Abstract The Collective Thomson Scattering (CTS) system will be the ITER diagnostic obtaining the plasma fast alpha-particle velocity distribution and will be implemented in drawer #3 of the Equatorial Port Plug #12 of the reactor. In this work, a neutronics analysis is presented for the in-vessel front-end parts of the CTS system, including neutron and gamma-ray fluxes and nuclear heat loads for the main components of the system calculated with the Monte Carlo radiation transport code MCNP6. In previous analyses the shielding materials were modelled as a homogeneous mixture, a crude approximation which did not consider the small gaps between the different components and between the CTS system and the shielding structure. In this work, a detailed model of the modular Diagnostics Shield Module (DSM) was developed, including all the shielding trays and all the individual boron carbide bricks. The results obtained with this model are compared with the ones obtained using a homogeneous mixture, to assess the effect of this approximation on the estimation of the neutron fluxes in the port interspace. The results show that the total neutron flux reaching the closure plate is estimated to be 2–3 times higher when the shielding is accurately modelled. This shows that the often-used homogeneous mixture approach underestimates the neutron fluxes during operation – a fact that could have great importance in the global shutdown dose rate estimates. On the other hand, the shielding implementation does not affect the heat loads in the front-end components of the system. Simulations to assess the Shutdown Dose Rates are performed using the D1S-UNED code. The results suggest that the entire port plug where the current CTS design is included will exceed the dose rate limit of 100 μSv/h in the port interspace. The contribution from the CTS system alone, however, is not sufficient to exceed the threshold.

中文翻译：

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ITER集体汤姆森散射系统的屏蔽分析

摘要 集体汤姆森散射 (CTS) 系统将成为 ITER 诊断工具，用于获取等离子体快速 α 粒子速度分布，并将在反应堆赤道口塞 #12 的 #3 抽屉中实施。在这项工作中，对 CTS 系统的船内前端部分进行了中子学分析，包括使用蒙特卡罗辐射传输代码 MCNP6 计算的系统主要组件的中子和伽马射线通量以及核热负荷. 在之前的分析中，屏蔽材料被建模为均质混合物，这是一种粗略的近似，没有考虑不同组件之间以及 CTS 系统和屏蔽结构之间的小间隙。在这项工作中，开发了模块化诊断屏蔽模块 (DSM) 的详细模型，包括所有屏蔽托盘和所有单独的碳化硼砖。将使用该模型获得的结果与使用均匀混合物获得的结果进行比较，以评估这种近似对端口间隙中子通量估计的影响。结果表明，当屏蔽被准确建模时，到达封闭板的总中子通量估计要高出 2-3 倍。这表明经常使用的均质混合物方法低估了运行期间的中子通量——这一事实在全球停堆剂量率估计中可能具有重要意义。另一方面，屏蔽实施不会影响系统前端组件中的热负载。使用 D1S-UNED 代码执行评估关闭剂量率的模拟。结果表明，包含当前 CTS 设计的整个端口插头将超过端口间隙中 100 μSv/h 的剂量率限制。然而，仅来自 CTS 系统的贡献不足以超过阈值。