Waste will see combination of repositories, boreholes, recycling
The long-term toxicity of nuclear waste is the most pervasive argument against nuclear power but spent fuel can be effectively, permanently, and safely dealt with through a combination of deep-hole repositories, boreholes, and recycling.
Recycling is being explored by several companies developing next-generation reactors, including Oklo, Orano, Moltex, and Elysium, but until these technologies are fully commercialized, and with the public uneasy over on-site storage, waste burial is the next best option.
Low-level waste (LLW), including clothing, instruments, and machinery, accounts for around 90% by volume of all the waste types produced by nuclear technologies and can be stored safely via land-based disposal immediately after it is packaged for long-term management, according to the World Nuclear Association.
Intermediate-level waste (ILW) contains long-lived radioisotopes and is stored pending permanent disposal, while high-level waste (HLW), or spent nuclear fuel (SNF) may be kept in ponds or dry casks.
The global solutions for ILW and HLW are currently framed as temporary – though many argue that dry cask storage at the reactor site or centrally is sufficiently secure – and the next step is recycling for the new advanced reactors or to bury it deep underground.
Today, the Posiva Oy facility Onkalo in Finland is the only permanent geological repository that is licensed and in construction.
The practice of consent-based siting, whereby a site is chosen after an exhaustive public inquiry into whether a particular location is acceptable, has tripped up governments worldwide.
So-called NIMBYism (Not In My Back Yard) is common in much of North America and Europe, where trust in public entities is low, and can lead to long delays.
There is about 86,000 tons of SNF stored on-site at 75 operating or shutdown power plants in 33 states in the United States and, of those who believe in nuclear power, less than half support keeping spent fuel within 50 miles of their own communities, according to a Morning Consult poll.
Meanwhile, one in three Americans already live within 50 miles of a nuclear waste storage site, according to the company Deep Isolation.
The U.S.’s long-preferred option of Yucca Mountain in Nevada was abandoned after strong opposition both locally and statewide by the public, local indigenous communities, and, consequently, many politicians.
The U.S. Congress directed the Department of Energy (DOE) to concentrate on the Yucca Mountain site from nine other candidates in 1987 and the Secretary of Energy recommended the site to the President in 2002.
Strong state opposition lead the government to drop the Nevada option more than 20 years later in 2009.
In Switzerland, the National Cooperative for the Disposal of Radioactive Waste (Nagra) announced in September 2022 it had selected a site at Nördlich Lägern, north of Zurich. Nagra expects to submit a construction license by 2024.
“A key difference that we've heard from our Swiss colleagues is that in their country there is a lot of trust in their government and government scientists, so if the government says that this is the most scientifically and technically sound sites, the public will generally accept that,” said Acting Office Director of Integrated Waste Management at the U.S. DOE Erica Bickford during the American Nuclear Society Webinar ‘Spending time on spent nuclear fuel.’
“I think we know that that may not be the case everywhere,” she added.
Overview of inventory suitability for Deep Borehole Disposal (DBD)
(Click to enlarge)
Source: Deep Isolation study "Deep Isolation and ERDO: Preliminary assessment of a Deep Isolation borehole repository as a disposal option for nuclear waste in the ERDO countries."
Deep and narrow
Berkeley, California-based company Deep Isolation attempts to apply directional drilling technology to nuclear waste management and, instead of building a repository with deep, wide caverns and storage units, focuses on inserting waste into narrow bore holes that can reach hundreds of meters into the earth.
“You don't have anybody underground, so you don't have the kind of mining concerns you'd have with humans underground, including the ventilation and other aspects. And, so, it does allow you to do this more safely and efficiently,” says Deep Isolation's Chief Operating Officer Rod Baltzer.
Each fuel assembly is around 15 feet (4.6 meters) long and fits into a standard canister of a little less than 15 inches (38.1 cm) wide or 47 cm wide for larger waste forms such as vitrified HLW. Each borehole, about 18-inch-wide, can hold some 200 canisters.
Borehole repositories leave waste in stable geological formations and are particularly well suited for HLW.
Following an initial study into the suitability of parts of the UK nuclear waste inventory for Deep Isolation’s boreholes, the country’s Nuclear Waste Service (NWS) found that, while a Geological Disposal Facility (GDF) would also be necessary, the company’s solution could be considered to dispose of all of the UK’s high heat generating waste inventory.
Deep Isolation found 11% of the UK’s Inventory for Geological Disposal (IGD) is operationally and commercially suitable for disposal in a deep borehole repository, or all the high heat generating waste (HHGW).
That would account for 96% of the IGD’s radioactivity levels in 2200, according to the Nuclear Decommissioning Authority’s (NDA’s) calculations.
HHGW would typically need to be spaced out within a mined repository so heat concentration doesn’t rise too high, a problem which can be solved by placing long canisters end-to-end in a borehole.
“You can have some bulky packages, large boxes the size of a desk, that are filled with lower activity waste and are not generating heat but are too big and bulky to fit down a borehole, and so that would still need some kind of repository, while we can take all the high heat generating waste,” says Baltzer.
Keep it simple
With the HHGW taken out of the equation, repository designs can be simplified, he says.
The boreholes can go directly into the bedrock or can go horizontally along seams of rock that have not moved for millions of years using technology that has been used by the oil and gas industry for decades.
As with geological repositories, the problem with boreholes is less the technology and more the public perception that will decide future use.
A GfK study, funded by Deep Isolation, found more than 80% of respondents would rather the waste be disposed of deep underground than transported (through people’s ‘backyards’) long distances.
While not all nuclear plants are built above the necessary rock formations, the flexibility of borehole technology means a disposal process that could minimize how far SNF would have to be moved from the plant before permanent disposal, Baltzer says.
“It depends on customers and sites and other things, but we're ready to deploy in a matter of years,” he says.
By Paul Day