Electron beam welding could cut reactor build costs by 85%

UK consortium using bespoke vacuum design to manufacture small modular reactor pressure vessel.

The welding system designed by Cambridge Vacuum Engineering, will be used by Sheffield Forgemasters to manufacture a SMR pressure vessel

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Engineering specialists Sheffield Forgemasters is leading a consortium of partners to explore the industrialization of Electron Beam Welding (EBW) in nuclear applications.

The company, based in the UK, says integrating EBW into the manufacturing process not only improves material strength and safety but also offers significant reductions in manufacturing costs of more than 85%. 

The UK Government’s Department for Business, Energy and Industrial Strategy (BEIS) has awarded 8 million pounds ($10.5 million) of funding for the initiative – the largest grant in its Nuclear Innovation Programme.

Jesus Talamantes-Silva, Research, Design and Technology Director at Sheffield Forgemasters, said this is a landmark project to refine the basic science of EBW in nuclear applications.

“Electron beam welding is used in both the automotive and aerospace industries in the manufacture of engine components,” Talamantes-Silva told Nuclear Energy Insider.

“Whilst EBW has been used on components with nuclear applications, such as welding the closures on spent fuel casks, it is envisaged that the technology can be utilized on components of greater size and section thicknesses. Sheffield Forgemasters want to use EBW to join primary vessel forgings, such as those used in steam generators, pressurizers and/or reactor pressure vessels.”

Talamantes-Silva says costs of the EBW system will vary depending upon the power requirement but would be a minimum of 3 million pounds ($3.9 million) for the main welder. Sheffield Forgemasters is aiming to implement this technology within two years.

"In two years the technology will be mature and developed enough for Sheffield Forgemasters to offer it to the nuclear industry," he says.

"EBW has been accepted as a suitable manufacturing method by certain reactor vendors as well as nuclear codes and standards bodies. More work is needed to build on the very encouraging preliminary results."

The company will install an EBW capable of welding 3m diameter cylinders under localised vacuum. It will then manufacture a 4.3m high and 3m diameter SMR pressure vessel.

Talamantes-Silva says using EBW, circumferential welding of pressure vessels can be reduced from around 150 days to 10 days.

Local vacuum design

Sheffield Forgemasters first started investigating EBW technology as part of an Innovate UK project led by the company. Along with Rolls-Royce, TWI and other consortium members, the project demonstrated that it was possible to use EBW to join forged material with a section thickness of approximately 200mm.

For the current project, a new bespoke system is being designed and manufactured by Cambridge Vacuum Engineering (CVE). It is based on a local vacuum design, meaning a jacket enveloping the weld line will be used to create a partial vacuum rather than using a chamber that would be used to create a hard vacuum. As the intention of the project is to industrialize EBW, the use of a local vacuum chamber could allow the flexibility to join a wide range of component sizes and dimensions in the future.

CVE's Ebflow electron beam welding system

Source: CVE

EBW promises time and cost savings over traditional tungsten inert gas (TIG) welding. TIG welding of thick-section items such as a reactor pressure vessel is an expensive and time-consuming process. One of the main drawbacks is that TIG welding can only penetrate to a shallow depth so a typical pressure vessel section of 140mm could involve up to 100 runs of weld. This can take weeks, or even months, to complete.

Due to the size and shape of nuclear pressure vessels, traditional vacuum chambers would be prohibitively expensive, given the low number of nuclear projects. CVE has developed EBW technology called Ebflow which aims to resolve these barriers, in a system which can be transported and operated on site and applied to structures significantly larger than those that can be accommodated in a vacuum chamber. Ebflow creates a localised vacuum only where it is needed.

Ebflow is a collaboration between CVE, TWI, U-Battery and Cammell Laird and aims to implement and validate the first Ebflow system within a large-scale fabrication facility for use in large-scale power generation infrastructure.

CVE says the Ebflow system could reduce welding costs by more than 85%.

Source: CVE

“Current inert gas processes require filler and flux material to produce a weld, both of which are inherently expensive due to the components required for nuclear application,” says Talamantes-Silva. “EBW removes the need for both filler material and fluxes as the weld is reliant on melting the component material. 

“In addition, as EBW produces a full penetration weld in a single pass, welding times can be reduced from months to days.”

Talamantes-Silva adds that using EBW at an earlier stage of vessel fabrication means work can be carried out to recover the material properties of the fusion and heat affected zones of the weld.

In-service inspection of welds in the nuclear industry is costly and logistically challenging. Research by Sheffield Forgemasters has shown that EBW could restore material properties back to parent levels, potentially reducing or eliminating in-service inspections.

For new build nuclear plants, EBW could prevent the delays and costs associated with inferior welding. In October 2019, French utility EDF stated that repairing the main secondary system penetration welds would increase the cost of constructing the Flamanville EPR by $1.6 billion.

To ensure that the research is relevant to the nuclear industry, Sheffield Forgemasters has assembled a steering committee which includes Rolls-Royce SMR and Cavendish Nuclear.

“For the components and weld thicknesses being used in this project, we are unaware of anyone else looking to use EBW in an integrated production environment,” says Talamantes-Silva.

Innovation in manufacturing

The EBW technology could be applied to the serial production of modular SMR reactor components, allowing for accelerated manufacture and deployment.

Innovation in manufacturing techniques is seen as increasingly important in order to bring SMRs to market that are cost-effective. Ontario Power Generation (OPG) is using on-site technology invention labs and a streamlined development process to transfer the latest advances to operational plants, including 3D printing (also known as additive manufacturing). Westinghouse and Siemens have also developed and deployed 3D printing. Holtec has previously stated that it was looking into EBW for reducing build costs of its SMR design.

Canadian Nuclear Laboratories (CNL) recently selected the first recipients of the Canadian Nuclear Research Initiative (CNRI) which seeks to accelerate the deployment of SMRs in Canada through collaborative research and development. Four companies in negotiations for the CNRI include Moltex Canada, Kairos Power, Ultra Safe Nuclear Corporation, and Terrestrial Energy.

Scott Birch