Powder Metallurgy manufacturing methods are yet to be embraced or approved by the civil nuclear industry, but some of Europe’s major nuclear organisations are now assessing this potential, reports Mark D’Souza-Mathew, Metallurgist at the UK’s Nuclear Advanced Manufacturing Research Centre in Rotherham, South Yorkshire.
As part of continuing efforts to improve the safety of future designs of nuclear power plants, reactor developers are exploring alternative methods for fabricating reactor pressure vessels. Powder Metallurgy (PM) offers several advantages over conventional methods by removing weak spots such as welds through near-net shape manufacture. PM parts also have reduced compositional segregation and a finer, more consistent grain structure, which is especially advantageous for bulk non-destructive evaluation techniques such as ultrasonic examination.
While studies have shown that PM parts can meet and often exceed the performance of wrought parts under test conditions, there are areas for improvement such as high porosity, oxygen levels, inclusions and epitaxial effects.
A consortium of reactor developers, manufacturers and research institutions are now exploring how PM can be developed for the nuclear industry. The PowderWay project is funded by the European Commission through Nugenia, the European association for R&D in nuclear fission technologies, and is led by the UK’s Nuclear Advanced Manufacturing Research Centre. Project partners include reactor developer Areva, utility group EDF, French nuclear suppliers association PNB, French energy commission CEA and Swedish materials research group Swerea.
The consortium has identified a number of candidate components for PM manufacture, and is now consulting with end users to better understand the benefits of PM over conventional manufacturing methods, the acceptance criteria for standardisation, and the current state of the art. Crucially, the research will also reveal any obstacles preventing uptake of PM methods. The results will be used to construct a development roadmap which will guide themes for future research funding.
This roadmap will benefit the wider PM industry by targeting research funding towards improving resistance to harsh environmental conditions, enhancing performance and reducing ageing in PM parts. It will also disseminate information about PM through the supply chain and promote the technology to other sectors.
The PowderWay project strategy is fairly straightforward, states D’Souza-Mathew. It is defining part requirements through consultation with the end users – this includes typical dimensions of candidate reactor pressure vessel parts, as well as thermal, mechanical, fatigue, corrosion resistance and microstructural characteristics.
At the same time, the PowderWay project is identifying the requirements and methodology for code acceptance, to determine the information required by the standardisation body so it can present a robust code case. Before PM methods can be deployed in the European nuclear industry, they must be accepted by the standardisation body AFCEN. The consortium is exploring a route for code acceptance within the RCC-M standards for mechanical component fabrication.
Code requirements will guide the search for available information in an attempt to qualify the materials, manufacturing processes, benefits, limitations, testing methods and comparative data. Gaps between current technology and potential uptake will be prioritised and recommended in the roadmap.
The consortium has evaluated a range of PM techniques on their maturity and potential for application, and is now focusing on three processes: Hot Isostatic Pressing, Additive Manufacturing, and Spark Plasma Sintering.
Current materials of interest are austenitic stainless steels, nickel-based superalloys, and ferritic steel. The intention is to evaluate parts made from these materials in monolithic and dissimilar weld joint configurations. To achieve this, novel and proven non-destructive testing techniques, which are sensitive to PM-specific defects, are also under investigation.
The consortium is keen to talk to established members of the PM industry in order to help it focus on high priority areas and avoid recommending R&D that is already being carried out elsewhere. Those who are interested in this or can help bring the benefits of PM to the nuclear industry, are requested to contact Mark D’Souza-Mathew, email: [email protected] (+44 (0) 7710 655002).