[en] The world's nuclear power stations risk becoming brittle as they age faster than expected. As Western engineers try to understand how, they are turning to Russia for practical help in giving their oldest stations a new lease of life. (author)

[en] The physical, mechanical and irradiation behavior of niobium and niobium base alloys have been widely studied over the last twenty-five years. Much of this interest stemmed from its favorable high-temperature strength and good low temperature ductility which prompted increasing emphasis on its use as a structural material in the aerospace industries in the 1960's. Its strength characteristics combined with a low neutron absorption cross-section, also prompted its use in the nuclear industries

[en] The role of alloying elements in modifying the resistance of structural metals to general and local corrosion is not fully understood, to the extent that corrosion resistant alloys cannot be designed from first principles. The development of this capability must await more detailed knowledge of the structural and electronic properties of the thin passive films that grow on corrosion-resistant metals and alloys. In this study, the authors investigated the segregation of Al/sup 3+/, Ti/sup 4+/, and Mo/sup 6+/ into the passive films that form on the dilute binary alloys Ni-X(X-Al, Ti, Mo) under potentiostatic conditions

[en] This paper reports that HEPA-filtered wet vacuum systems are used at many nuclear stations for decontamination and spill cleanup. One problem with a wet vacuum, however, in that the operator must periodically stop the unit and move it to a floor drain to empty the water that has been collected. Interrupting the job in this manner decreases productivity, increases personnel exposures, and increases the chances for the spread of contamination. Recognizing this, Indian Point Station personnel have modified some wet vacuum systems to allow the continuous direct pump-down of the units to a floor drain

[en] The report consist of three parts dealing with comparison of the irradiation behaviour of 'Eastern' and 'Western' steels, mechanisms of irradiation embrittlement and the role of compositional variations on the irradiation sensitivity of pressure vessels. Nickel, copper and phosphorus are the elements rendering the most essential influence on behaviour of pressure vessel steels under irradiation and subsequent thermal annealing. For WWER-440 reactor pressure vessel (RPV) steels in which nickel content does nor exceed 0.3% the main affecting factors are phosphorous and copper. For WWER-1000 RPV welds in which nickel content generally exceed 1.5% the role of nickel in radiation embrittlement is decisive. In 'Western' type steels main influencing elements are nickel and copper. The secondary role of phosphorus in radiation embrittlement of 'Western' steels is caused by lower relative content compared to 'Eastern' steels. The process of how copper, phosphorus and nickel contents affect the irradiation sensitivity of both types of steel seem to be similar. Some distinctions between the observed radiation effects is apparently caused by differences in the irradiation conditions and ratios of the contents of above mentioned elements in both types of steel. For 'Eastern' RPV steels the dependence of the recovery degree of irradiated steels due to postirradiation thermal annealing id obviously dependent on phosphorus contents and the influence of nickel contents on this process is detectable

[en] The AMES (Ageing Materials Evaluation and Studies) network started its activity in 1993 with the aim of studying the consequences and the mechanisms of the ageing process in materials used for nuclear reactor components. Together with ENIQ, NESC, EPERC, it forms the so-called ''Structural Integrity of Industrial Components'' cluster of networks operated by the Joint Research Centre - Institute for Advanced Materials of the European Commission. After two initial phases dedicated to the compilation of state-of-the-art reports on non-destructive monitoring techniques for thermal ageing, dosimetry, survey of regulatory requirements, predictive formulas for irradiation embrittlement, AMES has entered its third strategy phase with the fifth EURATOM Framework Program, Nuclear Fission Safety Key Action. Most of the projects proposed for this program and sustained by the Steering committee were selected for funding. Their focus is on the influence of chemical composition, namely phosphorus and nickel content, on the irradiation embrittlement of reactor pressure vessel materials, on the improvement of surveillance temperature measurement, on the validation of the Master Curve approach, and on ND techniques to monitor ageing of irradiated steels. The paper describes the objectives of the new fifth Framework Program projects and how they are part of the AMES strategy, pointing out the involvement of CEEC and NIS countries. (authors)

