Source term estimation of atmospheric release due to the Fukushima Dai-ichi Nuclear Power Plant accident by atmospheric and oceanic dispersion simulations

The source term of the atmospheric release of ¹³¹I and ¹³⁷Cs due to the Fukushima Dai-ichi Nuclear Power Plant accident estimated by previous studies was validated and refined by coupling atmospheric and oceanic dispersion simulations with observed ¹³⁴Cs in seawater collected from the Pacific Ocean. By assuming the same release rate for ¹³⁴Cs and ¹³⁷Cs, the sea surface concentration of ¹³⁴Cs was calculated using the previously estimated source term and was compared with measurement data. The release rate of ¹³⁷Cs was refined to reduce underestimation of measurements, which resulted in a larger value than that previously estimated. In addition, the release rate of ¹³¹I was refined to follow the radioactivity ratio of ¹³⁷Cs. As a result, the total amounts of ¹³¹I and ¹³⁷Cs discharged into the atmosphere from 5 JST on March 12 to 0 JST on March 20 were estimated to be approximately 2.0 × 10¹⁷ and 1.3 × 10¹⁶ Bq, respectively.     

日本福岛核电站事故后的海洋放射化学

由于对环境影响的关注,日本福岛核电站事故后,人们进行了大气、陆地和海洋环境人工放射性核素变化监测与研究,研究的主要核素是131I、137 Cs、134 Cs和129I。除了关注浓度水平的变化外,还进行了通过大气和海流对事故释放的放射性核素运行路径的模拟研究。研究表明,受气候条件的控制,事故释放进入大气的放射性核素先经过太平洋到达北美,然后越过大西洋到达欧洲,最后绕北半球一周后到达中国。除事故核电站周边外,全球大气中131I活度浓度在mBq/m3量级,137 Cs活度浓度在0.1~1mBq/m3量级。事故释放进入海洋的放射性核素将随海流向东输运,然后在北太平洋随环流输运。研究也发现在离开源地不远的海区,由于混合进入200m水深以下的次表层水,在远离事故核电站海区水体的137 Cs活度浓度可达100Bq/m3,但大部分水体137 Cs活度浓度在Bq/m3量级,仅稍高于本底水平。     

One-year time variations of anthropogenic radionuclides in aerosols in Tokyo after the Fukushima Dai-ichi Nuclear Power Plant reactor failures

We report on the results of monitoring of environmental radiation for one year (13 March 2011 to 12 March 2012), including air dose rates and the concentrations of radionuclides in aerosols in Tokyo, after the reactor failures at the Fukushima Dai-ichi Nuclear Power Plant. The air dose rates began to increase at 4:00–5:00 JST on 15 March 2011, and the maximum rate was observed at 10:00–11:00 JST. Two peaks were observed before 23 March 2011, and then the air dose rates decreased until March 2012. The time variations of concentrations of radionuclides in aerosols showed tendencies similar to those of air dose rates. Short-lived radionuclides (⁹⁹Mo (^99mTc), ^129mTe (¹²⁹Te), ^131mTe, ¹³²Te (¹³²I), ¹³³I and ¹³⁶Cs) were under the detection limit during April 2011. Iodine-131 was detected until early June 2011, and long-lived radionuclides (¹³⁴Cs and ¹³⁷Cs) were detected intermittently for one year. Based on our results, gamma doses and committed effective doses resulting from inhalation were estimated.     

福岛核事故后核电厂安全改进行动分析

介绍了福岛核事故后世界上主要核电国家相继开展的核电厂安全检查、再评价行动,并得出相应的检查和测试结论。法国、美国和中国等国家分别提出了福岛核事故后改进核电厂安全的建议、要求和行动,并制定了具体工程措施：在极端外部事件的设防,严重事故预防和缓解,水、电、通风实体改进,限制严重事故下的放射性释放和应急准备等主要方面开展的安全改进行动,将会提高核电厂的安全水平并提升缓解严重事故的能力。反思福岛核事故,总结福岛核事故对核电安全技术改进的促进作用,对未来核电安全技术的发展进行了展望。     

Formation of radioactive cesium microparticles originating from the Fukushima Daiichi Nuclear Power Plant accident: characteristics and perspectives

