Nuclear Containment Structures Research Articles

Leakage behavior of inflatable seals subject to severe accident conditions

Abstract The paper describes tests to determine the leakage behavior of inflatable seals when subjected to containment pressures that exceed the design basis. 2 Inflatable seals are used to prevent leakage around personnel and escape lock doors in about 10% of the commercial nuclear power plant containment structures in the United States. All of the installations are in either Pressurized Water Reactor (PWR) or Boiling Water Reactor (BWR) Mark-Ill type containments. This work is a part of an overall effort at Sandia National Laboratories to develop proven techniques for evaluating the performance of Light Water Reactor (LWR) containment buildings for beyond design basis loadings. Inflatable seals were tested at both room temperature and at elevated temperatures representative of postulated severe accident conditions. Parameters that were monitored and recorded during each test were the internal seal pressure and temperature, chamber (containment) pressure, leakage past the seals, and temperature of the test chamber and fixture to which the seals were attached. An empirically based, analytical method is presented to predict the containment pressure at which significant leakage past inflatable seals can be expected.

Reliability-based design code calibration for concrete containment structures

The safety of concrete nuclear containment structures should be secured against all kinds of loading due to various natural disasters or extraordinary accidental loads. Furthermore, the current design criteria or load combination criteria of concrete containment structures in Korea are not based on the probability-based design concept but rely on the conventional design concept. In this study, a load combination criteria for design and a probability-based reliability analysis were proposed on the basis of a FEM-based random vibration analysis. The limit state model defined for the study is a serviceability limit state of the crack failure that causes the emission of radioactive materials, and the results are compared with the case of strength limit state. More accurate reliability analyses under various dynamic loads such as earthquake loads were made possible by incorporating the FEM and random vibration theory, which is different from the conventional reliability analysis method. The uncertainties in loads and resistance available in Korea and the references were adapted to the situation of Korea, and especially in case of earthquake, the design earthquake was assessed based on the available data for the probabilistic description of earthquake ground acceleration in the Korea peninsula. The SAP V-2 is used for a three-dimensional finite element analysis of concrete containment structure, and the reliability analysis is carried out by modifying HRAS reliability analysis program for this study. In this study, the load factors for the design of concrete containment structures in Korea are proposed by considering appropriate load combination criteria for design, and the results are compared to the present those of ASME code.

Cracking of P/C Nuclear Containment Structures

Rules for determining the spacing and widths of both through-the-wall and surface cracks in post-tensioned concrete containment structures under internal pressure are presented. These involve the construction details and the average strain obtained from an analysis that accounts for concrete properties in the post-cracking range. To evaluate these rules and the concrete constitutive relationship used in the analysis, twelve quarterscale segments were designed to simulate construction and stress conditions at various locations of a containment structure. Major variables included ratio of prestressing, concrete cover, reinforcement spacing, lap splices and combined axial load and moment. It was observed that the crack spacing depended on the spacing of the reinforcement and prestressing tendons parallel to the cracks and that the final crack pattern was fully developed at the yield strain of the reinforcing steel. Concrete cover was not found to have a significant influence on crack spacing. The procedures developed to determine crack spacing and widths are used to predict the cracking of a one-fourteenth scale model of a containment structure tested later in the research project.

Failure of stiffened steel liners for nuclear reactor containment structures under construction

This paper presents a study of the behavior of stiffened steel liner plate for nuclear containment structures when subjected to wet concrete loading during construction. The presentation is focused on the failure criterion of the liner plate. Such failure will depend on the wet concrete pour height and thickness, loading distribution, rate of concrete placement and the arrangement of the stiffener.

Non‐linear rocking response of model containment structures

AbstractSmall (1/24‐ to 1/8‐size) nuclear containment structures were subjected to ground shaking from buried explosions and to oscillating forces. The apparent natural frequency or resonant frequency of rocking varies inversely with amplitude of the shaking. The present paper describes an explicit finite difference model of soil‐structure interaction induced by explosive loading. The results indicate that non‐linear rocking response is primarily a result of debonding‐rebonding and compaction of soil at the soil‐structure interface. Measurements of dynamic interface stress and post‐test inspection of the interface region tend to confirm these findings.

Mixed domain analysis of nuclear containment structures using impulse functions

An alternative method to analyze containment structures of Boiling Water Reactor (BWR) Nuclear plants is proposed. The proposed method reduces the computer cost and provides sufficient accuracy for the analysis of containment structures for hydrodynamic loads, which have a wide spectrum of frequency variation and are duration in excess of 5 sec. An impulse function time history of duration shorter than the actual forcing function duration is used in time-domain analysis to generate system characteristics functions or transfer functions for a linearly elastic multi degree of freedom structural system. The functions are then used in a frequency-domain analysis along with the Fourier transform of the actual input forcing function time history to obtain the response time histories at various points in the structures. Results of the analysis using a conventional time-history approach and the proposed method are compared to show that the accuracy is within 5%, while the cost advantage is significant for the proposed method.

