Preparation of Distribution Map of Radiation Doses, etc. (Maps of. Concentration of Tellurium 129m and Silver 110m in Soil) by MEXT

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1 October 31, 2011 Preparation of Distribution Map of Radiation Doses, etc. (Maps of Concentration of Tellurium 129m and Silver 110m in Soil) by MEXT A map of Te-129m concentration in soil and a map of Ag-110m concentration in soil were prepared in the course of the project commenced on June 6, 2011, under the 2011 Strategic Funds for the Promotion of Science and Technology, entitled Establishment of the Base for Taking Measures for Environmental Impact of Radioactive Substances Study on Distribution of Radioactive Substances. 1. Objective of the survey In order to continuously check the impact of radioactive substances deposited on the ground surface on the health of residents and the environment, MEXT measured air dose rates at around 2,200 locations within approximately 100 km from the Fukushima Dai-ichi NPP, and at the same time collected soil samples from the 5 cm surface layer at around five points at each location to analyze nuclides by using germanium semiconductor detectors, prior to the rainy season, before any changes occurred on the soil surface. (The results of the measurement of air dose rates were already publicized on August 2 and 12. The maps of radioactive cesium and iodine concentration in soil were released on August 30 and on September 21, respectively. The results of nuclide analysis of plutonium and strontium were released on September 30.) In the meantime, in the process of analyzing I-131 and radioactive cesium, it was confirmed that Te-129m *1 and Ag-110m, *1 which are also gamma-emitting nuclides, were detected throughout relatively wider areas. Therefore, we conducted analysis of all the soil samples again to ascertain the distribution of these nuclides. As a result, Te-129m and Ag-110m were detected in many of the soil samples. The Review Meeting for the Preparation of Distribution Map of Radiation Dose, etc. (Attachment 1), which was established in MEXT, examined the validity of the results of the measurement and discussed how to compile them into maps, and then we prepared this report. *1: When there are multiple nuclides with the same atomic number and mass number, such as Tellurium 129m and Silver 110m, the letter m showing that the substance is in a metastable state is added to distinguish a radioactive nuclide with a relatively higher energy level. 2. Details of the survey

2 Periods for collecting soil samples: First period: June 6 to June 14 Second period: June 27 to July 8 Entities for collecting soil samples: Osaka University, University of Tsukuba, The University of Tokyo, Japan Atomic Energy Agency, The Federation of Electric Power Companies of Japan Local support team, and others (see the List of Organizations Offering Cooperation in the Preparation of Distribution Map of Radiation Dose, etc. released on August 2 and 12 for details) Entities for conducting nuclide analysis: The Japan Chemical Analysis Center, the University of Tokyo, and 19 other organizations (see the List of Organizations Offering Cooperation in the Nuclide Analysis for the Preparation of a Distribution Map of Radiation Doses, etc. (Soil Concentration Map) released on August 30 for details) Targets: Concentration per unit area of Te-129m and Ag-110m deposited on the ground surface 3. Readings of this survey The soil concentration maps* compiling the results of nuclide analysis of Te-129m and Ag-110m contained in soil samples are as shown in Attachments 2-1 and 2-2. *The maps show the distribution of radiation levels per unit area that remain around the soil surface. In order to help evoke an image, the expression soil concentration map is used for descriptive purposes in this report. The soil concentration maps were prepared under the following conditions. The maps are based on the results of nuclide analysis of the soil samples that MEXT collected between June 6 and July 8 in the course of the project under the 2011 Strategic Funds for the Promotion of Science and Technology, entitled Establishment of the Base for Taking Measures for Environmental Impact of Radioactive Substances Study on Distribution of Radioactive Substances. Methods to collect soil samples and to conduct nuclide analysis are as shown in Attachment 3. Nuclide analysis of the soil samples was conducted by means of germanium semiconductor detectors at 21 research organizations nationwide. Because there was an interval between the first period and the second period for collecting soil samples, upon preparing maps, we corrected measured values into radiation levels as of June 14, the final day of the first period, taking into consideration the half-life period for each nuclide. The airborne monitoring in April revealed that spots showing high radiation doses were concentrated in areas within 80 km from the Fukushima Dai-ichi NPP. Therefore, MEXT, in principle, conducted measurement at one point per 2 2 km grid for these areas, and at one

