Nuclear power is unique from other thermal generation in that the heat source used to create the steam doesn’t result from combustion of a fuel, rather the heat is produced from a reaction within the fuel and the transformed energy is then extracted though heat transfer rather than combustion to create steam. The reaction within the fuel reduces or splits atoms to a smaller size. These atoms are retained within the fuel. This energy is transferred to water which is circulated within the reactor. This in turn creates the steam used to rotate the turbine generator.
An educational display shows a fuel bundle that could be used within a nuclear reactor in Figure 2. The fuel assembly consists of several thin long tubes. Each tube contains small cylindrical pellets stacked within the rod. These pellets are the nuclear fuel. Water flows past through the fuel bundle and removes heat created by reaction within the tubes. This water in turn is used to create the steam to rotate the turbine and produce electricity.
Figure 2, Fuel bundle.
All forms of thermal power generation utilize machinery such as turbines, condensers, heat exchangers, pumps, motors, valves and piping to connect these components into a system. This same type of machinery is typical to other industrial facilities. The lubrication engineer at a nuclear energy facility shares similar duties to his or her counterpart elsewhere. These would include goals of managing lube cleanliness while optimizing equipment reliability and machine efficiency. Notably, the Lubrication Engineer has some special additional duties.
A nuclear generating station has very specific design and quality of material requirements. This includes how lubricants are selected and later utilized. Each lubricant placed into service at the plant is carefully evaluated at the application level for expected performance and function. Lubricants are a vital but also a consumable part within a machine or system. Changes to the formulation constitute a change in the design of a part within the machine as the lubricant is a vital component of the machine. The lubricant changes are scrutinized and evaluated for compatibility and performance within the machine. An example of a nuclear energy plant is shown in Figure 3. The image contains 9 large cooling towers with plumes of evaporating water.
Formulation changes to lubricants unfortunately are common. Identifying these changes isn’t always obvious to the end user as product names will often be retained for the new formulation and the vendor provided product data information may or may not capture or announce changes have been made. The proprietary nature of lubricant formulations are an additional challenge to the evaluation process required of a lube engineer.
Figure 3, A three unit nuclear energy plant.
In addition to vendor notification of changes and to ensure that the exact product has been obtained; a receipt inspection to include qualification testing is another tool that can be used. Receipt inspection of parts and materials used in important machinery or systems ensures that the material meets the design. This is done by testing the material or parts to ensure they meet defined key characteristics. The extent of this testing and the instrumentation employed is established by the end user and may include technology such as Fourier Transform Infrared (FTIR), viscosity and elemental analysis. FTIR is an important tool used to identify the chemical fingerprint of the lubricant when it is received. When it is determined that the incoming lubricant does not match the expected chemical fingerprint of the material or if the lubricant fails other defined test properties, then the material if rejected for replacement or in the case of a discovered reformulation, the design process is used to determine if the lubricant meets its key performance and functional properties and characteristics.
A lubricant may be considered to have failed when one or more of its properties have failed. For example the failure could be related to the oil chemistry degrading, lube cleanliness or a loss of water separability. Radiation is a considered design element which can lead to the failure of a lubricant. The radiation environment can cause changes within a lubricant to include additive degradation and significant viscosity change. As such, radiation and its effects are a separate failure mechanism which is considered by the lubrication engineer at a nuclear energy site. Lubricants inherently have an extremely high tolerance in a radiation environment. In most cases, radiation is not the key environmental factor that degrades oil, although this must be considered. Commercially available lubricants have demonstrated acceptable performance when exposed to plant radiation environments.
Stewardship: We are citizens of the world and have a stewardship to use its resources in a careful and sustainable manner. This includes careful technical evaluation of technologies that reduce human impacts on the environment. The lubrication engineer is uniquely positioned to provide beneficial lubricant recommendations which directly relate to a reduction of friction and wear. When machine efficiency and its service life improve as a result, this directly decreases its impact to the environment and ultimately benefits the citizens of the world. This benefit is vital to the human enterprise and is an element of the lubrication engineer’s role that the lubrication industry should proudly promote and carefully manage.
LINK
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LUBE MAGAZINE NO.124 DECEMBER 2014
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