著者

長坂 秀雄 飛松 敏美 田原 美香 横堀 誠一 秋永 誠

出版者

一般社団法人 日本原子力学会

雑誌

日本原子力学会和文論文誌 (ISSN:13472879)

巻号頁・発行日

vol.2, no.3, pp.240-250, 2003-09-25 (Released:2010-03-08)

参考文献数

8

被引用文献数

1 2

---

This paper deals with the system interaction performance of the BWR drywell local cooler (DWC) in combination with containment spray as a Japanese Phase-II accident management (AM). By using almost full height simulation test facility (GIRAFFE-DWC) with volumetric scaling ratio of 1/600 for a typical BWR containment, the system integral tests simulating BWR low pressure vessel failure sequence were accomplished during about 14 hours. In case of DWC application, the containment pressure increase was found milder due to DWC heat removal performance. Initial spray timing was delayed about 3 hours and each spray period was reduced almost by half, which contributed to the containment gas compression. These containment pressure transients were confirmed by analyzing the severe accident analysis code of MELCOR. It was concluded that the application of a BWR DWC to Phase-II AM measure is quite promising from the point of delaying or preventing the containment venting.

著者

池田 孝志

出版者

一般社団法人 日本原子力学会

雑誌

日本原子力学会和文論文誌 (ISSN:13472879)

巻号頁・発行日

vol.2, no.2, pp.140-144, 2003-06-25 (Released:2010-01-21)

参考文献数

4

被引用文献数

1 1

---

The Rankine-Hugoniot relation for a detonation wave has been numerically analyzed for hydrogen-oxygen mixture to evaluate its explosion pressure taking radical products at high temperature into consideration. The present study elucidates a scheme of convergence to the Jouguet point obtained by triple iterations over temperature, specific volume, and mole fractions of product gases. The total number of product gas atoms changes monotonously in the iteration over the mole fractions under the condition of constant temperature and specific volume. The final solution is, hence, obtained by the interpolation of the last two iteration points that extend the point where the total number of gas atoms is conserved. Every term of the Rankine-Hugoniot relation also changes monotonously in the iteration over the specific volume under constant temperature condition. So the final specific volume is determined in the same way as the mole fractions. In conclusion, the Jouget point with corresponding explosion pressure obtained dose not depend on the iteration steps or the truncation conditions.

著者

深谷 裕司 國富 一彦 小川 益郎

出版者

一般社団法人 日本原子力学会

雑誌

日本原子力学会和文論文誌 (ISSN:13472879)

巻号頁・発行日

vol.14, no.3, pp.189-201, 2015 (Released:2015-08-15)

参考文献数

25

---

A study on reduction of potential radiotoxicity for spent fuel by using high-temperature gas-cooled reactors (HTGRs) has been performed. Unlike partitioning and transmutation (P&T), the reactor concept is investigated from the viewpoint of reduction of radiotoxicity generation itself. To reduce radiotoxicity, 238U, which generates Pu, Am and Cm, should be excluded. Therefore, we proposed HTGR fueled by new-concept fuels with alternative fuel matrixes instead of 238U. Those are yttria-stabilized zirconia (YSZ) and thorium, and the fissile material is highly enriched uranium (HEU) with an enrichment of 93%. With HEU, the radiotoxicity can be significantly reduced, and the cooling time to decay to a natural uranium level can be shortened to approximately 800 years. Fuel integrity and proliferation resistance can be maintained by dilution using YSZ, and the neutronic characteristics of self-regulation are maintained by the loading of erbium. The fuel can generate the same amount of heat as ordinary uranium fuel. The electricity generation cost is as cheap as GTHTR300. It is concluded that the proposed reactor concept can reduce the cooling time by less than 1% from 100 thousand years to 800 years without additional development of innovative technology.

