Phillip A. Pfeiffer

Post-test analysis for the nonlinear response of an internally pressurized one sixth scale reinforced concrete containment model

Abstract Pretest predictions have been previously made and reported by the Engineering Mechanics Program of the Reactor Analysis and Safety Division for the response of the one sixth scale reinforced concrete model tested by Sandia National Laboratories in July 1987. A series of axisymmetric models were studied with the two-dimensional computer program TEMP-STRESS. This report describes the comparison between the pretest predictions and the experimental results; a post-test analysis with a precracked concrete model is also compared to the pretest predictions and the experimental results. The post-test analysis is in excellent agreement with the experimental results. Explanations are given for the apparent precracked state of the containment vessel.

Concrete cracking simulations for nuclear applications

Abstract The need to understand concrete behavior under high temperatures in the nuclear industry has become rather acute. Previously, concrete has been used in nuclear industry as inexpensive material for construction and also for radiation shielding. Presently, we are concerned with the structural integrity of the containment, subject to accidental exposure of concrete to excessively high temperatures and chemical attack. Consequently, we are now seeking basic understanding of concrete behavior at extreme environmental condition. Indispensible in mathematical modeling of concrete behavior is the constitutive relation. A constitutive model developed by Takahashi [1] has been incorporated into the coupled thermal-stress analysis code, TEMP-STRESS, which gives the stress-strain relation up to the point of cracking. This paper describes the modeling of cracking behavior. Four crack propagation criteria: the J-integral, the energy release rate, the effective strength and the failure surface criterion are examined. Several numerical examples are given. Situations under which one method might be more convenient to use than the others are discussed.

Modeling of containment structures on high performance computers

With recent advances in parallel supercomputers and network-connected workstations, the solution of large scale structural engineering problems, such as containment structures, has now become tractable. High-performance computer architectures, which are usually available at large universities and national laboratories, now can solve large nonlinear problems. At the other end of the spectrum, network connected workstations can be configured to become a distributed-parallel computer. A description of the development of a parallelized finite element computer program for the solution of static nonlinear structural mechanics problems is presented here. Also, a finite element methodology is presented for use in finding the structural capacity of reinforced concrete structures. The method is applicable to both cylindrical and rectilinear geometries. Containment structures for nuclear reactors are the final barrier between released radionuclides and the public. Containment structures are constructed from steel, reinforced concrete, or prestressed concrete. US nuclear reactor containment geometries tend to be cylindrical with elliptical or hemispherical heads. The older Soviet designed reactors do not use a containment building to mitigate the effects of accidents. Instead, they employed a sealed set of rectilinear, interconnected compartments, collectively called the accident localization system (ALS), to reduce the release of radionuclides to the atmosphere during accidents. As an illustrative example, the methodology developed herein is applied to a generic VVER-440/V213 design subjected to internal overpressure.

Free drop impact analysis of shipping cask

Abstract The WHAMS-2D and WHAMS-3D codes were used to analyze the dynamic response of the RAS/TREAT shielded shipping cask subjected to transient leadings for the purpose of assessing potential damage to the various components that comprise the cask. The paper describes how these codes can be used to provide an intermediate level of detail between full three dimensional finite element calculations and hand calculations which are cost effective for design purposes. Three free drops were addressed: (1) a thirty foot axialdrop on either end; (2) a thirty foot oblique angle drop with cask having several different orientations from the vertical with impact on the cask corner; and (3) a thirty foot side drop with simultaneous impact on the lifting trunnion and the bottom end. Results are presented for two models of the side and oblique angle drops; one model includes only the mass of the lapped sleeves of depleted uranium (DU) while the other includes the mass and stiffness of the DU. The results of the end drop aalyses are given for models with and without imperfections in the cask. Comparison of the analyses to hand calculations and simplified analyses are given.

Reinforced flexural elements for TEMP-STRESS program

Abstract The implementation of reinforced flexural elements into the thermal-mechanical finite element program TEMP-STRESS is described. With explicit temporal integration and dynamic relaxation capabilities in the program, the flexural elements provide an efficient method for the treatment of reinforced structures subjected to transient and static loads. The capability of the computer program is illustrated by the solution of several examples: the simulation of a reinforced concrete beam; simulations of a reinforced concrete containment shell which is subjected to internal pressurization, thermal gradients through the walls, and transient pressure loads. The results of this analysis are relevant in the structural design/safety evaluations of typical reactor containment structures.

Pretest analysis of a 1:6-scale reinforced concrete containment model subject to pressurization

Abstract Pretest predictions were made by the Reactor Analysis and Safety Division of Argonne National Laboratory for the response of the 1 :6-scale reinforced concrete model to be tested by Sandia National Laboratories. For this purpose a series of axisymmetric models were studied with the two-dimensional computer program TEMP-STRESS and a three-dimensional circumferential segment model with the program NEPTUNE. The two-dimensional models predicted failure at 175–190 psig (1.207–1.310 MPa). However, two different failure mechanisms were indicated: (1) hoop failure of the vessel at midheight following failure of a splice in this area, (2) failure of a weld in the liner near the basemat due to excessive strains. The three-dimensional model predicted failure at an internal pressure of 180–185 psig (1.241–1.276 MPa) by failure of the splices of the hoop rebars just above cylinder midheight in a region away from the equipment hatch opening.