Sustaining Safe Nuclear Energy with Nondestructive Testing

Nondestructive testing is a multidisciplinary profession that blends quality assurance and materials science. Many industries rely upon it, but few uses are more important than in the nuclear power sector.

Accidents at Chernobyl, Fukushima, and even in the U.S. at the Three Mile Island Nuclear Power Plant, some occurring more than four decades in the past, cloud public perceptions about the safety of nuclear power to this day. Despite these persistent negative opinions, nuclear energy is, in fact, one of the world’s safest power sources. At 0.03 deaths per terawatt-hour of electricity, nuclear energy nearly clinches the top spot for least-risky power source, with only solar energy coming in slightly lower.

This is impressive enough, but among those who know nuclear energy well there are added advantages, including that it produces the cleanest energy our world has to offer. Those in the know are also aware that nuclear is not an inherently dangerous form of energy—just one that requires attention to specific operational and maintenance procedures, including a very particular and rigorous set of inspection protocols, many of which relay upon nondestructive testing (NDT).

The Role of Nondestructive Testing in Nuclear Energy

NDT is critical to ensuring safety in the maintenance and operation of all power generation systems, but it is vital in nuclear power facilities. In fact, the International Atomic Energy Agency (IAEA) recognizes NDT as a key tool for quality control, safety, and reliability, and promotes the use of NDT to maintain its stringent quality control standards for the safe operation of nuclear and other industrial installations.

NDT is used to inspect and evaluate materials, components, and assemblies without destroying their serviceability. Through a set of test methods—visual testing (VT), liquid penetrant testing (PT), ultrasonic testing (UT), microwave testing (MW), and more—skilled technicians identify cracks, voids, inclusions, and weld discontinuities, as well as potentially misassembled subcomponents.

Several examples illustrate the critical value of NDT in nuclear power generation. VT is the direct inspection of components for surface anomalies and structural integrity using various optical tools and techniques. It often is applied during routine surveillance because it can detect issues like corrosion, material degradation, and surface cracks—defects that could result in catastrophe if not addressed within nuclear reactors. Additionally, VT plays a role in pre-service and in-service inspections, helping to ensure that components meet the stringent standards required for safe nuclear operation.

Beyond VT, PT is highly reliable for detecting surface-breaking discontinuities on non-porous materials (Figure 1). It involves applying a liquid with high surface-wetting characteristics to the test material. The liquid then penetrates into flaws and becomes visible under ultraviolet light. This method is particularly important when inspecting critical welds. As many nuclear power plants utilize nonferromagnetic materials—eliminating magnetic particle testing as an NDT option—PT enables inspectors to locate discontinuities in nuclear reactor piping, thus helping to prevent large and dangerous malfunctions.

1. Liquid or dye penetrant testing (PT) is a non-destructive material testing method that uses capillary forces to find surface cracks or pores and make them visible. It can detect surface-breaking flaws such as cracks, laps, and porosity. Source: Shutterstock

Meanwhile, the use of composite materials, which have properties that work well with extreme radiation and high temperatures, in nuclear fission and fusion leads to testing using MW. This NDT method, especially effective in inspecting composite materials, has grown in use across multiple industries as more composites are adopted in lieu of heavier and more corrosion-vulnerable materials. With MW, electromagnetic radiation in the microwave frequency range is introduced into the object of the inspection and if the wave encounters an area with a different complex permittivity—identifying a flaw—some or all of the electromagnetic energy will be reflected to the transmitter. Not only does this method identify a flaw, but it can also, through the resulting data, reveal the location of the flaw.

Such NDT methods serve as low-risk, high-impact inspection solutions. For a type of power generation in which even a small oversight can lead to disastrous results, NDT is invaluable to ensuring the safety, structural integrity, and longevity of the facility. Employing regular and reliable NDT practices significantly reduces the chance of small, and otherwise possibly easily overlooked, errors in operations and maintenance activities.

Assigning the Correct Value to Inspection Activities

Benjamin Franklin once said, “An ounce of prevention is worth a pound of cure.” When it comes to nuclear energy, an apt adaptation of this sentiment would be “a shilling of prevention is worth a pound of cure.”