ABSTRACT

Following identification of radioactive Cs microparticles (CsMPs) in aerosol samples from the Fukushima Daiichi Nuclear Power Plant (FDNPP), numerous reports on CsMPs have been published. This paper reviews recent progress in the measurement and characterization of CsMPs by advanced analytical techniques, including advanced transmission electron microscopy (TEM) and synchrotron X-ray analysis. These analyses revealed that the CsMPs contained Si, Fe, Zn, Cs, and minor quantities of U together with some fission products. Uranium in the CsMPs was identified as being in the form of uraninite and (U,Zr)O₂. Detailed advanced TEM analysis has clarified some of the processes resulting in the alteration of constituents of the nuclear fuels and containment vessel materials during this severe accident. In addition, a detailed report on the elemental compositions and structures of the fuel debris fragments collected inside and outside of the primary containment vessel²⁵ highlighted the fact that the fuel debris fragments contained nanoparticles with the U and Zr components having similar structures to that of the CsMPs. This similarity in structures has stimulated further research on the structure and elemental constituents, especially for U and Zr in the CsMPs, and has opened up new avenues for studying the chemical characteristics of the fuel debris.     

日本311地震海啸导致福岛第一核电厂严重事故的三简

本文写于日本311大地震、海啸发生后的不同时段.首先,对福岛核事故的趋向进行了初步探讨,提出了发生堆芯熔化的可能性极大;其次,对我国的核安全检查进行了思考,述说了可能危及核电厂安全的外部自然事件和人为事件;最后结合地震后所发生的一些现象,提出了需要对地质、地震研究的问题.     

利用福岛第一核电厂事故期间环境监测资料反推事故释放源项

2011年3月11日,日本福岛核事故导致放射性物质向大气环境的大规模释放。本工作利用大气数值预报模式WRFV2.2.1和大气弥散模式CALPUFF,对事故期间放射性物质的大气输运和弥散进行了模拟。应用大气释放源项的逆推算方法,结合单位释放率条件下的大气弥散模拟结果和环境监测数据,对福岛第一核电厂1到3号机组向大气环境释放的放射性核素总量进行了评估,推算的131I和137 Cs气载释放量分别为8.6×1016 Bq和8.6×1015 Bq。     

Radioactivity of fission product and heavy nuclides deposited on soil in Fukushima Dai-Ichi Nuclear Power Plant accident

Based on periodically performed radioactivity measurements on soil samples in the site of Fukushima Dai-Ichi Nuclear Power Station, activity ratios to ¹³⁷Cs of fission product and heavy nuclides were obtained for Sr, Nb, Mo, Tc, Ru, Ag, Te, I, Ba, La, Pu, Am, and Cm isotopes. By exponentially fitting or averaging, the activity ratios at the core shutdown were estimated. Using correlations of activity ratios of ¹³⁴Cs to ¹³⁷Cs, and ²³⁸Pu to the sum of ²³⁹Pu and ²⁴⁰Pu against fuel burnup, burnup of the fuel sourcing the deposited activity of the soil was estimated. The activity ratios to ¹³⁷Cs of each nuclide on the deposited activity were divided by those calculated on the fuel at the shutdown to obtain the deposited activity fraction of each nuclide as a relative value to ¹³⁷Cs, which also corresponds to the deposited fraction of each element as a relative value to Cs. The obtained deposited fractions relative to Cs are the orders of 10^?4 to 10^?2 for Sr, 10^?5 to 10^?3 for Nb, 10^?2 to 10^?1 for Mo, 1 to 10 for I, 10^?3 to 10^?2 for Ba, 10^?2 for La, 10^?6 to 10^?3 for Pu, 10^?6 to 10^?4 for Am, and 10^?7 to 10^?5 for Cm. The deposited fractions for Tc, Ag, and Te were not estimated due to the lack of the calculated inventories in the fuel for the relevant measured radioactive nuclides.     

风险控制在福岛核事故剂量控制中的应用及启示

简要介绍风险的基本概念与风险控制方法,并根据风险控制方法,对福岛第一核电厂核事故中控制公众受照剂量和职业照射剂量的措施进行分析和评价,找出其中的薄弱环节,并对风险控制方法在核事故剂量控制中的应用提出具体建议。     

Measurements of 131I in the thyroids of employees involved in the Fukushima Daiichi nuclear power station accident

The Great East Japan Earthquake Disaster on 11 March 2011 caused an unprecedented accident at the Fukushima Daiichi nuclear power station operated by Tokyo Electric Power Company (TEPCO). Nuclear Fuel Cycle Engineering Laboratories of Japan Atomic Energy Agency performed internal dose measurements of 560 employees involved in the accident during the period from 20 April to 5 August in 2011 at the request of TEPCO. The present paper describes our measurements of ¹³¹I in the thyroid that is the predominant contributor to the internal dose. These measurements were carried out using an HPGe detector installed in a low-background shielded chamber made of 20-cm-thick steel and the detector was placed adjacent to the subject's neck. The typical minimum detectable activity of this technique was 10 Bq for a counting time of 10 min; however, this sensitivity made it difficult to identify a residual thyroid content of ¹³¹I corresponding to a committed effective dose of 20 mSv for late subjects. This paper discussed technical issues experienced through the measurements such as the influence of ¹³¹I in the rest of the body, the calibration phantom of use, and so on.     

