|Fig. 1: Perspective view of a three-sphere design of underwater reactor. After |
As a resource-constrained country, Singapore depends entirely on imported fuel for its energy consumption. Since alternative energy such as solar and wind is difficult to obtain, the Economic Strategy Committee has recommended the government to study the feasibility of nuclear power in Singapore.  Traditional nuclear power reactor need a safety zone of 20-30 km, and the problem of land scarcity in Singapore means that alternative locations have to be considered. Offshore nuclear power plants have recently gained popularity due to the development of small modularized nuclear reactor.
Possible offshore nuclear power systems include floating nuclear reactor and underwater nuclear reactor. Floating nuclear power stations are normally self-contained vessels that contain combined heat and power plant with low-power nuclear station. Russia is currently the main player in this technology with the Ministry for Atomic Energy of the Russian Federation (Rosatom) plans to build 7 such vessels by 2015 and one of them, Akademik Lomonosov, is under construction to house two 35 MW KLT-40S nuclear reactors. [2,3] However, floating nuclear power plant is difficult to be adopted in Singapore due to meterological problems. In addition, the limited coastline in Singapore houses one of the busiest container ports in the world and a floating nuclear reactor will be significant safety and security concern. Underwater nuclear power plant has several advantages. Since nuclear plants employ steam-generators, which require large amount of water to cool the condensers, the ocean environment serves as a huge heat sink with nearly unlimited amount of cooling water. Underwater sitting also reduces the potential effect ground motion due to seismic events. In addition, the effect of fume release in case of nuclear accident is reduced when the reactor is located underwater.
Possible underwater nuclear power plant designs have been conceived since the early 70s. One example of such a system proposed by Severs and Toll is illustrated in Fig. 1.  The system consists of a triangular tubular platform that supports three large interconnected spherical pressure vessels. The reactor spheres houses a pressurized water nuclear reactor and its associated nuclear steam system, a nuclear fueling system, and a containment system. The second sphere contains a steam turbine-generation unit, a reactor feed water purity control system and reprocessing facilities for chemical reactor control additives. The third sphere houses the control and operating system for the entire plant and other auxiliary systems. The spherical vessels allow the units to withstand not only the large external pressure of the surrounding water, but also the internal steam pressure in case of nuclear accident.
Currently France is the forerunner in the development of underwater nuclear reactor technology with DCNS prototyping a 100 meters cylindrical small nuclear power reactor called Flexblue.  The reactor is expected to have an output rating of around 50 to 250 MWe. The prototype is similar to a submarine in structure and can be transported to sea on a heavy lift ship, which lowers itself to allow Flexblue to maneuver by itself. Electricity generated is transmitted to the land by undersea cable. It is expected that the Flexblue has a safely level comparable to Generation-III reactor.
The high urban population density in Singapore means that safety will be a significant concern. Given the recent Fukushima nuclear accident, it is ever more important for Singapore to fully consider the feasibility and safety issues of nuclear energy. Advances in nuclear technologies mean that this concern could be alleviated by safety system that could reduce human error. The desire to tap on nuclear energy is not likely to be near term, but the feasibility of nuclear energy should be considered as an option for long term planning. It normally takes 10-15 years to build a nuclear power plant and Singapore should be prepared if nuclear energy become an inevitable option.
© Guangyuan Zhang. 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.
 "Economic Strategy Committee Key Recommendations," Government of Singapore, February 2010.
 "Russia Will Build Series of Floating NPS," (in Russian), Взгляд, 15 Apr 07.
 G. Stolyarova, "Nuclear Power Vessel Launched", St. Peterburg Times, 6 Jul 10.
 S. B. Severs and H. V. Toll, Underwater Nuclear Power Plant Structure," US Patent 4302291, 24 Nov 81.
 D. Geere, "France Plans Offshore Underwater Nuclear Power Plant", Wired News, 21 Jan 11.