Remember the New Horizons mission? Beautiful images of Pluto will remain our closest encounter with any planet for the next few centuries at least. It’s a momentous achievement for humanity – and it was realised largely thanks to an element after the planet itself – Plutonium.

In fact, almost all our photos of objects in the solar system have plutonium to thank – the Voyager missions that brought us Jupiter, Saturn, Neptune and Uranus – are still running multiple decades later thanks to a plutonium power source.

We have all sorts of energy sources for our machineries – from fossil fuels to nuclear reactors, and yes, solar power too. But the problem with them is that they need regular maintenance for their constant operation and are mostly bulky. And of course, none of them are as efficient as nuclear power. Plus, what about remote areas that have to operate unmanned for a very long duration – such as the deep-space missions and the bottom of the oceans? Nuclear power helps, of course. But it is specifically an isotope of plutonium – plutonium-238, that’s been helping us embark on new frontiers – both down here and up in the cosmos.

Related: Solar vs Nuclear – What energy future are we headed for?

Why Plutonium-238?

Plutonium-238 is one of the 15 isotopes of the element plutonium. It is highly radioactive, with a half-life of 87.7 years. Plutonium-238 undergoes alpha-decay to give uranium-234, releasing 5.6 MeV of energy in the form of heat while it’s at it. Of course, we have several other nuclear fuels we could use for energy generation; however, plutonium-238 stands out because of some special qualities it is endowed with.

P-238 is safer to handle than most radioactive fuels as it emits just alpha-particles – not any other form of radiation. It can be conveniently stored in a ceramic form as plutonium dioxide and can withstand high temperatures as well. Moreover, the half-life of plutonium-238 is quite ideal and it emits almost constant heat in small amounts for a very long duration. It is the best we have at the moment.

Related: Where does all the nuclear waste go?

P-238 doesn’t naturally occur on the planet – we have to yield it and the production is immensely expensive – even for a budget backed by an entire nation. Plutonium obtained as spent fuel from nuclear reactors usually contains roughly 2% of plutonium-238. But even this amount is fairly pointless – owing to difficulties in isotope separation. Generally, pure plutonium-238, when needed for energy generation, is produced by irradiating neptunium-237, which we source from spent-fuel from nuclear reactors.

 

Production is back

No amount of usable plutonium 238 was produced by humanity in the past 3 decades. All the plutonium we’ve been using so far was last made in the middle of the Cold War. With the end of the Cold War and USA’s subsequent slowdown of nuclear weapon development, the production of plutonium 238 ceased. Plutonium was never produced specifically for scientific missions – NASA used plutonium sourced from production that was originally meant for defence. Several kilograms produced during this period had been utilised by NASA to power its space crafts. It was good timing that changed how we look at our solar neighbourhood.

The New Horizons mission utilised among the last remaining sources we had of this special fuel – which meant deep space missions were in jeopardy again. You can’t rely on solar power at distances near Jupiter’s and beyond. But fortunately for humanity, production seems to be back.

Recently, the United States’ DOE announced that it successfully produced 50g of plutonium 238 at the Oak Ridge National Laboratory (ORNL).  This is the first production of the isotope by the US since 1988, when the Savannah River Plant of Carolina was banned. With some pressure and funding from NASA, the DOE had been working for the past two years to setup its High Flux Isotope Reactor at the ORNL in order to make plutonium-238. At the current rate, DOE estimates that an average of 1.5 kg of plutonium-238 can be produced in a year. This isn’t all that adequate if you consider existing requirements and the rising utility of plutonium-238. But it’s good news nevertheless.

The Possibilities are Endless

Plutonium 238 is an incredibly vital fuel and finds its use in many important fields. It acts as a source of heat energy and also electricity – a single gram of plutonium 238 can produce about 0.5 W of power. The most obvious application is as a core heat source in Radioisotope Thermoelectric Generators (RTGs) and Radioisotope Heater Unit (RHUs). RTGs are power generators for off-grid sites that do not require regular manual maintenance and has been used by NASA for over 50 years to power more than 30 space crafts. These space crafts are mainly designed to operate in deep-space where solar energy cannot be harnessed. We have had plutonium-238 powered RTGs used in space crafts like Voyager 1 and 2, Cassini-Huygens, Curiosity and so on. NASA has renovated the existing RTG to what it called ‘Multi Mission RTG’ or simply MMRTG which uses energy from plutonium-238 in a more efficient way. RHUs, too, are used in most space crafts in order to keep the components and systems warm throughout its journey.

Related: Nuclear Fusion – Persistently decades away

Another interesting use we’ve found for plutonium-238 is power generation for cardiac pacemakers for heart patients. In the late 1960s, Medtronic Company designed nuclear-powered pacemakers. It implanted 250 pacemakers out of which about 90 are still serving. Because the world stopped producing plutonium-238, the manufacturing had to be discontinued. There’s hope for revival, assuming we have some extra plutonium-238 after NASA grabs its share for space missions.

 

Plutonium-238 is being used to power sensors at the ocean bottoms. Russia had put up about 1000 lighthouse beacons that use power plutonium-238 and most of them are now in ruins. The US had also placed remote navigational systems and monitoring centers in the arctic areas which are powered by plutonium-238 generators.

The Future

Plutonium-238 potential is enormous. Futurists are hinting their possible use in everyday gadgets to replace conventional batteries, and perhaps even in automobiles. But the technology and the production of plutonium-238 are still exceedingly expensive and legal conditions are still very stringent. Moreover, many people are still scared of radioactive contaminations that can occur with uncontrolled accidents. In the US, government entities are the only legal suppliers of the plutonium-238. What we need is investments, more funding and more firms to work for the increase in the supply of plutonium-238.