Showing papers in "Nuclear Engineering and Design in 1973"

Review of two-phase flow instability

Abstract: Boiling flow in a water-cooled reactor, an evaporator, or an electronic cooling system is susceptible to thermal-hydrodynamic instabilities, which may cause flow oscillations of constant amplitude or diverging amplitude. These oscillations could induce boiling crisis, disturb control systems, or cause mechanical damage. This paper identifies the causes and mechanisms of these instabilities. Based on their mechanisms, various types of instabilities are classified and tabulated. The parametric effects on flow instability, observed experimentally, are systematically presented. Various analytical techniques for predicting the instability threshold are reviewed in terms of their applicability and accuracy.

The physics of rewetting in water reactor emergency core cooling

Abstract: Surface rewetting is essential for the re-establishment of normal and safe temperature levels following dryout in rod clusters or boiler tubes, or following postulated loss-of-coolant accidents in water reactors. Rewetting experiments have been performed with tubes and rods with a wide range of materials and experimental conditions (surface temperatures 300–800°C, constant water flows 0.1–30 g s−1). The physical processes involved in the rewetting of high temperature surfaces have been shown to be identical for both falling water films and bottom flooding. The variation of rewetting velocity with mass flow has been determined, and shown to be independent of hydraulic diameter over the range 0.2–6 mm of practical interest. Data have also been obtained on the mass ‘carryover’ fraction. Theoretical solutions for the rewetting velocities have been obtained by analysis of thermal conduction in the surface. At low mass flows, effectively one-dimensional (axial) conduction cools the surface ahead of the rewetting front, and gives agreement with experiment. At higher mass flows the rewetting velocity is substantially independent of surface thickness and conductivity. The present data and the available world data for rewetting are shown to be in agreement with the theory.

Soil-structure interaction of nuclear reactor structures considering through-soil coupling between adjacent structures

Abstract: The theoretical problem concerning the influence of through-soil coupling between adjacent structures on the seismic loading of nuclear reactors has been investigated by considering a soil-structure interaction model in which several three-dimensional flexible structures are bonded to an elastic half-space. These structures, which are allowed to be either similar or dissimilar, are modeled as conventional discrete systems mounted on separate base slabs of close proximity. For the purpose of this study, it is assumed that the stiffness of any structure such as piping connecting the adjacent buildings is negligible. For purposes of comparison, the seismic responses of structural masses are determined both with and without the influence of nearby structures. Both transient and steady-state results are presented and discussed for some typical simplified two- and three-structure complexes. Emphasis is placed on the effects of through-soil coupling on the dynamic response of the system rather than actual magnitudes of response which have previously been treated for plants erected on a single base slab. The significant findings are that nuclear power plants can be designed to achieve a reduction in seismic loads due to interaction with neighboring structures. Conversely, improper plant design and layout may result in mutual reinforcement of resonances with increased loads.

A note on the calculation of two-phase pressure losses

Abstract: The calculation of axial differences in static pressure for two-phase flow along a pipe is discussed in relation to the evaluation of two-phase friction. Two-phase friction equations derived from mixing length theory are summarised. The equations compare favourably with data covering the following fluid conditions at the wall: bubble flow, wavy gas-liquid interface, flow with very small bubbles, attached wall bubbles, and dry wall.

Identification of dynamic parameters of linear and non-linear structural models from experimental data

Abstract: Recent and new approaches to the identification of dynamic properties such as damping, eigenfrequencies, mode shapes, and non-linear effects are described. Special attention is paid to the philosophical and practical aspects of identifying such eigenparameters, as others have done much work in the adjustment of mass and stiffness parameters to reproduce these eigenparameters (once they are found). Application to an actual structure is discussed in an attempt to illustrate the effectiveness of the method and familiarize the reader with the type of problems encountered. A summary of typical procedures for vibration testing and parameter identification is presented.

Central station power generation by laser-driven fusion.

Abstract: The feasibility of using laser-driven fusion pulses for the commercial generation of electric power was investigated. The present paper discusses the general aspects of electric power plants based on laser-driven fusion energy sources, outlines the considerations that led to the wetted-wall concept on which the present study is based, presents detailed results of calculations that indicate the feasibility of the concept, discusses aspects of important areas that are not well defined, summarizes related needs for further study, and compares the concept with plants based on magnetically confined controlled thermonuclear reactions.

Problems of thermoplasticity

Abstract: The problems of irreversible deformation of metallic structures have come to the very focus of interest in nuclear reactor technology. The paper surveys developments of the theory of thermoplasticity. Starting with the notions of thermodynamics of continua a theory of rheological materials with internal changes implied by plastic deformations is presented. Both a general theory of elastic-viscoplastic materials and its experimental motivation are discussed. Thermoplastic relations at infinitesimal deformations are considered. The second part concerns thermo-plastic boundary value problems. Solutions and methods of solution are discussed for problems of quenching, thermal shocks, internal heat generation and machine parts design. Thermal cycling and combined thermo-mechanical loading are considered, methods of shakedown analysis being presented.

