Abstract Auxiliary Cold Boxes (ACBs) of ITER cryodistribution system has multiple cryogenic process volumes as well as interfaces with cryolines having isolated vacuum spaces. Cryogenic process volumes inside a single vacuum space have different temperature levels, 4 K and 80 K as well as different operating pressure, 5 bar(a) and 18 bar(a). Cryogenic process volumes including interfacing cryolines are protected with safety devices (e.g. Safety Relief Valves (SRVs) and Rupture Discs (RDs)). In an accidental event like Loss of Insulation Vacuum (LIV) of any particular vacuum space, incidental heat load of order of ∼6.5 kW/m2 results in rapid pressurization of cryogenic process volume; considering safety of cryolines excess pressure is to be relieved through SRVs. As per nuclear safety requirements of ITER, maximum helium inventory inside tokamak building is restricted; hence, a common relief header is necessary to collect SRVs discharge and carry it outside tokamak building. Due to long length of relief header, required information regarding backpressure on SRVs is not known in advance. The backpressure is a function of geometric condition of relief header, process condition of relieving process volume and relieving mass flow rate. The estimation of backpressure considering steady-state condition and maximum mass flow rate through all connected SRVs may result in a conservative and unrealistic value. Therefore, a dynamic simulation of safety relief event along with complete model of process volume, boundary conditions as well as geometric detail of relief header is performed using pressure-flow solver model in Aspen HYSYS®. Two simulation approaches are considered for present study to estimate backpressure (i) Steady state maximum mass flow model, which considers maximum relieving mass flows of SRVs computed from code (EN13648-3) (ii) Dynamic mass flow model, which considers the size of SRVs from code and process pressure, mass flow evolve with time based on heat load applied on process volumes. The results of backpressure from two simulation approaches are discussed and outcome of study is summarized.

中文翻译：

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iter低温分配系统绝缘真空损失事件的动态模拟

摘要 ITER 低温分配系统的辅助冷箱 (ACB) 具有多个低温处理容积以及与具有隔离真空空间的低温管线的接口。单个真空空间内的低温工艺体积具有不同的温度水平，4 K 和 80 K，以及不同的操作压力，5 bar(a) 和 18 bar(a)。包括接口低温管线在内的低温工艺体积受到安全装置（例如安全泄压阀 (SRV) 和破裂盘 (RD)）的保护。在任何特定真空空间的绝缘真空损失 (LIV) 等意外事件中，约 6.5 kW/m2 的附带热负荷会导致低温处理体积快速加压；考虑到cryolines 的安全性，超压将通过SRV 来缓解。根据 ITER 的核安全要求，托卡马克大楼内的最大氦气库存受到限制；因此，需要一个通用的减压头来收集 SRV 排放物并将其运出托卡马克大楼。由于泄压集管的长度很长，因此事先不知道有关 SRV 背压的所需信息。背压是卸压集管几何条件、卸压工艺体积和卸压质量流量的工艺条件的函数。考虑到稳态条件和通过所有连接的 SRV 的最大质量流量的背压估计可能会导致保守和不切实际的值。因此，使用 Aspen HYSYS® 中的压力-流量求解器模型执行安全泄压事件的动态模拟以及完整的过程体积模型、边界条件以及泄压集管的几何细节。本研究考虑了两种模拟方法来估计背压 (i) 稳态最大质量流量模型，它考虑了从代码 (EN13648-3) 计算的 SRV 的最大释放质量流量 (ii) 动态质量流量模型，它考虑了来自代码和过程压力的 SRV，质量流量基于施加在过程体积上的热负荷随时间变化。讨论了两种模拟方法的背压结果，并总结了研究结果。