28 research outputs found
Proposal for ultrasonic technique for evaluation elastic constants in uo2 pellets
Pellets of uranium dioxide are used as fuel in nuclear power reactors, in which are exposed to high thermal
gradients. This high energy will initiate fusion in the central part of the pellet. The expansion of the uranium
dioxide pellets, resulting from fission products, can cause fissures or cracks, therefore, the study of their
behavior is important. This work aims to develop and propose an ultrasonic technique to evaluate the elastic
constants of UO2 pellets. However, because of the difficulties in handling nuclear material, we proposed an
initial study of alumina specimens. Alumina pellets are also ceramic material and their porosity and dimensions
are in the similar range of dioxide uranium pellets. They also are used as thermal insulation in the fuel rods,
operating under the same conditions. They were fabricated and used in two different sets of 10
alumina pellets with densities of 92% and 96%. The developed ultrasonic technique evaluates the traveling time of ultrasonic waves, longitudinal and transverse, and correlates the observed time and the elastic constants of the materials. Equations relating the speed of the ultrasonic wave to the elastic modulus, shear modulus and Poisson's ratio have led to these elastic constants, with graphics of correlation that showed excellent agreement with the literature available for Alumina. In view of the results and the ease of implementation of this technique, we believe that it may easily be used for dioxide uranium pellets, justifying further studies for that application
Avaliação do comportamento meckntco de soldas TIG em tubos AISI 316 para varetas combustíveis
O comportamento mecânico sob tração e fluência e o efeito da temperatura de serviço, foram averiguados na selarem de um material proposto para vareta combustível de reatores nucleares. Os testes foram realizados em tubos sem costura de aço AISI 3x6, 20% deformado a frio, soldados pelo processo TIG autógeno, auto matizado
Influência da variação de temperatura nas medidas de tempo de percurso da onda ultrassônica durante um ensaio de ultrassom
Para definir a melhor metodologia e condições de trabalho na execução da pesquisa, avaliou-se a influência da variação de temperatura nas medidas de tempo de percurso da onda ultrassônica durante um ensaio de ultrassom, através da mesma técnica. Com a obtenção de dados novos e comparativos, definiu-se a melhor metodologia e condições de trabalho na aquisição dos sinais ultrassônicos, visando melhorar a confiabilidade desta técnica
Avaliação da metodologia de aquisição de sinais ultrassônicos
Para definir a melhor metodologia e condições de trabalho na execução da pesquisa, verificou-se a influência de diferentes metodologias para medidas do tempo de percurso da onda ultrassônica em um ensaio de ultrassom, através da técnica de birrefringência acústica. Com a obtenção de dados novos e comparativos, definiu-se a melhor metodologia e condições de trabalho na aquisição dos sinais ultrassônicos, visando melhorar a confiabilidade desta técnica
Evaluation of elastic constants of materials using the frequency spectrum
The characterization of materials made with the support of non-destructive techniques has great importance in industrial applications. The ultrasonic techniques are distinguished by good resolution to measure small variations of wave velocities as a result of changes in the character suffered by a particular material. In general these ultrasonic techniques are studied in the time domain, which represents an experimental difficulties when thin materials are analyzed, as well as to attenuate the ultrasonic signal drastically. An ultrasonic technique that uses the frequency domain is used in this study aiming to provide good time measurements to calculate the elastic constants of the first order in an aluminum alloy 6351. With the aid of a statistical approach was possible to have good results of tests performed when compared by a time domain technique already well explored in Ultrasound works produced in the Nuclear Engineering Institute Laboratory (LABUS / IEN) and also presented in most of the package, in good agreement with the theoretical model established in literature and used to validate the experiment, which was found in the results with good approximation. The relevance of this work in the nuclear area is associated with the interest to know the mechanical properties of structural components of the nuclear industry, which is currently studied as a rule, resorting to the computer simulations or previously during the operation of the system
Ultrasonic Spectral Analysis for Nuclear Fuel Characterization
