Inversion of 137Cs emissions following the fukushima accident with adaptive release recovery for temporal absences of observations

Sheng Fang; Xinwen Dong; Shuhan Zhuang; Zhijie Tian; Yungang Zhao; Yun Liu; Yuanyuan Liu; Li Sheng

doi:10.1016/j.envpol.2022.120814

Inversion of ¹³⁷Cs emissions following the fukushima accident with adaptive release recovery for temporal absences of observations

Environ Pollut. 2023 Jan 15:317:120814. doi: 10.1016/j.envpol.2022.120814. Epub 2022 Dec 3.

Authors

Sheng Fang¹, Xinwen Dong², Shuhan Zhuang², Zhijie Tian³, Yungang Zhao⁴, Yun Liu⁵, Yuanyuan Liu⁶, Li Sheng⁷

Affiliations

¹ Institute of Nuclear and New Energy Technology, Collaborative Innovation Centre of Advanced Nuclear Energy Technology, Key Laboratory of Advanced Reactor Engineering and Safety of Ministry of Education, Tsinghua University, Beijing, 100084, China. Electronic address: fangsheng@tsinghua.edu.cn.
² Institute of Nuclear and New Energy Technology, Collaborative Innovation Centre of Advanced Nuclear Energy Technology, Key Laboratory of Advanced Reactor Engineering and Safety of Ministry of Education, Tsinghua University, Beijing, 100084, China.
³ China Institute for Radiation Protection, Taiyuan, 030006, China.
⁴ Key Laboratory of Beam Technology of Ministry of Education, College of Nuclear Science and Technology, Beijing Normal University, Beijing, 100875, China; CTBT Beijing National Data Centre and Beijing Radionuclide Laboratory, Beijing, 100085, China.
⁵ China Nuclear Power Engineering Co., Ltd, Beijing, 100840, China.
⁶ Key Laboratory of Beam Technology of Ministry of Education, College of Nuclear Science and Technology, Beijing Normal University, Beijing, 100875, China.
⁷ CMA Earth System Modeling and Prediction Center (CEMC), Beijing, 100081, China.

PMID: 36473639
DOI: 10.1016/j.envpol.2022.120814

Abstract

Temporal absences in observation records lead to release losses during the source term inversions of atmospheric radionuclide emissions. Consequently, objectively-estimated source terms for the Fukushima accident contain fewer release details and present large discrepancies when compared with the expert-judged one. This paper describes an objective method that can adaptively recover the missing releases caused by the temporal absences of observations. The proposed method assumes that the accident releases of radionuclides are piecewise-constant and comprise both peaks and constant releases. The missing releases are adaptively recovered as either peaks or constant releases by minimizing the total variation of the estimated source term. The proposed method is applied to the Fukushima accident and evaluated against regional airborne and deposited ¹³⁷Cs observations. The results demonstrate that this method effectively recovers the missing releases, producing a source term that matches the timing of both on-site gamma dose rate peaks and accident events. The retrieved source term improves the simulation of air concentrations and reproduces most of the deposition patterns. This is the first time that an objective method has independently reproduced the details in the expert-judged one for the Fukushima accident.

Keywords: Atmospheric dispersion; Fukushima daiichi; Nuclear accident; Piecewise-constant prior; Source term inversion; Temporal absence of observations.

MeSH terms

Air Pollutants, Radioactive* / analysis
Cesium Radioisotopes / analysis
Fukushima Nuclear Accident*
Japan
Radiation Monitoring* / methods

Substances

Cesium-137
Air Pollutants, Radioactive
Cesium Radioisotopes