Additive manufacturing in the nuclear industry
Zirconium, boron steel and radiation: 3D printing of components for nuclear and fusion reactors.
1. Introduction: Radiation and Corrosion
The nuclear industry (nuclear power plants and future fusion reactors) places the most brutal demands on materials known to mankind. Components in the reactor core must withstand extremely high temperatures, enormous pressure, massive neutron radiation and corrosive cooling water.
For a long time, metal 3D printing was taboo here because pores or defects in the material could lead to catastrophic failures. However, with the perfection of PBF-LB and DED processes as well as the introduction of the strictest quality controls (CT scans, HIP), the additive revolution in nuclear technology is now beginning.
What does neutron radiation do in metal?
Neutrons “bombard” the metal lattice at the atomic level. They knock atoms out of their lattice positions (Frenkel defects). Over time, the material hardens extremely, loses all elasticity (ductility) and becomes extremely brittle (embrittlement). Additively manufactured structures with special, fine grain structures can often “heal” (absorb) this radiation damage better than coarse-grained castings.
2. Replacement parts for aging reactors
Many nuclear power plants in the world are over 40 years old. If a special impeller breaks down, there are often neither plans nor the original manufacturer (obsolescence).
Additive manufacturing offers the only economical solution here (reverse engineering). The broken part is digitized via 3D scanning and reprinted from corrosion-resistant stainless steel (like 316L) or nickel-based alloys in a few days, instead of waiting months for a newly manufactured casting tool.
3. Reactor components from the printer
The design freedom of 3D printing enables more efficient reactor designs:
- SMRs (Small Modular Reactors): The next generation of mini reactors relies heavily on AM. The US company Westinghouse printed a 3D titanium lattice structure (thimble plugging device) in 2020, which was installed as a debris filter directly in the fuel assembly of a commercial reactor.
- Uranium processing: Oak Ridge National Laboratory (ORNL) printed complete core components for the TCR (Transformational Challenge Reactor) project from silicon carbide and special metal alloys that surround the uranium.
4. Challenges with nuclear materials
Some metals are essential but difficult to print.
- Zirconium alloys (Zircaloy): The absolute standard for cladding of fuel rods, as zirconium absorbs extremely few neutrons. However, zirconium powder is highly reactive and extremely explosive in 3D printing, which makes processing extremely complex.
- Boron-doped steel: Boron absorbs neutrons and stops the chain reaction (control rods). However, alloying boron into steel powder for printing often leads to severe metallurgical cracking upon cooling from the laser melt.
5. Conclusion: A long road to approval
The physical possibilities are gigantic, but regulatory authorities (such as the NRC in the USA) demand absolute zero-defect guarantees. Every printed nuclear component must be HIPed, CT scanned and certified through years of irradiation testing. However, the change has begun: 3D printing will form the backbone of the new, modular reactor generation.