Lindsay Krall and Allison Macfarlane have written an important article in the Bulletin of the Atomic Scientists debunking claims that certain Generation IV reactor concepts promise major advantages with respect to nuclear waste management.1 Krall is a post-doctoral fellow at the George Washington University. Macfarlane is a professor at the same university, a former chair of the US Nuclear Regulatory Commission from July 2012 to December 2014, and a member of the Blue Ribbon Commission on America's Nuclear Future from 2010 to 2012.
Krall and Macfarlane focus on molten salt reactors and sodium-cooled fast reactors, and draw on the experiences of the US Experimental Breeder Reactor II and the US Molten Salt Reactor Experiment.
The article abstract notes that Generation IV developers and advocates "are receiving substantial funding on the pretense that extraordinary waste management benefits can be reaped through adoption of these technologies" yet "molten salt reactors and sodium-cooled fast reactors – due to the unusual chemical compositions of their fuels – will actually exacerbate spent fuel storage and disposal issues."
Here is the concluding section of the article:
"The core propositions of non-traditional reactor proponents – improved economics, proliferation resistance, safety margins, and waste management – should be re-evaluated. The metrics used to support the waste management claims – i.e. reduced actinide mass and total radiotoxicity beyond 300 years – are insufficient to critically assess the short- and long-term safety, economics, and proliferation resistance of the proposed fuel cycles.
"Furthermore, the promised (albeit irrelevant) actinide reductions are only attainable given exceptional technological requirements, including commercial-scale spent fuel treatment, reprocessing, and conditioning facilities. These will create low- and intermediate-level waste streams destined for geologic disposal, in addition to the intrinsic high-level fission product waste that will also require conditioning and disposal.
"Before construction of non-traditional reactors begins, the economic implications of the back end of these non-traditional fuel cycles must be analyzed in detail; disposal costs may be unpalatable. The reprocessing/treatment and conditioning of the spent fuel will entail costs, as will storage and transportation of the chemically reactive fuels. These are in addition to the cost of managing high-activity operational wastes, e.g. those originating from molten salt reactor filter systems. Finally, decommissioning the reactors and processing their chemically reactive coolants represents a substantial undertaking and another source of non-traditional waste. ...
"Issues of spent fuel management (beyond temporary storage in cooling pools, aka "wet storage") fall outside the scope of the NRC's reactor design certification process, which is regularly denounced by nuclear advocates as narrowly applicable to light water reactor technology and insufficiently responsive to new reactor designs. Nevertheless, new reactor licensing is contingent on broader policies, including the Nuclear Waste Policy Act and the Continued Storage Rule. Those policies are based on the results of radionuclide dispersion models described in environmental impact statements. But the fuel and barrier degradation mechanisms tested in these models were specific to oxide-based spent fuels, which are inert, compared to the compounds that non-traditional reactors will discharge.
"The Continued Storage Rule explicitly excludes most non-oxide fuels, including those from sodium-cooled fast reactors, from the environmental impact statement. Clearly, storage and disposal of non-oxide commercial fuels should require updated assessments and adjudication.
"Finally, treatment of spent fuels from non-traditional reactors, which by Energy Department precedent is only feasible through their respective (re)processing technologies, raises concerns over proliferation and fissile material diversion. Pyroprocessing and fluoride volatility-reductive extraction systems optimized for spent fuel treatment can – through minor changes to the chemical conditions – also extract plutonium (or uranium 233 bred from thorium). Separation from lethal fission products would eliminate the radiological barriers protecting the fuel from intruders seeking to obtain and purify fissile material. Accordingly, cost and risk assessments of predisposal spent fuel treatments must also account for proliferation safeguards.
"Radioactive waste cannot be "burned"; fission of actinides, the source of nuclear heat, inevitably generates fission products. Since some of these will be radiotoxic for thousands of years, these high-level wastes should be disposed of in stable waste forms and geologic repositories. But the waste estimates propagated by nuclear advocates account only for the bare mass of fission products, rather than that of the conditioned waste form and associated repository requirements.
"These estimates further assume that the efficiency of actinide fission will surge, but this actually relies on several rounds of recycling using immature reprocessing technologies. The low- and intermediate-level wastes that will be generated by these activities will also be destined for geologic disposal but have been neglected in the waste estimates. More important, reprocessing remains a security liability of dubious economic benefit, so the apparent need to adopt these technologies simply to prepare non-traditional spent fuels for storage and disposal is a major disadvantage relative to light water reactors. Theoretical burnups for fast and molten salt reactors are too low to justify the inflated back-end costs and risks, the latter of which may include a commercial path to proliferation.
"Reductions in spent fuel volume, longevity, and total radiotoxicity may be realized by breeding and burning fissile material in non-traditional reactors. But those relatively small reductions are of little value in repository planning, so utilization of these metrics is misleading to policy-makers and the general public. We urge policy-makers to critically assess non-traditional fuel cycles, including the feasibility of managing their unusual waste streams, any loopholes that could commit the American public to financing quasi-reprocessing operations, and the motivation to rapidly deploy these technologies. If decarbonization of the economy by 2050 is the end-goal, a more pragmatic path to success involves improvements to light water reactor technologies, adoption of Blue Ribbon Commission recommendations on spent fuel management, and strong incentives for commercially mature, carbon-free energy technologies."
