The thermally induced steam generator tube rupture (TI-SGTR) accident is a principal contributor to mean early and latent cancer fatality among the containment bypass accidents. To mitigate the consequence of a TI-SGTR accident, use of a bypass mitigation device has been proposed. This study investigated the feasibility of using the proposed bypass mitigation device based on computational fluid dynamics (CFD) analysis and structural safety assessment using a commercial simulation software (Fluent). As TI-SGTR accident may occur if main steam safety valve (MSSV) for preventing over pressurization is stuck-open in station black out (SBO) scenario, the analysis included the modeling of the flow of dry steam from MSSV to the capturing pipe of the mitigation system. According to CFD analysis results, after passing MSSV, the inlet pressure was decreased to the atmospheric pressure. The structural safety analysis was based on evaluating the equivalent stress distribution of the capturing pipe. Under three inlet pressure conditions, the largest concentrated stress on the capturing pipe was found to be less than 10% to tensile strength of the steel. For the concrete support, the safety margins may not be sufficient for 8.7 MPa inlet pressure condition. The thermal-mechanical analysis was performed for the period of 15 min, indicating that the effect of thermal expansion is small and that the resulting strain does not pose a concern. The results of this study can also be utilized to study externally released flow through MSSV or to identify directions for supplementing or reinforcing the migration system.

In this paper, the effect of hydrostatic testing internal pressure on the residual stresses of circumferentially butt-welded steel pipes is investigated by a three dimensional finite elements simulation based on ansys 11 code. Residual stresses due to welding process are calculated by an uncoupled analysis. In this analysis, at first, a transient heat transfer problem is solved. Output of this analysis is temperature distribution history .This output is used as the structural analysis load. Output of structural analysis is welding residual stresses. The most important part of such simulations is modeling of heat power source. In the present work, heat power of welding electrode is simulated by a moving heat source with Gaussian distribution on a spherical domain. The presented model is used for calculation of residual stresses in an 8 in. three pass butt-welded steel pipe. Finally, the effects of hydrostatic testing internal pressure on the residual stresses are studied by the proposed model. The results obtained from this study show that the hydrostatic testing pressure has a significant effect on residual stresses.

The fabrication of stainless steel tube-to-tubesheet joints of heat exchangers consists of welding after hydraulic expansion. Here, this process is simulated by use of the finite element method, which is carried out in a sequentially decoupled analysis: the welding temperature field is solved by a transient thermal analysis, and subsequently, a nonlinear elastic plastic stress analysis is carried out. The effect of the unexpanded zone length with reference to the expanded zone of the joints is investigated. The results indicate that welding after the expansion will produce a shrinkage deformation in the tube end. This further reduces the magnitude of the contact stress in the expanded zone and moves it toward the tubesheet secondary surface. The percentage reductions of the contact stress and the contact area are introduced to quantitatively describe the effect of the welding on the expansion zone of the joint. The results show that these reductions decrease linearly with change in the unexpanded zone length, and that the effect of the welding on the contact stress in the expanded zone cannot be neglected. Therefore, a reduction of the influence of the welding on the structural integrity of tube-to-tubesheet joints should be taken into account when utilizing the technique of welding after hydraulic expansion.

Using closed-form and finite element solutions derived in Part I of this paper together with a standard commercial finite element structural-analysis computer program, the joint and cross acceptances for tubes and beams with different boundary conditions are calculated as a function of the correlation length up to 10 times the length of the structures. The results are presented in the form of charts. Steps are given to show how to use these charts together with standard commercial finite-element structural-analysis computer programs to estimate the responses of single and multi-span tubes and beams to cross-flow turbulence-induced vibration. The importance of cross-modal coupling for multi-supported beams is investigated. Examples are given. [S0094-9930(00)03303-5]

This paper describes use of equivalent solid (EQS) modeling to obtain efficient solutions to perforated material problems using three-dimensional finite element analysis (3-D-FEA) programs. It is shown that EQS modeling in 3-D-FEA requires an EQS constitutive relationship with a sufficient number of independent constants to allow the EQS material to respond according to the elastic symmetry of the penetration pattern. It is also shown that a 3-D-FEA submodel approach to calculate peak stresses and ligament stresses from EQS results is very accurate and preferred over more traditional stress multiplier approaches. The method is demonstrated on the problem of a transversely pressurized simply supported plate with a central divider lane separating two perforated regions with circular penetrations arranged in a square pattern. A 3-D-FEA solution for a model that incorporates each penetration explicitly is used for comparison with results from an EQS solution for the plate. Results for deflection and stresses from the EQS solution are within 3 percent of results from the explicit 3-D-FE model. A solution to the sample problem is also provided using the procedures in the ASME B&PV Code. The ASME B&PV Code formulas for plate deflection were shown to overestimate the stiffening effects of the divider lane and the outer stiffening ring.

