Numerical Prediction of Flow in a Nuclear Fuel Bundle With Various Turbulence Models

The numerical predictions using the standard and RNG k–ε eddy viscosity models, differential stress model (DSM) and algebraic stress model (ASM) are examined for the turbulent flow in a nuclear fuel bundle with the mixing vane. The hybrid (first-order) and curvature-compensated convective transport (CCCT) schemes were used to examine the effect of the differencing scheme for the convection term. The CCCT scheme was found to more accurately predict the characteristics of turbulent flow in the fuel bundle. There is a negligible difference in the prediction performance between the standard and RNG k-ε models. The calculation using ASM failed in meeting the convergence criteria. DSM appeared to more accurately predict the mean flow velocities as well as the turbulence parameters.

Design of Conical Shaped Charges for Prompt Initiation of TNT Chemical Munition Bursters

The Explosive Destruction System (EDS) has been designed at Sandia National Laboratories for the disposal of chemical munitions (phosgene, mustard gas, sarin etc.), many dating back to World War I. EDS is a portable system that is trailer mounted and consists of a vessel into which a chemical munition can be loaded and neutralized with linear and conical shaped charges. Gases are contained within the sealed chamber. The linear shaped charges split the munition in two and the conical is aimed at the explosive burster, in each munition, which is detonated by the shaped charge jet. Toxic chemicals remaining in the vessel following detonation are neutralized and disposed of. This paper documents the development of a new conical shaped charge (CSC) needed to reliably detonate explosive bursters in an expanding array of chemical munitions that are beyond what the device was originally designed to neutralize. Design of this new CSC was controlled by the need to deliver energy above the detonation threshold into the explosive after penetrating the outer steel casing, fluid, the burster casing and finally the explosive. Design considerations were driven by jet conditions at the steel/explosive interface inside the burster. Parameters to consider in CSC design include: 1) diameter, 2) liner thickness, 3) liner position in body, 4) explosive weight, and 5) liner shape or interior angle. The effects of these parameters on final CSC performance are examined in detail. CSC’s meeting the design specifications have been manufactured and tested. The performance of these charges is compared with the original design requirements.

Effect of Compressive Stress on Longitudinal Wave Speed in Cementitious Material

The Air Force has been interested for some time in the development of computer codes that accurately predict the penetrator trajectory created when munitions are fired into concrete and geomaterial targets, as well as the resulting depth of penetration. Recent work has focused on experimental research performed to determine quasistatic, dynamic, unconfined and confined material properties for development of an elastic/viscoplastic constitutive equation. This constitutive equation has shown some promise in predicting stress and strains but lacks a consistent damage parameter to predict damage or fractures exhibited by the target material during experimental impact tests. Current damage level predictors that employ a scalar damage parameter are not sufficient to predict the directional damage or fracture that occurs in simple uniaxial compression tests of concrete and geomaterials. Tensorial or directional damage parameters coupled with constitutive relations are necessary for better understanding and accurate prediction of damage exhibited when munitions impact concrete and geomaterials. The primary objective of the study described herein was to identify, quantify and characterize damage parameters associated with certain constitutive responses of cementitious and geologic materials. To that end, longitudinal wave speed and biaxial strain data were collected simultaneously on a series of grout cubes as they were being loaded to failure in uniaxial compression. The results of these tests, and a comparison to existing related data [1, 2] are presented.

Penetration of a Rate Sensitive Geological Target by the Compaction Ring Theory

In an earlier paper, the authors presented a theory for the penetration of geologically based semi-infinite targets [5]. This theory was suitable for application to targets in which compaction due to the crushing of voids is the primary deformation mechanism. This phenomenon has been observed in concrete targets with a ring of dense material around the tunnel region, see figure 1 for a cat scan of a concrete target after penetration. This was the motivation for the model development. A number of simplifying assumptions were made in the application of the theory to data from concrete penetration experiments. One of the assumptions was that the target strength was constant, or independent of strain and strain rate. This assumption leads to generally consistent results for the same ogive nose geometry. However, it was noted that there was a discrepancy between the strength predictions when two different ogive nose geometries were used. This paper investigates the discrepancy by assuming that the target material is rate sensitive. The results indicate that the strain rates in the target are indeed affected by the nose geometry. A detailed analysis for a target material with linear rate sensitivity is provided in the paper and the results provide a favorable comparison with available experimental evidence.

Measurement of Pressure Drop in a Liquid Metal Reactor Fuel Assembly

An experimental study has been carried out to measure the pressure drop in a 271-pin fuel assembly of a liquid metal reactor. The rod pitch to rod diameter ratio (P/D) of the fuel assembly is 1.2 and the wire lead length to rod diameter ratio (H/D) is 24.84. Measurements are made for five different sections in a fuel assembly; inlet orifice, fuel assembly inlet, wire-wrapped fuel assembly, fuel assembly outlet and fuel assembly upper region. A series of water experiments have been conducted changing flow rate and water temperature. It is shown that the pressure drops in the inlet orifice and in the wire-wrapped fuel assembly are much larger than those in other regions. The measured pressure drop data in a wire-wrapped fuel assembly region is compared with the existing four correlations. It is shown that the correlation proposed by Cheng and Todreas fits the best with the present experimental data among the four correlations considered.

