Copyright © 2013 by JSME Abstract The supercritical CO2 gas turbine cycle can achieve high cycle thermal efficiency by reducing compressor work near the critical point. The achievable cycle thermal efficiency value is strongly dependent on the recuperator performance. Values of the achievable cycle thermal efficiency are calculated by assuming a value of average recuperator temperature-effectiveness of 91%. The turbine inlet pressure is 20 MPa. The effects of turbine inlet temperature are examined. The calculations are conducted both for the non-intercooling cycle and the intercooling cycle. Results show that the non-intercooling cycle is preferred to the intercooling cycle up to 600°C because of its simplicity. However, the latter is preferred to the former at temperatures greater than 600°C attributable to its approximately 2% higher efficiency. For the typical temperature of 527°C and also 650°C, the diagrams of mass and heat balance are given. The maximum cycle thermal efficiencies are, respectively, 43.4% and 48.9% for 527°C and 650°C. The effects of pressure are examined and 20 MPa is justified as an optimal value. Finally, the effects of recuperator effectiveness on the cycle thermal efficiency are examined, which are revealed to be linear and the cycle thermal efficiency increases about 0.5% for a 1% increase of the recuperator effectiveness.
Tidal power generation is viewed as a leading green energy approach. It is expected that the use of tidal power generation will become a primary method for local-supply-and-local-consumption energy, similar to photovoltaics and wind power. Because the current produced by tides changes with a definite periodicity, it is straightforward to forecast the production of electricity by tidal power generation. However, to cover the supply-and-demand differences in electric power, an accumulation-of-electricity system or a controllable electric power source is required. Hence, in this paper, the cost and electric power quality of an interconnection system constructed with a solid oxide type fuel cell (SOFC), photovoltaics (PV), and tidal power generators are investigated. By accessing the high-speed tidal current in the lake inlets of the Saroma Lake in Hokkaido, the demand of electric power and heat in a surrounding area are provided by the proposed system. As a result of the estimations of numerical analyses, the facility planning, costs, and electric power quality of the proposed system are identified, and the amount of time required to recover the cost versus the present energy cost is expected to be approximately ten years.
A prediction method for water temperature in a spent fuel pit of a pressurized water reactor (PWR) has been developed to calculate the increase in water temperature during the shutdown of cooling systems. In this study, the prediction method was extended to calculate the water level in a spent fuel pit during loss of all AC power supplies, and predicted results were compared with measured values of spent fuel pools in the Fukushima Daiichi Nuclear Power Station. The calculations gave reasonable results, but overestimated the decreasing rate of the water level and the water temperature. This indicated that decay heat was overestimated and evaporation heat transfer from the water surface was underestimated. Results of calculations with 80% decay heat and 155% (Unit 4 pool) or 230% (Unit 2 pool) evaporation heat flux were in good agreement with measured values. The data-fitted evaporation heat fluxes agreed rather well with the evaporation heat transfer correlation proposed by Fujii etal.
In order to establish a safety evaluation method of a steam generator of sodium-cooled fast reactors, a computer program called SERAPHIM calculating compressible multicomponent multiphase flow with sodium-water chemical reaction under tube failure accident has been developed. In this study, a numerical model for liquid droplet entrainment from an interface of the gaseous jet and its transport was newly constructed to evaluate the environment of the liquid droplet impingement erosion. The applicability of the SERAPHIM program which incorporates the droplet entrainment / transport model was investigated through the analysis of vertical discharging of water vapor in the liquid sodium pool under the actual condition of the steam generator. The analysis reproduced appearance of the underexpanded vapor jet. The calculated peak temperature agreed with the experimental results well. Also, appearance of the dispersed phase of droplets in the reacting jet and its acceleration by the supersonic gaseous flow were represented successfully.
