著者
古野 朗子 茅野 政道 山澤 弘実
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.229-240, 2006-09-25 (Released:2010-01-21)
被引用数
7 or 0

This paper describes a method of estimating source term, i.e., location, period and amount of atmospheric release of radioactive material in real-time during nuclear emergency. This method consists of: (1) trial simulations of atmospheric dispersions on the possible combinations of these parameters and (2) statistical comparison of model predictions with offsite measurements of air concentrations of radionuclides and/or air dose rates from monitoring stations, to find a set of release condition providing model prediction that fits best to the measurement. A parallel execution method for efficiently processing many possible initial conditions is also developed. The performance of this method is favorably evaluated by a verification study using the dataset from European Tracer Experiment.
著者
平山 英夫 松村 宏 波戸 芳仁 佐波 俊哉
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.1, pp.1-11, 2015 (Released:2015-02-15)
被引用数
2 or 0

Time histories of the I-131 concentration in air at monitoring posts in Fukushima prefecture in March 2011 were estimated using the pulse height distribution of a NaI(Tl) detector, which was opened to the public. Several corrections to the pulse height distribution were necessary owing to high count rates. The contribution to the count rates from I-131 accumulated around the monitoring post was estimated on the basis of the time history of the peak count rate by the method proposed by the authors. The concentrations of I-131 in air were converted from the peak count rates using the calculated response of the NaI(Tl) detector with egs5 for a model of a plume containing I-131 uniformly. The obtained time histories of the I-131 concentration in air at a fixed point in March 2011 were the first ones for Fukushima prefecture. The results at 3 monitoring posts, Naraha Town Shoukan, Hirono Town Futatunuma and Fukushima City Momijiyama, which can be analyzed during almost all of March, show that a plume including I-131 arrived after March 15. The results at other monitoring posts near Fukushima Daiichi Nuclear Power Station are used to characterize plume diffusion at the early period of the accident before March 15. The I-131 time-integrated concentrations in air at several monitoring posts were compared with those given in UNSCEAR 2013 ANNEX A, which were obtained using estimated time-dependent rates of release to the atmosphere. The agreement between the two results varies depending on the places compared, owing to the large uncertainties in the estimated release rate used in UNSCEAR. The results obtained in this study can be used to increase the accuracy of the time-dependent release rate estimation.
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
(Released:2015-06-30)

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
近藤 健次郎 平山 英夫 平 雅文 松村 宏 岩瀬 広 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
(Released:2015-06-30)

Strontium-90/Y-90 are major radionuclides observed in the water samples tested recently at the site of the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Company. A simple method of evaluating Sr-90 concentration in these water samples by measuring β rays from Y-90 with a GM-detector setup was developed. By applying the precipitation method, Sr-90 and Y-90 were separated and quantitatively collected with a filter. β rays from Y-90 in the filter were measured two times at appropriate intervals by inserting a polyethylene plate of 2 mm thickness as a β-ray absorber. The contribution of γ rays from Cs-134 and Cs-137 to the Y-90 count rates was quantitatively evaluated using a 10-mm-thick acrylic resin plate. From the parent-daughter relationship between Sr-90 and Y-90, the Sr-90 concentration was evaluated using the conversion coefficient of Y-90 count rate (cps) to Sr-90 concentration (Bq/cm3). It was verified that Sr-90 concentration of below 0.01 Bq/cm3 in water samples can be correctly measured by this simple method.
著者
武井 正信 小杉山 真一 毛利 智聡 片西 昌司 國富 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.5, no.2, pp.109-117, 2006-06-25 (Released:2010-01-21)
被引用数
8 or 0

Japan Atomic Energy Research Institute (JAERI) has been developing a graphite moderate and helium cooled High Temperature Gas-cooled Reactor (HTGR) with gas turbine, the GTHTR300 based on experience gained in development and operations of the High Temperature Engineering Test Reactor (HTTR) in JAERI. The GTHTR300 is a simplified and economical power plant with a high level of safety characteristics and a high plant efficiency of approximately 46%. Cost evaluation for plant construction and power generation is studied in order to clarify the economical feasibility of the GTHTR300. The construction cost is estimated to be about 200 thousands Yen/kWe. The power generation cost is estimated to be about 3.8Yen/kWh by the conditions of 90% load factor and 3% discount rate. The economical feasibility of the GTHTR300 is certified. The present study is entrusted from Ministry of Education, Culture, Sports, Science and Technology of Japan.
著者
川村 慎一 大木 俊 奈良林 直
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
(Released:2016-03-15)

Significant leakage of the primary containment vessel (PCV) occurred on March 15, 2011 at Unit 2 of Fukushima Dai-ichi Nuclear Power Station, causing land contamination over a large area. From the radiation dose rate map of Unit 2 and the temperature trend of the PCV, degradation of the PCV top head flange gasket was identified as the cause of the leakage. The design set point of the rapture disc and operability of the valves in the hardened containment venting system were further identified as factors contributing to the leakage. Based on the lessons from the leakage, the gasket material was improved to have greater heat resistance in a steam environment, the PCV cooling system was diversified to improve reliability, and the operability and operation methods of the PCV venting were improved for greater robustness of the PCV in severe accidents.
著者
藤原 了 橋本 紀彦 是永 眞理子 田宮 貴洋
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
(Released:2015-12-17)
被引用数
1 or 0