著者

平山 英夫 近藤 健次郎 海野 泰裕 松村 宏 岩瀬 広 柚木 彰 佐々木 慎一

出版者

一般社団法人 日本原子力学会

雑誌

日本原子力学会和文論文誌 (ISSN:13472879)

巻号頁・発行日

vol.14, no.3, pp.141-150, 2015 (Released:2015-08-15)

参考文献数

16

被引用文献数

1

---

A rapid and simple method to measure the concentration of 90Sr in water by measuring β-rays from 90Y was presented. Under the situation that 90Sr/90Y, 134Cs and 137Cs are the main radionuclides included in the water sample, only β-rays from 90Y can transmit through 1.5-mm-thick polyethylene. From this fact, it is possible to measure β-rays from 90Y using a β-ray detector, such as the GM-counter, set beneath the 1.5-mm-thick bottom of the water bottle containing the sample with 90Sr/90Y. The acrylic resin collimator having 0 cm, 1.00 cm, 1.50 cm or 3.00 cm diameter was made to detect β-rays at the fixed region of the GM-counter used. Contributions from bremsstrahlung produced by β-rays and γ-rays from radionuclides such as 134Cs and 137Cs/137mBa are removed by subtracting the count rate measured with a 1.00 cm acrylic resin collimator without a hole as the background count rate. The developed method was studied using the bottle routinely used at the Fukushima Daiichi Nuclear Power Station. It was confirmed that the developed method can be applied to measure the 90Sr concentration in water to the order of several Bq/cm3 if 134Cs and 137Cs concentrations are less than or equal to the 90Sr/90Y concentration.

著者

滑川 東 高木 直行 大岡 靖典 山崎 正俊

出版者

一般社団法人 日本原子力学会

雑誌

日本原子力学会和文論文誌 (ISSN:13472879)

巻号頁・発行日

vol.11, no.2, pp.118-126, 2012 (Released:2012-05-15)

参考文献数

14

被引用文献数

1 2

---

In the development of the above 5% enrichment fuel, which is one of the targeted concepts of the next-generation LWR, a reduction in power generation cost is expected. However, the introduction of the above 5% enrichment fuel has several adverse effects on the cost, such as SWU increase, newly required measures for criticality prevention, and increases in gamma, neutron and heat production levels. In addition, the power generation cost is greatly influenced by the uncertainty of uranium price; thus, the sensitivities of those parameters were analyzed. By sensitivity analysis, the range of parameters required to improve the generation cost was clarified. We assumed that the throughput of fuel fabrication is reduced by one third by employing the above 5% enrichment fuel and the spent fuel is reprocessed in the FBR reprocessing plant. In conclusion, it is demonstrated that the power generation cost can be reasonably reduced by increasing enrichment up to 7% or more in the case that the uranium price is less than ten times as much as the reference price and also the increase in fabrication cost is prevented by introducing Erbia credit.

著者

平山 英夫 川崎 将亜 松村 宏 大倉 毅史 波戸 芳仁 佐波 俊哉 滝 光成 大石 哲也 吉澤 道夫

出版者

一般社団法人 日本原子力学会

雑誌

日本原子力学会和文論文誌 (ISSN:13472879)

巻号頁・発行日

vol.13, no.3, pp.119-126, 2014 (Released:2014-08-15)

参考文献数

4

被引用文献数

3 6

---

A method of deducing the I-131 concentration in a radioactive plume from the time history of peak count rates determined from pulse height spectra obtained from an NaI(Tl) scintillation detector employed as a detector of a monitoring post was presented. The contribution to the count rates from I-131 accumulated around the monitoring post was subtracted in accordance with the time history, taking into consideration the cumulative attachment and its decay. The concentrations of I-131 in the plumes were estimated from the count rates using the calculated response of the NaI(Tl) detector with egs5 for a model of a plume uniformly containing I-131. This method was applied to the data from the monitoring posts at Nuclear Science Research Institutes of Japan Atomic Energy Agency (JAEA). The estimated time history variation of I-131 concentrations in plumes was in fair agreement with those measured directly by an air sampling method. The difference was less than a factor of 4 for plumes that arrived on March 15 and March 21, indicating relatively high I-131 concentrations among the plumes studied in this work.

著者

嶋田 善夫 宮崎 孝正

出版者

一般社団法人 日本原子力学会

雑誌

日本原子力学会和文論文誌 (ISSN:13472879)

巻号頁・発行日

vol.5, no.3, pp.167-178, 2006-09-25 (Released:2010-01-21)

参考文献数

21

---

In order to analyze large amounts of trouble information of overseas nuclear power plants, it is necessary to select information that is significant in terms of both safety and reliability. In this research, a method of efficiently and simply classifying degrees of importance of components in terms of safety and reliability while paying attention to root-cause components appearing in the information was developed. Regarding safety, the reactor core damage frequency (CDF), which is used in the probabilistic analysis of a reactor, was used. Regarding reliability, the automatic plant trip probability (APTP), which is used in the probabilistic analysis of automatic reactor trips, was used. These two aspects were reflected in the development of criteria for classifying degrees of importance of components. By applying these criteria, a method of quantitatively and simply judging the significance of trouble information of overseas nuclear power plants was developed.

