Aladár Czitrovszky

The Red Mud Accident in Ajka (Hungary): Characterization and Potential Health Effects of Fugitive Dust

As a result of a tragic industrial accident, a highly alkaline red mud sludge inundated settlements and agricultural areas near Ajka, Hungary on October 4, 2010. One of the major concerns about the aftermaths of the accident is the potential health effects of vast amounts of fugitive dust from red mud sediment. Thus, we studied the chemical and physical properties of particles of red mud and its respirable fugitive dust, and performed toxicity measurements. Under unfavorable meteorological conditions dry red mud sediment could emit very high amounts of respirable alkaline particles into the air. The number size distribution of fugitive dust peaks above 1 μm aerodynamic diameter; therefore, its inhalation is unlikely to affect the deep regions of the lungs. No significant mineralogical or elemental fractionation was observed between the sediment and dust, with the major minerals being hematite, cancrinite, calcite, and hydrogarnet. Although the high resuspension potential and alkalinity might pose some problems such as the irritation of the upper respiratory tract and eyes, based on its size distribution and composition red mud dust appears to be less hazardous to human health than urban particulate matter.

A new method for the simultaneous measurement of aerosol particle size, complex refractive index and particle density

Particle size measurement by means of optical spectrometry of single particles depends substantially on the angular range of light scattering and the refractive index of the particle. Knowledge of the latter determines implicitly the accuracy of measurement. In contrast to commonly used instrumental systems the configuration of the design concept presented here consists of two laser illumination sources with different wavelengths and four angular ranges for the collection of scattered light. As a result a set of four independent pulses from each measured particle can be obtained allowing simultaneous assessment of particle size and its complex refractive index. Based on the Mie theory of light scattering, light collection angles yielding a single-valued aerosol size measurement were identified and used to design a new optical system. Based on the modelling of the performance for an assumed instrumental arrangement the sizing errors were found to be about 2%. The accuracy of assessment of the complex index of refraction was found to be of the order of 10% over the range of particle diameters investigated (0.1-10 µm). The theoretical results show clearly the capability of this novel instrumental design for the measurement of aerosol particle sizes, their density and optical properties. Based on these model calculations an experimental set-up is under construction.

New design for a light-scattering airborne particle counter and its applications

A light-scattering airborne particle counter with a new optical design having the optical sampling chamber outside the laser resonator is presented. This device can be used to measure the size distribution of particles from a diameter of 0.3 μm in a wide concentration range with high reliability and stability. Some results of the applications of the device in highly contaminated environments are reviewed.

Interaction of Failed Fuel Rods Under Air Ingress Conditions

Abstract In the late phase of a severe reactor accident, the molten corium interacts with the vessel wall, and it can lead to the failure of the lower head. Through the failed bottom wall, part of the corium can flow into the cavity, and air can enter the primary circuit. The residual fuel in the core periphery will be further oxidized in air atmosphere. The degradation process will accelerate, and new chemical species will be formed, which can have an impact on the release of radioactive materials. Two experiments were carried out with electrically heated nine-rod pressurized water reactor-type bundles in the CODEX (COre Degradation EXperiment) facility to provide experimental data on the behavior of real fuel bundles under air oxidation conditions. The main objective of the tests was the investigation of oxidation phenomena, and some other important aspects (e.g., enhanced fission product release) were not addressed. The CODEX air ingress tests indicated the acceleration of oxidation phenomena and core degradation processes during the late phase of the vessel melt through accident, when air can have access to the residual fuel bundles in the reactor core. The degradation process was accompanied with zirconium-nitride formation and release of uranium-rich aerosols.

Behavior of VVER Fuel Rods Tested Under Severe Accident Conditions in the CODEX Facility

The early phase of severe accidents in VVER reactors was simulated in the CODEX (COre Degradation EXperiment) facility with electrically heated fuel rod bundles. The selected test conditions and applied measurement techniques made possible the observation of some specific phenomena, such as the protective role of oxide scale during quenching of high-temperature bundles, the composition of gases produced during the oxidation of boron-carbide control rods, and the interlink between the aerosol release and the oxidation process. The general behavior of the VVER bundles did not differ significantly from that of the Western-design light water reactor bundles tested under similar high-temperature conditions, but the experiments emphasized that the application of VVER-specific material properties and models is essential for comprehensive numerical simulations.

Quantum metal optics

Experimental and theoretical studies of the statistical properties of surface plasmon polaritons (SPOs) are described. Both classical and non-classical properties of surface plasmons are analysed. The temporal statistical behaviour at low excitation level, as measured by detecting the SPO emitted photon statistics as expressed by the correlation function and the temporal photon count distribution, show that the SPOs preserve the photon statistics of the laser. In the spatial distribution of the plasmon field as measured by an STM, squeezing, i.e. non-classical properties, were found. Independent simple model calculations confirmed the existence of both enhanced EM fields of surface plasmons and their squeezed character.

Half-magnitude extensions of resolution and field of view in digital holography by scanning and magnification

Digital holography replaces the permanent recording material of analog holography with an electronic light sensitive matrix detector, but besides the many unique advantages, this brings serious limitations with it as well. The limited resolution of matrix detectors restricts the field of view, and their limited size restricts the resolution in the reconstructed holographic image. Scanning the larger aerial hologram (the interference light field of the object and reference waves in the hologram plane) with the small matrix detector or using magnification for the coarse matrix detector at the readout of the fine-structured aerial hologram, these are straightforward solutions but have been exploited only partially until now. We have systematically applied both of these approaches and have driven them to their present extremes, over half a magnitude in extensions.

Measurement of quantum efficiency using correlated photon pairs and a single-detector technique

A new approach is proposed to the calibration of photodetectors and the determination of the absolute value of the quantum efficiency of photon-counting photomultipliers using entangled-photon pairs. It is based on a new single-photodetector technique and a special modulation of the entangled-photon flux. The absolute values of the quantum efficiency have been determined for several photon-counting photomultipliers.

Nanoparticle size distribution measurement in photon correlation experiments

We propose the measurement of particle size, which is based on the visibility measurement of the pre-detection signal corresponding to particle transit of the sensing volume in a photon correlation LDA arrangement. It is shown that a good estimate of the visibility is the ratio of the contents of two specific channels of the Fourier transform of the autocorrelation function. We show that in a wide range of experimental conditions this ratio is a monotonous function of particle size. This circumstance leads to the possibility of defining calibration curves for practical devices.

Designing a special light source with predetermined number of photons

We designed a special light source generating a pre-determined number of photons taking advantage of our previous experimental results and calculations that establish a new approach to the calibration of photodetectors and determination of the absolute value of quantum efficiency of photon-counting photomultipliers using a single detector and entangled-photon pairs. This source is capable of generating a known number of photons of specified wavelength, in specified direction, and polarization for high-accuracy optical measurements (optical metrology) at the ultra-low intensities. The design and the modeling have been performed taking into account the main time characteristics of electronics, efficiency of detectors, parameters of the signal, losses, etc. The data evaluation system has been designed and tested; the assembly of the experimental set-up has been performed. Main parts of the optical and electronic system (generation of photon pairs, detectors, Pockels cells, etc.) have been tested. Such light source can be successfully applied in different areas of optical metrology, especially in photometry.