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Converting existing coal-burning power plants to nuclear using TRISO technology
The remarkable thing about this idea is that there is nothing remarkable about it.
Climate Change’s gathering political storm
Inconvenient truths:
1. Mankind IS capable of altering something as large as the earth's atmosphere. And, in fact, has been doing it - 1 part per million (ppm) at a time for many years.
2. The world's fossil fuel electricity industry faces unending financial problems if it does not stop its production of Global Warming CO2 and other pollutants.
There are about 138,000 fossil fuel power plants in the world1. The CO2 they produce is 70% of the world’s accumulating climate-changing CO22. Now prime targets for environmentalists, eventually someone very powerful is going to decide that Global Warming’s “OFF” switch has to be connected to every fossil fuel power plant unit in the world.
Gone with the wind?
Wind electricity is only ½ of 1 percent of the world’s energy. Fossil fuel electricity powers nearly all mankind’s life support systems. In addition to the power plants themselves, over the years we have built an essential infrastructure of electrical grid right-of-ways, cooling water rights, railroad easements, and access roads. Broken apart like Humpty Dumpty, they would be nearly impossible to put together again in today’s legal and environmental environment.
There is a lot of life left in our fossil power plants - about 2/3 of our electrical generating capacity was built after 1980. That’s an enormous amount of relatively new power plant equipment that could be obsoleted prematurely in the increasingly frenzied effort to reduce Global Warming.
Survival of fossil fuel power plants depends entirely on their converting to an emissions-free heat source. Unfortunately, conventional water-cooled nuclear reactors won’t work. Conventional nuclear’s 600°F steam simply isn’t hot enough to drive a typical coal plant’s 1,000°F steam turbine to full power.
TRISO Pebbles: The Nuclear Coal
There is a nuclear heat that is as hot as coal’s heat. Called "TRI-SO" nuclear for tristructural-isotropic nuclear fuel, it is designed to run safely as hot as 3,600°F. Fire-hot TRISO nuclear fuels are tiny poppy-seed size specks of uranium encapsulated in three layers of silicon carbide and pyrolytic carbon shells. TRISO is the only developed nuclear technology available that is hot enough to consider using for converting coal-burning power plants to nuclear heated boilers3.
TRISO nuclear fuel heated reactors typically “cruise” at 1,700°F and a natural physics phenomenon called Doppler-broadening will keep the reactor from ever getting hotter than about 2,700°F. TRISO nuclear fuels typically come in the form of billiard-ball size pebbles and stapler-size prisms. A “Lite” nuclear technology, TRISO reactors do not need the costly large castings and forgings required by conventional nuclear reactors. (See also TRISO sidebar, below)
A TRISO nuclear power plant boiler made 1,000°F superheated steam 30 years ago in Colorado
The 1970s Ft. St. Vrain4 power plant in Platteville, Colorado, is an example of how a TRISO nuclear boiler was substituted for a fossil-fuel boiler and used to drive an ordinary fossil-fuel steam turbine for 13 years. General Atomics built the prototype reactor-boiler.
Ft. St. Vrain, Unit 1, was a very unusual nuclear power generating unit when it went on line in 1976. Producing 330 megaWatts electrical, it did not run on conventional water-cooled reactor rods filled with uranium pellets. Instead, it had a helium-gas-cooled reactor vessel pressurized to 688 psi and filled with prism-shaped TRISO nuclear bricks that produced 1,400° F heat – plenty hot enough to easily make 1,000° F superheated steam – something 600°F conventional water-cooled reactors cannot do. The helium gas was simply circulated through the reactor to heat it and then through the boiler to make steam. Seriously powerful for its day, FSV’s total mass flow was 395 tons/hour.
Ft. St. Vrain ran as nuclear until 1989 when its 1960’s-era prototype reactor-boiler was decommissioned. Converted in 1996 to be driven by a natural gas turbine exhaust-heated steam boiler, it is still in service today.
TRISO nuclear today
Today there is a resurgence of interest in TRISO nuclear reactors, both as readily mass-produceable commercial reactors and as a nuclear technology that can be developed even further in the multi-national Generation-IV reactors program. TRISO reactors are being developed for splitting water into hydrogen.
In addition to the new PBMR pebble bed reactor at Koeberg, South Africa, China has a teaching pebble bed reactor that has run since 2000 and will begin building a 19-pebble bed reactor facility at Rongcheng in 2009. As many as a thousand Chinese HTR-PM 100 MWe pebble bed reactor steam plants are planned as electricity and heat sources for China’s remote regions in addition to China’s planned 100 large 1,600 MWe PWR reactors.
Converting a modern coal power plant to TRISO nuclear. Walking away from the air pollution nightmare.
Using Ft. St. Vrain as the design concept and the modern 165 MWe South African PBMR pebble bed reactor as the heat source, the following design is suggested by the author5.
Ample space for the conversion reactor facility can be found in the coal storage yard adjacent to every coal-burning power plant in the world.
