Demonstration Project

Chapter Three, Section D, Index: Proposed Demonstration Projects
Part One:         Michigan: Proposed single reactor demonstration facility at the J. R. Whiting plant near Erie, Michigan.
Part Two:         Florida: Full scale demonstration: Add 12 pebble bed conversion boilers to Tampa's huge coal-burning Big Bend power plant.
Design Considerations Index:   Florida Project Index
Part One:         Why nuke our existing power plants? 1. Fast, 2. Cheap, 3. Effective         Why not? They got us into this Climate Change mess.
Part Two:          Reactor issue links.
Part Three:        Design Considerations                                                                           Design overview
Part Four:         Why we can't use conventional nuclear reactors.                                      Why conventional nuclear reactors won't work.
Part Five:          The reactor silos. What they are like and how they work.                         Think farm silos.
Part Six:           The Coal Yard Nuke conversion pebble bed reactor sketch
Part Seven:       Who is making and selling pebble bed reactors?                                    Becoming a commercial item in some countries.
Part Eight:        Cost estimates based upon crude numbers.                                             What do we know and how do we know it?
Part Nine:         How the reactors would be installed and connected.                                  Re-using the coal yard.

A Demonstration Facility will cause a flood of engineering feasibility studies to be made.

Michigan: Proposed single reactor demonstration facility at the J. R. Whiting plant near Erie, Michigan. Whiting
On the western shore of Lake Erie, just north of Toledo and south of Fermi II near Monroe, Michigan.

Florida: Full scale demonstration: Add 12 pebble bed conversion boilers to Tampa's huge coal-burning Big Bend power plant. Project index: Upgrading Big Bend

According to CARMA, TECO's Big Bend coal-burning power plant makes 30,000 TONs (or 60 million pounds) of CO2 per day. And the Big Bend 4-unit plant is just one of about 50,000 multi-unit power plants in the world for a total of 141,000 units. Big Bend has about 1 million customers. They own their own coal mine but their additional expansions will be natural gas turbines which are only 2/3s as dirty.

At 1,800 megaWatts, Big Bend is a huge power plant - larger than the newest nuclear power plants. Areva's biggest and best nuclear plant, the EPR, is only 1,600 megaWatts. It will take about a dozen PBMR 165 megaWatt pebble bed TRISO-fueled reactors to convert Big Bend from coal to nuclear. Tampa could put in two EPRs next door to Big Bend. There is an excellent transmission line corridor already established along I-75 to feed the entire Florida Gulf coast. Since the ground in that area is already more radioactive than anything Areva's reactors could ever produce (the government won't let Tampons make wallboard out of the area's gypsum due to it's radioactivity), I can't imagine the locals opposing all the money two EPRs would bring in for 50 years.

Climate Change can't possibly be stopped without cleaning up at least the world's 5,000 dirtiest power plants. It's unavoidable. Conversion from coal-burning to nuclear can be done quickly and should be done first because nothing else will reduce so much CO2 as quickly.

This is an excellent place to establish a zero-emissions "Coal Yard Nuke" demonstration plant: Michigan's Consumers Energy's "J. R. Whiting" power plant located north of Toledo on the western tip of Lake Erie near Erie, Michigan (Right).

This extremely well maintained 50+ year-old plant has three 102 MWe to 124 MWe superheated steam boilers. According to CARMA, it emits 2,780,000 tons of CO2 each year.

