Determination of Impurities in Nuclear Graphite by Chemical Methods
Abstract
Nuclear graphite is a type of graphite that is used in the production of nuclear fuels, such as uranium and plutonium, in nuclear reactors. It is one of the most important materials used in the power generation industry. However, it is also highly susceptible to contamination with other elements. This paper provides an overview of the types of impurities that can be found in nuclear graphite and the chemical methods available to determine their presence.
Introduction
Nuclear graphite is an isotropic graphite with a graphite-type structure composed of sp2 bonds and has a unique set of physical and chemical properties that make it ideal for use in the nuclear power industry. It is used in various components of nuclear reactors, including nuclear fuel elements, control rods, and the casing. Due to its high thermal resistance and low neutron absorption rate, nuclear graphite is essential for the safe operation of nuclear reactors. However, nuclear graphite is also highly susceptible to contamination with other impurities, primarily metal impurities such as nickel, cobalt, iron, and vanadium. These metal impurities can have a significant impact on the performance of the nuclear graphite and can result in safety issues if the concentration of the impurities exceeds certain limits. Therefore, it is important to have a thorough understanding of the types of impurities that are present in nuclear graphite and to ensure that the levels of these impurities are kept within acceptable limits.
Types of Impurities in Nuclear Graphite
The most common impurities found in nuclear graphite are metal impurities, and these can be present in various forms, such as dust particles, flakes and/or fine fibers. These metal impurities can be classified into three main categories: Trace, Minor and Major impurities.
Trace impurities include iron, nickel, cobalt, vanadium and chromium. These impurities are typically found in very small concentrations and, though not necessarily harmful, it is still important to keep the levels of these impurities within acceptable limits in order to ensure safety, as their presence may act as nucleation sites for further corrosion of the nuclear graphite.
Minor impurities include titanium, molybdenum, and manganese. These impurities are usually found in slightly higher concentrations than trace impurities and can cause changes to the graphite microstructure, which can lead to problems such as embrittlement or an increase in the neutron absorption rate.
Major impurities include aluminum and silicon. These impurities are typically found in much higher concentrations and can have a significant impact on the performance of the nuclear graphite. For example, silicon can increase the coefficient of thermal expansion and aluminum can promote corrosion.
Chemical Methods for Determination of Impurities in Nuclear Graphite
There are several methods available to determine the presence of the different impurities in nuclear graphite. These include wet chemical analysis and chromatographic techniques.
Wet chemical analysis typically involves the use of spectroscopic techniques such as atomic absorption spectroscopy and inductively-coupled plasma-optical emission spectroscopy (ICP-OES). The samples are treated chemically to produce an elemental analysis of the sample. This technique is usually used for the analysis of trace and minor impurities.
Chromatographic techniques, such as gas chromatography and high-performance liquid chromatography (HPLC), are used for the analysis of the major impurities. In this method, the samples are treated with a solvent to separate the various components and then analyzed to determine the concentration of each component.
Conclusion
Nuclear graphite is an important material used in the nuclear power industry and is highly susceptible to contamination with other elements. To ensure safety, it is important to have a thorough understanding of the types of impurities present in nuclear graphite and to monitor them regularly. Several chemical methods are available to determine the presence of impurities in nuclear graphite, including wet chemical analysis and chromatographic techniques.
