Evaluation of the minimum critical amount for heterogeneous lattice systems composed of fuel rods utilized in low-power water-moderated research and test reactors by using continuous-energy Monte Carlo code MVP with JENDL-4.0

Yanagisawa, Hiroshi

JAEA-Technology 2021-023, 190 Pages, 2021/11

JAEA-Technology-2021-023.pdf:5.25MB

Computational analyses on nuclear criticality characteristics were carried out for heterogeneous lattice systems composed of water moderator and fuel rods utilized in low-power research and test reactors, in which the depletion of fuel due to burnup is relatively small, by using the continuous-energy Monte Carlo code MVP Version 2 with the evaluated nuclear data library JENDL-4.0. In the analyses, the minimum critical number of fuel rods was evaluated using calculated neutron multiplication factors for the heterogeneous systems of the uranium dioxide fuel rod in the Static Experiments Critical Facility (STACY) and the Tank-type Critical Assembly (TCA), and the uranium-zirconium hydride fuel rod in the Nuclear Safety Research Reactor (NSRR). In addition, six sorts of the ratio of reaction rates, which are components of neutron multiplication factors, were calculated in the analyses to explain the variation of neutron multiplication factors with the ratio of water moderator to fuel volume in a unit fuel rod cell. Those results of analyses are considered to be useful for the confirmation of reasonableness and validity of criticality safety measures as data showing criticality characteristics for water-moderated heterogeneous lattice systems composed of the existing fuel rods in research and test reactors, of which criticality data are not sufficiently provided by the Criticality Safety Handbook.

Quantitative analysis method for radiation distribution in high radiation environment by gamma-ray image spectroscopy (Contract research); FY2018 Center of World Intelligence Project for Nuclear Science/Technology and Human Resource Development

Collaborative Laboratories for Advanced Decommissioning Science; Kyoto University*

JAEA-Review 2019-036, 65 Pages, 2020/03

JAEA-Review-2019-036.pdf:4.46MB

JAEA/CLADS, had been conducting the Center of World Intelligence Project for Nuclear Science/Technology and Human Resource Development (hereafter referred to "the Project") in FY2018. The Project aims to contribute to solving problems in nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2018, this report summarizes the research results of the "Quantitative Analysis Method for Radiation Distribution in High Radiation Environment by Gamma-ray Image Spectroscopy". Electron-tracking Compton camera (ETCC) has been developed originally for nuclear gamma-ray astronomy, and also applied to medical use as a technology that greatly improves the resolution of conventional Compton camera by measuring three-dimensional tracking of electrons using a gaseous 3-dimensional position detector (so called Time Projection Chamber) in the first stage. In the present study, based on the ETCC that has been developed for medical use, we produce a prototype of light weight ETCC with the emphasis on the operability at the site, and evaluate its practicability by field tests.

Numerical investigation on unstable behaviors of cellular premixed flames at low Lewis numbers based on the diffusive-thermal model and compressible Navier-Stokes equations

Thwe Thwe, A.; Kadowaki, Satoshi; Hino, Ryutaro

Journal of Thermal Science and Technology (Internet), 13(2), p.18-00457_1 - 18-00457_12, 2018/12

https://doi.org/10.1299/jtst.2018jtst0034

Two dimensional unsteady calculations of reactive flows were performed in large domain to investigate the unstable behaviors of cellular premixed flames at low Lewis numbers based on the diffusive-thermal (D-T) model and compressible Navier-Stokes (N-S) equations. The growth rates obtained by the compressible N-S equations were large and the unstable ranges were wide compared with those obtained by the D-T model equations. When the length of computational domain increased, the number of small cells separated from large cells of the cellular flame increased drastically. The stronger unstable behaviors and the larger average burning velocities were observed especially in the numerical results based on the compressible N-S equations. In addition, the fractal dimension obtained by the compressible N-S equations was larger than that by the D-T model equations. Moreover, we confirmed that the radiative heat loss promoted the instability of premixed flames at low Lewis numbers.

New reactor cavity cooling system (RCCS) with passive safety features; A Comparative methodology between a real RCCS and a scaled-down heat-removal test facility

Takamatsu, Kuniyoshi; Matsumoto, Tatsuya*; Morita, Koji*

Annals of Nuclear Energy, 96, p.137 - 147, 2016/10

https://doi.org/10.1016/j.anucene.2016.05.012

After Fukushima Daiichi nuclear disaster by TEPCO, a cooling system to prevent core damage became more important from the perspective of defense in depth. Therefore, a new, highly efficient RCCS with passive safety features without a requirement for electricity and mechanical drive is proposed. Employing the air as the working fluid and the ambient air as the ultimate heat sink, the new RCCS design strongly reduces the possibility of losing the heat sink for decay heat removal. The RCCS can always stably and passively remove a part of the released heat at the rated operation and the decay heat after reactor shutdown. Specifically, emergency power generators are not necessary and the decay heat can be passively removed for a long time, even forever if the heat removal capacity of the RCCS is sufficient. We can also define the experimental conditions on radiation and natural convection for the scale-down heat removal test facility.