Any of it's three generating units could be easily driven by a single 180 MWe PBMR pebble bed or all of three by a single 325 MWe GT-MHR prismatic reactor. The 875 acre site would also provide plenty of room for a new visitor's center. http://www.consumersenergy.com/content/hiermenugrid.aspx?id=21

Consumers Energy has a long and successful track record with nuclear power plants. They took the 1962 "Big Rock Point" nuclear power plant all the way through its life cycle and eventually decommissioned it to an empty green field. Only the temporary spent fuel storage remains. The Big Rock Point decommissioning story (1.5meg PDF file). http://www.consumersenergy.com/uploadedFiles/Environment/BRP_Journey_s End final.pdf

A project engineer for over 30 years, I'm certain many unanticipated issues will emerge during the design, fabrication, installation and operation of the world's first "Coal Yard Nuke." This site is located just south of the Fermi II power reactor facility near Monroe, Michigan. What better place to have a demonstration facility than near an existing nuclear plant and within several hundred miles of several of the country's leading schools of nuclear engineering, several of the nation's leading nuclear reactor laboratories, and the massive fabrication shop resources to be found in the Detroit area?

Many of the coal-burning power plants that are excellent candidates for nuclear conversion are small and almost forgotten, but usually very well-maintained, plants that are over 50 years old and could easily run another 50. This rejuvenation of the worlds oldest and dirtiest coal power plants also makes a darn good long-term investment in the world's energy future as well as eliminating the world's major source of carbon dioxide. Boilers heated by oxidizing direct flame burn out much sooner than boilers heated by inert pebble bed reactor gasses. The retail value of the electricity made by one of these old plants is often well over a half billion dollars a year.

This is a design exercise only! There are no actual plans to do this. This is just a drill.

Upgrading the "Big Bend" power plant at Apollo Beach, Tampa Bay, from coal to pebble bed nuclear.

Note: I have chosen to use Big Bend as an example because it is an excellent example of the generator size - 450 megaWatts - that will have to be converted worldwide. As far as I know, no one has ever discussed actually doing anything with Big Bend. This is a design exercise only! Again, a demonstration facility using a single 100 megaWatt generating unit must be built and test-run first before anything as large as Big Bend would even be contemplated.

Note: As a "bogey" reference for a typical modern coal-fired power plant, I picked the 4-unit TECO (Tampa Electric Company) "Big Bend" 1.8 GigaWatt plant located on the Alafia River near Apollo Beach, Florida, in the Tampa South Bay region. It's equipped with state-of-the-art emissions controls. Big Bend is unusual in that a reverse-osmosis desalination plant that supplies 25% of the area's fresh water is also located on their site. The Big Bend site has become a wildlife refuge for manatees that winter in the plant's warm discharge water. TECO also operates a super-high-efficiency, low-emissions combined cycle plant in nearby Polk County - only one of several in the entire country in addition to their lower CO2 emissions gas-fired Bayside plant (natural gas produces only 2/3 the CO2 of coal). TECO's current electricity mix is: Purchased Power 13%, Oil & Gas 35%, and Coal 52%. Through this engineer's eyes, TECO is a world-class operation. According to the press, TECO is experiencing a 150 megaWatt increase in electricity demand every year.

Three of Big Bend's four boilers are 445 MWe (MegaWatts electric) Riley Turbo® opposed wall-fired, wet-bottom coal units, and one is a 486 MWe Combustion Engineering tangentially fired coal unit. Typically, the boilers are designed for a safe drum operating pressure of 2,875 psig and can produce 2,868,000 lb/hr of steam continuously at 2,600 psig and 1,000°F at the superheater outlet when supplied with feedwater at 487°F at the economizer inlet. The steam outlet temperatures of the superheater and high temperature reheater are both 1,000°F, and the pressures are 2,600 psig and 552 psig, respectively.

The boilers are fired with low-sulfur bituminous coal. Everything running flat-out for a year might burn 6.4 million tons of 25 million BTU/Ton coal, or 17,000 tons of coal per day at 33% efficiency. http://www.tecocoal.com/COpremier.html - TECO's Elkhorn coal mine near Myra, Kentucky. At average coal spot prices spring 2007 of $35/ton, 6.4 million tons = $224 million per year. That much energy is about the same as 2 days worth of oil for the entire United States.

