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A nuclear power station makes electricity from fission, the splitting of heavy atoms such as uranium. The heat released boils water, and the steam spins turbines, just as in a coal or gas plant. Nuclear power supplied about 9 per cent of the world's electricity in 2023.

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When an atom of uranium-235, the form of uranium that powers most reactors, absorbs a neutron, one of the particles found in an atom's nucleus, it splits in two, releasing heat and two or three more neutrons. These can split further atoms, a process called a chain reaction. Control rods made of materials that soak up neutrons are moved in or out to keep the reaction steady. The fuel is extremely concentrated: a kilogram of typical reactor fuel holds about 120,000 times as much energy as a kilogram of coal, and the plant gives off almost no carbon dioxide while running. The first plant to feed a power grid opened at Obninsk, near Moscow, in 1954, and Britain's Calder Hall followed in 1956. The difficulties are long-lived radioactive waste, high building costs and the need for strict safety, as the Chernobyl accident in 1986 and Fukushima in 2011 showed.

Türkçe oku
Nükleer santraller elektriği fisyonla, yani uranyum gibi ağır atomların bölünmesiyle üretir. Açığa çıkan ısı suyu kaynatır; buhar da tıpkı kömür ya da doğal gaz santrallerinde olduğu gibi türbinleri döndürür. 2023'te dünyadaki elektriğin yaklaşık yüzde 9'u nükleer santrallerden geldi.

Nötron, atom çekirdeğini oluşturan parçacıklardan biridir. Reaktörlerin çoğunda enerji, uranyum-235 atomlarının bölünmesinden gelir. Bir uranyum-235 atomu bir nötron yakaladığında ikiye bölünür; bu sırada ısı açığa çıkar ve iki üç yeni nötron serbest kalır. Bu nötronlar başka atomları da böler; buna zincirleme tepkime denir. Tepkimeyi dengede tutmak için, nötronları emen maddelerden yapılmış kontrol çubukları reaktörün içine indirilir ya da dışarı çekilir. Nükleer yakıt son derece yoğun bir enerji kaynağıdır: Tipik reaktör yakıtının bir kilogramında, bir kilogram kömürdekinin yaklaşık 120.000 katı enerji vardır. Santral çalışırken de neredeyse hiç karbondioksit salmaz. Elektrik şebekesine bağlanan ilk nükleer santral 1954'te Moskova yakınlarındaki Obninsk'te açıldı; İngiltere'deki Calder Hall 1956'da onu izledi. Nükleer enerjinin zorlukları da var: Atıklar çok uzun süre radyoaktif kalır, santral kurmak pahalıdır ve güvenlik son derece sıkı tutulmalıdır. 1986'daki Çernobil ve 2011'deki Fukuşima kazaları güvenliğin ne kadar önemli olduğunu gösterdi.

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Background reading: Nuclear power plant
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WonderHistory

When Neil Armstrong radioed “Houston, Tranquility Base here. The Eagle has landed” on 20 July 1969, his words reached Earth about 1.3 seconds later. Radio waves travel at the speed of light, and the Moon is about 384,000 km (239,000 miles) away.

Eagle was the lunar module that carried Armstrong and Buzz Aldrin down to the surface. Light, and so radio, travels at almost 300,000 km per second. At the Moon's average distance of about 384,400 km, a signal takes roughly 1.28 seconds each way, so every exchange with Mission Control in Houston had a built-in pause of about 2.6 seconds before an answer could arrive. Large dish antennas at Goldstone in California and at Honeysuckle Creek and Parkes in Australia picked up the signals; the clearest pictures of the first steps came through Australia and were watched live by an estimated 600 million people. Before leaving, the crew set up a panel of reflectors on the surface. Scientists still fire lasers at it and time the light's return, which is how we know the Moon is drifting away from Earth by about 3.8 cm a year.