Fabrication and properties of lithium hydride

Abstract: Lithium hydride is a crystalline material that is a relatively stable compound. Uses include neutron shielding or moderating because of a high hydrogen density and the employment of the 6Li isotope. Fabrication by powder techniques can supply compacts of near theoretical density. The material is chemically reactive and must be protected from atmospheric moisture.

A new approach to the finite-element formulation and solution of a class of problems in coupled thermoelastoviscoplasticity of crystalline solids

Abstract: The application of the general thermoviscoelastic-plastic theory to the analysis of the coupled thermomechanical response of a class of crystalline solids is considered. After a brief review of the essential features of the theory, the manner in which finite-element models of the generalized plastic behaviour can be formulated is discussed. Available experimental data are used to solve a representative example problem in transient, nonlinear, coupled thermoviscoelastoplasticity of a three-dimensional solid of aluminum.

SAP — A structural analysis program for linear systems

Abstract: The current version of the computer program SAP for the static and dynamic analysis of linear structural systems is described. The analysis capabilities of the program, the finite element library, the numerical techniques used, the logical construction of the program and storage allocations are discussed. The main advantages of the program as a general purpose code become apparent. Results of analyses as comparisons with other existing solutions are given, and running times which demonstrate the efficiency of the program are included.

Determination of heat flow shape factors for hollow, regular polygonal prisms

Abstract: Steady state heat flow in domains of regular polygonal shape with inner circular boundaries is analyzed. The method of conformal mapping is used and an approximate expression is derived for the shape factor.

In-plane vibration of continuous curved beams

Abstract: An analytical technique is developed for determination of the frequencies of continuous curved beams. A detailed analysis is carried out for periodically-supported beams. It is shown that in an infinite periodic beam, alternate passing bands and stopping bands exist, and in a finite periodic beam, all natural frequencies are in the passing bands. Simple formulae are derived for determining the frequencies of periodically-supported rings and continuous beams with the two extreme ends hinged-hinged, hinged-fixed, and fixed-fixed.

Offshore nuclear power plants

Abstract: Offshore Power Systems, a joint enterprise of Westinghouse and Tenneco, has been formed to manufacture floating nuclear power plants. Commitments for the first two offshore plants have been received from the Public Service Electric and Gas Company. This paper describes the floating nuclear plant concept with special reference to its advantages and its novel features. The novel features are a consequence of the floating aspect and include the design of the platform, the safety analysis and also the analysis and specification of plant motions due to environmental effects such as wind, waves and earthquakes. Site-related aspects such as the breakwater and mooring systems are discussed. The nuclear power plants will be manufactured in a central facility and this manufacturing concept is described.

Calculations of the transport of neutrons and secondary gamma rays through concrete for incident neutrons in the energy range 15 to 75 MeV.

Abstract: Earlier work by Alsmiller et al. considered coupled neutron and secondary-gamma-ray transport through a thick shield of silicon dioxide with 5% water by weight for neutron sources with energies of 50, 100, 200, 300 and 400 MeV. In that work, the approximation was made that gamma rays were produced only by neutron capture. In the present work, coupled neutron and secondary-gamma-ray transport through a thick shield of concrete for neutron sources with energies of 15, 25 and 75 MeV is considered. In this study, gamma-ray production for all interactions involving neutrons with energies up to 15 MeV was included; i.e., the approximation made here is that gamma-ray production can be neglected for interactions by neutrons with energies > 15 MeV. For incident neutron energies of 15, 25, 50, and 75 MeV, results of total and gamma-ray dose equivalents are given as a function of depth into the slab. For the 50- and 75-MeV incident neutron energies, the gamma-ray dose equivalent was found to be no more than 5% of the total dose equivalent at all depths considered (⩽ 1500 g/cm2). For the 15- and 25-MeV incident neutron energies, however, the gamma-ray dose equivalent dominates at greater depths into the slab. A conservative estimate of the effect of including gamma rays produced in interactions with neutrons of energies > 15 MeV indicates that the calculated total dose equivalent would increase by no more than 5%.

