[en] Experimental results are presented on the dynamics and elastic buckling of thin hemispherical shells fluid-coupled with a concentric rigid vessel, the excitation being the vessel vertical harmonic displacement. Such tests were performed to provide information about the behaviour of this kind of shell interacting with a liquid and subjected to an earthquake. The tests confirm that the variation of the liquid level following shell motion yields a softening nonlinearity of the vibrating shell-liquid system. Static buckling pressures predicted by theoretical work on imperfect shells are compared with both static and dynamic buckling pressures measured in tests on aluminium shells, the comparison being made via the measurement of the initial geometric imperfections of the shells. An explanation of the systematic scatter between static and dynamic critical values is proposed. (author)

[en] An analytical model, based on the perturbation theory, has been utilized to analyse the creep deformation, bulge behaviour (local instability) and time-to-failure for Zircaloy tubes (claddings). The model incorporates the effect of anisotropy of Zircaloy and employs Norton's creep law to obtain the expressions for radial, axial and bulge displacements and time-to-failure for claddings. The effects of anisotropy, initial geometric imperfections and temperature perturbations on these quantities have also been studied. The shortening of Zircaloy claddings observed in experiments is explained on the basis of the present model. Good agreement between the theoretical predictions and experimental observations for the time-to-failure has also been observed. The anisotropy is found to have a strengthening effect on claddings and the temperature perturbations affect the bulge growth more severely than do the geometric imperfections. (author)

[en] The MABEL-2D code has been used to study the effect of different mechanical restraint conditions on the ballooning response of fuel rods in the MT-3 experiment. Changing the restraint conditions from those considered appropriate to MT-3, where the rods pushed apart before flattening, to those appropriate to a large, uniformly ballooning array, was predicted to lead to increases in the axial extent of ballooning, in rupture times and in rupture strains, for a given pellet eccentricity within the cladding. At an eccentricity of 0.35, corresponding to a constant minimum to maximum pellet/clad gap ratio of about 1:2, the time to rupture was increased from 180 s to 185 s and the rupture strain from 43% to 45%. The increases in rupture strain and time were generally the same or smaller than differences, calculated in earlier work, resulting from the movement of rods relative to each other during ballooning. Pellet stack asymmetry within the cladding remains the dominant source of azimuthal temperature gradients. The results are discussed. (author)

[en] A survey of basic equations is presented to describe some aspects of the mechanical behaviour of a fuel rod. The relations formulated enable the stress-strain distribution to be computed as a function of non-elastic strains. The strains considered are due to thermal expansion, cracking creep, and plasticity. Some numerical results are given for a VVER-type fuel rod cross section, also illustrating the possibilities provided by the model. (author)

[en] An evaluation is presented of power ramp data of Mitsubishi's PWR fuel rods tested in R-2, Studsvik, which was analysed by FROST and THERMOST codes. The analyses give good predictions for measured diameter changes and on-power rod elongations. The work indicates that FROST is capable of analysing both radial and axial pellet-cladding mechanism interaction (PCMI) appropriately, and that predicted states of PCMI (i.e. stress and strain which cannot be measured directly) are considered to be reliable. The ramp data used in the present analyses were obtained in two joint programmes with five Japanese PWR utilities (KEPCO, KYEPCO, SEPCO, HEPCO, and JAPCO). (UK)

[en] This paper presents the results from theoretical analyses of two models that are used to investigate the stability of a circumferential through-wall crack in a stainless steel piping system containing bends, and which is subjected to fixed deformations. In each case the piping configuration is such that the cracked cross-section is subjected to both a tensile force and a bending moment, and by varying the configuration's geometrical parameters, it is possible to assess the effect of a wide range of combinations of bending and tensile loadings on the instability criterion. The results clearly show that a simple procedure, which is currently used to give the instability criterion for a crack in a piping system, is strictly accurate only if the deformation at the cracked section occurs solely by bending. (author)

[en] Plastic deformation behaviour of Zircaloy cladding has been extensively examined in the past and can be described best by a model for asymmetric deformation. Slight displacement between the pellet and cladding will always exist and this will lead to the formation of azimuthal temperature differences. The ballooning process is strongly temperature dependent and, as a result of the built up temperature differences, differing deformation behaviours along the circumference of the cladding result. The calculated ballooning of cladding is mainly influenced by its temperature, the applied burst criterion and the parameters used in the deformation model. All these influencing parameters possess uncertainties. In order to quantify these uncertainties and to estimate distribution functions of important parameters such as temperature and deformation the response surface method was applied. For a hot rod the calculated standard deviation of cladding temperature amounts to 50 K. From this high value the large influence of the external cooling conditions on the deformation and burst behaviour of cladding can be estimated. In an additional statistical examination the parameters of deformation and burst models have been included and their influence on the deformation of the rod has been studied. (author)

[en] A failure model for Zircaloy-4 fuel sheaths has been developed and used to predict the effect of circumferential temperature variation (ΔT) on fuel-sheath failure in inert and steam atmospheres. The model, in the form of the BURST-3 computer code, assumes that the deformation of the thin-walled tube can be described using a steady-state creep rate relationship, and that a relationship exists between the tangential stress and the temperature at the instant of failure. Experimental data have been obtained for fuel-sheath failures, as a function of ΔT, in an inert atmosphere in the α- and (α+β)-phase regions, and in a steam atmosphere in the (α+β)- and β-phase regions. Good agreement is found between the BURST-3 predictions and the experimental results. Results are presented. (author)

[en] A recent experimental study has shown that the slope of the Jsub(R) curve for a A533B pressure vessel steel is reduced significantly by the presence of an aggressive environment. This state of affairs is modelled, and the experimental observations are explained in terms of the effect of the environment on the correlation between the crack tip opening angle and crack velocity. (author)

[en] The paper describes the development and sample use of a computer code which automates both the Monte Carlo and response surface approaches to probabilistic fuel performance modelling utilising the SLEUTH-82 deterministic program. A number of the statistical procedures employed, which have been prepared as independent computer codes, are also described. These are of general applicability in many areas of probabilistic assessment. (author)