Engineering360: "Hydrogen storage using depleted uranium"

It would be nice if some metrics were given,, such as lb of hydrogen storage per lb of depleted uranium,, temperature differential requirement,, availability of depleted uranium...

The announcement says the hydride is UH₃, which means 3 grams of hydrogen per 238 grams of uranium. This sounds like a very low ratio but the relative densities of the two elements needs to be considered. For uranium it is 19.1g/cm³ and for liquid hydrogen it is 0.071g/cm³.

The announcement mentions hydrogen storage at quantities double the amount in the liquid form, so the effective density of the hydrogen in the hydride is closer to 0.14g/cm³. This is a similar amount of storage compared to hydrides of aluminum and a few other metals which have been investigated as methods for storing hydrogen in motor vehicles since the 1980's.

To effectively allow the reversible chemical reaction in fairly short time periods, the uranium metal would have to be in a finely divided form, which would reduce its density somewhat.

Worldwide, the amount of depleted uranium created from the weapons and atomic energy industries is much greater than 1x10⁶ kg. Therefore I would doubt that its supply as a chemical is a significant problem. It is "routinely" used in munitions as well as counter weights and armor, so the technology to convert it from uranium fluoride or uranium oxide is in regular use.

I see two significant problems or dangers:

1. The biggest is flammability of uranium. In a finely divided form it spontaneously combusts in the presence of air at room temperature. This oxidation reaction produces a very high amount of heat, with a flame temperature greater than 3000ºC. Therefore the hydrogen flowing into the storage container must be extremely pure to avoid contamination of the uranium bed by the oxide form and the risk of fire.
2. The toxicity of uranium is a serious caution--both as a chemical poison more dangerous than lead or plutonium and as an alpha-emitter which is ingested and transferred into the blood stream in its microscopically-divided oxide. These two forms of toxicity potentiate each other.

--JMM