3 point per km grid for the areas 80 to 100 km from the Fukushima Dai-ichi NPP and other parts of Fukushima prefecture. The arithmetic average of the results of nuclide analysis of multiple soil samples collected at the same point was adopted as the amount of Te-129m and Ag-110m deposited on the ground surface at each monitoring point. The results of nuclide analysis include values under minimum limit of detection. Therefore, in preparing the maps, amounts of Te-129m and Ag-110m deposition at each point was obtained by the same manner of preparing the Map of Iodine 131 Concentration in Soil. The measures are described below (see Attachment 4). (i) When the results of nuclide analysis of multiple soil samples collected at the same point are all below the minimum limit of detection, it is deemed that Te-129m and Ag-110m were not detectable at the point. (ii) When any one of the results of nuclide analysis of multiple soil samples collected at the same point is above the minimum limit of detection, even if all the remaining results are below the limit, the arithmetic average calculated between the values above the limit and the reference values obtained in the case of measured values below the limit is to be used as amount of the deposition at the point. When the results of nuclide analysis of multiple soil samples collected at the same point are all above the detection limit, the arithmetic average among these values is to be obtained. 4. Discussion 4.1 Overall discussion As soil samples for this survey were collected at places with certain space free from disturbance, we were able to ascertain the distribution of Te-129m and Ag-110m as of June to July widely and in detail. Therefore, the obtained results are expected to be utilized as valuable data to examine the radioactive plume released initially from the NPP, and ascertain how radioactive substances have been deposited on the ground surface. In the report on the Chernobyl accident, an assessment was conducted for the release of Te-129m, but not for the release of Ag-110m. Nor is the estimated release of Ag-110m shown in the publication entitled Regarding the Evaluation of the Conditions on Reactor Cores of Unit 1, 2 and 3 related to the Accident at Fukushima Dai-ichi Nuclear Power Station, Tokyo Electric Power Co. Inc. by the Nuclear and Industrial Safety Agency (dated June 6, 2011). Therefore, this map of Ag-110m concentration in soil is expected to be also utilized as valuable data when estimating the source of released Ag-110m, as well as from the viewpoint of assessing air doses. As the analysis of Te-129m and Ag-110m was not originally scheduled in this survey, measurement results were not available for all of the soil samples. Therefore, we will conduct an additional survey in order to elaborate the maps of Te-129m and Ag-110m concentrations in soil. For some points where the largest amounts of Te-129m and Ag-110m depositions were detected in this survey, *1 we calculated possible inhalation exposure caused by resuspension from the soil and accumulated external exposure from the soil supposing that a person would stay there for 50

4 years (hereinafter referred to as the estimated effective dose over 50 years ), based on the Generic Assessment Procedures for Determining Protective Actions During a Reactor Accident proposed by IAEA. *2 As a result, it was confirmed that the estimated effective doses over 50 years for these points were considerably smaller than the estimates for the locations where the largest deposition amounts of cesium 134 or 137 were detected. *1: These points are located in the restricted areas and planned evacuation areas, in which nobody resides at present. *2: Method to assess exposure levels described in IAEA-TECDOC-955, 1162 Presuming that a radioactive nuclide deposited on the ground stays on that spot, this method defines the procedures to assess accumulated effective doses for a certain period of time after the nuclide is deposited on the ground surface (for the first month, for the second month, and for 50 years). The effective doses thus obtained include external exposure doses and committed doses caused by the inhalation of resuspended radioactive nuclides. In the calculation of accumulated effective doses, consideration was given to the effects of radionuclide decay, nuclear transmutation, and weathering. Furthermore, in order to assess inhalation exposure caused by resuspended radioactive nuclides on the safer side, 10-6 /m was adopted as the resuspension factor, which is larger than the value actually measured at the time of the nuclear accident. (Reference 1) Estimated effective doses for 50 years at the points where the largest amounts of Te-129m and Ag-110m depositions were detected in this survey (i) Te-129m : 0.6 msv (ii) Ag-110m : 3.2 msv (Reference 2) Estimated effective doses for 50 years at the points where the largest amounts of Cs-134 and Cs-137 depositions were detected in this survey (v) Cs-134 : 71 msv (vi) Cs-137 : 2.0 Sv (2,000 msv) Compared with the estimated effective doses for 50 years of Cs-134 and Cs-137, those of Te-129m and Ag-110m were very small. Therefore, when assessing exposure doses or implementing decontamination measures in the future, we should focus attention on deposition amounts of Cs-134 and Cs Discussion on the measurement results of Te-129m and Ag-110m When comparing the ratios of deposition amounts of Te-129m and Ag-110m to those of Cs-137, respectively, although the deposition of Cs-137 was not large, and Te-129m was confirmed to be deposited on the ground surface in the southern coastal areas at different ratios from those observed at monitoring points in the northern areas and the southern inland areas, as seen in Attachment 5. At some of the inland parts in the southern coastal areas, the ratios of deposition