著者

茶木 雅夫 日野 哲士 松浦 正義 守屋 公三明 日比 宏基 瀧本 洋樹 坂場 弘 雨夜 隆之 沼田 守

出版者

一般社団法人 日本原子力学会

雑誌

日本原子力学会和文論文誌 (ISSN:13472879)

巻号頁・発行日

vol.5, no.4, pp.257-267, 2006-12-25 (Released:2010-01-21)

参考文献数

10

---

A new small reactor concept named Package-Reactor has been developed through a joint research of Hitachi, Ltd., and Mitsubishi Heavy Industries. Several key design of its nuclear steam supply system have been investigated, taking into account both Boiling Water Reactor (BWR) and Pressurized Water Reactor (PWR) technologies. The PackageReactor is a stand-alone energy supply system, and is designed to attain high reliability, high safety, good maintainability, good operability and low construction cost. To achieve these aims, the reactor adopts natural-circulation core cooling systems. The reactor has no active devices inside its high pressure boundary. Combining a turbine electric power generation and biomass refining, which is supported by JGC Corporation or chemical heat pipe systems attains a perfect base load operation. The whole system is simple and small to be easily constructed with a very short period even at remote regions with poor infrastructures. The Package-Reactor is an innovative nuclear power plant concept to pioneer and develop new markets of the nuclear power business.

著者

大越 実 鳥井 弘之 藤井 靖彦

出版者

一般社団法人 日本原子力学会

雑誌

日本原子力学会和文論文誌 (ISSN:13472879)

巻号頁・発行日

vol.6, no.4, pp.421-433, 2007 (Released:2012-03-07)

参考文献数

15

被引用文献数

2 2

---

Siting of radioactive waste management facilities frequently raise arguments among stakeholders such as a municipal government and the residents. Risk communication is one of the useful methods of promoting mutual understanding on related risks among stakeholders. In Finland and Sweden, siting selection procedures of repositories for spent nuclear fuels have been carried out successfully with risk communication. The success reasons are analyzed based on the interviews with those who belong to the regulatory authorities and nuclear industries in both countries. Also, in this paper, risk communication among the Japan Radioisotope Association (JRIA), a local government and the general public, which was carried out during the establishment process of additional radioactive waste treatment facilities in Takizawa Village, Iwate Prefecture, is analyzed based on articles in newspapers and interviews with persons concerned. The analysis results showed that good risk communication was not carried out because of the lack of confidence on the JRIA, decision making rules, enough communication chances and econmic benefits. In order to make good use of these experiences for the future establishment of radioactive waste management facilities, the lessons learned from these cases are summarized and proposals for good risk communication (establishment of exploratory committee and technical support system for decision making, and measurements to increase familiarity of radioactive waste) are discussed.

著者

和田 隆太郎 田中 知 長崎 晋也

出版者

一般社団法人 日本原子力学会

雑誌

日本原子力学会和文論文誌 (ISSN:13472879)

巻号頁・発行日

vol.8, no.1, pp.19-33, 2009 (Released:2012-02-22)

参考文献数

28

被引用文献数

4 4

---

Generally speaking, a vast, advanced and unfamiliar science and technology are unacceptable to the public for fear of their unknown nature. Here, the social acceptance process model was examined on the basis of the analysis of the cause phenomenon and numerical grounds, by referring to the problems on the application of literature documentation for location examination of a high-level radioactive waste disposal site in Toyo town in Kochi Pref. in April 2007. In analyzing the Toyo town case, we have found a possibility that the majority of local residents knew very little about the object opposed by the fringe route processing. To ensure a healthy decision making by the public, it is vital to convey fundamental information using sufficient wide-area PR media before the issue becomes actual. After the issue becomes actual, dialog with residents through a careful technology assessment is indispensable. The authors focus attention on the decision-making process of human beings from the social and psychological viewpoints, and point out that it is desirable for promoting social acceptance by adopting two approaches: a direct approach aiming at better intelligibility for the different resident layers and a deductive approach in technological essence.

