Abstract

For the helium-cooled pebble bed breeding blanket concept improved in 2016 and the associated primary heat transfer system (PHTS) following EU DEMO Baseline 2015, an ex-vessel loss-of-coolant accident (LOCA) has been investigated with the assumption of a double-ended guillotine break of a main pipe in an outboard (OB) loop of the PHTS. The break leads to helium blowdown into the tokamak cooling room. A fast plasma shutdown followed by a plasma disruption is activated after the detection of the LOCA due to the design basis accident. Regarding three affected first-wall (FW) areas in one or two OB loops, three main cases are considered. If the FW temperature reaches the defined temperature limit of 1000°C, the FW is assumed to be failed such that an in-vessel LOCA results. In total five scenarios are simulated using MELCOR 1.8.6 for fusion with respect to the affected FW areas, mitigated or unmitigated plasma disruption conditions, the options of the dry or wet suppression tank, and the transport of source terms performed in the case of the beyond design basis accident without the plasma shutdown. The transient results are discussed for the time evolution of the accident sequences, pressurization in the systems, temperature behavior in volumes and structures, and tritium and dust transport behavior.

摘要

对于 2016 年改进的氦冷却卵石床育种毯概念和欧盟 DEMO 基线 2015 之后的相关主传热系统 (PHTS)，已在假设PHTS 外侧 (OB) 回路中主管的双端断头台断裂。中断导致氦气排入托卡马克冷却室。由于设计基准事故，在检测到 LOCA 后，将启动快速等离子体关闭，然后是等离子体中断。对于一个或两个 OB 环路中的三个受影响的第一壁 (FW) 区域，考虑了三种主要情况。如果 FW 温度达到定义的温度限制 1000°C，则假定 FW 失效，从而导致船内 LOCA。总共使用 MELCOR 1.8 模拟了五个场景。6 对于受影响的 FW 区域、减轻或未减轻的等离子体破坏条件、干式或湿式抑制罐的选择以及在没有等离子体停堆的超设计基准事故情况下执行的源项传输的聚变。讨论了事故序列的时间演变、系统加压、体积和结构的温度行为以及氚和粉尘传输行为的瞬态结果。