Report assesses nuclear waste potential of three small modular reactor designs

The designs of these reactors have greater flexibility and lower capital costs.

A study finds that small modular reactors can provide more flexible energy generation and, in terms of nuclear waste, are roughly comparable proportionally to large light water reactors. | Photo Credit: International Atomic Energy Agency

Nuclear technologists have now advanced the concept of small modular reactors (SMRs), and their designs have greater flexibility and lower capital costs.

Since the power output from SMRs ranges from a 10th to a third of what large reactors generate, experts believe that they can be deployed at a variety of scales for locally distributed electricity generation. Although the technologies and economics of SMRs have been studied widely, there are contrary views about the generation and appropriate disposal of spent fuel from them.

Argonne National Laboratory (ANL) and Idaho National Laboratory of the US Department of Energy (DOE) recently published a report on their assessment of the nuclear waste potential of three different SMR designs, which are expected to be constructed and operationalised by the end of the decade: (1) VOYGR being developed by NuScale Power based on a conventional pressurised water reactor design but scaled down and modularised; (2) Natrium, a sodium-cooled reactor that uses metallic fuel, being developed by TerraPower; and (3) Xe-100, cooled by helium gas, being developed by X-energy. The report used the metrics that were evolved as part of a comprehensive assessment of nuclear fuel cycles in 2014. “We’ve really just begun to study the nuclear waste attributes of SMRs,” said senior nuclear engineer Taek Kyum Kim of ANL.

“It’s not correct to say that they will have more problems proportionally with nuclear waste, just because these reactors are smaller, and [therefore], they have more surface area compared to the core volume,” Kim said. “Each reactor has pluses and minuses that depend upon the discharge burnup, the uranium enrichment, the thermal efficiency, and other design features,” he added.

Burnup refers to the amount of thermal energy produced from a certain quantity of fuel, and this influences the amount of nuclear waste a reactor produces: higher the burnup, lower the nuclear waste production. According to Kim, Natrium and Xe-100 have a significantly higher burnup than conventional light water reactors (LWRs) and also apparently have higher thermal efficiency. That is, the heat they produce is more efficiently turned into electricity. On the other hand, VOYGR has a slightly lower burnup and thermal efficiency because of its smaller size.

“All told, when it comes to nuclear waste, SMRs are comparable with conventional pressurised water reactors, with potential benefits and weaknesses depending on which aspects you are trying to design for,” Kim said.