Masaya Ohtsuka

Numerical analysis of swirling non-reacting and reacting flows by the Reynolds stress differential method

Abstract So et al. s isothermal He-air mixing experiment and Wilhelmis propane-air diffusion-controlled combustion experiment were analyzed with a differential Reynolds stress model. For both experiments, the IPC (isotropization of production and convection) model of Fu et al. for the rapid term improved the normal stress distribution in the large swirl velocity region and the Hanjalic and Launder model for the diffusion term improved the normal stress distribution near the centreline, in comparison with the IP (isotropization of production) model for the rapid term and the Daly and Harlow model for the diffusion term. For Wilhelmis experiment, the IPC model and the Hanjalic and Launder model yielded improved mixture fraction distributions near the centreline. The intensity of axial and swirl velocities near the centreline was still underestimated, however, and the model requires further improvement.

Experimental Study of Acoustic and Flow-Induced Vibrations in BWR Main Steam Lines and Steam Dryers

The boiling water reactor (BWR-3) in the Quad Cities (QC) Unit 2 Nuclear Power Plant experienced a significant increase in steam moisture under extended power up-rate (EPU) conditions. Inspection of the stem dryer showed it was likely that BWR steam dryer had been damaged by high cycle fatigue due to acoustic-induced vibration. The cause of the dryer failure was considered as flow-induced acoustic resonance at the stub pipes of safety relief valves (SRVs) in the main steam lines (MSLs). Acoustic resonance was considered to be generated by interaction between the sound field and an unstable shear layer across the closed side branches of the SRV stub pipes. We have started a research program on BWR dryers to develop their loading evaluation methods. Moreover, it has been necessary to evaluate the dryer integrity of BWR-5 plants which are the main type of BWR in Japan. In the present study, we used 1/10-scale BWR tests and analysis to investigate the flow-induced acoustic resonance in SRV stub pipes and propagation of fluctuating pressure from SRVs to the dryer through the MSLs. The test apparatus consisted of a steam dryer, a steam dome and 4 MSLs with 20 SRV stub pipes. Acoustic analysis was also applied to evaluate the propagation of fluctuating pressure from MSLs to the dryer. We demonstrated that acoustic resonance occurred in SRV stub pipes at higher velocity flows than in the normal operation and fluctuating pressure propagated from SRVs to the dryer. The amplitude of the fluctuating pressure due to several stub pipes was much larger than that in one stub pipe because of interaction between them. The fluctuating pressure generated in stub pipes was propagated to the dryer through the MSLs with decreasing amplitude. The amplitude of the fluctuating pressure observed at the top of stub pipes was reduced significantly in the MSLs and maintained fairly well in the steam dome. The flow-induced acoustic resonance did not occur for Strouhal number above 0.6 in the MSLs system of the BWR-5. Results of the tests were compared with those of acoustic analysis. The acoustic analysis could well predict the dryer loading.Copyright

Combustion Oscillation Analysis of Premixed Flames at Elevated Pressures

A new analytical time lag flame model based on Bloxidge’s flame model was introduced for calculating combustion oscillation of premixed flame to take into account the distribution of heat release rate and flame speed which was calculated by analytical formulas dependent on pressure, temperature, fuel-to-air ratio and velocity. The transfer matrix technique using the new flame model was applied to the calculation of acoustic resonance. To verify the model, combustion oscillation experiments were performed for methane-air premixed flames stabilized by a swirl burner at elevated pressures between 0.6–0.9MPa. Fluctuating pressure had the maximum peak at the specific value of fτf. Here f is the frequency of resonance and τf is the passing time of premixed gas through flame length. The analysis could simulate the dependency of fuel-to-air ratio and static pressure for dynamic pressure local peak.© 1998 ASME

Development of numerical analysis method of flow-acoustic resonance in stub pipes of safety relief valves

The boiling water reactors (BWRs) have steam dryer in the upper part of the pressure vessel to remove moisture from the steam. The steam dryer in the Quad Cities Unit 2 nuclear power plant was damaged by high-cycle fatigue due to acoustic-induced vibration during extended power uprate operation. The principal source of the acoustic-induced vibration was flow-acoustic resonance at the stub pipes of the safety relief valves (SRVs) in the main steam lines (MSLs). The acoustic wave generated at the SRV stub pipes propagates throughout the MSLs and eventually reaches and damages the steam dryer. Therefore, for power uprate operation of the BWRs, it has been required to predict the flow-acoustic resonance at the SRV stub pipes. The purpose of this article was to propose a numerical analysis method for evaluating the flow-acoustic resonance in the SRV stub pipes. The proposed method is based on the finite difference lattice Boltzmann method (FDLBM). So far, the FDLBM has been applied to flow-acoustic simulations of laminar flows around simple geometries at low Reynolds number. In order to apply the FDLBM to the flow-acoustic resonance simulations of turbulent flows around complicated geometries at the high Reynolds number, we developed computationally efficient model by introducing new function into the governing equation. The proposed method was compared with the conventional FDLBM in the cavity-driven flow simulation. The proposed method was validated by comparisons with the experimental data in the 1/10-scale test of BWR-5 under atmosphere condition. The following three results were obtained; the first is that the proposed method can reduce the computing time by 30% compared with the conventional FDLBM; the second is that the proposed method successfully simulated the flow-acoustic resonance in the SRV stub pipes of the BWR-5, and the pressure fluctuations of the simulation results agreed well with those of the experimental data; and the third is the mechanism of the flow-acoustic resonance in the SRV stub pipes. Acoustic waves causing the flow-acoustic resonance in the SRV stub pipes are generated by the unsteady vortices in the SRV stub pipes.

