In any discussion of disposal of waste one should first pause and consider whether one is actually dealing with waste. This is especially true of used nuclear fuel waste as defined in the Nuclear Fuel Waste Act, as it emerges from our CANDU reactors.
Used CANDU fuel, although some of its heavy atoms have a radioactive life of close to a million years, is not waste. Therefore should not even be considered for disposal. Less than 1% of the uranium fuel has been used and converted into already massive amounts of non-carbon energy. To jettison the remainder is like licking a chocolate bar once and chucking the rest.
The very first reactor to produce electricity from nuclear energy, the EBR-I in 1951, showed how to utilize the other 99% of the fuel. It required enriched fuel, which Canada wanted to forego since it easily leads to a path of nuclear weapons. We built the CANDU, a thermal reactor fuelled with natural uranium, yielding an industry best 0.74% of the nuclear energy in the fuel. All other thermal reactors are worse at about 0.55% of the potential energy of mined uranium. The remainder for all of them is considered waste, wrongly.
But the EBR-I was a fast-spectrum reactor, like some of the small modular reactors (SMRs) proposed for Canada at present. With recycling of its fuel, as shown for its larger cousin, the EBR-II, it could consume all of the heavy atom in the uranium fuel, leaving only split-atom fission products that decay in days, weeks, months and years, with only to atom types, Sr-90 and Cs-137, having half-lives of 30 years, much shorter than the million year life of current used fuel.
Two SMRs proposed now for Canada, the SSR-W of Moltex and the ARC-100 of Advanced Reactor Concepts have recycling of used CANDU fuel as part of their modus operandi. Both processes involve electrorefining in molten salt, like pyroprocessing worked out at the Argonne National Laboratories and operating there since then. The process residues are those fast-decaying fission products, with heavy atoms recycled as fuel and working fluid salts recycled as electrolytes. The remainders are therefore minimal, requiring temporary storage until they decay to valuable stable atoms and minerals whose worth can be calculated as about $3 million per ton.
However, that number pales in comparison to the $60 trillion of non-carbon electricity plus process heat that can be extracted from the heavy atoms in the current used CANDU fuel.
With such an imminent prospect planned even now for Canada’s expansion for nuclear energy, disposal should not even be part of the discussion for used CANDU fuel, nor for any such fuel emerging from future SMRs. We just have to pick recycling through fast-spectrum reactors.