抄録
As a part of studies on the development of swaging process for fabrication of the UO2 fuel rod, energetics in swaging was dealt with mainly by investigation of temperature rise during the process. The temperature was measured by means of a thermocouple of Chromel-Alumel or Pt-PtRh which was inserted into UO2 powder in a container of stainless steel tube. Optical and electron microscopic observation and specific heat measurements were also carried out. The conclusions are summarized as follows.
(1) Preliminary heating of the sample results in a great deal of temperature rise; the rise is as high as 1680°C for hot swaging at 720°C, whereas it is about 170°C for cold swaging.
(2) Plastic deformation of UO2 and friction between UO2 particles are main causes for the heat generation. The former is dominant in hot swaging, and the latter in cold swaging.
(3) Excellent compactability of UO2 powder in swaging process is due to atomic diffusion activated both by the temperature rise and the stress during swaging.
(4) In hot swaging, most of working energy is consumed by plastic deformation of UO2, leading to a pronounced temperature rise, and a minor part of the energy is stored in UO2 as internal energy connected with lattice distortion and lattice defects.
(5) In cold swaging, friction between particles, fracture of particles, and lattice distortion play important roles in consuming the working energy. Since a considerable part of the lattice distortion during cold swaging is elatic, working energy for the elastic distortion of lattice is consumed by impact between die backer, and roll.
(6) Specific heat measurements show that some of the internal energy stored in cold swaged compact is released at the temperature range between 450°C and 900°C. The internal energy resulting from cold swaging is also demonstrated by the fact that bonding among particles in cold swaged compact become better after room temperature aging for several months.
