Abstract The Water-Cooled Lithium-Lead (WCLL) Breeding Blanket (BB) is a key component in charge of ensuring Tritium production, shield the Vacuum Vessel and remove the heat generated by plasma thermal radiation and nuclear reactions. It relies on PbLi eutectic alloy adopted as breeder and neutron multiplier and refrigerate by subcooled pressurized water. The last function is fulfilled by two independent cooling systems: First Wall (FW) that faces the plasma heat flux and the Breeding Zone (BZ) that removes the deposited power of neutron and photon interaction. Several layouts of WCLL BB system have been investigated in the last years to identify a configuration that guarantees Eurofer temperature below the limit (550 °C) and good thermal-hydraulic performances. This research activity focuses on the FW cooling system based on the WCLL BB 2018 design of DEMO 2017 baseline, investigating the cooling performances in order to optimize the FW design, reducing the amount of water that affects the Tritium Breeding Ratio (TBR) and improves the efficiency of the Primary Heat Transfer System (PHTS), verifying the reliability to deliver coolant at adequate design temperature (328 °C) to the PHTS. Different solutions have been considered and analyzed focusing on three specific positions along the poloidal direction: the equatorial cells in the Central Outboard Segment (COB) and Inboard Segment (IB), where there is the maximum deposited power and low Heat Flux (HF), and the apical cell of the IB, impacted by the highest HF but with low deposited power. For each FW design, several thermal-hydraulic steady-state analyses have been performed, as well as sensitivity analyses to evaluate the response of the systems under different cooling configuration, changing the position and the number of channels. Furthermore, a transient analysis reproducing the Dwell-Pulse phase of the DEMO fusion reactor with the optimized configuration of the Outboard FW layout has been performed to study the behavior of the FW cooling system subjected to the pulsed operation. The research activity aims at laying the basis for the finalization of the WCLL BB design, pointing out relevant thermal-hydraulic aspects. The analyses have been carried out using a CFD approach, thus a 3D finite volume model of each configuration has been developed, adopting the commercial ANSYS CFX code. The goal of the study is to compare the different FW cooling system layouts, identifying and discussing advantages and key issues from the thermal-hydraulic point of view. The results show that the coolant system of FW can safely remove the high plasma HF and nuclear heat deposition with a reduction of water channels, delivering coolant to the FW PHTS heat exchanger at the design temperature.

中文翻译：

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优化 DEMO WCLL 毯的第一个壁冷却系统

摘要 水冷铅酸锂（WCLL）育成毯（BB）是保证氚生产、屏蔽真空容器、排除等离子体热辐射和核反应产生的热量的关键部件。它依靠PbLi共晶合金作为增殖剂和中子倍增剂，并通过过冷加压水进行制冷。最后一个功能由两个独立的冷却系统实现：面向等离子体热通量的第一壁 (FW) 和去除中子和光子相互作用的沉积功率的繁殖区 (BZ)。WCLL BB 系统的几种布局在过去几年中进行了研究，以确定一种能够保证 Eurofer 温度低于极限 (550 °C) 和良好的热工水力性能的配置。本研究活动的重点是基于 DEMO 2017 基线的 WCLL BB 2018 设计的 FW 冷却系统，研究冷却性能以优化 FW 设计，减少影响氚育种率 (TBR) 的水量并提高主要传热系统 (PHTS) 的效率，验证以足够的设计温度 (328 °C) 向 PHTS 输送冷却剂的可靠性。已经考虑和分析了不同的解决方案，重点是沿极向方向的三个特定位置：中央外侧段 (COB) 和内侧段 (IB) 中的赤道单元，其中存在最大沉积功率和低热通量 (HF)，和 IB 的顶端细胞，受到最高 HF 的影响，但沉积功率较低。对于每个 FW 设计，已经执行了几个热工水力稳态分析，以及敏感性分析，以评估系统在不同冷却配置、改变位置和通道数量下的响应。此外，为了研究 FW 冷却系统在脉冲操作下的行为，使用优化配置的舷外 FW 布局再现了 DEMO 聚变反应堆的驻留脉冲阶段的瞬态分析。研究活动旨在为 WCLL BB 设计的最终确定奠定基础，指出相关的热工水力方面。分析是使用 CFD 方法进行的，因此采用商业 ANSYS CFX 代码开发了每种配置的 3D 有限体积模型。该研究的目标是比较不同的 FW 冷却系统布局，从热工液压的角度识别和讨论优势和关键问题。结果表明，FW的冷却系统可以安全去除高等离子体HF和核热沉积，减少水道，在设计温度下向FW PHTS换热器输送冷却剂。