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.     

Estimation of release rate of iodine-131 and cesium-137 from the Fukushima Daiichi nuclear power plant

The atmospheric release rates of I-131 and Cs-137 from the Fukushima Daiichi nuclear power plant in March 2011 were estimated by comparing environmental monitoring data of air concentration and deposition rate on a regional scale with calculated values from an atmospheric dispersion model. Although the release rates were not estimated for all days after 11 March, because of lack of monitoring data, temporal changes in the release rates were reasonably estimated with estimated uncertainties in a factor of 3.3 and 2.9 for I-131 and Cs-137, respectively. A large release was estimated from the night of 14 March to at least the afternoon of 15 March, with maximum values of 7.2 × 10¹⁵ Bq h^?1 for I-131 and 1.5 × 10¹⁴ Bq h^?1 for Cs-137. The release rates during other periods were estimated at one- to two-orders of magnitude smaller than the largest release rate on 15 March. Uncertainty in the estimated release rate for 15 and 20 March was larger than for other periods. The significant release during 14 and 15 March and the trend of the release rate by the end of March were consistent with previous reports. This agreement, despite using different datasets, shows robustness of the temporal changes estimated in the studies.     

Examination of 131I and 137Cs releases during late phase of Fukushima Daiichi NPP accident by using 131I/137Cs ratio of source terms evaluated reversely by WSPEEDI code with environmental monitoring data

To investigate what happened in reality during the Fukushima Daiichi Nuclear Power Plant accident, the phenomena within reactor pressure vessel and the discussion of ties with the environmental monitoring measurement are very important. However, the previous study that treats phenomena of the both has not necessarily advanced up to the present time. The source terms predicted by simulation codes such as MELCOR has not yet been consistent with the reverse estimation by WSPEEDI code using environmental measurement data. This study investigated ¹³¹I and ¹³⁷Cs release behaviors during the late phase of the accident to contribute to such examination using the ¹³¹I/¹³⁷Cs ratio of the new source terms predicted by Katata. The ¹³¹I release by the gas–liquid partition from the contaminated water in the 1F2 and 1F3 reactor buildings which was pointed out in the previous study was reevaluated using the new source terms. In addition, paying attention to the similarity of the core conditions between the Fukushima accident and the Phébus FPT3 experiment using the B₄C control rods, the release of organic iodine (CH₃I) during the 1F3 suppression pool venting, formation of CsBO₂ and its release behavior were examined which have not yet been sufficiently studied so far.     

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。     

Air concentration estimation of radionuclides discharged from Fukushima Daiichi Nuclear Power Station using NaI(Tl) detector pulse height distribution measured in Ibaraki Prefecture

Air concentrations of ¹³³Xe, ¹³¹I, ¹³²I, ¹³³I, ¹³²Te, ¹³⁴Cs, ¹³⁶Cs, and ¹³⁷Cs in the early stage of the Fukushima Daiichi Nuclear Power Station (FNPS1) accident were estimated for six locations in Ibaraki Prefecture from pulse height distributions measured with NaI(Tl) scintillation detectors continuously operated as a part of monitoring station systems. Air concentration of ¹³³Xe in Ibaraki was estimated for the first time, which showed the maximum value of 150 kBq m^?3 in the plume arrived at the southern part of Ibaraki around noon of 15 March 2011. The plume was found to consist mainly of noble gases without other nuclides at significant level and to correspond to the hydrogen explosion at Unit 3. Spatiotemporal distributions of ¹³¹I and other nuclides were discussed for the plumes detected during the periods of 15–16 and 20–21 March. Variations in radionuclide composition among the plumes and within each plume were also discussed.     

Distribution of radionuclides in surface seawater obtained by an aerial radiological survey

We investigated the distribution in seawater of anthropogenic radionuclides from the Fukushima Daiichi Nuclear Power Plant (FNPP1) as preliminary attempt using a rapid aerial radiological survey performed by the U.S. Department of Energy National Nuclear Security Administration on 18 April 2011. We found strong correlations between in-situ activities of ¹³¹I, ¹³⁴Cs, and ¹³⁷Cs measured in surface seawater samples and gamma-ray peak count rates determined by the aerial survey (correlation coefficients were 0.89 for ¹³¹I, 0.96 for¹³⁴Cs, and 0.92 for¹³⁷Cs). The offshore area of high radionuclide activity extended south and southeast from the FNPP1. The maximum activities of ¹³¹I, ¹³⁴Cs, and ¹³⁷Cs were 329, 650, and 599 Bq L^?1, respectively. The ¹³¹I/¹³⁷Cs ratio in surface water of the high-activity area ranged from 0.6 to 0.7. Considering the radioactive decay of ¹³¹I (half-life 8.02 d), we determined that the radionuclides in this area were directly released from FNPP1 to the ocean. We confirm that aerial radiological surveys can be effective for investigating the surface distribution of anthropogenic radionuclides in seawater. Our model reproduced the distribution pattern of radionuclides derived from the FNPP1, although results simulated by a regional ocean model were underestimated.     

