福岛核事故137Cs释放源项反演研究

目的 研究并反演福岛核事故¹³⁷Cs释放源项，为事故评价与辐射防护提供依据。方法 采用截断总体最小二乘变分核事故源项反演模型（TTLS-VAR），平衡利用环境监测数据，修正扩散模型算子与监测向量以降低大气扩散模型误差的影响，反演计算¹³⁷Cs释放源项，提高源项反演的准确性。结果 反演计算的福岛核事故¹³⁷Cs释放总量为1.74×10¹⁶~3.73×10¹⁶ Bq，释放的最高峰出现在2011年3月18日，释放率超过1.00×10¹² Bq/s。比较表明，¹³⁷Cs释放总量与国际原子能机构（IAEA）和联合国原子辐射效应科学委员会（UNSCEAR）公布结果相接近，释放序列与日本的事故源项与进程分析具有较好的一致性，释放率最高峰值对应福岛3号机组的泄漏事件。结论 采用TTLS-VAR事故源项反演模型，计算福岛核事故¹³⁷Cs释放源项，为事故评价与辐射防护提供依据。

Estimation of 137Cs source term from Fukushima nuclear accident

Objective To study the ¹³⁷Cs source term from the Fukushima Daiichi nuclear power plant, based on inverse modeling, so as to provide reference for accident assessment and radiation protection. Methods The ¹³⁷Cs source term was estimated by means of inverse modeling of nuclear accidents based on variational data assimilation combined with truncated total least squares (TTLS-VAR). The environmental monitoring data was balanced, and the dispersion model operator and monitoring data vector were corrected, in order to reduce the influence from atmospheric dispersion model error, and then improve the accuracy of inverse modeling of source term. Results The total amount of ¹³⁷Cs released was estimated to be 1.74×10¹⁶-3.73×10¹⁶ Bq, with the highest peak of release rates estimated appearing on March 18, 2011 and the average release rate in exceed of 1.00×10¹² Bq/s. The estimated total amount of ¹³⁷Cs was close to the data published by IAEA and UNSCEAR. Also, the estimated release sequences were in good consistent with Japanese analytical results of source terms and sequence of events. The highest peak of the estimated release rate curve corresponds to the leakage incident of unit 3. Conclusions In this study, the ¹³⁷Cs source term from the Fukushima Daiichi nuclear power plant is estimated by using TTLS-VAR inverse modeling, which could provide the basis for accident assessment and radiation protection.