The ALM process can provide a number of advantages, both business and technical, over traditional manufacturing methods. The justification for considering ALM arises from the volume of the market. For a small reactor with product lifespans of 40 to 60 years it is clear that no single supply chain can support the surge of production volumes at product launch and then sustainment for replacement parts towards the tail end of the product life with the same supply chain. This again is a new challenge for the nuclear industry that has evolved around a culture of bespoke engineering, where support for a plant through life from the same bespoke supply base is acceptable. For a small reactor delivered as a volume product the sustaining engineering challenge to the manufacturing supply base is different. Sustaining the product through life can no longer use the same original equipment manufacturer (OEM) supply chain economically. Automotive manufacturers do not supply replacement door panels for 10-year-old vehicles using the same line that delivers for their current year models. The small reactor supply chain faces the same set of challenges. Techniques such as ALM that have lower volume applications come into play offering significant economic advantages over the initial OEM supply chain. This is part of a strategy to maintain the competitive support of the plant through its operating life.

More specifically the attributes of ALM can be considered as two groups, OEM benefits and through-life benefits. ALM-OEM benefits include the following:

• Unit and/or through-life cost saving from reduced material quantity and/or machining costs offered by the ALM process.

• Unit and/or through-life cost savings from a reduced part count, e. g. manufacturing an assembly of multiple parts as a single component.

• The availability of welding test pieces, non-destructive examination (NDE) test pieces and other assembly and manufacturing aids significantly ahead of lead units can greatly reduce development programmes.

ALM — through-life benefits include the following:

• ALM can provide an alternative strategic sourcing route to the traditional forging, casting or fabrication route. It is highly suited to the low-volume, high-quality requirements of supplying nuclear-grade components. It can therefore be used to mitigate the risk of an existing manufacturing route that is threatened and/or may not be viable in the future for through-life sustainment.

• Where the existing manufacturing route is causing significant difficulties in supporting build, due to length of the manufacturing timescales.

By manufacturing components in layers, geometries that could not previously be

manufactured can now be produced. This enables a number of potential benefits:

• Optimisation of design definition for improved performance.

• Assemblies can be consolidated into a single component, thus simplifying manufacturing processes, reducing through-life costs, removing welds and fabrication, reducing inventory.

• Multi-functional parts can be produced by integrating cooling channels, electrical controls and instrumentation and/or cable management channels within structures.

• A structural integrity improvement may be realised, e. g. elimination of welds.

• High stiffness to weight ratio parts can be manufactured with internal lattice structures driven by finite element analysis (FEA) optimisation algorithms. These structures have thicker lattices where loading is high and thinner lattices where loading is low.

• Graded structures can be produced, where the material type is varied within a single structure, e. g. a tube can be manufactured that is Type 316L stainless steel at one end and Inconel 625 at the other, without the need for a transition weld.

12.3.1 Electron beam melting (EBM)

Additive manufacture by electron beam manufactures parts by melting metal powder layer-by-layer using an electron beam in a high vacuum environment. Parts produced by electron beam melting (EBM) are usually smaller than those produced by the laser process, but the EBM process does yield components that are fully dense, void-free and extremely strong.

As with ALM, CAD geometry, a power source and metal powder is required. However unlike ALM, EBM-fabricated components do not require heat treatment because of their high densification and operating temperature of typically 700-1000 °C during the fabrication phase. EBM is used in the aerospace sector where titanium and titanium-alloy components are produced, although systems do exist which can produce components up to 450 mm X 100 mm X 100 mm in a small variety of high — value metals.

Nuclear component materials in nickel-based alloys could be manufactured by the EBM process, but a cost-benefit analysis should be made to determine the viability when compared to existing fabrication techniques.