Paper presented at Propulsion '95, a conference of maritime professionals sponsored by the Marine Log. New Orleans, LA. Oct 30-31 1995.
Nuclear Power for Commercial Ships
Rodney M. Adams
Atomic engines offer capabilities that cannot be achieved with fossil fuel engines. Nuclear fission requires no oxygen and produces no exhaust gases, and nuclear reactors are reliable, compact sources of continuous heat that can last for years without new fuel. These beyond competition capabilities have encouraged the development of certain types of nuclear systems without much regard for cost. Economic concerns are low on the priority list if the desired product is a high endurance submarine or a speedy aircraft carrier capable of independent operations. Of course, contractors love to work for a customer who has a "cost is no object" mentality.
Conventional wisdom states that the high cost of military nuclear ships proves that nuclear power cannot compete in less specialized markets. That is roughly equivalent to stating that the cost of military toilet seats and hammers proves that those items will be beyond the reach of the average American worker.
Advanced nuclear technologies and a careful focus on cost conscious design can result in nuclear propulsion systems that are economically superior to conventional systems for a wide variety of commercial applications. The nuclear gas turbine, for example, offers the simplicity and low capital investment of combustion gas turbines combined with the high endurance, low fuel cost and zero emission characteristic of nuclear powered systems. This concept should attract the attention of commercial shipping industry decision makers in their unending quest for a competitive advantage.
On January 17, 1955, the Nautilus reported "Underway on nuclear power." Her success clearly demonstrated that nuclear reactors could be used as the heat source for marine engines. In the forty years since that first nuclear propelled voyage, five of the world's navies have combined for well over a hundred million miles of nuclear powered ocean travel using over 700 marine nuclear reactors. Nuclear power, however, has had essentially no impact on commercial shipping. Only a handful of non- military nuclear powered ships were ever completed; most of them were launched more than 30 years ago. The only ones still in operation are Russian icebreakers.
This situation was not what was predicted by 1950s vintage visionaries. At first, the idea of nuclear engines for civilian ships seemed like a natural extension of the success of the nuclear submarine. Large passenger liners like the United States and the Queen Mary were prodigious oil burners, consuming 50 tons per hour at high speed. Fast cargo ships, like those used to transport perishable items were not as large or powerful, but they could consume 10-20 tons per hour. Even with oil priced at $20.00 per ton, fuel represented a significant operating cost, but even more critical was the fact that the fuel storage space needed for long-range, high speed travel limited the operating range of the ship.
In September, 1955, J. J. McMullen produced a report for the Maritime Administration which found that the following characteristics were important in determining whether or not nuclear power should be considered for a given ship type.
- Long trade route
- Quick turn around in port
- Dense cargo in unlimited supply
- Large deadweight capacity
- Minimum shaft horsepower of 20,000
- Fuel for the round trip taken on at same port as payload
- Payload carried both ways
- Regular home port at one end of voyage
- Smoke elimination to be an advantage
- Cargo suitable for secondary nuclear shielding
The N.S. Savannah experience
McMullen's carefully considered criteria were ignored in the process of designing the first nuclear powered merchant. Instead, the design criteria for N.S. Savannah came from a politician. In the words of President Eisenhower, "Visiting ports of the world, it will demonstrate to people everywhere this peacetime use of atomic energy, harnessed for the improvement of human living. In part, the ship will be an atomic exhibit, carrying to all people practical knowledge of the usefulness of this new science in medicine, agriculture, and power production." (April 25, 1955)
N.S. Savannah was a show boat. She had beautiful lines, more resembling a very large yacht than a bulk cargo ship. She carried thirty spacious passenger cabins, a swimming pool, a public lounge, and dining facilities for a hundred people. Her cargo handling equipment was designed and placed for beauty, not function and her holds had a maximum capacity of about 9,000 tons.
Her propulsion plant was built by Babcock and Wilcox, a boiler manufacturer that had never before constructed a nuclear power plant. One goal of the program that had little to do with economically producing a competitive merchantman was to qualify another nuclear reactor manufacturer so that the navy contractors did not completely dominate the civilian market.
As might be expected, Savannah was never self-supporting. She spent three years in the demonstration business, visiting 55 domestic and foreign ports. She hosted dignitaries and received many admiring visitors. Following the successful completion of the planned demonstration phase, she was chartered to First Atomic Ship Transport, Inc. a wholly owned subsidiary of the American Export Isbrandtsen Lines, Inc.
She operated as a subsidized general cargo ship from 1965 until 1971. During this phase of operation, she did not attempt to carry passengers because the cost of serving them would have been more than their fares. She also did not attempt to maximize revenue, often waiting in port for several days for delivery of a cargo that did not even fill her holds. Her operating subsidy averaged approximately $2.9 million per year or approximately $2 million more than a conventionally fueled ship of similar size. According to the Comptroller General of the United States, $1.9 million of Savannah's subsidy could be attributed to the costs of initial nuclear training, a nuclear shore staff and a nuclear servicing facility. As a one of a kind ship, Savannah had to support these specialized facilities by herself.
