Radiation growth of quenched uranium

In this paper we consider the results of some investigations carried out with full-sized rod fuel elements [4].* We studied fuel elements of the rod type with a core of metallic uranium about 4 m long and 4 to 6 mm in diameter. In order to prevent the interaction of the uranium with the heat carrier, the cores were enclosed in sheaths of magnesium-beryll ium alloys of the PMB-2 type [5], the thickness of the coating being 0.5 to 0.8 ram. The rods were assembled in cylindrical cassettes (10 to 20 each) and suspended in a vertical position in the channel of the reactor. The fuel elements were cooled by a current of CO 2 passing from top to bottom. The pressure of the heat carrier was 52 to 55 abs. atm. The temperature of the surface of the fuel element varied from 120~ (in the upper part of the element) to 500~ (in the lower part). Thus the range of worldng temperatures of the fuel elements included both the temperature of intense radiation growth (up to 350~ and the temperature range in which one might expect considerable cavitation swelling of the uranium core (400 to 500~ Textures differing in character and degree were created by regulating the parameters of the fl-heat treatment of the uranium, namely, the conditions of heating to the temperatures corresponding to the existence of the fi-phase, the holding period at these temperatures, and the cooling. For describing the texture we used the method of the "growth index" proposed in [6]. The quantitative parameter (growth index GI) is determined on the basis of x-ray measurements similar to those used for plotting reciprocal pole figures; this gives a single quantitatively-d etermined value of the texture. Figure 1 shows curves characterizing the change in the shape of two batches of fall-sized rod fuel elements in the course0f irradiation in the reactor with thermal loadings of ~20 MW/ton, proceeding to a burn-up of 1500 MW.days/ton. The cores of the first batch had a sharp texture of i;he [010] type along the axis of the core (mean grown index GI=I.5), the rods of the second batch were characterized by a weak