The radioactivity calculation model in loss of coolant accident (LOCA) for AP1000 was established based on AST method and the change of radioactivity in containment and environment was studied after LOCA.The results show that the nuclide radioactivity in containment atmosphere first increases and then decreases with time,and reaches maximum at 40 min.According to the natural characteristics,the radionuclides can be divided into nuclides without nucleus decay and nuclides with nucleus decay.After 40 min of the accident,the activity of the former in containment exponentially decreases,such as 131-135I and 83Krm,while the activity of the latter decreases slowly due to nucleus decay,such as 85Kr,133Xem,133Xe and 135Xe.After several hours of LOCA,the cumulative release amount of I and Cs to environment increases slowly because of natural removal mechanism.For Kr and Xe,the cumulative release amount of the longer half-life nuclides to environment increases with time,while that of the shorter half-life nuclides reaches balance after a few hours of LOCA.%根据AST方法建立了AP1000 LOCA放射性核素活度计算模型,研究事故后安全壳及环境中放射性核素活度的变化.结果表明:事故后安全壳气空间内各核素的放射性活度呈先增大后减小的趋势,40 min时达到最大.根据核素性质,将其分为不考虑母核衰变的核素和考虑母核衰变的核素.事故发生40 min后,前者在安全壳内的活度指数减小,典型核素有131～135I、83Krm等,后者由于母核衰变的影响导致其在安全壳内的活度减小趋势放缓,典型核素有85Kr、133Xem、133Xe和135Xe等.I和Cs由于受自然去除机制的去除作用,事故几小时后其向环境的累积释放量增长非常缓慢;对于Kr和Xe,半衰期较长的核素向环境的累积释放量不断增大,半衰期较短的核素在事故几小时后向环境的累积释放量趋于平衡.
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