|Fig. 1: The USS Nautilus (SSN-571).(Source: Wikimedia Commons)|
The USS Nautilus (SSN-571) was the world's first nuclear powered submarine. It became operational in December of 1954 and represented a revolution in both submarine and maritime technology. It was the experimental platform that served as a proof of concept for the now fleets of military surface ships and submarines as well as a handful of commercial shipping vessels that are powered by nuclear energy.
The US Navy recognized the potential for nuclear energy in submarine propulsion as early as 1939 when a small research group was set up to examine the problem of practical nuclear fission.  All research was stopped on this project in 1942 when allied nuclear research efforts went towards the newly established Manhattan Project to develop an atomic bomb.  After the end of the Second World War in 1945, there was a push in the United States to develop peaceful uses of the new atomic energy, specifically in the form of nuclear reactors for the production of electricity.  The US Navy had a strong advocate for the nuclear propulsion of its ships, an electrical engineer named Captain H. G. Rickover (see Fig. 2). Rickover became the lead in an effort to build the world's first nuclear submarine which earned him the rank of Admiral and later became known as the father of the nuclear navy. 
Since no one had built a large scale nuclear reactor before, the Navy had a test reactor built near Arco in the Idaho dessert.  Due to the urgency placed on the project, the haul of the submarine and the prototype reactor were built in parallel.  Construction began on the Nautilus in June of 1952 by Electric Boat (now a division of General Dynamics) in Groton, Connecticut.  The prototype pressurized water reactor in Idaho was built by Westingtonhouse and became known as Submarine Thermal Reactor (STR) Mark I.  The STR Mark I was the land prototype of the STR Mark II that would later be installed on the Nautilus.  The Mark I was used to find and correct design flaws, simulate performance, and to train the crew in its operation.  It achieved criticality in March of 1953 and made its first successful simulated 96 hour voyage in June of that year. 
The STR Mark I/II and subsequent Naval reactors were designed to operate using highly enriched uranium fuel, a relative amount of the isotope uranium-235 of 93% or greater. [3,4] This was done in order to maximize the amount fissile fuel in the core, giving rise to both compactness of the reactor, as well as the added benefit of longer core life.  Compare this to typical commercial light water reactors used for electricity production which use uranium fuel enriched to 1.5% - 4%.  Highly enriched uranium is a more controlled substance as it is synonymously known as weapons grade uranium, i.e. it is of the necessary concentration needed to construct an atomic bomb. Thus, it is not surprising that this type of fuel is found only in military applications. The STR reactors were designed to operate using uranium fuel in the amount of 9 pounds, giving rise to a fuel bundle assembly approximately the size of a football.  This is equivalent to the energy content in 5,760 tons of coal.  The final design of the reactor produced 10 MW (13,400 hp) of power.  The Mark II reactor was started on December 30, 1954 and the Nautilus made its first voyage on January 17, 1955 where Commander Eugene P. Wilkinson made the historic message, "underway on nuclear power." 
|Fig. 2: Admiral H. G. Rickover. (Source: Wikimedia Commons)|
Prior to 1960, US federal limits on annual radiation exposure was 15 rem (roentgen equivalent in man). [6,7] Assuming a 50 week year, this gave rise to standard of 300 millirem per week by the Atomic Energy Commission, a standard which was employed by the Nautilus at the time of its initial operation.  Compare this to the estimated value of world- wide average annual exposure to natural radiation sources at 2.4 millisieverts (240 millirem).  If the Nautilus were allowed to operate at this level, its crew would reach a typical yearly dosage in just over a week.  After 1960, these standards were changed, to a recommended maximum of 3 rem per quarter and 5 rem per year and was adopted as a hard limit by the US Navy in 1967.  However, the crew of the Nautilus never saw any large radiation doses due to the safety standards employed by Admiral Rickover who wanted the exposure for the crew to be less than a couple of chest x-rays, an amount around 140 millirem. [1,8] This mark was met as the average annual exposure for a crew member on the Nautilus was reported as being 173 millirem per year on average, with 77 of its crew being less than 33 millirem.  The design philosophy employed by the Nautilus and subsequent US nuclear submarines is that personnel stationed outside the nuclear propulsion plant be subject to lower amounts of radiation than would be encountered from natural sources on shore.  This is the result of a combination of low natural radioactivity materials used in the ship construction, shielding techniques used on the reactor, and a lower exposure to cosmic background radiation while under the ocean. 
|Fig. 3: The Nautilus' position log at the North Pole. (Source: Wikimedia Commons)|
The Nautilus was the first vessel to traverse the North Pole by sea, albeit under the Arctic ice cap. [1,2,5,9] The arctic mission was undertaken as a technology demonstration mission, a challenge which took three attempts to achieve.  While submerged, there could be no radio communications or navigational aid from the outside world as they would not be in sight of stars for navigation nor would they be in range for terrestrial radio communications.  In addition to these challenges, there was almost no available sea charts for the arctic, a navigational challenge that still remains to this day.  On its first attempt in August of 1957, the Nautilus became lost due to failures of its navigational equipment and ultimately had to turn back.  At the time, the Nautilus was equipped with relatively primitive navigational aids, namely, a gyrocompass and magnetic compass, both of which are problematic near the poles. 
In response to failures on its first attempt, a new navigation system was installed on the Nautilus, a N6A-1 inertial guidance system, originally produced by North American Aviation for the Navaho cruise missiles.  There were serious doubts about this system's capability on the Nautilus as it was designed to support missiles traveling at fast speeds and for short periods of time, whereas a submarine moves slowly for months.  The inertial guidance system turned out to be an essential and reliable navigation tool.  In addition, there was a new found urgency to complete this mission in response to a the launch of the first artificial satellite, Sputnik by the Soviet Union.  In April of 1958, under the code name Project Sunshine, the Nautilus again attempted to traverse the Arctic Ocean.  This time it could not find a safe route through the Chukchi Sea to enter the Arctic Ocean due to shallow waters and thick ice conditions.  On its third attempt in August of 1958, a safe passage to the Arctic Ocean was found near point Barrow, Alaska allowing the Nautilus to complete the voyage across the North Pole.  Fig. 3 shows the Nautilus' position log at the North Pole. It reads latitude 90 degrees, representing the North Pole, and longitude 'indefinite' as the great circles representing the lines of longitude all converge at the Poles and thus longitude is undefined.
The USS Nautilus was the first and only of its class of submarine as it was meant to serve as an experimental platform, proving the concept of a nuclear powered vessel.  This lead to the nuclear powered navy of the United States and other countries, as well as a handful of nuclear powered Russian commercial shipping vessels for use in mining operations in the Arctic.  During its first 2 years of operation it traversed over 62,000 nautical miles without refueling, akin to the Nautilus submarine dreamt up by Jules Verne in 1870 whose advanced power system allowed it to travel 20,000 leagues (equivalent to 60,000 nautical miles since 1 nautical mile = 3 leagues) under the sea.  The Nautilus was decommissioned in 1980 and is now a museum near New London, Connecticut. 
© Tyler Reid. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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