Nuclear Reactor Fabrication: Welds to ABB Robots

A reactor pressure vessel is one of the heaviest and most closely inspected steel parts anyone builds. The basic method of nuclear reactor fabrication has changed little in decades: forge thick rings, weld them together, line the inside with stainless steel and check every millimetre of the seams. Small modular reactors, or SMRs, are trying to turn that one-off craft into factory work. This post covers how the first vessels were made, how welding and forging became more automated, what the SMR push of 2026 means for the shop floor, and where ABB welding robots could fit. Decommissioning has its own post and is left out here.

A reactor vessel wrapped for shipping arrives by rail at the V.C. Summer site in South Carolina, June 2013. Photo: US Nuclear Regulatory Commission via Wikimedia Commons (public domain)

How the first reactor vessels were welded

The first commercial reactor vessels came from boilermakers who already built heavy pressure vessels for steam plants and refineries. At Shippingport in Pennsylvania, the first full-scale nuclear power station in the United States, the reactor vessel arrived by rail in October 1956 and was lifted into place before the plant started up in 1957. Vessels of that era were rolled from thick plate or forged, then joined with long multi-pass welds. Each seam was ground, checked by radiography and repaired by hand wherever a flaw showed up.

The Shippingport reactor vessel clear of its railroad car, 10 October 1956. Photo: US Nuclear Regulatory Commission via Wikimedia Commons (public domain)

Automation reached the welding process first. Submerged arc welding heads on booms, with the vessel turning on rolls beneath them, laid down the deep circumferential seams far faster than a welder with a stick electrode, and strip cladding put the stainless steel lining inside a vessel in wide bands. Vessel makers also moved toward large ring forgings, since a forged ring has no long vertical seam to weld and inspect. Only a handful of heavy forge shops can make those rings, and their capacity has limited every wave of new reactor building since.

Inside a VVER-440 reactor pressure vessel at the closed Greifswald nuclear plant in Germany, 2025. Photo: Siarhei Besarab / Wikimedia Commons (CC BY-SA 4.0)

Newer welding methods brought the next jump. Electron beam welding in a vacuum can join very thick steel in a single pass, and in 2023 Sheffield Forgemasters in the UK reported welding a full-size SMR vessel section this way in under 24 hours, a job that takes far longer with arc welding. Research centres such as the Nuclear AMRC near Sheffield have worked for years on robotic welding and cladding for nuclear parts, because most nuclear welding is still done by hand and skilled nuclear welders are hard to find.

The Sheffield Forgemasters works in Sheffield, England, 2016. Photo: Stephen Craven / Wikimedia Commons (CC BY-SA 2.0)

Why small reactor factories need robots in 2026

The record of large plants explains the push. When Georgia's Vogtle Unit 3 started in 2023, seven years late, it was the first new reactor built in the US in over 30 years, as MIT News pointed out on 22 October 2026. The same article profiled Blue Energy, an MIT spinoff that plans to prefabricate plant blocks of about 1,500 tons at shipyards and send them to the site by barge. Shipyards already build huge steel structures for offshore oil and gas this way, and Blue Energy wants to point that supply base at nuclear plants.

NRC officials tour the inside of the Vogtle Unit 3 containment during construction, January 2018. Photo: US Nuclear Regulatory Commission / Wikimedia Commons (CC BY 2.0)

SMR projects are getting closer to real hardware. In October 2026 the NRC approved TVA's construction permit for the first US small modular reactor, a BWRX-300 at Clinch River, and X-energy and AEP signed an agreement to study a 960 MW SMR project in Indiana. All of these designs rely on smaller pressure vessels and modules built in a factory many times over. That repetition is what makes robotic welding worth it, since a weld cell that builds the same vessel ten times spreads its programming and qualification cost across every unit.

A full-height mockup of the upper third of a NuScale reactor module at Oregon State University, 2020. Photo: Oregon State University / Wikimedia Commons (CC BY-SA 2.0)

We know of no ABB robot welding a reactor vessel today, so what follows is a possibility. ABB's arc welding robots, such as the IRB 2600 and IRB 6700, work with positioners that turn heavy parts so the torch always welds in the best position, and MultiMove coordinates a robot and its positioner as one system. The large IRB 7710 and IRB 7720 can be set up for friction stir welding. ABB's SafeMove software can fence off the zones where the robot and positioner may move, which helps when a welding engineer has to step in and check a seam between passes. For long multi-pass welds, engineers can plan and check every pass offline in RobotStudio before the arc is struck.

An ABB arc welding robot with a positioner. Photo: Ana / Wikimedia Commons (CC BY-SA 4.0)

What comes next for reactor module factories

Over the next decade I expect reactor parts to be built more like ships and offshore platforms. Shipyards already run robotic welding lines for steel panels and blocks, and Blue Energy's shipyard plan points the same way. SMR vendors also want dedicated factories for pressure vessels and modules. There, robots could weld nozzles, cladding and support structures with the same program on every unit, while sensors track each seam and record the data inspectors ask for.

Visitors look at an automated robotic welding facility at the Odense Steel Shipyard in Denmark, 2007. Photo: US Navy via Wikimedia Commons (public domain)

Qualification is the hardest step. Every nuclear weld procedure must be approved under strict codes, and the robot, its program, the filler wire and the welding parameters all become part of that approved record, so changing any one of them can mean requalifying the procedure. The record usually covers heat input and the temperature between passes too. Inspection is slow as well. Ultrasonic and radiographic testing of thick welds takes time, and robots that carry inspection probes along a seam may end up as useful as the ones holding the torch.

An ABB IRB 7710 or IRB 7720 robot set up for friction stir welding. Photo: ABB

Skills and cost are still open problems. Nuclear welders take years to train, so robots are partly a way to make each skilled person go further. A welder can teach a cobot such as the GoFa CRB 15000 by guiding its torch by hand and then look after several cells at once. Qualifying robot cells is expensive, though, and that money only comes back if SMR order books grow the way their developers expect.

Guiding the GoFa torch to a pipe joint before the cobot repeats the weld. Photo: ABB

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