Unfortunately, the importance of inspection is, at times, overlooked and undervalued, especially when it comes to the equipment directly used to produce energy, despite its impact on the operations. Despite the clear motive behind performing such activities, to do so outside of what is ultimately required or regulated, can bring about debate. In the same vein that most people would choose not to travel with an airline that does not perform routine inspection and maintenance on their aircraft, and yet those same people will not give a second thought to not performing inspections and maintenance on their personal vehicles. This is true even though your chances of injury are far greater from traveling in a personal vehicle versus an airplane. So why is this the case?

At the root of it all is a simple, yet detrimental miscalculation. When evaluating the cost and timing issues involved with performing these inspection activities, many people would often rather avoid the hefty upfront price and immediate sacrifice of time if everything, to their best knowledge, is running smoothly. This decision is then made without considering the risks of not performing those activities, which in many cases outweigh the costs of performing them in the first place.

In the case of nuclear energy production, the stakes are even higher. Therefore, when it comes to key inspection activities, such as NDT, it is important when calculating the total cost of an inspection activity to assign and incorporate the correct value of not performing that inspection activity.

Linked with a need to accurately value inspection activities is the idea that it is never too early for an inspection to take place. In an ideal world, a well-thought-out product would not need to be tested for a respectively long period of time. Even more ideal, a costly inspection would be unnecessary unless an issue occurs.

Unfortunately, this does not apply to power generation, especially not nuclear power. In general, there is always more to be gained from routine inspections using NDT (Figure 2) and other advanced testing methods—and, not taking that into consideration every step of the way can be to the detriment of any operations in nuclear energy.

2. Non-destructive testing is used to identify components in need of repair. Finding and fixing flaws prior to catastrophic failure saves time, money, and potentially lives. Source: Shutterstock

Prioritizing Timing

When it comes to nuclear energy safety, timing is everything. From the very beginning until the very end, operators need to be aware of their decisions and actions in the greater scope of multiple timing considerations.

First, all actions should be made with the awareness of where the system stands in terms of starting up and shutting down, including the active avoidance of the latter. Like a commercial plane trip where risks are highest during takeoff and landing, the riskiest times in a nuclear power plant’s lifetime are at startup and shutdown. Once a plane is in the air—or a unit is up and running—the risk of any incident occurring goes down significantly, if all operational activities are carried out properly.

At this stage in the evolution of the nuclear industry, there is a significant aversion to shutting down operations when an issue arises. NDT offers the opportunity to perform comprehensive testing without compromising the integrity or continuity of operations. With new technologies, including the automation of some maintenance and inspection activities, there is greater capacity for operators to complete essential inspection tasks with little to no interruption in operations. Inspectors can take certain component systems offline, perform NDT activities, and put the system back into operation without needing to resort to entering the more challenging phase of a reactor shutdown, which should most always be considered only as a last resort. Overall, if the proper timing considerations are made, utilizing NDT helps operators run more efficient and safe inspections, resulting in better operations across the board.

The Future of Safe Nuclear Energy Production

Nuclear energy has always represented a large opportunity for the U.S. to lessen its dependence on fossil fuels while incorporating a safer energy with minimal impact on the climate. Yet, as it currently stands, nuclear energy represents only about 20% of U.S. electricity generation.

One of the major components in getting the nuclear power industry to where it is today, and the push to get it where it could be, comes from a solid understanding of and investment in maintenance and operations activities, such as NDT. Despite historical setbacks and public misconceptions, nuclear power has consistently demonstrated its ability to evolve, adapt, and enhance its safety protocols. The rigorous application of NDT methods, steadfast commitment to maintenance and operations best practices, and a forward-thinking approach to problem-solving have all played pivotal roles in this journey.

As we look toward the future, the continued investment in and refinement of these practices are essential. They not only ensure the safe and efficient operation of nuclear facilities but also solidify nuclear energy’s position as a cornerstone in the quest for a cleaner, more sustainable energy landscape. By embracing the lessons of the past and the innovations of the present, we can confidently forge a path toward a brighter, greener future powered by nuclear energy, an embodiment of safety, reliability, and environmental stewardship.

—Robert (Bob) Stakenborghs is a Microwave Committee member with the American Society for Nondestructive Testing (ASNT).