A Theoretical Study of MHD Power Generation, (II)

The electric potential drop near the electrode surfaces in MHD power generators is studied theoretically by considering a simple model, in which the current flows in the direction normal to the electrode surfaces. In order to simplify the situation so as to permit analytic solution, the idea of a “boundary layer” near the electrodes is introduced, and the problem is treated entirely macroscopically, wherein the following assumptions are made:

1. The electrical conductivity is constant.

2. The Hall effect and the induced magnetic field can be neglected.

3. The behavior of the flow in the boundary layer may be described by equations for laminar flow.

4. The temperature variation in the boundary layer perpendicular to the electrode surfaces may be neglected.

The theory predicts that the magnitude of the electric potential drop near the electrode is of the order of 10 V in typical MHD power generators.     

用于磁流体发电的超高温反应堆堆芯设计

本文对磁流体反应堆的堆芯方案进行了探索,对石墨基体燃料和金属陶瓷燃料进行了比较,选择了金属陶瓷燃料进行磁流体反应堆的设计,给出了堆芯方案及堆芯物理、热工计算结果,并对发射掉落事故进行了计算和分析。计算结果可满足设计要求。     

Self-Limiting Power Excursion Characteristics of Light Water Reactor, (I)

The Doppler limited power excursion characteristics of a light water reactor and the shutdown mechanism by scram were analyzed on the Hitachi Training Reactor (HTR). For the purpose of the pulse operation tests, modifications were applied to the HTR to provide pulsing capability; a pulse rod was added, together with a back up device for shutdown, and provision of three instrumented fuel assemblies, equipped with thermocouples; the Al-clad fuel rods were replaced by stainless steel clad rods.

About 100 runs of pulse operation tests were performed in fullest security with reactivity insertions ranging up to 1.0 % Δk/k, in which last case the peak power reached 38 MW, with a reactor period of 29 msec.     

A Numerical Study on Faraday-Type Electromagnetic Flowmeter in Liquid Metal System, (I)

To predict the three-dimensional steady-state structure of electromagnetic phenomena in the Faraday-type Electromagnetic Flowmeter (EMF), a numerical simulation method using the Galerkin finite element method has been adopted and formatted as a computer code, FALCON.

As the induction equation for the induced magnetic field that is important in a liquid metal system, we have presented B-φ formulation for the induced magnetic field and the electric potential field and A-φ formulation for the vector potential field and the electric potential field, and compared the computational efficiency of both formulations. We have selected the B-φ formulation. The computer simulation of the EMF of the MONJU secondary cooling system has been performed and the calculations have shown a good agreement with the calibration test data. We have investigated qualitatively how far the influence of the end effect extends and the characteristics of the voltage response.

Overall, this study has indicated that the present method can be applied to the estimation of the characteristics of an EMF and the design of a new EMF.     

Pressure Drop of Liquid Mercury MHD Power Generators

This paper deals with experimental studies of performance characteristics of both constant-area (34×7×295 mm) and diverging-area (23×7 to 43×7×295 mm) MHD power generators with liquid mercury as working fluid, with particular reference to the pressure drop created in the inlet and outlet ducts as well as inside the generator channel, and comparisons are made with various theoretical results. Discussions are presented on the following aspects. In respect of the constant-area channel, pressure drop in laminar and turbulent flow inside the channel, transition Reynolds number for given Hartmann number, pressure drop in the inlet duct and eddy current created near the end of electrode, output electrical power. For diverging channel, applied magnetic field intensity required for zero pressure drop inside the channel, pressure distribution inside the channel, output electrical power in the case of zero pressure drop. The experimental conditions were as follows: Re10<⁵ and Ha<60.     

Theoretical Study of Two-Phase Flow Oscillation in a Hot Channel, (II)

The kinetic behavior of two-phase flow is considered by conventional linear control theory. This study considers only the essential factors so as to simplify the interpretation of the mechanisms involved in the observed phenomena. A change in heat flux due to a change in coolant velocity is taken into account to study the influence of heat transfer characteristics on the flow stability. While this influence has not appeared as clearly as in the previous numerical experiment⁽¹⁾, agreement was obtained with measurements reported from RWD RL.     

