JPS60198485A - Multilayer coated nuclear fuel particle - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] TECHNICAL FIELD The present invention relates to an improvement in a multiple-enforced nuclear fuel single particle.

As a fuel for a high-temperature gas reactor, particles are used in which a fissile material is used as a core and the outside thereof is coated with heat component #r carbon or silicon carbide. This coated fuel particle.

It is required that the overall breakage rate be low during manufacturing and use in the coating process and compact molding process.

The present invention provides coated fuel particles with a low breakage rate by devising the structure of the coating layer of coated fuel particles.

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Y-! It was made to wait for 1S Hr of confinement of I2η, and from the inside to the outside of the cedar lik square) degree heat J! Pf, carbon, pyrolytic carbon layer, silicon carbide 1, teeth 1w pyrolytic carbon coated, silicon carbide 1, 1 dust is theoretically the best dog death book ( , 3,215,9/atη). 417. of silicon carbide Iso CIX river-like fission products. It plays the role of barrier and [7 roles 1 to 11, and the role of particle size θ]. In order to eliminate the role of M people, silicon carbide such as 1' M degree silicon carbide 1
If the stomach is naked, it may get wet during handling during covering, which may eventually cause damage. In the compact molding process.

The addition of compression carts to the silicon carbide layer may lead to failure. Additionally, during use, the silicon carbide may be damaged by tensile forces caused by internal pressure due to the accumulation of gaseous fission products within the coated fuel particles.

TRl5O(11) type coated fuel particles have high-density pyrolytic carbon layers inside and outside the silicon oxide layer, and the outer pyrolytic carbon layer may be damaged by its own shrinkage mainly during use. , subsequently the silicon carbide layer may cause failure due to the tensile stress caused by the internal pressure. If there is a low-density IW silicon carbide layer between the A silicon oxide layer and the outer high-density pyrolytic carbon layer, the stress caused by irradiation shrinkage of the high-density W pyrolytic carbon layer can be alleviated, and damage can be prevented. I can do it.

In addition, if there is a low-density silicon carbide layer between the silicon carbide layer and the inner pyrolytic carbon layer, it can alleviate the tensile stress in the silicon carbide layer caused by the increase in internal pressure due to the accumulation of gaseous fission products. It could be reduced.

According to experiments conducted by the present inventors, a layer of low-density pyrolyzed carbon and a layer of areal-density pyrolyzed carbon were applied to the core of a simulated nuclear fuel material by a known method, and then a layer of pyrolyzed carbon with a density of 3.12.9/Cn1~ 3.1
The one with sg/7 silicon carbide coating.

Density required for solid fission product confinement: 3.20
It was found that the failure rate during aging was two to three orders of magnitude lower than that of silicon carbide coatings with a g/cri of 1 or more.

Based on this knowledge, the present inventors previously determined that in multi-coated nuclear fuel particles having a silicon carbide coating layer as a solid fission product confinement layer, the inner 1μ of the silicon carbide layer ([and/or the outer 11111 The present invention provides "multi-city nuclear slag" particles characterized by flowing at least one layer of silicon carbide having a lower density than the silicon layer (%Gan Sho 58-0174).
No. 15). however.

These particles still had some inadequacies against the Sanshakei army.

The present inventors attempted to change the density of the silicon carbide layer in the direction of the thickness of the layer and developed the present invention.

According to the present invention, in a multi-If coated nuclear fuel particle having a silicon carbide coating layer as a solid fission product confinement layer, the silicon carbide layer changes from the inside to the outside (from low density to high density from the inside toward the Coated fuel particles are provided with a transition from *m to low density.

In the present invention, the word transition does not necessarily mean continuous change, but has a meaning similar to continuous.

It is known that pyrolytic carbon layers are formed by thermal decomposition of hydrocarbons, and silicon carbide layers are formed by thermal decomposition of silane compounds, and that layers of various densities are formed depending on the conditions of thermal decomposition.

Next, the present invention will be explained by examples.

Nuclear fuel material (UO2, (U Th ) 02 + (U
-, l)++) 02) centering on the core, a low-density pyrolytic carbon layer, a sieve-density pyrolytic carbon layer, a silicon carbide layer,
An areal density pyrolytic carbon layer was applied.

℃ UO2 fuel nuclear particles with a diameter of 60 (l μm) are
Acetylene is used as a raw material gas at a coating temperature of 60 mm.
A low-density pyrolytic carbon layer with a thickness of μm is formed, and a layer of 1 μm is formed on the outside.
Propylene was used as the raw material gas at 440°C.

A high-density (W) pyrolytic carbon layer with a thickness of 30 μm was applied.

A silicon carbide layer is applied on top of this, and a high-density silicon carbide layer of 3.20 g or more is obtained at a coating temperature of about 1600°C or more, while a low-density silicon carbide layer of about 3.18 g/i or less is obtained. , obtained at a coating temperature of about 1500° C. or less. A good coating speed is 0.3 to 0.5 μm/min.

That is, hydrogen was bubbled and vaporized into methyltrichlorosilane kept at 25°C at a flow rate of 1001/min for 10 minutes at 1400°C at a hydrogen flow rate of 2.5 d/min.
．． A silicon carbide layer of 1.2 g/Cnt was applied to a thickness of about 3 μm, and a silicon carbide layer of 16
00°C; 3. x2y/crd to 3.21
A silicon carbide layer of 3 μm with a continuous dense tV gradient of up to 1.5 μm was applied and kept at 1600°C for 83 minutes at about 25 μml. A silicon carbide layer of z1g/~ is applied, and the silicon carbide layer has a continuous dense 1fil gradient of about 3 μm in thickness at a cooling rate of 20°C/min to 1400°C.

Subsequently, the temperature was maintained at 1400° C. for 10 minutes to form a 3 μm thick low density carbon layer.

Finally, a 40 μm dense pyrolytic carbon layer was formed at a coating temperature of 1460° C. using zolopyrene as a raw material gas.

The test fuel particles obtained in this way had a higher fracture strength than coated fuel particles having a silicon carbide layer with a discontinuous density.

tljFFtB Applicant Masahiro Matsui, patent attorney representing Nuclear Fuel Industries Co., Ltd.

Claims (1)

[Claims] 1. Silicon carbide as a solid fission product confinement layer 1
Multilayered with gastric layers8. In nuclear fuel particles. A multi-coated nuclear fuel particle characterized by a transition of the silicon carbide layer from low density to high density from inner 1111 to outer 11111, and from 1S to low density.