Interest in new nuclear power is growing. Large reactor and small modular reactor designs are moving through licensing and early construction, and utilities and regulators are preparing for a new generation of projects. This moment presents an opportunity not only to build new plants, but to modernize how they are built, especially when it comes to quality assurance.
One area where modernization can deliver real benefits is weld inspection. For decades, radiographic testing (RT), which relies on ionizing radiation, has been the standard method for checking weld quality in nuclear construction. While RT has a long history, advances in ultrasonic testing (UT) now offer a safer, more informative, and more efficient alternative for new construction.
Recent research from EPRI has examined whether UT can be used in place of RT for new nuclear welds (Technical Basis for Performing UT in Lieu of RT for New Construction). The conclusion is clear: modern UT can meet or exceed the safety intent of RT while reducing cost, schedule risk, and worker radiation exposure.
Why radiography has become a bottleneck
RT earned its place decades ago because it could reveal internal weld flaws and produce a permanent image that could be used for reference later. But experience from both construction sites and operating plants has shown that RT also brings significant drawbacks.
The most visible challenges are safety and logistics. Radiography requires strict radiation controls. Large areas of a construction site must be cleared during each exposure, other work must stop, and specialized personnel must manage safety boundaries. On complex nuclear projects, these interruptions slow progress and complicate coordination between trades.
RT also has important technical limitations. Because it produces a flat, two‑dimensional image, it does not show how deep a flaw is or how close it is to the inner or outer surface of the weld. These details matter when evaluating whether a flaw could affect long‑term component performance.
Even more importantly, RT often struggles to detect the types of flaws that pose the greatest structural risk, such as cracks or incomplete fusion between weld materials. These flaws can be difficult to see with radiography and are sometimes only discovered later, during ultrasonic inspections performed before plant startup. When that happens, repairs occur late in the schedule, when they are most costly and disruptive.
Finally, RT standards frequently require repairs for small, embedded imperfections like slag or porosity. Operating experience has shown that these imperfections rarely cause problems in service. Ironically, repairing them can introduce new stresses and material changes that increase the chance of future cracking.
What modern ultrasonic testing does differently
Ultrasonic testing has changed dramatically over the past two decades. Automated and phased‑array UT systems now create detailed, three‑dimensional images of welds. Instead of relying on density differences, UT uses sound waves that reflect off material boundaries and flaws.
This approach offers several advantages. First, UT is especially effective at finding cracks and lack‑of‑fusion flaws, the very defects that RT can miss. Because UT responds to the surface area of a flaw rather than its volume, it is better aligned with structural risk.
Second, UT provides precise information about flaw size, depth, and location. This allows engineers to distinguish between harmless fabrication imperfections and flaws that could matter over decades of operation. Acceptance decisions can be based on engineering judgment and performance, not just workmanship rules.
Third, UT significantly improves safety and efficiency on construction sites. Because it involves no radiation, inspections can be performed without evacuating work areas or stopping nearby activities. This reduces schedule disruptions and improves overall site productivity.
Reducing duplication and improving consistency
Today, welds accepted using RT during construction must still be examined using UT before the plant enters service. By using qualified UT from the beginning, construction inspections can also serve as the baseline for preservice inspection. This eliminates duplicate examinations and simplifies quality‑assurance workflows.
Importantly, UT acceptance approaches are already in use for repairs and replacements in operating nuclear plants under existing ASME provisions. Aligning new‑construction rules with these proven practices would create consistency across the plant lifecycle while maintaining safety margins.
A practical step forward
Moving from RT to UT for new nuclear construction is not a step into the unknown. The technology is mature, the operating experience is strong, and the safety case is well established. What remains is updating codes and expectations to reflect today’s inspection capabilities.
For utilities, regulators, and suppliers, adopting UT offers a practical way to improve safety, reduce unnecessary rework, and keep projects on schedule. As the industry prepares for a new build cycle, modernizing weld inspection is a straightforward change with long‑term benefits for plant reliability and public confidence.