In a sodium-cooled fast reactor (SFR), if a heat transfer tube in the steam generator (SG) is failed, high pressurized water vapor blows into the liquid sodium and sodium-water reaction (SWR) takes place. SWR may cause damage to the surface of the neighboring heat transfer tubes by thermal and chemical effects. Therefore, it is important to clearly understand the SWR for safety assessment of the SG. From recent study, sodium (Na)–sodium hydroxide (NaOH) reaction as secondary surface reaction of the SWR phenomena in a SFR was identified by ab initio method [1]. However, kinetics of this reaction is a still open question. It is important to obtain quantitative rate constant of sodium monoxide (Na2O) generation by Na-NaOH reaction because Na2O may accelerate the corrosive and erosive effects. Differential thermal analysis (DTA) provides us with the valuable information on the kinetic parameters, including activation energy, pre-exponential factor (frequency factor) and reaction rate constant. Thus, kinetic study of Na–NaOH reaction has been carried out by using DTA technique. The parameters, including melting points of Na and NaOH, phase transition temperature of NaOH, Na-NaOH reaction temperature and the decomposition temperature of sodium hydride (NaH) were identified from DTA curves. Na, NaOH, and Na2O as major chemical species were observed from the X-ray diffraction (XRD) analysis of the residues after the DTA experiment. It was inferred that Na2O could be generated as a reaction product. Based on the measured reaction temperature, the first-order rate constant of Na2O generation was obtained by the application of the laws of chemical kinetics. From the estimated rate constant, it was found that Na2O generation should be considered during SWR. The results can be the basis for developing a chemical reaction model used in a multi-dimensional sodium-water reaction code, SERAPHIM, being developed by the Japan Atomic Energy Agency (JAEA) toward the safety assessment of the SG in a SFR.
The authors develop a small and simple steam-reforming reactor in a home-use size for n-dodecane as a heavy-hydrocarbons fuel. Under the thermal condition controlled by electric heaters and a gas burner with a thermal diffuser, the authors measure the inside-temperature profile and the hydrogen-molecule ratio (concentration) RH2, together with the molecule ratios RCH4, RCO and RCO2 of other main gas components such as CH4, CO and CO2, respectively. Besides, the authors conduct numerical simulations based on a thermal-equilibrium theory, in addition to experiments. As a result, the authors successfully achieve suitable inside-temperature profiles. And, the effects of the liquid-hourly-space velocity LHSV upon RH2, RCH4, RCO and RCO2 are shown, experimentally. For LHSV ≤ 1, the experimental results agree well with the thermal equilibrium theory. This is in consistent with high conversion ratio XC12H26 ≳ 80%. Furthermore, the authors reveal the effects of the temperature T inside the reactor upon the molecule ratios, comparing with the thermal-equilibrium theory.
A lab scale trickle bed reactor (TBR) has been employed to investigate the effect of particles and liquid flow rate on the phase distribution in TBR. The TBR module, made up of 100 mm inner diameter acrylic column, was randomly packed with inert porous alumina particles of different average diameters that are used in actual reactor. Water was fed from the top of the column by "point feed" and "homogenous feed" strategies and cross-sectional liquid distributions were captured at several axial positions from the top to the bottom of the column by employing electrical resistance tomography (ERT) technique. ERT is a non-invasive cross-sectional imaging technique that provides the cross-sectional conductivity distribution by injecting current and measuring voltages between the several electrodes (16 electrodes in our case) that are attached around the column. The cross-sectional conductivity thus obtained represents the liquid hold up and degree of maldistribution of the liquid. In the experiment, quicker and more homogenous distribution of liquid was obtained for the particles with smaller diameters. That is due to capillary force that cancels the randomness of packing. Electrical resistance tomography seems to be reliable non-invasive instrumentation technique to optimize the design and operations of the trickle bed reactors.
Horizontal axis wind turbines can experience significant time varying aerodynamic loads, potentially causing adverse effects on structures, mechanical components, and power production. As designers attempt lighter and more flexible wind energy machines, greater accuracy and robustness will become even more critical in future aerodynamics models. Aerodynamics modeling advances, in turn, will rely on more thorough comprehension of the three dimensional, unsteady, vortical flows that dominate wind turbine blade aerodynamics under high load conditions. These variations may express the incidence angle and wind velocity changes over a 2-D S809 airfoil with the surface roughness effect. To numerically characterize these flows, the instantaneous speed and wind direction variations, represented by a peak function were used to characterize dynamic stall vortex kinematics and normal force amplification. For lack of experimental data in the pulsating motion case, the present numerical approach has been validated by comparing our results with an oscillating S809 airfoil experimental data. The results show the importance of taking into account the behaviour of the unsteady flow subject to abrupt variation of wind direction and velocity. As well as the influence of the surface roughness in the modelling of wind turbine flow. These results give an accurate estimation of aerodynamic loads which will subsequently improve the design of wind turbines.
