Energy Glossary

Nuclear Reactor

A nuclear reactor is that part of a nuclear power plant which contains the nuclear fuel and produces heat.

The heat from a current reactor model is removed by a cooling liquid, typically light water, which also works as a moderator. A heat exchanger uses that water to produce steam in a separated cycle which powers the steam turbines. The steam turbines convert heat into motion with a calculable efficiency, the carnot efficiency which is always below one. The rotating turbine drives the generator to produce electricity which is feed into the grid.

Nuclear reactor types:

Historical reactor types:

  • Heavy water reactor: Uses D2O instead of light water. The fuel is non-enriched (natural) uranium. These reactors are very large to support the chain reaction which is necessary to keep the reactor running.

Currently running nuclear reactor types:

  • Light water reactors: Boiling water reactors (BWR) and pressurized water reactors (PWR) are subtypes of this category. They are medium sized, cheap and reliable. PWRs have higher reliability and provide higher safety. Most of the currently operated reactors are PWRs.
  • RBMK reactors were built in the former soviet union. An RBMK-1000 exploded (mostly a chemical reaction) 1986 in Chernobyl. This rector type has some inherent unsafe behaviour because it is moderated by graphite. These reactors have been used to produce plutonium for nuclear weapons.

Future nuclear reactors:

  • EPR, the European pressurized water reactor is an evolutional design comparte to the PWR. Several construction features enhance the safety of that system substantially. The melting of the reactor core is very unlikely but may happen -- the construction should hold the melting core inside the containment by a large water basin below the reactor itself. Moderate operating temperatures allow only lower power conversion efficiencys of about 30 percent and the safety margin between the operating temperature of about 350 degree celsius (620 K) and dangerous temperatures of round 400 degree celsius (670 K) make the system inherently unsafe -- it has to be made safe by the above mentioned measures.
  • HTR concepts involve graphite ceramics as moderator and construction material for core components. They are cooled by the noble gas helium. HTR stands for high temperature reactor. All components are compatible with temperatures of about 1000--1200 degree celsius (1300-1500 K). Interesting concept for the production of heat for chemical processes like hydrogen production. This reactor type allows also higher efficiencies for electricity production of about 55 percent. Inherently safe designs are possible because the reactor core withstands temperatures of 1700 degree celsius (2000 K) without damage.

Nuclear reactor categories

Generation II: The current light water reactors.

Generation III: E.g. the european pressurized water reactor with additional safety measures. A first nuclear power plant with such a reactor is currently under construction in finland.

Generation IV: Future concept of nuclear reactors with revolutional design wich is from ground up different to all the light water reactors (Gen II and Gen III). High potential for inherent safety during operation and less harmful nuclear waste.

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