Nuclear power corrosion problems

Nuclear and magneto-hydrodynamic electric power generation systems have been produced on a scale which could lead to industrial production, but to-date technical problems, mainly connected with corrosion of the containing materials, has hampered full-scale development. In the case of nuclear power, the proposed fast reactor, which uses fast neutron fission in a small nuclear fuel element, by comparison with fuel rods in thermal neutron reactors, requires a more rapid heat removal than is possible by water cooling, and a liquid sodium-potassium alloy has been used in the development of a near-industrial generator. The fuel container is a vanadium sheath with a niobium outer cladding, since this has a low fast neutron capture cross-section and a low rate of corrosion by the liquid metal coolant. The liquid metal coolant is transported from the fuel to the turbine generating the electric power in stainless steel... 

Intake water tunnels are generally made from concrete, and absorption of water by concrete is the main reason for corrosion in reinforcement. In intake structures the problems are due to concrete failure from salts penetrating into the concrete and corroding the rebar. Hard, dense concrete with ample cover to reinforcement and without cracks and porosity has good resistance to corrosion against seawater. In Indian nuclear power plants, the experience with concrete intake tunnels with respect to corrosion behavior is not bad except that special care is required for protection against algae, clams, mussels, etc. which attach to the tunnel surface. 

The primary motivation for predicting the electrochemical properties of the coolant circuits of water-cooled nuclear power reactors has been that of explaining and predicting tenacious operating problems that include SCC and CF, mass transport of corrosion products and subsequent fouling of heat transfer surfaces, activity transport due to the movement of neutron-activated radionuclides from the core to out-of-core surfaces that are not shielded, and, in the case of PWRs, the axial offset anomaly (AOA). This latter phenomenon results from the deposition of boron... 

As an industrial problem stress corrosion cracking is of considerable importance. There is a long history of major and minor failures, particularly in the chemical industry and in the transport industry, particularly of components in ships and planes. It is a major potential source of failure in the nuclear power industry in which, for excunple, austenitic stainless steels may fail in high purity water containing oxygen and chloride ions at the level of ppb. 

The total cost of material fracture is about 4% of gross domestic product in the United States and Europe (88,89). Fracture modes included in the cost estimates were stress-induced failures (tension, compression, flexure, and shear), overload, deformation, and time-dependent modes, such as fatigue, creep, SCC, and embrittlement. The environmentally assisted corrosion problem is very much involved in the maintenance of the safety and reliability of potentially dangerous engineering systems, such as nuclear power plants, fossil fuel power plants, oil and gas pipelines, oil production platforms, aircraft and aerospace technologies, chemical plants, and so on. Losses because of environmentally assisted cracking (EAC) of materials amount to many billions of dollars annually and is on the increase globally (87). 

This industry has most of the corrosion problems of other industries and some that are all of its own. Right from the start, the potential for disaster was recognized and tackled by using high-grade materials in many parts of the systems. Zirconium alloys were needed, which had their own corrosion problems and solutions. Growing worldwide demands for acceptable environmental performance have alienated others to the cause of nuclear power, in particular, after events at Three Mile Island and Chernobyl. 

The widespread use of welding has increased the number of corrosion problems. The development of industrial sectors like nuclear power production and offshore oil and gas extraction has required stricter mles and control. 

New designs and new types of advanced nuclear power plants (e.g., supercritical steam) present the same need for in-depth understanding of corrosion processes and the associated means to control corrosion s detrimental effects. Indeed, for new plant concepts, knowledge gained from current R D should be used prescriptively (rather than remedially and reactively, as in earlier generations of plants) in the design of components and control systems to avoid operational problems from... 

Because of the intensive research and application of the research to problem correction, over 90 % of these corrosion problems are understood, the mechanisms and root causes can be identified, and there are engineering solutions to these problems. Major contributions have been made by Electric Power Research Institute, main vendors of equipment, and by technical societies such as ASME 4], the American Society for Materials International (ASM) [5], ASTM, American Nuclear Society (ANS), and the National Association of Corrosion Engineers (NACE). 

The materials in a conventional power plant have to be capable of operating reliably under conditions of high temperature and pressure and of withstanding chemical corrosion for long periods of time. These problems are well understood on the basis of extensive experience. The nuclear power plant, however, introduces a range of new problems associated with the use of materials in a high radiation environment. 

The total cost of the listed items is approximately 11.7 billion or 76 percent of the total 15.4 billion cost of corrosion for 1998. The balance of the corrosion cost ( 3.7 billion) likely stems from many miscellaneous less costly corrosion problems. As shown in Table 8.10, corrosion costs in the nuclear power and fossil steam power sectors dominate corrosion costs in the electric power industry. The very large cost problems in the nuclear and fossil sectors at the top of the list warrant serious attention. 

The Nuclear Navy provided an enormous impetus to the development of the PWR type. Rickover used a parallel path development program to ensure that the Navy achieved a nuclear, air-independent propulsion system that would revolutionize submarine technology. By investigating both the PWR and sodium cooled reactor, Rickover managed to create an organization that produced the nuclear powered Nautilus in the 10-year period from the end of World War II until the submarine s launch in 1955. In the end the PWR became the dominant, and indeed sole propulsion system adopted by the Navy. The corrosion problems associated with the sodium coolant led to it falling into disuse. 

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