Coolant mixing in a fuel pin assembly utilizing helical wire wrap spacers

Abstract: Coolant mixing in a helically wire-wrapped, 217 pin, full-scale model of an LMFBR fuel assembly is presented. Salt-injection-conductivity techniques were employed, using water as the coolant. Over four hundred probes were concentrated in a one-sixth sector of the assembly to exhaustively measure the salt distribution. The basic results are presented for use in the verification of thermal hydraulic computer codes and wire-wrap mixing models. Interior channel gross mixing rates were about 9%/cm (effectively 3% per cm per gap); this was more than three times the natural turbulence level. There existed only a small peripheral (swirl) flow around the bundle; its direction averaged only slightly greater than half helical wire wrap angle. The results were reduced into an effective turbulent mixing model, and a wire-wrap forced diversion cross flow model is also presented.

A comparison of experimental methods for seismic testing of equipment

Abstract: Mathematical models of various types of electrical distribution equipment are generated from the results of forced vibration tests. The models are then subjected to four types of base motion input: digitized historical earthquakes, computer-generated artificial earthquakes, sine beats, and steady state sines. The responses of the various models to the different types of base motion inputs are presented and statistically analyzed. Aside from slight difference in the scattering of results and difference in the maximum response obtained which can be corrected using appropriate scaling factors, the results obtained using the earthquake-like base motion are found to be in fairly close agreement. With regard to sine beat and steady state sine testing, certain problems arise which must be considered if this type of analysis is to be substituted for analysis involving earthquake-like base motion.

On the convergence of a mixed finite element scheme for plate bending

Abstract: The convergence of a mixed finite element scheme for plate bending, previously proposed by the present authors, is discussed on the basis of functional analysis. First, the outline of the formulation is presented with some mathematical preliminaries. Then, several kinds of energy inequalities are established to assure the stability of the approximate solution. Thus, the rate of convergence may be obtained by the evaluation of the degrees of the completeness and consistency of the employed shape functions. Some remarks are also given with respect to the extension of the method to initial value problems.

Some geometrical properties of packings of equal spheres in cylindrical vessels

Abstract: Experimental and analytical methods are described for establishing some of the mean geometrical properties of unbiased random packings of equal spheres in cylindrical vessels. Experimental determinations have been made of the volumes of the spheres in an outer region of thickness equal to the sphere diameter, and in the remaining central region. Related properties, such as the mean void fractions of the two regions, can be calculated from these. Several preparation methods were used, including some which give rise to packings with axial or radial bias. A model is developed for computing the relevant properties of packings in a semi-infinite vessel with a plane wall. The model is then adapted to unbiased packings in cylindrical vessels, by means of quadratic equations whose coefficients depend on the cylinder-to-sphere diameter ratio. It is shown that commonly used preparation methods, such as placing or pouring spheres on the top surface, can result in packings with radial bias. Two methods of preparing unbiased random packings are described.

Simulation of strong motion earthquake effects on structures using explosive blasts

Abstract: This paper presents the results of three separate test programs which were conducted to determine the feasibility of simulating strong motion earthquake effects using dynamite blasting techniques. The three programs measured blast induced structural responses at: (1) the UCLA Field Station; (2) the Enrico Fermi Nuclear Power Plant, Monroe, Michigan; and (3) the experimental gas-cooled reactor facility (EGCR), Oak Ridge National Laboratory. The evaluation of the tests indicates that the simulation of strong earthquake excitations using subsurface blasting techniques is a valuable testing tool. Each of the three discussed tests indicate that reliable estimates of natural frequencies and mode shapes of vibration can be obtained directly.

Creep of a straight pipe under combined bending and internal pressure

Abstract: Several analyses are presented for the isothermal creep behaviour of a thin, constant thickness, circular crosssection cylindrical shell under the action of conbined bending and internal pressure loading. Results are presented in a way that should be helpful for general pipework design. Previous analyses are summarised and discussed.

Thermal analysis of plates with circular inclusions

Abstract: A least square boundary point matching method is employed to determine the temperature distributions and deformations of rectangular plates with circular elastic inclusions. Solutions for two problems have been obtained. The first problem is concerned with the determination of the temperature distribution in a finite rectangular plate having a circular inclusion and subjected to prescribed temperature distribution and thermal conditions along the edges. The plate is heated uniformly through the thickness. The second problem is concerned with the deflection and moment distribution in the same plate model with simply supported edges and prescribed temperature variation across the thickness but no temperature variation over the plate surface. Numerical results are presented.

The radii of surface nucleation sites which initiate sodium boiling

Abstract: Values for the radii of nucleation sites are calculated from incipient boiling superheat measurements obtained in several different experiments. The radii predicted by applying the pre-boiling pressure history theory to a new cavity model are in agreement with the experimental results.

Experimental determination of damping in nuclear power plant structures and equipment

Abstract: A summary of damping values for structures and equipment obtained in several full-scale dynamic tests performed on a research reactor, three experimental power reactor plants, and a commercial power reactor plant is given. The testing techniques used include steady state shakers, dynamite blasting, and snapback. In an appendix, guidelines are presented for required frequency resolution and record length for damping estimation from blast or snapback records. The influence of system non-linearity upon damping interpretations is also discussed.

