Power market developments: nuclear shipping
The nuclear propulsion of merchant ships15 August 2011
Environmental and economic considerations are turning the heads of shipping companies toward nuclear power for propulsion, particularly using small-to-medium size reactors. Although reactor technology may be well-understood, the way nuclear ships are built and operated will require organisational changes in the shipping industry. By John Carlton
The nuclear propulsion of ships was first introduced into submarine practise in 1955 when the USN Nautilus sailed on its maiden voyage. Since that time some 700 nuclear reactors have served at sea and today there are about 200 reactors providing the power for marine vehicles. Following the USN Nautilus, the NS Savannah sailed as a passenger-cargo demonstrator ship under US president Dwight Eisenhower’s Atoms for Peace programme. The Otto Hahn and Mutsu followed, again both designed as technology demonstrators. Since that time a number of other nuclear propelled merchant ships have been designed, most notably the Russian icebreaker classes, as well as a few ships engaged on specialist duties. More recently, the Yamal and the 50 Years of Victory have worked as dual-purpose passenger cruise ships and icebreakers.
Significant changes in the normal design process of a merchant ship would need to be introduced to incorporate nuclear propulsion. The design process will have to be driven by a safety case in which building, operation, maintenance and decommissioning are the principal features. These safety cases will embrace the nuclear, mechanical, electro-technical and naval architectural aspects of the ship design with the safety and integrity of the nuclear plant taking precedence. Such procedures would be required to involve all parties concerned with the ship including the builder, classification society, flag state and national nuclear administration, as well as the ship owner, who, as the duty holder, would in addition need to demonstrate its ability to operate the ship in a competent manner. This entire process would need to embrace the principles and requirements set out by the International Atomic Energy Agency (IAEA), albeit adapted for the marine environment.
Most commonly, enrichment of the uranium fuel to a level of 3.5% to 5% might be anticipated, from which a refuelling interval for a merchant ship might be around 5 to 7 years; not dissimilar to classification survey intervals.
The majority of reactors that have been deployed at sea have been of the pressurised water reactor type. Consequently, a significant body of experience has built up around these reactors, and it is likely that any early applications of nuclear technology in merchant ships would aim to utilise this accumulated knowledge. In the longer term, high-temperature reactors and other types might find applications. If suitably marinised, nuclear batteries (small reactors with replaceable, pre-fuelled, tamper-resistant cores) might also find deployment. Fuel usage in a reactor will be considerably less than the quantities of heavy fuel burnt in conventionally-powered large ships. For example, the amount of fuel required to power the voyage of a 12500 TEU container ship from Rotterdam to a port on the east coast of the USA at a speed of 25 knots would be on the order of 1550 tonnes of fuel oil, or about 2.2kg of uranium fuel enriched to 3.5%.
Steam produced by the heat of a nuclear reactor could be expanded through a turbine, either forming part of a direct-drive transmission system to the propeller or, alternatively, a turbo-electric power station system from which power might be drawn for the ship’s hotel, cargo handling or storage and propulsion purposes. The latter could become a particularly attractive option for some types of ship. Direct-drive propulsion systems have a number of disadvantages relating to the transmission system, particularly with respect to the gearbox. Alternatively, the turbo-electric concept would more readily facilitate the use of complex steam cycles to gain a higher overall cycle efficiency, since reversing of the turbine would no longer be necessary for astern operation of the ship.
The positioning of the reactor within the ship would likely present some constraint on the overall ship general arrangement. Clearly, it is beneficial that the reactor plant is protected as far as is reasonably possible from undue sea induced motions and vibration and the most benign location would be around the centre of floatation of the ship. The reactor and containment location will also need to be protected from the effects of collision between ships. As the deployment of nuclear power is perhaps only likely, for large merchant ships in the foreseeable future, vessel size offers significant scope for a protection system to be designed, since the size of the reactor containment will be significantly smaller than the breadth of the ship. This, therefore, gives ample opportunity to design an arrangement which will distribute the energy of the collision into the hull and away from the reactor location. Typically, this might be achieved by the transfer of technology from the automobile industry in the use of elasto-plastic principles of design for crash protection. Similar energy principles should also form the design basis for resisting a piracy attack on a ship using missiles and the fundamental principles to be utilised would derive directly from the safety case for the ship.
Nuclear propulsion deployment in a merchant ship could change other aspects of ship design. For example, nuclear fuel’s relative cheapness might enable operation of a ship at much faster speeds than oil-powered ships sail at today; 35 knots for a container ship, or 21 knots for a tanker (see box) compared with around 22 and 15 knots today. Running a fast ship on a liner route might save the deployment of one ship when moving a fixed volume or weight of cargo. Alternatively, the minimal mass and volume of fuel used may give scope for increased deadweight capacity or, alternatively, provide greater flexibility in the hull design.
In terms of procurement, the purchase price of the nuclear propelled ship would be considerably greater than that of an equivalent conventional ship, assuming that the nuclear plant were purchased by the ship owner. However, for the conventionally-propelled ship, the through-life fuel costs are high and are likely to rise further with the phasing out of heavy fuel and any introduction of carbon tax. In contrast, the price of uranium enriched to commercial levels is much cheaper than conventional fuels. Therefore, the fuel costs become very much less for the nuclear ship. These, together with the other known costs, can be offset against the high initial cost to show a break-even point sometime between the first and second decade of the ship’s life. Clearly, however, there are other cost elements about which little is known at present, such as insurance, maintenance, pilotage and port dues and survey fees.
