ITER极向场线圈PF4维修区域停堆剂量率分析

Assessment of Shutdown Dose Rate in ITER PF4 Coil Maintenance Zone

根据国际热核聚变实验堆ITER设计标准,ITER极向场线圈(PF Coils)的人工检测和连接维修任务的制定,需要确保维修过程中工人所受到的辐射剂量水平不超过剂量限值。基于ITER中子学基准模型B-lite,利用二步法停堆剂量计算方法,在大型集成中子学计算分析系统VisualBUS和HENDL数据库支持下,计算并分析了三种维修方案下PF4维修区域内的停堆光子剂量场分布,以分析降低维修工人辐射剂量水平的有效措施。结果表明,与推迟维修工人进入:PF4维修区域时间相比,采用临时屏蔽的措施更能显著降低PF4维修区域内的辐射剂量水平,建议后续采用临时屏蔽措施。

To bridge the failed ITER PF Coils double pancake, hands-on access is required for the inspection and installation in cryostat. As the activated component in cryostat will induce radiation hazard, assessing the decay gamma dose rate inside cryostat is needed to determine and schedule personal accessibility to perform this repair. For this purpose, this paper has designed three cases to study the feasibility methods to reduce the absorbed dose of worker. Case A＊ is the reference case and assume time after shutdown dose is 106 sec; Case B assume the time after shutdown is 1 month to assess the decrease of dose by extending cooling time; Case C assume the time after shutdown is 106 sec with 3 cm lead added above PF4 coil to assess how much can the radiation dose be reduced. The neutronics calculations and analyses were performed by using CAD-based multi-functional 4D neutronics ＆ radiation simulation system named VisualBUS and Nuclear Data Library named HENDL. The preliminary results showed that the gamma dose rate around PF4 coil in Case A＊ is 164.2 μSv/h, Case B is 111.8 μSv/h and Case C is 64.1 μSv/h lower than the limited radiation level required in ITER Requirement. We can find marked decrease of radiation dose rate by temporary shielding compared with extended cooling time.