I’m no expert, but I don’t believe that “high-assay low-enriched uranium” is the sort you can use in nuclear weapons, per it being “low-enriched”. According to the DOE, HALEU only goes up to 20% enrichment [0]. Nuclear weapons, it seems, need it to be enriched beyond 20% [1]
[0] https://www.energy.gov/ne/articles/what-high-assay-low-enric... [1] https://en.wikipedia.org/wiki/Enriched_uranium
Dirty bombs
Uranium-235 isn't useful for dirty bombs: it's too long-lived and not radioactive enough. Making dangerous levels of radiation requires short-lived isotopes. Some of these are the products of uranium fission, which is why spent uranium fuel is a radiation hazard. But isolating U-235 just to fission it to get radioactive isotopes like cesium-137 would not be the easiest way to get them.
"Uranium-235 isn't useful for dirty bombs"
It is when your goal is to throw a ton of alpha emitters into the environment for the population to ingest. Do you remember your nuclear cookie thought experiment?
Uranium-235 has a half-life of 704 million years.
It emits so slowly that the main hazard is heavy metal poisoning, which you'd also get from the depleted uranium that's a waste product from enrichment.
From the numbers I see on https://www.iaea.org/topics/spent-fuel-management/depleted-u..., if a dirty bomb with 1kg of 100% pure Uranium-235 exploded and evenly deposited a fine dust over a 170 by 170 meter square of typical soil, the total Uranium-235 (and specifically that isotope) of the top meter would only double; the total mass of uranium in that volume would only go up by 0.7%.
- ibid[dead]