[en] A new calibration procedure is proposed for the application of recoil implantation of radioactive heavy ions (energies between a few hundred keV and a few MeV) into the near surface of materials as part of a research programme on sub-micrometric wear or corrosion phenomena. The depth profile of implanted radioelements is performed by using ultra thin deposited films obtained by cathode sputtering under argon plasma. Two curves for ⁵⁶Co ion in nickel have been determined for implantation depths of 110 and 200 nm, respectively, and stress the feasibility and reproducibility of this method for such activated depths. The achieved surface loss detection sensitivities are about 1 and 2 nm respectively. The on line detection mode is performed directly on the sample of interest. A general description of the method is presented. A study of the reaction kinematics followed by a general treatment on the irradiation parameters to be adopted are also developed with the intention of using the ultra thin layer activation method (UTLA) to further applications in research and industry. (author)

[en] The high nickel austenitic alloys are generally considered to have good resistance to chloride stress corrosion cracking. In the standard boiling magnesium chloride solution tests, alloys with more than 40% nickel are immune. Nevertheless, more recent data show that cracking can occur in both Alloys 600 and 690 if the solution is acidified. In other low pH media, such as boric acid solution at 100 deg C, transgranular and intergranular cracking are observed in Alloy 600 in the presence of minor concentrations of sodium chloride (2g/I). In concentrated boric acid at higher temperatures (250 and 290 deg C), intergranular cracking also occurs, either when the chloride concentration is high, or at low chloride contents and high oxygen levels. The role of pH and a possible specific action of boric acid are discussed, together with the influence of electrochemical potential. (author)

[en] One of the fundamental discoveries involving radiation effects on the oxidation of Zircaloy in low-oxygen aqueous environments is the influence of thick oxide films. Zircaloy oxidation rates in low-oxygen (hydrogen-rich) coolants initially proceed at relatively low rates, often almost uninfluenced by radiation. Marked upturns in oxidation rate have signaled the onset of radiation effects, appearing to correlate with a threshold oxide thickness. The oxide thickness effects were first recognized in a series of experiments in the Engineering Test Reactor (ETR) and Advanced Test Reactor (ATR). Results of the test reactor experiments lead to formulation of the thick-film hypothesis: beyond a threshold oxide thickness, radiolysis of water that infiltrates oxide cracks and pores controls the oxidation rate; radiation creates microenvironments inside the oxide film, producing highly oxidizing conditions, that are no longer suppressed by the coolant-borne hydrogen. The threshold oxide thickness for the ATR/ETR test series was in the range of 10 to 13 μm. More recently, thick-film behavior has been observed on Zircaloy in several reactors with low-oxygen coolants, including pressure tubes in the Hanford N Reactor, Pickering Units 1 and 2, and the NPD reactor. Radiation enhancements of oxidation also have been reported on PWR fuel cladding in several reactors and on unfueled assembly components. Hydriding in the thick-film regime is also accelerated, which appears to present a dilemma, namely, how can oxidizing and hydriding conditions exist simultaneously within the oxide. A potential explanation is that the effective radiolysis reactions occur at or near the metal/oxide interface. Adsorption on oxide or metal surfaces facilitates separation of oxidizing and reducing species. This paper summarizes the early evidence for thick-film behavior, including oxidation and hydriding trends, updates confirmatory evidence from Zircaloy reactor and fuel assembly components, and highlights other observations from the test reactor series that have potential fundamental significance to explanations of radiation effects on Zircaloy. (author). 24 refs, 9 figs, 3 tabs

[en] The corrosion of a tube made up of 9Cr-1Mo, 2.25Cr-1Mo, and 2.25Cr-1Mo-Nb ferritic steels and containing artificial defects has been investigated under realistic steam generator conditions (355⁰C, 17.6 MPa) with acid chloride fault water chemistry (2 mg/kg HCl). Four regions of corrosion and magnetite deposition behaviour were observed on the tube surface. In non-heat flux regions, magnetite deposition was affected by mass transfer and probably also by surface potential. In low heat flux regions (<660 kW m^-2) observed increases in the rates of magnetite deposition and corrosion were probably due to rises in the degree of iron supersaturation and HCl concentration, brought about by boiling. Enhanced HCl concentrations in the normal heat flux region (660 kW m^-2) prevented magnetite deposition and caused an increase in corrosion of the three steels. Increases in corrosion and magnetite deposition were also observed at the weld between the 9Cr-1Mo and 2.25Cr-1Mo steels. In defects, accelerated corrosion was seen only in the 9Cr-1Mo steel and was confined to the top 0.15 mm. It is concluded that the corrosion behaviour observed in this work is determined by the residence time and concentration of solutions of HCl on tube and defect surfaces. (author)

