Analysis of Sentitivity of Fission Product Iodine in Containment to Various Factors under Severe Accidents
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摘要: 反应堆发生事故最严重的后果是放射性裂变产物弥散到环境中，为了研究严重事故工况下放射性裂变产物碘在安全壳内的分布特点，本研究假设核电厂已经发生严重事故，一回路裂变产物碘释放到安全壳内。使用事故源项评估程序（ASTEC）构建核电厂安全壳结构模型，并设置边界条件，计算了裂变产物碘在不同pH值、有无金属银注入和气相辐照工况下的化学形态、化学特性、分布情况以及不同化合物的变化趋势。研究结果表明，碱性环境下可以降低安全壳内挥发性碘的生成；银的存在可以增加液相中碘的捕获和降低碘的挥发；气相辐照环境可以提高气相CH3I 和IOx的形成。本研究可以为严重事故工况下安全壳内放射性碘的去除提供支持。Abstract: The most serious consequence of reactor accident is that the radioactive fission products are dispersed into the environment. To study the distribution characteristics of radioactive fission product iodine in the containment under severe accident conditions, this paper assumes that the fission product iodine is released from the primary system into the containment due to the occurrence of severe accident in the nuclear power plant (NPP). Then, using the accident source term evaluation code (ASTEC), this study builds a containment construction model for the NPP, sets the boundary conditions, and calculates the chemical form, chemical properties, distribution, and change trends of different compounds, of the fission product iodine under different pH values, with or without silver (Ag) injection and under gaseous radiation conditions. The results show that the production of volatile iodine in the containment can be inhibited under alkaline conditions; the silver can promote the iodine trap in the liquid phase and reduce the iodine volatility; and the gaseous radiation environment can promote the formation of gaseous CH3I and IOx. As a result, this study can provide guidance for the removal of radioactive iodine in the containment under serious accidents.
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Key words:
- ASTEC /
- Severe accident /
- Iodine /
- pH /
- Ag /
- Gaseous radiation
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图 1 安全壳内裂变产物输运行为示意图
Figure 1. Diagram of Fission Product Transport Behavior in Containment
图 3 安全壳中注入的气溶胶碘和气体碘的变化
Figure 3. Changes of Aerosol and Gaseous Iodine Injected into Containment
图 4 安全壳中悬浮态和沉积态气溶胶的变化
Figure 4. Changes of Suspended and Deposited Aerosol in Containment
图 5 pH = 5.5 时安全壳中关键种类碘变化
Figure 5. Changes of Key Species of Iodine in Containment with pH=5.5
图 6 pH = 9.5时安全壳中关键种类碘变化
Figure 6. Changes of Key Species of Iodine in Containment with pH=9.5
图 7 无银添加时安全壳中气溶胶碘分布
Figure 7. Aerosol Iodine Distribution in Containment without Ag Addition
图 8 有银添加时安全壳中气溶胶碘分布
Figure 8. Aerosol Iodine Distribution in Containment with Ag Addition
图 9 无银添加时安全壳中不同种类碘的分布
Figure 9. Distribution of Different Species of Iodine in Containment without Ag Addition
图 10 有银添加时安全壳中不同种类碘分布
Figure 10. Distribution of Different Species of Iodine in Containment with Ag Addition
图 11 无气体辐照时气相
${{\rm{I}}_{\rm{2}}}$ 、IOx和CH3I质量变化Figure 11. Mass Changes of Gaseous
${{\rm{I}}_{\rm{2}}}$ , IOx and CH3I in Containment without Gaseous Radiation
图 12 有气体辐照时气相
${{\rm{I}}_{\rm{2}}}$ ，IOx和CH3I质量变化Figure 12. Mass Changes of Gaseous
${{\rm{I}}_{\rm{2}}}$ , IOx and CH3I in Containment with Gaseous Radiation表 1 主要事故进程
Table 1. Main Event Sequence
时间/s 主要事件 0 一回路裂变产物碘和铯、蒸汽、水开始释放，堆坑水中pH值为5.5 300 气溶胶碘释放速率为5.0×10−4 kg/s，气体单质I2释放速率为6.0×10−5 kg/s 600 气溶胶碘释放速率为0.05 kg/s，气体单质I2释放速率为0.006 kg/s，温度550 K的蒸汽和水继续释放 1200 气溶胶碘释放速率为1 kg/s，气体单质I2释放速率为0.06 kg/s 6000 气溶胶碘释放速率为5 kg/s，气体单质I2释放速率为0.6 kg/s 7200 水的释放速率为1 kg/s，温度500 K 9000 冷却剂水停止释放 10800 蒸汽释放速率为3 kg/s，温度为550 K 12000 气溶胶碘释放速率为12 kg/s，气体单质I2释放速率为0.6 kg/s 12300 蒸汽停止释放 100000 事故进程结束 
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