5 amounts of Te-129m to those of Cs-137 were considerably high. Although no clear correlation of the deposition amount was found between Ag-110m and Cs-137, relatively higher ratios of deposition amounts of Ag-110m to those of Cs-137 were confirmed along the coast in the northern and southern areas, compared with the surrounding areas. The reasons may be as follows. The ratios of Te-129m and Ag-110m to Cs-137 contained in formed radioactive plumes and their physical and chemical forms varied due to a difference in when each radioactive substance was released from the NPP. Weather conditions were not the same when multiple radioactive plumes with different compositions of Te-129m, Ag-110m, and Cs-137 passed away. In the case of the Chernobyl accident, it was confirmed that the ratios of deposition amounts of other radioactive nuclides to those of radioactive cesium were generally decreased according to the distance from the reactor. However, there was a report which Te-129m was deposited almost evenly at similar ratios, irrespective of such distance. This survey also showed a similar trend in ratios of deposition amounts of Te-129m to those of Cs-137. This may be because Cs-137 and Te-129m are both volatile radionuclides with a boiling point of 671 C and 988 C, respectively, and they may have been deposited in a similar manner. On the other hand, ratios of deposition amounts of Ag-110m to those of Cs-137 in this survey vary widely, which indicates that Ag-110m has been deposited in a different manner from that of Cs-137. This may be because the boiling point of silver is 2,164 C, being higher than that of radioactive cesium and Te-129m, and therefore, Ag-110m was released not in the form of gas but as a particulate substance into the environment due to the accident and took on a different behavior from that of radioactive cesium. 5. Future plans Regarding the results of the measurement of radioactive nuclides other than iodine-131, radioactive cesium, radioactive strontium, and plutonium, as well as the results of the survey on the movement of radioactive substances, we have verified their validity and have discussed how to compile them, based on opinions from experts. We will prepare a report compiling the results of this survey and will release it later. We will also publicize anything that we find necessary to release immediately in the process of preparing the report. Contacts Emergency Operation Center Horita, Oku Tel : Ex.4604, 4605

6 Attachment 1 Concerning the Review Meeting for the Preparation of Distribution Map of Radiation Dose, etc. 1. Objective of the meeting Based on the Plan to Strengthen Environmental Monitoring (Nuclear Emergency Response Headquarters; April 22, 2011) and the Policies for Emergency Responses for Those Affected by the Nuclear Incident (Nuclear Emergency Response Headquarters; May 17, 2011), MEXT decided to prepare a distribution map of radiation doses and other maps for the purpose of utilizing them to ascertain the overall picture of the accident and consider the removal of the designation of evacuation areas. Prior to the preparation of the maps, the Review Meeting for the Preparation of Distribution Map of Radiation Dose, etc. will be held to discuss technical matters. 2. Matters to be discussed Technical matters related to the preparation of an air dose rate map for the purpose of ascertaining the distribution of radioactive substances Technical matters related to the preparation of a soil concentration map for the purpose of ascertaining the accumulation of radioactive substances in the surface layer of soil Technical matters related to the preparation of a radiation concentration distribution map for farmland soil for the purpose of ascertaining the accumulation of radioactive substances in farmland soil Technical matters related to the confirmation of movements of radioactive substances from the soil surface (movements to rivers and groundwater, etc., splash from the soil surface, and infiltration into soil, etc.) 3. Clerical work Clerical work of the meeting will be handled by the Nuclear Safety Division of the Science and Technology Policy Bureau.