Atmospheric radionuclides from Fukushima Dai-ichi nuclear accident detected in Lanzhou,China

After the Fukushima Dai-ichi nuclear power plant accident on March 11,2011,the radioactivity released from the accident was transported around the globe by atmospheric processes.The radioactivity monitoring program on atmospheric particulate in Lanzhou,China was activated by GSCDC to detect the input radionuclides through atmospheric transport.Several artificial radionuclides were detected and measured in aerosol samples from March 26 to May 2,2011.The peaked activity concentrations(in m Bq/m3)were:1.194(131I),0.231(137Cs),0.173(134Cs)and 0.008(136Cs),detected on April 6,2011.The average activity ratio of131I/137Cs and134Cs/137Cs in air were 13.5 and 0.78.The significant increase of137Cs activity concentration,one order of magnitude higher than pre-Fukushima accident levels,in ground level aerosol was observed in 2013,as its resuspension from soil.The back-trajectory analysis simulated by NOAA-ARL HYSPLIT shows a direct transfer of the air masses released from Fukushima to Lanzhou across the Pacific Ocean,North America and Europe at the height close to 9000 m AGL.The value of effective dose for inhalation is close to one millionth of the annual limit for the general public.     

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.     

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.     

Measurements of 134Cs and 137Cs in urine and estimation of the inter nal dose of an adult exposed to the Chernobyl Accident

To estimate the internal dose of a Chinese visiting scholar internally contaminated because of the Chernobyl Accident, the contents of 134Cs and 137Cs in urine were measured using a Ge（Li） γ-spectrometer. The internal doses were calculated based on data from the ICRP Publications. The effective doses from ^134Cs and ^137Cs were estimated to be 61 μSv and 98 μ Sv, respectively. The sum of 159 μSv was lower than the total effective dose （310 μSv）, from the inhalation and ingestion of natural radionuclides. The dose of ^131I was also reviewed referring to the UNSCEAR 2000 Report. The equivalent effective dose of ^131I was estimated to be 2.9 mSv, 18 times more than the amount of ^134Cs and ^137Cs. Therefore, it is considered that the earlier estimation of internal doses of ^131I is important in evaluating radiation injuries from a nuclear reactor accident.     

福岛核事故后上海气溶胶中~(131)I、~(134)Cs和~(137)Cs的来源途径分析

利用对气溶胶中典型放射性核素(~(131)I和134,~(137)Cs)的分析,可以评估福岛核事故产生的放射性物质对上海及全球的大气放射性本底水平造成的影响。本工作结合核事故释放过程、核素的天然衰变以及气象条件等因素,获得核事故期间上海的气溶胶中~(131)I和134,~(137)Cs活度浓度及其比值的分布特征:~(131)I被检出的时间(2011-03-27)早于~(134)Cs(2011-04-06)和~(137)Cs(2011-04-08),~(131)I的活度浓度(0.01~1.20 mBq/m3)比~(134)Cs(0.01~0.58mBq/m3)和~(137)Cs(0.01~0.65mBq/m3)大2~10倍,而且在不同的时间段出现相应的多峰值现象;~(131)I/~(137)Cs活度浓度比值(1.3~10.6)在2011年4月5日之后呈递减趋势,但是~(134)Cs/~(137)Cs活度浓度比值(0.8~2.9)则一直在1.1左右波动。利用HYSPLIT模型模拟放射性气团运移轨迹的分析方法,表明在核事故期间输入到上海的放射性气溶胶的途径有东北和西北两条主要迁移路径。同时通过结合国内相关城市核事故期间大气放射性监测数据,证实了东北路径在中国境内的控制地位。另外,通过总结和分析北半球大气监测数据中~(131)I/~(137)Cs和~(134)Cs/~(137)Cs活度浓度比值最大值的分布特征,验证了日本核事故产生的放射性气溶胶在北半球的传输过程。     

