Orano and UNC Charlotte study additive manufacturing for nuclear transport cask impact limiters

Orano Federal Services and the University of North Carolina at Charlotte have completed an updated investigation into using additive manufacturing to produce impact limiters for transportation casks used to ship spent nuclear fuel (SNF). The study examined whether advances in commercial metal printing could address deficiencies identified in earlier research from 2019.

Impact limiters are external protective structures fitted to transportation casks — sometimes called transportation overpacks — that absorb energy during accidents, including 9-meter (30-foot) free drops onto an unyielding surface, crushing loads, puncture events, 30-minute fully engulfing fires at 800°C (1,475°F), and 15-meter (50-foot) water immersion. 

Current designs rely on balsawood, redwood, or honeycomb aluminum structures that cost approximately $1 million per unit to fabricate.

Gyroid geometry shows cost and performance advantages

The updated study identified two commercial metal printing technologies capable of producing large AM components: selective laser melting (SLM) and fused filament fabrication (FFF). The largest commercially available SLM printer cited by the investigation produces components up to 600 mm × 600 mm × 600 mm using stainless steel powder. The largest FFF printer evaluated produces components as large as 5,791 mm × 1,219 mm × 1,219 mm, also in stainless steel, though with less dimensional precision.

Compression testing and ANSYS simulation work led the team to a final design consisting of 36 bricks — each 508 mm × 508 mm × 1,016 mm (20 in. × 20 in. × 40 in.) — produced on FFF printers and enclosed within stainless steel cladding. The gyroid internal infill pattern, selected over honeycomb after comparative testing, offered up to 80% weight savings and exhibited inward, accordion-style collapse under compressive load — a behavior more favorable than the outward collapse recorded for honeycomb samples. 

At 5% infill density, the gyroid produced a maximum stress of 68 kilopounds per square inch (ksi), approximately equivalent to the 67 ksi recorded for redwood under a 30-foot drop scenario.

Cost modeling placed the FFF AM design’s breakeven point at 10% gyroid infill density relative to a $1 million redwood impact limiter. At the 5% infill density found to meet drop performance criteria, FFF AM components were projected to save more than $1m per unit, while an SLM-based design at equivalent infill was projected to save more than $1.7m.

Standards gaps remain a barrier to implementation

Despite the technical progress, the study identified the absence of nuclear-grade AM standards as a primary obstacle to qualification. Existing frameworks, such as ISO/ASTM 52900, cover general AM principles but do not address nuclear safety function requirements. 

The study was published in the April 2026 issue of Radwaste Solutions.