National and international efforts to develop new sources of carbon free energy are exploring a reactor concept first introduced in the
1950s and 60s: The Molten Salt Reactor. The first molten salt reactor experiments
were conducted by Oak Ridge National Laboratory. The design was radical for its time and offered many advantages worth a fresh look today. Molten salt reactors differ from most nuclear power plants in operation today, such as light water reactors. To understand how, let's review the basics. Nuclear power plants generate power through
a fissile chain reaction. Fissionable isotopes like uranium 235, 233
or plutonium 239 absorb a neutron and then fission, that is, split apart into fission
products. In that process they generate heat. As well, they eject more neutrons to continue
the chain reaction. A moderator is usually employed to slow down the neutrons so they are more likely to cause another fission when they impact the fuel. In the case of light water reactors, solid
fuel rods contain the fissile material. Water surrounding the fuel acts as both a
moderator and coolant. The coolant carries heat to turbines that generate electricity. In a molten salt reactor, the core operates
very differently. The primary coolant is a salt heated above its melting point so it is a fluid. While private industry is developing several distinct designs, here is the most commonly proposed configuration. Instead of fuel rods, fissile material is
dissolved in the molten salt. The fuel flows around graphite rods, which moderate the energy of the neutrons to support the nuclear chain reaction. Other designs include liquid or solid fuel
contained in rods similar to current reactors but with molten salt as a
coolant. These reactors can use a broad range of fuel and salt compositions and there are even designs that do not require a moderator at all and are a class called fast reactors. Several designs would employ Thorium fuel, which offers many benefits. There is at least 3 times more Thorium than Uranium on the planet, and its waste largely decays in 100’s of years
instead of 10,000’s. Other advantages of molten salt reactors include
safety and efficiency. Replacing water as the coolant removes possibility of steam explosions and the generation of flammable hydrogen gas. Low pressure operation also places less demand
on containment systems. The nuclear reactions are easier to control
because liquid salt expands. In the event of an unanticipated rise in temperature,
this expansion shuts down the reaction. Additionally, a freeze plug can dump the fuel
into tanks and stop the reaction. This option provides a failsafe in the event
of power outages or other events. Because these reactors can operate at higher temperature, their steam cycle generates electricity more efficiently. The use of liquid fuel allows for real time
waste processing. And finally, there is no need to shut down
the reactor for refueling. New fuel can be introduced to the system during operation. While the test molten salt reactor
of the 60’s ran over a period of years, several challenges remain before construction
and operation of a full scale commercial plant. These include: Understanding and mitigating
the corrosion of structural materials. Development of reliable and efficient chemical
separations, including tritium. Instruments and controls for real-time monitoring
of the reactor. And, licensing and risk assessment for a non-lightwater reactor design. Researchers at Pacific Northwest National
Laboratory are working on many of these challenges, We have expertise in: Radiochemistry. Real-time online monitoring. As well as materials design and performance
testing. Contact us to learn more about how we are advancing molten salt reactor technology.
