Glossary of terms/fact page (COntinually updated)

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Glossary/Fact Page


BDB FLEX - a program created in the US after the Fukushima disaster. BDB stands for “Beyond Design Basis.” It involves diesel-powered equipment on site to ensure plants remain safe even if they experience an event that exceeds the safety calculations. 


BREEDER REACTOR - A reactor that generates its own fuel while operating.  Excess neutrons are absorbed base materials and will transform into fuel over time


CRITICAL - The point in a reactor where it is creating power itself, a self-sustaining and controlled operation.  This is normal.


DOE - Department of Energy


FAST FUEL - A nuclear fuel that absorbs high energy neutrons


FISSION - When certain elements absorb a neutron and become unstable thereby splitting in two.  This event also generates neutrons to cause further fission.


GENERATION IV Reactor - See Gen IV


Gen IV REACTOR - A new Design Reactor that is designed to fail safely indefinitely (Walk-Away-Safe)


Gen III+ REACTOR - An existing design reactor that fails safely for days before requiring human intervention to maintain it safely


INPO - Institute of Nuclear Power Operators (implemented in response to Three Mile Island) that promotes sharing between on power plants to improve operations. Provides grading criteria for commercial reactors


MODERATOR - A material that reduces the energy of neutrons from high to low


NEUTRON - A small subatomic particle that is necessary for a nuclear reactor to operate.  It causes the reaction to work, it is used to convert Uranium 238 and Thorium 232 into useable fuels and it is also the source of many long term radioactive materials.


NRC - Nuclear Regulatory Commission


PLUTONIUM - A fuel made when Uranium-238 absorbs a neutron


THERMAL FUEL - A nuclear fuel that absorbs low energy neutrons


THORIUM - A naturally occurring element that absorbs neutrons to generate Uranium-233, a nuclear fuel.


URANIUM - A material that is natural and can be made. The natural isotope U-235 is the standard material used in current reactors and naturally makes up 0.7% of all natural uranium.  U-238 is the other isotope of naturally occurring uranium that is the base material that aborts a neutron to become Plutonium. U-233 made when Thorium absorbs a neutron to become a fuel


VC SUMMER UNITS 2 & 3 - Two Gen III+ Reactors that were under construction but was halted in 2018. 


VOGTLE UNITS 3 & 4 - Two Gen III+ reactors under construction in Georgia. Expected to start full operation in 2021 and 2022


WALK-AWAY-SAFE - A feature of Gen IV Reactors wherein a loss of power/cooling incident no operator action is required as the reactor has been engineered to be safe from a meltdown.


WATTS BAR UNITS 1 & 2 - Two Power plants that started construction in the 1980s but stopped. The DOE determined they were vital to national security and unit 1 was completed in the mid-1990s and unit 2 was completed in 2016. 


The three major nuclear sectors in the United States:

The United States Navy - regulated by Naval Reactors as defined by executive order 12344

Commercial Power - regulated by the NRC

Department of Energy - self-regulated

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