New Generation Reactors - Part 2
Unforeseeable risks
This is a continuation of the discussion of so-called Generation IV (G-4) nuclear reactors, and the variation on that theme that is referred to as Small Modular Reactors (SMRs). I resume by continuing the discussion of safety before addressing cost claims.
As before, most of the information I used from nuclear industry sources came from the Generation IV International Forum. I used their technology roadmaps from 2002 [2] and 2014 [3]as well as their annual progress report for 2021 [4].
In the earlier post, I noted that the G-4 Forum has not explicitly included lessons learned from prior molten Sodium reactors, especially the maintenance nightmare that was the USS Seawolf, SSN-575, and the two core meltdowns involving US research reactors. I was unaware of a Sodium fire at a Japanese Sodium-cooled reactor. And I did not mention problems with the other sort of molten metal reactors, i.e. molten Lead-Bismuth reactors. As it turns out, Russia, nee USSR, has considerable operational experience with such reactors, their having powered one research- and seven Alfa-class submarines. A total of three accidents were experienced, one (the K27 boat) involving core damage and two others (the K64 and K123) involving molten metal leaks [5]. Other problems were experienced as well. Unfortunately, Bi209 is transmuted to Po210 via a neutron absorption and subsequent beta decay. Fortunately, the Russians developed a method for removing the Po210 from the Pb-Bi coolant. Unfortunately, the Russian state uses Po210 to poison dissidents and other enemies of the state. Though not related to safety, per se, it is worth noting that when the seven Alfa class submarines were decommissioned, since the molten metal solidified when the reactors were shut down, the fuel rods became fused with the coolant so that conventional methods for disassembling the reactor became inapplicable. Per the Union of Concerned Scientists critique [6], decommissioning problems appear also to apply to molten salt reactors.
As a final note on safety, note that all of the G-4 reactor designs as well as all the included SMR designs are for critical reactors, which are inherently unstable and achieve stability only through the application of active control measures. The safety improvements proposed, if not offset by other unforeseen safety problems, will address behavior in the event of accidents of certain kinds, and inherently do little in the way of accident prevention.
Development costs are certainly higher that initially projected: In the initial roadmap, exemplars of all six types were projected to reach the commercialization stage by 2030. However, between 2002 and 2013, the average development time increased approximately 7.5 years, and the referenced progress report hints at further slippage. It is telling that the roadmap has not been updated, and that the annual progress reports do not include milestone schedules. This, plus the documented schedule slip mentioned above, leads one to expect that G-4 nuclear power will contribute nothing whatsoever to the Paris Agreement goal of halving CO2 emissions by 2030. Moreover, with the passage of time it has become clear that the aggressive schedules for commercialization are based on the assumption that regulatory approval will be granted to skip the prototype phase of development. A word about what that means. Ordinarily, when a complex system such as an airplane or a nuclear reactor is developed, a prototype is built and tested extensively to identify design and construction faults. Only after extensive testing of the prototype(s) is completed is the design finalized and the system put into production. Moreover, it is traditionally left to the user community, via their agent (e.g., the FAA in the case of an airplane) to participate in the testing and be vested with the sole authority to grant approval for production. Regarding the US SMR program, per the cited UCS report, "The DOE has selected two NLWR designs, the Natrium SFR and the Xe-100 pebble-bed HTGR, for demonstration of fullscale commercial operation by 2027. However, the NRC has yet to evaluate whether these designs are mature enough that it can license them without frst obtaining data from prototype plants to demonstrate novel safety features, validate computer codes, and qualify new types of fuel in representative environments. Without such an evaluation, the NRC will likely lack the information necessary to ensure safe, secure operation of these reactors." [7] A normal prototyping phase, if imposed as it should be, would bring further delays and increase the costs of G-4 reactor deployment.
Purported cost advantage appears to be a myth. The history of nuclear power shows succeeding generations of reactors being more expensive than their predecessors [8]. SMR proponents want to reverse that, pointing to the very substantial reduction in cost versus time of wind and solar but they do not see the fault with their logic. Wind and solar are comparatively simple technologies, built on many decades, even centuries, of development, and supported by a huge manufacturing infrastructure, while SMRs are new and highly complex, and will probably never achieve the scale in production to allow the economies of scale via numbers to apply. How can one compare SMRs, with maximum annual production rates in the tens, with solar panels, with monthly production rates in the millions?
