**2. The coating methods for NFKs**

The first layer deposited on the kernels is porous carbon, this is followed by a thin coating of pyrolytic carbon (a very dense form of heat-treated carbon), a layer of silicon carbide and another layer of pyrolytic carbon. Each coating process is performed at a defined temperature and for a defined duration of time. The schematic diagram of the experimental facility is shown in Fig. 2. This experimental facility can be divided into two main parts: the left part is the gas distribution system and the right part is the conical spouted bed coating system. The gas distribution system contains argon, the hydrocarbon gas (ethyne and propene), hydrogen and methyl trichlorosilane (MTS) vapor supply device, flow control system and the gas distribution device. The conical spouted bed coating system contains the spouted bed, the cooling water system, the heating system, the thermal insulation system, the gas airtight device and the temperature control device.

The whole coating process can be described as follows: In the pyrolytic carbon coating process, ethyne and propene as the reactive gas and argon as the fluidization gas are injected into the coating furnace, they are pyrolyzed at the high temperature about 1300ºC and then PyC layers are prepared. The SiC coated layer is prepared by MTS vapor as the reactive gas which is entrained by hydrogen and is pyrolyzed at about 1600 ºC. The integrity and property behavior of the SiC layer of the Tri-isotropic (TRISO) coated particle (CP) for high temperature reactors (HTR) are very important as the SiC layer is the main barrier for gaseous and metallic fission

**MTS**

**Gas inlet**

**A**

**Gas outlet**

**B**

**spouted bed Gas pressure** 

**signal transmitter**

**PC**

**Heating furnace**

Coating Technology of Nuclear Fuel Kernels: A Multiscale View

**Water cooling system**

**infrared pyrometer**

**Conical**

\*\*\*\* **Temperature**

http://dx.doi.org/10.5772/55651

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The fluidized bed chemical vapor deposition (FB-CVD) method is a suitable technique for preparing various kinds of films/layers on the spherical materials by initiating chemical reaction in a gas. FB-CVD has the advantage of large reactor volume to offer sufficient space with uniform mass and heat transfer condition. This technique can be used for other purposes, such as synthesizing carbon nanotube composite photocatalyst ((CNT)/Fe-Ni/TiO2). Also, some modified method based on FB-CVD, such as plasma-enhanced FB-CVD, has been used to prepare the transparent water-repellent thin films on glass beads in modern surface engineering treatment. So the investigation of FB-CVD method is helpful and important for

If we only do the coating experiments in the lab scale, it can be done in a very small reactor and the efficiency can be very high, but now the question is the how to develop coating

product release.

H2

**Figure 2.** The schematic diagram of the spouted bed coating system

H2

**CxHy**

**Ar**

**Flowmeter**

**Valve**

modern surface treatments.

**3. Multiscale analysis**

The spherical UO2 kernel as fuel particles are fluidized by the fluidization gas and coated by the reactive gas in the conical spouted bed coating furnace. The thickness, coating time, coating temperature, reactive and fluidization gas of four coating layers should be determined beforehand in the coating experiments as shown in Table 1.


**Table 1.** Experimental parameters in the coating process of TRISO particle

**Figure 2.** The schematic diagram of the spouted bed coating system

The whole coating process can be described as follows: In the pyrolytic carbon coating process, ethyne and propene as the reactive gas and argon as the fluidization gas are injected into the coating furnace, they are pyrolyzed at the high temperature about 1300ºC and then PyC layers are prepared. The SiC coated layer is prepared by MTS vapor as the reactive gas which is entrained by hydrogen and is pyrolyzed at about 1600 ºC. The integrity and property behavior of the SiC layer of the Tri-isotropic (TRISO) coated particle (CP) for high temperature reactors (HTR) are very important as the SiC layer is the main barrier for gaseous and metallic fission product release.

The fluidized bed chemical vapor deposition (FB-CVD) method is a suitable technique for preparing various kinds of films/layers on the spherical materials by initiating chemical reaction in a gas. FB-CVD has the advantage of large reactor volume to offer sufficient space with uniform mass and heat transfer condition. This technique can be used for other purposes, such as synthesizing carbon nanotube composite photocatalyst ((CNT)/Fe-Ni/TiO2). Also, some modified method based on FB-CVD, such as plasma-enhanced FB-CVD, has been used to prepare the transparent water-repellent thin films on glass beads in modern surface engineering treatment. So the investigation of FB-CVD method is helpful and important for modern surface treatments.
