Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Oba, Masaki
no journal, ,
Dimension reduction was performed using PCA on 462 types of training data obtained by processing Gd
O
, TiO, ZrOdata. After learning, the content rates of elements were analyzed using 62 types of data from actual samples as test data. Similar to last time, create a calibration curve of the true value and analytical value of the actual sample and analyze the content ratio. The neural network used this time had a configuration of input layer, middle layer (2 layers), and output layer, and the middle layer used 2 layers with 100 nodes each. As a result of PCA on the training data, we were able to significantly reduce the 7944 dimensions (pixels) of the training data to 5 dimensions. As a result of training using this and analyzing test data, the difference from the true value was approximately 10%, which was almost the same as the previous value.
Uesawa, Shinichiro; Ono, Ayako; Yamashita, Susumu; Yoshida, Hiroyuki
no journal, ,
To evaluate the thermal behavior of fuel debris of porous media in PCVs of TEPCO's Fukushima Daiichi Nuclear Power Station for air cooling, JAEA has developed a numerical simulation method with JUPITER. In this presentation, we report the numerical simulation results of the thermal behavior in the PCV considering three effective thermal conductivity models for fuel debris. The results showed the temperature and the velocity distributions and the heat removal amount from the fuel debris were different for each model. It is important to understand the internal structure of the fuel debris and choose the appropriate effective thermal conductivity model for the analysis of the thermal behavior because the model affects the simulation results.
Maeda, Makoto; Komeda, Masao; Toh, Yosuke
no journal, ,
no abstracts in English
-emitting nuclides analysis of the stagnant water including sediments in Fukushima Daiichi NPS, 11; Dissolution of fine particles and -emitting nuclides by immersing in an acid solutionYomogida, Takumi; Morii, Shiori; Oka, Toshitaka; Koma, Yoshikazu; Kitatsuji, Yoshihiro
no journal, ,
Most of -emitting nuclides in sediment of stagnant water exist as iron particles and U particles. An attempt was made to selectively dissolve iron particles by immersion in an acid solution and investigate the abundance of -nuclides in these particles. Most of the uranium in the sediment is present on iron particles like other alpha nuclides, and the proportion of uranium present as U particles is estimated to be 5% or less.
-emitting nuclides analysis of the stagnant water including sediments in Fukushima Daiichi NPS, 7; Analysis of U and Np in the stagnant water at the Unit 1 reactorMorii, Shiori; Ouchi, Kazuki; Yomogida, Takumi; Oka, Toshitaka; Kitatsuji, Yoshihiro; Koma, Yoshikazu; Konno, Katsuhiro*
no journal, ,
The existence of -emitting nuclides on the sediment contained in the stagnant water of the Unit 1 reactor of Fukushima Daiichi Nuclear Power Station was investigated. The stagnant water was fractionated using filters and U and Np concentrations in the solid fraction and filtrate were determined using ICP-MS. Most of them were present in the fraction which pore size is larger than 10 
m, like those in the Units 2 and 3. Some were present in the stagnant water on fine particles or ions smaller than 0.1 m.
-emitting nuclides analysis of the stagnant water including sediments in Fukushima Daiichi NPS, 9; Analysis of fine particle containing -emittersYomogida, Takumi; Ouchi, Kazuki; Morii, Shiori; Oka, Toshitaka; Kitatsuji, Yoshihiro; Koma, Yoshikazu; Konno, Katsuhiro*
no journal, ,
Fine particles containing -nuclides in sediment of stagnant water of Unit 1 were analyzed. We have detected several sub-m to a few m size particles containing U by SEM-EDX, these particles contain elements derived from fuel cladding materials such as Zr, suggesting the possibility that these particles are fine fuel debris. On the other hand, by the alpha-track method, we have detected fine particles main composed of iron oxide with a diameter from 10 m to a few hundred m, which attached Pu, Am and Cm on their surface. These results indicated that the existence forms of -nuclides were similar to those in the stagnant water of torus room in Units 2 and 3.
Yamada, Susumu; Machida, Masahiko
no journal, ,
For the safe and efficient decommissioning of the Fukushima Daiichi Nuclear Power Plant, it is essential to know the distribution of radiation sources. We have proposed a method for estimating the source distribution using LASSO, and the method requires the observed air dose rates and the damping rates (contribution rates) from the sources to the observation points. We have also proposed a method that focuses on direct radiation and evaluates its contribution rates. The method requires solving linear equations in three variables. Since the number of the equations increases quadratically with the size of the model, the calculation time becomes enormous when the model is large. Therefore, it is desirable to calculate the rates faster to estimate source distribution on-site. In order to solve this problem, we proposed a GPU-based algorithm to solve the equations and evaluated its efficiency. The result indicated that our method is several times faster than the CPU-based method.