Analysis of cesium isotope compositions in environmental samples by thermal ionization mass spectrometry – 1. A preliminary study for source analysis of radioactive contamination in Fukushima prefecture

Cesium was recovered from plant samples obtained from Fukushima prefecture. The isotopic ratios of ¹³⁴Cs/¹³⁷Cs and ¹³⁵Cs/¹³⁷Cs were analyzed by thermal ionization mass spectrometry with a single filament method using a TaO activator. Samples containing 5 Bq of ¹³⁷Cs were analyzed with typical analytical errors of approximately 0.5% for ¹³⁴Cs/¹³⁷Cs and approximately 0.1% for ¹³⁵Cs/¹³⁷Cs. Measurements of both ratios showed profiles that were characteristic of the measurements of among other environmental samples reported in the literature. The results showed the isotopic ratios of ¹³⁴Cs/¹³⁷Cs and ¹³⁵Cs/¹³⁷Cs were applicable for the source analysis of radioactive Cs in Fukushima prefecture.     

Radiological assessment of the South Sakhalin Region during the Fukushima-1 accident (Japan)

The results of ¹³¹I, ¹³⁷Cs, and ¹³⁴Cs measurements in the South Sakhalin atmosphere performed with a gamma spectrometer placed in a mobile radiation surveying laboratory are presented. The measurements were performed in March–April 2011 as part of radiation monitoring performed by Rosgidromet in connection with the Fukushima-1 accident in Japan. The maximum recorded ¹³¹I volume activity of inhaled air in South Sakhalin is 8700 times lower than the admissible yearly-average value for the general public. The values for ^137,134Cs are 10⁵ times lower than the corresponding norms.     

Distribution of the 134Cs/137Cs ratio around the Fukushima Daiichi nuclear power plant using an unmanned helicopter radiation monitoring system

Large amounts of radioactive substances were released into the environment by the Fukushima Daiichi nuclear power plant (FDNPP) accident. Several research institutes have mapped the distribution of nuclides with long half-lives, such as ¹³⁴Cs and ¹³⁷Cs. Although the ratio of ¹³⁴Cs and ¹³⁷Cs has been believed to be equal without depending on the location of the contaminated area, several researchers report that it is different depending on places quite a little. We measured the energy spectrum of gamma rays in high resolution within an approximately 3-km radius of the FDNPP by using an unmanned helicopter equipped with a LaBr₃(Ce) scintillation detector. Then, we analyzed the ¹³⁴Cs/¹³⁷Cs ratio in the area from these measured data in detail. The results show that the ¹³⁴Cs/¹³⁷Cs ratio is different between the plume trace extending north and the other plume traces. We have obtained valuable data for identification of which radioactive substances were released by individual reactor units.     

Analysis of cesium isotope compositions in environmental samples by thermal ionization mass spectrometry-3

Cesium was recovered from soil samples obtained in Fukushima prefecture. Isotopic analysis of Cs was performed by γ-spectrometry to determine the activity ratio of ¹³⁴Cs/¹³⁷Cs and thermal ionization mass spectrometry was used to determine the isotopic ratios of ¹³³Cs/¹³⁷Cs and ¹³⁵Cs/¹³⁷Cs. The analytical results showed that both the activity ratio of ¹³⁴Cs/¹³⁷Cs and the isotopic ratio of ¹³⁵Cs/¹³⁷Cs were within the expected values for the Fukushima Daiichi Nuclear Power Plant estimated using the ORIGEN-II code, suggesting that most of the radioactive Cs in the soil sample originated from the Fukushima Daiichi Nuclear Power Plant. The concentration of ¹³⁷Cs and the contribution of radioactive Cs from global fallout were correlated to the distance from the Fukushima Daiichi Nuclear Power Plant, while the contribution of radioactive Cs from each reactor did not show any similar distance dependence.     