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WonderTechnology

Telomeres are stretches of repeated DNA that cap the ends of chromosomes, a little like the plastic tips on shoelaces. They get shorter as many of our cells divide, but their length cannot predict how long a particular person will live.

In the mid-1970s the Australian-born biologist Elizabeth Blackburn, working at Yale, found that chromosome ends carry a short DNA “word” repeated many times; in humans it is TTAGGG. She shared the 2009 Nobel Prize in Physiology or Medicine with Carol Greider and Jack Szostak for showing how telomeres, and an enzyme called telomerase that rebuilds them, protect chromosomes. Each time most body cells divide, the copying machinery cannot quite reach the very end, so a little telomere is lost; when it gets too short, the cell stops dividing, which is why telomeres are often called a clock. But it is a poor clock for comparing people or species: mice have much longer telomeres than humans yet live only two or three years, and telomere length varies widely between people from birth. Many scientists therefore doubt commercial tests that claim to read your “biological age” from them.

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WonderTechnology

The atomic clocks on GPS satellites run about 38 millionths of a second a day faster than clocks on the ground, an effect predicted by Einstein's theories of relativity. Left uncorrected, the drift would put your position out by about 11 km within a single day.

A GPS receiver, such as the one in your phone, works out where it is by timing signals from several satellites orbiting about 20,200 km up. Radio signals travel about 300 metres in a microsecond, a millionth of a second, so even tiny clock errors matter. Relativity pulls the clocks apart in two ways. Special relativity says moving clocks run slow: travelling at almost 4 km a second, the satellite clocks lose about 7 microseconds a day. General relativity says clocks in weaker gravity run fast: high above Earth they gain about 46. The net gain is about 38 microseconds a day. So before launch, each satellite clock is set to run slightly slow, at 10.22999999543 million cycles a second instead of 10.23 million, and in orbit it keeps step with clocks on the ground.

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WonderTechnology

The Apollo Guidance Computer that steered astronauts to the Moon had about 4 kilobytes of rewritable memory and 72 kilobytes of permanent memory. Its programs were woven by hand into “rope memory”: a wire threaded through a tiny magnetic ring stored a 1, and a wire passing it by stored a 0.

Designed at the MIT Instrumentation Laboratory and built by Raytheon, the computer was one of the first to use silicon chips (integrated circuits) and fitted into about 28 litres. Its memory was counted in “words” of 16 bits, or binary digits: 2,048 rewritable and 36,864 permanent. During Apollo 11's descent on 20 July 1969 it flashed 1202 and 1201 alarms: a radar left on in case the landing had to be abandoned was stealing processing time and overloading it. Its operating system, designed by J. Halcombe Laning, dropped less urgent jobs and restarted in a moment while the landing programs kept running, so Mission Control told the crew to carry on. The flight software was written by a team led by Margaret Hamilton, who received the Presidential Medal of Freedom in 2016. Its power was similar to that of the first home computers of the late 1970s.

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WonderTechnology

In 1984 and 1985, John Clarke, Michel Devoret and John Martinis showed that a whole electrical circuit on a chip, cooled almost to absolute zero, can behave as a single quantum object, just like an atom. The discovery earned them the 2025 Nobel Prize in Physics.

The experiments were done at the University of California, Berkeley, in Clarke's group; Martinis was his doctoral student and Devoret a postdoctoral researcher. Absolute zero, −273.15 °C, is the lowest temperature possible. At the heart of the circuit was a Josephson junction: two superconductors, metals that carry current with no resistance when very cold, separated by an insulating layer only a few atoms thick. Vast numbers of electrons moved together as if they were one particle. The team saw two signs of quantum behaviour: the circuit escaped from a trapped state by tunnelling, slipping through an energy barrier it could not climb over, and it absorbed microwave energy only in fixed steps, or quanta, as an atom does. Circuits of this kind are now the qubits, the basic units of information, in the superconducting quantum computers built by companies such as Google and IBM.

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