It is estimated that more than 500,000 tons of obsolete and unwanted conventional weapons exist in the United States. The disposal of these unexploded ordnances, in an environmentally sound and cost-effective way, is of paramount importance. Open-air burning and open-air detonation (OB/OD) are two of the most widely used methods to dispose of these unwanted energetic materials. This paper describes our efforts to improve OB/OD operations through the design and testing of a new, large-scale, partially confined facility that minimizes the adverse affects of far-field noise and maximizes the afterburn of explosive by-products. Several designs were evaluated by a series of axisymmetric, time-dependent numerical simulations using FAST3D, a flux-corrected transport-based code optimized for parallel processing. The simulations are used to test various facility geometries and placements and sizes of charges to determine combinations that result in acceptable environmental impact. Comparisons of the pressure and structural analyses for 50 and 100 lb of spherically shaped RDX charges show that the 50-lb spherically shaped charge placed at a height of approximately 2.0 m resulted in an efficient detonation and maintained the structural integrity of the detonation facility.

More than 500,000 tons of obsolete and unwanted conventional weapons exist in the United States. The disposal of these unexploded ordnances, in an environmentally sound and cost-effective way, is of paramount importance. Different types of incinerators and detonation chambers have been proposed to eliminate these unwanted energetic materials. However, questions about the design of such facilities and the environmental consequences of their use must be answered. This paper describes numerical simulations of a large-scale, partially confined detonation facility. Detonation facility designs were evaluated by a series of axisymmetric, time-dependent simulations using FAST3D, a numerical model based on flux-corrected transport coupled to the virtual cell embedding algorithm for simulating complex geometries. The simulations assisted in determining the shape and size of the detonation charge mass that maintained the structural integrity of the facility. Comparisons of the pressure and structural analyses for spherically and cylindrically shaped RDX charges in a fixed volume show that the 50-lb spherically shaped charge resulted in an efficient detonation and maintained the structural integrity of the detonation facility.

This paper presents the results of an investigation into the frangible joint behavior of tanks designed to API 650 rules. In such tanks, the roof-to-shell joint is intended to fail in the event of overpressurization, venting the tank and containing any remaining fluid. The reasoning behind present API design formulas is reviewed. Combustion analyses, structural analyses, and the results of testing are presented. Results show that higher pressures are reached before frangible joint failure than predicted by the present API 650 calculation. One consequence is that (for empty tanks) uplift of the bottom can be expected to occur more frequently than predicted using API 650. However, uplift does not necessarily mean bottom failure. Instead, the relative strength of the shell-to-bottom and roof-to-shell joints will determine failure. This ratio is larger for larger tanks. Recommendations are made as to possible changes in the design approach of API 650.

By introducing the application of the differential quadrature method (DQM) to the dynamic analysis of thin circular cylindrical shells, the work of this paper makes a step forward in furthering the potential of the DQM in the area of structural mechanics. The problem is identified by an eighth-order system of coupled partial differential equations in terms of the three displacement components. The proposed differential quadrature solution is semi-analytical in that Flu¨gge’s representation of the displacement components by trigonometric sine and cosine functions of the circumferential coordinate is employed. The results of the differential quadrature solutions of the natural frequencies of various shell cases are compared and shown to be in excellent agreement with the published, and also some recalculated, results of exact solutions for freely supported, clamped-clamped, clamped-free, and free-free shells. Comparisons are also made with the published experimental data of clamped-clamped and clamped-free shells.

A fluid analysis method using an analogy relating the pressure wave equation of fluid to elasticity equations is applied to sloshing analysis, where existing FEM structural analysis codes are available. It is seen from theoretical consideration that the present method is equivalent to the classical FEM formulation of linear sloshing analysis. The numerical analyses of liquid sloshing in a rigid cubic tank and of vibration of tubulous fluid under gravitational force are performed by using the present method. The results are shown to be in excellent agreement with the theoretical values.

This article describes a technique to calculate the risk from failure of passive components over time, and demonstrates the technique by applying it to a weld in the auxiliary feedwater (AFW) system. It uses a modified version of the PRAISE computer code to perform a probabilistic structural analysis to calculate the probability that crack growth due to aging would cause the weld to rupture. It then uses the weld rupture probability as input to a modified existing PRA to calculate the change in plant risk with time. The results show an insignificant effect on plant risk because of the low calculated rupture rate of the weld in this particular calculation over 48 yr of service. A decreasing yearly rupture rate for this weld is calculated. This results from infant mortality; that is, most of those initial flaws that will eventually lead to rupture will do so early in life.

