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Preface

We (the contributing authors) collectively recognized the renewed relevance of nuclear power in the US, after decades of stagnation. We felt that it was imperative to develop an up-to-date, scholarly work on containment structures, incorporating the underlying regulations, safety significance, history, design philosophy, design experience, operating experience, and application to new design. It would benefit the nuclear industry as it transitions to a new generation of designers, constructors, and regulators. We think the book will be a valuable asset to the nuclear utilities, nuclear regulators, A/Es, and international organizations involved in the design and construction of nuclear power plants (NPPs).

With this basic purpose, coupled with my extensive experience in various aspects of NPP containment design, construction, inspection, and testing, principally, with the Nuclear Regulatory Commission (NRC), where I worked for the last 36 years before retiring in December 2010, I thought about developing this type of book in early 2010. As I wanted to explore historical background, as well as how and when of the nuclear reactors and containments, I first contacted Dr. Samuel J. Walker, the NRC historian, and requested him, if he could write this preface for the book, or help me construct the historical background related to nuclear reactors and containments. At the time (~June 2010), when I contacted him, he was preparing to retire from the NRC and told me that he could not find time to write such a preface. However, he assured me that I would find the required historical information in two NRC published books: (1) Controlling the Atom, and (2) Containing the Atom, the books, he was involved in authoring. Most of the historical background that I have compiled in the Preface and in Chapters 1 and 2 are based on the contents of these books.

Among a number of potential technical publishers, such as American Society of Civil Engineers (ASCE), American Society of Mechanical Engineers (ASME), American Nuclear Society (ANS), and Elsevier, I finally corresponded with ASME, because of my long-term association with ASME in the development of the standards related to the NPP containment structures. I had also realized that I am not an expert in various specialized subjects (e.g. severe accident considerations), I started looking for appropriate experts in these areas. Fortunately, I found these experts in National Laboratories, NRC, and in Nuclear Industry.

This preface provides an overview of the historical developments relevant to the content of the book. It briefly provides historical background related to the development of commercial use of nuclear energy, as well as a brief description of the physical processes involved during the operation of nuclear reactors.

In the late 1930s, scientists had discovered that when an atom of uranium was bombarded by neutrons, the uranium atom would sometimes split or fission. Later, the scientists found that when the atom of uranium fissioned, additional neutrons were emitted and became available for further reaction with other uranium atoms. These facts demonstrated that it was possible to device perpetual chain reactions. In December 1942, underneath the West Stands of Stagg Field at the University of Chicago, a team of scientists led by Enrico Fermi created man’s first controlled nuclear chain reaction. A crude reactor, remembered, as the first pile (CP-1), consisted of uranium embedded in a matrix of graphite. With sufficient uranium in the pile, the few neutrons emitted in a single fission may accidentally strike neighboring atoms, which in turn undergo fission and produce more neutrons. The atomic pile was controlled and prevented from burning itself by cadmium- plated rods which absorbed neutrons and stopped the process. The pile was square at the bottom and flattened sphere on the top. Around the pile, there was a tent of cloth fabric balloon provided so that the reactor could be sealed to minimize unproductive loss of neutrons.

Following the success of the CP-1 experiment, in February 1943, the U.S. Army moved the CP-1 pile to the south of Chicago, where it was reassembled as CP-2. CP-2 was considerably larger than CP-1, and had a 5-ft concrete shield building around it to protect the personnel working around the pile. The shield building can be termed as a containment structure that protected the general public and the staff against radiation hazard. However, readers should recognize that the early use of the technology was in developing atomic weapons during World War II. The neutrons that are produced in a fission reaction are fast neutrons and are less likely to cause fission than slower neutrons. As a consequence, in the most common type of power reactors, the kinetic energy of the fissionable neutrons is reduced to a value, where it is more likely to cause fission. This is accomplished by introducing a medium between the fuel rods that would slow down the fission neutrons. The medium used is called the moderator. Light water, graphite, heavy water, and other materials have been used as moderators in commercial and research reactors. Approximately, 90% of the energy released in a nuclear reactor manifests itself as heat energy near the point of fission in the core of the reactor.

