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Conclusions and recommendations of safety assessment of advanced nuclear reactors – non-light-water ones

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.

Recommendations

The DOE should suspend the advanced reactor demonstration program pending a finding by the NRC whether it will require full-scale prototype testing before licensing the two chosen designs as commercial power reactors.

The DOE has selected two NLWR designs, the Natrium SFR and the Xe-100 pebble-bed HTGR, for demonstration of full-scale commercial operation by 2027. However, the NRC has yet to evaluate whether these designs are mature enough that it can license them without first obtaining data from full-scale 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. The DOE should suspend the Advanced Reactor Demonstration Program until the NRC—in consultation with the agency’s Advisory Committee on Reactor Safeguards and external experts—has determined whether prototypes will be needed first.

Congress should require that an independent, transparent, peer-review panel direct all DOE R&D on new nuclear concepts, including the construction of additional test or demonstration reactors.

Given the long time and high cost required to commercialize NLWR designs, the DOE should provide funding for NLWR R&D judiciously and only for reactor concepts that offer a strong possibility of significantly increasing safety and security—and do not increase proliferation risks. Moreover, unlike the process for selecting the two reactor designs for the Advanced Reactor Demonstration Program, decision-making should be transparent.6 Congress should require that the DOE convene an independent, public commission to thoroughly review the technical merits of all NLWR designs proposed for development and demonstration, including those already selected for the ARDP. The commission, whose members should represent a broad range of expertise and perspectives, would recommend funding only for designs that are highly likely to be commercialized successfully while achieving clearly greater safety and security than current-generation LWRs.

The DOE and other agencies should thoroughly assess the implications for proliferation and nuclear terrorism of the greatly expanded production, processing, and transport of the high-assay low-enriched uranium (HALEU) required to support the widespread deployment of NLWRs.

Large-scale deployment of NLWRs that use HALEU fuel will require establishing a new industrial infrastructure for producing and transporting the material. The DOE is actively promoting the development of HALEU-fueled reactor designs for export. Given that HALEU is a material of higher security concern than lower-assay LEU, Congress should require that the DOE immediately assess the proliferation and nuclear terrorism implications of transitioning to the widespread use of HALEU worldwide. This assessment should also address the resource requirements for the security and safeguards measures needed to ensure that such a transition can occur without an unacceptable increase in risk.

The United States should make all new reactors and associated fuel facilities eligible for IAEA safeguards and provide that agency with the necessary resources for carrying out verification activities.

The IAEA, which is responsible for verifying that civilian nuclear facilities around the world are not being misused to produce materials for nuclear weapons, has limited or no experience in safeguarding many types of NLWRs and their associated fuel cycle facilities. NLWR projects being considered for deployment in the United States, such as the Natrium SFR and the Xe-100 pebble-bed HTGR, would provide ideal test beds for the IAEA to develop safeguards approaches. However, as a nuclear-weapon state, the United States is not obligated to give the IAEA access to its nuclear facilities. To set a good example and advance the cause of nonproliferation, the United States should immediately provide the IAEA with permission and funding to apply safeguards on all new US nuclear facilities, beginning at the design phase. This would help to identify safeguard challenges early and give the IAEA experience in verifying similar facilities if they are deployed in other countries.

The DOE and Congress should consider focusing nuclear energy R&D on improving the safety and security of LWRs, rather than on commercializing immature NLWR designs.

LWR technology benefits from a vast trove of information resulting from many decades of acquiring experimental data, analysis, and operating experience—far more than that available for any NLWR. This gives the LWR a significant advantage over other nuclear technologies. The DOE and Congress should do a more thorough evaluation of the benefits of focusing R&D funding on addressing the outstanding safety, security, and cost issues of LWRs rather than attempting to commercialize less mature reactor concepts. If the objective is to expand nuclear power to help deal with the climate crisis over the next few decades, improving LWRs could be a less risky bet.

Endnotes………

This is a condensed, online version of the executive summary. For all figures, references, and the full text, please download the PDF.  https://ucsusa.org/resources/advanced-isnt-always-better#read-online-content

March 19, 2021 - Posted by | Reference, safety, technology

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