Generation IV reactor

Generation IV reactors are new designs for nuclear power plants that could replace the ones we use today. These reactors are being developed to be safer, more efficient, and better for the environment. An international group called the Generation IV International Forum picked six different types of these reactors to focus on.

These new reactors aim to work better than older ones and could start being used in factories before 2030. They include designs like reactors cooled by special metals, reactors that use melted salt, and reactors that work at very high temperatures.

Right now, most nuclear power plants around the world are older designs. But China made history by operating the world's first Generation IV reactor in December 2023. This reactor, located in Shandong, uses a special kind of technology called a pebble-bed high-temperature gas-cooled reactor. China also plans to build the first nuclear power station using thorium molten salt technology, which could be ready by 2029.

Generation IV International Forum

The Generation IV International Forum (GIF) is an international group that works together to develop new kinds of nuclear reactors. These reactors aim to be safer, better for the environment, and more efficient than older ones. GIF helps countries share research and ideas about these new reactor designs.

As of 2021, countries like Australia, Canada, China, and many others are active members of GIF. The group started in January 2000, led by the Office of Nuclear Energy of the U.S. Department of Energy. In May 2019, a private company called Terrestrial Energy joined, making it the first private company to become a member. In October 2021, the group decided to focus on using nuclear heat for things like providing clean water and making hydrogen on a large scale.

Timelines

The GIF Forum has created plans for developing six new types of nuclear reactors. These plans are split into three steps. First, they test basic ideas to make sure they work. Next, they improve these ideas under real conditions. Finally, they build and test a full-sized model.

In 2000, GIF said that after the improvement step, each reactor would need at least six years and several billion dollars to build a test model. By 2013, they pushed back these dates, and they don’t have specific goals for when these reactors will be ready for everyday use. GIF estimates it will take at least 20 to 30 years before these new reactors can be used widely.

Reactor types

Many different types of reactors were looked at first. The list was narrowed down to focus on the most promising ones. Three systems use slow, or thermal, neutrons, and three use fast neutrons. The very high temperature reactor (VHTR) could provide high-quality heat for industrial uses. Fast reactors can burn certain materials to reduce waste and can create more fuel than they use. These systems aim for better safety, sustainability, efficiency, and cost.

Thermal reactors

A thermal reactor is a nuclear reactor that uses slow, or thermal, neutrons. A neutron moderator is used to slow down the neutrons from fission, making them more likely to be captured by the fuel.

Very-high-temperature reactor (VHTR)

The very-high-temperature reactor (VHTR) uses a core with graphite and a fuel cycle that uses uranium, with helium or molten salt as coolant. This design aims for an outlet temperature of 1,000 °C. The core can be either a prismatic-block or a pebble bed design. The high temperatures allow uses such as providing heat for industry or making hydrogen.

Molten-salt reactor (MSR)

A molten salt reactor (MSR) is a type where the coolant or the fuel itself is a molten salt mixture. It runs at high temperature and low pressure.

Supercritical-water-cooled reactor (SCWR)

The supercritical water reactor (SCWR) is a reduced moderation water reactor concept. It uses supercritical water as the working fluid. SCWRs are basic light water reactors that run at higher pressure and temperatures with a direct heat exchange cycle. They aim to produce electricity at lower cost.

Fast reactors

A fast reactor uses fission neutrons directly without slowing them down. Fast reactors can be set up to "burn," or fission, certain materials, greatly reducing the amount of waste from current reactors, or they can create more fuel than they use.

Gas-cooled fast reactor (GFR)

The gas-cooled fast reactor (GFR) uses a fast-neutron spectrum and a closed fuel cycle. It is cooled by helium and has an outlet temperature of 850 °C. It uses a direct gas turbine cycle for high efficiency. Different fuel forms are being studied.

Sodium-cooled fast reactor (SFR)

Sodium-cooled fast reactors (SCFRs) have been used in several countries since the 1980s.

Lead-cooled fast reactor (LFR)

The lead-cooled fast reactor (LFR) uses a fast-neutron-spectrum lead or lead/bismuth coolant with a closed fuel cycle. Proposals include small, medium, and large reactors. The fuel contains certain materials, and the reactor cools by natural convection, reaching high temperatures for uses like making hydrogen.

Assessment

The GEN IV Forum changes how we think about nuclear reactor safety. Instead of just trying to manage accidents, the goal is to make severe accidents physically impossible. These reactors would use both active and passive safety systems that are just as good as those in older reactors.

Gen IV reactors have several benefits over older types. They produce nuclear waste that stays radioactive for a few hundred years instead of thousands. They can get 100–300 times more energy from the same amount of fuel. They can use a wider range of fuels, including raw fuels that are not encapsulated (like in MSR and LFTR designs). They can also use existing nuclear waste to produce electricity, creating a closed fuel cycle. These reactors are safer because they operate at ambient pressure, can automatically shut down without human help, and use different coolants.

One specific concern with some designs, like the SFR, is the use of metallic sodium as a coolant. If it breaks and touches water, it can react very strongly. Argon is used to prevent this, but it can reduce oxygen in the air, which could be dangerous for workers. Using lead or molten salt as coolants avoids this issue because they are less reactive and work at normal pressure, though they have their own challenges.

Several experimental Gen IV designs have been tested. For example, reactors at the Fort St. Vrain Generating Station and HTR-10 are similar to proposed Gen IV VHTR designs. The pool type EBR-II, Phénix, BN-600, and BN-800 reactors are similar to proposed pool type Gen IV SFR designs.

Some experts warn that with new reactors, unexpected situations can occur that are hard to plan for, and human mistakes can still happen. As one laboratory director said, building and operating new reactors comes with a steep learning curve and carries risks, even with proven technology.

Design projects

Radiation resistant materials

The development of generation IV reactors has led to interest in new materials that can resist radiation. These materials help keep nuclear plants safe and working longer. One recent discovery is the High-entropy alloy, which has shown great promise. Other materials, like high entropy carbide ceramics, also resist radiation well because of their special properties.

Even though these materials are very exciting, they are still new and need more study. Their complex chemistry makes them hard to design for use in reactors. More research is needed to understand how they will behave over long periods and under high temperatures, before they can be used in future reactors. Scientists are continuing to study these materials at a very small level to learn more about their strength and durability.