DE2036545C3 - - Google Patents

Description

Ceramic Society (1966) from P. Koss Sections 2.2 and 3 on pages 242 to 244

Fuel assemblies for high-temperature reactors or Fig. 6 and 10 known to use sintered plates as gas containing the fuel, usually in the form of 45 feed. In the special case, they lead to coated particles. For this purpose, spherical coating of nuclear fuel particles in the case of moderate fuel particles made of uranium and thorium char sizes over 2 kg of unsatisfactory oxide or carbide is produced, with layers of results. It has been found that precisely pyrolytic carbon alone or in combination with defined flow conditions are enveloped for the coating with silicon carbide. The diameter and carrier gas are necessary and that these such particles are between 100 and 1000 μ. cannot be achieved with porous plates.
The coating is usually carried out in vortices In the reference by JL Kaae (1969) in beds by thermal decomposition of coal - "Journal of Nuclear Materials" only the hydrogen. These layers have the task of calculating radial temperature gradients that hold back through the layers themselves during the fuel and during the burn-off of the fission products arising in the reactor in the particle core in the individual particles. This gives rise to the form; they are negligibly small. Due to the fact that these layers withstand the thermal and mechanical loads and the production of the elements and are not damaged during the burn-off due to the structural changes during irradiation. 60 mechanical tensions occur in the layers It has been shown that the dose of which is calculated in a manner similar to that in fast neutrons has a considerable influence on the literature already mentioned,
which has layers of pyrocarbon; According to the invention, the production takes place the belenstoff shrinks, the fuel core expands from layered fuel parts in that the and there are tensions which lead to the formation of cracks in the amount of per time unit and coating surface of the layer. Attempts have been made to reduce the rate of growth of successive individual layers by means of the coating gas offered on the surface by subtracting various properties

Coating or by increasing the coating gas nut is kept constant during the coating and that the growth rate is equal to the limit growth rate in the characteristic coating zone.

In order to make this problem underlying the invention understandable, must be here on the Coating process will be discussed in more detail.

For coating, the particles are in a fluidized bed, which in the simplest case consists of a to vertical heated tube with a conical

Floor is made. In the top of the Cor _JS opens the

Nozzle through which the carrier material required for whirling

gas (argon, helium) and the coating gas (e.g.

Methane, propylene, acetylene) are blown in.

The hydrocarbon gas is when entering the

Bed heated up and decomposed over several

Intermediate steps to carbon and hydrogen The properties of the particles deposited on the

of carbon depend on the temperature and

on the amount of offered hydrocarbon

gases from; the amount of gas offered results from

the concentration and the total gas throughput or the flow rate. At constant

maintenance of these coating parameters during the as

entire coating process is obtained

a certain coating time at each

salmon speed and the associated

correct layer properties. tungsgasl ^ B

It has now been recognized that there are two causes, 30 surface matched

the changes made during a coating process

genes in growth speed and layer properties:

A process for ^Messun & p _"n ^ StsTchwankungen can Ausbi dung ^ ^^ vorg

^{about dl} , - ^ * _m example of coating

From ^b - ^{x 2} ^ _a j _ter nating fluctuations

charge υυ jd / iv

the anisotropy at giei
speed,
Fig. _ Show.

^ _charge WM 381 the over- fig. _ show. . Fluctuations and the

storage of the changing anisotropy with falling unified anaerization u property sera

Wake-up speed. d ^ b _layer ~ _ge _

used b ^ mmen η ^b ^ _h ^ _{htei ionen} to communicate the values of all ^ ™ ^ei B

strah ^ «^, ^" Jng adientenfrcien layers

For the manufacture W _{will be;}

the following conditions _B

Wake-up speed wedge must be consistent during the ^Λ ) ~ "f L * coating time (see;

I h b η

j; » Wake-up speed must be in all parts

^D > ^ particle bed be the same size.

