How Service Modernizations for Nuclear Power Plants Can Make a Difference on the Road to Decarbonization

Since the advent of Nuclear Power Plants (NPPs) in the mid-20th century, this energy source has consistently been an important part of the global energy mix. However, the growth of nuclear power generation significantly decelerated after the mid-80s primarily due to safety and environmental concerns.?

But we now see a renewed momentum towards nuclear power. This nuclear renaissance has been driven by several factors where nuclear has distinct advantages over alternative generation sources such as increasing fuel prices, concerns about climate change and the imperative for stable power supply. ?When coupled with increasing global electricity demand, it is clear that the role of nuclear power will be increasingly important beyond 2040.

To build up new NPPs faster, some regions plan to include advanced, more flexible concepts in their energy landscape – the Small Modularized Reactors (SMRs). As an example, the U.S. Department of Energy (DOE) has announced their intention to fund up to $900 million to advance SMRs in the US. In addition, the US government created the Accelerating Deployment of Versatile, Advanced Nuclear for Clean Energy (ADVANCE) Act, which the president signed into law on July 9. The ADVANCE Act aims to create the necessary framework for a rapid nuclear ramp-up and has far-reaching implications for the regulations of the DOE, as well as the regulations and the mission of the Nuclear Regulatory Commission (NRC).

For many countries around the world, nuclear power represents the primary means to reach their emissions targets. ?Considering that many NPPs are approaching the end of their projected lifetime, and that building new ones using traditional methods or with SMRs could easily take between 10 to 15 years, extending the life of existing NPPs becomes crucial.

There are 2 primary functions that servicing turbine-generators at existing NPPs plays:

-????? The first is continual routine maintenance to ensure safe and reliable operation of the existing plants, including planned lifetime extensions

-????? The second is performing modernization upgrades that increase the efficiency and output of the NPP

Lifetime Extensions for Nuclear Power Plants

Since new installations have significantly slowed over the last few decades, many operating NPP’s are now 40-50 years old. ?For example in the US, two thirds of the 94GW of installed nuclear capacity fall into this category. ?At this scale new installations alone will not be sufficient to reach the emission targets – some part of the solution must come from existing NPPs.

For this reason – and because it also makes economic sense – many plant owners are currently looking to extend the lifetime of their plants, in some cases for up to 40 more years. ?Many components will need to be replaced and modernized incorporating state-of-the-art technology into the existing fleet. ?The best way to start is a Lifetime Assessment (LTA), which will consider details like operating regime and service history of the specific plant, resulting in an optimized plan to modernize and potentially extend the lifetime of the plant.

The Significant Potential of Modernizations

When discussing the services provided by Siemens Energy, the primary focus for most generators is on the turbine package. ?In NPPs, the turbine is?driven by steam produced from the reactor by boiling ordinary water.? While the actual lifespan of a steam turbine is influenced by various factors such as operational stresses and material degradation, in general, steam turbines are designed for decades of continuous operation. ?However over time this continual wear causes the turbine components to suffer from typical aging and they must be replaced.? Typically, a modernization will include the replacement of key components such as highly loaded rotors, casings, blades, seal elements and valves, which contribute the most to reliability, availability, and efficiency.

As a manufacturer of steam turbines since the late 1880s, we have gained unique expertise in this field. ?Our team of several hundred experienced field service and engineering personnel possesses unparalleled expertise in servicing Steam Turbines for NPPs, a level of knowledge that is not easily replicated. This complex task requires a deep understanding of the machinery, as well as the strict regulations and safety protocols inherent to the nuclear power industry. Our team's proficiency in navigating these complexities sets us apart, guaranteeing our clients exceptional service and maintenance they can trust.

When considering NPPs, we have successfully modernized more than 150 nuclear steam turbine building blocks worldwide, with over 80 references in North America alone. ?Drawing from this experience we can increase power output by up to 10%, recover efficiency losses due to degradation by up to 2%, improve resistance to erosion, and increase the efficiency of the turbine train by up to 3%.

