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Seki, Akiyuki; Yoshikawa, Masanori; Nishinomiya, Ryota*; Okita, Shoichiro; Takaya, Shigeru; Yan, X.
Nuclear Technology, 210(6), p.1003 - 1014, 2024/06
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Two types of deep neural network (DNN) systems have been constructed with the intent to assist safety operation of a nuclear power plant. One is a surrogate system (SS) that can estimate physical quantities of a nuclear power plant in a computational time of several orders less than a physical simulation model. The other is an abnormal situation identification system (ASIS) that can estimate the state of the disturbance causing an anomaly from physical quantities of a nuclear power plant. Both systems are trained and tested using data obtained from the analytical code for incore and plant dynamics (ACCORD), which reproduces the steady and dynamic behavior of the actual high Temperature engineering test reactor (HTTR) under various scenarios. The DNN models are built by adjusting, the main hyperparameters. Through these procedures, these systems are shown able to perform with a high degree of accuracy.
Yasuda, Hiroshi*; Saito, Tatsuo; Fumoto, Hiromichi*; Sugawara, Shinetsu*; Tsuchida, Shoji*; Kasai, Atsushi*; Furuta, Sadaaki*
Hoken Butsuri (Internet), 58(3), p.120 - 134, 2023/11
This paper is a summary of the activity report of the specialized study group of the Japan Health Physics Society on handling of naturally occurring radioactive wastes from humanities and social sciences perspective. To ensure the reliability of the long-term assessment, this special committee first reviews options for disposal of uranium waste depending on its concentration, especially those adopted or considered in Japan and overseas (U.S.A., U.K.) for uranium concentrations exceeding a sufficiently small amount of uranium (an average of 1 Bq/g of the sum of 
U, 
U, and 
U).
Togawa, Orihiko; Okura, Takehisa; Kimura, Masanori
JAEA-Review 2022-049, 76 Pages, 2023/01
JAEA-Review-2022-049.pdf:3.74MB
Before construction and after operation of nuclear facilities, environmental consequence assessments are conducted for normal operation and an emergency. These assessments mainly aim at confirming safety for the public around the facilities and producing relief for them. Environmental consequence assessments are carried out using observations/ measurements by environmental monitoring and/or model predictions by calculation models, sometimes using either of which and at other times using both them, according to the situations and necessities. First, this report investigates methods, roles, merits/demerits and relationship between observations/measurements and model predictions which are used for environmental consequence assessments of nuclear facilities, especially holding up a spent nuclear fuel reprocessing plant at Rokkasho, Aomori as an example. Next, it explains representative examples of utilization of data on observations/measurements and results on model predictions, and considers points of attention at using them. Finally, the report describes future direction, for example, improvements of observations/measurements and model predictions, and fusion of both them.
Saito, Tatsuo
FNCA Radiation Safety and Radioactive Waste Management Newsletter (Internet), (17), p.6 - 7, 2022/03
In the Asian Nuclear Cooperation Forum (FNCA) newsletter, the mechanism for disposal of low-level radioactive waste generated from nuclear research facilities and facilities using RI was briefly explained. The outline of domestic guidelines on the handling of NORM was also explained, which has been the theme of FNCA since last year.
Yasuda, Hiroshi*; Fumoto, Hiromichi*; Saito, Tatsuo
Nihon Genshiryoku Gakkai-Shi ATOMO
, 63(8), p.610 - 614, 2021/08
Regarding the handling of uranium bearing waste, which is contaminated with uranium, which is a naturally occurring radionuclide, and its descendant nuclides, in recent years, the Japan Nuclear Regulatory Commission, etc. have been carefully and actively deliberated based on the knowledge of natural science and safety engineering. It was carried out, and as of March 2021, a certain policy has been shown. On the other hand, when disposing of uranium waste, which may cause dose exposure to future generations, the authors consider not only the science and engineering perspectives that have been conducted so far, but also the humanities and social science perspectives. We have been discussing with experts in related fields, thinking that it is necessary. In this report, we will introduce the background that brought about such an idea and the direction of future discussions.
