Takashi Takata

Development of unstructured mesh-based numerical method for sodium–water reaction phenomenon in steam generators of sodium-cooled fast reactors

ABSTRACT When pressurized water or vapor leaks from a failed heat transfer tube in a steam generator of sodium-cooled fast reactors, a high-velocity and high-temperature jet with sodium–water chemical reaction may cause wastage on the adjacent tubes. For safety assessment of the steam generator, a computational fluid dynamics code called SERAPHIM calculating compressible multicomponent multiphase flow with sodium–water chemical reaction has been developed. The original SERAPHIM code is based on the finite difference method. In this study, unstructured mesh-based numerical method for the SERAPHIM code was developed to advance a numerical accuracy for the complex-shaped domain including multiple heat transfer tubes. Numerical analysis of an underexpanded jet experiment was performed as part of validation of the unstructured mesh-based SERAPHIM code. The calculated pressure profile showed good agreement with the experimental data. To investigate the effect of the introduction of the unstructured mesh and to confirm applicability of the numerical method for the actual situation, water vapor discharging into liquid sodium was analyzed. The calculated behavior of the reacting jet agreed with the previous experimental knowledge. It was demonstrated that the proposed numerical method could be applicable to evaluation of the sodium–water reaction phenomenon.

Development of Unstructured Mesh-Based Numerical Method for Sodium-Water Reaction Phenomenon

Abstract When pressurized water or vapor leaks from a failed heat transfer tube in a steam generator (SG) of sodium-cooled fast reactors, a high-velocity, high-temperature jet with sodium-water chemical reaction may cause wastage on the adjacent tubes. For safety assessment of the SG, a computational fluid dynamics code SERAPHIM, in which a compressible multicomponent multiphase flow with sodium-water chemical reaction is computed, has been developed. The original SERAPHIM code is based on the finite difference method. In this study, an unstructured mesh-based numerical method was developed and introduced into the SERAPHIM code to advance a numerical accuracy for a complex-shaped domain including multiple heat transfer tubes. The multiphase flow under the tube failure accident is calculated by the multifluid model considering compressibility. The governing equations are solved by the Highly Simplified Marker And Cell (HSMAC) method. The original HSMAC method was modified for compressible multiphase flows in the unstructured mesh. Validity of the unstructured mesh-based SERAPHIM code was investigated through the analysis of an underexpanded jet experiment, which is a key phenomenon in the tube failure accident. The calculated pressure profile showed good agreement with the experimental data. Numerical analysis of water vapor discharging into liquid sodium was also performed. The calculated behavior of the reacting jet agreed with the previous experimental knowledge. It was demonstrated that the proposed numerical method could be applicable to evaluation of the sodium-water reaction phenomenon.

Event sequence assessment of deep snow in sodium-cooled fast reactor based on continuous Markov chain Monte Carlo method with plant dynamics analysis

ABSTRACT Margin assessment of a nuclear power plant against external hazards is one of the most important issues after Fukushima Dai-ichi Nuclear Power Plant Accident. In this paper, a new approach has been developed to assess the plant status during external hazards and countermeasures against them in operation quantitatively and stochastically. A continuous Markov chain Monte Carlo (CMMC) method is applied and coupled with a plant dynamics analysis. In the CMMC method, a subsequence plant status is determined by the latest state (Markov chain) and the status is evaluated from the plant dynamics analysis. A failure or success of safety function of plant component is also evaluated stochastically based on a latest state of plant or hazard. A numerical investigation of plant dynamics analysis against a snow hazard is also carried out in a loop type sodium-cooled fast reactor so as to assess the margin against the hazard.

Evaluation of Sodium Pool Fire and Thermal Consequence in Two-Cell Configuration

Evaluation of accidental sodium leak, combustion, and its thermal consequence is one of the important issues to be assessed in the field of sodium-cooled fast reactor (SFR). The present paper deals with the sodium pool fire and subsequent heat transfer behavior in air atmosphere two-cell geometry both experimentally and analytically because such two-cell configuration is considered as a typical one to possess important characteristic of multi-compartment system seen in an actual plant. The analyses of the experimental data clarify the basic characteristics of sodium pool combustion and consequential heat and mass transfer in the cells, for instance, suggesting several features of multidimensional thermal-hydraulic behaviors such as the strong gas mixture at the combustion cell and the thermal stratification near the opening between the two cells. As a result of the numerical analysis using a lumped-parameter based zonal model safety analysis code ‘SPHINCS’, the applicability of the ventilation model implemented in SPHINCS has been demonstrated. It is also investigated that the buoyancydriven ventilation is dominant in the experiment.

ICONE19-43534 Numerical Simulation of Dynamic Flow Structure and Thermal Stratification Phenomena in LMFBR

The three-dimensional analysis of thermal stratification in the upper plenum of MONJU is conducted using the commercial CFD code, FLUENT ver. 12.0. Since the temperature gradient near the thermal stratification interface would cause thermal stress in the reactor components, it is important to understand the characteristics of thermal stratification. As the result of numerical analysis, it is understood that the interface of thermal stratification is influenced by the flow pattern in the upper plenum of MONJU. After the jet from the core outlet is impinged on the upper core structure, the hot fluid flows obliquely upward to the inner barrel under the steady-state condition. On the other hand, the jet from core outlet flows to the lower part of the upper plenum, and then cold fluid flows through the flow holes under the transient condition. Hence, the flow structure has changed from the steady-state condition as the flow rate and temperature of the core outlet decrease due to the turbine trip. It is considered that the flow path of flow holes comes to govern under the transient condition, since the hot sodium acts as the plug due to the buoyancy.

OS8-7 Pseudo Three-Dimensional Modeling of Particle-Fuel Packing Using Distinct Element Method

200 [Hz] frequency 2.50E-5 [m] amplitude vibration 0.5 [sec] duration time 1.0E-7 [sec] time step size calculation 0.17 coefficient of friction 0.25 Poisson’s ratio 3.90E+9 Young’s modules 2.00E-2 [m] height 1.00E-2 [m] width container 1200 number of fine particles 26 number of coarse particles 0.25 [-] coefficient of friction 0.28 [-] Poisson’s ratio 1.00E+10 [Pa] Young’s modules 1.10E+4 [kg/m3] density 2.00E-4 [m] fine particles diameter 1.40E-3 [m] coarse particles diameter particles