Cold Trapping of Fission Products in a Stainless Steel Sodium Loop

The behavior of fission products in sodium system was studied using a cold trap installed in the Toshiba Fission Product Loop, which is a stainless steel inpile sodium loop. The fission products were generated within the liquid sodium by irradiating UO² fuel under sodium convection. The cold trapping behavior of ⁹⁵Zr, ⁹⁵Nb, ¹³²Te, ¹³¹I ¹³⁷Cs and ¹⁴⁰La (¹⁴⁰Ba) was examined by measuring the γ-rays in the cold trap and in the sodium dump tank by means of Ge(Li) detectors. Such fission product nuclides as ^{131 132}Te and ¹³⁷Cs were found to be reversively removed by the cold trap at lower temperatures, with negligible hysteresis. The distribution coefficient K(cm) for the cold trap surface was found tobe expressible by log K=(3.08±0.17)-(0.0112±0.0006)×T(°C) for ¹³¹I, and by log K:=-(4.55±0.29) + (1830±1/140) × 1/T(K) for ¹³⁷Cs. The behavior of ¹³¹I and ¹³⁷Cs during cold trapping can be explained clearly by adsorption model using these K values. While ⁹⁵Zr, ⁹⁵Nb, ¹⁰³Ru and ¹⁴⁰La(¹⁴⁰;Ba) also were detected in the cold trap, the efficacy of cold trapping is far lower for these nuclides than for ¹³¹I and ¹³⁷Cs, and changing the cold trap temperature did not appear to have any appreciable effect on the cold trapping. Presence of ¹⁴¹Ce and ¹⁴⁴Ce was not detectable in the cold trap, although small amounts of these nuclides were detected in the sodium dump tank.     

福岛核事故期间日本至杭州飞机外表面放射性污染监测

报道2011-03-16~03-30从日本抵达杭州的飞机外表面放射性污染监测情况.监测结果表明,从日本抵达杭州的飞机外表面主要受到了131 I 、132 I 、134 Cs 、136 Cs 、137 Cs 等裂变产物的污染,但沾染灰尘数量极少,表面污染轻微,不会对机组人员及乘客产生有健康影响的外照射污染.     

Retrospective Determination of the Internal Irradiation Dose Due to 131I to the Thyroid Gland According to the 137Cs Local Fallout Density

A method is proposed for performing retrospective determination of the internal irradiation dose to the thyroid gland in man as a result of ¹³¹I uptake with fresh cow milk according to the total local ¹³⁷Cs fallout density resulting from nuclear explosions. It is shown that during local fallout the ratio of the numbers of ¹³¹I and ¹³⁷Cs atoms on particle surfaces is about 0.46 and is independent of the fissioning material (²³⁹Pu or ²³⁸U) used in the nuclear charge. This makes it possible to determine the fallout density of ¹³¹I on soil from the local component of the total ¹³⁷Cs fallout density. The information about the total ¹³⁷Cs fallout density on soil is used to calculate the effect of the irradiation dose of ¹³¹I to the thyroid gland in children and adults who lived in the populated points in Altai krai during the nuclear tests conducted in the Semipalatinsk test area. The estimates agree satisfactorily with those obtained by a different method.     

Exact solutions to gaseous flow time and temperature dependent parent and first-daughter fission-product plateout problems

Exact solutions are obtained to the parent and first-daughter time and temperature dependent convective-diffusion equations with radioactive decay in an axisymmetric cylindrical conduit. Time invariant nominal gaseous flow conditions are assumed for which piecewise polynomial spatial representations of the axial temperature distribution are considered. The time dependence of the daughter-product inlet concentration due to parent decay is included. A mass transfer model incorporating these solutions is developed to predict the fission-product plateout on the conduit wall. The temperature dependence of both the diffusion and wall mass transfer coefficients is characterized using Arrhenius relationships. Comparison with experimental ¹³⁴Cs, ¹³⁷Cs, and ¹³¹I data demonstrates model viability in correctly predicting temperature dependent plateout under relevant flow conditions.     

Determination of within-rod caesium and europium isotopic distributions in high burnup fuel rods through computerised gamma-ray emission tomography

Computerised gamma-ray emission tomography has been applied to single PWR UO₂ fuel rods, with pellet averaged burnups of 52, 71, 91 and 126 GWd/t respectively, for the determination of ¹³⁴Cs, ¹³⁷Cs and ¹⁵⁴Eu internal radial distributions. State-of-the-art image reconstruction techniques, analytical and iterative, have been applied, evaluated and compared using test phantoms first and, in a second step, the actual measured data. Further, linear attenuation maps, previously derived on the same samples by means of gamma-ray transmission tomography, have been used to correct for density inhomogeneities. The final results have indicated large central depressions in the caesium distributions, but of varying extent from sample to sample. Particularly interesting is the case of the 126 GWd/t sample, showing a very deep central depression (periphery-to-centre ratios of ∼2.5 for ¹³⁷Cs and ∼3 for ¹³⁴Cs). In addition, a difference in the relative activity distributions of ¹³⁷Cs and ¹³⁴Cs has been observed for all the samples. In contrast, the europium shows an almost flat distribution.