The transient critical heat fluxes (transient CHFs) in SUS304-circular tubes with various twisted-tape inserts are systematically measured for mass velocities (G = 3988–13,620 kg/m2s), inlet liquid temperatures (Tin = 287.55–313.14 K), outlet pressures (Pout = 805.11–870.23 kPa) and exponentially increasing heat inputs (Q = Q0 exp(t/τ), exponential periods, τ, of 28.39 ms to 8.43 s) by the experimental water loop comprised of a multistage canned-type circulation pump controlled by an inverter. The SUS304-circular tube of inner diameter (d = 6 mm), heated length (L = 59.4 mm), effective length (Leff = 49.4 mm), L/d (=9.9), Leff/d (=8.23), and wall thickness (δ = 0.5 mm) with average surface roughness (Ra = 3.89 μm) is used in this work. The SUS304 twisted-tapes with twist ratios, y [H/d = (pitch of 180 deg rotation)/d], of 2.40 and 4.45 are used. The transient critical heat fluxes for SUS304-circular tubes with the twisted-tapes of y = 2.40 and 4.45 are compared with authors' transient CHF data for the empty SUS304-circular tube and a SUS304-circular tube with the twisted-tape of y = 3.37, and the values calculated by authors' transient CHF correlations for the empty circular tube and the circular tube with twisted-tape insert. The influences of heating rate, twist ratio and swirl velocity on the transient CHF are investigated into details and the widely and precisely predictable correlations of the transient CHF against inlet and outlet subcoolings for the circular tubes with various twisted-tape inserts are given based on the experimental data. The correlations can describe the transient CHFs for SUS304-circular tubes with various twisted-tapes of twist ratios (y = 2.40, 3.37, and 4.45) in the wide experimental ranges of exponential periods (τ = 28.39 ms to 8.43 s) and swirl velocities (usw = 5.04–20.72 m/s) obtained in this work within −26.19% to 14.03% difference. The mechanism of the subcooled flow boiling critical heat flux in a circular tube with twisted-tape insert is discussed.
Flow accelerated corrosion (FAC) thinning rate downstream from an orifice was measured under different velocity conditions in a high-temperature water test loop to understand the effects of flow velocity on FAC thinning rate. The FAC tendency differed downstream and upstream from the orifice. The metal loss increased linearly with time downstream from the orifice, though metal loss rate gradually decreased with time upstream. FAC rate increased as flow velocity increased, particularly from 1D to 3D. The maximum FAC thinning rate increased in proportional to the 0.51th power of the mean cross-sectional velocity in this experiment. The root mean square (RMS) of wall shear stress predicted by large eddy simulation (LES) had a clear relationship with FAC thinning rate. This result indicated that FAC thinning rate can be described as a function of the wall shear stress. Additionally, the mass transfer coefficient estimated from the RMS of wall shear stress had an almost linear correlation with FAC thinning rate.
