By: Erica Libra-Sharkey
From the US Department of Energy, Office of Nuclear Energy, “The demanding environments of an operating nuclear reactor may impact the ability of a broad range of materials to perform their intended function over extended service periods. Routine surveillance and repair/replacement activities can mitigate the impact of this degradation; however, failures still occur. With reactors being licensed to operate for periods up to 60 years, with further extensions under consideration, and power uprates being planned, many of the plant systems, structures, and components will be expected to tolerate more demanding environments for longer periods. The longer plant operating lifetimes may increase the susceptibility of different systems, structures, and components to degradation and may introduce new degradation modes.
While all components potentially can be replaced, decisions to simply replace components may not be practical or the most economically favorable option. Therefore, understanding, controlling, and mitigating materials degradation processes and establishing a sound technical basis for long-range planning of necessary replacements are key priorities for extended nuclear power plant operations and power uprate considerations. https://www.energy.gov/ne/materials-aging-and-degradation”.
By: Edward Dougherty
Has the heat conversion efficiency of your heat exchangers degraded? Is the flow of your cooling water system being impeded? Are you repairing or replacing equipment due to localized corrosion causing through-wall failure? Inefficiencies and equipment failures are big problems in any industrial process, but the cause of the problem may be smaller than you think. You might have a biofilm problem. Bacteria floating in a cooling or process water can become colonies on wetted surfaces and can form robust biofilms over remarkably short times. Biofilms are collections of living and dead cells that are enclosed in an extracellular polymeric substance matrix secreted by living organisms. The unchecked growth of biofilms can significantly decrease thermal efficiency on surfaces as the biofilm acts as an insulating layer. Highly localized chemical effects can also be created that lead to microbiologically influenced corrosion (MIC).
By: Gerry Davina
The modernization of plant automation controls represents a step change in performance that optimizes Operations and Maintenance resources, shifting their focus to performance maintenance and plant monitoring and away from inefficient corrective maintenance and troubleshooting.
According to the U.S. Energy Information Administration, the average age of the U.S.-based nuclear power plant is approximately 38 years old. Three of the “youngest” plants (Watts Bar, Nine Mile Point 2 and River Bend) all began construction in the mid-1970’s with their designs approved years earlier. In terms of industrial control systems, this means that most, if not all, of the plants in the U.S. nuclear fleet, continue to operate with 1970s in automation equipment and technology. Although it can be argued that the equipment and technology have proven to stand the test of time, the reality of the digital age, with low cost and high-powered processors, is that relay-based control systems are long-obsolete and no longer practical for any automation system that requires more than a handful of relays and switches. In an industry that has publicly advocated a commitment to improved reliability and efficiency, ironically, the most evident impact for any plant with the continued use of 40-year-old automation equipment and technology is poor system reliability and inefficiency burdening both Operations and Maintenance resources.
By: Ed Dougherty and Al Jarvis
for Bottom Tubesheet Filter/Demineralizers Initial Installation and Performance at Browns Ferry Nuclear StatioThe Browns Ferry Nuclear Station (BFNS) intends to implement an extended power uprate (EPU) at all three units beginning in 2018 for Unit 3 and Unit 1, and in 2019 for Unit 2. EPU implementation will increase the total thermal power of each unit by 494 MWth resulting in a total uprate of 20% from the originally licensed thermal power of 3293 MWth.
Each BFNS unit is currently designed with ten bottom tubesheet condensate filter/demineralizers (CF/Ds) in the condensate treatment system that require an application of a powdered resin precoat to perform the function of demineralization. The precoat material is applied as an overlay on top of vertical filter septa. The filter septa have an inner pleated area, and with a precoat overlay, perform the function of demineralization as well as particulate iron removal. In the absence of circulating water leakage into the condenser, the primary function of the CF/Ds is to remove particulate iron that collects in the condenser hotwell. The iron source is from the corrosion of carbon steel piping and components in contact with main steam and heater drain systems.
By: Jen Jarvis and Al Jarvis
Nuclear plant workers accrue most of their radiation exposure during refueling outages, when many plant systems are opened for corrective and preventive maintenance. The total refueling outage radiation exposure can be 100-200 person-Rem at a typical Boiling Water Reactor (BWR), and 30-100 person-Rem at a typical Pressurized Water Reactor (PWR). Accrued refueling outage radiation exposure values can be significantly greater than these values depending upon radiation fields, outage work scope, and emergent work. Outage radiation exposure is one metric used by a plant to determine outage success and by industry regulators in assessing the overall performance of a plant. Plants with high personnel radiation exposure tend to be those plants with more equipment problems and more unscheduled shutdowns; consequently, they may be subjected to increased regulatory oversight.
Radiation source term assessments are performed to understand the causes of high collective radiation exposure and to help plants evaluate their strategies for source term reduction. This involves understanding how a plant’s material choices and chemistry and operational history influence the radiation fields that develop in the plant systems. Consequently, a source term evaluation is very plant-specific, but can help a plant identify which strategies may be most effective for their specific situation.
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