Since the 2011 Tohoku-Oki Earthquake, evaluations based on a tsunami simulation approach have had a very important role in promoting tsunami disaster prevention measures in the case of mega-thrust earthquakes. When considering tsunami disaster prevention measures based on the knowledge obtained from tsunami simulations, it is important to carefully examine the type of tsunami source model. In current tsunami simulations, there are various ways to set the tsunami source model, and a considerable difference in tsunami behavior can be expected among the tsunami source models. In this study, we carry out a tsunami simulation of the 2011 Tohoku-Oki Earthquake around Fukushima Daiichi (I) Nuclear Power Plant and Fukushima Daini (II) Nuclear Power Plant in Fukushima Prefecture, Japan, using several tsunami source models, and evaluate the difference in the tsunami behavior in the tsunami inundation process. The results show that for an incoming tsunami inundating an inland region, there are considerable relative differences in the maximum tsunami height and wave pressure. This suggests that there could be false information used in promoting tsunami disaster prevention measures in the case of mega-thrust earthquakes, depending on the tsunami source model.
著者
川村 慎一 木村 剛生 大森 修一 奈良林 直
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.15, no.1, pp.12-20, 2016 (Released:2016-02-15)

A filtered containment venting system was developed for nuclear power plants. In the Fukushima Dai-ichi Nuclear Accident, widespread land contamination was caused by cesium-137. This system was developed to filter aerosol particles and reduce the amount of radioactive particle release, while protecting the primary containment vessel from over pressure by venting gas from the vessel. Performance tests were conducted under various vent gas flow rate conditions to ascertain decontamination factors for aerosol particles with various diameters. It was observed through the tests that aerodynamic diameter was a good index for characterizing various aerosol particles for the filtered containment venting system. Test results showed that the decontamination factors were well over 1,000 for aerosol particles with aerodynamic diameters larger than 0.4 μm. For aerosol particles with aerodynamic diameters larger than 0.2 μm, the decontamination factors significantly increased with the diameter. This suggested that inertial deposition was the governing mechanism for filtering aerosols in this system. The decontamination factor of the water scrubber section of the filter increased with the increase in Stokes number.
著者
川村 慎一 奈良林 直
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.15, no.2, pp.84-96, 2016

Three nuclear reactors at Fukushima Daini Nuclear Power Station lost all their ultimate heat sinks owing to damage from the tsunami caused by the Great East Japan Earthquake on March 11, 2011. Water was injected into the reactors by alternate measures, damaged cooling systems were restored with promptly supplied substitute materials, and all the reactors were brought to a cold shutdown state within four days. Lessons learned from this experience were identified to improve emergency management, especially in the areas of strategic response planning, logistics, and functions supporting response activities continuing over a long period. It was found that continuous planning activities reflecting information from plant parameters and response action results were important, and that relevant functions in emergency response organizations should be integrated. Logistics were handled successfully but many difficulties were experienced. Therefore, their functions should be clearly established and improved by emergency response organizations. Supporting emergency responders in the aspects of their physical and mental conditions was important for sustaining continuous response. As a platform for improvement, the concept of the Incident Command System was applied for the first time to a nuclear emergency management system, with specific improvement ideas such as a phased approach in response planning and common operation pictures.
著者
竹上 弘彰 高松 邦吉 伊藤 主税 日野 竜太郎 鈴木 敬一 大沼 寛 奥村 忠彦
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.13, no.1, pp.7-16, 2014

One of the important problems in the control of the Fukushima Daiichi Nuclear Power Plant is the removal of fuel debris. As preparation, a nondestructive inspection method for identifying the position of fuel debris is required. Therefore, we focused on a nondestructive inspection method using cosmic-ray muons, which is utilized for ground investigation. In this study, the applicability of this method for internal visualization of the reactor was confirmed by a preliminary test of the internal visualization of the High-Temperature Engineering Test Reactor (HTTR) of Japan Atomic Energy Agency. By using cosmic-ray muons, main components in the HTTR reactor, such as concrete walls and the reactor core, can be observed from the outside of the containment vessel of the HTTR. From the results of the preliminary examination, it appears that the inspection method with muons is promising for searching for fuel debris in a reactor. Based on the results, we also proposed some improvements of this system for its application to inspection at the Fukushima Daiichi Nuclear Power Station.<br>
著者
牟田 仁 古屋 治 村松 健
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.15, no.2, pp.70-83, 2016 (Released:2016-05-15)

