Local Power Density Research Articles

Using the offset-power diagram to monitor the local linear power density of fuel elements in a VVER-1000 core

A method for real-time monitoring of jumps in the local linear power density of fuel elements in a VVER-1000 core is described. Monitoring jumps in the local power is one component of the improved algorithms for reactor control which ease the operating conditions for the fuel assemblies.

Suprathermal hard X-rays and energetic particles from plasmas "dust"

This work concerns some novel aspects of the simple production of high power density matter in vacuum discharges [1,2] and related energy transport. We study the ensembles of cold grains - hot microplasmas created by an intense energy deposition into the cold solid density, low volume dust target collected in the interelectrode space (clusters, grains, microparticles of different size from anode material). Some effects of the high local power density were realised to allow production of the different ensembles of cold grains with fraction of hot microplasmas (T ∼ 1 KeV and n e ∼10 20 -10 22 cm -3 ). The hard x-ray yield registered and well reproduced in the vacuum discharges (just at ∼ 1 J of energy stored) is about 0.1 - 0.3%. Time of flight measurements show that hard x-ray production may be accompanied by energetic ions (∼ 0.1 -1 MeV) like those for irradiated clusters [3]. Thermal and suprathermal levels of x-ray emission, laser-like behaviour of potentially amplifying media of plasmas dust as well as x-ray trapping are discussed. The last phenomenon suggests a partial random walk of photons inside of x-ray ball due to the regulated level of multiple scattering and reflecting in disordered media of cold and hot grains of any sizes (x-ray random laser [4,5]). Single pass ASE [6] regime of x-ray lasing as particular case of x-ray yield is considered also.

A comparative study of emittance measurements using different techniques

The pepper-pot method and two slit-and-collector type techniques are tested for their applicability to measure the emittance of low energy ion beams. The exposure of Kapton foil, used here as the detector in the pepper-pot method, has been found to show a nonlinear behavior of the image contrast with the local power density of He+ beam for energy less than 10 keV. Therefore, the emittance measurement with the pepper-pot method must be made with the calibration of the contrast of the Kapton film in advance. The measured values of emittance, obtained by the different diagnostic schemes, are similar. From the view point of the negative ion beam measurement, the pepper-pot type system using Kapton film and the multislit-and-Faraday-cup system are proved to be promising.

A methodology for benefit assessment of using in-core neutron detector signals in core protection calculator system (CPCS) for Korea standard nuclear power plants (KSNPP)

Core Protection Calculator System (CPCS) is a digital computer based safety system generating trip signals based on the calculation of departure from nucleate boiling ratio (DNBR) and local power density (LPD). Currently, CPCS uses ex-core detector signals for core power calculation and it has some uncertainties. In this work, a quantitative economic benefit assessment of using in-core neutron detector signals is carried out. In-core detector signals which directly measure the inside neutron flux of core are applied to CPCS to obtain more accurate power distribution profile, DNBR and LPD to reduce the calculation uncertainties. In order to improve axial power distribution calculation, piecewise cubic spline method is applied. Simulation is also carried out to verify its applicability to power distribution calculation in this work. Simulation result shows that the improved method reduces the calculational uncertainties significantly and it allows larger operational margin. It is also assured that no power reduction is required while Core Operating Limit Supervisory System (COLSS) is out-of-service when the improved method is applied.

Modelling of core protection and monitoring system for PWR nuclear power plant simulator

A nuclear power plant simulator was developed for Younggwang units 3 and 4 nuclear power plant (YGN Nos 3 and 4) in Korea; it has been in operation on training center since November 1996. The core protection calculator (CPC) and the core operating limit supervisory system (COLSS) for the simulator were also developed. The CPC is a digital computer-based core protection system, which performs on-line calculation of departure from nucleate boiling ratio (DNBR) and local power density (LPD). It initiates reactor trip when the core conditions exceed designated DNBR or LPD limitations. The COLSS is designed to assist operators by implementing the limiting conditions for operations in the technical specifications. With these systems, it is possible to increase capacity factor and safety of nuclear power plants, because the COLSS data can show accurate operation margin to plant operators and the CPC can protect reactor core. In this study, the function of CPC/COLSS is analyzed in detail, and then simulation model for CPC/COLSS is presented based on the function. Compared with the YGN Nos 3 and 4 plant operation data and CEDIPS/COLSS FORTRAN code test results, the predictions with the model show reasonable results.