How much CO2 can a plant this size make? I don't have official figures but can use some government data (http://tonto.eia.doe.gov/FTPROOT/environment/co2emiss00.pdf ) to come up with an educated guess. They say a well-running coal-burning power plant produces about 2 pounds of CO2 for each kiloWatt hour of electricity it generates. So, using that rule-of-thumb:

Adding up Big Bend's 4 boilers comes to about 1,800 megaWatts electrical = 1.8 *10³megaWatts = 1.8 *10⁶ kiloWatts;

1.8 *10⁶ kW * 8,760 hours / year = 15,768 *10⁶ or about 16 *10⁹ kiloWatt hours / year.

At 2 pounds of CO2 per kWh, that's 32 *10⁹ pounds of CO2 or 32 billion pounds of CO2 per year.

Converting to tons: 32 *10⁹ pounds CO2 per year / 2 *10³ pounds per ton = 16 *10⁶ tons of CO2 per year is the maximum possible.

This is 16 million tons of CO2 per year or about 44 thousand tons of CO2 per day maximum.

I read somewhere a large power plant like Big Bend makes as about much CO2 as 4 MILLION automobiles.

How can the weight of the CO2 in the air be greater than the weight of the fuel? Burning is the process of attaching two oxygen atoms from the air to a carbon atom from, say, coal to make a molecule of carbon dioxide (a molecule is a bunch of atoms http://en.wikipedia.org/wiki/Molecule ). This process is exothermic or, the process releases heat - which is why we did it in the first place. A carbon atom has an atomic weight of 12. When burned, two oxygens, each of which have an atomic weight of 16, become attached to each carbon atom, so the total weight of a CO2 molecule is 12 + 16 + 16 or 44.

TECO, Consumers Energy, Westinghouse, Combustion Engineering, Riley, ESKOM-PBMR, and General Atomics have nothing to do with this paper. They are entirely unaware I am using their plants and products as "concrete" examples in my advocating the principle of converting coal-burning power plants to nuclear power.

ENERGY SPEAK. Technically Speaking: A Watt (W) is a basic unit of energy as is a British Thermal Unit (BTU). You will see both MWe (MegaWatts electric) and MWt (MegaWatts thermal) a lot when reading about power plants. Three MegaWatts thermal usually gets you about one MegaWatt electric because power plants are about 33% efficient. When you see a thermal device like a boiler rated in MWe, just multiply by three to approximate its wattage or 10 to approximate its BTUs. Remember also that one Watt-hour equals 3.41 British Thermal Units (BTU). A BTU is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. In electrical terms, a Watt is defined as the energy passing through a 1 Ohm resistor when energized by 1 Volt or, 1 Volt-Ampere. This is important because the electric company charges you by the Kilo Watt-hour or KWh.

It's "Errors and Omissions" time. Please, everyone, let me know what is wrong with my plan. Or, if you know of a better idea, let me know about it also. You can always email me. Please mention Coal2Nuclear in the subject line to keep it from being automatically deleted. Thank You.

Everything needed to upgrade fossil-burning power plants has been developed.

Existing power plants are already wired to our cities - (NO NEW TRANSMISSION LINE RIGHT-OF-WAYS NEEDED), usually have ample land for several additional future units - (NO NEW LAND NEEDED), already have access roads - (NO NEW RIGHT-OF-WAYS NEEDED), already have railroad tracks - (NO NEW RIGHT-OF-WAYS NEEDED), and already have cooling water - (NO NEW RIPARIAN RIGHTS NEEDED) - no new construction delays or costs - they are already running! Talk about recycling! The confluence of so many essential power plant resources at one location means that the chances are very good that eventually there will be a 'big breeder' nuclear power plant at that site after the fossil fuel plant is worn out. This is one of those ideas that's as green as Geico's gecko.

The key to keeping both time and cost to a minimum is to make as few changes as necessary. Locate the conversion reactors away from the fossil fuel plant as far as possible. The penalty for doing this is long supercritical water lines. The benefit is there will be no changes to the existing plant other than the new steam generator and its feedwater and steam line tie-in points and the plant could continue to run on its original fossil fuel.