Ceramic materials have been widely used for various purposes in many different industries due to certain characteristics, such as high melting point and high resistance to corrosion. Concerning the areas of applications, automobile, aeronautics, naval and even nuclear, the characteristics of these materials should be strictly controlled. In the nuclear area, ceramics are of great importance once they are the nuclear fuel pellets and must have, among other features, a well controlled porosity due to mechanical strength and thermal conductivity required by the application. Generally, the techniques used to characterize nuclear fuel are destructive and require costly equipment and facilities. This paper aims to present a nondestructive technique for ceramic characterization using ultrasound. This technique differs from other ultrasonic techniques because it uses ultrasonic pulse in frequency domain instead of time domain, associating the characteristics of the analyzed material with its frequency spectrum. In the present work, 40 Alumina (Al2O3) ceramic pellets with porosities ranging from 5% to 37%, in absolute terms measured by Archimedes technique, were tested. It can be observed that the frequency spectrum of each pellet varies according to its
respective porosity and microstructure, allowing a fast and non-destructive association of the same characteristics with the same spectra pellets
Evaluation of two ultrasonic systems for analysis of porosity in ceramic
The Ultrasound Laboratory of the Nuclear Engineering Institute (LABUS / IEN) has developed an ultrasonic
technique to measure porosity in nuclear fuel pellets (UO2). By difficulties related to the handling of UO2
pellets, Alumina (Al2O3) pellets have been used in preliminary tests, until a methodology for tests with pellets
of UO2 could be defined. In a previous work, in which a contact ultrasonic technique was used, good results
were obtained to measure the porosity of Alumina pellets. In the current studies, it was found that the frequency
spectrum of an ultrasonic pulse is very sensitive to the porosity of the medium in which it propagates. In order
to define the most appropriate experimental apparatus for using immersion technique in future tests, two
ultrasonic systems, available in LABUS, which permit to work with the ultrasonic pulse in the frequency
domain were evaluated . One system was the Explorer II (Matec INSTRUMENTS) and the other the ultrasonic
pulse generator Epoch 4 Plus (Panametrics) coupled with an oscilloscope TDS 3032B (Tektronix). For this
evaluation, several frequency spectra were obtained with the two equipment, by the passage of the ultrasonic
wave in the same pellet of Alumina. This procedure was performed on four different days, on each day 12
ultrasonic signals were acquired, one signal every 10 minutes, with each apparatus. The results were compared and analyzed as regard the repeatability of the frequency spectra obtained
Analysis of ultrasonic techniques for the characterization of microfiltration polymeric membranes
The use of polymeric membranes is extremely important in several industries such as nuclear, biotechnology,
chemical and pharmaceutical. In the nuclear area, for instance, systems based on membrane separation
technologies are currently being used in the treatment of radioactive liquid effluent, and new technologies using
membranes are being developed at a great rate. The knowledge of the physical characteristics of these
membranes, such as, pore size and the pore size distribution, is very important to the membranes separation
processes. Only after these characteristics are known is it possible to determine the type and to choose a
particular membrane for a specific application. In this work, two ultrasonic non destructive techniques were
used to determine the porosity of membranes: pulse echo and transmission. A 25 MHz immersion transducer
was used. Ultrasonic signals were acquired, for both techniques, after the ultrasonic waves passed through a
microfiltration polymeric membrane of pore size of 0.45 μm and thickness of 180 μm. After the emitted
ultrasonic signal crossed the membrane, the received signal brought several information on the influence of the
membrane porosity in the standard signal of the ultrasonic wave. The ultrasonic signals were acquired in the
time domain and changed to the frequency domain by application of the Fourier Fast Transform (FFT), thus
generating the material frequency spectrum. For the pulse echo technique, the ultrasonic spectrum frequency
changed after the ultrasonic wave crossed the membrane. With the transmission technique there was only a
displacement of the ultrasonic signal at the time domain
Soldagem TIG de tubos de aço inox AISI 316 para varetas combustíveis
Foi realizado um estudo da selagem de tubos de aço inoxidável austenítico AISI 316, 20% de formado a frio, a pinos de material similar pelo processo de soldagem TIG autógeno, visando a sua utilização como vareta de combustível para reatores nucleares. Inicialmente foram executadas soldas preliminares, empregando-se dois projetos de pino tampão, que permitiram a seleção de uma solda considerada ideal. A seguir procedeu-se à confecção de corpos de prova soldados, com os parâmetros escolhidos, a fim de se averiguar o comportamento mecânico do componente. Foi também realizado um tratamento térmico na temperatura de serviço em corpos de prova soldados visando examinar o efeito causado no componente em serviço através de observações microestruturais e do comportamento mecânico. Este componente foi comparado ao como soldado. Concluiu-se que a recristalização causada pela soldagem diminuiu as propriedades mecânicas do componente. O tratamento térmico aumentou as propriedades mecânicas do componente. O tratamento térmico aumentou as propriedades mecânicas, mas diminuiu o tempo de vida do componente quanto à ruptura