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This is a study of the feasibility of and equipment layout for reliable, accurate, and high-speed detection of releases of dangerous substances from nuclear fuel cycle objects by various local and remote laser diagnostic techniques.One of the most dangerous components of accidental releases from objects in the nuclear fuel cycle is volatile uranium hexafluoride, the most chemically active of the known fluorine-containing compounds of uranium. Uranium hexafluoride releases are accompanied by a rapid increase in the atmospheric concentration of hydrogen fluoride and the formation of uranyl fluoride, UO 2 F 2 . In addition, the surfaces of equipment get contaminated by uranium or other characteristic materials, as does waste water. In practice, IAEA inspectors analyze releases, waste water, and water used for washing equipment to discover hidden efforts to enrich uranium or other nuclear technologies.Recently, special attention has been devoted to studies of atmospheric chemistry in a search for the vapor of heavy water, which is a basic constituent of liquid and gaseous releases from most nuclear power stations and chemical plants for the enrichment and reprocessing of nuclear fuel. The presence of superheavy water vapor in the atmosphere may be evidence of plutonium production. Thus, monitoring the atmosphere for heavy and superheavy water vapor is of great interest as it can be used both to establish the degree of contamination of the environment and to detect unsanctioned nuclear weapons production activity.These things have all stimulated a search for new techniques and the development of data and measurement systems for high-speed monitoring of the state of the air basins of large industrial centers, the waters in and surrounding lakes, rivers, seas, and oceans, large stands of plant growth, etc. In creating such systems, laser diagnostic techniques have come to be of ever greater interest, since they can operate at a distance (up to several km), with high sensitivity (ppb) and obtain information about the environment under study in real-time (fractions of a second) [1].In this paper, we describe some techniques and the associated apparatus for reliable, accurate, and high-speed detection of trace releases of dangerous substances at nuclear fuel cycle objects, in both local and remote probe variants employing laser diagnostic techniques.Uranium Hexafluoride. During an accidental release, it interacts actively with the atmospheric humidity to form UO 2 F 2 , which decomposes into uranyl fluoride UOF 4 . The hydrolysis of uranium hexafluoride is usually described by the equations

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A diode laser is used to measure the absorption spectra of 238 UF 6 and 235 UF 6 molecules in the composite vibrational band ν 1 + ν 3 at wavelength λ = 7.68 µm. To determine the possibility of measuring the isotopic ratio 235 UF 6 / 238 UF 6 with the required accuracy, the absorption coefficients of isotopic samples of 235 UF 6 and 238 UF 6 are measured, and the sources of errors and ways to minimize them are determined.The isotopic composition of uranium hexafluoride, found in the chemical form UF 6 , is measured in separation plants to a high degree of accuracy using gamma spectrometers and specialized mass spectrometers [1]. But at the same time a sufficiently reliable, accurate, and rapid method for evaluating the degree of enrichment of UF 6 when checking research laboratories and facilities which are under IAEA control is not available.At the present time, diode laser spectroscopy is one of the most promising rapid methods of isotopic analysis for obtaining reliable information about the degree of enrichment of UF 6 [2]. An important feature is its high sensitivity and resolving power, and the possibility of tuning the wavelength of the laser radiation smoothly makes it possible to measure the isotopic composition of atoms and molecules containing stable and radioactive nuclei [3,4].The fundamental possibility of using laser spectroscopy for fast analysis of the degree of enrichment of UF 6 was shown in [5,6], where the IR spectra obtained for uranium hexafluoride by Fourier transformation were analyzed and the choice of the lasing frequency in the mid-IR range at the wavelength λ = 7.68 µm was substantiated. The IR absorption spectra of UF 6 with the natural isotopic composition were studied using such a laser in the range of the composite vibrational band ν 1 + ν 3 . The absorption coefficient in this band is 500 times lower than the absorption coefficient in the ground vibrational band ν 3 but it is sufficient for measuring the IR absorption spectra in 10-20 cm long cells. On the basis of these spectra and the known isotopic shaft of the ν 3 vibration of UF 6 molecules, model spectra were calculated for the two isotopic modifications 238 UF 6 and 235 UF 6 . However, the accuracy with which the degree of enrichment of UF 6 is determined on the basis of the model spectra was found to be too low for measuring the isotopic composition of uranium under real conditions [6]. To increase the accuracy with which the isotopic ratio 235 UF 6 / 238 UF 6 , it is necessary to know the real spectroscopic characteristics of UF 6 molecules with different isotopic composition.In the present work, the IR absorption spectra of 235 UF 6 , 238 UF 6 , and mixtures of these compounds are studied experimentally in the region of the composite vibration ν 1 + ν 3 using a λ = 7.68 µm diode laser. Special attention is focused on the measurement of the absorption cross sections of the two isotopic modifications of uranium hexafluoride 238 UF 6 and