Pyroprocessing: the integral fast reactor waste fiasco
In theory, integral fast reactors (IFRs) would gobble up nuclear waste and convert it into low-carbon electricity. In practice, the IFR R&D program in Idaho has left a legacy of troublesome waste. This saga is detailed in a 2017 article2 and a longer report3 by the Union of Concerned Scientists' senior scientist Ed Lyman. This will be of particular relevance if the US Department of Energy proceeds with its plan to support the construction of a 'versatile test reactor' based on GE-Hitachi's 'Power Reactor Innovative Small Module' (PRISM) design, which is based on IFR designs.4
Lyman notes that the IFR concept "has attracted numerous staunch advocates" but their "interest has been driven largely by idealized studies on paper and not by facts derived from actual experience."2 He discusses the IFR prototype built at Idaho ‒ the Experimental Breeder Reactor-II (EBR-II), which ceased operation in 1994 ‒ and subsequent efforts by the Department of Energy (DOE) to treat 26 metric tons of sodium-bonded metallic spent fuel from the EBR-II reactor with pyroprocessing, ostensibly to convert the waste to forms that would be safer for disposal in a geological repository. A secondary goal was to demonstrate the viability of pyroprocessing ‒ but the program has instead demonstrated the serious shortcomings of this technology.
"Pyroprocessing is a form of spent fuel reprocessing that dissolves metal-based spent fuel in a molten salt bath (as distinguished from conventional reprocessing, which dissolves spent fuel in water-based acid solutions). Understandably, given all its problems, DOE has been reluctant to release public information on this program, which has largely operated under the radar since 2000.
"The FOIA [Freedom of Information Act] documents we obtained have revealed yet another DOE tale of vast sums of public money being wasted on an unproven technology that has fallen far short of the unrealistic projections that DOE used to sell the project to Congress, the state of Idaho and the public. However, it is not too late to pull the plug on this program, and potentially save taxpayers hundreds of millions of dollars. …
"Pyroprocessing was billed as a simpler, cheaper and more compact alternative to the conventional aqueous reprocessing plants that have been operated in France, the United Kingdom, Japan and other countries.
"Although DOE shut down the EBR-II in 1994 (the reactor part of the IFR program), it allowed work at the pyroprocessing facility to proceed. It justified this by asserting that the leftover spent fuel from the EBR-II could not be directly disposed of in the planned Yucca Mountain repository because of the potential safety issues associated with presence of metallic sodium in the spent fuel elements, which was used to "bond" the fuel to the metallic cladding that encased it. (Metallic sodium reacts violently with water and air.)
"Pyroprocessing would separate the sodium from other spent fuel constituents and neutralize it. DOE decided in 2000 to use pyroprocessing for the entire inventory of leftover EBR-II spent fuel – both "driver" and "blanket" fuel – even though it acknowledged that there were simpler methods to remove the sodium from the lightly irradiated blanket fuel, which constituted nearly 90% of the inventory.
"However, as the FOIA documents reveal in detail, the pyroprocessing technology simply has not worked well and has fallen far short of initial predictions. Although DOE initially claimed that the entire inventory would be processed by 2007, as of the end of Fiscal Year 2016, only about 15% of the roughly 26 metric tons of spent fuel had been processed. Over $210 million has been spent, at an average cost of over $60,000 per kilogram of fuel treated. At this rate, it will take until the end of the century to complete pyroprocessing of the entire inventory, at an additional cost of over $1 billion.
"But even that assumes, unrealistically, that the equipment will continue to be usable for this extended time period. Moreover, there is a significant fraction of spent fuel in storage that has degraded and may not be a candidate for pyroprocessing in any event. …
"What exactly is the pyroprocessing of this fuel accomplishing? Instead of making management and disposal of the spent fuel simpler and safer, it has created an even bigger mess. …
"[P]yroprocessing has taken one potentially difficult form of nuclear waste and converted it into multiple challenging forms of nuclear waste. DOE has spent hundreds of millions of dollars only to magnify, rather than simplify, the waste problem. This is especially outrageous in light of other FOIA documents that indicate that DOE never definitively concluded that the sodium-bonded spent fuel was unsafe to directly dispose of in the first place. But it insisted on pursuing pyroprocessing rather than conducting studies that might have shown it was unnecessary.
"Everyone with an interest in pyroprocessing should reassess their views given the real-world problems experienced in implementing the technology over the last 20 years at INL. They should also note that the variant of the process being used to treat the EBR-II spent fuel is less complex than the process that would be needed to extract plutonium and other actinides to produce fresh fuel for fast reactors. In other words, the technology is a long way from being demonstrated as a practical approach for electricity production."
1. Lindsay Krall and Allison Macfarlane, 2018, 'Burning waste or playing with fire? Waste management considerations for non-traditional reactors', Bulletin of the Atomic Scientists, 74:5, pp.326-334, https://tandfonline.com/doi/10.1080/00963402.2018.1507791
2. Ed Lyman / Union of Concerned Scientists, 12 Aug 2017, 'The Pyroprocessing Files', http://allthingsnuclear.org/elyman/the-pyroprocessing-files
3. Edwin Lyman, 2017, 'External Assessment of the U.S. Sodium-Bonded Spent Fuel Treatment Program', https://s3.amazonaws.com/ucs-documents/nuclear-power/Pyroprocessing/IAEA...
4. World Nuclear Association, 15 Nov 2018, 'PRISM selected for US test reactor programme', http://www.world-nuclear-news.org/Articles/PRISM-selected-for-US-test-re...