Savannah was laid up during the fall of 1971. During the early to mid 1970s, there were some studies funded by nuclear suppliers and the federal government that investigated the possibility of using nuclear power for specialized applications. Again McMullen's criteria were ignored when the high level criteria specified was a 2000 ton surface effect ship with 140,000 SHP. Understandably, there was little interest in building such a ship on the part of commercial ship owners. There has been essentially no discussion of nuclear power for merchant ships in the industry for at least twenty years.
Nuclear Ship Criteria for the 1990s
The shipping business has changed dramatically since 1955. Ships have grown, the container revolution has cut in port turn-around times for general cargo ships, and international trade in high value cargos like automobiles and construction equipment has steadily increased. Many ships in busy port cities are now required to install expensive equipment and/or restrict their operations to meet anti-pollution laws that limit discharges of oil, stack gases, and ballast water. In order to decide if nuclear power is now right for a particular ship, the following additional factors should be considered:
- Speed requirements
- Volume limits
- Emissions limits
- Oil handling limits
- Ballast water limits
- Deck space limits
- Need for flexible operation
- Local cost, availability, and quality of fuel
The following types of ships may benefit from nuclear power. Operators of these ships would be well advised to learn more about what uranium fuel can do. As usual, a detailed economic analysis will be required to reach a correct propulsion plant decision.
- Large container ships
- Automobile carriers
- Refrigerated cargo ships
- Long distance passenger ships
- Logistics support ships
- Commercial submarines
- Bulk cargo carriers
The Need For Speed
An example calculation might help explain the characteristics of nuclear propulsion that allow it to claim a speed advantage over oil burning ships. If a ship needs 26,000 shaft horsepower to travel at 17 knots, it will burn about 1700 gallons (6.4 tons) of bunker fuel every hour. If the same ship wished to increase speed to 25 knots to make a delivery schedule, the fuel rate would increase to 8500 gallons (32 tons) per hour while the power needs would increase to 130,000 SHP. It is obvious why fast ships are not generally considered to be an economical way to transport bulk cargo.
Even if oil is cheap, the space required for storage for a long trade route becomes a major concern. A ship like the above carrying goods from New York to Cape Town, South Africa would need at least 2.3 million gallons of fuel (6900 tons) to make the trip at 25 knots versus 673,000 gallons (2019 tons) at 17 knots. Even though the trip takes five days longer, space and fuel costs favor the slower journey.
With nuclear ships, fuel expenditures are minor, both in terms of weight and cost. At current nuclear fuel prices an SHP hour produced by fissioning slightly enriched uranium fuel costs less than one sixth as much as an SHP hour produced by burning residual oil. The advantage is even more dramatic when compared to distillate fuels. There is virtually no change in weight on a nuclear powered ship because of fuel consumption.
There are obvious advantages to increased speed if fuel consumption is less constraining. More cargo can be moved with the same number of ships. Cargo will spend less time at sea and more time where it is needed. Shippers will pay higher rates for certain types of cargo since they will save on financial carrying costs. Since a faster ship requires the same crew size as a slow one, productivity can increase be improved without painful layoffs.
Nuclear ships have demonstrated a high degree of reliability. They have operated for decades in some of the world's harshest climates including the Persian Gulf and the Arctic Ocean. They are not subject to clogged fuel filters, burst fuel lines, loss of compressed starting air, contaminated fuel from substandard suppliers, bent rods, failed gaskets, or a whole host of other problems common to combustion engines. Even single reactor plant submarines comfortably operate under the Arctic ice cap where a loss of propulsion power can be deadly. The engines rarely fail. Since a substantial portion of the marine accidents can be blamed on propulsion casualties, this characteristic is an important advantage for nuclear power.
Power Density Comparisons
Conventional wisdom holds that the weight of shielding needed for nuclear powered ships is more than the weight saved by the lowered fuel consumption. Savannah's propulsion plant weighed about 2500 tons including the shielding. Her specific power ratio was 238 lbs/hp (151 kg/kw), which is obviously not very competitive with today's medium speed diesels or gas turbines. However, Savannah's propulsion plant weight included enough fuel for 340,000 miles of operation. In contrast, a diesel engine system with a specific weight of 36 lbs/SHP (23 kg/kw) and a specific fuel consumption of .3 lbs/hp-hr (.2 kg/kw-hr) would match Savannah's characteristics if its required voyage lasted 28 days (13,000 miles at 20 knots), ignoring the weight of tanks, and piping and reserve fuel requirements.
Actually, the comparison between a modern diesel and a 1950s first generation nuclear plant with a low pressure saturated steam plant does not provide a realistic picture of what a nuclear plant can achieve. The below table, which includes ducts and foundations, provides better information:
Power density of typical engine types Engine type Specific weight combustion gas turbine 2.9 kg/kw medium speed diesel 10 kg/kw nuclear gas turbine (including shielding) 15 kg/kw nuclear steam plant (including shielding) 54 kg/kw
Total system power density comparisons
Engine power density is not the only consideration for vehicles like ships that must carry their fuel. One of the main reasons for converting ships from coal to oil rested on the fact that oil has more energy per unit weight. Therefore, we need to compare the power density of various types of engines including stored fuel. When fuel for a 10 day voyage is taken into consideration, nuclear plants can have a decided advantage over combustion plants. This advantage allows a greater portion of the ship to be dedicated to carrying revenue generating cargo.