著者

八木 絵香 高橋 信 北村 正晴

出版者

一般社団法人 日本原子力学会

雑誌

日本原子力学会和文論文誌 (ISSN:13472879)

巻号頁・発行日

vol.6, no.4, pp.444-459, 2007 (Released:2012-03-07)

参考文献数

17

被引用文献数

2 5

---

An action research project called dialogue forum has been conducted in this study. The essential constituent of the project is a series of repetitive dialogue sessions carried out by lay citizens, nuclear experts, and a facilitator. One important feature of the project is that the study has been conducted based on the qualitative research methodology. The changes in opinions and attitude of the dialogue participants have been analyzed by an ethno-methodological approach. The observations are summarized as follows. The opinions of the citizen participants showed a significant shift from emotional to practical representations along with the progression of the dialogue sessions. Meanwhile, their attitude showed a marked tendency from problem-statement-oriented to problem-solving-oriented representation. On the other hand, the statements of the expert participants showed a significant shift from expert-based to citizen-based risk recognition and description, and their attitude showed a clear tendency from teaching-oriented to colearning-oriented thinking. These changes of opinions and attitude have been interpreted as a coevolving rather than a single process. It can be stressed that this type of change is most important for the reestablishment of mutual trust between the citizens and the nuclear experts. In this regard “The Process Model of Coevolution of Risk Recognition” has been proposed as a guideline for developing a new scheme of public communication concerning nuclear technology. The proposed process model of coevolution of risk recognition is regarded to be essential for appropriate relationship management between nuclear technology and society in the near future.

著者

山田 英司

出版者

一般社団法人 日本原子力学会

雑誌

日本原子力学会和文論文誌 (ISSN:13472879)

巻号頁・発行日

vol.6, no.4, pp.383-392, 2007 (Released:2012-03-07)

参考文献数

27

被引用文献数

3 3

---

In response to the recent structural imbalance of oil supply and demand, Japan has placed energy security at the top agenda of its energy policies. A review of the energy security level has importance in formulating and steering energy policies. Although energy security meant national energy security that puts the main priority on a stable energy supply, we are now required to consider energy security from wider viewpoints of global energy security, which includes environment, nuclear concerns, international relations and others as its priority aspects. This report is prepared to suggest a method of estimating energy security level in a quantitative manner. In this method, Japan's energy supply and demand structure is evaluated on the selected aspects and indexes as standard deviation among eight advanced nations and one area. The aspects and indexes include energy consumption, environment and economics as well as energy supply. The outcomes prepared by this method show that Japan is now placed at a lower position than most advanced nations and area, although its energy security level has been improved mainly with the contribution of the diversification of energy supply sources. The estimation also shows that Japan's energy security could improve until the portion of nuclear energy in the power supply reaches around 60% on the assumption of its present energy supply and demand structure. The future task is to determine the aspects and indexes to be picked up or the possible weight to be distributed among the aspects and indexes in response to the situations surrounding energy.

著者

大越 実 鳥井 弘之 藤井 靖彦

出版者

一般社団法人 日本原子力学会

雑誌

日本原子力学会和文論文誌 (ISSN:13472879)

巻号頁・発行日

vol.6, no.4, pp.393-403, 2007 (Released:2012-03-07)

参考文献数

29

---

Clearance is one of the useful concepts to manage large amounts of slightly contaminated solid radioactive materials generated from the decommissioning of nuclear facilities. Cleared materials are expected to be disposed of as conventional wastes or recycled to produce consumer goods. In Japan, the legal framework for clearance was established in 2005 by amending the Law to regulate nuclear materials, reactors and so on. However, it is not so clear whether the general public understands clearance well. In this paper, major concerns about clearance from the general public are analyzed based on the public comments for reports on clearance prepared by the Nuclear Safety Commission and the Nuclear Institute Safety Agency. The major anxieties for clearance expressed by the general public are the safety of clearance, unknown factors of radiation effects, possibilities of excess radiation exposure due to inadequate measurements of radioactivities and fairness in decision making. In order to deal with those anxieties, some countermeasures including the confidence in nuclear operators and regulatory authorities and controllability of clearance by the general public are discussed to promote the social acceptance of clearance by the general public.