Two major considerations associated with the products of fission process were (1) the products that include radio isotopes could damage the fuel elements and thus limit the time the fuel can be allowed to remain in the reactor, and (2) the fission products are the sources of most of the radioactivity in irradiated fuel. It is the second consideration that the reactor designers and operators have to control and provide containment for the fission products, under both the normal and abnormal conditions. Thus, maintaining adequate protection of the health and safety of the general public was a major requirement in exploring power reactor design for commercial use of nuclear energy.

The Atomic Energy Act of 1946, signed by President Truman, paved the way for transferring the function of civilian use of the Atom in the jurisdiction of Atomic Energy Commission (AEC). It was in December 1953, when President Dwight D. Eisenhower’s “Atoms for Peace” speech to the United Nations General Assembly, envisaged peaceful nuclear technology which would be made available to all nations under appropriate international controls. Subsequently, the 1954 Atomic Energy Act made it possible to encourage the commercial use of atomic energy in the U.S. for producing power.

The earlier reactors built as research and demonstration reactors, e.g. Hanford, Savannah River, and the Idaho National Laboratory Reactor Testing Station were located at remote locations away from the population centers. These reactors normally had concrete shield buildings enclosing the reactors for protecting the working personnel against ionizing radiation. However, some other AEC facilities, constructed in early 1950s, such as, Argonne Research Reactor, near Chicago, and the Submarine Intermediate Reactor at West Milton, NY, indicated the need for reliance on engineered safety features that would compensate for their proximity to population centers. The General Electric (GE), designer of the West Milford reactor, sets a major safety precedent by enclosing the reactor in a large steel containment structure. Later, the Argonne Research Rector was enclosed in a leak tight concrete building. Containment was also a major design feature of the Westinghouse designed Shippingport reactor. Except for a few experimental reactors, constructed at remote sites, and some gas-cooled reactors, all power reactor facilities in the United States after that time included provisions for containment structures, as the major safety features of the reactor facilities.

This book is devoted to the subject of containment structures in the United States. The following is a brief description of the content of this book.

Readers should note that “containment structure” is a part of the containment or containment system. Sometimes, these phrases (containment, containment systems) are used interchangeably with containment structure, as the final physical barrier that would prevent release of the ionizing radiation. Containments are also described as “containment vessels,” i.e., reinforced concrete containment vessels (RCCVs) and prestressed concrete containment vessels (PCCVs).

The book is divided into nine chapters. Each chapter describes specific aspect of containment structures. I am one of the seven prime contributors of the book. The four co-authors provided specialized inputs. The table below provides information regarding the chapter titles and the authors. It should be noted that Chapters 1 to 5 principally discuss History, Design, Construction, Inspection, and License Renewal aspects of operating reactors. Chapters 6 to 8 discuss more generic aspects of containment analysis under various loadings, and Chapter 9 discusses containment systems of Advanced Reactors.

Chapter Title

Author

Affiliation

Co-Authors

1. Evolution of Reactors and Containments

Hansraj Ashar

HKPrefessional, LLC

2. Regulatory Requirements and Containments

Hansraj Ashar

HKPrefessional, LLC

3. Design, Construction, Inspection and Testing of Containment Structures

Javeed Munshi

Bechtel Power Corporation

Shen Wang and Abdul Sheikh

4. 1 nservice Inspection and Leak Rate Testing of Containments

Hansraj Ashar

HKPrefessional, LLC

5. License Renewal and Aging Management for Continued Service

Dan Naus

Oak Ridge National Laboratory

Hansraj Ashar

6. Containment Structure Testing, Modeling and Degradation

Jason Petti

Sandia National Laboratories

7. Containment System Challenges Under Severe Accidents

Dana Powers

Sandia National Laboratories

Shawn Burns and Hansraj Ashar

8. Design Basis and Beyond Design Basis Considerations of Natural Phenomena

Nilesh Chokshi

Nuclear Regulatory Commission

Goutam Bagchi

9. Evolution of Containment Systems for Gen III Reactors

Jim Xu

Nuclear Regulatory Commission

As the chapters are authored by 11 individuals, it is possible that there may be some duplication of information. However, extreme care has been taken to avoid excessive duplication. Each chapter has its own figures, tables, and references. Some chapters may have appendices to address some special information relevant to the chapter. The following is a summary of each chapter.

In Chapter 1, the author describes the development of commercial nuclear power plants, concept of containment, and historical debates that took place in constructing NPPs. The chapter describes a short historical background as to how light water reactors (LWRs) became the accepted technology for commercial nuclear power plants in the U.S. The chapter also describes various types of reactors and containment structures and how various designs of leaktight containments were developed.

