• Assembly-level analysis on temperature coefficient of reactivity in a graphite-moderated fuel salt reactor fueled with low-enriched uranium

    分类: 物理学 >> 核物理学 提交时间: 2023-06-07

    摘要:To provide a reliable and comprehensive data reference for core geometry design of graphite-moderated and low-enriched uranium fueled molten salt reactor, the influences of geometric parameters on temperature coefficient of reactivity (TCR) at an assembly level are characterized. The four-factor formula is introduced to explain how different reactivity coefficients behave in terms of fuel salt volume fraction and assembly size. The results show that fuel salt temperature coefficient (FSTC) is always negative due to a more negative fuel salt density coefficient in the over-moderated region or a more negative Doppler coefficient in the under-moderated region. Depending on the fuel salt channel spacing, the graphite moderator temperature coefficient (MTC) can be negative or positive. Further, an assembly with a smaller fuel salt channel spacing are more likely to exhibit a negative MTC. As fuel salt volume fraction increases, the negative FSTC weakens first and then increases, owing to the fuel salt density effect gradually weakening from negative feedback to positive feedback and then decreasing. Meanwhile, MTC weakens as the thermal utilization coefficient caused by the graphite temperature effect deteriorates. Thus, the negative TCR weakens first and then strengthens mainly because of the change in fuel salt density coefficient. As assembly size increases, the magnitude of FSTC decreases monotonously due to a monotonously weakened fuel salt Doppler coefficient, whereas MTC changes from gradual weakened negative feedback to gradual enhanced positive feedback. And then, the negative TCR weakens. Therefore, to achieve a proper negative TCR, particularly a negative MTC, an assembly with a smaller fuel salt channel spacing in the under-moderated region is strongly recommended.