TEM/STEM Observation of ZrC‐Coating Layer for Advanced High‐Temperature Gas‐Cooled Reactor Fuel

Abstract

The Japan Atomic Energy Agency (JAEA) has started to study and develop ZrC‐coated fuel particles for advanced high‐temperature gas‐cooled reactors. The ZrC‐coating layer was fabricated using the bromide process at JAEA. In the early stage of the project, however, the deposition temperature was varied. This paper mainly focuses on the microstructures of the ZrC‐coating layer developed in the early stage of the project. Some circumferential stripes were observed in the ZrC‐coating layer on optical micrographs. It was found that the stripes were caused by the nonuniform distribution of the free carbon phase. It was also revealed by means of transmission electron microscope /scanning transmission electron microscope observations that crystal grains of the ZrC were small and columner in shape, and were not equiaxed especially near the surface. It appears that the oscillated deposition temperature results in the nonuniform distribution of the free carbon region. The structure of the free carbon region formed in the ZrC‐coating layer appeared to be such that the c‐plane was roughly parallel to its lengthened direction. The ZrC‐coating layer appeared to be bound to the PyC layer. Fibrous carbon existing at the PyC/ZrC boundary was also observed.

TEM/STEM Observation of ZrC Coating Layer for Advanced High‐Temperature Gas‐Cooled Reactor Fuel, Part II

“…These appeared to be lattice fringes, similar to the free carbon region observed in the ZrC layer of the ZrC‐05‐2003 batch, 6 in the above‐mentioned laminar features when observed with a high‐resolution TEM. It is therefore reasonable to assume that these laminar features consisted of mainly free carbon 6 . The free carbon regions were distributed in the ZrC layer uniformly (in micrometer order) and quite densely (Fig.…”

“…We have reported some characteristics of the microstructures of the ZrC layer produced in an early stage of the project (batch number: ZrC‐05‐2003) 6 . The deposition temperature for the ZrC‐05‐2003 batch was not constant but oscillated in a temperature range of 1493–1823 K 6 .…”

“…We have reported some characteristics of the microstructures of the ZrC layer produced in an early stage of the project (batch number: ZrC‐05‐2003) 6 . The deposition temperature for the ZrC‐05‐2003 batch was not constant but oscillated in a temperature range of 1493–1823 K 6 . Because the ZrC layer is usually deposited using some exothermic and endothermic reactions, it was difficult to keep the deposition temperature constant 7 .…”

Effect of Heat Treatment on TEM Microstructures of Zirconium Carbide Coating Layer in Fuel Particle for Advanced High Temperature Gas Cooled Reactor

“…The dark contrast areas seen in the ZrC layers correspond to voids or free carbons region. 11) Before the heat treatment, the voids or free carbons region had a thin ($10 nm) layered feature and were distributed densely (some 10 nano-meters interval) 9) (see Fig. 1(a)).…”

Fabrication of uniform ZrC coating layer for the coated fuel particle of the very high temperature reactor

“…5 [11]. From this figure, it was indicated that the high-dense regions designated as (b) and the low-dense regions as (a) were layered with a relation to the deposition direction.…”