著者

木村 浩 田中 博 勝村 聡一郎 古田 一雄

出版者

一般社団法人 日本原子力学会

雑誌

日本原子力学会和文論文誌 (ISSN:13472879)

巻号頁・発行日

vol.8, no.3, pp.197-210, 2009 (Released:2012-02-22)

参考文献数

24

被引用文献数

2 2

---

Risk communication about high-level radioactive waste (HLW) disposal is necessary for public acceptance of the HLW disposal program in Japan. To support risk communication, we developed the Online Risk Communication Assistant Tool (ORCAT) system on the World Wide Wed (WWW). In this research, we analyzed the changes in participants' attitudes to HLW disposal through the test operation of the ORCAT system. We carried out the test operation of the ORCAT system from Oct. 29 to Dec. 12, 2005. One hundred fifty nonexpert participants, five experts, and two facilitators participated in this operation. To measure the changes in participants' attitudes to a HLW disposal program, we carried out web questionnaires before and after the test operation. Consequently, we found that most of the participants exhibited on increased level of concern about HLW as well as increased understanding regarding the necessity of HLW disposal. Nonetheless, they did not necessarily reduced their perceived risk of HLW disposal. In addition, we also found that the active participants drew conclusions based on thorough review of the information that experts posted on the ORCAT system, while the inactive participants made decisions primarily based on the context of the information presented on the ORCAT system.

著者

井上 尚子 久野 祐輔

出版者

一般社団法人 日本原子力学会

雑誌

日本原子力学会和文論文誌 (ISSN:13472879)

巻号頁・発行日

vol.9, no.3, pp.305-317, 2010 (Released:2012-02-08)

参考文献数

56

被引用文献数

2 2

---

The fabrication of fast neutron reactor cycles is intended for next-generation nuclear energy systems. This is in line with the fact that the amount of plutonium, which should be reprocessed, increases significantly. Techniques for increasing the nuclear proliferation resistance, especially extrinsic measures including safeguards, are essential for such systems to be accepted by the international community. A highly resistant system with a high detection capability, as well as satisfying current safeguards requirements, was studied for an advanced aqueous reprocessing, and its technical practicability and operational compatibility were discussed. The effect of the proposed safeguards system in this paper was evaluated using the Markov model approach developed by the GIF Proliferation Resistance and Physical Protection Working Group (PR & PP WG). The proposed safeguards system includes a high-detection-capability system and the accountancy/verification measures based on the monthly interim inventory taking or verification that should be performed at a similar level of quality to the normal physical inventory verification with very little impact to the practical plant operation. This can only be realized with “safeguards by design.”

著者

中田 翔治 高嶋 隆太 長野 浩司 木村 浩 班目 春樹

出版者

一般社団法人 日本原子力学会

雑誌

日本原子力学会和文論文誌 (ISSN:13472879)

巻号頁・発行日

vol.9, no.3, pp.252-270, 2010 (Released:2012-02-08)

参考文献数

16

被引用文献数

1 3

---

Replacement of nuclear power plants has the possibility of affecting the management of electric power suppliers. Therefore, in the nuclear policy, a depreciation method as an equalization method, which means that part of the investment cost is accumulated as an allowance, and after the start of operation, the depreciation cost in the replacement project is equalized, has been introduced in Japan. In this paper, we evaluate the replacement of nuclear power plants by taking into account the uncertainty of operating costs and the depreciation cost in order to examine the effect of the depreciation method on the decision criteria of the replacement. We found that the equalization method is effective for inducing the acceleration of the replacement. Furthermore, we show the relationship between the uncertainty and the depreciation method. It turns out that as uncertainty increases, the difference in investment threshold between the equalization method and the existing depreciation method decreases, and that in option value increases.

著者

菅原 慎悦 城山 英明

出版者

一般社団法人 日本原子力学会

雑誌

日本原子力学会和文論文誌 (ISSN:13472879)

巻号頁・発行日

vol.9, no.4, pp.368-383, 2010 (Released:2012-02-08)

参考文献数

35

被引用文献数

2 2

---

In France, there exist organizations called “Commission Locale d'Information” (CLI) in all the siting areas where nuclear facilities located. Previously, the CLI organizations were established voluntarily by some local governments or nuclear utilities. Since 2006, however, the Nuclear Transparency and Safety Act has obliged the establishment of CLI in all the siting areas in conjunction with reforming the nuclear regulatory agencies. This means that the concerned local governments are officially part of nuclear safety regulation. In this study, we investigated present conditions of the CLI organizations through some interviews in France and consider their roles from the standpoint of nuclear regulatory governance. As a result, we found that the CLI plays the following roles: (1) medium of communication among concerned parties (not only between nuclear utilities and local habitants but also between the national nuclear regulatory agency and various local governments) and (2) implementing various activities in accordance with each local condition through the participation of local assembly members. In addition, we clarified that CLI's activities are supported by related institutional infrastructures, such as cost burden between central and local governments, and some other systems of citizen participation in building or expanding nuclear facilities.

