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Chapter Three, Part Three:   Low-cost, quick to build, Hybrid TRISO Pebble Power Plants

Abundant additional electricity made locally.

If you do nothing else, check out the history of the first hybrid - the Fort St Vrain, Colorado, prismatic high temperature reactor:  Fort St Vrain  

Nuclear Reactor + Coal Plant Turbine-Generator = Hybrid Power Plant. Taking advantage of the fact pebble bed reactors run 1,000 °F hotter than conventional nuclear reactors and can duplicate coal's very hot steam, this simple, extremely low cost, new nuclear plant can be quickly built from common coal-burning power plant parts and a mass-produced pebble bed reactor.

This is the same basic idea as the late 1960s Fort St Vrain  Colorado, plant but using a 40-year newer pebble bed reactor.

Scalable and Multi-reactor capable, this hybrid power plant can be either a 180 megaWatt, single reactor facility, or with two reactors running in tandem, it would be a 360 megaWatt power station. With three reactors running in tandem, it would become a very substantial 540 megaWatt facility. 

This provides a wide spectrum of inexpensive power plants, all readily available by using very common fossil fuel power plant parts available from many different global suppliers - Translation: Really inexpensive compared to conventional nuclear power plants.  And powerful.  Two Multi-reactor Hybrids would power most of the world's small to medium cities.  They are serious, industrial-strength electric power.  Great for incremental growth.  16 of them would easily power all of New York City - an 8 gigaWatt load.

In this form, nuclear pebbles present an enabling technology to both governments and their citizens.  Nuclear pebbles are a disruptive technology to conventional nuclear power plant manufacturers.  Nothing they are making and selling - neither reactor nor turbine - is needed here.

Like the Coal Yard Nuke conversion, this is an obvious idea for power plant engineers but rarely put into writing for the public.

Pebble beds offer both the heat and electricity needed to do a clean job of making synthetic gasoline, diesel, and jet fuel from coal.   http://www.liquidcoal.com/ 

Original image: http://en.wikipedia.org/wiki/Fossil_fuel_power_plant   GNU Free Documentation License 

Engineering is the art of making what you want from things you can get.

Single reactor Hybrid: Since the reactors don't have to be very remote from the steam generator, the supercritical water loop can be replaced with short 1,300 psi helium ducts carrying heat from the reactor to a calandria-type helium heated steam generator (drumless fire-tube & water-tube boiler, but still with liquid lead pressure isolation) being used instead, thereby eliminating the cost of the supercritical water components. 

Scalable Multiple Reactor Hybrid: As in the 'Coal Yard Nuke' system, a supercritical water loop would be needed to collect and reconcile the heat from the individual reactors into a common thermal source for driving a single thermal load.  Scalable: You could begin with a three-reactor size generator but start at reduced capacity with only one reactor, adding reactors later as needed.  Three PBMR reactor/water heaters per steam generator is likely a good economic cut-off point.

Two identical special 200 ton storage vault railroad cars, equipped with with elliptically-keyed wheels, (temporarily removed) would be temporarily welded to the rails next to the silo to supply and remove pebbles through pneumatic tubes connected to the car bottoms.  The Germans used automated pneumatic transport systems on their pebble bed reactors, the U.S. MIT pebble bed reactor design is even more sophisticated.  The pebbles would be held in metal clips on a conveyor belt storage system in the railroad cars.  A full load of 450,000 pebbles is about 112 tons containing perhaps 9 tons of uranium.

The gray rods sticking into the ground provide a passive conductive, rather than radiative, thermal path into the environment in the event reactor goes into Doppler thermal limiting mode.  Also, the standard PBMR reactor has a 1 meter layer of graphite insulation located between the toroidial vertical pebble chamber and the reactor wall to stop both neutrons and heat.  This feature makes the Doppler mode efficient.

The Hybrid power plant should be more efficient than either a conventional coal-fired steam plant that has stack losses of up to 25% of its coal heat or a conventional nuclear reactor with it's 600°F lower steam temperature powering a lower-efficiency two, not three-stage, turbine.  Every 100°F increase in steam temperature usually gets you another 1% in efficiency.  A single pebble's run-down cycle appears to the author to produce much heat energy as about 3.3 tons ($124) of delivered coal.  A PBMR reactor will hold about 450,000 pebbles.  At the commonly used 1 to 3 million ratio, a pebble's 0.3 ounces of uranium is supposed to equal 30 tons of coal.

See also: Licensing Coal Yard Nukes and Hybrid Nukes