`Triggerless' triggering of vacuum arcs

Vacuum arcs can be initiated without external means of power enhancement at the cathode surface (by using a high-voltage trigger, laser triggering, and so on). Arc initiation by simply applying the relatively low voltage of the arc power supply is possible if the cathode-anode-separating insulator is coated with a conducting layer and the current at the layer-cathode interface is concentrated at one or a few contact points. The local power density at these contact points can exceed which is sufficient for plasma production and thus arc initiation. This `triggerless' principle has been tested successfully with a large number of cathode materials. One extended test was performed with titanium and more than pulsed vacuum arc initiations have been obtained.

Taiwan Power Company’s Power Distribution Analysis and Fuel Thermal Margin Verification Methods for Pressurized Water Reactors

Taiwan Power Company`s (TPC`s) power distribution analysis and fuel thermal margin verification methods for pressurized water reactors (PWRs) are examined. The TPC and the Institute of Nuclear Energy Research started a joint 5-yr project in 1989 to establish independent capabilities to perform reload design and transient analysis utilizing state-of-the-art computer programs. As part of the effort, these methods were developed to allow TPC to independently perform verifications of the local power density and departure from nucleate boiling design bases, which are required by the reload safety evaluation for the Maanshan PWR plant. The computer codes utilized were extensively validated for the intended applications. Sample calculations were performed for up to six reload cycles of the Maanshan plant, and the results were found to be quite consistent with the vendor`s calculational results.

MR gradient coil heat dissipation

The temperature responses of five different gradient coil designs were modeled using simplified engineering equations and measured. The model predicts that the coil temperature approaches a maximum as an inverse exponential, where the maximum temperature is governed by two parameters: a local power density and a cooling term. The power density term is a function of position and is highest where the current paths have minimum widths and are closely packed. The cooling parameter consists of convective, conductive, and radiative components which can be controlled by (1) providing forced cooling, (2) having a coil former with high thermal conductivity and thin walls, and (3) varying the emissivity of the coil surfaces. For a given gradient strength, the average temperature rise is minimized by designing a coil with a small radius and thick copper. The model predicted the local temperature rise, which is also dependent on the current density, to within 5 degrees C of measured values.

Efficient calculations of gas radiation from turbulent flames

A calculationally efficient method of calculating time-averaged thermal radiation from flames is presented. The algorithm is derived by ensemble averaging the solution to the equation of radiative transfer. It is shown that, to a good approximation, the local power density can be decorrelated from factors that are functions of path averages. The ensemble averages of path-dependent functions can be calculated using time-averaged properties; the ensemble averages of the local power densities can be carried out by fast numerical quadratures using the local fluctuation probability density function. The result is a predictive technique that requires only one path integration per molecular band. The time-consuming approach of setting up statistical realizations of optical paths, calculating intensity for each realization, and building up the intensity fluctuation statistics is avoided. Sample calculations are given for a turbulent CH 4H 2 diffusion flame.

A First-Guess Feature-Based Algorithm for Estimating Wind Speed in Clear-Air Doppler Radar Spectra

Abstract Algorithms for deriving winds from profiler range-gated spectra currently rely on consensus averaging to remove outliers from the subhourly velocity estimates. For persistent ground clutter in the echo return that is stronger than the atmospheric component, consensus averaging of the spectral peak power densities fails because the peak power density is derived from the ground clutter and not the atmosphere. To negate the deleterious effects of persistent ground clutter, as well as to attempt to improve performance during periods of poor signal-to-noise ratio, an algorithm was developed that uses the local maxima in power density in each spectrum to build multiple profiles of possible radial velocity estimates from the first to last range tale. To build profiles of radial velocity estimates from a set of spectra, the spectra are smoothed, the local power density maxima are identified, chains are formed across range gates by connecting those local power density maxima that satisfy a continuity cons...

