Speaker
摘要
随着全球越来越多核反应堆进入退役阶段，退役过程中放射性气溶胶的防控已成为辐射防护与环境安全中的关键问题。等离子体切割作为核反应堆退役中广泛采用的热切割技术，在作业过程中会快速产生大量粒径分布动态变化显著的气溶胶。然而，目前对该过程中气溶胶的时序演化规律及形成机制仍缺乏系统认识，导致源项评估及污染控制存在较大不确定性。本研究采用双极电迁移率粒径谱仪（bSMPS）与光学粒子计数器（OPS）联用，对等离子体切割过程中10 nm–20 μm范围内的气溶胶进行高时间分辨率（≤1.5 min）监测。结果表明，亚微米气溶胶呈现典型的双峰粒径分布特征，包括小于30 nm的成核模态和100–500 nm的积聚模态。气溶胶动力学分析表明，蒸发–冷凝和凝并过程主导了颗粒生长，而成核模态颗粒的形成与等离子体环境中高浓度离子诱导成核密切相关。不同材料及工艺参数对气溶胶特征具有显著影响。其中，碳钢切割产生的颗粒物数浓度最高，峰值粒径最大，而铝材切割产生的颗粒物浓度最低。对于碳钢切割，板材厚度对粒径分布影响较小，而较高切割电流（100 A）会显著提高成核模态颗粒的占比。通风条件可使气溶胶数浓度降低近一个数量级，并有效抑制颗粒进一步生长。本研究为核反应堆退役过程中放射性气溶胶的形成机制认识及控制策略优化提供了理论依据，可为通风时机选择、切割参数优化及作业现场辐射防护提供参考。
Abstract
As many reactors around the world are decommissioning, the prevention and control of radioactive aerosols during this process have emerged as a key challenge. Plasma arc cutting or simplified as plasma cutting is a widely-used decommissioning technique, during which aerosols are generated rapidly and variably. However, the temporal evolution and formation mechanisms of these aerosols are usually unknown, leading to uncertainties in aerosol pollution control. This study comprised a combination of a bipolar electric mobility particle sizer and optical particle sizer to measure aerosols in the size range of 10 nm–20 μm with high time resolution (≤1.5 min). The submicron aerosols show a bimodal particle number size distribution (PNSD) with the coexistence of a nucleation mode (<30 nm) and an accumulation mode (100–500 nm). Aerosol modeling indicates that evaporation-condensation and coagulation dominate particle growth, and nucleation-mode particles can be caused by ion-induced nucleation due to high concentration of ions in the plasma. The number concentration of aerosols produced by cutting carbon steel is the highest, while cutting aluminum is the lowest. The peak particle diameter from cutting carbon steel is the largest, and the aluminum the lowest in the size range of 100–200 nm. For carbon steel, the thickness of the plate exerts a negligible influence on the PNSDs, while the percentage of nucleation-mode particles is found to be significantly higher at 100 A current than at 50 A current. The ventilation can reduce the aerosol number concentration by one order of magnitude and suppress the growth of aerosols. The study provides a theoretical basis for the optimization of the radioactive aerosol control (e.g., ventilation timing, current parameters, etc.) during the decommissioning cutting process.
| 关键词 | 核反应堆退役；等离子体切割；放射性气溶胶；颗粒数浓度粒径分布（PNSD）；蒸发–冷凝与凝并机制 |
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| Keywords | Nuclear decommissioning; Plasma cutting; Radioactive aerosols; Particle number size distribution; Evaporative-condensation and coagulation |
