Three Ways to Improve Nuclear Power Plant Lifetimes

by Administrator on ‎11-07-2016 09:00 AM

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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.

 

Replacing Equipment

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. 

 

For more information, visit us online at www.cat.com/powergeneration or contact your local Cat® dealer.

 

  • What has your experience been with aging nuclear power plants?
  • What other ways can facility managers extend nuclear power plant equipment?
  • How can Caterpillar help improve nuclear power plant lifetimes?

Comments
by Super Contributor
on ‎12-26-2016 01:34 PM

While dong a contract job for CAT many years ago in Armenia at their nuclear plant (Russian built, supposedly same design as Chernobyl) a group of us got togther for dinner one evening and had a discussion on this very topic. Here as some of the comments from that discussion.

 

A prime mover designed for ultra critical applications should first and foremost be designed for reliability, in my mind that means a medium speed prime (or possibly a 1000 of 1200rpm rated units) mover with a low pressure fuel system tolerant of fuel impurities and contamination (think pintle nozzle type fuel systems from old 300 series engines). 

 

It should have a multiple cranking system, as an example both electric and air starters, and either starting system should be capable of being manually engaged by an operator.

 

It should have a non-electronic hydra mechanical governor that requires no electrical power to maintain rated speed.

 

The control system should be energize to shutoff, with a manual shutdown capablity. And have minimum automatic shutdowns, in reality I think it should only have an overspeed and an emergency shutdown, all other monitoring and protection should be alarm only.

 

The generator should be controlled by a robust analog voltage regulator with a seperate manual voltage control module, with VERY limited electrical protections.

 

Now this all sounds pretty old school, but if you look at units running around the world, in multiple applications sometimes you find old technology engines still chugging away long after the "modern" engines have failed.

 

First issue with a modern engine with electronic controls, it is energize to run, needs power and in a SHTF situation, your control power may not be reliable. Also with electronic controls on most engines you need a proprietary computer based service tool, and while some manufacturers offer customer level service tools, they are not fully capable and may not allow for needed access in an emergency. Do you really want to wait for a technician to show up to get your emergency generator running again when the reactor is melting down?

 

The challenge to this is that environmental regulations drive manufacturers away from "dirty" engine technology, and while great strides have been made in improving fuel consumption, horsepower to weight ratios and exhaust emissions, you have to admit that newer engines are less fuel tolerant and more prone to nuisence failures.

 

Another issue with "dumb" engines and generators is that they require more highly skilled and trained operators. Modern engine/generator controls do an amazing job of paralleling and managing real and reactive loads without operator interface, but they can also be a possible point of failure, and have an ever decreasing service life of their own due to changes in technology.

 

In reality decisions will have to be made using modern engine technology, however manufacturers should be required to supply limited protection system and "open" access to the control system with reliability being the absolute number one priority. We shold also ensure we don't further burden these critcal applications with balance of plant equipment, such as exhaust aftertreatment, that could have a negative impact on reliability in an emergency situation.

 

My two cents, MikeL.

by SEO en México
on ‎03-14-2017 11:07 AM

It's pretty interesting to analyze the improvements that energy efficency has gone trough, doubtlessly, engineering has come a long way since the first nuclear power plant was built. I'm looking forward to see what is future deparing to us.
I hope humans realize that money can't be eaten, we can't breath CO2. The better we take advantage energy, the better we will live.

by Emanuel Jons
on ‎04-27-2017 07:59 AM

Contrary to the average man's belief, nuclear power plants are the safest options we have. However, at the same time any hazard can potentially be catastrophic. Chernobyl is an example and so is the Fukishima power plant.

 

I think you have addressed the right issue and I hope most of the NPP out there are aware of how they are aging. 

by New member pedrosegura
on ‎10-18-2017 07:36 PM

Very interesant article.

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