Results of environmental radiation monitoring at the Nuclear Fuel Cycle Engineering Laboratories,JAEA, following the Fukushima Daiichi Nuclear Power Plant accident

In response to the accident at the Fukushima Daiichi Nuclear Power Plant, emergency monitoring of the environmental radiation was performed at the Nuclear Fuel Cycle Engineering Laboratories (NCL), Japan Atomic Energy Agency (JAEA). This article describes the results of the monitoring, including air absorbed dose rate and radionuclide concentration in air and fallout. The air absorbed dose rate began to increase from about 1 am on 15 March 2011 and varied over time, with three peaks: 4.8 μGy/h, 2.1 μGy/h and 3.1 μGy/h at 8 am on 15 March, 5 am on 16 March and 4 am on 21 March, respectively. The increase in the radionuclide concentrations in air and fallout showed a tendency similar to that in the case of the dose rate. The ¹³¹I/¹³⁷Cs concentration ratio in air varied considerably every day, and the maximum was about 100. The ¹³⁷Cs amount in the fallout for a month from 15 March to April 15 was about 120 times higher than that after the Chernobyl accident in May 1986 and about 30 times higher than that in Tokyo in June 1963 during the atmospheric nuclear weapon tests. The committed effective dose due to inhalation was estimated from the observed radionuclide concentration in air.     

Public opinion changes after the Fukushima Daiichi Nuclear Power Plant accident to nuclear power generation as seen in continuous polls over the past 30 years

In this study, the results of surveys conducted over the past 30 years were analyzed. The surveys include continuous opinion polls conducted by seven organizations, those conducted by eight news media one year after the Fukushima Daiichi accident, and those conducted by Institute of Nuclear Safety System (INSS) 14 times from 1993 to December 2011. The results were as follows: (1) negative opinions towards nuclear power generation (NPG) suggesting ‘abolition or reduction,’ which was 20%–30% over the past 30 years, increased to 70% from four to six months after the accident, when there was also much news about renewable energy. (2) Even after the accident, 60% regarded NPG as ‘inevitable,’ but many opposed future replacement or new construction of NPG facilities. (3) After the accident, recognition of the usefulness of NPG and concerns about electric power shortages in the near future remained unchanged, while anxiety and distrust toward NPG increased significantly. When considering power generation options, people now tend to focus on accident risks. (4) Nevertheless, people are neither aware of various possible problems caused by reducing NPG nor willing to accept a significant rise of electricity rates caused by the shift to renewable energy.     

Quantities of I-131 and Cs-137 in accumulated water in the basements of reactor buildings in process of core cooling at Fukushima Daiichi nuclear power plants accident and its influence on late phase source terms

During the process of core cooling at Fukushima Daiichi nuclear power plants accident, large amount of contaminated water was accumulated in the basements of the reactor buildings at Units 1–4. The present study estimated the quantities of I-131 and Cs-137 in the water as of late March based on the press-opened data. The estimated ratios of I-131 and Cs-137 quantities to the core inventories are 0.51%, 0.85% at Unit 1, 74%, 38% at Unit 2 and 26%, 18% at Unit 3, respectively. According to the Henry's law, certain fraction of iodine in water could be released to atmosphere due to gas–liquid partition and contribute to increase in the release to environment. A lot of evaluations for I-131 release have been performed so far by the MELCOR calculation or the SPEEDI reverse estimation. The SPEEDI reverse predicted significant release until 26 March, while no prediction in MELCOR after 17 March. The present study showed that iodine release from accumulated water may explain the release between 17 and 26 March. This strongly suggests a need for improvement of current MELCOR approach which treats the release only from containment breaks for several days after the core melt.     

不同扩散参数与气象条件对核电厂年均大气扩散因子的影响

基于田湾核电厂厂址1997～1999年和福建惠安核电厂厂址1995～1997年百米逐时气象数据，对四组不同扩散参数(厂址实测、IAEA推荐值、Briggs以及Pasquill参数系)对两核电厂厂址的年均大气扩散因子计算值的影响作了估算，分析表明，采用IAEA和Briggs扩散参数与厂址实测值的偏差小于20％。同时估算了不同年份气象数据对年均大气扩散因子的影响。