Influence Of Environmental Conditions And Proton Irradiation On Molten Salt Corrosion Of Metals

Author : Cody Falconer
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (138 download)

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Download or read book Corrosion in Molten Fluoride Salt written by Cody Falconer and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: As the concentration of greenhouse gases in the environment continues to reach levels that have never been recorded in history, the demand for low greenhouse gas emitting forms of energy is reaching an all-time high. With current public opinion and geopolitical changes occurring, Generation IV nuclear energy systems are ready to help transition energy production away from the consumption of fossil fuels. While not necessarily a new idea, the Generation IV Molten Salt Reactor (MSR) design has garnered a significant amount of interest from both government agencies and private companies alike, making it a critical reactor design for research.Originally developed in the mid-twentieth century, the MSR was successfully demonstrated by Oak Ridge National Laboratory, but little interest has been expressed in MSR designs until recently. In order for the development and deployment of MSRs to be successful today, there is a need for understanding how code-certified alloys, as well as new materials, are going to perform in a molten salt environment. A prototypical approach in literature at investigating the performance of materials in molten salt environments has become the use of static isothermal salt exposure testing cells. Unfortunately, there exists no standard method for these tests which has resulted in a large scattering of material data coming out of research efforts. Literature has suggested that this scattering is a direct result of variations in the design of the static isothermal salt exposure test cell. In this dissertation, several aspects that go into the design of static isothermal salt exposure test cells are studied to see how variations in the test cell can affect the material's behavior in these tests. The size of the test cell effectively creates a limit on a test parameter referred to as the volume of salt to exposed surface area ratio (Vol/SA). In this work, it is shown that adjusting this ratio results in dramatically different rates of corrosion in 316H stainless steel (316HSST) samples exposed to a LiF-NaF-KF salt mixture known as FLiNaK. At small ratios, the corrosion rate of 316HSST actually appears to plateau after only 500 hrs of salt exposure whereas a higher ratio continues corroding 316HSST beyond 1000 hrs. This result shows an obvious challenge then for determining the true behavior of 316HSST in FLiNaK salt. It is then speculated that a new way of ranking material's performance in salt qualitatively could be by determining the corrosion plateau time for a given material in a given Vol/SA ratio at a given temperature. Intimately tied to the Vol/SA ratio is the effect that the purity of the FLiNaK salt has on the material performance. Molten salts are highly sensitive to the levels of impurities in them and changes to the impurity levels can dramatically change how aggressive the salts are towards materials in them. In this dissertation, 316HSST was exposed to purified and as-received FLiNaK salt and it can clearly be observed that the purification process for the FLiNaK salt improved the corrosion rate of the 316HSST as a result of impurity removal. The final area of investigation in this dissertation was the effects that dissimilar materials have on one another when coexisting in the same FLiNaK salt. Traditional interaction mechanisms between dissimilar materials like galvanic coupling were shown to have little if no effect on the interaction of dissimilar metals submerged in FLiNaK. The main driving force for interaction of dissimilar materials in FLiNaK was demonstrated to be through a mechanism referred to as activity gradient driven mass transportation which is primarily enabled through the disproportionation reaction of corrosion products. Activity gradient driven mass transportation is accurately predicted through computational tools and is shown to dramatically alter how 304SST samples behave in FLiNaK. Additionally, this mechanism is expected to have a large effect on materials interactions with graphite in MSR designs, and a novel design for eliminating this interaction is investigated.