Flow regime and void fraction predictions in vertical rod bundle flow channels

Han, X.*; Shen, X.*; Yamamoto, Toshihiro*; Nakajima, Ken*; Sun, Haomin; Hibiki, Takashi*

International Journal of Heat and Mass Transfer, 178, p.121637_1 - 121637_24, 2021/10

https://doi.org/10.1016/j.ijheatmasstransfer.2021.121637

Study on double heterogeneity effect of Pu-rich agglomerates in mixed oxide fuel using cross section homogenization method for particle-dispersed media

Yamamoto, Toshihiro

Annals of Nuclear Energy, 37(3), p.398 - 405, 2010/03

https://doi.org/10.1016/j.anucene.2009.11.016

A cross section homogenization method for media containing randomly and uniformly dispersed particles has been applied to MOX fuels containing Pu-rich agglomerates. This method (Shmakov method), which is incorporated into a Monte Carlo code MCNP, has been applied to lattice calculations of an infinite MOX fuel rod array. Shmakov method can accurately reproduce the calculation results for a heterogeneous arrangement of Pu-rich agglomerates. A correction factor used to define an effective microscopic cross section provides a quantitative indication of the double heterogeneity of Pu-rich agglomerates. The correction factors exhibit an obvious double heterogeneity effect. However, the double heterogeneity effect of Pu-rich agglomerates on k-eff seems to be unexpectedly minor because the underestimate of the reaction rates in the resonance energy range is offset by the overestimate of the reaction rates in the thermal energy range.

Benchmark critical experiments and FP worth evaluation for a heterogeneous system of uranium fuel rods and uranium solution poisoned with pseudo-fission-product elements

Tonoike, Kotaro; Yamamoto, Toshihiro; Miyoshi, Yoshinori; Uchiyama, Gunzo; Watanabe, Shoichi*

Journal of Nuclear Science and Technology, 46(4), p.354 - 365, 2009/04

https://doi.org/10.3327/jnst.46.354

A series of critical experiments were performed using heterogeneous cores at the Static Experiment Critical Facility in Japan Atomic Energy Agency in order to obtain systematic benchmark data concerning dissolving process in a reprocessing plant. Focusing on the introduction of the burn-up credit, critical mass measurement was conducted for a combination of uranium dioxide fuel rods (5wt% U) and uranyl nitrate solution (6wt% U) poisoned with pseudo fission product (FP) elements - samarium, cesium, rhodium, and europium. Fuel rods were arrayed with an 1.5-cm lattice interval in the poisoned fuel solution in a 60-cm diameter cylindrical tank. The uranium concentrations of the solution was roughly kept at about 320gU/L, and the FP element concentrations were adjusted to be equivalent to a burn-up of about 30GWd/t. The result provides basic experimental data for validation of computational methods to evaluate a reactivity effect of each FP element, as well as benchmark criticality data for validation of neutron multiplication factor calculation of heterogeneous systems of spent fuel. In the report, detail of the experiments and its benchmark models will be presented as well as the procedure and the result of separate reactivity worth evaluation for each FP element. The experimental result and the computational evaluation will also be compared.

Benchmark critical experiments and FP worth evaluation for a heterogeneous system of uranium fuel rods and pseudo FP doped uranium solution

Tonoike, Kotaro; Miyoshi, Yoshinori; Uchiyama, Gunzo; Watanabe, Shoichi*; Yamamoto, Toshihiro*

Proceedings of 8th International Conference on Nuclear Criticality Safety (ICNC 2007), p.222 - 227, 2007/05

In order to obtain systematic benchmark criticality data concerning dissolving process in a reprocessing plant for LWR spent fuel, a series of critical experiments were performed using heterogeneous cores at the Static Experiment Critical Facility (STACY) in Japan Atomic Energy Agency (JAEA). Focusing on the introduction of the burn-up credit to the process, critical mass measurement was conducted for a combination of uranium fuel rods and uranium solution where pseudo fission product (FP) materials were doped. In this report, the "pseudo FP materials" means elements such as Sm, Cs, Rh and Eu whose isotopic composition is natural but which contains some FP nuclide(s). The result is going to provide basic experimental data for validation of computational methods to evaluate a reactivity effect of each FP material, as well as benchmark criticality data for validation of neutron multiplication factor calculation of heterogeneous systems of spent fuel. In the report, detail of the experiments including a differential reactivity worth curve over the solution level variation is going to be provided as well as the procedure and the result of separate reactivity worth evaluation of each pseudo FP material. Comparison of the experimental result and the computational evaluation will also be presented.