Condition number estimation of preconditioned matrices

Kushida, Noriyuki

PLOS ONE (Internet), 10(3), p.e0122331_1 - e0122331_16, 2015/03

https://doi.org/10.1371/journal.pone.0122331

The present paper introduces a condition number estimation method for preconditioned matrices. The newly developed method provides reasonable results, while the conventional method which is based on the Lanczos connection gives meaningless results. The Lanczos connection based method provides the condition numbers of coefficient matrices of systems of linear equations with information obtained through the preconditioned conjugate gradient method. Estimating the condition number of preconditioned matrices is sometimes important when describing the effectiveness of new preconditionerers or selecting adequate preconditioners. Operating a preconditioner on a coefficient matrix is the simplest method of estimation. However, this is not possible for large-scale computing, especially if computation is performed on distributed memory parallel computers. This is because, the preconditioned matrices become dense, even if the original matrices are sparse. Although the Lanczos connection method can be used to calculate the condition number of preconditioned matrices, it is not considered to be applicable to large-scale problems because of its weakness with respect to numerical errors. Therefore, we have developed a robust and parallelizable method based on Hager's method. The feasibility studies are curried out for the diagonal scaling preconditioner and the SSOR preconditioner with a diagonal matrix, a tri-daigonal matrix and Pei's matrix. As a result, the Lanczos connection method contains around 10% error in the results even with a simple problem. On the other hand, the new method contains negligible errors. In addition, the newly developed method returns reasonable solutions when the Lanczos connection method fails with Pei's matrix, and matrices generated with the finite element method.

Structural analysis of (Ga,Mn)N epilayers and self-organized dots using MeV ion channeling

Kuroda, Shinji*; Marcet, S.*; Bellet-Amalric, E.*; Cibert, J.*; Mariette, H.*; Yamamoto, Shunya; Sakai, Takuro; Oshima, Takeshi; Ito, Hisayoshi

Physica Status Solidi (A), 203(7), p.1724 - 1728, 2006/05

https://doi.org/10.1002/pssa.200565396

no abstracts in English

Estimation of covariance matrices for nuclear data of , and

Nakagawa, Tsuneo

Journal of Nuclear Science and Technology, 42(11), p.984 - 993, 2005/11

https://doi.org/10.3327/jnst.42.984

no abstracts in English

Size of small Si and Ge clusters on Si(111) and Ge(111) surfaces

Asaoka, Hidehito; Cherepanov, V.*; Voigtlnder, B.*

Surface Science, 588(1-3), p.19 - 25, 2005/08

https://doi.org/10.1016/j.susc.2005.05.022

We determined the average size of small Si and Ge clusters conned to one half of a (77) or (55) unit cell of a Si or Ge(111) surface. The size of Si and Ge clusters conned to a Si(111)-(77) half unit cell was determined to be 8.31 atoms and 7.51 atoms, respectively for a growth temperature of 400 K. This is the same value within the error and shows, that the material of the clusters is less important for the cluster size. On the Ge surface it was found that the reconstruction unit cell is important for the cluster size. On the (55) reconstructed Ge(111) surface the Si clusters have a smaller size of 4.71 atoms compared to 8.21 atoms for Si clusters on the Ge(111)-(77) surface.

The Impedance of the ceramic chamber in J-PARC

Shobuda, Yoshihiro; Chin, Y. H.*; Omi, Kazuhito*; Toyama, Takeshi*

Proceedings of 2005 Particle Accelerator Conference (PAC '05) (CD-ROM), p.1898 - 1900, 2005/00

At 3GeV RCS(Rapid Cycle Synchrotron) in J-PARC, the ceramic chamber is adopted to aviod the excess eddy current. This ceramic chamber is surrounded by Cu-stripes to supress the leak field caused by the beam. The inner surface of the chamber is coated with TiN to suppress the secondary electron emission. In order to discuss the beam instability, we have to calculate the impedance for this chamber. Previously, the impedance was calculated by replacing the Cu-stripes to the conducting beam pipe. In this paper we deal with Cu-stripes realistically, and compare the results with the previous results. The resistivity of Cu-stripes and the TiN are also considered.

First measurement of time-resolved neutron yield on JT-60U using a microfission chamber

Hayashi, Takao; Nishitani, Takeo; Ishikawa, Masao

Review of Scientific Instruments, 75(10), p.3575 - 3577, 2004/10

https://doi.org/10.1063/1.1785261

Micro fission chambers, which are pencil sized ionization chamber with fissile material inside, to be installed in the vacuum vessel as neutron monitor for the International Thermonuclear Experimental Reactor (ITER). The micro fission chamber has been installed inside toroidal field coils in JT-60U, in order to investigate the technical validity as neutron monitor in a magnetic field of about 2 T. Compared with the neutron yield measured by three U fission chambers which are used as neutron monitors in JT-60U, neutron yield measured by micro fission chamber has a good linearity with them. The influence of the magnetic field on the micro fission chamber has not been observed. However improper signals caused by plasma disruption and breakdown event of Neutral Beam Injection were observed, probably due to long wiring between the detector and the preamplifier. Therefore, by enhancement of noise protections, micro fission chambers can be available as neutron monitor for ITER.