Nuclear batteries sound futuristic, but they have been in use for more than sixty years. Their record shows where they shine and where they go wrong. It also helps separate what they can realistically do from the headlines.
In space: the big success
Solar panels become nearly useless past Jupiter, in the long lunar night, or on a dusty Martian winter day. That is where radioisotope thermoelectric generators (RTGs) have proved themselves. The United States has flown them since 1961. They powered experiments that Apollo astronauts left on the Moon, the Viking landers on Mars, Cassini at Saturn and New Horizons at Pluto. The two Voyager probes, launched in 1977, are still sending data from beyond the edge of the solar system on theirs, although their power has dropped over the decades as the plutonium decays and the thermocouples wear.
NASA’s Curiosity and Perseverance rovers each carry a Multi-Mission RTG, which started out producing about 110 watts. That isn’t much. The rovers store it in rechargeable batteries so they can use bursts of power for driving and drilling. But it keeps running day and night, through dust storms and winter, which is why Curiosity has worked on Mars since 2012.
In the body: plutonium pacemakers
In the 1970s, before long-life lithium batteries, pacemaker batteries lasted only a couple of years, so patients needed repeated surgery. Manufacturers’ answer was a pacemaker with a tiny plutonium-238 power source. A study of the US program found that 151 of these units were implanted in 131 patients before the last one went in, in January 1983. They worked remarkably well: one patient was paced by the same device for 35 years. Their drawback was paperwork, not performance. Each one had to be tracked for life and recovered after the patient died, and lithium batteries soon became good enough that the trouble wasn’t worth it.
On the ground: a cautionary tale
The Soviet Union built RTGs on a much larger scale, powering hundreds of lighthouses and navigation beacons along its Arctic coast with strontium-90. When the Soviet Union collapsed, many were abandoned. Some were broken open by scrap-metal hunters. In December 2001, three woodcutters near the village of Lia in Georgia found two unmarked, unshielded strontium-90 cores in a forest and used them to keep warm overnight. All three suffered severe radiation injuries, and one of them died. The International Atomic Energy Agency then helped Georgia and other former Soviet states recover the remaining sources.
The lesson isn’t that nuclear batteries are inherently dangerous. It is that a device lasting for decades needs someone keeping track of it for decades too.
What about phones and smartwatches?
Every few years a headline promises a phone that never needs charging. The numbers don’t support it. Today’s commercial betavoltaic cells produce microwatts, while a smartwatch needs thousands of times more and a phone far more still. A realistic role for small nuclear batteries is trickle-charging a conventional battery, or powering low-power devices that are hard to reach and must run for decades: sensors inside bridges, pipelines and machinery, seabed instruments, and perhaps one day medical implants.
To learn how the technology works, start with Nuclear Batteries: How They Turn Radioactive Decay into Electricity.
