The first comprehensive rules for floating NPPs have been unveiled by American Bureau of Shipping (ABS) at a forum for nuclear industry leaders held jointly with Idaho National Laboratory (INL). As well as presentations on the latest reactor technologies from leading companies the event saw publication of a detailed study from ABS and Herbert Engineering modelling the design, operation and emissions of a floating NPP.

The 70-page ABS Requirements for Nuclear Power Systems for Marine and Offshore Applications, provides the first classification notation for nuclear power service assets such as floating nuclear power plants or nuclear-powered floating production, offloading and storage units. Uniquely, the requirements allow designers to consider any type of reactor technology and propose a framework for nuclear regulators to collaborate with Flag administrations and ABS for complete regulatory oversight and licence.

“We demonstrated today that nuclear’s potential in the maritime domain is so much more than a reactor on a ship,” said ABS Chairman & CEO Christopher J Wiernicki. “Nuclear energy can link energy demands across the electric, industrial and shipping transportation sectors to optimise energy generation and use, maintain grid reliability and support decarbonisation of shipping and industry. Not to mention its vast potential for the production of clean fuels such as e-ammonia and e-hydrogen.”

He added: “It is clear that nuclear energy has the potential to be a disruptor for the maritime industry. This is why we are proud to produce the first comprehensive rule set for the industry as an important step forward for the adoption of the technology.”

ABS is playing a leading role in helping government and industry work towards the adoption of advanced nuclear technology in commercial maritime, including key research with the U.S. Department of Energy and multiple New Technology Qualification and Approval-in-Principle projects with industry.

“This is an exciting time for nuclear energy. Idaho National Laboratory (INL) is growing and working with industry partners like ABS to test and demonstrate advanced reactor technologies,” said Brad Tomer, COO of the National Reactor Innovation Center headquartered at INL. “Collaboration and discussions like these will be critical as we move forward in delivering the low-carbon, affordable and reliable power that nuclear energy provides.”

The regulatory landscape around nuclear power plants was another key feature of the event, followed by workshops with offshore industry leaders to explore their requirements and understand operational challenges floating nuclear power plant technology will have to overcome.

The ABS Requirements for Nuclear Power Systems for Marine and Offshore Applications was developed to provide requirements for design, construction, and survey for class review and approval of vessels having onboard nuclear power system installations. “The document specifies ABS requirements for the mandatory notation Power Service (Nuclear) for nuclear power generation for purposes other than self-propulsion.”

The document notes: “It is the responsibility of the Nuclear Regulator to license the reactor and applicable nuclear safety structures, systems and components. Therefore, collaboration with other regulators, including those of the intended Port Authority/Port State, Coastal State, Port State Administration of operational site, or Nuclear Regulator … early in the design process is recommended to align the division of responsibilities for each authority regarding the design approval.”

The document applies to barges, ships, site-specific floating offshore installations, fixed offshore installations, and mobile offshore units. It covers new construction or conversion of vessels fitted with nuclear power systems for power service supplied to external or onboard industrial consumers. It says it is the responsibility of the Nuclear Regulator to license the reactor and applicable nuclear safety structures, systems and components. “These Requirements and any use thereof does not replace the review, certification, license, or other approval of Nuclear Power Plant (NPP) technology by a Nuclear Regulator.”

As well as a general introduction, the document has sections on: Risk Assessment; Hull Design and Arrangement; Nuclear System; Radiological Protection & Nuclear Material Handling; Machinery, Electrical, Piping & Equipment; Fire Safety; Control, Monitoring & Safety Systems; and Survey & Testing. However, it does not tackle regulatory requirements.

ABS has also produced a joint study with naval architect Herbert Engineering Corporation on Pathways to a Low Carbon Future Floating Nuclear Power Plant (FNPP) intended to be aligned with the release of the ABS Requirements for Nuclear Power Systems for Marine and Offshore Applications.

In his Foreword to the 16-page study, Michael Kei, ABS Vice President, Technology, Americas says: “The goal of creating concept vessel designs, even those without substantial technical detail, is to begin the iterative design process at a high level, conceptualise the potential hazards of the new technology, and prepare to implement engineering solutions to address potential risks.”

He adds: “Considering the demand of ports to supply low-carbon power to cold-iron vessels, especially visiting containerships and cruise ships, the FNPP Nuclear Navigator was designed with supply to the shore grid in mind to increase the available energy to support maritime decarbonization in port. This study reviewed existing ports fitted with onshore power supply (OPS) in the United States and the typical energy consumption from large ships such as cruise vessels.”

With these parameters in mind, an FNPP supplying a maximum of 70 MWe to the port electric grid was considered sufficient to meet the need of up to six visiting cruise ships at once. “The ability to deliver the FNPP to its site location and connect to the local grid from the pier can ease many portside challenges of increasing available power for port operations.”

To conceptualise the possible design, “the design team invited a reputable small reactor designer to provide information regarding the use of their reactor design for the FNPP. This reactor design has been supported by the US Department of Energy’s Advanced Reactor Demonstration Program (DOE ARDP) to demonstrate the commercial viability of SMRs.”

The study assumes that the FNPP, arranged on a barge, would have to be designed to accommodate a number of different installation locations and commercial needs, thus necessitating reasonable flexibility both in terms of power output and restricted water access. “A cluster of advanced reactors currently under development was therefore chosen to provide a power output of 35–70 MWe, corresponding to the highest electrical power demand of four to six large cruise liners in port. This conservatively high power may also be used for onshore power supply or battery charging services to containerships or other vessels in port.”

The reactors used in this concept study “have been designed for land-based applications and have not considered special provisions for marine operations”. Three modular reactor types of various sizes were considered: 5 MWe, 17.5 MWe and 30 MWe. Ultimately, the 17.5 MWe reactor was chosen, “as it offers the best compromise between output flexibility, design complexity and capital expense”. (

The study focused on a 17.5 MWe high temperature gas cooled reactor (HTGR). The design tried to extend the modular reactor philosophy to the entire FNPP, with four identical modules and two barge ends. “This is intended to reduce building costs and provide improved levels of redundancy, independence and segregation, thus enhancing plant reliability and safety.”

It is assumed that the nuclear reactors will be refuelled off-site every five years. “The issue is … not how long it would take to refuel these reactors, but rather the availability of shipyards which have appropriate radiological protection arrangements and know-how to carry out such specialised activities.”

The HTGR concept used is characterised as a modular, factory-fabricated system that is small and light enough to be transported via rail, ship, or truck. It is helium-cooled and uses high-assay low-enriched uranium (HALEU) uranium oxycarbide (UCO) TRISO (TRI-structural ISOtropic) fuel and graphite matrix as a moderator to produce 50 MWt.

The study concludes that “the maturity of advanced nuclear technologies that may be implemented for a FNPP is currently low”. Therefore, the level of detail provided “is limited to engineering information available from the design of terrestrial applications for engineering postulation and recommendations for future design optimisation”. Modular reactor philosophy “can successfully be carried over to the FNPP design with significant advantages in terms of safety and cost”. Furthermore, “the modularity concept allows the FNPP output to be reasonably flexible to adapt to the cold-ironing needs of large ports”.

In 2020, ABS completed a feasibility study for a Compact Molten Salt Reactor (CMSR) developed by Danish nuclear company Seaborg Technologies to investigate whether could be installed on a power barge to provide electric power to shore. In 2022, ABS was awarded a contract by DOE to research barriers to the adoption of advanced nuclear propulsion on commercial vessels. DOE has also contracted ABS to support research by the University of Texas into thermal-electric integration of a nuclear propulsion system on a commercial vessel.