|Fig. 1: Map of the Arctic region showing the Northeast Passage (dotted line). (Source: Wikimedia Commons)|
It is believed that the Arctic North of Russia contains approximately a quarter of the world's oil reserves. The extraction of this reserves is a tough goal due to severe Arctic conditions such as extreme weather and thick ice crusts, which hinder the transportation of black gold to the refineries. While the extraction of oil from that zone is only projected in the future, the Northern Sea Route (Fig. 1) is currently actively used by ships for scientific expedition and transportation of goods. The only way to navigate through six to ten foot thick ice is to use powerful icebreakers that can smash it and clear the path for other ships. While there is a number of conventional diesel powered icebreakers used around the world, these do not provide enough power to be able to crush thicker ice and require frequent refueling which makes them inconvenient for long periods of continuous operation.  The nuclear icebreakers are designed to solve these issues and provide a number of advantages compared to the diesel powered icebreaker. The only country that has been making and using nuclear powered icebreakers is Russia (and USSR in the past).  So far, Russia has built nine nuclear-powered ice-breakers, six of which are currently in operation.
Icebreakers have very smooth shaped bows, as opposed to pointed bows used by regular ships designed to slice the waves and add stability in open waters. When the icebreaker smashes ice the smooth bow hits the ice first from the above and causes it to break under the massive weight of the ship (Fig. 2).  The hull of the icebreaker is reinforced and coated with low- friction compounds to facilitate gliding over ice. Furthermore, the hull is designed push the crushed ice away from the ship to keep the propulsion system safe.
The heart of the ship contains a small nuclear reactors to generate heat which is converted into mechanical energy.  The reactor can provide power up to 60 megawatts which is enough to get through 8-10 feet thick ice at speed up to 10 knots (12 mph). The reactor uses nuclear fuel such as highly enriched uranium or uranium-zirconium to boil water that then rotates the turbine which, in turn, powers the turbo electric drive system. The latter spins the propeller. 
|Fig. 2: Nuclear icebreaker Yamal. (Source: Wikimedia Commons)|
Nuclear-powered icebreakers are much more powerful than diesel icebreaker. That enables them propel through very thick crust of ice at relatively fast speed as mentioned before. The fuel demands of this task using any other source of fuel (such as diesel) would be enormous: approximately 90 metric tons of fuel a day compared to just one pound of uranium at full power (for "50 years of Victory" icebreaker). The icebreakers are usually refueled once every 5-7 years.  This provides an enormous cost advantage as well as convenience of not depending on the presence of ports and refueling locations at remote areas. Nonetheless, the installation and maintenance of the nuclear propulsion system and the fuel itself is quite costly.
As mentioned by Melis Tekant the nuclear ships produce and utilize cleaner energy that diesel powered counterparts - the nuclear fission releases no greenhouse gases.  Nonetheless, there is a risk of catastrophic damage that could be cause by the nuclear fuel leakage or other accident. Luckily, there has been no precedent of that in the history of nuclear powered icebreakers.
Furthermore, the shape of the bow makes the icebreaker less stable in open water where waves can reach up to 40 feet. The normal pointed bow pierces through the wave and reduces the impact on the ship, while the rounded bow cannot prevent the wave from slamming into the ship. This makes the icebreaker roll from side to side making the crew very seasick. Furthermore, the harsh sound that the icebreaker produces when it crashes thick ice can significantly irritate people on board.
The instability issue cause by the rounded bow has been partially solved by introducing two ship design modifications. The new propulsion system, designed in the 1990s, introduced innovative azimuth thruster pods (Fig. 3) which allowed to rotate each pod under the ship 360 degrees facilitating thrust in any direction. Previously, the ships were only able to either propel forward or backward with rudder arrangement for steering. The propellers were typically installed at the back of the ship and were facing forward to create a pulling motion. It has been noticed that the ice breaks easier in agitated water. When the azimuth thruster pods were introduced, the crew could rotate the azimuth thruster pods by 180 degree and run the ship backwards. In this case the pods would be positioned at the new front (back before rotation) of the ship with propellers facing the ice. Thus, the propellers would be able to create agitating power to help break the ice easier. With this technology new icebreakers have been built with piercing bow at the front and rounded bow at the end (the propellers would also be at the end in this case). These icebreakers are called double acting reverse ships and can be efficiently utilized both in icy (up to 5 feet of thickness) and open waters. 
|Fig. 3: Azimuth thruster pods. (Source: Wikimedia Commons)|
Nonetheless, bigger icebreakers are still required to break ice thicker than 5 feet. In fact, Russia has recently announced that it plans to build the new 558-foot long, dual-reactor nuclear icebreaker. The new ship will be powered by two 60-meggawatt pressurized water reactors. It will be 46 feet longer and 12 feet wider than the largest nuclear icebreaker ever built. The new icebreaker will be able to alter its draught, which will allow it to enter shallow rivers deep into Russia.
The United States icebreaker fleet currently includes three operational ship and one ship in caretaker status. None of these ships is nuclear powered. Two of the ships, the Polar Star and the Polar Sea, are the most powerful non-nuclear powered icebreakers in the world, each capable of breaking through six feet ice crust at a speed of three knots. A study conducted on US icebreaker has found that both maintenance and operation of polar icebreakers have been underfunded for numerous years causing the US icebreaking fleet capabilities to substantially diminish.  Today, the US is reviewing all choices of building new icebreakers that will help it maintain leadership in polar research. The Arctic zone is becoming particularly interesting as the Arctic ice melts (as a result of global warming), opening up important sea transportation routes and making possible exploration of oil and gas reserves under the seabed. Furthermore, the renovation of the icebreaker fleet will reinforce the US position of defending its sovereignty in the Arctic and in the U.S. exclusive economic zone (EEZ) by maintaining a presence in these regions. At the same time, the fleet will also help monitor sea traffic in the Arctic and conduct other Coast Guard missions such as rescue and law enforcement. It has been estimated that the production of two new diesel/gas-powered icebreakers to substitute two existing ones (the Polar Star and the Polar Sea) would cost approximately $1.6-1.9 billion (for both ships). The estimated production time is about nine years and ships are designed to have 30 years of lifetime. 
One of the biggest questions is whether the new icebreakers should be nuclear-powered as the ones in Russia. This will allow for operational advantages of unrestrained cruising endurance at any speed and abilities to operate in thicker ice environment. In this case the US can reduce the total number of icebreaker that it needs to build since the nuclear powered icebreakers will be able to make high-speed trips to different polar regions to respond to sudden situations without losing time for refueling. At the same time, building the nuclear-powered icebreakers will improve economies of scale in manufacturing nuclear propulsion systems for U.S. Navy nuclear powered ships.  In time, this will reduce the cost of the nuclear propulsion systems overall as well as the cost of nuclear-powered icebreakers themselves. Nonetheless, in the current situation of harsh budget constraints, the additional cost of several hundred million dollars might reduce the number of projected icebreaker to be built from two to one. Even though the nuclear powered icebreaker will provide a number of advantages outlined earlier, one ship will most likely not be enough to meet the U.S. needs. Moreover, the introduction of nuclear-powered ships will require the Coast Guard to create the maintenance and training infrastructure to support the operation of the ships. This will require additional funds and time. The option of using the Navy infrastructure might be too costly and economically unviable. 
© Georgy Zerkalov. 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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