著者

島田 隆 松井 嶺迪 西村 正史 石田 安弘 森 行秀 黒田 一彦

出版者

一般社団法人 日本原子力学会

雑誌

日本原子力学会和文論文誌 (ISSN:13472879)

巻号頁・発行日

vol.10, no.4, pp.310-322, 2011 (Released:2011-11-30)

参考文献数

6

---

This paper discusses the reprocessing plant concept suitable for the transition period from the Light Water Reactors (LWRs) to the Fast Breeder Reactors (FBRs). This transition requires the reprocessing of spent fuels in order to supply an adequate volume of fissile plutonium (Pu-fissile) for the FBRs. The transition period would continue for more than 60 years, and the reprocessing plant should match with the change in the power generation plan during the transition period. The ability to supply Pu-fissile has been evaluated for two plant concepts. One is the independent-type concept, which contains two processes for reprocessing either LWR or FBR fuels. The other is the modularized-type concept, which contains only one process for reprocessing both the LWR and FBR fuels. The result showed the superiority of the modularized-type concept over the independent-type concept, because the former can enhance the ability to supply Pu-fissile with less reprocessing capacity. Therefore, the reprocessing plant suitable for the transition period is that based on the modularized-type concept.

著者

鳥飼 誠之 小澤 通裕 鐘ヶ江 直道 谷 雅明 班目 春樹 宮越 直樹

出版者

一般社団法人 日本原子力学会

雑誌

日本原子力学会和文論文誌 (ISSN:13472879)

巻号頁・発行日

vol.9, no.4, pp.347-359, 2010 (Released:2012-02-08)

参考文献数

12

被引用文献数

1 2

---

On March 30, 2007, Japan's electric utilities reported the results of a complete review of their power-generating units to the Nuclear and Industrial Safety Agency of the Ministry of Economy, Trade, and Industry (METI). The Ethics Committee of the Atomic Energy Society of Japan (AESJ) then recommended an assessment method to analyze the seriousness of the problems from multiple perspectives in order to support the public's understanding of the reported problems. Accordingly, the Ethics Committee conducted the assessment. The assessment considered each reported problem associated with nuclear power-generating units and the preventive measures completed between June 2007 and September 2008 (corrective measures continued beyond that period). The results were presented at the autumn conferences of AESJ in 2007 and 2008, and are discussed in this report.

著者

坂本 文徳 大貫 敏彦 香西 直文 山崎 信哉 吉田 善行 難波 謙二

出版者

Atomic Energy Society of Japan

雑誌

日本原子力学会和文論文誌 (ISSN:13472879)

巻号頁・発行日

vol.12, no.4, pp.257-266, 2013

被引用文献数

5

---

The local area distribution and relocation of radioactive cesium deposited in trees after the 2011 tsunami-related accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) have been studied by measuring the spatial distribution of cesium on/in trees by autoradiography analysis. Samples of trees were collected from places located between 4 and 55 km from FDNPP approximately 2, 8, 20, and 22 months after the accident. The autoradiography analyses of <i>Cryptomeria japonica</i>, <i>Torreya nucifera</i>, and <i>Thujopsis dolabrata</i> var. <i>hondae</i> samples collected approximately 2 and 8 months after the accident showed that radioactive Cs was mainly distributed as spots on the branches and leaves of the trees emerged before the accident, and was detected in negligible amounts in new branch and leaves that emerged after the accident. On the contrary, radioactive Cs was detected at the outermost tip of the branches in the trees collected 20 months after the accident. <i>Morus alba</i> samples collected 22 months after the accident contained radioactive Cs inside and outside their stems, even though no radioactive Cs was detected in their roots, strongly suggesting that a certain amount of radioactive Cs was translocated from the outside to the inside of stems. These results indicate that the distribution of radioactive Cs deposited on/in the trees gradually changes with time (scale: year).<br>