In 1870 the French science fiction writer Jules Verne published his epic adventure Twenty Thousand Leagues Under the Seas—the story of a modern day Odysseus named Captain Nemo. Nemo is commander of a submarine The Nautilus constructed at a secret location to his own design. Its lavish interior includes a library and an elegant dining room furnished with valuable artworks and a grand pipe organ that Nemo plays while cruising the ocean deeps.
The Nautilus
The Nautilus is a cigar-shaped vessel, seventy metres long and eight metres wide. It is propelled by electricity from sodium-mercury batteries, and has a top speed of eighty kilometres an hour. The crew has plentiful supplies of water produced by distilling sea water, but there is no way to replenish the air, so the ship has a limit of five days beneath the waves.
The technology of the fictional Nautilus was beyond anything feasible in the nineteenth century. The reality was rather different. Although numerous enterprising individuals and several navies had experimented with underwater craft on and off for centuries, there was a long history of disappointment. Optimism was regularly followed by the swift abandonment of each project as the underwater craft’s impracticalities became apparent. The main issue was the source of propulsion. In Verne’s day power was usually supplied by a steam engine fuelled by coal. Unfortunately, burning coal would rapidly exhaust the onboard oxygen supply.
By the end of the First World War submarines were becoming more practical. Diesel or kerosene engines would propel the boat on the surface whilst replenishing the batteries that powered the vessel when submerged. Even with very large batteries, however, the underwater range and speed of such craft was limited.
The Coffin Service
Hyman G. Rickover (1900-1986) joined the U.S. Navy in 1918 and trained as a marine engineer. In 1929 he volunteered for submarine duty and commanded the submarines S-9 and S-48. It was a dangerous assignment. The submarine corps was referred to as the coffin service—accidents were frequent and casualties were not uncommon. From 1933 Rickover served on surface vessels, but his first-hand experience of life beneath the waves in a vulnerable tin can remained at the forefront of his mind. He was determined to improve the welfare of submariners.
Rickover rose through the ranks during the Second World War and in late 1945 he was appointed Inspector General of the 19th Fleet on the west coast of the United States. This was the dawn of the nuclear age and the new technology seemed to offer unlimited possibilities. Rickover was tasked with supervising a nuclear propulsion system that General Electric were developing for naval destroyers. But he could see a much better application for the nuclear reactor—submarine propulsion.
Nuclear power could solve the submarine’s biggest problems. It was a reliable power source that did not consume oxygen and would run for long periods on very small amounts of fuel. For several years Rickover struggled to convince the naval bureaucracy of the huge potential of nuclear submarines. The Navy wasn’t interested, responding rather like a battleship whose course had been set. But Rickover was persistent and eventually the battleship was turned around. In July 1951 Congress approved construction of the world’s first nuclear powered submarine. Like a twentieth century Nemo, Captain Rickover insisted that it be called the USS Nautilus.
The Pressurized Water Reactor
Many designs for nuclear reactors had been dreamt up by physicists such as Enrico Fermi and Leo Szilard in the years since Fermi’s first reactor. These ranged from those using heavy water or graphite as the moderator to Szilard’s much more exotic fast reactor cooled with liquid sodium. But Rickover needed a safe and reliable design that was compact and easy to operate. It would have to function for long periods without refuelling or maintenance and without the attention of highly-trained technicians.
Rickover settled on a design that matched all his requirements. It is known as a pressurized water reactor (PWR). In these reactors water acts as both the moderator and the coolant, and the water is pressurized to 150 atmospheres so it remains liquid within the reactor core at temperatures of around 300° C. In Rickover’s submarine the fuel would be highly enriched weapons-grade uranium composed of 93% uranium-235. This would dramatically extend the periods between refuelling and reduce the reactor’s physical size.
Water has a dual role in a PWR, acting as both moderator and coolant. This means that a loss of coolant, due to a leak or the formation of vapour bubbles also implies a loss of moderator, which dampens down the nuclear chain reaction. More generally, if the temperature in the core increases the water density decreases, which reduces the effect of the moderation, so the nuclear reaction slows, bringing the temperature back down. This gives the reactor an inbuilt stability. These inherent safety features have led to the widespread commercial deployment of PWRs around the world.
Rickover’s nuclear reactor for the Nautilus produced 10 MW (megawatts) of electricity, which was sufficient to provide the submarine’s propulsion and power all its vital life support systems such as maintaining air quality, regulating the temperature and distilling fresh water from sea water.
The Mightiest Motion Picture of Them All!
Disney’s Deep Sea Adventure Story.
Walt Disney played his part in selling Rickover’s revolutionary submarine to the American public. In 1954 Disney released its steampunk blockbuster 20,000 Leagues Under the Sea based on the Jules Verne masterpiece. It was the most expensive Hollywood film up to that date and starred James Mason as the dark anti-hero Captain Nemo. Although the film is set in the nineteenth century, it suggests that Nautilus is powered by a new and mysterious source of energy discovered by Nemo. The nature of this energy would be all too obvious to the cinema-goers of the 1950s who were very familiar with the nuclear ambitions of the United States.
The film was released on 23 December 1954, and less than a month later on 17 January, nuclear reality emulated science fiction with the launch of the USS Nautilus. At almost one hundred metres in length, she was somewhat bigger than her fictional namesake. Prior to her launch, all submarines might more accurately be regarded as submersibles. Most of their time was actually spent on the surface, with their dives restricted to relatively short periods. But Nautilus suffered from no such limits. By February 1957 she had logged 60,000 nautical miles, or twenty thousand leagues, under the sea.
The USS Nautilus.
Her most famous mission came the following year. On 3 August 1958 Nautilus cruised beneath the polar icecap and became the first vessel to reach the North Pole. This was a big boost to American prestige, and ratcheted up the Cold War arms race another notch. The United States was still recovering from the shock of the previous October when the Soviet Union had launched Sputnik, the world’s first artificial satellite. Now the implied threat of Intercontinental Ballistic Missiles (ICBM) was countered by the threat of Submarine Launched Ballistic Missiles (SLBM). The nuclear-powered submarine armed with nuclear missiles would be the ultimate Cold War deterrent. Able to operate throughout the world’s oceans submerged for months at a time and essentially untraceable, it would be capable of launching a devastating nuclear strike even after its homeland had been wiped off the map.
Nuclear Proliferation
The American monopoly on seaborne nuclear propulsion did not last. Nuclear submarines are now found in the fleets of six nations: the United States, Russia, China, the United Kingdom, France and India. There are currently about 200 nuclear powered ships in the world. Most are submarines but they also include aircraft carriers and ice breakers. The reactors in these vessels typically generate around 100 MW of electricity and run on highly enriched uranium containing 20% to 93% uranium-235, which enables them to operate for decades without refuelling. Diesel generators are used as a back-up system in case of a reactor shut-down.
The only nuclear-powered submarine ever to fire on an enemy ship is the British HMS Conqueror which sunk the Argentine cruiser the General Belgrano with two torpedoes during the Falklands War in 1982. Of the almost one thousand on board the Belgrano, 323 were killed.
Atoms for Peace
The PWR was first developed for Rickover’s nuclear submarine programme. It is now the most widely used source of commercial nuclear energy. The first, and to date only, commercial PWR nuclear power station in the UK is Sizewell B on the Suffolk coast in southern England. It came into service in 1995 and generates 1.2 GW (gigawatts) of electricity.
Sizewell B, the UK’s first PWR nuclear power station.
Out of the 441 commercial nuclear reactors around the world, 299 are PWRs. They are capable of generating a combined total of 284 GW of electricity.
