Nuclear reactor

The heavy nucleus splits into two or more lighter nuclei, (the fission products), releasing kinetic energy, gamma radiation, and free neutrons.

[14] Nuclear reactors generally have automatic and manual systems to shut the fission reaction down if monitoring or instrumentation detects unsafe conditions.

These systems insert large amounts of poison (often boron in the form of boric acid) into the reactor to shut the fission reaction down if unsafe conditions are detected or anticipated.

For this reason many designs use highly enriched uranium but incorporate burnable neutron poison in the fuel rods.

[21] This allows the reactor to be constructed with an excess of fissionable material, which is nevertheless made relatively safe early in the reactor's fuel burn cycle by the presence of the neutron-absorbing material which is later replaced by normally produced long-lived neutron poisons (far longer-lived than xenon-135) which gradually accumulate over the fuel load's operating life.

[24][25] Even when a license is extended, it does not guarantee the reactor will continue to operate, particularly in the face of safety concerns or incident.

[28] The British branch of the French concern EDF Energy, for example, extended the operating lives of its Advanced Gas-cooled Reactors (AGR) with only between 3 and 10 years.

In 2014, Greenpeace warned that the lifetime extension of ageing nuclear power plants amounts to entering a new era of risk.

It estimated the current European nuclear liability coverage in average to be too low by a factor of between 100 and 1,000 to cover the likely costs, while at the same time, the likelihood of a serious accident happening in Europe continues to increase as the reactor fleet grows older.

The U.S. was not yet officially at war, but in October, when the Einstein-Szilárd letter was delivered to him, Roosevelt commented that the purpose of doing the research was to make sure "the Nazis don't blow us up."

The following year, the U.S. Government received the Frisch–Peierls memorandum from the UK, which stated that the amount of uranium needed for a chain reaction was far lower than had previously been thought.

Soon after the Chicago Pile, the Metallurgical Laboratory developed a number of nuclear reactors for the Manhattan Project starting in 1943.

The primary purpose for the largest reactors (located at the Hanford Site in Washington), was the mass production of plutonium for nuclear weapons.

[33] "World's first nuclear power plant" is the claim made by signs at the site of the EBR-I, which is now a museum near Arco, Idaho.

U.S. President Dwight Eisenhower made his famous Atoms for Peace speech to the UN General Assembly on 8 December 1953.

Used by thermal reactors: In 2003, the French Commissariat à l'Énergie Atomique (CEA) was the first to refer to "Gen II" types in Nucleonics Week.

Research into these reactor types was officially started by the Generation IV International Forum (GIF) based on eight technology goals.

Though some generation V reactors could potentially be built with current or near term technology, they trigger little interest for reasons of economics, practicality, or safety.

Under 1% of the uranium found in nature is the easily fissionable U-235 isotope and as a result most reactor designs require enriched fuel.

Theft risk of this fuel (potentially used in the production of a nuclear weapon) has led to campaigns advocating conversion of this type of reactor to low-enrichment uranium (which poses less threat of proliferation).

A higher percentage of U-235 in the core at the beginning of a cycle will permit the reactor to be run for a greater number of full-power days.

[citation needed] The disposition and storage of this spent fuel is one of the most challenging aspects of the operation of a commercial nuclear power plant.

A number of incidents connected with the unmanned nuclear-reactor-powered Soviet RORSAT especially Kosmos 954 radar satellite which resulted in nuclear fuel reentering the Earth's atmosphere from orbit and being dispersed in northern Canada (January 1978).

Almost two billion years ago a series of self-sustaining nuclear fission "reactors" self-assembled in the area now known as Oklo in Gabon, West Africa.

[116] Fifteen fossil natural fission reactors have so far been found in three separate ore deposits at the Oklo uranium mine in Gabon.

Radioactive decay of formerly more abundant uranium-235 over the time span of hundreds of millions of years has reduced the proportion of this naturally occurring fissile isotope to below the amount required to sustain a chain reaction with only plain water as a moderator.

The natural nuclear reactors formed when a uranium-rich mineral deposit became inundated with groundwater that acted as a neutron moderator, and a strong chain reaction took place.

Nuclear reactors produce tritium as part of normal operations, which is eventually released into the environment in trace quantities.

This molecule is chemically identical to H2O and so is both colorless and odorless, however the additional neutrons in the hydrogen nuclei cause the tritium to undergo beta decay with a half-life of 12.3 years.

[120] The amounts of strontium-90 released from nuclear power plants under normal operations is so low as to be undetectable above natural background radiation.

An example of an induced nuclear fission event. A neutron is absorbed by the nucleus of a uranium-235 atom, which in turn splits into fast-moving lighter elements (fission products) and free neutrons. Though both reactors and nuclear weapons rely on nuclear chain reactions, the rate of reactions in a reactor is much slower than in a bomb.
The Chicago Pile , the first artificial nuclear reactor, built in secrecy at the University of Chicago in 1942 during World War II as part of the US's Manhattan project
Lise Meitner and Otto Hahn in their laboratory
Some of the Chicago Pile Team , including Enrico Fermi and Leó Szilárd
Primary coolant system showing reactor pressure vessel (red), steam generators (purple), pressurizer (blue), and pumps (green) in the three coolant loop Hualong One pressurized water reactor design
Pressurized Water Reactor Boiling Water Reactor Gas Cooled Reactor Pressurized Heavy Water Reactor LWGR Fast Breeder Reactor
Pressurized Water Reactor Boiling Water Reactor Gas Cooled Reactor Pressurized Heavy Water Reactor LWGR Fast Breeder Reactor
NC State 's PULSTAR Reactor is a 1 MW pool-type research reactor with 4% enriched, pin-type fuel consisting of UO 2 pellets in zircaloy cladding.
Treatment of the interior part of a VVER-1000 reactor frame at Atommash
In thermal nuclear reactors (LWRs in specific), the coolant acts as a moderator that must slow the neutrons before they can be efficiently absorbed by the fuel.
Diablo Canyon – a PWR
The CANDU Qinshan Nuclear Power Plant
The Ignalina Nuclear Power Plant – a RBMK type (closed 2009)
The Magnox Sizewell A nuclear power station
The Torness nuclear power station – an AGR
Scaled-down model of TOPAZ nuclear reactor
The Superphénix , closed in 1998, was one of the few FBRs.
Three of the reactors at Fukushima I overheated, causing the coolant water to dissociate and led to the hydrogen explosions. This along with fuel meltdowns released large amounts of radioactive material into the air. [ 112 ]