[en] Although methods are available for the assessment of flow induced vibration in process equipment tube arrays such as nuclear steam generators, they are generally limited to linear vibration in single phase flow regimes. Specifically, work on forcing functions for nonlinear vibration has been relatively successful in modelling turbulent two phase flows using an empirical approach, however, work on the mechanism of fluidelastic instability (FEI) has been slow. One reason for this, is the fact that nonlinear analysis relies on time domain solutions while fluidelastic instability using empirical approaches merely give threshold flow velocities for unstable behavior. In this paper, the formulation and implementation of a time domain forcing function equivalent to Connors' equation for FEI is presented. Results indicate that the formulation provides results consistent with Connors' equation

[en] Transportation packages for radioactive materials must withstand severe impact conditions without loss of integrity and without excessive permanent distortions in the seal regions. The compliance with the requirements may be shown either through extensive testing, elastic-plastic impact analysis, or a combination of both. Elastic-plastic finite element analysis, although less costly than testing, is usually expensive and time consuming. In this paper, simplified methods for determining the impact force are presented for the following impact cases of solid-walled casks: impact on a pin, impact on an edge, and impact on a corner. The results of the simplified methods are in good agreement with the results of elastic-plastic finite element analysis. It is shown that in each case almost the entire impact energy is dissipated by the plastic deformation of the materials in the impact zone

[en] A computer code (AXSHEL2) utilizing the finite element method is developed to analyze elastoplastic thin shells of revolution under axisymmetric loading. The solution is based on a doubly curved axisymmetric thin shell element formulated using Novozhilov's theory. The element is well suited for all ranges of latitude angles of rotational shells. The element accommodates rigid body translation which improves element convergence behaviour. The tangent stiffness method in conjunction with incremental flow theory of plasticity is used in the solution technique. The computer program is set up to analyze thin shells of elastic - perfectly plastic and isotropic hardening materials using Von Mises yeild criteria. In addition, the program can analyze elastic or elasto-plastic buckling problems. Several numerical examples are given to illustrate accuracy, convergence and suitability of the computer code for practical applications. The computer code provides an efficient 'in-house' capability for solving linear and non-linear structural problems associated with nuclear power plant equipment

[en] Successful life management of nuclear steam generators requires proactive planning to monitor and assess all potential degradation mechanisms. One such degradation mechanism is tube fretting as a result of flow induced vibration. Traditional flow induced vibration predictive methods are based on deterministic nonlinear structural analysis techniques and are routinely used for design purposes. The authors have proposed the application of probabilistic techniques to better understand and assess the risk associated with operating nuclear generating stations with aging re-circulating steam generators. These probabilistic methods are better suited to address the variability of the parameters in operating steam generators, e.g., flow regime, support clearances, manufacturing tolerances, tube to support interactions, and material properties. This paper describes an application of a Monte Carlo simulation to predict the propensity for fretting wear in an operating re-circulation steam generator. Tube wear damage is evaluated under steady-state conditions using two wear damage correlation models based on the tube-to-support impact force time histories and work rates obtained from nonlinear flow induced vibration analyses. (author)

[en] In certain instances, such as in the modeling of manufacturing process, undesirable dynamic effects may accompany the use of an explicit transient solution, while the use of full dynamic relaxation is inefficient for this class of problem due to critical damping. In this paper, an approach that merges the salient features of dynamic relaxation with those of the fully explicit solution, is presented. The key objective of the method is the removal of unwanted dynamic (e.g., inertial) effects, while providing for a transient kinematic loading history. This work focuses on the development of an adaptive mass algorithm consistent with specified damping and time step for use within the framework of explicit time integration. The paper describes the hybrid solution formulation and the implementation of the proposed algorithm. Applications include an experimental punch test used for material characterization and a rolled joint expansion manufacturing process used for installation of tubes in steam generators, both involving three-dimensional finite deformation