Melting and thermocapillary convection under the action of pulsed laser radiation with an inhomogeneous spatial distribution

A theoretical study is reported of melting and thermocapillary convection under the action of laser radiation with a nonmonotonic spatial distribution of the power density. An analysis is made of changes in the geometry of the molten bath with time. The transition from a nonmonotonic boundary of a melt, corresponding to the spatial distribution of the radiation, to a monotonic one occurs in a time of the order of 1 ms when the power density of laser radiation is 105 W/cm2. The vortex structure of the flow in the molten bath is governed by the spatial distribution of the laser radiation in such a way that each local power density maximum corresponds to two vortices with oppositely directed velocity components.

Hadamard transform photothermal deflection desitometry of electrophretically blotted proteins

Hadamard transform spatial multiplexing techniques are applied to laser densitometry in order to prevent the photo-induced degradation of sensitive materials. Photochemical and thermal degradations can often occur in point focused scanning laser densitometry. In spatial multiplexing, the excitation source is defocused and efficiently distributed throughout the sample, reducing local power density. In this paper, we describe the application of Hadamard transform spatial multiplexing to transverse photothermal deflection spectroscopy (PDS). Proteins western blotted on nitrocellulose membrane are line imaged using the Hadamard transform PDS densitometer. For comparison, the blots are imaged with a high-dynamic-range video densitometer.

Local photocurrent and high power density investigations of oxide films on valve metals with a focused laser beam

With the focused laser beam, local photocurrent investigations could be realized. Microscopic structures such as grains and defects can be distinguished. Local photocurrent potential curves for various grains show different shapes due to their different properties. Focusing of the laser beam to dimensions less than 20 μm leads to high power densities. The reactions of the involved minority carriers are then determined by slow transfer processes at the oxide—electrolyte interface. Hence, an accumulation of holes occurs at the surface for power densities > 5 W cm −2. Under potentiostatic conditions the hole concentration at the surface induces an additional local potential drop of some 100 mV in the Helmholtz-layer, which is the main reason for the observed laser induced oxide growth. Further increasing power density enhances the hole accumulation and an increasing lateral potential drop of radial symmetry. Therefore, photo-holes travel parallel to the surface causing lateral extension of the oxide growth even at the dark surface. The Butler—Gaertner model is no more valid for such conditions for various reasons.

Large area bolometers for millimeter-wave power calibration

An accurate monolithic power meter has been developed for millimeter-wave applications. The detector is a large-area Bismuth bolometer, integrated on a fused-Quartz substrate. It simply measures the temperature change caused by the absorption of millimeter-wave radiation. The power meter is simple to fabricate, inexpensive, and can be easily calibrated using a low-frequency network. The measured responsivity for a 50Ω bolometer, with an area of 1×1cm, at a bias of 1V. and a video modulation of 100Hz, is 1mV/W. The noise spectrum exhibits a 1/f rolloff till 1KHz, and is limited by the Johnson noise for higher frequencies. The NEP of the detector is 3μWHz−1/2 at a video modulation of 1KHz. It is possible to decrease the current NEP by fabricating bolometers with higher responsivities. Possible application areas are absolute power calibration and localized power density measurements at millimeter and submillimeter wavelengths.

