Development of coated fuel particle for VHTR reactor

The VHTR reactor is a high temperature reactor concept with a 1000^oC outlet temperature and it is one of IV generation reactor that is being developed. This reactor is developed based on GT-MHR reactor with higher outlet temperature reactor, burn-up and electricity efficiency. Accordingly, material improvement is necessary, such as: SiC in correlation to elevated temperature of 850^oC to 1000^oC. The SiC layer plays an important role. Beside retaining metallic fission products (Cs-137, Ru-106) released from fuel kernel, it also provides mechanical strength and dimension stability to fuel particle. The ZrC layer can be considered to replace SiC because of its higher temperature capability. ZrC has a melting point of 3540⁰C whereas SiC has a melting point of 1800^oC. The ZrC-TRISO coated fuel particle did not fail until ∼6000 seconds at 2200^oC heating, while a few percent of the conventional TRISO-coated fuel particles failed already by 2200^oC, and almost 100% instantaneously at 2400^oC. In the whole temperature range, ZrC layer showed more resistance to chemical corrosion by fission products, especially by palladium (Pd) which is known to corrode the SiC layer. However, The ZrC layer capability to retention of Ru-106 was inferior to SiC. The retention of the other metal fission products such as barium, silver and promethium appears to be better than SiC. (author)