Bedineune 1 can be z. Am Compliance with the condition 1

^^^ J ^ S ^ J ^ v ^ a and so the ongoing Partike " ^a ^ s ^e ^ ßeschichtungs-

entire pa ^ surface ™ t ^α _hih

one

_{for the as} in

(see the _tapering bed,

tion to let mc ^ ^ine ^ ^k ~ _{is only} eraas eangetromt from a D ^, rich, when the verbal ™ * J ° ^r - _"d J _calibration

almost no relation to the volume de

processing zone g 1 «t ^

upper gp

in the latter case then

Abbot \ * ™ f ^s ^ ™ _{requires that} the Aufwachsges ^ hwnSeft in all parts of the ^g Parükelbettes

1. The coating, which enters the fluidized bed _{35 of the} same size ^ «- £ 5, decomposes while it flows through the particle (see Fig. 1 and bed, so that in the upper part of the ß h

Bettes the coating concentration is smaller than in the lower part. Parallel to the concentration gradient more or less strong temperature gradients occur. Because of the different coating conditions present at different points of the particle bed Different growth rates also occur at these points and layers with the most varied of properties are created deposited. The individual particles

wander through depending on the circulation rate ^ _R ^ _n ^ _nu

the individual coating zones and with larger pitches and the like

the overall layer consists of a series of thinner volumetric 50 fli .dized ™ cells ner individual layers of different properties ^ TS & ^^ f ^ Ä

2. Dtesen ^and alternating fluctuations are superimposed on a uniform, unidirectional change in the _coating .

^^ _s ^ _mgsg approximately ion an B ^e » ^lu ß% _{d volume}

constant isJ; ^ "ρ'rti _k Tlbetti the characteris <i _K -hen

of the entire particle bed aer cna

^ ^ih ^ ^bb ^ "according to size-

«Memspr ^

One possibility is to use ^ emes Gas routing »« ^^ ™ "* ^ J ^" "*

thereby expanded processing zone at constant coating gas flow.

With one of

SGAH-Seibersdorf developed ten-free layers can be achieved

1 sheet of drawings

Claims (3)

overcome. So are ζ. B. Carbide particles with two claims: layers, oxide particles with three layers made of pyro- lytic carbon women and oxide 1. Nuclear fuel particles that are coated with pyrolytic carbon with five layers of pyrolytic carbon alone or in combination with silicon carbide and silicon carbide IB ic κ er α ι c κ c, bid, thereby identified Ranson, Vivanie, Ul-. K. ^lj y ^TOj j,
It was noted that the layers of pyrolytic carbon were next recognized that pyrocarbonic material did not break up any monotonous material layers under neutron bombardment, or alternating gradients of the optical interaction with the inner light, anisotropy and the other properties, namely when they are strongly * anisotropically wise. Model calculations have shown dall 2. Process for the production of coated layers, internal stresses occur. Nuclear fuel particles according to Claim 1, which lead to rupture (literature e.g. J. Yv. 1 radurch characterized that the amount of per dos and J. L. Scot t, Nuclear Applications, VuI _ Time unit and coating surface offered 15 [1966], p. 402). . The degree of anisotropy of the rails of a growth rate by pulling off a batch of particles is determined by the Baconscnen Απιμ, part of the particles from the fluidized bed during tropiefakior indicated that attached to the layers the coating or by increasing the amount of graphite platelets that the stratified gas flow is measured during coating 20 the particle batch during coating / ug -_- is kept constant and that the wax-ups were mixed. The anisotropy factor grows with it speed is equal to the limit growth of increasing anisotropy and is for isotropic layers speed in the characteristic range 1.0. In radiation tests, sxn now has a y. Stratification zone is. shows that a low Baconian anisotropy 3. The method according to claim 2, characterized ge 25 tor ^ for em good irradiation behavior is necessary that the correspondence of dig, but is not sufficient, that is, one finds z. l \. total growth rate and limit up to below particle types with a Bacon factor <1. ( dcfiniet particles residing in it are still intact, as well as those whose layers are torn or due to the use of a gas (literature: irradiation experiment in the DFR guide tube with a defined volume and Dounreay). The resulting investigations into defined particle searches led to the present invention, quantities or by using a cone, which is based on "the knowledge that the specification of the graphite soil, the number of boreholes 35 average Bacon factor and others over the layer of different thicknesses for the injection of averaged properties to characterize the carrier gas as well as single or multiple nozzles layer quality is not sufficient, but that for the coating gas contains is achieved existing property gradients a decisive 40 play a role. It is in itself from the reports of the Germans