How nuclear waste could fuel future power plants

By Stephen Beech

Nuclear waste could be a source of fuel in future reactors, say scientists.

American researchers are working on new systems to use waste products from the current fusion process to make a rare version of hydrogen called tritium.

The world is facing a growing need for electricity - from electric-powered cars to artificial intelligence (AI) data centers.

In theory, nuclear fusion - the process that fuses atoms together, releasing heat to turn generators - could provide huge energy supplies with minimal emissions.

But nuclear fusion is an expensive prospect because one of its main fuels is tritium.

Dr. Terence Tarnowsky, a physicist at Los Almos National Laboratory (LANL), New Mexico, explained that today’s nuclear power plants generate energy through a process called nuclear fission.

During nuclear fission, a plutonium or uranium atom splits to release energy and particles called neutrons, which go on to split more atoms.

The fission chain reaction provides a "steady stream" of energy, but also results in long-lived nuclear waste.

Dr. Tarnowsky says proposed nuclear fusion power plants would generate energy by combining atomic nuclei.

He said: "With fusion, forms of hydrogen, called deuterium and tritium, would join to create heavier atoms.

"This process, which powers stars in the universe, releases a large amount of energy and, unlike fission, produces very little radioactive waste."

But while deuterium is readily available, the US currently lacks a secure and predictable supply of tritium.

Dr. Tarnowsky said: “Right now, the value of commercial tritium is about $15 million per pound, or $33 million per kilo, and the US doesn’t have any domestic capability to create it.

“So, we have this tritium supply shortage.”

He says tritium occurs naturally in the upper atmosphere, and the current major commercial source is fission reactors in Canada.

Dr. Tarnowsky said: “The total tritium inventory on the planet is about 55 plus or minus 31 pounds.

“Making some assumptions, 55 pounds is enough tritium to power more than 500,000 homes for six months.

"This is more than the residential units in Washington, D.C.”

Unlike its stores of tritium, the US has thousands of tons of nuclear waste produced by commercial nuclear power plants.

It contains highly radioactive materials, which require expensive storage to keep it safely contained.

Long-term storage raises concerns about radiation leaks into the environment with the potential to harm plants and wildlife or cause cancer in humans.

Dr. Tarnowsky saw an opportunity to assess the feasibility of using still-radioactive nuclear waste to generate valuable tritium.

He has conducted multiple computer simulations of potential tritium reactors to evaluate the designs’ production and energy efficiency.

Dr. Tarnowsky said: "The simulated reactor designs use a particle accelerator to jump-start atom-splitting reactions in the nuclear waste.

"As atoms divide in the simulation, they release neutrons and ultimately produce tritium after a series of other nuclear transitions.

"The accelerator feature would allow operators to turn these reactions on or off and is considered safer than the chain reactions that take place in a typical nuclear power plant.

"Although the basic principles of the design are not new, advances in technology could make it more efficient than when it was first considered in the 1990s and early 2000s."

So far, he estimates that the theoretical system running on one gigawatt of energy, or the total annual energy needs of 800,000 U.S. homes, could produce about 4.4 lbs (two kilos) of tritium per year.

That amount is on par with the total yearly output from all reactors in Canada, according to Dr. Tarnowsky.

He says a key advantage to his system would be the "efficiency" of tritium production.

Dr. Tarnowsky projects that the design would produce more than 10 times as much tritium as a fusion reactor at the same thermal power.

He plans to calculate the financial cost for tritium production once he has more sophisticated calculations of the reactor’s efficiency.

Dr. Tarnowsky will refine his simulations to more precisely evaluate the efficiency and safety of the reactor’s design, most of which have been previously engineered but not yet combined in such a way.

For example, he plans to develop new code for a model that surrounds the nuclear waste with molten lithium salt, an established design for reactors with uranium fuel that has only been used for scientific experiments.

Dr. Tarnowsky says the salt’s cooling properties offer a potential safety measure, and the setup would make it difficult to extract the waste for weapons development.

The ultimate goal is for the modelling to help decision-makers understand which simulation has the most potential for future implementation.

Dr. Tarnowsky says it’s all part of a plan to use existing technology to lower costs.

He added: “Energy transitions are a costly business, and anytime you can make it easier, we should try."

Dr. Tarnowsky is due to present his results at the fall meeting of the American Chemical Society (ACS) in Washington, DC.