Saturday, January 27, 2007
Factory-build PBRs, ship, and assemble on site
A pebble bed reactor unit can be assembled within a containment building approximately 25 x 40 meters in size. Such a unit would generate approximately 100 megawatts, at a capital cost of roughly $200 million. Most large coal or nuclear electric power plants in the US are much larger, about 1,000 megawatts. An advantage of the relatively smaller PBR unit is that the modules can be grouped and added to as demand increases. From a business investment point of view, a utility company would be making a series of $200 million investments, adding to them as profitability is proven, rather than making a $2 billion investment all at once.
Distributed 100 MW power plants would have advantages over centralized 1,000 MW plants. About 8% of all generated US electrical power is lost in transmission. Having generation closer to consumption reduces these costs. Such localization of power during disruptions can lessen the chance of massive power blackouts caused by cascading failures of the transmission system. Today's electric power grid has become more strained and lossy with deregulation, which can encourage customers to buy power generated a long distance away. Utility companies have difficulty getting site approvals for new nuclear power plants. However, gaining ten times more approvals for smaller plants would not be possible today. Therefore ganged, centralized PBRs would be the most attractive to uilities. Public attitudes about the safety of PBR power plants will have to change before the nation can take advantage of the distributed power generation benefits.
Prefabricated units can be shipped by truck and rail
Marc Berte and Andrew Kadak of MIT have published a presentation Modularity Approach to the Modular Pebble Bed Reactor. The conceptual design of the heat exchangers, turbines, intercoolers, recuperators, and manifolds have been constrained to sizes that can be put into boxes and shipped standard truck and rail facilities. The large reactor vessel, approximately 14 feet in diameter by 50 feet long, will require special transportation. All units can be brought together on site and assembled. One of the design goals is that the units bolt together, without the requirements for specialized welding at the site. Central, factory production of standardized PBR components allows improved quality control, lower costs, and rapid on-site assembly.