Nuclear

Part 21 - Nuclear Power Reactors

Nuclear fuel contains millions of times the amount of energy available from a similar mass of chemical fuel, such as diesel or gasoline, making it a very attractive power source for military shipping. It is also an excellent power source for generating electricity, especially in countries with no carbon based fuels such as coal, oil or natural gas, and, it releases no carbon dioxide to the atmosphere.

The world's first practical nuclear power plant was developed by the U.S. Atomic Energy Commission for the US Navy. In February 1949, after training at Oak Ridge, Captain (later Admiral) Hyman G. Rickover, became Director of the Naval Reactors Branch specifically to develop the S1W power reactor. 

Rickover selected a Pressurized Water Reactor (PWR) design because it was the most compact, and least difficult to operate, compared to alternatives.    And, it would fit inside a submarine.

WW-2 submarines, like the German U-boats, were powered by diesel engines that could be used only while on the surface. These charged batteries that drove the submarine underwater at a maximum speed of 8 mph. Under water it had a range of up to 300 nautical miles at a speed of 5 mph before the batteries became flat. On the surface the diesel engine provided a maximum speed of 20  mph.

The power of a nuclear reactor allows submarines to operate underwater at speeds up to 30 mph for a virtually unlimited range and, as a nuclear reactor does not need air, nuclear powered submarines do not need to surface frequently to recharge batteries. Current nuclear submarines need to be refuelled only every 25 years; which is the fatigue lifetime of the ship. 

The only limits on underwater cruise duration are crew morale and the need to restock food.

The S1W power reactor used uranium enriched with 235-uranium as fuel and water as neutron moderator and coolant in the primary system. The heated, pressurized water from the primary system was pumped through heat exchangers to generate high pressure saturated steam in a separate water system. The steam drove turbines for propulsion and also generated electricity for all other purposes. 

Unlike atom bombs, power reactors need to fission at very much slower rate. And, as Enrico Fermi had demonstrated, it was possible to use natural uranium surrounded with a moderating material that slowed down the neutrons, that were spontaneously and occasionally, emitted from the tiny amount of 235-uranium naturally present with 238-uranium. The fission rate could be controlled by the insertion of (poison) control rods, that absorb neutrons. 

The prototype reactor was built into a section of a submarine hull and the turbines drove a single propeller against a water brake to simulate the operation in a real submarine and also to train operators.

On March 30, 1953, the S1W reactor went critical and, in May, it began power tests, operating continuously for a 100-hour run to simulate a submerged voyage from the United States to Ireland; clearly demonstrating the revolutionary nature of nuclear propulsion.

On January 17, 1955, the world's first nuclear submarine, the USS Nautilus was delivered to the Navy and was the first submarine to complete a submerged, under ice, transit of the North Pole on 3 August 3, 1958.

Another revolution occurred with the launch of the USS George Washington, on November 1, 1958. It was the first nuclear-powered submarine equipped with strategic ballistic missiles that could be launched underwater.

By 1960, three more nuclear submarines and another seven nuclear powered ships were under construction in addition to two new reactor prototypes.

The Obninsk Power Plant in the USSR was the world's first nuclear power plant to generate electricity for a power grid on June 27, 1954. Using 5% enriched uranium, a graphite moderator and water cooling, it produced 6 megawatts of electricity. Two years later, the Calder Hall reactor at Windscale, England, producing about 5 megawatts of electricity. This used natural uranium with a graphite moderator and carbon dioxide gas cooling.