Design considerations for concrete nuclear containment structures subjected to simultaneous pressure and seismic shear

Improvements in design code provisions for tangential shear in secondary concrete nuclear containment vessels are needed. This paper presents a brief summary of an experimental research program conducted at Cornell University on tangential shear. Six inch thick reinforced concrete panels were subjected to combined in-plane tension and shear as a behavioral model of a section of the wall of the containment under the combined loading of internal pressurization and seismic shear. Approximately 50 panels were tested. Parameters studied included: tension level and direction (biaxial or uniaxial), shear level and type (monotonic, cyclic, or a combined mode), sequence of applied loading, and reinforcing ratio and orientation. The results of the research indicate that current code provisions are overly conservative with regard to the amount of tangential shear to be carried by the orthogonally reinforced concrete. By increasing the allowable stress, the required amount of diagonal reinforcing would be reduced. This would result in savings in fabrication costs and construction time, and improved structural reliability through improved concrete placement. The research also indicates a need for a more exact consideration of containment displacements. Shear stiffnesses for the panels were extremely low, indicating that containment displacements may be larger than anticipated. The code provisions in this area are limited and unsubstantiated.

Application of frequency domain analysis to transient response of nuclear containment structures

A combination of frequency domain and time domain analyses is proposed to obtain the dynamic responses of nuclear power plant containment structures. A soil-structure model of a boiling water reactor containment subjected to an assumed safety relief valve blowdown load is used as illustration. Linear time-invariant systems are analyzed using input forcing functions with varying frequency contents. Time domain analysis is performed using a synthesized input forcing function. The system characteristic function is generated in the frequency domain through Fourier transforms of the response time history and the synthesized input time history. The frequency response due to any other forcing function is obtained in frequency domain by using the system characteristic function, and the response time history is obtained by inverse Fourier transforms of the frequency response. The results obtained by the proposed method are in close agreement with the conventional time domain dynamic finite element analysis.

Research requirements for improved design of reinforced concrete containment structures

Reinforced concrete is a competitive material for the construction of nuclear power plant containment structures. However, the designer is constrained by limited data on the behavior of certain construction details which require him to use what may be excessive rebar quantities and lead to difficult and costly construction. This paper discusses several design situations where research is recommended to increase the designer's options, to facilitate construction, and to extend the applicability of reinforced concrete to such changing containment requirements as may be imposed by an evolving nuclear technology.

Prestressed Concrete Nuclear Plant Containment Structures

A lthough prestressed concrete nuclear plant containment structures came into prominence only about 10 years ago, nevertheless, their design and construction features have undergone rapid development. So much so, that in this short time period we can identify three generations of evolution in containment design and construction practice. This paper will review past and present containment concepts and point to what we can expect in the future.

Development of the Report

Committee 344 was established in 1961 with a mission that included nuclear containment structures. However, early in the assignment, the mission was changed to read as follows: Develop a recommended practice for design and construction of circular prestressed-concrete structures such as water-containing structures and bulk storage structures. Particular attention shall be given to the protection of prestressing wire from corrosion.

WEDGE ANCHORAGE SYSTEM FOR STRAND POST-TENSIONING

The need for a new high capacity strand post-tensioning system in the United States, was apparent by late 1967. The demand for long span, cast-in-place post-tensioned structures in the United States seemed certain to expand rapidly, and comparative costs of tendon materials indicated that strand would economically meet this growing need. Pullthrough tendon systems, which require neither fixed tendon lengths nor factory-attached anchorages, have considerable cost advantages for long span cast-in-place bridges, buildings, and nuclear reactor containment structures. Existing European pull-through tendon systems were well represented in the United States and licenses were unavailable. In response to these factors the authors began development of the S/H Wedge Anchorage System.

PWR Containment Structures Design Experience

The design philosophy being used in the construction of a number of concrete nuclear power reactor containment structures is analyzed. A brief description of the pressurized water reactor (PWR) thermal generating system is also presented. Loading and stress criteria as well as the engineered safeguard systems currently being employed are summarized in detail. Specific comparisons between design parameters for four containment structures are presented in tabular form for ease of reference.

Prestressing systems for secondary and primary containment structures

Prestressing systems used in primary and secondary concrete containment structures are reviewed, along with the implications of various systems with respect to design construction and surveillance. There will be illustrations of existing installations and testing. Bonded and non-bonded post-tensioning for nuclear containment structures will be discussed.