7 4. Members of the review meeting Name IKEUCHI Yoshihiro KIMURA Hideki KOYAMA Yoshihiro SAITO Kimiaki SHIBATA Tokushi SHIMO Michikuni SUGIURA Nobuyuki TAKAHASHI Takayuki TAKAHASHI Hiroyuki TAKAHASHI Tomoyuki CHINO Masamichi NAGAOKA Toshi NAKAMURA Hisashi HASEBE Akira HISAMATSU Shunichi MURAMATSU Yasuyuki YOSHIDA Satoshi Professional affiliation Commissioner, Japan Chemical Analysis Center Vice Counselor, Nuclear Safety Division, Department of Environment and Public Affairs, Aomori Prefectural Government Division Chief, Nuclear Safety Division, Department of Living Environment, Fukushima Prefectural Government Chief of Senior Researcher, Headquarters of Fukushima Partnership Operations, Japan Atomic Energy Agency Visiting Researcher, Japan Proton Accelerator Research Complex, Japan Atomic Energy Agency Visiting Professor, Fujita Health University Director, Research Center for Radiation Emergency Medicine, National Institute of Radiological Sciences Vice President (in charge of research) and Library Director, Fukushima University Professor, Department of Nuclear Engineering and Management, The University of Tokyo Associate Professor, Division of Nuclear Engineering Science, Kyoto University Research Reactor Institute Vice Directorate Head, Nuclear Science and Engineering Directorate, Japan Atomic Energy Agency Head of the Safety Management Division, Japan Synchrotron Radiation Research Institute Professor Emeritus, Tohoku University Research Supervising Chief, National Institute for Agro-Environmental Sciences Department Director, Department of Radioecology, Institute for Environment Sciences Professor, Department of Chemistry, Faculty of Science, Gakushuin University Unit Chief, Operation and Planning Unit, Research Center for Radiation Protection, National Institute of Radiological Sciences

8 Map of Tellurium 129m Concentration in Soil Attachment 2-1 Fukushima Dai-ichi NPP Legend Planned Emergency evacuation evacuation preparation areas areas (Removed on September 30, 2011) Accumulation of Te-129m (As of June 14) Above the detection Below the detection limits for all limits for at least samples one sample Habitable (2km 2km) 10km 10km) Non-habitable (2km 2km)

9 Map of Silver 110m Concentration in Soil Attachment 2-2 Fukushima Dai-ichi NPP Legend Planned evacuation areas Emergency evacuation preparation areas (Removed on September 30, 2011) Accumulation of Ag-110m (As of June 14) Above the detection Below the detection limits for at least limits for all samples one sample Habitable (2km 2km) 10km 10km) Non-habitable (2km 2km)

10 Attachment 3 Method to Collect Soil Samples and Means for Nuclide Analysis of Soil Samples 1. Method to collect soil samples We collected soil samples at around five points selected at each of the accessible locations, preferably within an area of 3m 3m. We tried to collect samples at intervals as equal as possible. Through a preliminary survey, it was confirmed that I-131, Cs-134, and Cs-137 exist in soil within 5 cm from the ground surface. Therefore, we used the U8 containers (100 ml plastic containers) to collect soil samples taken from the soil surface to the depth of 5 cm. We sufficiently stirred collected soil samples and put them in the U8 containers. In order to ascertain the deposition of radioactive substances released from the Fukushima Dai-ichi NPP, we collected soil samples together with weeds or other vegetation if there were any of them at the relevant points. We also collected root zones as soil samples. We took photos to record and identify collected soil samples, clearly showing labels with sample numbers, soil types, and soil colors. We put each soil sample into a bag separately and attached a label with the sample number, date and time on which the sample was collected, and the name of the person who collected it. We thus tried to make sure not to mix up samples. We measured and recorded dose equivalent rate of the surface of sample containers as reference data to be used when conducting nuclide analysis. We changed cotton gloves and rubber gloves each time we collected soil sample. Thus, we tried to avoid cross-contamination and mixture of nuclides among samples. In order to avoid cross-contamination, we decontaminated tools used for collecting soil samples after each use. After confirming that containers were completely sealed, we wiped their surfaces with alcohol tissue, etc. for decontamination, put them into bags, and transported them to analysis organizations. When transporting them, we complied with the regulations for Type-L packages. 2. Means for nuclide analysis of soil samples Measurements of radiation concentration in soil samples were conducted by using germanium semiconductor detectors (Ge detectors), which were calibrated based on standard radiation sources with known radiation levels. Considering the possibility of detecting short-half-life radionuclides, measurement was conducted for a maximum of one hour. Even if the measurement values of short-half-life radionuclides were below the detection limits, obtained nominal radiation levels are also indicated as reference values (< A LD (lower limit of detection) Bq/m 2 ; A B Bq//m 2 ). After finishing the measurement of each soil sample, we definitely conducted decontamination of the inside of the detector cover to place samples or confirmed that no radioactive substances

