Different fuel type could make nuclear power plants safer

EPJ N special issue presents the latest research into molten salt reactors

One of the world’s biggest challenges is how to reliably produce energy to power the planet without releasing carbon into the atmosphere. Nuclear fission has been used to produce carbon-free electricity for decades, but the process is not without its faults. Now, a special issue of the open-access journal EPJ Nuclear Sciences & Technologies (EPJ N) highlights the latest research into a reactor type that could make fission safer and cleaner.

In most nuclear fission reactors, the fuel is a solid. Using a different type of fuel could provide nuclear energy while producing waste that can be stored more safely, for much shorter times, than that of conventional nuclear reactors.

“In conventional light-water reactors, fissile matter is solid, encapsulated in tall, skinny metal rodlets,” says Jean Ragusa of Texas A&M University, USA, a guest editor of the issue entitled Progress in the Science and Technology of Nuclear Reactors using Molten Salts. “This type of reactor, which uses water to extract the heat generated in about 50,000 of these rodlets, makes up the overwhelming majority of commercial reactors around the world.”

In a molten salt reactor (MSR), the fuel is dissolved in a salt, which also acts as a coolant in the reaction. The idea was first introduced during the 1950s, when nuclear engineering was in its early stages, but it was not developed for long.

“The molten salt reactor program was rather abruptly stopped in the 1970s and the technology remained dormant for twenty to thirty years, with only a few researchers maintaining and improving the technology,” says Ragusa. In 2001, an international forum was established to find the next generation of nuclear power reactors, and MSRs were selected as one of six technologies to explore.

This research showed that MSRs have a range of benefits over light-water reactors. One such advantage is that their fuel can be recycled.

“During reactor operation, you could tap small amounts of the fuel salt, extract the fission products and add new thorium or fissile nuclides, then feed the stream back to the reactor core”, says guest editor Jan Leen Kloosterman, from Delft University of Technology in the Netherlands.

This recycling means the resulting waste contains fewer radioactive elements known as actinides and transuranics. “Geological storage for that type of waste may need to be certified for only a few thousands of years, rather than the current tens to hundreds of thousands,” says Ragusa.

Another benefit is safety. In 2011, a nuclear power plant in Fukushima, Japan, was damaged during a tsunami triggered by an earthquake. A breach in the emergency power supply meant the pumps circulating coolant stopped working to combat the decay heat, which continues to be produced even when the fission reaction stops. The result was a series of three nuclear meltdowns, hydrogen explosions and the release of radioactive material.

This would not happen in a molten salt reactor, as Ragusa explains: “If excessive temperatures are reached in the salt, for instance during a station blackout scenario of Fukushima-type, the freeze plug stops being mechanically cooled, allowing the fuel to drain in tanks by gravity.”

With their potential safety benefits, molten salt reactors are of great interest to researchers around the world. The special issue of EPJ N brings together the most up-to-date findings on molten salt reactors from a range of fields, including chemistry, reactor physics, nuclear materials and fuel-cycle studies.

“To me, the most exciting part of the special issue is the breadth and depth of knowledge gathered,” says Ragusa. “It covers a wide range of disciplines and topics, including safeguards, high-end modeling and simulation, reactor and component design, and fuel cycle assessment.”

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