The Oscillation Power Range Monitors (OPRM) have been installed in some boiling water reactors (BWRs) to detect core regional oscillation by coupled neutronic/thermal-hydraulic instabilities under certain operating conditions, and to trigger a reactor trip signal before the oscillatory amplitude exceeds the safety limit for the fuel cladding integrity.A typical OPRM algorithm monitors the oscillatory periods for each OPRM cell responses that are constructed by Local Power Range Monitor (LPRM) signals at each OPRM cell corner, and determines the inception of instability events by the number of successive oscillatory periods within a certain tolerance and oscillation amplitude. This method might pile up the counts by picking up noise peaks and minima during stable operation conditions. A small tolerance, however, could delay instability detection, as OPRM signal noise is likely to displace the oscillatory peak intervals beyond the tolerance and cause the count to reset. Therefore setpoints should be determined carefully for reliable detection performance.We studied a new algorithm for the OPRM system to address the above-stated technical challenges. Focusing on the oscillatory period coherency, the new method evaluates the standard deviation for the oscillatory periods instead of monitoring them directly. A trip signal is triggered when the standard deviation remains lower than a setpoint for a certain elapsed time. This method aims at excluding the impact of the perturbation caused by the OPRM noise to the detection performance, utilizing statistics that represents the oscillatory characteristics for the instability criterion.To examine the applicability of the new algorithm, we simulated the OPRM signals by Advanced Boiling Water Reactor (ABWR) instability analysis data with the estimated signal noise superimposed, as there are no test data for the ABWR instability events. The new algorithm showed that the trip signal could be generated for the simulated regionally instable condition before the fuel cladding safety limit was reached.Copyright © 2012 by ASME
We conducted an experiment to quantify the increase in efficiency of energy extraction from a constant flow that can be obtained by attaching a pair of tripping wires to an elastically mounted cylinder under influence of vortex-induced vibrations. Free oscillation tests were carried with three different cylinder configurations: smooth, with tripping wires positioned at angular positions equal to 60° and 75°. The Reynolds number varied from 2.9×103 to 2.2×104. We measured the amplitude of oscillation and the output voltage to calculate the power generated and conversion efficiency. The maximum power generation occurred when tripping wires were positioned at 60° and reduced velocity was 12, but only a 2.88% efficiency was achieved at this case. The maximum efficiency obtained was 12.47% and occurred when tripping wires were positioned at 75°, with reduced velocity 6.5. The maximum efficiency with tripping wires attached was about four times larger than the maximum efficiency obtained on smooth cylinder case. The presence of tripping wires also widen the lock-in region and when they were placed at 75° an almost constant power generation was obtained within reduced velocity ranging from 6 to 8.5, meaning that it is possible to design a system that generates the same amount of power even with variations on flow speed.
Since the beginning of this century, the so-called 3Ss (Nuclear Safety, Nuclear Security and Safeguards) have become major regulatory areas for peaceful uses of nuclear energy. In order to rationalize the allocation of regulatory resources, interrelationship of the 3Ss should be investigated. From the viewpoint of the number of the parties concerned in regulation, nuclear security is peculiar with having “aggressors” as the third party. From the viewpoint of final goal of regulation, nuclear security in general and safeguards share the goal of preventing non-peaceful uses of nuclear energy, though the goal of anti-sabotage within nuclear security is rather similar to nuclear safety. As often recognized, safeguards are representative of various policy tools for nuclear non-proliferation. Strictly speaking, it is not safeguards as a policy tool but nuclear non-proliferation as a policy purpose that should be parallel to other policy purposes (nuclear safety and nuclear security). That suggests “SSN” which stands for Safety, Security and Non-proliferation is a better abbreviation rather than 3Ss. Safeguards as a policy tool should be enumerated along with nuclear safety regulation, nuclear security measures and trade controls on nuclear-related items. Trade controls have been playing an important role for nuclear non-proliferation. These policy tools can be called “SSST” in which Trade controls are also emphasized along with Safety regulation, Security measures and Safeguards.
Open solicitation system of research and development ideas in The Japan Atomic Power Company (JAPC) is introduced. This system is established in 1999 to solve various subjects existing in JAPC’s nuclear power stations by using highly advanced technique possessed by the enterprises or the organizations limited in Fukui Prefecture, and also to contribute them to become more advanced in their skill of technology. We have improved this system to make the results more applicable. We think it is important to coexist with the local community for the company engaged in nuclear energy as to cooperate together for the improvement of the local society.