Sakai, Kenji; Oi, Motoki; Teshigawara, Makoto; Naoe, Takashi; Haga, Katsuhiro; Watanabe, Akihiko*
Journal of Neutron Research, 22(2-3), p.337 - 343, 2020/10
For operating a spallation neutron source and a muon target safely and efficiently, a general control system (GCS) operates within Materials and Life Science Experimental Facility (MLF). GCS administers operation and interlock processes of many instruments under various operation status. Since the first beam injection in 2008, it has operated stably without any serious troubles for more than ten years. GCS has a data storage server storing operational data on status around target stations. It has functioned well to detect and investigate unusual situations by checking data in this server. For continuing stable operation of MLF in future, however, introduction of abnormality sign determination system (ASDS) will be necessary for picking up potential abnormalities of target stations caused by radiation damages, time-related deterioration and so on. It will judge abnormalities from slight state transitions of target stations based on analysis with various operational data throughout proton beams, target stations, and secondary beams during long-term operations. This report mentions present status of GCS, conceptual design of ASDS, and installation of an integral data storage server which can deal with various data for ASDS integrally.
Katano, Ryota; Endo, Tomohiro*; Yamamoto, Akio*; Tsujimoto, Kazufumi
Journal of Nuclear Science and Technology, 55(10), p.1099 - 1109, 2018/10
Times Cited Count：4 Percentile：33.30(Nuclear Science & Technology)In this study, we propose the penalized regression "adaptive smooth-lasso" for the estimation of sensitivity coefficients of the neutronics parameters. The proposed method estimates the sensitivity coefficients of the neutronics parameters using the variation of the microscopic cross sections and the neutronics parameter obtained by random sampling. The proposed method utilizes only the forward calculations. Thus, the proposed method can be applied for the complex reactor analysis for which the application of the adjoint method is difficult. In this study, we proposed a penalty term considering the characteristics of the sensitivity coefficients of the neutronics parameter to the microscopic multi-group cross sections. Through verification calculation, we show that the proposed method achieves high accuracy with less computational cost compared to the method based on random sampling proposed in the previous studies.
Yokoyama, Kenji; Yamamoto, Akio*; Kitada, Takanori*
Journal of Nuclear Science and Technology, 55(3), p.319 - 334, 2018/03
Times Cited Count：8 Percentile：56.73(Nuclear Science & Technology)A new formulation of the cross-section adjustment methodology with the dimensionality reduction technique has been derived. This new formulation is proposed as the dimension reduced cross-section adjustment method (DRCA). Since the derivation of DRCA is based on the minimum variance unbiased estimation (MVUE), an assumption of normal distribution is not required. The result of DRCA depends on a user-defined matrix that determines the dimension reduced feature subspace. We have examine three variations of DRCA, namely DRCA1, DRCA2, and DRCA3. Mathematical investigation and numerical verification have revealed that DRCA2 is equivalent to the currently widely used cross-section adjustment method. Moreover, DRCA3 is found to be identical to the cross-section adjustment method based on MVUE, which has been proposed in the previous study.
Ito, Kei; Kunugi, Tomoaki*; Ohno, Shuji; Kamide, Hideki; Ohshima, Hiroyuki
Journal of Computational Physics, 273, p.38 - 53, 2014/09
Times Cited Count：24 Percentile：78.17(Computer Science, Interdisciplinary Applications)Yoshino, Ryuji
Nuclear Fusion, 45(11), p.1232 - 1246, 2005/11
Times Cited Count：43 Percentile：76.88(Physics, Fluids & Plasmas)Prediction of major disruptions observed at the 
-limit for tokamak plasmas has been investigated in JT-60U with developing neural networks. A sub-neural network is trained to output a value of the 
limit every 2 ms. The target limit is artificially set by the operator in the first step training and is modified in the second step training using the output limit from the trained network. To improve the prediction performance further, the difference between the estimated limit and the measured and the other 11 parameters are inputted to a main neural network to calculate the stability level. Major disruptions have been predicted with a prediction success rate of 80% at 10 ms prior to the disruption while the false alarm rate is lower than 4%. This 80% is much higher than about 10% previously obtained. A prediction success rate of 90% has been also obtained with a false alarm rate of 12% at 10 ms prior to the disruption. This 12% is about a half of previously obtained one.