Study of Plasma MHD Equilibrium in HL-2A Tokamak

EFIT（Equilibrium Fitting） code is successfully transplanted for HL-2A tokamak parameters. The evolution of the equilibrium configurations for shot 2898 is simulated. It is shown that the discharge starts with a limiter configuration and develops into a divertor configuration gradually after t = 200 ms. The latter lasts until the end of the discharge at t = 900 ms. The evolution of the major plasma shape parameters such as the boundary magnetic fluxes, the positions of the x-point and magnetic axis, and the minor radii obtained are calculated and compared with the experimental results. The agreement between the simulation and experiments are shown to be reasonable. The possibility for discharge quality improvement is discussed.     

Unified Description of Tokamak Ideal MHD Instabilities(Ⅰ)

By using a coordinate system associated with magnetic surfaces, a unified eigen-mode equation for describing the tokamak ideal MHD instabilities is derived in the shear-Alfvenapproximation. Based on this equation having a general operator form, the eigen-mode equationgoverning the large-scale perturbation (such as the kink mode, the low-n ballooning mode and theAlfven mode) and small-scale perturbation (such as the high-n ballooning mode, the local mode)can be further deduced. In the first part of the present study, the small-scale perturbation isdiscussed in detail.     

A Linear Stability Analysis of Supercritical Water Reactors, (I)

This paper summarizes the analysis results of the thermal-hydraulic stability of a high-temperature reactor cooled and moderated by supercritical-pressure light water (SCLWR-H). A linear stability analysis code in the frequency domain was developed to study the thermal-hydraulic stability of SCLWR-H at constant supercritical pressure. The analysis method is based on linearization by perturbation of numerically-discretized one-dimensional single-channel single-phase conservation equations. The effect of water rods on stability is considered. The thermal-hydraulic stability of SCLWR-H for full-power and partial-power normal operations was investigated by frequency domain method. Our analysis reveals that though SCLWR-H has low coolant flow rate and large density change in the core, the thermal-hydraulic stability can be maintained both at normal operation and during power raising phase of constant pressure startup by applying an orifice pressure drop coefficient at the inlet of the fuel assemblies. A parametric study was also carried out to determine the parameters affecting the stability.     

Coupled Reactor Kinetics, (I)

The transfer function of the two slab loading core of Argonaut is measured and analyzed by a coupling model. The measurement shows good agreement with predicted behavior. The coupling constants and subcriticality of the component reactors are obtained and compared with the values obtained from independent statical measurements.     

Preparation of Plutonium Metal, (I)

Ammonium plutonium(IV) fluorides, PuF₄.7/6NH₄F and PuF₄.2NH₄F, were prepared by the addition of an acidic solution containing Pu(IV) to a mixed solution of NH₄F and HF. Anhydrous PuF₃ was obtained by thermal decomposition of the ammonium plutonium(IV) fluorides under reduced pressure or else in an inert gas flow. The anhydrous fluoride was then reduced with Li vapor to Pu metal. Cerium metal was prepared by the same method.     

A Polywell Fusion Reactor Designed for Net Power Generation

A brief history of Polywell progress is recounted. The present PIC simulation explains why the most recent Polywell fusion reactor failed to produce fusion energy. Synchronized variations of multiple parameters would require DC power supplies, not available in historic model testing. Even with DC power, the simulation showed that the trapping of cold electrons would ruin plasma stability during start-up. A theoretical solution to this trapping problem was found in Russian literature describing diocotron-pumping of electrons out of a plasma trap at Kharkov Institute. In Polywell, diocotron-pumping required matching the depth of the potential-well to the electron-beam current falling on a special aperture installed in one of the electromagnets. With diocotron-pumping the reactor was simulated to reach steady-state, maximum-power operation in a few milliseconds of simulated time. These improvements, validated in simulating small-scale DD reactors, were scaled up by a factor of 30 to simulate a large, net-power reactor burning p + ¹¹B fuel. Power-balance was estimated from a textbook formula for fusion power density by numerically integrating the power density. Unity power-balance required the size of the p + ¹¹B reactor to be somewhat larger than ITER.     

