Antinuclear

Assessing the Safety, Security, and Environmental Impacts of Non-Light-Water Nuclear Reactors,Union of Concerned Scientists, Edwin Lyman Mar 18, 2021  “Advanced” Isn’t Always Better  ”

”……….Conclusions of the Assessment

The non-light-water nuclear reactor landscape is vast and complex, and it is beyond the scope of this report to survey the entire field in depth. Nevertheless, enough is clear even at this stage to draw some general conclusions regarding the safety and security of NLWRs and their prospects for rapid deployment.

Based on the available evidence, the NLWR designs currently under consideration (except possibly once-through, breed-and-burn reactors) do not offer obvious improvements over LWRs significant enough to justify their many risks. Regulators and other policymakers would be wise to look more closely at the nuclear power programs under way to make sure they prioritize safety and security. Future appropriations for NLWR technology research, development, and deployment should be guided by realistic assessments of the likely societal benefits that would result from the investment of billions of taxpayer dollars.

Little evidence supports claims that NLWRs will be significantly safer than today’s LWRs. While some NLWR designs offer some safety advantages, all have novel characteristics that could render them less safe.

All NLWR designs introduce new safety issues that will require substantial analysis and testing to fully understand and address—and it may not be possible to resolve them fully. To determine whether any NLWR concept will be significantly safer than LWRs, the reactor must achieve an advanced stage of technical maturity, undergo complete comprehensive safety testing and analysis, and acquire significant operating experience under realistic conditions.

The claim that any nuclear reactor system can “burn” or “consume” nuclear waste is a misleading oversimplification. Reactors can actually use only a fraction of spent nuclear fuel as new fuel, and separating that fraction increases the risks of nuclear proliferation and terrorism.

No nuclear reactor can use spent nuclear fuel directly as fresh fuel. Instead, spent fuel has to be “reprocessed”—chemically treated to extract plutonium and other TRU elements, which must then be refabricated into new fuel. This introduces a grave danger: plutonium and other TRU elements can be used in nuclear weapons. Reprocessing and recycling render these materials vulnerable to diversion or theft and increases the risks of nuclear proliferation and terrorism—risks that are costly to address and that technical and institutional measures cannot fully mitigate. Any fuel cycle that requires reprocessing poses inherently greater proliferation and terrorism risks than the “once-through” cycle with direct disposal of spent fuel in a geologic repository.

Some NLWRs have the potential for greater sustainability than LWRs, but the improvements appear to be too small to justify their proliferation and safety risks.

Although some NLWR systems could use uranium more efficiently and generate smaller quantities of long-lived TRU isotopes in nuclear waste, for most designs these benefits could be achieved only by repeatedly reprocessing spent fuel to separate out these isotopes and recycle them in new fuel—and that presents unacceptable proliferation and security risks. In addition, reprocessing plants and other associated fuel cycle facilities are costly to build and operate, and they increase the environmental and safety impacts compared with the LWR once-through cycle. Moreover, the sustainability increases in practice would not be significant in a reasonably foreseeable time frame.

Once-through, breed-and-burn reactors have the potential to use uranium more efficiently without reprocessing, but many technical challenges remain.

One type of NLWR system that could in principle be more sustainable than the LWR without increasing proliferation and terrorism risks is the once-through, breed-and-burn reactor. Concepts such as TerraPower’s traveling-wave reactor could enable the use of depleted uranium waste stockpiles as fuel, which would increase the efficiency of uranium use. Although there is no economic motivation to develop more uranium-efficient reactors at a time when uranium is cheap and abundant, reducing uranium mining may be beneficial for other reasons, and such reactors may be useful for the future. However, many technical challenges would have to be overcome to achieve breed-and-burn operation, including the development of very-high-burnup fuels. The fact that TerraPower suspended its project after more than a decade of development to pursue a more conventional and far less uranium-efficient SFR, the Natrium, suggests that these challenges have proven too great.

High-assay low enriched uranium (HALEU) fuel, which is needed for many NLWR designs, poses higher nuclear proliferation and nuclear terrorism risks than the lower-assay LEU used by the operating LWR fleet.

Many NLWR designs require uranium enriched to higher levels than the 5 percent U-235 typical of LWR fuel. Although uranium enriched to between 10 and 20 percent U-235 (defined here as HALEU) is considered impractical for direct use in nuclear weapons, it is more attractive for weapons use—and requires more stringent security—than the lower-assay enriched uranium in current LWRs.

The significant time and resources needed to safely commercialize any NLWR design should not be underestimated.

It will likely take decades and many billions of dollars to develop and commercially deploy any NLWR design, together with its associated fuel cycle facilities and other support activities. Such development programs would come with a significant risk of delay or failure and require long-term stewardship and funding commitments. And even if a commercially workable design were demonstrated, it would take many more years after that to deploy a large number of units and operate them safely and reliably.

Vendors that claim their NLWRs could be commercialized much more quickly typically assume that their designs will not require full-scale performance demonstrations and extensive safety testing, which could add well over a decade to the development timeline. However, current designs for sodium-cooled fast reactors and high-temperature gas-cooled reactors differ enough from past reactor demonstrations that they cannot afford to bypass additional full-scale prototype testing before licensing and commercial deployment. Molten salt–fueled reactors have only had small-scale demonstrations and thus are even less mature. NLWRs deployed commercially at premature stages of development run a high risk of poor performance and unexpected safety problems.

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To help inform policy decisions on these questions, the Union of Concerned Scientists (UCS) has evaluated certain claims about the principal types of NLWRs. In particular, this report compares several classes of NLWRs to LWRs with regard to safety and security, the risks of nuclear proliferation and nuclear terrorism, and “sustainability”—a term that in this context includes the often-claimed ability of some NLWRs to “recycle” nuclear waste and use mined uranium more efficiently. The report also considers the potential for certain NLWRs to operate in a once-through, “breed-and-burn” mode that would, in theory, make them more uranium-efficient without the need to recycle nuclear waste—a dangerous process that has significant nuclear proliferation and terrorism risks. Continue reading →