Experimental Study on Thermal Striping in Mixing Tees With Hot and Cold Water

Thermal striping tests in mixing tees with hot and cold water were conducted for three types of flow conjunctions in order to establish an evaluation method for high-cycle thermal fatigue of piping systems. Two kinds of examinations were planned. The preliminary tests were flow visualization tests carried out using acrylic pipes to obtain flow pattern characteristics and flow temperature fluctuations. The main tests were temperature fluctuation measurement tests carried out using metal pipes to evaluate the unsteady heat transfer coefficient based on measured temperature fluctuations of fluid and pipe wall. This paper reports visualization test results. The flow patterns were visualized by injection of methylene blue and compared with flow analysis results by the k-e turbulence model. Temperature fluctuations of fluid 3mm from the inner pipe wall were measured with C-A thermocouples. Fundamental features such as locations with a large fluctuating temperature, the fluctuating temperature amplitude and its frequency were identified.Copyright

Fluctuating Pressure Generating in BWR Main Steam Lines Acoustic Excited by Safety Relief Valve Stub Pipes and Dead Legs

During operation, the BWR-3 steam dryer in the Quad Cities Unit 2 Nuclear Power Plant was damaged by high cycle fatigue. The dryer failure was attributed to flow-induced acoustic resonance at the stub pipes of safety relief valves (SRVs) in the main steam lines (MSLs). The acoustic resonance was considered to be generated by interaction between the sound field and an unstable shear layer across the closed side branches with SRV stub pipes. We HITACHI and CRIEPI have started a research program on BWR dryers to develop their loading evaluation methods. Moreover, it has become necessary to evaluate the dryer integrity of BWR-5 plants in particular which are the main type of BWR in Japan. In the present study, we used 1/10-scale BWR tests and analyses to investigate the flow-induced acoustic resonance and characteristics of fluctuating pressure in MSLs. The test apparatus consisted of a steam dryer, a steam dome and 4 MSLs with 20 SRV stub pipes. A finite element method (FEM) was applied for the calculation of three-dimensional wave equations in acoustic analysis. We demonstrated that remarkable fluctuating pressures occurred in high and low frequency regions. Intensity of three peaks observed in the spectrum of fluctuating pressure in MSLs was increased with St. High frequency fluctuating pressures were generated by the flow-induced acoustic resonance in the SRV stub pipes. Low frequency fluctuating pressures were excited by the acoustic resonance in the dead leg. Frequency of fluctuating pressure generating in the SRV stub pipe was changed with St. On the other hand, frequency of fluctuating pressure excited by dead leg was almost constant. Fluctuating pressure in low frequency range increased gradually with flow velocity and its intensity was roughly proportional to the square of flow velocity. The flow-induced acoustic resonance did not occur for St larger than 0.6 in the BWR MSLs for both low and high frequency ranges. Operating conditions of the BWR-5 from 100 to 115% were in the range of St larger than 0.6, so intense acoustic resonance would not occur in the BWR MSLs.Copyright

Safe and Simplified Boiling Water Reactor (SSBWR)

A safe and simplified BWR (SSBWR) has been developed as an innovative future reactor to provide a super-long life core of 20 years and to realize a passive core safety system with infinite grace period. Operability and maintainability can be largely improved by using the super-long life core, cutting the number of active components, and using a one-batch core with no exchange of fuel assemblies, which can also significantly reduce the possibility of nuclear proliferation. Np-237 of MAs (Minor Actinides) can be effectively transmuted using the very hard neutron spectrum of SSBWR and high level radioactive wastes can be reduced.Copyright

Application of the Resource-Renewable Boiling Water Reactor for TRU Management and Long-Term Energy Supply

The RBWR (resource-renewable boiling water reactor) is an innovative BWR that has a capability to breed and burn trans-uranium elements (TRUs) using a multi-recycling process. The RBWR can be used as a long-term energy supply, and it reduces the negative environmental impact that TRUs cause as they are otherwise long-lived radioactive wastes. Various design concepts of the RBWR core have been proposed. The RBWR-AC is a break-even reactor and the RBWR-TB and RBWR-TB2 are TRU burners. The RBWR-TB is designed to burn TRUs from the RBWR-TB itself and to burn almost all the TRUs by repeating their recycling. The RBWR-TB is assumed to be applied for a nuclear power phase-out scenario. The RBWR-TB2 is intended to burn TRUs from LWR spent fuels. The RBWR-TB2 is assumed to be applied for reducing the amount of TRUs to be managed in storage facilities. The RBWR cores achieve their TRU multi-recycling capability under the constraint that the void reactivity coefficient must be negative by introducing the parfait core concept. This chapter reviews details of the specific design and core characteristics of the RBWR.

Theoretical Evaluation of Blow-Off and Flash Back Limits on a Bunsen Burner.

The quenching effect due to flame stretch and heat loss was evaluated based on a HTA (Hyperbolic Tangent Approximation) theory for a counter premixed flame. The main results are as follows : (1) Reaction progress variable c at the stagnation point of the counter flow decreases with flame stretch and heat loss. The flame quench occurs under the condition of c=0.7 at the stagnation point. (2) Blow-off of a Bunsen burner occurs under the condition of g>(1.62-Nu(δ/d)2) (Su/δ) (g : velocity gradient, δ : thickness of laminar flame, Su : laminar flame speed, Nu : Nusselt number, d : diameter of burner). This condition was in good agreement with experimental data. (3) Flash back occurs under the condition of g<0.697 (Su/δ).