Fault Tree and Event Tree analysis is almost exclusively relied upon in the assessments of seismic Core Damage Frequency (CDF). In this approach, Direct Quantification of Fault tree using Monte Carlo simulation (DQFM) method, or simply called Monte Carlo (MC) method, and Binary Decision Diagram (BDD) method were introduced as alternatives for a traditional approximation method, namely Minimal Cut Set (MCS) method. However, there is still no agreement as to which method should be used in a risk assessment of seismic CDF, especially for uncertainty analysis. The purpose of this study is to examine the efficiencies of the three methods in uncertainty analysis as well as in point estimation so that the decision of selecting a proper method can be made effectively. The results show that the most efficient method would be BDD method in terms of accuracy and computational time. However, it will be discussed that BDD method is not always applicable to PSA models while MC method is so in theory. In turn, MC method was confirmed to agree with the exact solution obtained by BDD method, but it took a large amount of time, in particular for uncertainty analysis. On the other hand, it was shown that the approximation error of MCS method may not be as bad in uncertainty analysis as it is in point estimation. Based on these results and previous works, this paper will propose a scheme to select an appropriate analytical method for a seismic PSA study. Throughout this study, SECOM2-DQFM code was expanded to be able to utilize BDD method and to conduct uncertainty analysis with both MC and BDD method.
We apply a data assimilation technique, inspired from meteorological applications, to perform an optimal reconstruction of the neutronic activity field in a nuclear core. Both measurements and information coming from a numerical model are used. We first study the robustness of the method when the amount of measured information decreases. We then study the influence of the nature of the instruments and their spatial repartition on the efficiency of the field reconstruction.
This paper describes simple flow rate monitoring using the Ultrasonic Velocity Profile method (UVP), for disturbed flow just after double elbows and large pipes with high Reynolds numbers. This method utilizes the linearity between the flow rate and the velocity at the pipe center under the following flow conditions. The Reynolds number is from 4.1×106 to 5.1×106, the dihedral angle of double elbows is 30° and the distance between double elbows is six diameters. The measuring position is set at two diameters distance downstream of the second elbow. The Computational Fluid Dynamics (CFD) simulations and experimental results indicate that it can monitor flow rate changes with an accuracy of less than 1% under these flow conditions.
The paper considers a Rod Ejection Accident (REA) which has been calculated by the coupled-code system ATHLET-QUABOX/CUBBOX. For the present study, a MOX/UOX mixed core loading was developed on the basis of a generic PWR. The results are particularly focused on the fuel enthalpy rise which is the main safety criterion for such transient. A parametric REA study has been performed, showing the influence of some important thermal-hydraulic and neutron-physical parameters. Simulations have been performed using realistic or artificially decreased delayed neutron fractions for two different core states (HZP and 30% of the nominal power). Effective fuel rod temperature influence (i.e. Doppler coefficient) has been studied by using different correlations (0.5/0.5 weighting factors or the typical TDoppler = 0.7 TSurface + 0.3 TCenter) or by changing the fuel gap conductance. It is shown that the maximum enthalpy (and enthalpy increase) does not always appear in the affected fuel assembly but can also appear in the neighboring ones. This result is a direct consequence of the burn up dependence of the enthalpy. The paper also considers the case of local delayed neutron parameters and briefly describes the future REA studies foreseen at GRS such as an investigation of quantitative uncertainty propagation from the nuclear data to the transient behavior.
The feasibility study of a liquid lithium type proton beam target was performed for the neutron source of the boron neutron capture therapy (BNCT). As the candidates of the liquid lithium target, a thin sheet jet and a thin film flow on a concave wall were chosen, and a lithium flow experiment was conducted to investigate the hydrodynamic stability of the targets. The surfaces of the jets and film flows with a thickness of 0.5 mm and a width of 50 mm were observed by means of photography. It has been found that a stable sheet jet and a stable film flow on a concave wall can be formed up to certain velocities by using a straight nozzle and a curved nozzle with the concave wall, respectively.
Flow accelerated corrosion (FAC) rate downstream from an orifice was measured in a high-temperature water test loop to evaluate the effects of flow field on FAC. Orifice flow was also measured using laser Doppler velocimetry (LDV) and simulated by steady RANS simulation and large eddy simulation (LES). The LDV measurements indicated the flow structure did not depend on the flow velocity in the range of Re = 2.3×104 to 1.2×105. Flow fields predicted by RANS and LES agreed well with LDV data. Measured FAC rate was higher downstream than upstream from the orifice and the maximum appeared at 2D (D: pipe diameter) downstream. The shape of the profile of the root mean square (RMS) wall shear stress predicted by LES had relatively good agreement with the shape of the profile of FAC rate. This result indicates that the effects of flow field on FAC can be evaluated using the calculated wall shear stress.
