Siemens eyes hundreds of 3D printed parts after world’s first reactor install

Following pioneering work at a Slovenian reactor, Siemens plans to expand its Additive Manufacturing (AM) facilities as progress on gas-fired turbines expands the temperature limits of AM components, Thorbjoern Fors, Siemens CEO for Power Generation Services, Distributed Generation and Oil & Gas, told Nuclear Energy Insider.

Siemens is pioneering 3D printed gas turbine blades and has tested components at over 1,250 degrees Celsius. (Image credit: Siemens)

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As nuclear operators seek greater competitiveness, additive manufacturing (AM), aka 3D printing, is emerging as a new way to increase manufacturing efficiency and optimize spare parts replacement.

Earlier this year, Siemens became the first company to install and test an AM component in an operational nuclear power plant.

The German group reverse-engineered and installed a 108-mm diameter impeller for a fire protection pump at the operational Krsko nuclear power plant in Slovenia, replacing an obsolete part no longer available in the supply chain.

Like many AM developers, Siemens predicts significant gains from the new technology. According to the company, AM can cut lead times for power generation components by around 50% and reduce R&D time by around 75%, including design iteration loops.

Siemens has developed its own software for the entire AM process, including automation, control and design software, and the company is now advancing into higher temperature component applications and expanding its industrial capabilities.

Following on from its recent acquisition of Materials Solutions, a specialist in high performance parts for high temperature applications, Siemens plans to expand its AM factory in Finspong, Sweden, Fors told Nuclear Energy Insider.

"We will add additional printer capacity and expand the number of serial manufacturing parts from a smaller number today to several hundred in the course of the next couple of years,” he said.

                Global AM market potential 

                               (Click image to enlarge)

Source: UK government's 'Additive Manufacturing UK National Strategy 2018-25' report.

Turbine gains

Siemens is making notable advances in AM components for gas-fired power plants, which should provide numerous benefits for nuclear applications, through increased knowledge of technology and materials.

Siemens recently completed its first full load engine tests for gas turbine blades entirely produced using AM technology. These included tests at over 1,250 degrees Celsius.

Siemens favors the AM method of Selective Laser Melting (SLM), a type of Powder Bed Fusion (PBF), because it produces high density material at over 99.7% solid material, according to the company.

A 3D CAD model of the desired object is created, then the SLM system produces the 3D object by building it up, one layer at a time, from a special powder material. This replaces several process steps including casting, machining, drilling, milling and lathing.

SLM provides high geometrical accuracy as the powder is static- “lying still not blown or wire fed)," Fors told Nuclear Energy Insider.

"The energy source can be directed with the highest degree of accuracy, within 1/100ths of a millimetre,” he said.

One way in which AM improves component performance is through its ability to produce lightweight designs with thin walls and lattice structures, Fors noted.

"The smart use of cellular lattice structures changes the vibration response of a system and dampens shockwaves which otherwise would damage the component over time," he said.

Siemens’ immediate AM priorities:

1. The development of new materials by melting metal powders and making them accessible to its design community.

2. The development of digital quality assurance measures for selective laser melting (SLM), a type of Powder Bed Fusion (PBF), “to accommodate the needs of a fully industrial process”.

3. Setting up AM operations in several additional locations and increasing the number of highly skilled personnel in the field, both through recruitment and training.

Other technology groups such as Westinghouse and GE Hitachi Nuclear Energy are advancing AM research.

Westinghouse aims to be the first company to install an additive manufacturing fuel component in a commercial reactor, Clint Armstrong, Advanced Manufacturing Expert at Westinghouse, told Nuclear Energy Insider last month.

Westinghouse is planning to install a thimble plugging device, made of AM 316L stainless steel and non-AM 304, in a commercial reactor by Fall 2018, he said.

Approval challenge

AM is seen as a key future method for replacing obsolete nuclear parts, typically designed and procured in the 1970s and 1980s.

The impeller which Siemens installed in the Krsko plant earlier this year supports a fire protection pump system, which is in constant rotating operation. Material testing of the part at an independent institute and a separate computerised tomography (CT) scan showed that the material properties of the 3D-printed part were superior to those of the original component.

Regulatory approval of AM-manufactured components is a key challenge for developers, due to the nuclear industry’s strict safety requirements.

Fors described the qualification of the Krsko plant impeller as a "significant accomplishment.”

“Meeting the Krsko NPP’s stringent quality and safety assurance requirements required extensive testing that was performed jointly with the Krsko operations team over several months, ensuring that the new 3D-printed part would perform safely and reliably,” he said.

AM is still in its infancy with regards to quality assurance standards as only a few materials have been used to date. According to Fors, the current level of development is comparable to that of computers in the 1980s.

AM developers are working to expand the framework of accepted standards and deepen the pool of material performance data, including irradiation performance data.

“The main challenge in qualifying AM materials is the variability of material properties and overall part quality based on the feedstock material, AM process parameters and part geometry,” Armstrong told Nuclear Energy Insider in October.

In the U.S., officials from the Nuclear Regulatory Commission (NRC) recently met with nuclear power AM proponents, including from within the industry, university and national laboratory communities. A two-day workshop in Washington DC is also planned for late November.

“There are multiple people working on this in the nuclear industry, so there is momentum…We are all working together. Getting all codes and standards in place is a lot of work,” Armstrong said.

By Neil Ford