|Fig. 1: Diagram of Nuclear Reactor within SSNs. (Source: Wikimedia Commons)|
Unlike conventional diesel-electric submarines, SSNs use nuclear reactors to provide the energy necessary to propel the vehicle through the water. USA SSNs use enriched uranium to fuel the reactors, creating large quantities of heat through nuclear fission.  A pressurized light water system pumps water through chambers in the reactor, where energy from the nuclear fission heats the liquid until it becomes pressurized steam. This steam turns a turbine which is connected to the gearbox and shaft of the propellers, rotating them and thus providing thrust. To prevent radiation exposure for the crew, the nuclear and water pressure portion of the system is housed in a shielded radioactive compartment, while the turbine and drive shaft are in a separate housing, as shown in Fig. 1. 
The major difference between diesel-electric and nuclear submarines are their resource requirements. Diesel-electric runs on a combination of lead-acid batteries and diesel engines, which require the submarines to resurface periodically in order to charge the batteries and refuel.  Nuclear submarines, however, run exclusively on the uranium stored on the vessel, therefore giving them an unlimited capacity to stay underwater. Surfacing is when submarines are most vulnerable, therefore minimizing this time is important to survival.
Furthermore, agility and the ability to take evasive action is a crucial requirement for submarines. Speeds of 25-30 knots are imperative for Naval evasion and combat, however the diesel-electric submarines were limited to 1 hour of operation under these conditions before needing to resurface.  Nuclear submarines can achieve high speeds with endurance, able to travel across the globe at such speeds without ever having to surface.
Nuclear submarines on average have reactors that can survive up to a 33-year lifespan, however newer SSNs in production are pushing these limits to 40-years.  The result of this is that crewmen and naval officers are below the surface for very long periods of time without ever surfacing. General rotations last for 3 months between on-land positions and at-sea crew, where the normal life patterns of on-land are replaced by fragmented, 18 hour, shift oriented sleep cycles at-sea.  Research done on the working and lifestyle conditions of SSNs concluded that although there is a lack of natural sunlight and fresh air, the working time, sleep quality, and sleep amount are comparable to on-land conditions. 
The problems for crew arise not from the obvious assumption, radioactive exposure, but rather atmospheric quality. Due to the effectiveness of the shielded compartment and the lack of an in-depth study, there is little concern about the adverse health effects of living with close exposure to a nuclear reactor. The biggest problem is the air, specifically the breaching of maximum contaminant levels for contaminants such as mercury, carbon monoxide, and 86 others.  The closed- environment of the submarine prevents contaminants from escaping the local atmosphere, increasing carcinogenic exposure for crewmen. This problem can be directly associated to the ability of SSNs to remain underwater, which prevents the circulation system from disposing the contaminants out of the vessel. 
The problem of air quality is just one of the concerns researchers have about SSNs due to the nuclear reactors' capabilities and properties. Specifically, the two endpoints on the life cycle of a nuclear submarine, the construction and disposal, pose threats towards humans due to radioactivity. In terms of construction, the largest problem arising is the significant increase in cancer mortalities amongst ship workers.  In New Hampshire, Maine, there was a large spike in leukemia-related deaths over the period of 18 years by workers on nuclear submarine components, while other workers not exposed to the nuclear work experienced zero increase in cancer-related deaths.  This data, acquired from a study done by Boston University, found that across the nation at similar working facilities, workers in the nuclear sector were seen to have a greater proportion of cancer-related ailments.
In terms of disposal, the concern of proper containment of radiation is becoming more common as the fleet of SSNs continues to expand. The US Navy alone operates 73 nuclear submarines, all of which have a finite lifespan.  What this means is that whether they are destroyed during battle or retired out of duty, they eventually end somewhere to decompose. This poses a huge problem, as there lacks regulation on disposal requirements, which can lead to radioactive waste leaks.  Furthermore, nuclear decay lasts for thousands of years, which evolves the problem into a very long term ailment for the environment.
Overall, these benefits and problems associated with nuclear submarines constructs the question of whether nuclear reactors are favorable for long term societal benefit. Do the benefits of unlimited submersion and maneuverability surpass the costs and concerns of crew and worker health?
© Charles Skolds. 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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