Environmentally Assisted Cracking Research of Engineering Alloys for Nuclear Waste Repository Containers
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Environmentally Assisted Cracking Research of Engineering Alloys for Nuclear Waste Repository Containers Raul B. Rebak GE Global Research, Schenectady, NY 12309, USA ABSTRACT All the countries that operate commercial nuclear power plants are planning to dispose of the waste in underground geologically stable repositories. The materials being studied for the fabrication of the containers include carbon steel, stainless steel, copper, titanium and nickel alloys. The aim of this work is to review results from research performed using the alloys of interest regarding their resistance to environmentally assisted cracking (EAC) under simulated repository conditions. In general, it is concluded that the environments are mild and that the studied metals may not be susceptible to cracking under the planned emplacement conditions. INTRODUCTION In the last decade many reports associated climate change to the release of greenhouse gases that may be generated by the burning of fossil fuels. The climate change debate has reignited the consideration of alternative sources of energy such as wind, solar, fuel cells and nuclear power. Of the alternative energies, the amount of electricity produced by nuclear power plants is definitely the largest; however the percentage varies from country to country, from 78% in France to 19% in USA to 2% in China [1]. Nuclear power produces the lowest amount of greenhouse gases of any type of energy [2]. However, nuclear power produces nuclear waste, which needs to be isolated from the environment for thousands of years [3]. All the countries currently operating nuclear power reactors agree that the best alternative to deal with nuclear waste is to bury it in a geologically stable repository. The hypothesis is that by the very nature of these geological sites, they will contain the waste for long times, limiting their spread, for example, through water flow. Commercial nuclear power has been around for 50 years; however no country is currently operating a nuclear waste repository [3]. The countries that have the most advanced concept for nuclear waste repositories include Finland and Sweden. In a nuclear waste repository the waste will be confined in metallic containers; which will be exposed to the environment at the repository. The candidate material for the external layer of the containers include a wide range of alloys, such as carbon steel, copper, titanium and nickel alloys [3]. CHARACTERISTICS OF THE PROPOSED REPOSITORIES More than 30 countries are currently studying the options for disposing of HLW in deep stable geologic formations, which will be the primary barrier for accomplishing this isolation [3]. All the repository designs also plan to delay the release of radionuclides to the environment by the construction of engineered barrier systems (EBS) which are planned to be installed to limit water reaching the repository and to restrict radionuclide migration from the waste. In all the repositories, the groundwater associated with the containers should be relatively benign to most materia
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