An analysis published by the Institute for Energy and Environmental Research [9] contradicts the SMR proponents' claims: "First, in contrast to cars or smart phones or similar widgets, the materials cost per kilowatt of a reactor goes up as the size goes down. This is because the surface area per kilowatt of capacity, which dominates materials cost, goes up as reactor size is decreased. Similarly, the cost per kilowatt of secondary containment, as well as independent systems for control, instrumentation, and emergency management, increases as size decreases. Cost per kilowatt also increases if each reactor has dedicated and independent systems for control, instrumentation, and emergency management." In fact, these are the reasons why the industry at large has attempted to bring costs down by building ever larger plants. Why have they not has more to do with the shape of the learning curves than to the economies of scale. Simply postulating that reversing the process by building smaller rather than larger does not solve the problem. It is interesting that South Korea has seen reductions of cost per kilowatt with increasing reactor size, which provides evidence of the validity of the aforementioned scaling laws, U.S. experience notwithstanding. Finally, a report [10] comparing electricity prices finds that nuclear energy is currently more expensive than solar, and that, for a SMR for which the producer has published a target price, even that target is more than 50% greater than that of current solar facilities.
In summary the six families of designs that comprise the G-4 and DOE-advocated SMR reactors share the following undesirable characteristics:
As all use U235 (and in some cases U235/Pu239) fuel, none are compatible with the objective of eliminating nuclear weapons and, with the exception of designs using TRISO fuel offer no significant reduction in proliferation risk;
The proponents greatly exaggerate the ability of the designs to avoid production of long-lived minor Actinide waste and ignore the problem of long-lived fission products;
Nuclear power based on Uranium is not sustainable: if its use were scaled up to meaningfully contribute to combating climate change, readily available stocks would be expended before the end of the century; deployment of HTGRs would lead to depletion of Helium as well;
We cannot be assured that G-4 reactors will be any safer than current light water reactors. Enhanced safety in some areas may well be offset by degradation in others. Hurrying to bring systems online without normal much less thorough prototype experience largely eliminates the ability to test exhaustively and incorporate lessons learned into the design of production systems to realize improved safety;
There is no rational basis for assuming that G-4 reactors will provide electric power at costs competitive with renewable energy;
Even with the proposed accelerated process of licensing, G-4 reactors will make essentially no contribution to meeting the requirement of halving CO2 emissions by 2030.
In another post I will discuss nuclear power based on the Th-U233 fuel cycle, and in particular sub-critical accelerator driven systems (ADS). Could such reactors, which are inherently stable, use a much more abundant and widely distributed fuel, and which almost entirely avoid producing long-lived minor Actinide waste, provide a safe and secure nuclear future? Stay tuned!
Notes
[1] "Because it is a technology having residual risks with unforeseeable consequences." Angela Merkel, Chancellor of Germany and physicist, explaining why her country decided to shut down its nuclear reactors. Image credit: CDU
[2] https://www.gen-4.org/gif/jcms/c_40481/technology-roadmap
[3] https://www.gen-4.org/gif/upload/docs/application/pdf/2014-03/gif-tru2014.pdf
[4] https://www.gen-4.org/gif/jcms/c_177525/gif-2021-annual-report
[5] https://en.wikipedia.org/wiki/Nuclear_submarine#Accidents
[6] https://www.ucsusa.org/sites/default/files/2021-05/ucs-rpt-AR-3.21-web_Mayrev.pdf
[7] Reference [6], p. 116
[8] Loverling, J.R. and J.R. McBride, Chasing Cheap Nuclear: Economic Tradeoffs for Small Nuclear Reactors, The Bridge 50(3) Fall 2020, pp. 38-44
[9] https://ieer.org/resource/energy-issues/small-modular-reactors-solution/
[10] https://www.counterpunch.org/2023/07/20/the-forever-dangers-of-small-modular-nuclear-reactors/
Reposted with format changes 29 Oct 2024