On the practicalities of producing a nuclear weapon using high-assay low-enriched uranium

It was recently argued by Kemp et al. that HALEU (high-assay low-enriched uranium, or uranium enriched up to 19.75%) can conceivably be used to produce a nuclear weapon and on this basis civilian enrichment limits should be lowered to 10% or 12%. We find their argument unconvincing in several respects.