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thorium content for the SBT, SBU, and WASB levels. However, it increases in the range of thorium content from 0 to 40% and decreases when the thorium content is larger than 40%.

The tight relationship between fuel cycle cost and initial inventory of U-235 mainly results from the composition of the cost. Figure 17 presents the composition of fuel cycle cost for three different reactor cores, including natural uranium purchase, thorium purchase, uranium conversion, uranium enrichment, the fabrication of fuel blocks, and storage and the deposal of spent fuels. Because the required amount of natural uranium is 13 times of the inventory of heavy metal in the reactor core due to 0.7% U-235 in natural uranium, both the natural uranium purchase and uranium enrichment are 70% of total fuel cycle cost. The thorium purchase is only 2.5% because the thorium need not be enriched, and the required amount of thorium is by far less than the amount of the natural uranium. The fabrication cost is the highest unit price (777 \$/kg HM) and the fabrication involves all heavy metals, so it is about 20% of the total cost. Although the unit price of the disposal of spent fuel is also high (610 \$/kg

The fuel cycle cost is mainly determined by natural uranium purchase (35–40%), uranium enrichment (32–35%), and the fabrication of fuel blocks (18–21%). The total of three items is 85– 96% fuel cost. The fabrication cost is the same for all reactor cores because the inventory of heavy metal in the reactor core is the same. The natural uranium purchase and uranium enrichment are directly related to the initial inventory of U-235. The more is the inventory of U-235, the more are the required natural uranium and the uranium enrichment. As a result, the fuel cycle cost is the

In order to utilize thorium fuel in block-type HTRs with the features of inherent passive safety, high burnup, and hard neutron spectrum, two key factors of thorium content and spatial separation levels are chosen to be investigated. The thorium content represents the thorium/ uranium fuel composition and the spatial separation level represents the spatial distribution of thorium/uranium fuels. For every thorium content,the spatial distribution of thorium and uranium fuels are concluded into four spatial separation levels, that is, no separation level (Th/U MOX), TRISO level (SBT), channel level (SBU), and block level (WASB) for the thorium-

HM), the disposal cost is only about 0.5% because of so-called time value.

116 Recent Improvements of Power Plants Management and Technology

same trend as the initial inventory of U-235 or the initial effective enrichment.

Figure 17. Composition of fuel cycle cost for some typical reactor cores.

4. Conclusions

fueled block-type HTRs.

Ming Ding<sup>1</sup> \* and Jie Huang1,2

\*Address all correspondence to: dingming@hrbeu.edu.cn