Design and experimental investigation of the ability of large superconducting magnets to operate under nuclear heating

Abstract Development testing in the Large Coil Task (LCT) has included investigation of superconducting coils' tolerance for various forms of healing, such as may be encountered in the magnets of a fusion reactor. The nuclear heating in coils is strongly influenced by the reactor design. The LCT coils are the first large superconducting magnets to provide experimental perspectives on nuclear heating. The Japanese LCT coil is one of three pool-boiling cooled coils in a six-coil toroidal array at Oak Ridge National Laboratory. The coil size is about one half that of fusion reactor coils. Simulated nuclear heating tests were performed on the Japanese coil. The coil was designed to be fully cryostable at the magnetic field of 8 T, and experimental results indicated that a local nuclear heating power density of 55 mW/cm3 has negligible influence on the stability of the coil. It corresponds to an equivalent nuclear heating power density of 5 mW/cm3 in the innermost turn of the winding. Excessive heating power resulted in a coil quench due to vapor accumulation. While the boundary of the tolerance was not surveyed, the value of 5 mW/cm3 is considered to be the limit for nuclear heating in a pool-boiling cooled coil. As for a forced-flow cooled coil, its tolerance seems to be smaller.

Effect of laser focus on ion production in the laser ion source for elemental analysis

Optimization of the laser ion source is best done via ion beam diagnostics rather than by visual focusing to the specimen surface or to a minimum diameter brightest plasma. Doubly charged ions signals are especially useful for the optimization of both the laser focus and the local laser power density level.

Some unique applications of solid state track recorder autoradiography in the nuclear industry

CR-39 solid state track recorder alpha autoradiography has been applied to the inspection of sectioned weld samples of parts containing plutonium. In addition to determining the amounts of plutonium present, information on the distribution and physical form of the plutonium has been obtained. In a separate application, autoradiographic methods developed previously for analysis of airborne actinide aerosols are extended to the analysis of fuel debris at TMI-2. Autoradiographic determination of the alpha decay rate and thermal neutron induced fission rate allows the 239Pu/ 235U ratio to be calculated on a particle-by-particle basis. This ratio is in turn dependent on local power density in the reactor core. Correlations of the 239Pu/ 235U ratio with particle size should provide useful data on mechanisms for core degradation and transport through the primary coolant system of the reactor.

How far does thermal damage extend beneath the surface of CO2 laser incisions?

One of the principal advantages of the CO2 surgical laser over other types available is that there is little evidence of thermal injury extending very far beyond the surface of the laser wound. The degree of such damage is of interest because it affects tissue healing and the likelihood of post-operative infection. This paper presents a simple physical model of tissue irradiated by a CO2 laser beam. The depth of damage is predicted for the case where the ablation front and the damage wave ahead of it advance together at the same speed. The depth of damage is also calculated for the case of laser pulses of short duration where there has not been time to establish dynamic equilibrium. The results are plotted against local laser power density and show a trend of narrower damage depths with short laser pulses and high power densities. As a consequence, care should be taken not to ablate tissue at low power densities, as occurs when the laser beam is defocused. The predicted damage depths are in broad agreement with histopathological experience.

Evaluation of Statistical Reliability Measures for a Program for the Limitation of Power Density in a Reactor Vessel

Errors within an assembler program for limiting the local power density in a reactor vessel are to be identified and corrected during two test phases. According to the special features for error detection of the testing facilities, the errors are classified, and an appropriate software reliability model is applied to each error class. These models allow prediction of certain reliability parameters from the observation of the test. Depending on the model employed these parameters can be e.g. the number of remaining errors, the probability for the occurance of an error within a given time interval, the meantime between successive errors. In this contribution references are only made to the number of remaining errors.

A Posteriori Evaluation of the Coarse-Mesh Calculation Results in Boiling Water Reactor Dynamics

A coupled and transient calculation method for a posteriori evaluation of coarse-mesh boiling water reactor core calculation results was developed.An analysis of the local power density shape in the environment of the topmost end of the control element was made.The influence on the sections of the fuel pins being exposed by a small control-element withdrawal has been investigated. The transient calculation results of response in the power density to a 16-cm-long, 4 cm/s speed control-element ramp are discussed.