In this paper, the buckling strength of the lining shells inside the pressure vessel was investigated both theoretically and experimentally. First, the bifurcation buckling analysis of the lining shells was carried out with the aid of the newly developed computer program. In the analysis, the lining could be considered to be a shell subjected to external pressure and encased in a rigid cavity. The concepts of the matrix displacement approach to discrete element structural analysis were extended to predict the instability of shells of revolution encased in rigid cavity. The equilibrium solution for prebuckling was axisymmetric, but the perturbation-displacement field within each element was represented by Fourier circumferential components of the generalized displacements. Second, several experiments on the buckling of cylindrical shell under uniform external pressure were conducted. In the experiments, outward radial displacement of the shell specimen was constrained. The experimental results agreed with the analytical ones by the computer program. Furthermore, numerical calculations were conducted for several kinds of lining shells, whose results were compared with the analytical ones for unrestrained shells.

In the field of finite element structural analysis, the computation of collapse states of structures prone to unstable behavior has long been considered a difficult if not intractable problem. Only recently have procedures that deal effectively with this difficulty found their way in general-purpose finite element codes. Although the explanation for the cause of the so-called limit point obstacle is actually simple—an inappropriate parameterization of the governing equations in the neighborhood of the limit point—this cause does not seem to have been widely understood in the period of development of the finite element technique. In this paper, some of the remedies that have been proposed to overcome the problems are reviewed, including the principle of adaptive parameterization which is now the basis of a new procedure for collapse analysis in the finite element code STAGS. The discussion also includes the treatment of simple bifurcation points because unstable bifurcation can be considered a special form of collapse. It can be concluded that collapse problems, in the sense discussed in this paper, no longer present difficulties that exceed those normally encountered during the solution of nonlinear deformation paths. Further developments, in particular those with respect to improved efficiency, are in progress. Some of the promising ventures in this direction are indicated.

This paper describes the stress analysis performed to assess structural adequacy of the Clinch River Breeder Reactor (CRBR) core removable shield assemblies. Removable shield assemblies are located in the peripheral region of the core (between blanket assemblies and the fixed radial shield), and are subjected to severe cross-sectional thermal gradients and seismic loads requiring a relatively complex duct load pad design. For cost-effectiveness, the analysis was conducted in two stages. First, an elasto-plastic seismic stress analysis was performed using a detailed nonlinear finite element model (with gaps) of the load pad configuration. Next, in order to determine the total strain accumulation and the creep-fatigue damage the maximum seismic stresses combined with the “worst” thermal stresses from a single assembly model were used to perform a simplified inelastic analysis using two sets of material properties to bound the changing material conditions during reactor operation. This work demonstrated the necessity and applicability of the two simplified analysis techniques in elevated temperature structural design, i.e., the treatment of time-dependent degradation of material properties due to temperature and nuclear irradiation, and the use of time-independent finite element stress analysis results to perform a simplified creep-fatigue analysis.

A semi-analytical and computer experimental procedure is described for developing the bend and adjacent span reduction factors for an alternate method of seismic restraint spacing, based on stress and frequency invariance considerations. The results, in terms of fundamental frequency, deflection, stress and support loads are shown to be in good agreement with, or more conservative than, those obtained from formal analysis of a quasi-system with bend using a piping structural analysis computer program. A simple curve is presented relating the bend and the adjacent span reduction factors obtained from the method.

The Pressure Vessel Research Committee (PVRC) Subcommittee on Elevated Temperature Design has been actively engaged in an International Benchmark on Simplified Methods for Elevated Temperature Design. At the Third International Seminar on Inelastic Analysis and Life Prediction in High Temperature Environment held in conjunction with the 6th International Conference on Structural Mechanics in Reactor Technology (SMiRT), August 1981, a progress report on the International Benchmark Project was first reported. This paper is an update of the results of that project. A brief description of the PVRC activities on Elevated Temperature Design is first given. The International Benchmark Problems I, II, and III will then be described. The comparisons between analyses and the recently released experimental results of the French Commissariat l’ Energie Atomique test on fluctuating sodium level in a pool reactor model is now included in this paper. Potential benchmark problems for future consideration by the Subcommittee are also mentioned.

In a large class of dynamic problems occurring in nuclear reactor safety analysis, the forcing function is derived from the fluid enclosed within the structure itself. Since the structural displacement depends on the fluid pressure, which in turn depends on the structural boundaries, a rigorous approach to this class of problems involves simultaneous solution of the coupled fluid mechanics and structural dynamics equations with the structural response and the fluid pressure as unknowns. Such an approach requires that the computer codes used to derive the forcing function and to analyze the structural response be radically modified or even abandoned. This paper offers an alternate approach to the foregoing problems. It is shown that for this kind of problem, the effect of fluid-structure interaction can be accounted for by a fluid mass matrix, which can be computed by the series expansion method. The advantage of this approach is that neither the computer code used to calculate the forcing function nor the ones for structural dynamics analysis need be modified. In fact, once the proper fluid mass matrix is computed, the problem can be solved by ordinary methods of structural dynamic analysis. Furthermore, since the fluid mass matrix is computed by a series expansion method, interfacing with a finite-element structural analysis computer code is relatively simple. On the other hand, the technique is restricted to small structural displacement with cylindrically symmetric fluid-structure boundaries. In addition, the fluid must be single phase.