[en] The AMES (Ageing Materials European Strategy) European network started its activity in 1993 with the aim of studying ageing mechanisms and remedial procedures for structural materials used for nuclear reactor components. Operated by JRC-IE, it has been supporting the co-ordination of the project cluster throughout the 4th and 5th EURATOM Framework Programs, carrying out projects on with plant life management implications. Among them we can list the development of non-destructive techniques applied to thermal ageing and neutron embrittlement monitoring (AMES-NDT and GRETE), improved surveillance for VVER 440 reactors (COBRA), dosimetry (AMESDOSIMETRY, MADAM and REDOS), chemical composition effects on neutron embrittlement (PISA) and advanced fracture mechanics for integrity assessment (FRAME). Main frame of the network in the 5th Framework Programme is the ATHENA project, which is aimed at summarizing the obtained achievements and edit guidelines on important issues like the Master Curve, Effect of chemical composition on embrittlement rate in RPV steels, Re-embrittlement models validation after VVER-440 annealing and open issues in embrittlement of VVER type reactors. In the 6th EURATOM Framework Programme started in 2003 the network will be part of a broader initiative on PLIM including in a more integrated way NESC, ENIQ, NET and AMALIA networks. This paper shows an overview of the concluded projects, achievements of the running ones and open issues tackled in the 6th EURATOM FWP and a summary of the plans for a new broader network on NPP Plant Life management (SAFELIFE). (author)

[en] Drift velocity saturation (at some characteristic value,$v_d^{sat}$) is a critical process that limits the ultimate current-carrying capacity of semiconductors at high electric fields (~10⁴ V/cm). With the recent emergence of two-dimensional (2D) semiconductors, there is a need to understand the manner in which velocity saturation is impacted when materials are thinned to the monolayer scale. Efforts to determine vsatd are typically hampered, however, by self-heating effects that arise from undesirable energy loss from the active 2D layer to the dielectric substrate that supports it. In this work, we explore this problem for an important 2D semiconductor, namely monolayer molybdenum disulfide (MoS₂). By applying a strategy of rapid (nanosecond duration), single-shot, pulsing, we are able to probe the true hot-carrier dynamics in this material, free of the influence of self-heating of its SiO₂ substrate. Our approach allows us to realize high current densities (~mA/μm) in the MoS₂ layers, representing a significant enhancement over prior studies. We similarly infer values for the saturated drift velocity ($v_d^{sat}$ ~ 5-7 x 10⁶ cm s^-1) that are higher than those reported in earlier works, in which the influence of self-heating (and carrier injection into oxide traps) could not be excluded. In fact, our estimates for $v_d^{sat}$ are somewhat close to the ideal velocity expected for normal (parabolic) semiconductors. Lastly, since a proper knowledge of this parameter is essential to the design of active electronic and optoelectronic devices, the insight into velocity saturation provided here should provide useful guidance for such efforts.

[en] Much work has been carried out over the past 40 years on the oxidation of zirconium alloys used for nuclear fuel cladding, but there is no consensus as to the critical factors that control kinetics, even though this is vital for the design of materials for higher burn-up regimes. One unanswered question is the role of porosity in controlling oxidation. Here we show that the nature of the nanoscale porosity can be correlated to different stages of the oxidation process.

[en] Predictions for the corrosion behaviour of Zircaloy cladding are based on empirical models. This results in significant uncertainties for forecasts beyond existing data e.g. for high burn-up, or when there has been a change in operating conditions. To allow for a more accurate prediction of corrosion behaviour a better understanding of the mechanisms involved is required. A program has been initiated with the aim of developing a detailed mechanistic understanding of out-of-pile Zircaloy corrosion behaviour. This paper reports the results of isothermal exposures of Zircaloy-4 to PWR water at 350 Celsius degrees. A variety of analytical techniques have been employed to analyse the corroded specimens, including scanning and transmission electron microscopy, atom probe tomography, micro-beam synchrotron X-ray diffraction and electron energy loss spectroscopy. When the results of these techniques are compared, it becomes evident that the periodic transition from slow to fast oxidation rates results from the accumulation of stress relief processes in the metal (particularly plastic deformation, but also oxygen and hydrogen dissolution); at the metal-oxide interface (decomposition of the flat interface into undulations); and in the oxide (cracking). These reduce the in-plane compressive stresses near the metal-oxide interface but ultimately balance them with in-plane tensile stresses which encourage through-thickness cracking, and the percolation of the environment to the metal-oxide interface. This is noticed only if allowance is made for out-of-plane stresses in the thin oxide. (authors)