In the past, nuclear power plant (NPP) life requirements were 30 - 40 years. Today, those requirements have doubled as new NPPs need a 60-to-80-year design life. Factor in the emergency diesel generators (EDG) and station blackout generators (SBOs) that could have been built several years prior, as well as the need to be ready to run during the decommissioning phase, and we could be in a range of a 70-to-90-year design life. Today’s blog will focus on the impact of requiring a longer life design for the EDGs and SBOs as a consequence of the evolution of NPPs.
Much time and effort is spent on a new nuclear project reducing the early-hour failures, including multiple quality checks, numerous verifications and extensive testing just to name a few. However, we’ll only concentrate on approaching the ‘acceptable’ level of failure for the purpose of this blog.
To maintain reliability for an EDG/SBO over 70-90 years, there are three options that that should be considered:
Keep the units in operation for the entire duration of the design life.
Replace the units at some point, perhaps midlife, with newer units.
Add a new diesel engine-driven system to supplement the existing units.
Each option has benefits and downfalls, so it’s important to assess your individual circumstance to determine which direction is best for you.
Maintain Existing Units
Aging is inevitable and keeping a generator set in peak operational condition can be daunting. This approach consists of proactively performing regular and predictive maintenance at specific intervals in an attempt to preserve acceptable reliability.
This path generally leads to obsolescence and or supply issue. A major challenge is change in suppliers over time, which can complicate the process of getting validated parts. Also, as the unit ages there is usually more work to perform and in some cases not enough time to perform the actual work without getting a special permit or in some cases requiring the shutdown of the reactor.
Some NPP operators consider adding ‘Swing Diesels’ in order to buy enough time for maintenance procedures on existing EDGs and SBOs. While this can address the time issue, the costs are not low, and you’ll still have to solve the problem of keeping the generator sets running during maintenance.
Completely removing the major equipment and replacing it with new EDGs/SBOs has its benefits. For example, the newer equipment can relieve the operator of obsolescence and/or supplier issues, and comply with new regulations or meet new plant requirements, such as having more power available for emergency loads.
On the other hand, facility managers could find that the equipment cannot fit into the available space in the existing power station or that timing the replacement is difficult if the NPP has to be offline. Most refueling opportunities are accomplished in just a few weeks, which isn’t enough time to perform the removal and replacement of equipment. Alternatively, extended outages, such as the mid-life plant refurbishment projects, may be an option.
Another factor to consider is the capability of sufficient redundancy when replacing the generators while the NPP is operational. If it is, that makes the project much easier. If not, facility managers should use portable backup generators during the removal, installation and commissioning to maintain operation.
Adding to an Existing NPP
Instead of focusing solely on maintenance or replacement, adding equipment to existing EDGs/SBOs is another viable option. Utilizing new equipment can alleviate any obsolescence, regulatory or supplier issues while improving reliability at the same time. With a fresh start, facility managers can begin with a design that includes concepts from the latest strategies.
Space restrictions are the biggest concern with this strategy as it may be too crowded around the reactor to install a new system and building. Also, new procedures will have to be created and training will have to be considered.
Which Option is the Best Fit?
Facility managers should conduct ongoing analyses of the maintenance costs, system reliability and supplier services to accurately analyze nuclear power plants. There may be a point when one of the options listed above makes sense in terms of cost, reliability or both. The key is to determine whether or not that point will occur within the lifetime of the NPP, and proactive planning is the best way to stay ahead of equipment aging.