Steam Generator Inspection: Tube Robots and ABB

In a pressurized water reactor, the heat from the reactor's cooling water reaches the turbine side through thousands of thin metal tubes inside each steam generator. Steam generator inspection means checking those tubes for cracks, dents and thinning during refuelling outages, and today small robots push eddy current probes through them one after another. This post follows the work from people feeding probes in by hand to robots that walk across the tubesheet. It then looks at what this year's outages and replacement projects show, and at where ABB, which once owned the steam generator maker Combustion Engineering, could fit in.

The U-bends and upper supports of the tube bundle in a Combustion Engineering vertical steam generator. Photo: U.S. Nuclear Regulatory Commission / Wikimedia Commons (public domain)

How steam generator tubes were checked before robots

Each steam generator holds anywhere from 3,000 to 16,000 tubes, each about 19 mm across, and in American plants they are made of Inconel Alloy 600 or Alloy 690. Annealed Alloy 600 turned out to be prone to denting and thinning caused by water chemistry. Plants responded by changing their chemistry, plugging damaged tubes to remove them from operation and, in some cases, replacing Alloy 600 tubing with Alloy 690. Plugging a tube is usually easier than repairing it. Whole steam generators are often replaced in mid-life too, and most US pressurized water reactors have now had theirs swapped.

A reactor at the Oconee Nuclear Station in South Carolina flanked by two 570-ton steam generators, around 1973. Photo: U.S. Department of Energy / Wikimedia Commons (public domain)

Eddy current testing, the method used on these tubes, goes back to the 1830s. Michael Faraday discovered electromagnetic induction in 1831, Léon Foucault is credited with discovering eddy currents in 1855, and Friedrich Förster turned the effect into industrial instruments in Germany during the Second World War, founding his own company in 1948. In a steam generator the probe travels inside each tube, and for years people delivered it by hand. Nuclear Engineering International describes a manual, time-consuming process in which personnel inserted the probe into each tube, one by one. To cut their radiation dose, engineers built remotely operated delivery robots, in use since the late 1970s.

Engineers at NASA's White Sands Test Facility use eddy current testing to look for small cracks inside a pressure vessel, 2019. Photo: NASA / Reed P. Elliott via Wikimedia Commons (public domain)

The first robots still needed people nearby. Early units mounted on the tubesheet moved on X and Y axes under remote control, but staff had to move them by hand to each new location, and manway-mounted robots fed through the channel head's access hole fought with cable routing and alignment. Arm-and-mast robots that anchored in a tube hole and braced a foot against the channel head then did the heavy work on first-generation units: plugging, tube removal, shot peening and sleeving. Combustion Engineering, which built steam generators in Chattanooga, Tennessee, became a wholly owned ABB subsidiary in 1990, and Westinghouse bought its nuclear unit around 2000.

A 623-ton, 65-foot nuclear steam generator leaves Combustion Engineering's plant in Chattanooga, Tennessee, around 1976. Photo: U.S. Department of Energy / Wikimedia Commons (public domain)

What steam generator inspection looks like in 2026

A spring 2026 outage at Beaver Valley Unit 2 in Pennsylvania shows the routine. Each of the plant's three Westinghouse Model 51M steam generators holds 3,376 mill-annealed Alloy 600 tubes. According to an NRC summary dated 8 June, eddy current testing found 1,490 axial stress corrosion indications at the tube support plates, all below the 2.0 volt repair limit. The operator was also pulling old plugs and sleeving those tubes to return them to service, after checking each deplugged tube full length with eddy current probes. In France, Mitsubishi Heavy Industries reported this month that it had delivered three new steam generators for EDF's Cruas unit 2, each with more than 4,500 tubes.

Beaver Valley Power Station in Shippingport, Pennsylvania, in 2003. Photo: U.S. Nuclear Regulatory Commission / Wikimedia Commons (public domain)

The robots doing this work are small walkers. Framatome's FORERUNNER weighs 39.7 lb, is set in place by a motorized carriage and then walks across the tubesheet on pneumatic grippers, reaching more than 200 tubes from one stance. Framatome says running it remotely over a single controller and cable cuts dose by 30 percent. Zetec's ZR-100 weighs under 35 pounds, two can be set up in under 20 minutes, and together they run four probes in one channel head. In spring 2017 Areva NP's Trident system inspected more than 17,000 tubes in under 77 hours at a US plant, and probe scan speeds have climbed from 12 to over 80 inches per second.

A steam generator for the first unit at Calvert Cliffs in Maryland is moved to the containment building, around 1971. Photo: U.S. Department of Energy / Wikimedia Commons (public domain)

We found no ABB robot working inside a channel head today. ABB's inspection robotics are in factories. Its 3DQI cell carries a white light 3D scanner on a robot, captures millions of points per shot and compares them with the part's CAD model, finding defects smaller than half the width of a human hair, and ABB says it works ten times faster than a coordinate measuring machine. Like tube inspection, it collects dense sensor data along a planned path and judges the result against a standard. Our post on transformer inspection looks at another power plant asset that robots now check from the inside.

The 3D scanner head mounted on an ABB robot in ABB's 3DQI inspection cell. Photo: ABB

Where steam generator inspection goes next

EDF runs 57 pressurized water reactors in France and has been replacing steam generators as part of a policy to keep its plants running beyond 40 years. Mitsubishi has orders for nine replacements from EDF, and the remaining six are due from 2028. Analysis is changing too. In September Nuclear Engineering International reported that DeepEye, a South Korean startup, used its DeepAgent AI to analyse eddy current data from thousands of heat exchanger tubes in the condensers and feedwater heaters at all four Barakah units in the UAE. The software flags suspect signals for workers to review, and it holds EPRI certification for AI-based inspection.

The Barakah nuclear power plant in the United Arab Emirates under construction in 2017. Photo: Wikiemirati / Wikimedia Commons (CC BY-SA 4.0)

Any ABB role here is a possibility, since no project exists. The walkers succeed because they are small and manage their own cables, which is exactly where the early manway robots struggled. ABB's new IRB 1700ID routes its cables and hoses inside the arm, and OmniCore EyeMotion with AI Robot Trainer turns camera images into robot motion with automatic collision-free path planning, which ABB says cuts commissioning time by up to 90 percent. Ideas like these could carry over to service work outside the channel head, planned first in RobotStudio, which runs on a virtual copy of the real robot controller.

An engineer programs a robot cell in RobotStudio next to an ABB industrial robot. Photo: ABB

Cost is the first limit. San Onofre in California shows the stakes: its Mitsubishi replacement steam generators, finished in 2011 in a $671 million project, showed premature wear on over 3,000 tubes after a leak in January 2012, and Southern California Edison retired both units in June 2013. Dose still drives tool design, and Framatome ties FORERUNNER's dose savings to an 80 percent cut in installation time. ABB sells sealed IP67 and Foundry Plus 2 versions of its IRB 1300 for liquids and dust, but its pages make no claim about radiation. People still make the calls, too: at Barakah, workers review each flaw candidate the AI flags.

A white ABB foundry robot works in steam at a Bühler die casting cell. Photo: ABB

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