To meet an increasing demand for minerals, mining operations are moving to ever more remote regions. The lack of a local energy supply and infrastructure, coupled with social and regulatory demands for lowered environmental impact of mining operations, presents an opportunity for a rather unlikely competitor – a nuclear power plant. The Modular Pebble Bed Reactor, currently in various stages of research and development around the world, offers a high degree of reliability and safety with minimal consequences for the local or global environment. The passive safety features of this design eliminate the need for the extensive active safety systems that add significantly to the cost of current water-cooled reactors.
With the MPBR, as with all nuclear plants, there are no appreciable quantities of waste products released to the environment during normal operations. However, in contrast with conventional reactor designs, under the most severe abnormal circumstances, the MPBR would still not release appreciable quantities of harmful materials. The key to the design is the fuel element. Enriched uranium microspheres are coated with various layers of pyrolytic carbons to form a highly-temperature resistant particle that effectively retains all fission products. These particles are mixed with graphite and formed into 6cm pebbles. A randomly packed vessel of such pebbles forms the reactor core through which helium is circulated as a coolant. Computer models and tests performed on actual pebble reactors confirm that fuel failure temperatures are not reached even during a complete loss of coolant accident.
The reactor drives a gas turbine cycle with resulting efficiencies as high as 48%, comparable to natural gas-fired units. The low price of uranium fuel and low maintenance requirements translates into competitive operating costs. However, high capital costs prevent the MPBR from competing with natural gas in most markets. In remote applications where no fossil supplies are readily available, the playing field is rather more level. A plant designed by the Dutch firm NRG would produce 17 MW of electricity and 18 MW of process heat. It would require about 50 pebbles per day during full power operation, obviating the need for expensive and environmentally risky fuel delivery services.