11 adhered to the detector. 3. System to verify analysis results In order to avoid mixing up soil samples at the time of measurement and to ensure the validity of measurement results, we prepared check lists for each procedure as measurement records and repeated checks by multiple people. In order to ensure that the means of spectral analysis for nuclide identification can be checked in any time, we retained all information, including spectral data, count numbers, and measurement results for standard samples. All data were tabulated by responsible persons of respective measurement organizations, and the analytical methods and results were checked independently by the organization in charge of compiling the overall results. 4. Cross-checking of nuclide analysis results In 3 % of the collected soil samples, the same samples were analyzed by the Japan Chemical Analysis Center and another organization, or by the University of Tokyo and another organization, for cross-checking.

12 Attachment 4 Deposition Amounts of Te-129m and Ag-110m at Respective Monitoring Points to be Used for Preparing Soil Contamination Maps 1. Background As the half-lives of Te-129m and Ag-110m are relatively short (Te-129m: 33.6 days; Ag-110m: days), their nuclide analysis had not been originally scheduled in this survey. Therefore, at many monitoring points, significant values were not obtained with germanium semiconductor detectors, or were measured only values below the lower limits of detection. Furthermore, we were not able to conduct nuclide analysis for all of the collected soil samples. 2. Deposition amounts of Te-129m and Ag-110m at respective monitoring points to be used for preparing soil contamination maps With regard to multiple soil samples collected at each of the monitoring points, measurement results above the lower limits of detection were obtained at around 800 points for Te-129m and at around 350 points for Ag-110m. For preparing soil contamination maps, the deposition values at each monitoring point were used, which were obtained as the same manner of preparing the Map of I-131 Concentration in Soil, as described below. (i) When the results of nuclide analysis of multiple soil samples collected at the same point are all below the lower limit of detection, it is deemed that Te-129m and/or Ag-110m were not detectable at said point, because no statistically significant values were made available. (ii) When any one of the results of nuclide analysis of multiple soil samples collected at the same point shows a significant value above the lower limit of detection, it is judged that Te-129m and/or Ag-110m were detected at said point, and the deposition amounts of Te-129m and/or Ag-110m at said point are to be determined as follows. When any one of the results of nuclide analysis of multiple soil samples collected at the same point is above the lower limit of detection, said value(s) above the limit and reference values obtained in the case of measured values below the limit are to be used for calculating the arithmetic average, for the purpose of obtaining the most probable average. When the results of nuclide analysis of multiple soil samples collected at the same point are all above the lower limit of detection, the arithmetic average among these values is to be used. When negative reference values are obtained due to statistical dispersion, the measurement result of said point is considered to be zero in calculating the average. Also when reference values are not indicated although the measured values are below the lower limit of detection, the measurement result of the relevant point is considered to be zero.