One of the most important issues of the current PRA methodology is the precise modeling of dynamic changes such as state transitions among several states including fault(s) or maintenance of the nuclear facility, safety-related systems or components by fault-tree analysis and event-tree analysis. Moreover, though safety-related systems are usually in the stand-by state during normal operating conditions of a nuclear power plant, modeling of the dynamic changes in safety functions, along with changes in component failure rates due to the aging effect in the stand-by state or continuous/intermittent effects originating from external hazards, is also carried out under the same situation. On the basis of the background described above, the authors proposed a reliability analysis methodology of using the Markov state transition model applied to the digital reactor protection system of an ABWR plant, and demonstrated the applicability of the developed methodology using the component failure modes discussed in DIGREL, the task group of WGRisk belonging to OECD/NEA/CSNI. These studies showed that the PRA methodology including the state transition model can consider state transitions of components and time-dependent changes in component failure rates, and the relationship between this methodology and minimal cut sets for calculating the core damage frequency was also clarified.
著者
波戸 真治 木名瀬 栄
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.15, no.3, pp.146-150, 2016 (Released:2016-08-15)

It is important to accurately estimate the intake quantity for reliable internal exposure assessments. The intake quantity has been estimated by using the least-squares method. However, to use the least-squares method, the number of radioactivity measurements must be more than the number of intakes. To remedy this restriction, this study suggests an estimation method using singular value decomposition that is available regardless of the relation between the numbers of measurements and intakes. Moreover, this study introduces a procedure to calculate the intake quantity from the measurements with uncertainty.
著者
尾方 義人 川崎 和男
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.1, pp.76-80, 2006-03-25 (Released:2010-03-08)

The expected nuclear powered battery is the isotope battery, which applies photoconduction or radiant rays, in other words, releases electron. Because of its lightweight and constant stability and 80 years long (=half time of radiant rays energy) running span, this battery is very effective for artificial satellites, desert island, and artificial hears. For this small battery, production method, waste disposal method, and emergency risk management need to be designed as international standards. To make that possible, design of the battery should achieve universal consensus with its form and shape. True meaning of peace could be shared worldwide, this isotope battery will be international standard.And, On this research as Design Development of Thermoelectric Generator by Design Engineering, we used a "Design Activities Theory" in which the activities involved in Knowledge Management and Project Management aimed at ensuring the efficiency of that Knowledge Management function as a single system.
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)

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)

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
平山 英夫 松村 宏 波戸 芳仁 佐波 俊哉
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
(Released:2015-01-28)
被引用数
2 or 0

Time histories of the I-131 concentration in air at monitoring posts in Fukushima prefecture in March 2011 were estimated using the pulse height distribution of a NaI(Tl) detector, which was opened to the public. Several corrections to the pulse height distribution were necessary owing to high count rates. The contribution to the count rates from I-131 accumulated around the monitoring post was estimated on the basis of the time history of the peak count rate by the method proposed by the authors. The concentrations of I-131 in air were converted from the peak count rates using the calculated response of the NaI(Tl) detector with egs5 for a model of a plume containing I-131 uniformly. The obtained time histories of the I-131 concentration in air at a fixed point in March 2011 were the first ones for Fukushima prefecture. The results at 3 monitoring posts, Naraha Town Shoukan, Hirono Town Futatunuma and Fukushima City Momijiyama, which can be analyzed during almost all of March, show that a plume including I-131 arrived after March 15. The results at other monitoring posts near Fukushima Daiichi Nuclear Power Station are used to characterize plume diffusion at the early period of the accident before March 15. The I-131 time-integrated concentrations in air at several monitoring posts were compared with those given in UNSCEAR 2013 ANNEX A, which were obtained using estimated time-dependent rates of release to the atmosphere. The agreement between the two results varies depending on the places compared, owing to the large uncertainties in the estimated release rate used in UNSCEAR. The results obtained in this study can be used to increase the accuracy of the time-dependent release rate estimation.
著者
高橋 啓三
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.2, pp.152-165, 2006-06-25 (Released:2010-01-21)
被引用数
1 or 0

As for the nuclear fuel reprocessing of the spent fuel, although there was argument of pros and cons, it was decided to start Rokkasho reprocessing project further at the Japan Atomic Energy Commission of "Long-Term Program forResearch, Development and Utilization of Nuclear Energy" in year 2004. The operation of Tokai Reprocessing is goingsteadily to reprocess spent fuel more than 1, 100 tons.In this paper, history, present status and future of reprocessing technology is discussed focusing from military Puproduction, Magnox fuel reprocessing to oxide fuel reprocessing. Amount of reprocessed fuel are estimated based on fueltype.Then, history of reprocessing, US, UK, France, Germany, Russian, Belgian and Japan is presented and compared ontechnology, national character, development organization, environmental protection, and high active waste vitrification.Technical requirements are increased from Pu production fuel, Magnox fuel and oxide fuel mainly because of higherburnup.Reprocessing technology is synthetic of engineering and accumulation of operational experience. The lessonslearned from the operational experience of the world will be helpful for establishment of nuclear fuel reprocessing technology in Japan.
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)

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)

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
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

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>