The results of experimental and computational investigations of microfuel behavior under the action of neutron pulses in the BIGR reactor are presented. The methods used in the present work made it possible to determine the change in the structure of the irradiated samples, specifically, to record interlayer gap formation in the microfuel and the actual fracture of the microfuel. The results of this work could be helpful for evaluating the service life of microfuel and the consequences of emergency situations in HTGR as well as for developing and perfecting the corresponding computational software.

The results of our experimental investigation of the turbulent mixing occurring at a Richtmayer-Meshkov instability driven by a shock wave (SW) in gases at different Mach numbers (M) ranging from approximate to 1.4 to approximate to 9 are presented in this paper. The experiments were performed by using an air shock tube with a channel section of 40 x 40 mm(2). The SW passed from 'light' to 'heavy' gases. Air (helium) was used as a 'light' gas and Xe, CO2 and Ar were used as 'heavy' gases. The gases were initially separated by a thin (approximate to 1 mu m) polymer film, which was failed after the passing of the SW. A film of the flow was made using a high-speed camera by the Schlieren method.

To allow the detailed analysis of the two-phase coolant flow and heat transfer phenomena in a boiling water reactor fuel bundle the CFD-BWR model is being developed for use with the commercial code STAR-CD which provides general two-phase flow modeling capabilities. The paper reviews the key boiling phenomenological models, describes the overall strategy adopted for the combined CFD-BWR and STAR-CD boiling models validation and presents results of a set of experiment analyses focused on the validation of specific models implemented in the code. The location of vapor generation onset, axial temperature profile and axial and radial void distributions were calculated and compared with experimental data. Good agreement between computed and measured results was obtained for a large number of test cases.

This paper presents recent advances in the development and validation of the two-phase flow topology models implemented in CFD-BWR, an advanced Computational Fluid Dynamics (CFD) computer code that allows the detailed analysis of the two-phase flow and heat transfer phenomena in Boiling Water Reactor (BWR) fuel assemblies under various operating conditions. The local inter-phase surface topology plays a central role in determining the mass, momentum, and energy exchanges between the liquid and vapor phases and between the two-phase coolant and the fuel pin cladding. The paper describes the topology map used to determine the local inter-phase surface topology and the role of the local topology in determining the inter-phase mass, momentum, and energy transfer. It discusses the relationship between the local interphase surface topology and the traditional channel flow regimes and presents results of experiment analyses in which computed local topologies are aggregated into flow regimes and compared with experimental observations.

The experimental technique for investigation of turbulent mixing is presented in this report. Turbulent mixing (TM) arises at Richtmayer-Meshkov instability at the interface gas-gas accelerated by a shock wave. Helium (He) and air (Air) was used as light gas, as heavy gas - sixfluorine sulfur (SF6). In all the experiments a shock wave propagated from light gas to heavy gas. Mach number of a shock wave in SF6 has changed from 2 to 9. The flow was recorded by the use of shlieren method during rapid motion-picture recording.

We present the results of the experimental study of viscosity effect on turbulent mixing development (TM) occurring at Raylegh-Taylor instability at the boundary of a liquid layer accelerated by compressed gas. In the experiments dynamic viscosity of liquid has varied from mu=1 cP to mu=1,480 cP. As liquid we used: water, glycerol, aqueous solution of glycerol having known viscosity. The value of acceleration of a liquid layer has amounted to: g congruent to 10(3) g(0) and g congruent to 10(5) g(0). As gas we used helium compressed previously up to pressure 4.5-500 atm. It has been demonstrated that when changing liquid viscosity a mixing zone structure changes. This influences on a mixing character of substances.