[en] Transportation packagings for radioactive materials must withstand severe impact conditions without loss of integrity and without excessive permanent distortions in the seal regions. The compliance with the requirements may be shown either through extensive testing, elastic- plastic impact analysis or a combination of both. Elastic- plastic finite element analysis, although less costly than testing, is usually expensive and time consuming. This paper presents simplified methods for determining the impact force for the following impact cases of solid walled casks: impact on a pin, impact on an edge, and impact on a corner. The results of the simplified methods are in good agreement with the results of elastic-plastic finite element analysis. It is shown that in each case almost the entire impact energy is dissipated by the plastic deformation of the material in the impact zone

[en] Ontario Hydro has recently designed a new Type B(M) Tritiated Heavy Water Transportation Package (THWTP) for the road transportation of tritiated heavy water from its operating nuclear stations to the Tritium Removal Facility in Ontario. These packages must demonstrate the ability to withstand severe shock and impact scenarios such as those prescribed by IAEA standards. The package, shown in figure 1, comprises an inner container filled with tritiated heavy water, and a 19 lb/ft³ polyurethane foam-filled overpack. The overpack is of sandwich construction with 304L stainless steel liners and 10.5 inch thick nominal foam walls. The outer shell is 0.75 inch thick and the inner shell is 0.25 inch thick. The primary containment boundary consists of the overpack inner liner, the containment lid and outer containment seals in the lid region. The total weight of the container including the 12,000 lb. payload is 36,700 lb. The objective of the present study is to evaluate the hydrodynamic effect of the tritiated heavy water payload on the structural integrity of the THWTP during a flat end drop from a height of 9 m. The study consisted of three phases: (i) developing an analytical model to simulate the hydrodynamic effects of the heavy water payload during impact; (ii) performing an impact analysis for a 9 m flat end drop of the THWTP including fluid structure interaction; (iii) verification of the analytical models by experiment

[en] Packages used in the road transportation of tritiated heavy water (T₂O) must demonstrate the ability to withstand severe shocks and impacts, such as those prescribed by IAEA Regulations. The paper describes part of the analytical assessment of a proposed package design to determine its structural integrity under impact conditions resulting from postulated accidents. The focus of the work described is on the mathematical modelling of the polyurethane foam used in the sandwich construction of the overpack and on the development of acceptance criteria to evaluate the design. Versions of the computer codes DYNA3D and HONDO incorporating these material models were utilized in performing the numerical computation. Comparison of the predicted results of a punch drop with those of experiments show excellent agreement. Results of the 1 m punch drop and the 9 m edge drop on the lid end are presented. The proposed design meets the specified acceptance criteria, thus demonstrating it will retain its structural integrity under the impact conditions imposed. (author)

[en] The failure of the Liquid Zone Control (LZC) assembly at a nuclear generating station was investigated. The work was performed in order to determine the cause of structural failure in the LZC assembly guide tube at the location of the bearing pads. The failure resulted in leakage of light water into the moderator. Removal of the defective unit revealed that severe fretting wear had occurred on the guide tube at the location of the bearing pad to calandria bushing contact area. The observed wear pattern was orientated approximately 90⁰ to the direction of the bypass inlet flow. Structural features of the system and results of the investigation including the mathematical simulation models used are described in this paper. Vibro-impact forces were determined in the damaged area using a relatively new and efficient procedure. They were found to be of sufficient magnitude to cause the damage. (orig.)

[en] An analytical method is presented which simulates the non-linear dynamic-impact response of multi-supported tubes including U-bends and the effect of non-uniform gap clearances at the supports and between adjacent tubes. Restraints are modelled using gap elements with non-linear damping and force-deflection, characteristics to enable proper simulation of the contact mechanism. An implicit numerical integration scheme for the non-linear equations of motion is developed which is unconditionally stable and includes equilibrium iteration to provide accurate simulation of the impact. One of the salient features of the method is the variable time step scheme which ensures that solution errors are minimized, while avoiding the use of specifying extremely small constant time steps and repeated solutions to confirm that convergence has been achieved. The approach is incorporated into a general structural computer code based on the finite element method which includes a module for analyzing such flow induced excitation mechanisms as fluidelastic instability, periodic wake shedding and flow turbulent excitation. (orig./GL)