The objective of the present scientific-research work was to develop a method and the technical means for efficient nondestructive monitoring of airtightne___~ and gas parameters of both fuel elements and fi~el assemblies of power reactors during the production process as well as the spent fuel under the conditions of a hot chamber, holding pond, or burial site.System for automatic measurement of pressure (SAMP) of hefium in fuel dements. The desked parameter is the gas pressure under the cladding. The crux of the thermophysical method which forms the basis of the pressure measurement is the production of a normalized thermal disturbance of the cladding in a local region of the gas collector of a fuel element, resulting in the appearance of natural convection and the accompanying thermodynamic processes in a closed volume of gas. Heat transfer between the heated cladding with the gas and the surrounding medium depends on the type, the physical properties, and the pressure of the gas. Information about the measured parameter can be obtained by recording the spatial distribution and time dependence of the temperature of the cladding. The information is interpreted using a calibrated characteristic obtained beforehand on standard samples fiUed with the same gas as the part being investigated but having parameters which are known with a high degree of accuracy in the required range. In so doing, however, it is necessary to overcome the effect of factors such as the variance of the geometric dimensions and thermophysieal properties of the cladding material, the instability of the parameters of the surrounding medium, the multicomponent composition of the gas being monitored, the presence of an oxide fdm and deposits (for the spent fuel elements) on the surface of the cladding, as well as the fuel and solid fission products in the fuel element.It is obvious that in the process of measurement the temperature field carries information not only about the parameter being measured but also, to a large extent, about the influencing factors indicated above. The sensor construction, the method of measurement, and the special data processing methods which we developed made it possible to separate information about the gas pressure with acceptable accuracy.The technical problems were solved with the aid of well-known approaches. These include the choice of materials and elements, automation of the measurement process, fabrication of standard samples, insertion of existing means of measurements into the production process, and metrological certification of these means.At the present time two modifications of a system for measuring the gas pressure in fuel elements, based on the method developed, are being used; this is due to the different areas of application. The first area is intended for exit monitorhag of the helium pressure in the fuel elements during the fuel element production process (SAMP).Until recently such monitoring was performed at fuel production plants by the method of selective perforation of the cladding of som...