But let us look a bit deeper into some examples of the technology behind those modernizations:

-????? The latest blade path technology incorporates three-dimensional blading with variable degrees of reaction, also known as 3DV?, which optimizes the blade path using automated computational methods.

-????? The advanced shrink-fit disc design helps to reduce the potential for stress-corrosion related cracks of LP rotor blade attachment areas through optimized disc geometry, heat treatment during manufacturing, steel shot peening of disc surface and attachment areas, and rolling of specialized areas.

-????? The improved steam inlet ring design for the HP turbine helps reduce inlet pressure losses and protects the rotor from moisture, washouts, and temperature changes. The diagonal stage makes it possible to carry out further modernization of the HP turbine in the future, to potentially increase the thermal power of the reactor to the range of 105% to 107% of the rated power by only replacing one component, the steam inlet ring.

-????? The generator can be upgraded with technologies like the Rigi-FlexTM stator end-winding, which makes the end-winding less sensitive to grid impacts, improves the vibration behavior, and with this the overall reliability.

-????? Additional generator modernizations like the stator core donut technology can reduce core replacement time by up to 75%.

-????? To extend the lifetime of the overall unit, at some point in time it might be necessary to renew the auxiliary systems for both the steam turbine and the generator.

-????? For balance of plant (BoP) optimization, we can apply advanced tools such as computational fluid dynamic simulations to develop unit specific turbine design and blade path geometry to help achieve the maximum power plant output.

Beyond the Steam Turbine Train

With over 130 years of experience in manufacturing and servicing steam turbines, this is clearly a major expertise Siemens Energy can offer. ?However, our services go well beyond this part of the plant. ?Another crucial component of the NPP is its I&C system, which also contributes heavily to ?raising the overall plant output, efficiency, reliability, and availability. ?Siemens Energy has developed a standard which can be implemented both in new builts and in existing power plants: the Omnivise T3000 control system.?

The Omnivise T3000 control system addresses the evolving needs of NPPs by providing practical solutions for distributed power generation, cybersecurity, simulation, and virtualization. These capabilities are essential for ensuring the reliability, security, and adaptability of I&C systems in the face of changing energy market dynamics.

The T3000 SCADA component is designed to enable efficient management of distributed power generation within large-scale distribution grids. ?It aims to facilitate centralized control and data acquisition from remote units at various production locations, as well as to conduct root cause analysis to identify and address issues promptly. These capabilities are essential for adapting to the evolving energy markets and ensuring seamless operation across diverse power generation sites.

Cybersecurity is a paramount concern for NPPs, and the T3000 Cybersecurity strategy aims to identify and rectify vulnerabilities and misconfigurations specific to standard T3000 plants. The built-in cybersecurity measures and defense-in-depth concept are geared towards safeguarding NPPs against external threats, bolstering the resilience of the control system in the face of potential security breaches.

The T3000 Simulator serves as a digital twin of the Omnivise T3000, providing a platform for simulating real plant behavior and conducting detailed testing before implementing any changes or adjustments in the control system. This capability allows NPP operators to assess the potential impact of modifications and optimize system performance without disrupting actual plant operations.

Furthermore, the innovative virtualization techniques employed in T3000 Virtual offer improved availability, lower life cycle costs, and simplified spare part handling and lifecycle management by decoupling hardware and software. This approach enhances the flexibility and resilience of the control system, aligning with the need for adaptable and cost-effective solutions in the dynamic energy landscape.

In summary NPP turbine and controls modernizations are an increasingly important option to help generators achieve their carbon reduction targets.? Modernizations lead to an extended plant life – a sustainable solution that can save considerable time, costs and resources compared to a new installation. ?In addition it can also increase the overall plant performance on key factors such as power output and efficiency.? With our long history and successful track record at performing NPP modernizations Siemens Energy is committed to being a trusted partner that our customers can count on well into the future.