[en] Problems is considered of development of the microbiological corrosion of the NPP equipment. The main attention is paid to the selective character of microbiological corrosion in zones of welded joints of austenitic steels. It is noted that the presence of technological defects promotes growth of corrosional damages. Methods for microbiological corrosion protection are discussed

[en] The present paper is focussed in the study of the properties of a clad layer of stainless steel on a mild steel. By blowing powder of the alloy into a melt pool generated by a laser of 2 KW, an homogeneous layer of 316 stainless steel can be obtained. Structure, composition and corrosion behaviour are similar to those of a stainless steel in as-received condition. (Author)

[en] Corrosion losses of tungsten covered by the layer of glass-enamel melt were determined at 800, 850, 900, 950 deg C. It is shown that the rate of high-temperature oxidation of tungsten decreases after application of glass-enamel melt on its surface. This is probably conditioned by reduction of area of metal interaction with oxidizing atmosphere

[en] A coating of nickel with La₂O₃ particles was electrodeposited on the surface of γ-TiAl to improve its high-temperature oxidation resistance. The experimental results showed that contrary to the oxidation of bare specimens, the electro-deposited Ni-La₂O₃ composite-coated ones exhibited much better resistance to both isothermal and cyclic oxidation in air at 1000 and 900 C. For the oxidation of the Ni-La₂O₃ composite-coated γ-TiAl EPMA/EDX microanalyses revealed that after the composite film had been thoroughly oxidized, a La₂O₃-rich NiO layer close to the gas-scale interface and two alumina-rich layers, with one beneath the NiO layer and the other adjacent to the γ-TiAl matrix, were produced in the scale. The results indicated that the preferentially formed la₂O₃-doped NiO layer retarded the growth of rutile and favored the formation of two alumina-rich layers. The mechanism of the effects of the electrodeposited Ni-La₂O₃ composite on the oxidation behavior of γ-TiAl is discussed in detail

[en] The corrosion of Co-15 wt.% Y has been studied at 600--800 C in H₂-H₂S-CO₂ mixtures providing a sulfur pressure of 10^-8 atm at 600--800 C and of 10^-7 atm at 800 C and an oxygen pressure of 10^-24 atm at 600 C and of 10^-20 atm at 700--800 C. The corrosion rates in such sulfidizing-oxidizing atmospheres were compared with those of pure cobalt and yttrium. The addition of yttrium to cobalt is only slightly beneficial, since for a yttrium content of 15 wt.% the corrosion rate is reduced quite significantly with respect to pure cobalt at 800 C under 10^-7 atm S₂, only to a limited extent at 600 C, and even slightly increased at 700 C. Moreover, the alloy corrodes considerably more rapidly than pure yttrium at 800 C, when the latter behaves protectively. At 600 and 7600 C, yttrium exhibited breakaway behavior, while the alloy corroded more rapidly than yttrium at short times, but more slowly at long times. Under all conditions, except at 800 C under 10^-8 atm S₂, the alloy forms an external layer of cobalt sulfide overlying an intermediate region of very complex composition containing a mixture of the compounds of the two metals and in innermost region of internal attack containing compounds of yttrium with both oxygen and sulfur. Thus, cobalt can still diffuse through the intermediate region to form the outer cobalt-sulfide layer at nonnegligible rates. The scaling behavior of the Co-15% Y alloy is discussed by taking into account the limited solubility of yttrium in cobalt as well as the presence of an intermetallic Co-Y compound in the alloy

[en] The oxidation behavior of a series of single- and two-phase Nb-Ti-Al alloys, selected from the same extended γ + σ tie-line, was investigated at 1200 C in air. The single-phase σ alloy suffered from extensive internal oxidation and oxidized at a much higher rate than the single-phase γ alloy. In a two-phase γ + σ microstructure, the γ phase was preferentially attacked to form internal alumina and Ti-rich nitride. This preferential attack of γ limited the extent to which the σ phase was internally oxidized, but also interrupted the formation of a continuous alumina scale. The single-phase γ alloy also did not form a continuous alumina scale. The inability of the γ phase to form continuous alumina was attributed to a combination of nitride formation and internal oxidation. The oxidation behavior of the two-phase γ + σ Nb-Ti-Al alloys is discussed in terms of mechanisms developed for the oxidation of binary, two-phase alloys