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Nuclear-Powered Merchant Ships - Rebirth??

The IMO (International Maritime Organization) member countries are discussing about the prevention of air pollution from ships to inc1ude some new Annex on MARPOL convention. The air pollution from ships includes three categories as SO2, NOx and CO2emissions. The SO2 and NOx problems are essential1y localized near-shore problems, because, in far from the shoreline, those pollutants are falling down with rain on the sea surface and soluble within bulk sea water. On the other hand, CO2 is connected to the global warming problem.

Early in 2007, Lloyd's Register began research into the implications of nuclear propulsion for merchant ships. By 2009 Lloyd's Register announced a research program revisiting the technical challenges of nuclear propulsion for tankers, bulk carriers, container ships and cruise ships, as well as refueling and waste-disposal issues. Lloyd's Register commenced an internal research program directed towards the implications arising from the nuclear propulsion of merchant ships. This work built on the extensive and ongoing experience of Lloyd's Register in the land based nuclear industries.

Utilizing nuclear power for liquefied natural gas (LNG) vessels would provide a number of benefits, including low emissions, as the nuclear plant aboard an LNG vessel would eliminate carbon dioxide (CO2), nitrogen oxide and sulfur oxide emissions, a recent study has found. In its 2010 study, Babcock International Group's Marine Division sought to determine the commercial feasibility of utilizing nuclear power for the main propulsion and auxiliary power generation on board an LNG carrier.

Nuclear powered commercial marine vessels could reduce greenhouse gas emissions, but the commercial application of this technology is complicated. As of 2010 there were 150 nuclear powered vessels operating globally; this vessel population is composed of military vessels (e.g., submarines and aircraft carriers), and a few government agency icebreakers. The US Department of Transportation's April 2010 report to Congress, Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2 concluded that "Current concerns regarding national security (e.g., piracy and terrorism), complex maintenance issues (e.g., refueling, preventive and scheduled maintenance activities), and longer-term issues concerning disposal of spent rods and decommissioning of vessel reactors, make this technological option more complicated to implement then other technologies presented in this study. For these reasons, this report evaluates implementation only of nonnuclear technologies."

On 15 November 2010 it was announced that the BMT Group Ltd., specialists in maritime design, engineering and risk management, and Lloyd's Register's Technical Committee, were joining with Greek bulk tanker and container ship operators Enterprises Shipping and Trading S.A. and US based atomic energy experts Hyperion Power in a bid to investigate the practicability of small modular nuclear reactors as the power plants for freight vessels of the future.

Hyperion Power Generation Inc. is a privately held company formed to commercialize a small modular nuclear reactor [SMR] designed by Los Alamos National Laboratory ("LANL") scientists leveraging forty years of technological advancement. The reactor, known as the Hyperion Power Module ("HPM"), designed "to fill a previously unmet need for a transportable power source that is safe, clean, sustainable, and cost-efficient." Liquid Metal-Cooled small modular reactors such as the Hyperion Power Module (HPM), do not require a pressure vessel because the lead-bismuth [PbBi] coolant operates at ambient pressure. Light water reactors (LWRs) operate under high pressure and have a variety of extra safety components to consider because of this.

The agreement for the joint industry project was signed today at the offices of Enterprises Shipping and Trading in Athens, Greece. Enterprises' Victor Restis, commenting at the signing said, "Despite the fact that shipping is the industry that contributes much less in the World's atmospheric pollution compared to other shore based industries, we believe that no effort is enough towards safeguarding a better world for the future generations. We are extremely honored and proud to be part of this consortium at this historic event as we strongly believe that alternative power generation is the answer for the shipping transportation."

The consortium believes that SMRs, with a thermal power output of more than 68 megawatts, have the potential to be used as a plug-in nuclear 'battery'. The research is intended to produce a concept tanker-ship design based on conventional and 'modular' concepts. Special attention will be paid to analysis of a vessel's lifecycle cost as well as to hull-form designs and structural layout, including grounding and collision protection. "This a very exciting project," said Lloyd's Register CEO, Richard Sadler. "We believe that as society recognises the limited choices available in the low carbon, oil scarce economy and land based nuclear plants become common place we will see nuclear ships on specific trade routes sooner than many currently anticipate."

Heavy liquid metals considered for both terrestrial and space reactors include mercury, bismuth, lead, tin, and lead-bismuth [PbBi] eutectics. Lead-Bismuth (PbBi) forms a eutectic at 55.5 wt. % Bi and 45.5 wt. % Pb. The creation of the PbBi eutectic reduces the melting points from 327C and 271C for lead and bismuth respectively to 123.5C. Heavy metal-coolants are not fire or chemical explosive hazards, and exhibit very low vapor pressures. The low vapor pressure of heavy metal coolants provides the safety advantages ofpreventing loss of coolant accidents due to rapid coolant evaporation, and precludingexplosive release of a high-pressure coolant. Furthermore, heavy metal cooled reactors have negative void coefficients of reactivity. The thermal mechanical propertiesof PbBi provide for a large operating temperature range (melts at 123.5C and boils at 1670) so that guarding against boiling is easy. The boiling point of PbBi is 167C so there is a largeoperating temperture range and boiling is unlikely. In addition, PbBi is chemically inert so someaccident concerns are reduced.

Of course, as with any option, there are some undesirable features of PbBi. The three primary concerns are its corrosiveness, its radioactivity after irradiation and its toxicity. PbBi candissolve steels and can be contaminated by solid admixtures due to interactions with construction materials. This corrosive concern has been handled in Russia by the development of appropriate materials and the use of oxygen control to allow a protective oxide coat to form for protection ofthe materials. The oxygen control is sensitive since both too much oxygen and too little oxygen can cause problems. The Russians have, through experience, solved this problem for use insubmarine reactors but these systems did not have spallation products in the coolant.

A major disadvantage of PbBi coolants is the activation product 210Po resulting from an n,/ reaction with 209Bi and subsequent beta-decay to 210Po. Polonium-210 is very toxic and difficult to contain. Bismuth plus a neutron creates 210Po with a half-life of 138 days. This half life is short enough that it is not a waste concern but it is an operational concern. Fortunately, 210Po stays in the PbBi coolant as PbPo which self shields the 210Po. In addition, Lead and Bismuth are both heavy metal poisons which will require adequate separation from the environment. When irradiated, they represent a "mixed" waste which further complicates disposal.

Nonetheless, the former Soviet Union developed and used PbBi-cooled reactors in the Russian nuclear-powered submarine program. Russia built and operated 7 "Alpha Class" Submarines (~70-140 Mwe), built 2 on shore prototypes, with a total of 80 reactor-years experience. The United States has little experience with heavy metal reactor coolants. Cooperation with Russian developers could be important if heavy metal cooled reactors are pursued.





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Page last modified: 16-07-2012 18:49:44 ZULU