Acoustic and Structural Modeling of Farley Main Steam Flow-Induced Vibration

Piping vibration has been observed in the Farley Unit 2 main steam system since plant start-up. Dynamic pressure and accelerometer data obtained during operation indicated that this was flow induced vibration. Acoustic modeling was utilized to evaluate potential origination locations of the pressure oscillation in the main steam system. Forcing pressure oscillations or “exciters” over a broad range of frequencies were imposed at various locations to simulate turbulent sources within the system. The relative magnitude of the acoustic response at the measured locations was compared to the data and used as a basis for determining the location of the source oscillation. The acoustic model was also used to generate forcing functions for a piping structural model that was used to evaluate measured accelerometer data.

Numerical Modeling of Fragmentation Characteristics of Explosive Fragmentation Munitions

Numerical simulations of explosive fragmentation munitions presented in this work integrate three-dimensional axisymmetric hydrocode analyses with analytical fragmentation modeling. The developed analytical fragmentation model is based on the Mott’s theory of break-up of cylindrical “ring-bombs” (Mott, 1947), in which the average length of fragments is a function of the radius and velocity of the ring at the moment of break-up, and the mechanical properties of the metal. The fundamental assumption of the model is that the fragmentation occurs instantly throughout the entire body of the shell. Adopting Mott’s critical fracture strain concept (Mott, 1947), the moment of the shell break-up is identified in terms of the high explosive detonation products volume expansions, V/V0. The assumed fragmentation time determined from the high-speed photographic data of Pearson (1990) had been approximately three volume expansions, the fragmentation being defined as the instant at which the detonation products first appear as they emanate from the fractures in the shell. The newly developed computational technique is applied to both the natural and preformed explosive fragmentation munitions problems. Considering relative simplicity of the model, the accuracy of the prediction of fragment spray experimental data is rather remarkable.

An Estimate for Mass Loss From High Velocity Steel Penetrators

Analytical models of the penetration process focus on estimating depth of penetration based on target density, target strength (sometimes associated with the unconfined compressive strength of the target for geological targets), the areal density of the penetrator (W/A), and the impact velocity. In this paper, an expression for work is used in conjunction with thermodynamic considerations to devise a simple estimate for mass lost by a high velocity projectile during the penetration process. The result shows that the mass loss is directly proportional to the tunnel length and the target shear strength. The constant of proportionality is not easy to deduce, however, in that it contains an unusual factor from the work analysis. A method for estimating target shear under high pressure from penetration experiments is introduced.

Numerical Analysis of Unsteady Conjugate Heat Transfer and Thermal Stress for a PWR Pressurizer Surge Line Pipe Subjected to Thermal Stratification

This paper addresses three-dimensional numerical analyses of the unsteady conjugate heat transfer and thermal stress for a PWR pressurizer surge line pipe with a finite wall thickness, subjected to internally thermal stratification. A primary emphasis of the present study is placed on the investigation of the effects of surge flow direction on the determinations of the transient temperature and thermal stress distributions in the pipe wall. In the present numerical analysis, the thermally stratified flows (in-surge flow and out-surge flow) in the pipe line are simulated using the standard κ-ε turbulent model and a simple and convenient numerical method of treating the unsteady conjugate heat transfer on a non-orthogonal coordinate system is developed. The unsteady conjugate heat transfer analysis method is implemented in a finite volume thermal-hydraulic computer code based on a non-staggered grid arrangement, SIMPLEC algorithm and higher-order bounded convection scheme. The finite element method is employed for the thermal stress analysis to calculate non-dimensional stress distributions at the piping wall as a function of time. Some numerical calculations are performed for a PWR pressurizer surge line pipe model with shortened length, subjected to internally thermal stratification caused either by insurge or outsurge flow with a specified velocity, and the results are discussed in detail.

An Experimental Study of Slip Behavior of Large Scale Model Tank

We recognized the importance of the seismic capability against earthquakes of the thermal power plant on the occurrence of the Hyogoken-Nanbu Earthquake in 1995. In this respect, seismic proving tests on the equipment of the thermal power plant had been planned and carried out. Vibration tests and FEM analysis were performed to demonstrate the seismic capability of the equipment. LNG tank was selected as one of the subjects. One of the remarkable nonlinear phenomena was lateral slip for an actual large tank. To investigate the slip behavior of the tank, vibration test of the large scale model tank and FEM analysis of actual tank were conducted. We estimated the slip behavior of the tank under severe seismic excitation. As the results, we confirmed that lateral slipping was mainly partial slip and total slip did not occur at severe seismic excitation.