Westinghouse to install first 3D-printed reactor fuel part in 2018
Westinghouse aims to be the first company to install an additive manufacturing fuel component in a commercial reactor as the group targets lower replacement parts costs and faster qualification of 3D-printed materials, Clint Armstrong, Advanced Manufacturing Expert at Westinghouse, told Nuclear Energy Insider.
As nuclear power plant operators seek greater competitiveness against other generation types, technology suppliers are developing new manufacturing methods to reduce construction and maintenance costs.
Additive manufacturing (AM), more commonly known as 3D printing, is well suited to the nuclear industry's requirements for low volume, wide variety and highly critical plant components, Armstrong said.
After several years of research, Westinghouse is now 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.
Over the next year, Westinghouse researchers will focus on reducing the cost and lead times for replacing obsolete and difficult to procure parts, as well as fuel structural components and prototypes for next generation plants. These will include impellers and microchannel heat exchangers.
Westinghouse is currently demonstrating the use of AM casting moulds to produce safety-related castings, including replacement large brackets and bearing housings, for electric motors. The process could be used to reduce the cost and lead time of many cast parts including valve bodies and piping sections and connections. It also allows designers to create more complex castings that would not be possible using traditional sand casting.
Other 2018 priorities include the “material development, testing and support” for the development of AM codes and standards,” Armstrong said.
Westinghouse is also planning to develop AM uses for robotics, sensors, models for manufacturability and tooling, among other areas, he said.
A number of technology companies are developing new additive manufacturing applications. In March, Siemens announced it had installed an AM component at the operational Krsko nuclear power plant in Slovenia.
The component, a 108-mm diameter impeller for a fire protection pump that is in constant rotating operation, replaced an obsolete design.
Other proponents of nuclear AM research include GE Hitachi Nuclear Energy, which is also leading a project to manufacture replacement parts for operational plants.
Westinghouse’s AM research includes two multi-year projects supported by the US Department of Energy (DOE).
In 2016, the DOE allocated Westinghouse $8 million towards several R&D projects focused on advancing innovative technologies, including a three-year effort focused on qualifying powder bed fusion additive manufacturing processes for nuclear components. In July 2017, DOE allocated Westinghouse a further $830,000 in federal funding to study the neutron radiation effects on zirconium alloys produced via the additive manufacturing process for light water reactors (LWRs).
Researchers will conduct post-irradiation examination of zirconium material that was irradiated at the Massachusetts Institute of Technology reactor.
Westinghouse is currently assessing the benefits of three AM processes:
1. Laser powder bed fusion is useful in the production of smaller, complex fuel structural components, prototype components and to some extent tooling. It can produce complex parts that cannot be manufactured using traditional methods and/or at reduced cost/lead time.
“For many prototype parts, AM becomes cost competitive due to the fact that it does not require custom tooling or fixturing, which might be required for traditional manufacturing methods,” Armstrong said.
2. Directed energy distribution (DED) can be used to add features, for instance nozzles, bosses or flanges to existing castings or forgings. There are several available technologies that could be used to significantly reduce the size, complexity, and machining and materials cost for larger components.
DED processes can reduce costs and lead-times when used for weld repair or automated cladding operations, or to produce larger prototypes or complex structures.
3. Binder jetting can produce relatively complex, smaller metallic components at a fraction of the cost of powder bed fusion AM processes. This makes it a cost-effective method of producing metal prototypes, models, tooling and fixturing, as well as various components with lower strength requirements. There are also potential time and cost savings from the use of binder jetting to produce casting moulds.
“Similar to traditional sand casting, this process does require some upfront investment. This includes producing 3D CAD modules of the casting and associated sand mould,” Armstrong said.
Other AM technologies under investigation include friction stir, ultrasonic and various metal spray processes. Each application will involve material development and testing and regulatory approval requirements. The amount of work with each will depend on the proposed uses and novelty of the metal deposition or melting process.
“These cost and lead time reduction estimates still look appropriate for certain replacement castings, using current cost estimates for AM casting moulds and the associated foundries/casting processes,” Armstrong said.
The firm has reduced some costs by converting tooling from traditional manufacturing processes to AM. In one example, the Westinghouse Specialty Metals Plant combined five individual parts into one AM piece. The plant used a specific AM alloy which improved wear resistance of the part and also increased tooling lifespans.
The cost and lead time savings vary by component and the quantity produced. Initial estimates for producing one of Westinghouse’s larger multi-piece motor brackets using AM moulds reduced costs by 50% and cut lead times by 75%, according to the company.
For one of the smaller replacement cast parts, the supplier recorded a slight cost increase but also a slight reduction in lead time for a single casting. If Westinghouse were to purchase a second casting using the same AM process, it would achieve a 75-90% reduction in lead time, Armstrong said.
Nuclear industry AM developers are looking to expand the limited 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 said.
“To combat this, most users are printing multiple parts for destructive testing, as well as multiple test specimens with production parts,” he said.
This approach can significantly increase the cost of advancing an AM part to commercial production. Westinghouse is currently collaborating on a DOE funded project, with the Electric Power Research Institute (EPRI), Oak Ridge National Laboratory’s Manufacturing Demonstration Facility, the University of Tennessee and Rolls-Royce, to develop an “in-process monitoring and integrated computational materials engineering process,” to reduce the qualification process for AM, Armstrong said.
Westinghouse has also participated on various ASTM F42 subcommittees on AM and is a member of several America Makes & American National Standards Institute (ANSI) Additive Manufacturing Standardization Collaborative (AMSC) working groups.
Officials from the U.S. Nuclear Regulatory Commission (NRC) also 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