Ryuhei Kawabe

Numerical Analysis Method for Two-Dimensional Two-Fluid Model Using Control Volume Formulation

A numerical calculation technique for the two-dimensional two-fluid model has been developed. The control volume formulation and non-staggered mesh scheme are employed in order to confirm that solutions satisfy the conservation equations of the two-fluid model. Numerical instability due to the non-staggered mesh is overcome by considering additional flows induced from a local pressure gradient on control volume boundaries. The Godunov method and SIMPLE method are used to estimate the additional flow for compressible and incompressible two-phase flows, respectively. These methods are modified to take the density difference between the phases and the added mass effect into account. The present method has been applied to analyses of two-dimensional two-phase flow discharge from a pipe and phase separation due to gravity in a horizontal circular pipe in order to investigate the capability of dealing with fundamental phenomena of two-dimensional two-phase flow. The present technique enables a small scale compu...

Analysis of radiant heat transfer in a BWR fuel assembly

Abstract A computer code ‘CIDER’ was developed which analyzes radiant heat transfer in a BWR fuel rod bundle under loss of coolant conditions. In the code, (1) a channel box and fuel rods are considered to be gray bodies, (2) reflection and absorption of radiation beams in the atmosphere is neglected, (3) a fuel rod is approximated by a regular polygonal rod, and (4) radiant heat flux is calculated considering circumferential temperature distribution on each fuel rod surface, which is determined from radial and circumferential heat conduction calculations in a fuel rod. It was found that the conventional model with uniform cladding temperature overestimated heat flux about 30% in a typical situation, or correspondingly underestimated the temperature rises.

A study on sodium spray combustion

Abstract Sodium spray combustion was studied through experiments and analysis, in order to clarify the burning rate, pressure and temperature transients in a sodium spray fire. In the experiments, about 400 g sodium was sprayed in a closed vessel of 2 m3, containing nitrogen and 0–21 vol% oxygen. Pressure, temperature and oxygen concentration were measured during and after sodium injection. The experimental results revealed that the temperature in the spray outer region was higher than that of inner region and observed oxygen consumption was not more than 80% of that expected for complete combustion of sodium. To analyze the experiments, a computer program SOFIA-II was developed based on an analytical single droplet combustion model and a two-dimensional temperature and oxygen concentration distribution model in the vessel. The calculated pressure agreed with the experimental pressure on the whole and the peak pressure difference was within 10% error.

An analytical method for thermal-hydraulic transients in piping networks

To predict the thermal-hydraulic transients, an analytical method has been developed for single and two-phase flow in arbitrary piping networks. In this method the piping network is represented by vessels and flow channels. The thermal-hydraulic transients in the channel are described by partial differential equations derived from mass, momentum and energy conservation laws. The partial differential equations are solved implicitly, simultaneously for the whole network, with the ordinary differential equations that describe the change of vessel pressures and enthalpies. Numerical calculation error is evaluated in the implicit method for the integration of partial differential equations of channel flow. In the numerical calculation an artificial diffusion appers with a diffusion coefficient Δt λ2/2, where Δt is a time step and λ denotes the propagation velocity of the perturbation.

SENHOR-IV: A computer code for small pipe-break analysis of pressure-tube type reactors

Abstract A computer program SENHOR-IV was developed which describes blowdown phenomena associated with a small pipe-break accident in pressure-tube type reactors. Thermal-hydraulic transients of single-phase and two-phase flow in a primary cooling system, which is composed of the pressure tubes, a steam drum, downcomers, a lower header and pipings connecting these components, were calculated from the conservation equations of mass, momentum and energy by assuming pressure propagation and flow rate distribution to be quasi-steady and by applying the method of characteristics to enthalpy transport. The void propagation velocity in two-phase flow was given from Smiths equation for void-quality relationship to the program. Calculation of a flow transient, which has an exact solution, with use of this program showed small deviations from the exact solution. Predicted transients of pressure and water level in the steam drum indicated a good agreement with those observed in a full scale test facility at O-arai Engineering Center.

Senhor-II — A computer code for loss-of-coolant accidents of pressure tube type reactors

Abstract An ATR LOCA analysis code, SENHOR-II, was developed which evaluates the loss-of-coolant accident in a reactor primary loop composed of parallel pressure tubes and downcomers connecting a steam drum to a lower header. The reactor system is divided into reservoirs and channels. The reservoirs are assumed to be saturated and equilibrated. The channels are treated one-dimensionally and their flows are assumed quasi-steady. The reservoir effect of piping, the heating up of fuel rods, the thermal capacity of structures, and the effects of steam separators and water level in the steam drum are considered. Calculated results are compared with the experimental results of the blowdown test performed with the mock-up test loop in Ō-arai Engineering Center of PNC, and the adequacy of the calculation model and formulae is confirmed.

Sodium Tests of Head-Flow Characteristics for Prototype Annular Electromagnetic Flow Coupler

A prototype annular electromagnetic flow coupler was tested with high temperature sodium and it worked successfully, verifying the operational principle. The pump head-flow characteristics of the coupler were first clarified from an analysis of its equivalent electric circuit. The pump head and the generator pressure drop decrease linearly with the pump flow rate under the conditions of constant generator flow rate and external magnetic flux density. The gradients of the linear changes are given by ratios of equivalent resistances in the electrical analog, and are independent of the generator flow rate, if the magnetic flux density is kept constant. Sodium tests of the prototype confirmed the above results when the Hartmann number of the test conditions is larger than 170. Both ratios of the differential pressures and the volumetric flow rate between pump and generator ducts exceed 50% while the wall loss of around 40% appears at peak efficiency due to the lack of electrical insulation and the relatively ...