Extension of cross section homogenization method for particle-dispersed media to layered particles

Yamamoto, Toshihiro

Annals of Nuclear Energy, 33(9), p.804 - 812, 2006/06

https://doi.org/10.1016/j.anucene.2006.04.004

A cross section homogenization method for media containing randomly dispersed particles, which was originally developed by Shmakov et al., and then was improved by Yamamoto et al., is extended to layered particles, such as coated fuel particles of gas-cooled reactors. A new extended formulation is derived for concentric double-layered spherical particles. This formulation is successfully implemented into a continuous energy Monte Carlo code MCNP, and is applied to some examples including a simplified gas-cooled reactor core. The extended method for double-layered spherical particles provides as accurate results as the previously developed method for mono-layered particles does. For the simple gas-cooled reactor core, the new method reproduces keff within several hundreds of pcm as compared to the direct heterogeneous calculation in which double-layered spherical particles are explicitly distributed in the fuel compact. Whereas the previously developed method for mono-layered particles can be performed analytically, this new technique requires numerical integration, making the computation efficiency of the new method deteriorate. However, this method allows one to perform Monte Carlo criticality calculations for double-layered particle-dispersed media with much less computing time than direct heterogeneous calculations.

Education method on Monte Carlo Analysis in atomic energy

Sakurai, Kiyoshi; Yamamoto, Toshihiro

Nihon Genshiryoku Gakkai Wabun Rombunshi, 4(4), p.248 - 258, 2005/12

https://doi.org/10.3327/taesj2002.4.248

no abstracts in English

A Estimation methods of lower weight bound on neutron deep penetration problem with Monte Carlo method

Sakurai, Kiyoshi; Yamamoto, Toshihiro

Nihon Genshiryoku Gakkai Wabun Rombunshi, 4(2), p.172 - 176, 2005/06

https://doi.org/10.3327/taesj2002.4.172

Typical weight estimation methods with Monte Carlo method such as MCNP default, empirical formula, mono-energy neutron attenuation curve, MCNP wwg and adjoint flux are described. The mono-energy neutron attenuation curve method is proposed by authors. Weights estimated by methods except MCNP default and adjoint flux methods are compared with those calculated by MCNP wwg method.

Effect of mixing condition of MOX powder and additives on criticality safety

Yamamoto, Toshihiro; Miyoshi, Yoshinori

Transactions of the American Nuclear Society, 91, p.583 - 584, 2004/11

MOX powder and additives are mixed in the process of MOX fuel fabrication. A non-uniform mixing state of MOX powder and additives occurs during the homogenization mixing process. However, ordinary criticalit safety evaluations for mixtures assume that the mixtures have a uniform distribution of the mixing state. A non-uniform distribution of the mixing state in a sphere, which maximizes the effective neutron multiplication factor, was obtained using a concept of the fuel importance. As a result, the central portion of the sphere is composed of an optimal moderation region, and the surrounding region is composed of pure MOX powder. While keff is 0.545 for the uniform distribution, keff for the optimal non-uniform distribution is 0.590. That is, keff increases by 0.045.

Real time value measurement with Feynman- method utilizing time series data acquisition on low enriched uranium system

Tonoike, Kotaro; Yamamoto, Toshihiro; Watanabe, Shoichi; Miyoshi, Yoshinori

Journal of Nuclear Science and Technology, 41(2), p.177 - 182, 2004/02

https://doi.org/10.3327/jnst.41.177

As a part of the development of a subcriticality monitoring system, a system which has a time series data acquisition function of detector signals and a real time evaluation function of alpha value with the Feynman- method was established, with which the kinetic parameter (alpha value) was measured at the STACY heterogeneous core. The Hashimoto's difference filter was implemented in the system, which enables the measurement at a critical condition. The measurement result of the new system agreed with the pulsed neutron method.

Validating JENDL-3.3 for water-reflected low-enriched uranium solution systems using STACY ICSBEP benchmark models

Yamamoto, Toshihiro; Miyoshi, Yoshinori; Kiyosumi, Takehide*

Nuclear Science and Engineering, 145(1), p.132 - 144, 2003/09

https://doi.org/10.13182/NSE03-A2369

no abstracts in English