In Chapter 2, the author describes the historical concept of regulations developed to ensure public health and safety. The chapter discusses regulations that dictate various factors to be considered in designing, constructing, and maintaining the containment structures, so they can perform their intended function under various natural phenomena and design basis accidents. The chapter describes the regulatory framework and some of the regulations that are important for the integrity of the containment system as a whole. The chapter also describes how the containment related regulations are implemented.

In Chapter 3, the authors describe the design and construction requirements together with quality assurance requirements, preoperational inspections and tests used to ensure the adequacy of the constructed containment structures. Specifically, the authors describe in detail, how the containments are analyzed, designed, and constructed using the requirements of national codes and standards. The chapter also describes how the containment structures are tested for structural adequacy, and leak rate tested prior to the start of the plant operation. The authors briefly describe how the impactive and impulsive loads are considered in the containments of operating reactors and in the containments of the standardized Advanced Reactors.

In Chapter 4, the author describes in-service inspection (ISI) requirements for steel and steel-lined concrete containments, and periodic leak rate testing (LRT) of the containment structure, as well as that of the system piping penetrating the containment structure. In combination, the ISI and the LRT provide containment availability and reliability. The chapter describes how the deterministic ASME Code requirements, in combination with the regulatory requirements, have been successfully used to monitor the condition of the containment structure. As the regulatory requirements for performing the leak rate testing have been transitioned from the deterministic to the performance based requirements, the chapter provides detailed discussion of the performance based criteria. The use of risk-informed approach for LRT requirements has been discussed.

In Chapter 5, the author describes the regulation and guidance developed to review the applications for extending the operational life of containments of NPPs. The chapter describes how the regulatory requirements in 10 CFR Part 54 are implemented to ensure the integrity of passive components, such as the safety related structures and components. The author also points out the use of the guidance documents prepared by the NRC and the nuclear industry. For certain structural components, subjected to time limited behavior, such as metal fatigue, and prestressing tendon forces, the author discusses the logical process. For trending analysis of prestressing tendons (required for Time-Limited Aging Analysis — TLAA), Appendix 5A provides historical discussion of the process. Appendix 5B provides a detailed discussion of the major degradation found in the U.S. containment structures.

In Chapter 6, the author provides information on the small-scale and large-scale containment models tested to understand the containment behavior under severe (beyond design basis) accident loadings. The results of a number of tests have been scrutinized through consensus process to predict the potential behavior under beyond design basis loadings. The model tests have been conducted on small scale steel containments, as well as on large scale reinforced concrete and prestressed concrete containments. Based on the test results, attempts have been made to generate probabilistic model to arrive at the containment response to severe accidents. In the same chapter, the author has discussed the models with degraded containments to assess the response of various containment designs to severe accident loading. Finally, the author provides comparison of responses (in terms of fragility curves) for degraded and non-degraded containment structures.

In Chapter 7, the authors describe severe accident processes that threaten the containment are examined. Also, in this chapter, processes within the containment that affect the inventory of radioactive material suspended in the containment atmosphere and available for release, should there be a loss of structural integrity, are examined. This chapter principally describes (1) severe accident phenomena that load the containment, (2) source terms developed during and after the core melt, and (3) the regulatory requirements and guidelines provided to address severe accident threats.

In Chapter 8, the authors discuss how the NPP systems including containments are affected by the design basis, as well as low probability extreme natural phenomena, such as the low probability earthquakes and tsunamis. The chapter describes the historical perspective of the beyond design basis Natural phenomena, evolution of understanding the hazards, and methods for evaluating beyond design basis loadings. The chapter describes the use of containment capacity and fragility analysis in evaluating containment response to various beyond design basis loadings. The authors also discuss current initiatives following the Fukushima event.

In Chapter 9, the author defines the Advanced Reactors as Generation III/III+ reactors and provides their descriptions compared to the Generation II reactors, that is, the existing operating reactors. The author discusses: (1) design and analysis considerations for Standard designs, (2) technical considerations and challenges in structural designs for standardized design and analysis, and (3) containment features of Generation III/III+ reactors, that includes BWRs as ABWR, and ESBWR, and PWRs, as AP 1000, US EPR, and US APWR.

Hansraj Ashar

 
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