Dirty Pebbles
On the radioactive-waste side, the pebble-bed reactor is slightly better
than conventional reactors, but the picture still isn't pretty. A reactor of
the anticipated scale would generate about 19 tons of spent fuel pebbles
per year. That's mostly the weight of the graphite. Less than one ton
would be depleted uranium.
Spent pebbles are easier to store than fuel rods, because the silicon-carbide coating around the fuel particles will keep the radioactive decay
products isolated for approximately a million years—if they're kept safe
somewhere. The real problem lies in the virtue of pebble-bed reactors:
They're small-scale power generators that lend themselves to a geographically distributed power-production model. That adds up to a lot of trucks
hauling fresh and depleted carbon spheres full of uranium hither and
thither across the landscape.
Pebbles Worldwide
The first effort to create a commercial pebble-bed reactor, the South
African PBMR (pebble bed modular reactor), is a project of Eskom, the
South Africa electrical utility, and some partners. As of 1998, construction of a demonstration plant was supposed to begin in 1999 with completion by 2003. Commercial orders would follow. At that time, Eskom
projected a worldwide market of about 30 units per year.
This year, the May 3 Business Day reported that "The PBMR Company has set itself the deadline of 2011 for the construction of a pilot pebble bed nuclear reactor in Cape Town
and a pilot fuel plant at Pelindaba
outside Pretoria. Commercial production is scheduled to commence in
2012." To be fair, the causes of the
schedule slippage appear to have
been legal challenges more than
technical problems. But that's part of
the environment we live in, and engineers and entrepreneurs need to take
it into account.
Alternative designs include the gas-turbine modular helium reactor (GTMHR) (). The most fascinating
thing about the GT-MHR is that it was
developed in Russia under a joint U.S.-Russia agreement to cooperate on the
development of systems for the disposition of surplus weapons plutonium.
Apparently, pebbles can contain plutonium, uranium, thorium, or spent fuel
from conventional reactors.
The GT-MHR's ability to function as
a commercial power generator is
frosting on the cake. Partners in the
GT-MHR include General Atomics in
the U.S., the Russian Federation Ministry for Atomic Energy (MINATOM),
Framatome in France, and Fuji Electric in Japan.
The earliest pebble-bed research, on
which the South African design is based,
was carried out in Germany. The latest
pebble-bed reactor to be fired up is the
HTR-10, which uses steam rather than
helium as its working fluid. It is located
at the Institute of Nuclear Energy Technology (INET), a unit of Tsinghua University, near Beijing.
The Chinese State Council approved
the project in March 1992. Ground
was broken in 1994, and construction
was completed in 2000, with criticality
achieved on December 1, 2000. It
began full operation in 2003. In 2006,
HTR-10 operated for a total of 97 days
and reactor power reached 458.2 Megawatt Days (MWD). That provided
660 MWh to the grid as well as steam
heating for the INET campus.