The US Department of Energy’s Oak Ridge National Laboratory has restarted production of plutonium-238 after almost 30 years.
Submitted by IWB, on December 29th, 2015
PU-238 is used to power heat generators that make electricity for deep space probes.
In an effort to avert an outer space energy crisis, the US Department of Energy’s Oak Ridge National Laboratory (ORNL) has restarted production of plutonium-238 (PU-238) after almost 30 years. The civilian stockpile of the plutonium isotope used to power the radiothermal generators (RTG) that make electricity for US deep space probes has dwindled to only 35 kg (77 lb), so the first 50 g (1.7 oz) of plutonium oxide produced by the laboratory marks a major turnaround in American space capabilities.
PU-238 is an unstable isotope of plutonium with a half life of 87.7 years. As it decays into uranium-234, each gram produces about 0.5 watts of thermal power, which allows small RTGs to power spacecraft far from the Sun or on the surface of planets without the need for solar panels.
It’s a system that’s been very successful since the Apollo program, but since the Savannah River Plant in South Carolina stopped producing PU-238 in 1988, NASA has been relying on a stockpile of the element purchased from Russia in 1993. Only half of what remains meets specifications, so ORNL says that there’s only enough left to power two or three NASA missions. Though PU-238 is produced in nuclear reactors, extracting it requires a prohibitively expensive isotopic separation process, so special production lines are needed.
To remedy this, ORNL is developing a new production line under a US$15 million program. The process involves taking neptunium-237 (NP-237) feedstock from the Idaho National Laboratory, converting it to neptunium oxide, then mixing it with aluminum, and pressing it into high-density pellets. These are then bombarded with radiation in ORNL’s High Flux Isotope Reactor to turn the NP-237 into NP-238. This, in turn, decays quickly into PU-238.
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