[en] A sudden drop in power after a beam interruption leads to thermal fatigue effects in structural components in the blanket of an accelerator driven system. These thermal fatigue effects limit component lifetimes. A sudden return to power after a beam interruption can contribute significant additional thermal fatigue and greatly reduce component lifetimes. One obvious solution is a gradual return to power after a beam interruption. There are two potential problems with this solution. One problem involves interruptions that are longer than the thermal time constants of thin structural members but shorter than the time constants of thick structural members. In such a case, a gradual return to power reduces the additional thermal fatigue in the thin structural members but increases the thermal fatigue in thick structural members. Some compromise is necessary. The other problem is that for thick components with long thermal time constants a long, gradual return to power is required to minimize additional thermal fatigue. Such a slow return to power can reduce the utilization or the effective load factor of the system. Specific examples of beam interruptions with various assumptions on return to power are provided for a preliminary design for the blanket of the Accelerator Driven Test Facility. Also, mitigation options to increase component lifetime are discussed. These mitigation options include improving beam reliability and modifying the blanket design to better tolerate beam interruptions

[en] Design codes and their backgrounds are reviewed critically in the light of current knowledge and experience. Rationalizing on the scope of strain limits and on the various parameters they depend on and considering of their interference with other means of assessment of structural integrity leads to proposals for a categorizing and functional relations. (author)

No abstract available

[en] Thermoplastic analysis and more precisely fatigue analysis of nuclear components working at high temperature is usually very difficult and very expensive. Simplified methods have been proposed and are generally used to perform analysis of these structures. These simplified methods require elastic analysis of the component. For a fatigue analysis it is necessary to obtain a very precise value of the strains so the elastic strains must be corrected in order to take plasticity into account. This later appears in two different ways. Non linearity of material which induces strain amplification when working in the plastic field especially near by geometric discontinuities. That can be taken into account with a coefficient Ke. Triaxiality and isovolumic character of strains in the plastic field. That also induces strain amplification with regard to elastic computation. It is proposed in this work to introduce a coefficient Kv to estimate this strain amplification. Several elastic and plastic calculations for typical geometries, have been done in order to test the importance of these parameters and to set up methods for evaluating the coefficients Ke and Kv

[en] This paper describes the methodology adopted for the definition of accelerator reliability requirements and the preliminary results obtained by the European Industrial partnership involved in the development of an accelerator-driven subcritical system (ADS) demonstrator. The current feedback from the operation of high power accelerators exhibits a tendency toward a significant number of beam trips of varying duration. Thus, the number of shutdown transients is potentially significantly higher than for critical reactors. In order to specify reliability targets for accelerator development, the influence of a large number of beam trips on the structural integrity of ADS reactor subsystems (window/target, fuel, structures, components) has to be assessed. As far as the reactor structures are concerned, the analysis can be based on the large experience gained on structural mechanics for sodium-cooled critical fast breeder reactors (FBR) and extrapolated to both gas-cooled and liquid metal [sodium or lead-bismuth eutectic (LBE)] cooled ADS. (authors)

[en] The evaluation of resistance to fatigue (90% of industrial fractures) is codified and generally based on elastic analyses. To take into account local yielding effects, the elastic results are further corrected to compute the real strain range with which the fatigue analysis is performed. In some particular areas where the maximum stresses are embedded in plastic zones, this correction does not hold and an effective elastic-plastic analysis has to be performed. Framatome has developed its own computer program (SYSTUS), in which 2 models have been implemented for industrial fatigue applications and this paper describes their essential differences. An industrial application, performed with the 1st model, is presented and proposes a methodology to evaluate crack initiation in region of high stress concentration which are nested in large plastic areas when subjected to thermal shocks. (orig.)

[en] The effects of cathodic protection on corrosion fatigue of alloys can vary widely, ranging from strongly beneficial to strongly detrimental. This paper provides a concise synopsis of the subject, based upon a review of selected literature. Attempts are made to discern important generalizations concerning the effects of various cathodic protection levels on crack initiation and crack propagation in ferrous and nonferrous alloy systems

No abstract available

[en] During the operation of nuclear plants, components experience low-cycle fatigue due to thermal transients. A good knowledge of the local strain range is therefore highly desirable for low-cycle fatigue analysis. There are two basic discrepancies between the plastic behaviour of the material and the linear elastic model. The first is the non-linear stress/strain relationship, which mainly affects the strain range in the vicinity of stress raisers. The second is that plastic deformation shows no change in volume. This paper covers the corrective action related to this absence of volume variation. Current practice is to require that stresses are evaluated on an elastic basis, although with a P.R. (Poisson's ratio) value different from the elastic P.R. This procedure is rather inconvenient, and seldom used. It appears preferable to use an alternative rule requiring only multiplying the computed equivalent elastic strain range by a corrective factor. Under plane stress conditions (e.g., close to a wall), the actual equivalent strain range can be computed using an equivalent P.R. This permits deriving the corrective factor Ksub(ν) and plotting curves showing Ksub(ν) as a function of the elastic strain range for a given material

[en] Current metallurgical limitations necessarily impose a number of restrictions on the efficiency of power plant and combustion systems. These limitations include both temperature and corrosion resistance. If significant improvements can be made in these areas, then not only will it be possible to obtain higher system efficiencies, but it will also be possible to further exploit new technologies. Consequently, there is appreciable interest in the development of ceramic tubes for heat exchangers. Such tubes would offer the potential of operation at much higher temperatures combined with a much improved resistance to chemical attack. They are unlikely to be suitable for high pressure operation, at least in the foreseeable future, and hence their use would be limited generally to gas to gas exchangers. In spite of the limitations on details and specific technological solutions imposed by industrial property conditions, this report provides an overview on the development of these components, which is in charge of all the major international industrial companies of the field, in consideration of the relevant benefits coming from their large industrialization. After an analysis of the industrial situation of the product, in terms both of possible applications and economical impacts on the market, an overview of major on-going R and D programmes is carried out. At present, these programmes are mostly within the general frame of the study of advanced thermomechanical components and the related manufacturing technologies development