INTRODUCTIONTrends in the development of modern nuclear power engineering require an increase in the efficiency of using nuclear fuel, placing new demands on the already strict conditions for the materials employed in nuclear technology [1]. The shells of fuel elements are some of the most important elements of an active reac tor zone. The material capabilities of the shells directly affect the operational efficiency and safety of thenu clear reactor. A whole set of demands is imposed on shell material, e.g., high specific strength (shell thick ness, <1 mm; length, up to 4 m), resistance to wear, high heat transfer, compatibility with nuclear fuel, and resistance to corrosion in the flow of heat carrier. The possibilities of traditional treatments for improving the characteristics of shell material, e.g., bulk doping, mechanical treatment, and mechanical-thermal treatment, are now virtually exhausted. One possible solution to the problem of improving the industrial properties of fuel element shells would be to introduce ion beam treatment to finish the outer surfaces of fuel element tubes via cleaning and polishing, instead of resorting to power consuming mechanical grinding [2]. This technology is environmentally friendly and requires no physical contact with the tubes. The geom etry of the tubes remains virtually the same and can be easily transformed for additional doping of the near surface layers of shell material in the ion mixing mode and the controlled oxidation of the surface.
EXPERIMENTALAs samples for our investigations, we used plant tubes (length, 500 mm; outer diameter, 9.15 mm; wall thickness, 0.65 mm) made of E110 zirconium alloy, the composition of which is described in Table 1. The roughness of the samples' outer surfaces in the initial state was R a = 2.0 ± 0.3 μm.Ion treatment of the samples was performed on the specialized KVK 10 installation [2], the layout of which is shown in Fig. 1. The main characteristics of the technique are presented in Table 2. The working chamber of the installation is equipped with two gas discharge ion sources for cleaning and polishing the outer tube surfaces with a wide aperture Ar + beam, and with three magnetrons for the deposition of metal films (e.g., Al, Fe, Mo).The operating principle behind ion sources (Fig. 2) is based on the formation of high density plasma by ionizing the working gas in the glow discharge in crossed electric and magnetic fields [3]. A metallic cathode (Fig. 2, pos. 2) that serves simultaneously as a magnetic guide is placed under zero potential, while high voltage (up to 3.5 kV) is supplied to an isolated anode (Fig. 2, 1). The geometry of the electrode and constant magnet arrangement is such that the mag netic field has a predominantly transverse component in the region of working gas ionization (Fig. 2, 5), while the electric field has a predominantly longitudi nal component. A double azimuthally uniform electric layer is thus formed in the anode-cathode gap. Under Abstract-The effect ion beam treatment with a wide aperture beam of a...
