This is part of IEEE Spectrum's special report: Nuclear Power Gets a Second Look
By next summer, Chicago's Exelon Corp., the largest operator of nuclear plants in the United States, and three international partners will make a decision that could jump-start a nuclear revival. Led by South Africa's state utility Eskom, of Johannesburg, the four will decide whether to continue investing in the pebble-bed modular reactor technology. The concept originated in West Germany in the 1960s and 1970s, and now is experiencing a startling revival.
Specifically, the four companies will decide whether to fund a full-scale prototype pebble-bed reactor in South Africa, at Koeberg, near Cape Town, at the site of Eskom's 17-year-old, twin pressurized-water reactor nuclear station. The other major milestone, assuming the companies give the go-ahead, will come more or less concurrently, by mid-2002, when the South African government is expected to resolve, on the basis of the companies' feasibility and environmental impact studies, whether to allow the construction of a pebble-bed demonstration plant to show the technology works as designed and could be commercialized.
Other evolutionary and exotic reactor concepts continue to be developed in corporate and national laboratories [see "Other Advanced Reactor Concepts"]. But Exelon is, so far, the only nuclear operating company to fully embrace a particular new technology and declare itself committed to building multiple plants if the technology is deemed workable and the economics prove competitive. If the South African pebble-bed project moves ahead, Exelon will seek design certification from the U.S. Nuclear Regulatory Commission (NRC), Rockville, Md., so that the technology could be sold as a standardized, off-the-shelf design, like the three advanced light-water designs already precertified by the NRC [see "Advanced reactor development rebounding," IEEE Spectrum, November 1997, pp. 41-48].
Exelon hopes to submit an application for a pebble-bed modular-reactor license to the commission in late 2002, start construction around mid-2005, and begin operations for the first unit about three years later.
What is pebble-bed technology?
The pebble-bed concept builds on the high-temperature gas-cooled reactor technology developed in the 1960s in Europe and the United States. Typical of this technology is the use of a helium coolant and a graphite moderator. In the pebble-bed version, the fuel--uranium dioxide enriched in 235U to 8-10 percent--consists of particles coated with two layers of carbon and one of silicon carbide, embedded in a carbon matrix, which act as the principal barrier against radioactive releases [see diagram].
The forerunners of the pebble-bed design produced somewhat mixed results. An experimental 15-MW research reactor operated for 21 years at a German national laboratory in Jülich, near Aachen. Its German successor, a 300-MW demonstration reactor, ran for just four years.
In the United States, high-temperature, gas-cooled designs were evaluated in two reactors built by General Atomics, in San Diego, Calif.: Peach Bottom 1, a demonstration plant that ran from 1967 to 1974 in Pennsylvania, and Fort St. Vrain, which operated from 1974 to 1989 in Colorado. After some initial mistakes with the fuel design, demonstration of the gas-cooled technology generally was successful in Peach Bottom 1. But that success did not transfer to the scaled-up Fort St. Vrain, which also got a drubbing in the financial press at the time for poor management.