Comparisons of Thermal SCWR Assembly Designs by In- or Inter-assembly Moderation

Abstract

As one of the six GEN-IV reactor systems and the only one with water as coolant, SCWR is thought to be the most hopeful future nuclear energy system. Many designs have already been proposed worldwide. For thermal SCWR designs, a key consideration factor is how to provide the dedicated moderation, which leads to various designs with water as moderator. It is much like BWR, where under-moderation is an important issue and central water rods are adopted to account for it. Naturally, water rods can be adopted in SCWR assemblies too, but with counter-flow scheme to increase the outlet temperature and thermal efficiency which is unlike the co-flow scheme in BWR. This type can be seen in the American, Japanese and European HPLWR designs. As the other option, moderation could be provided with inter-assembly gap like CANDU-SCWR design. It is worthy of review of these designs for better understanding the water moderating effects and putting forward any new designs.