Nuclear fuel considerations in the development of advanced reactors

December 8, 2021, 12:04PMNuclear NewsGary Mignogna

Mignogna

The world faces an urgent need to decarbonize and expand clean energy systems. Earlier this year, the United States announced goals to achieve a 100 percent clean electricity grid by 2035 and net-zero emissions across the entire economy by 2050. Today, nuclear energy plants provide more than 50 percent of the United States’ carbon-free energy. Existing plants, along with the advanced technologies currently being developed and demonstrated, are crucial to the United States’ and the world’s clean energy future.

Technologies such as advanced non-light water reactors, which have higher operating temperatures than today’s light water reactors, will be vital to meeting economy-wide decarbonization goals. For example, process heat applications and chemical and synthetic fuel production require higher temperatures and currently rely on fossil fuels. Advanced reactors are the only carbon-free technologies that can provide the high temperatures these processes need.

Using nuclear fuel more efficiently The next generation of reactors offers advanced safety systems and security features, and opportunities to reduce construction and operating costs. In addition, they may be able to load follow more quickly and efficiently, positioning them to operate well on decarbonized electricity grids with greater wind and solar resources. Many advanced technologies also feature small modular reactors, enabling incremental capacity additions that can be matched more easily to near-term market demands with reduced financial outlays. Another benefit of many advanced reactor technologies is that they are designed to use fuel more efficiently. As a result, these reactors produce smaller amounts of used fuel per unit of energy produced. This increased fuel efficiency is possible due to two primary characteristics: increased burnup and higher reactor operating temperatures.

Increased burnup: Burnup refers to the amount of fuel used to make a unit of electricity and is typically measured in megawatt days per metric ton. Many advanced reactor technologies can achieve a much higher burnup, meaning they can produce more electricity from the same volume of fuel. This increased energy density is possible due to the use of higher levels of uranium enrichment in fuel for advanced reactors. Existing light water reactors use low-enriched uranium with enrichment levels up to 5 percent. Many advanced reactors will need high-assay low-enriched uranium (HALEU), which is enriched above 5 percent but below 20 percent.

Another essential factor in achieving higher burnup is the use of advanced materials for fuel encapsulation. For example, the ceramic barriers used to encapsulate TRISO particle fuel are capable of withstanding very high burnups even at higher operating temperatures.

Higher reactor operating temperature: The higher a reactor’s operating temperature, the more efficient its thermodynamic cycle. Many advanced, non-light water reactors operate at temperatures between 500°C and 900°C, depending on the technology. This is compared to existing light water reactors, which operate at around 300°C. The higher operating temperature means these advanced reactors can generate electricity more efficiently and thus produce less used fuel.

Fueling advanced reactors with used fuel

Some advanced reactor technologies have the potential to reduce the amount of used fuel even further by consuming it. However, used fuel must be reprocessed and recycled before it can be used again in a reactor. After recycling, the recovered fuel can be reintroduced into practically any advanced or light water reactor.

Recycling is necessary to remove certain fission products and minor actinides from used fuel before it can be manufactured into new fuel for advanced reactors. The ability of a reactor to use recycled fuel is limited by the fuel’s isotopic content. Various advanced reactor technologies require different formulations. For example, some light water reactors can burn MOX fuel, which is a mixture of uranium and plutonium. Reactors with a fast or epithermal spectrum have greater flexibility to burn fuel with higher concentrations of plutonium and other minor actinides.

A major benefit of recycling used fuel is to reduce the actinide content in the final waste. Actinides are the primary, long-lived isotopes that make used fuel radioactive for thousands of years. By recycling the fuel, the resulting waste concentrates the more energetic fission products, but shortens its lifetime substantially. This means that a used fuel repository needs to be designed for only a few hundred years instead of thousands of years.

Developing innovative solutions

As the nuclear energy industry develops and demonstrates advanced reactors, companies are partnering on innovative solutions to make the clean energy future a reality. Framatome has decades of experience and expertise designing, qualifying, and manufacturing fuel, and it has developed designs and analyses for technologies such as sodium fast reactors and high-temperature, gas-cooled reactors. In addition, Framatome continues to supply the existing fleet of light water reactors with robust and accident tolerant fuel technology to continue enhancing their safety and economics.

Such expertise is essential to developing and deploying advanced reactors in time to meet U.S. and global decarbonization and clean energy goals. Framatome’s experience and knowledge make it an excellent partner to support today’s existing fleet and advance the future of nuclear energy.


Gary Mignogna is president and chief executive officer of Framatome Inc.


Related Articles

Nuclear FOMO

August 4, 2022, 2:49PMNuclear News

At the June ANS Annual Meeting in Anaheim, Calif., our Executive Director/CEO Craig Piercy used an interesting acronym: he said, “This meeting is so exciting we are going to give nuclear...