Al cable-in-conduit conductorKoizumi, Norikiyo; Matsui, Kunihiro; Kume, Etsuo; Okuno, Kiyoshi
IEEE Transactions on Applied Superconductivity, 15(2), p.1363 - 1366, 2005/06
Times Cited Count：0 Percentile：0.00(Engineering, Electrical & Electronic)The NbAl Insert was developed by JAERI aiming at the demonstration of a NbAl conductor to fusion reactor magnets. A quench test was performed on the NbAl Insert at 13 T with various temperature margins, which are defined as a difference between current sharing temperature and operating temperature. The initial normalcy was initiated by using an inductive heater and a coil current was kept for several seconds. The normal zone propagation velocity was accelerated after 3 s from the onset of heating in case that the temperature margin was set at 0.5 K. A simulation using one-dimensional stability and quench simulation code was performed. The calculation results indicate that such rapid propagation occurred due to a temperature rise beyond a current sharing temperature because of a large pressure increase even at the location where the normal front did not reach yet. This large pressure rise was caused since the coolant was contained in the closed circulation circuit of the cooling system, which is usually applied to a large magnet cooling system.
Matsumoto, Atsushi; Tobias, I.*; Olson, W. K.*
Journal of Chemical Theory and Computation, 1(1), p.117 - 129, 2005/01
Times Cited Count：11 Percentile：35.01(Chemistry, Physical)We have extended a newly developed approach to study the low frequency normal modes of mesoscopic fragments of linear DNA in order to investigate the dynamics of closed circular molecules of comparable size, i.e., a few hundred base pairs. We have added restraint energy terms and a global minimization step to treat the more complicated, spatially constrained duplex in terms of the intrinsic conformation and flexibility of the constituent base-pair "step" parameters.
Matsumoto, Atsushi; Tobias, I.*; Olson, W. K.*
Journal of Chemical Theory and Computation, 1(1), p.130 - 142, 2005/01
Times Cited Count：9 Percentile：29.44(Chemistry, Physical)Fine structural and energetic details embedded in the DNA base sequence, such as intrinsic curvature, are important to the packaging and processing of the genetic material. Here we investigate the internal dynamics of a 200 bp closed circular molecule with natural curvature using a newly developed normal-mode treatment of DNA in terms of neighboring base-pair "step" parameters. As superhelical stress is accumulated in the DNA, the frequency, i.e., energy, of the dominant bending mode decreases in value, and if the imposed stress is sufficiently large, a global configurational rearrangement of the circle to the figure-8 form takes place. We combine energy minimization with normal-mode calculations of the two states to decipher the configurational pathway between the two states.
Tamaki, Hitoshi; Yoshida, Kazuo; Watanabe, Norio; Muramatsu, Ken
Proceedings of International Topical Meeting on Probabilistic Safety Analysis (PSA '05) (CD-ROM), 11 Pages, 2005/00
A probabilistic safety assessment (PSA) procedure for Mixed Oxide (MOX) fuel fabrication facilities is being developed applicable to nuclear facilities at Japan Atomic Energy Research Institute (JAERI). As part of the PSA procedure, the approach to hazard analysis was established, which consists of two analysis steps: Functional Failure Modes and Effects Analysis (Functional FMEA) and Risk Matrix Analysis. In the Functional FMEA, a variety of functions of equipment composing the facility are analyzed to identify potential abnormal events exhaustively. In the second step, these potential events are screened to select abnormal events as candidate events to be analyzed for frequency and consequence by using two-dimensional matrix based on the rough estimation of likelihood and maximum unmitigated release of radioactive material. The applicability of the hazard analysis approach established was demonstrated through the trial application of the PSA procedure being developed to model plant of MOX fuel fabrication facility.
-values in the ITB events in JT-60U reverse shear plasmasNeudatchin, S. V.*; Takizuka, Tomonori; Hayashi, Nobuhiko; Isayama, Akihiko; Shirai, Hiroshi; Fujita, Takaaki; Kamada, Yutaka; Koide, Yoshihiko; Suzuki, Takahiro
Nuclear Fusion, 44(9), p.945 - 953, 2004/09
Times Cited Count：20 Percentile：53.52(Physics, Fluids & Plasmas)The formation of internal transport barriers (ITBs) near =2,3 surfaces in normal shear (NrS) discharges of JT-60U and JET is known. In reverse shear (RS) JT-60U plasmas, the role of minimum (
) equal to 3.5,3,2.5,2 is not obvious for ITB formation. In this paper, the effect of low rational values on ITB-events in JT-60U NrS and RS plasmas is investigated. Under sufficient neutral beam power (
8MW for 1.2-1.5MA/3.8T pulses), ITB-events are seen at rational and non-rational values of . The space-time evolutions of 
and 
are similar, suggesting the same mechanism for and transports. The temporal formation of stronger ITB under passing =3 (after periodical improvements and degradations via ITB-events) in RS H-mode with =8MW is presented. Under smaller power, ITB-events are observed only at rational values. In a weak RS shot with =4MW, the abrupt rise of is seen at =3.5, while more cases of rise are observed. The difference between the and evolutions for the low power suggests the decoupling of and transports.