The tall silo shape (90 feet high and 20 feet in diameter) of the PBMR reactor suggests installing it in an underground silo with a removable lid to facilitate servicing. Located next to the reactor in the same underground silo would be a “supercritical” water heater. (Supercritical water is a gas with the density of the liquid.) The supercritical water would be piped into the power plant to a location near the existing coal boiler.
At the boiler location, a new steam generator would be installed. The supercritical water would heat the steam generator to produce the same or better quality steam as the coal boiler produced. After all the new equipment was installed and tested as much as possible, the coal boiler would be shut down and the feedwater and turbine piping would be relocated to the new steam generator.
Older coal-burning steam plants with units smaller than the MWe capacity of the pebble bed reactor would have several small steam generators all heated by the same reactor. Newer coal-burning steam plants with units larger than the MWe capacity of the pebble bed reactor would have several reactors in several silos heating water in parallel to bring the large unit to full power. Plants already running on supercritical steam could have several reactors arranged in a ring around a central boiler.
TRISO heated converted fossil plants should be more efficient
A more efficient plant should result from having a nuclear rather than a coal boiler. Since stack losses will disappear and we are retaining the 1,000° F steam used in coal plants, the converted plant should be more thermally efficient than it was in coal-burning form and substantially more efficient than its 600°F conventional nuclear plant competition.
Water efficiency is also important. We are running out of it. Due to its lower running temperature, a conventional nuclear reactor uses 125% as much cooling water per kiloWatt hour as a fossil fuel power plant. This efficiency advantage would not be lost by converting a coal plant to TRISO nuclear.
Automatic continuous operation. The Germans would blow their pebbles through tubes to and from fuel supply, monitoring, and storage facilities. Pressure locks on the top and bottom of the reactor vessel allowed the hard, smooth, TRISO pebbles to flow like a liquid into and out of the reactor, enabling their reactors to refuel while running, thereby avoiding the annual month-long nuclear refueling shutdown that is part of conventional reactor operation. PBMR describes similar capabilities for their reactor on their web site.
Conclusion
This insight constitutes a major addition to the world’s Global Warming CO2 mitigation options. The author urges the U.S. Department of Energy to immediately initiate a comprehensive feasibility study of converting existing fossil-fuel power plants to TRISO nuclear power.
SIDEBAR: About TRISO nuclear fuels
TRISO nuclear fuels are called "TRI-SO" for the tristructural- isotropic poppy-seed size micro-particles of nuclear fuels (uranium, thorium, plutonium) that make up their bulk. This multi-coating containment of the fuel particles with layers of silicon carbide and pyrolytic carbon is necessary to keep the fission waste products from getting loose in the reactor. Nuclear waste is produced as the heavy energy-metal atoms of uranium, etc., (called major actinide metals) are converted by fission (atom-splitting) to, among other things, xenon-135 gas (loose xenon-135 can stop the reactor) and lighter minor actinide metals.
TRISO’s triple coatings also provide three additional levels of radioactive fuel containment in addition to the two containment barriers created by the reactor itself and its underground silo for a total of five levels of containment. Conventional water cooled nuclear power reactors provide only one or two levels of containment and also cause large amounts of water to come into direct contact with the uranium. Unlike water, helium does not become radioactive.
Producing pebbles: To produce an 8 ounce nuclear pebble containing about 9 grams of nuclear fuel, some 15,000 of these tiny triple-coated TRISO fuel particles are mixed with a graphite powder/phenolic resin paste and pressed into the shape of a 50 mm diameter ball. A 5 mm thick outer shell of pure carbon is then added and the pebble is sintered, annealed, and machined smooth to 60 mm to withstand the abrasion, impacts, and heat of automated machine handling and fluidized travel through the reactor’s pebble bed.
When fresh, a TRISO pebble can produce more than 1,000 watts of heat continuously for two years equaling about 30 tons of coal’s heat. That’s about $1,000 at today’s $35/ton coal delivered to the power plant. A PBMR reactor can hold as many as 450,000 pebbles.
End of SIDEBAR
The
author does not guarantee the accuracy, relevance, timeliness, or completeness
of the information contained in this presentation of his personal opinion.
The copyright holder allows anyone to use this article in its entirety, provided
that the copyright holder is properly attributed.
© 2008 James P Holm
References:
2. http://www.coal2nuclear.com/end_global_warming.htm (Author’s web site)
3. http://en.wikipedia.org/wiki/Nuclear_fuel#TRISO_fuel (Wikipedia informational web site)
4. http://www.fsvfolks.org/FSVHistory_2.html (Ft. St. Vrain historical web site)
5. http://www.coal2nuclear.com/coal_yard_nuke.htm (Author’s web site)
6. http://en.wikipedia.org/wiki/Supercritical_fluid (Wikipedia informational web site)
Coal Yard
Steam Generator (above) Water Heater Pebble Bed Reactor
Note: Heavy black line lifts away the now-unneeded coal portion of the power plant.