Power density for various engines with 10 day fuel supplies Engine type Specific weight nuclear gas turbine 15 kg/kw nuclear steam plant 54 kg/kw diesel engine (.2 kg/kw-hr) 58 kg/kw combustion gas turbine (.24 kg/kw-hr) 60 kg/kw
Specific volume comparisons
Many of today's ships are more limited by space than by displacement. Nuclear propulsion plants, with high density materials making up a large portion of their weight, have an advantage over fossil fueled ships. A nuclear gas turbine plant would require approximately 60% of the volume of an equivalent combustion gas turbine for a nominal 10 day voyage; the advantage increases for longer ranges.
Container ships, like aircraft carriers, need as much free deck space as possible. This requirement is one thing that has inhibited the use of marine gas turbines, which require a high air flow and subsequently require large intakes and exhausts. Nuclear gas turbines, however, have no need for intakes and exhausts. The space saved on deck can increase operating efficiencies and revenues for the life of the ship.
In most ports, it is illegal to discharge oil contaminated water. This has led to the development of segregated ballasting systems to ensure that compensating water is not contaminated. There are also limits associated with biological hazards that prevent the discharge of ballast water taken in at a different port. Nuclear ships have no need to compensate for changes in fuel weight during a voyage so they can have simpler ballasting systems.
Governments have implemented air emission limits in certain busy ports that require costly modifications to existing propulsion systems. Simple, but somewhat costly, solutions include separate bunkers with low sulfur (but more expensive) oil, and ship speed (power) limits when within certain boundaries. There is increasing pressure for the installation precipitators, selective catalytic reformers and scrubbers. Aside from the expense, these technologies can be difficult to adapt to ships because of space limitations. Nuclear ships do not emit any exhaust gases, a fact that is clearly demonstrated by the success of nuclear powered submarines.
Finally, rules on liability for oil spills are increasing the cost of bunkering. Provisions must be made for containment booms and stand-by response teams. Separate fueling piers are becoming common, requiring extra time in port and extra expense for tugs and pilots. Bottom tanks now need double hull protection, increasing the cost of both construction and operations. Nuclear ships will be refueled during scheduled maintenance periods; it is easily possible to design cores that can last for six to ten years of normal ship operation.
There is currently little interest in the United States on the part of either the government or major corporations to consider the possibility of uranium fueled ships. There are obvious hurdles that must be overcome, but the benefits of nuclear propulsion make the effort worthwhile. The benefits are enough to encourage Japan to continue to support nuclear ship research, though they have yet to develop any commercial vessels.
In order to make nuclear ship propulsion a viable alternative for those applications that can achieve benefits from the inherent characteristics of nuclear energy, the following actions should be taken.
- Industry should agree on certain standards that allow operators and parts to be exchanged between several different engine configurations.
- Governments should establish reasonable regulatory oversight. The model should be the Federal Aviation Administration which sees its role as supporting safe air travel instead of the current Nuclear Regulatory Commission which sees itself as a cop policing an industry that seems to be unneeded and unwanted.
The future is bright, the benefits are apparent, and the technology is available. The impact of nuclear power on ocean shipping can be as great as that of containerization. Because of the increased speed and flexibility of operation, atomic energy can allow ships to compete more effectively with aircraft in the market for international deliveries.
Comptroller General of the United States "Costs of Operating the Nuclear Merchant Ship Savannah" Maritime Administration, Department of Commerce B-136209 June 26, 1970.
H.F. Crouch Nuclear Ship Propulsion, Cornell Maritime Press, Cambridge MD 1960.
J.M. Dukert, Nuclear Ships of the World Coward, McCann and Geoghegan, Inc. New York, NY 1973.
G. H. Farbman and R. E. Thomson, "Application of Nuclear Rocket Technology to Light Weight Nuclear Propulsion and Commercial Nuclear Process Heat Systems," AIAA paper No. 75-1261 presented at AIAA/SAE 11th Propulsion Conference, Anaheim CA, September 29- October 1, 1975.
E. C. Hunt and B. S. Butman Marine Engineering Economics and Cost Analysis Cornell Maritime Press, Centreville, MD 1995.
L. C. Kendall and J.J. Buckley, The Business of Shipping Sixth Edition Cornell Maritime Press, Centreville, MD 1994.
D. Kuechle, The Story of The Savannah: An Episode in Maritime Labor-Management Relations Harvard University Press, Cambridge, MA 1971.
D. L. Luck "Gas Turbine Marine Applications and The Strategic Sealift Ships" Propulsion '94.
R. T. Miller and R. E. Thomson "Maritime Applications of an Advanced Gas-Cooled Reactor Propulsion System," The Society of Naval Architects and Marine Engineer, 1977 Spring Meeting and STAR Symposium, San Francisco, CA May 25-27, 1977.
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