New high-efficiency nuclear fuel meant to burn longer and stronger may prove unstable in an emergency and hard to dispose of, experts say.

By further enriching the uranium used to power nuclear reactors, operators have been able to extract more electricity from a given amount of fuel, a measure expressed in gigawatt-days per tonne of uranium (GWd/tU).

Ramping up fuel efficiency has worked especially well in the pressurised water and boiling water reactors used in the US and elsewhere.

A new generation of nuclear plants in the US and the UK is poised to use reactors designed for burn-up rates of 60 GWd/tU, according to the magazine New Scientist, which canvassed experts.

Disposal is also a potential problem because the new, high-efficiency fuel is up to 50% more radioactive than fuel currently in use, thus generating far more heat during storage.