Free vibrations of shells of revolution with variable thickness

Abstract: The partition method is used to formulate a set of equations which are used to calculate the natural frequencies and mode shapes of shells of revolution with variable thickness. Several examples are given for the cylinder and the hyperboloidal cooling tower. Results indicate that moderate variations in shell thickness do not appreciably affect the natural frequencies, but may significantly affect mode shapes.

Monte-Carlo simulation of gamma-ray backscatter soil density gauges

Abstract: The Monte-Carlo code OGRE-G is modified to calculate spectral and spatial distributions of the z-component of the backscattered gamma-ray current Calculation l procedures are developed and demonstrated for translating this current into the response of the most common types of gamma-ray soil density gauges Results were obtained for the four materials average soil, chalk, aluminum, and magnesium The source considered was 137Cs and six photon energies and 10 spatial distances were considered Parameters are given for an empirical model determined by a linear regression analysis of all the predicted current results The explicit dependence of the model on density could be specified by a technique involving translating the differential current to cumulative current and then reversing this process The results and procedures developed in this study should prove useful for the calibration of gamma-ray soil density gauges by determining the model constants from experimental responses on chalk, aluminum, and magnesium The results should also prove useful in the optimum design of these gauges

Forced vibration tests and analyses of nuclear power plants

Abstract: Methods for conservatively predicting the response of a constructed nuclear power plant to earthquake excitations are presented. This approach is based on experimental testing of the reactor plant and using test results to develop a mathematical model of the system. First, steady state forced vibration tests are conducted using structural vibrators attached to the reactor structure to determine dynamic response characteristics. Second, modal analysis applied on a digital computer is used to create a linear multiple-degree-of-freedom model that has dynamic response characteristics nearly the same as the physical system for the experimental inputs. Finally, the input force levels are extrapolated from the levels of the inertial vibrators to earthquake levels and the response of the model is calculated for strong-motion earthquakes. Tests have been conducted on three nuclear power plants: the experimental gas-cooled reactor (EGCR) at Oak Ridge, Tennessee; the Carolinas-Virginia tube reactor (CVTR) at Parr, South Carolina; and the San Onofre Nuclear Generating Station (SONGS), San Onofre, California. Analyses in varying detail have been performed; the most extensive work has been done at San Onofre. This article summarizes test results, dynamic models, and the results of seismic response calculations for each plant.

Monte-Carlo calculations for the subsurface gamma density gauge

Abstract: Some characteristics of the subsurface gamma density gauge are investigated by means of a Monte Carlo model. The model, which is one-dimensional and spherical, accounts for the effect of the shielding between source and detector in a simplified manner. The influence of Zeq, ZA and a finite volume of the measured medium on the gauge response is studied attentively. For densities above 1 g/cm3, the radius of the sphere of importance is about 26–40 cm and considerably large at lower densities. Attention is further paid to the dual-gauge concept with two different source-detector distances. Important advantages of this concept are diminished influence of Zeq and somewhat increased density measuring range, whereas longer counting times and a more complicated gauge configuration seem to be the main drawbacks. Good agreement between the calculations and measurements with the BASC gauge is obtained, if maximally two experimentally determined parameters are introduced.

Vertical soil-structure interaction of nuclear power plants subjected to seismic excitation

Abstract: The vertical soil-structure interaction problem is investigated by coupling an N -mass lumped mass structure to a two-dimensional elastic half space. This problem is formulated as an integral equation of the Volterra type. Numerical results are obtained by iteration for an idealized threemass two-mode model of a nuclear power plant containment structure. The effects of interaction are evaluated by comparing free-field acceleration spectrum response curves with similar curves determined from foundation motion.

A general theory for elastic solids with temperature dependent mechanical properties

Abstract: In this paper the linear theory of thermoelasticity is modified to include the case where the thermal and mechanical properties of the material depend on temperature. The study is motivated by a review of experimental data which clearly demonstrate that the properties of steel and aluminum vary significantly which moderate changes in temperature. The governing coupled equations are derived using the principles of mechanics and thermodynamics. The structure of the coupling between the temperature and strain rate is analyzed, and the requirements for uncoupling are discussed. The paper is concluded with the governing equations of the Airy stress function for thermal plane stress problems and the Helmholtz potential vector for three-dimensional problems.

On spectral treatment of actions of three earthquake components on structures

Abstract: The procedure proposed in a recent paper for applying response spectrum techniques to compute the simultaneous actions of three earthquake components is reviewed This paper argues that neither such a proposition is necessary, nor is the evidence conclusive enough to justify the change of a practice where the 3-D phenomena of the earthquake has long been recognized