Based on a proven, established technology

Sodium-cooled reactors have safely operated at many sites around the world. PRISM’s coolant, liquid sodium, allows the neutrons in the reactor to remain at a higher energy (or speed, hence the common reference of “fast reactor”). This allows PRISM to more efficiently react with things like plutonium and other very heavy elements that make used nuclear fuel so difficult to dispose of. The result of the reaction produces heat energy which is then converted into electrical energy in a conventional steam turbine.

PRISM, coupled with electrometallurgical processing, is a technology solution that can help close the nuclear fuel cycle using the energy contained in spent nuclear fuel or plutonium.

The PRISM Reactor

PRISM is a pool-type, metal-fueled, small modular Sodium Fast Reactor. PRISM employs passive safety, digital instrumentation and control, and modular fabrication techniques to expedite plant construction. A PRISM has a rated thermal power of 840 MW and an electrical output of 311 MW. Two PRISM reactors make up a power block that combined produce 622 MW of electrical output.

Each PRISM reactor has an intermediate sodium loop that exchanges heat between the primary sodium coolant from the core with water/steam in a sodium/water steam generator. The steam from the sodium-water steam generator feeds an advanced steam turbine.

Unique Safety Features of PRISM

Metallic fuel “passive safety” design

Unlike the current generation of light-water nuclear reactors, PRISM uses metallic fuel, such as an alloy of zirconium, uranium, and plutonium, and PRISM’s fuel rods sit in a bath of a liquid metal – sodium – at atmospheric pressure, which ensures that the transfer of heat from the metal fuel to the liquid sodium coolant is extremely efficient.


In the event of a worst-case-scenario accident, the metallic core expands as the temperature rises, and its density decreases slowing the fission reaction. The reactor simply shuts itself down. PRISM’s very conductive metal fuel and metal coolant then readily dissipates excess heat without damaging any of its components. This is what is described as “passive safety,” a design feature that relies upon the laws of physics, instead of human, electronic or mechanical intervention, to mitigate the risk of an accident.

Reactor Vessel Auxiliary Cooling System


The PRISM reactor vessel auxiliary cooling system has the capability to maintain reactor temperatures well below design limits using natural circulation to remove heat from the reactor module. Unlike most other reactors, air flowing naturally around the lower containment vessel is all that is needed to keep the reactor fuel cool at all times. The system is always operating and removing heat from the reactor module, thereby providing positive indication this system is working.

Waste to Watts

Recycling used nuclear fuel would generate additional electricity to help meet growing electricity needs and enhance our energy security.

The PRISM reactor, as part of the Advanced Recycling Center, would recycle all the uranium and transuranics (elements heavier that uranium) contained within used nuclear fuel. This is a substantial improvement over previous reprocessing methods.

About 95 percent of the available energy remains in used fuel removed from light water reactors. This energy becomes accessible in a different kind of reactor, PRISM.

GEH believes that modern recycling technologies should be used to address used nuclear fuel. This would generate at least a hundred times more electricity from used nuclear fuel and decrease the long-term radiotoxicity of the remaining wastes.

The potential also exists to initially deploy PRISM to address UK civil plutonium stockpiles with a future option to later expand the facility to provide complete recycling of the resulting used PRISM fuel.

Over its estimated 60-year operating life, for example, PRISM could conceivably process and disposition the entire civil plutonium stockpile in the UK. It could also make use of other materials the UK Government wishes to disposition including reprocessed uranium and unused fuel from past nuclear reactor programs.

GEH Can Help Solve Nuclear Waste Problem with
Advanced Recycling Center (ARC)


Looking For More Information About PRISM?

This site is focused on PRISM's potential application in the UK. To learn more about PRISM’s capabilities and its selection for the U.S. Department of Energy’s Versatile Test Reactor project please click here.