size of less than 53 μm Range from 2 to 5 # It is therefore essential to determine that these regrinds are satisfactory »Details of the regrinds are given in Table IV and those with them The results obtained are shown in Table V. It turns out that up to 7 ^ particles with a size of less than 53 / um are tolerable

Table IY

Regrind
err. above
422
/around composition 124-251
/around (Weight? I 53-70
/around less than
53 / um 76A 2 251-422
/around 27 70-124
/around 6th 3 76B 1 45 28 17th 5 5 760 2 46 27 15th 6th 7th 43 15th

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ORIGINAL INSPECTED

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d —J Q · OO cn VO OO O H OO Oil O O Ρ »· OO t- O ri OO OO οο OO H H ri OO ri H S B cn Η H : 4 * 3 ö
-P Φ
toi ° • η , P P. P. Αι π -f "
Il __ ^
H At t Oil CM. CO CM CO H * CM ; I.
approx te I. »; A. P. •H A. Ct P » ΙΛ ρ ». • ρ- 'm
i-i. in H VO ι ». VO S. P ^ H H VO H r-l O H OO if O «TV cn #
H p «. OO IA Ρ «· P ^ H- H* Ρ «. H H CM H CM Oil oT s-
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CM Oil CO
Oil gens CM OO
Oil - φ 760 to
(D H CM Ο » CO ΙΛ «9 O CM Oi τι * Oil CM CM

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Example 26

Instead of using reactor graphite "A" to form the starting material, another graphite was used for nuclear engineering Purposes used of a grist with a composition like the millbase used in Examples 1 to 11 resulted in This millbase underwent a treatment similar to that of Example 1 subjected, the burning and maching operations all being at atmospheric pressure and the fired item was impregnated twice · IXLe fourth of B_ and, of D be

•• 11 18

for the graphitized end product 2.0 10 or 6.1 χ 10. This experiment: shows that the invention is not limited to the use of a specific type of graphite to form the starting material.

Patent claims:

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Claims (1)

Patent withdrawn 1 »Graphite object, characterized in that a large proportion of the volume of the open pores consists of pores with a size of 5 μm Ms 10 μm . consists, while the remaining open pores are essentially micropores with a size of less than 0.1 / um « Article according to claim 1, characterized in that about 50 # of the open pores consist of pores with a size of 5 to 10 μm, while the remaining 50 i> of the open pores are smaller than 0.1 μm and a few pores in. of the order of 0.1 to 5 μm are present 3 »Object according to claim 1 or 2, characterized in that the permeability constant to viscous substances • ■ • 11 ρ less than 3 x 10 cm and the degree of penetration opposite Fission product gases is less than 10 ~ om / see » 4. A method for the production of a graphite object, characterized in that one of a graphite powder or -mahl * · 009850/1662 'w V 1 i 157H51 goes well, in which the particles essentially have a size of meh ^ ls about 50 / .mu.m, and this powder mixes with a binder to form a raw mixture, whereupon the mixture is processed into a raw article to form the fired article impregnated the fired article with a pitch impregnant that impregnated Fired article and the fired impregnated article is heated to a graphitization temperature will ο 5 ο method according to claim 4, characterized in that the Ausgangsmahlgut contains particles / um / um are within the size range of 50 to 425, wherein no more than · 7 weight percent of the millbase are above or below this size range ₀ The method of claim 4 oder.5, characterized in that the Ausgangsmahlgut that a weight basis from 0 to 2 ° / o of particles having a size of more than 422 / um, 43 to 48 $ particles of a size from 422 to 251 / um, 27 to 28 ^a / o particles with a size between 251 and 124 / um, 15 to 17 ° ß> particles with a size between 124 and 70 / um, 5 to 7 ^σ /> particles with a size between 70 and 53 / um and 0 to 7 i> particles with a size of less than 53 / um composed » 009850/1662 -ir- Method according to one: the "Ans prüche 4 to 6, dadurGh; labeled in * characterized in that the binder iat a KohlenteerpeGh *: ,, the ewichtaprozent · G in a Verhältnis.- from 27 to JQ ^of:;. Is used gemisehs" 8ο method according to one of claims 4 to 7, characterized in that; gefe draws ,, that the impregnation · and. Burning processes before Cr'raphitieren v / be repeated "