A key question that would need resolution for merchant ship application would be whether the nuclear plant were purchased or leased by the shipowner. A leasing arrangement may simplify the execution of those duties by the plant manufacturer undertaking the complete machinery cycle process through the design, certification, manufacture, operation and eventual disposal of the propulsion plant. Such an arrangement would not relieve the ship owners from their responsibilities as duty holders. Indeed, nuclear plant operation and disposal are particularly onerous aspects that would require detailed knowledge on the part of the ship owner which, at present, few possess. Achieving that level of knowledge would require establishing training programmes analogous to those operated by nuclear Navies.
Even in the leasing model, some lesser level of nuclear operation expertise would still be required of the ship’s officers, since the nuclear propulsion plant would need to be integrated within the ship’s overall command structure. Clearly, in both respects the current Standards of Training, Certification and Watchkeeping code requirements are deficient. Moreover, training would need to be reactor-specific with revision periods and recertification necessary. These requirements would have serious implications for many of the current employment contractual arrangements within the merchant navy.
In 1981 the International Maritime Organisation (IMO) adopted a code of safety for nuclear merchant ships, Resolution A.491(XII), and although it has not been implemented it is still extant. However, although relatively farsighted at the time, it would need updating so as to be aligned with current thinking on nuclear safety. Prior to that resolution, Lloyd’s Register also maintained a set of provisional rules for nuclear-propelled merchant ships. These have recently been completely revised [see box].
The role of the land-based nuclear regulator and the views of the flag and port state controls will be critical for the successful implementation of marine nuclear propulsion. Mutual acceptance of certification between different countries will become the key to nuclear ship operation and voyage planning.
An analogous issue is the question of plant maintenance. While normal hull and structural maintenance is unlikely to be a significant issue, any maintenance involving either directly or indirectly the nuclear plant is of concern. Plant-related maintenance will need to be embraced by the safety case for the ship and then planned accordingly together with the possibility of having to use dedicated berths or ports where such desired activity can be carried out.
In the case of public opinion, it is clear that there is a perception that CO2 and greenhouse gases present a significant threat for the future. There is some growing acceptance that the use of nuclear power for ship propulsion is beneficial. Some countries, however, remain opposed to nuclear-propelled ships entering their ports, while other federally-organised countries have states with conflicting views. Notwithstanding these differing views, other countries are suggesting that serious consideration should be given to nuclear propulsion for merchant ships. For example, in a recently-produced UK government memorandum detailing options for decarbonising Britain by 2050, the section on international shipping suggests “building and maintaining a new fleet of nuclear-powered container ships and passenger ships.”
Decommissioning the ship is another major issue, particularly for a non-state owned shipping company, although this is not an insoluble problem. A number of dismantling options are available and the immediate dismantling and safe storage options have been used, in part, for the Otto Hahn and Savannah respectively. The third option is entombment, of which there are a number of naturally-occurring examples.
The question of the insurance of nuclear propelled ships raises a number of issues. The first is clearly the stance of hull and machinery underwriters and that of Protection & Indemnity Clubs. In the former case nuclear technology and its mechanical risks are comparatively well-understood and, if not, lend themselves to probabilistic analysis of the risk. In the latter case if one member of a club purchased a nuclear ship which was subsequently subject to a claim, the claim could place the other members of the mutual club to considerable financial exposure. It is unlikely that governments or flag states, for the most part, would enter into the underwriting process for commercial ships.
If a nuclear-propelled ship came into difficulties while on passage the salvage or rescue process would need some careful analysis. It is unlikely that the standard Lloyd’s procedure would suffice and an amendment to that would almost certainly be required. Such a scenario would clearly be an extreme case, since a ship would need to have an auxiliary means of propulsion if it was fitted with only a single reactor plant. Typically, this would be a diesel engine capable of propelling the ship at six or seven knots towards a safe haven. Again, this might suggest specifying a turbo-electric main propulsion system so that the auxiliary diesel generator could then contribute to the onboard electric power station, from which propulsion power would be derived. If two or more independent small nuclear power plants were provided, the need for an auxiliary propulsion diesel engine would not exist.
In summary, it is clear that the technical aspects of nuclear propulsion are well-understood as there has been a considerable body of experience accumulated with marine platforms. The principal issues relate to training, insurance, perception and operational change that a nuclear-powered ship would place upon an owner. These are in addition to the reorientation of the ship procurement process that would be necessary, so that all parts of the design, construction, operation, maintenance and decommissioning processes would become explicitly governed by the safety case for the ship. Indeed, the production of the safety case would require the involvement at the design conception stage of all of the interested parties including the appropriate nuclear inspectorates, flag states, classification societies, shipbuilder and nuclear plant manufacturer and the ship owner, who is the duty holder.
|Nuclear propulsion for LNG tankers?|
Babcock International Groupâ€™s Marine Division investigated the commercial implications of developing a nuclear-powered LNG carrier in a feasibility study. Babcockâ€™s report covered engineering and design issues, recent technical developments, and statutory regulations, to operational aspects, through-life maintenance, training requirements, and vessel disposal. Babcock experts in ship design, nuclear plant systems installation, maintenance, and decommissioning were involved in the study.
|Nuclear-powered shipping: the Lloyds view|
A consortium of Lloyds Register, small nuclear reactor developer Hyperion Power Generation, NMT Nigel Gee (marine architect) and shipowner Enterprises Shipping and Trading launched a research programme to investigate nuclear-powered commercial ships in October 2010. The programme follows the conclusion of a two-year Lloyds study of whether it should develop rules for marine nuclear power plants for shipping: the answer was a resounding yes. The first draft rules were put to a committee in December 2010, says Vince Jenkins, Lloyds Register global marine risk advisor.