Determination of Neutron Multiplication, (I)

In a highly subcritical system with reflector, it is demonstrated that none of the methods so far developed serves usefully in determining the value of the multiplication factor with good accuracy, and that the fundamental difference between the essential properties of the prompt and the delayed neutron modes makes it to be extremely difficult to develop a new method to fulfil this need. Based on this judgement, it is proposed to abandon the widely used concept of multiplication factor, and to look for a new concept to represent the state of neutron multiplication, in the case of reflected highly subcritical systems. In this paper the authors present a new concept in which a fundamental prompt neutron decay constant α₀₀₀ is adopted to measure the neutron multiplication, this constant being of such nature as to satisfy the following two fundamental conditions: (1) It is uniquely measurable free from spatial and energetic dependence, and (2) it is amenable to direct calculation from the fundamental equation for neutron transportation.     

Studies of Actinium (III) in Various Solutions, (I)

A solvent extraction method using a mixture of 0.1M thenoyltrifluoroacetone and 0.1M tributylphosphate in carbon tetrachloride has been developed for the separation and purification of ²²⁸Ac in ²²⁸Ra solutions. The ²²⁸Ra was first purified by a preliminary extraction cycle. The ²²⁸Ac which had accumulated int his ²²⁸Ra fraction after the purification was separated and purified by a second solvent extraction cycle. Since commercially available ²²⁸Ra solution very often contains ²²⁶Ra, the γ-radioactive decay products of the ²²⁶Ra have to be carefully removed. The ²²⁸Ac thus prepared was found to be pure enough for use as tracer.     

Vertically Downward Two-Phase Flow, (I)

Fully developed vertically downward two-phase flow of air-water mixture was investigated on void distribution and average void fraction among the three basic flow regimes; bubbly, slug and annular flows. The annular flow further was divided into two regimes of falling film flow and annular drop flow. Test channel is in form of inverted U-tube and tests were carried out at 100 tube diameters downstream from the curved part. Distributions of local void fraction were measured by means of a conductance needle probe method and the average void fraction was obtained from numerical integration of the measured local void fraction According to the results, profiles of local void fraction in bubby and slug flows showed characteristic natures with a peak in the middle region between the center and the wall of tube The average void fraction in downward flow depended greatly on the flow regimes. Accordingly correlation for each flow regime was developed to predict the average void fraction, based on flow mechanisms and experiments. The correlations were compared with experimental results for atmospheric air-water flow and showed satisfactory agreement.     

REDOX Decontamination Technique Development, (I)

The decontamination technique is required to have a high decontamination rate and decontamination factor, to apply to irregularly formed metallic waste, and minimize secondary waste volume for component replacement and decommissioning. The authors were developed a new decontamination technique using Ce⁴⁺ for decommissioning, which was named “REDOX decontamination technique”. This paper has investigated decontamination conditions and regeneration conditions in a non-radioactive (namely cold) fundamental test. The decontamination conditions, namely dissolution conditions for stainless steel and carbon steel were selected using simulated samples in nitric acid solutions in varying Ce⁴⁺ concentrations, HNO₃ concentration, temperatures, and linear flow rate of decontamination solutions. The regeneration conditions for decontamination reagent were selected in various electrode materials and varying electrode separation distance, anode area/cathode area ratio, current density, Ce³⁺ concentration, and HNO₃ concentration. The REDOX decontamination technique was ascertained to have a high dissolution rate and the decontamination reagent was ascertained to be regenerated effectively by electrolysis.     

Piping Cracks in JPDR, (I)

In JPDR, primary coolant leaked in August 1972 through a crack in the heat affected zone between nozzle safe end of pressure vessel and pipe. And other piping systems were then investigated, and cracks were detected in two systems. Then relations between stress and cracks in the pipes were studied. Stress was analyzed by elastic theory and examined by mockup fatigue test of pipe. Initiation of cracks are not caused by stress alone, indicating the existence of other factor involved.     

Neutron Transport Benchmark Calculations, (I)

Five benchmark problems were selected as standards for the evaluation of calculations on neutron penetration. For three of these problems there were available reliable experimental results obtained in absolute intensities of the neutron angular spectrum in graphite and in water and of the neutron reaction rate in a two-dimensional water shield. The two remaining problems were based on PALLAS transport calculations in graphite and in water in plane geometry. For the first three problems, comparisons were made between the results of PALLAS calculations using ENDF/B-I cross sections and those obtained by experiment. It is concluded that the PALLAS calculations result in fairly good agreement with experiment, except at certain spatial meshes in two-dimensional geometry, due to ray effect. Comparisons are also made of the angular flux spectrum in graphite between calculations using ENDF/B-I and B-III data, as well of the scalar flux spectrum in water between those by PALLAS and by ANISN codes.