Endo, Ryo*; Akiyama, Daisuke*; Yomogida, Takumi; Okamoto, Yoshihiro; Tanida, Hajime; Kirishima, Akira*
no journal, ,
In the Fukushima Daiichi Nuclear Power Plant accident, fuel debris were formed by the reaction of molten fuel and reactor structural materials. The fuel debris is composed of many elements and crystalline phases. Therefore, it is inevitable to study various solid phases for debris analysis. In this study, we focused on (U,Zr)O solid solution, which is assumed to be formed in the reactor by the reaction of molten nuclear fuel (UO) and oxide of cladding components (ZrO). First, the crystalline phase of (U,Zr)O solid solution in the bulk region were determined by X-ray diffraction. The elemental composition in the micro region was analyzed by scanning electron microscopy-energy dispersive X-ray spectroscopy, and the crystalline phase in the same region was analyzed by micro-Raman spectroscopy. In addition, local elemental and valence analyses of micro regions were performed by -XRD, -XRF, and -XAFS. The U valence determined by XANES spectra was compared to the crystalline phase of (U,Zr)O solid solution. The objective of this study is to develop techniques which determine the chemical state from multiple angles by combining multiple spectroscopic analyses.
Kitayama, Yoshiharu; Nogami, Mitsuhiro*; Hitomi, Keitaro*
no journal, ,
We have been developing a new gamma-ray imaging method, in which the gamma-ray flux field in the measurement environment is locally modulated by multiple shields randomly placed in space, and the gamma-ray source distribution is estimated from the three-dimensional flux intensity pattern. We have fabricated a gamma camera, C3G, using this method and have conducted imaging experiments using a single source. In this study, we evaluate by simulation the imaging for gamma-ray sources with linear and areal distributions. Two nuclides, 
Cs (662 keV) and 
Co (122 keV), were used as targets. As a result, it was confirmed that imaging results were obtained according to the geometry of the distributed source. It was also found that the imaging accuracy varies depending on the gamma-ray energy.
Nogami, Mitsuhiro*; Kitayama, Yoshiharu; Hitomi, Keitaro*; Tamura, Yusuke*; Kaneko, Shinichiro*; Takada, Eiji*; Torii, Tatsuo*
no journal, ,
no abstracts in English
-emitting nuclides analysis of the stagnant water including sediments in Fukushima Daiichi NPS, 8; Behavior of moving to sediment of Pu and AmNitta, Ayako; Hinai, Hiroshi; Kitawaki, Shinichi; Koma, Yoshikazu
no journal, ,
no abstracts in English
Sr/Y in high gamma radiation backgrounds utilizing Cherenkov radiation directivityTerasaka, Yuta; Sato, Yuki; Furuta, Yoshihiro*; Kubo, Shin*
no journal, ,
no abstracts in English
at temperature range 170 - 290 
CLuu, V. N.; Nakajima, Kunihisa
no journal, ,
Nakamura, Yuki*; Kojima, Yoshihiro*; Yamashita, Takuya; Shimomura, Kenta; Mizokami, Shinya
no journal, ,
no abstracts in English
Shimomura, Kenta; Yamashita, Takuya; Nagae, Yuji
no journal, ,
no abstracts in English
Sakae, Kazuaki*; Hashimoto, Akihiko*; Yamashita, Takuya; Shimomura, Kenta
no journal, ,
no abstracts in English
Nagae, Yuji; Sato, Takumi; Ito, Ayumi*; Ueda, Shigeru*
no journal, ,
We summarized the results of small-scale tests conducted at Tokyo Tech, Tohoku Univ. and JAEA, and will report the results of evaluating damage behavior of lower plenum by metal debris during severe accident. Molten Zr concentration contributed to the reactivity with the structure and to the reaction with oxide debris during the formation of the molten metal pool. Although Zr concentration tends to decrease due to various reactions, there is a possibility that metal debris with low oxygen concentration might form a molten pool at the pedestal. If the metal debris would have a high zirconium concentration, it might cause a eutectic reaction with the structural materials. In contrast, if Zr concentration would be low, the reaction with the structural material could be limited, and thermal damage and creep damage due to temperature rise are considered to be dominant.
Araki, Shohei; Gunji, Satoshi; Yoshikawa, Tomoki; Arakaki, Yu; Izawa, Kazuhiko; Suyama, Kenya
no journal, ,
The first criticality of the statistical criticality assembly called "STACY", which JAEA has been modifying, is scheduled for 2024. After the first criticality, experiments using debris structure material rods are being prepared. At the spring 2023 annual meeting, we presented the results of a study on the core characteristics of the experimental core under the condition of using 900 fuel rods. However, it is requested to consider the core configuration with 400 fuel rods due to the fuel procurement. In this study, we reanalyzed the core with 400 fuel rods and confirmed that the core characteristics are included in that of the previous presentation.
Mizokami, Shinya; Yamashita, Takuya; Shimomura, Kenta; Nakamura, Yuki*; Kojima, Yoshihiro*
no journal, ,
no abstracts in English
Kato, Tomoaki; Horita, Takuma; Yamagishi, Isao
no journal, ,
no abstracts in English