-values in the ITB events in JT-60U reverse shear plasmasNeudatchin, S. V.*; Takizuka, Tomonori; Hayashi, Nobuhiko; Isayama, Akihiko; Shirai, Hiroshi; Fujita, Takaaki; Kamada, Yutaka; Koide, Yoshihiko; Suzuki, Takahiro
Nuclear Fusion, 44(9), p.945 - 953, 2004/09
The formation of internal transport barriers (ITBs) near q=3 surfaces in normal shear (NrS) discharges of JT-60U is known. In reverse shear (RS) JT-60U plasmas, the role of q minimum (qmin) equal to 3.5,3,2.5,2 was not obvious for ITB formation. ITB-events (non-local confinement bifurcations inside and around ITB) are found in various NrS and RS plasmas. Under sufficient heating power, ITB-events are seen at rational and not rational values of qmin. The space-time evolution of Te and Ti is similar, suggesting the same mechanism of Te and Ti transport. The temporal formation of strong ITB under passing of qmin=3 (after periodical improvements and degradations via ITB-events) in RS mode is presented. Under smaller power, ITB-events are observed only at rational values of qmin. In a weak RS shot, abrupt rise of Te is seen at qmin=3.5, while more cases of Ti rise are observed. The difference of Te and Ti evolutions seen regularly under the low power, suggests decoupling of Te and Ti transport.
Chankin, A. V.
Physics of Plasmas, 11(4), p.1484 - 1492, 2004/04
Times Cited Count：14 Percentile：41.78(Physics, Fluids & Plasmas)no abstracts in English
Nakano, Junichi; Tsukada, Takashi; Tsuji, Hirokazu; Terakado, Shogo; Koya, Toshio; Endo, Shinya
JAERI-Tech 2003-092, 54 Pages, 2004/01
JAERI-Tech-2003-092.pdf:14.05MB
Irradiation assisted stress corrosion cracking (IASCC) is a degradation phenomenon caused by synergy of neutron radiation, aqueous environment and stress on in-core materials, and it is an important issue in accordance with increase of aged light water reactors. Isolating crack initiation stage from crack growth stage is very useful for the evaluation of the IASCC behavior. Hence facility for in-situ observation during slow strain rate test (SSRT) for irradiated material was developed. As performance demonstrations of the facility, tensile test with in-situ observation and SSRT without observation were carried out using unirradiated type 304 stainless steel in 561 K water at 9 MPa. The following were confirmed from the results. (1) Handling, observation and recording of specimen can be operated using manipulators in the hot cell. (2) In-situ observation can be performed in pressurized high temperature water and flat sheet type specimen is suitable for the in-situ observation. (3) Test condition can be kept constantly and data can be obtained automatically for long test period.
Ono, Tomio*; Subekti, M.*; Maruyama, Yuta*; Nabeshima, Kunihiko; Kudo, Kazuhiko*
Dai-13-Kai Interijento, Shisutemu, Shimpojiumu Koen Rombunshu, p.212 - 217, 2003/12
In this research, we present nuclear power plant simulation method using Multilayer Perceptron, which is one of the models of Artificial Neural Networks(ANNs). The major characteristics of ANNs are to obtain the model through learning, analogy and very high speed processing. Furthermore, 'time synchronizing signal' and 'progress synchronizing signal' are added as the inputs to adapt the abnormal events with various scales or progress rates. This ANN, learned some sample data, can be flexibly adapted to simulate the abnormal events with different scales including explicit progress rates. In the verification using PWR simulator, we confirmed that this method could model NPP abnormal events by learning data and simulate the data which have different progress rates from learning data.
HT and T+TT
in 
He-
He quantum media under saturated vapor pressure at 1.6 KAratono, Yasuyuki; Iguchi, Kazunari; Okuno, Kenji*; Kumada, Takayuki
Journal of Physical Chemistry A, 107(19), p.3741 - 3746, 2003/05
Times Cited Count：4 Percentile：11.40(Chemistry, Physical)An influence of superfluidity on recombination reactions of H+THT, T+TT in He-He quantum media was studied under saturated vapor pressure at 1.6 K. A change of reaction mechanism was observed at transition point from normalfluid to superfluid phase. Tunneling reaction mechanism by H and T bubble atoms was proposed on the basis of large isotope effect.