13 Attachment 5 Ratios of Deposition Amounts of Te-129m and Ag-110m to Those of Cs-137 at Points Where Soil Samples Were Collected 1. Objective In order to check the deposition of Te-129m and Ag-110m on the ground surface, we compared the ratios of their deposition amounts against those of Cs-137 at monitoring points located to the north (the northern areas) and to the south (the southern areas) of the Fukushima Dai-ichi NPP. 2. Results of the survey 2.1 Deposition of Te-129m (i) Ratios of deposition amounts of Te-129m to those of Cs-137 The ratios of deposition amounts of Te-129m to those of Cs-137 are indicated on a map, with regard to monitoring points where the measurement results of Te-129m are available (see Reference 1). As a result, it was confirmed that the ratios of deposition amounts of Te-129m to those of Cs-137 are larger at monitoring points located in the south and within 28km to the west of the Fukushima Dai-ichi NPP (hereinafter referred to as the southern coastal areas ) than at monitoring points located also in the south but 28km or further to the west of the NPP (hereinafter referred to as the southern inland areas ) and at monitoring points in the northern areas. (ii) Detailed comparison between the deposition of Te-129m and Cs-137 in the northern areas and the southern areas (inland areas and coastal areas) In order to compare the deposition of Te-129m and Cs-137 in detail, we made a graph to show deposition amounts of Te-129m and Cs-137 at monitoring points located in the northern areas and the southern areas (inland areas and coastal areas) (see Reference 3). The result shows that the average ratio of deposition amounts of Te-129m to those of Cs-137 in the northern areas was around 0.19, while that in the southern coastal areas was around It was confirmed that the ratios of deposition amounts of Te-129m to those of Cs-137 are relatively higher in the southern coastal areas than in the northern areas. Such average in the southern inland areas was around 0.23, showing a similar trend as in the northern areas. At some of the inland parts in the southern coastal areas (within a circle in red in Reference 3 (viii)), the ratio of deposition amounts of Te-129m to those of Cs-137 was considerably high, at Deposition of Ag-110m (i) Ratios of deposition amounts of Ag-110m to those of Cs-137 The ratios of deposition amounts of Ag-110m to those of Cs-137 are indicated on a map, with regard to monitoring points where the measurement results of Ag-110m are available (see References 2 and 4). Ratios vary significantly and no correlation was found between deposition amounts of

14 Ag-110m and those of Cs-137, but it was confirmed that relatively higher ratios of deposition amounts of Ag-110m to those of Cs-137 were confirmed along the coast in the northern and southern areas.

15 Ratio of deposition amounts of Te-129m to those of Cs-137 (Reference 1) Fukushima Dai-ichi NPP Legend Planned evacuation areas Emergency evacuation preparation areas (Removed on September 30, 2011) Ratio between Te-129m and Cs-137 (As of June 14) Habitable (2km 2km) 10km 10km) Non-habitable (2km 2km)

16 Ratio of deposition amounts of Ag-110m against those of Cs-137 (Reference 2) Fukushima Dai-ichi NPP Legend Planned evacuation areas Emergency evacuation preparation areas (Removed on September 30, 2011) Ratio between Ag-110m and Cs-137 (As of June 14) Habitable (2km 2km) 10km 10km) Non-habitable (2km 2km)

17 (Reference 3) Relation of deposition amount between Te-129m and Cs-137 in the northern areas and the southern areas (inland areas and coastal areas) (part 1) Relation of deposition amount between Te-129m and Cs-137 Average ratio of deposition amounts of Te- 129m to those of Cs Relation of deposition amount between Te-129m and Cs-137 in the northern areas Average ratio of deposition amounts of Te- 129m to those of Cs Northern areas

18 (Reference 3) Relation of deposition amount between Te-129m and Cs-137 in the northern areas and the southern areas (inland areas and coastal areas) (part 2) Relation of deposition amount between Te-129m and Cs-137 in the southern coastal areas Average ratio of deposition amounts of Te- 129m to those of Cs Southern coastal areas Relation of deposition amount between Te-129m and Cs-137 in the southern inland areas Average ratio of deposition amounts of Te- 129m to those of Cs Southern inland areas

19 (Reference 4) Relation of deposition amount between Ag-110m and Cs-137 in the northern areas (inland areas and coastal areas) and the southern areas (part 1) Relation of deposition amount between Ag-110m and Cs-137 Average ratio of deposition amounts of Ag- 110m to those of Cs