If we built nothing but new nuclear, what would we do with all the existing fossil-fuel burning power plants we now have? This is a major economic and grid logistics question no one is asking. Most important in the much less wealthy second and third world.

There are over 1,000 major conventional coal-burning plants with over 5,000 big boilers in the United States alone. Industry is lobbying the government to "Grandfather" these existing fossil-fuel plants, allowing them to continue to make CO2 pollution for up to 50 more years. Do you really want that? Worldwide, it's 141,000+ boilers in 50,000+ power plants in 225+ countries. Most of them are like J. R. Whiting where one pebble bed reactor has enough power to drive all the generating units in the entire plant.

Otherwise, we'd need to build 200+ MORE large nuclear power plants in addition to our existing 104 medium nukes to completely eliminate power plant coal burning in the United States. Another hazard we would be walking into by building nothing but new nukes is that we would wind up with a much more highly centralized electrical system with fewer, but larger, generation points. We would loose even more grid diversity as existing coal-burning plants are closed down. A sure recipe for more frequent huge blackouts.

The 1,000+ coal-burning power plants we now have will soon be joined by another 100 to 150 additional new super-size coal-burning plants that are under way in the governmental approval process. In my humble opinion, new CO2-emitting coal and natural gas power plants should be outlawed immediately and only new conventional nukes built instead. Approximately 35 new nukes are also being talked about but the government is moving very slowly on approving them in spite of the fact they are superior in every way to what we have on-line now. Conventional and breeder nukes are what the future demands to prevent new Climate Change problems in the future. Coal burning should never, ever, be allowed again anywhere in the world.

The "Coal Yard Nukes" being advocated on this web site apply only to existing fossil-burning power plants because they are the fastest and least expensive way to remedy the Climate Change situation. Coal Yard Nukes will enable us to complete the service life of existing power plants at reasonable cost while also ending the major part of the Climate Crisis. Additional units of the Coal Yard Nuke type should be built along side the converted fossil fuel units where possible to quickly expand our generation capacity to enable conversion of our CO2 producing industrial, commercial, and residential coal, natural gas, and oil heating systems to electricity. Example: The coal being burned to produce ethanol from corn.

Keep in mind that coal and natural gas are our future oil, far too precious to burn just to make electricity and CO2.

Again: Every coal burning power plant in the world has ample space in its coal yard for small nuclear boilers. Let's take advantage of that fact.

Nuking existing fossil-burning power plants is more than a good idea. It's also a damn good environmental science project idea. It's a CO2 mitigation project that has excellent scientific value in that easily trackable data on a significant CO2 change will be generated. The data collected should vastly improve the quality of environmental computer models as more and more fossil-burning plants stop emitting CO2 over a several year time span.

Design Considerations

"Three of Big Bend's four boilers are 445 MWe (MegaWatts electric) Riley Turbo® opposed wall-fired, wet-bottom coal units, and one is a 486 MWe Combustion Engineering tangentially fired coal unit. Typically, the boilers are designed for a safe drum operating pressure of 2,875 psig and can produce 2,868,000 lb/hr of steam continuously at 2,600 psig and 1,000°F at the superheater outlet when supplied with feedwater at 487°F at the economizer inlet. The steam outlet temperatures of the superheater and high temperature reheater are both 1,000°F, and the pressures are 2,600 psig and 552 psig, respectively." --- This came from a government study report on Big Bend that was posted on the web.

I am looking to duplicate each of Big Bend's four coal burning boilers with three PBMR reactors (Westinghouse has a stake in PBMR) running in tandem per coal-fired boiler. A PBMR reactor is rated at 180 MW Electrical on the EIA certification status board. At 40% efficiency, that comes to about 450 MW Thermal per PBMR reactor, or about 1,350 MWT for the combined output of three reactors. If Big Bend delivers 35% overall efficiency, the combined output of three PBMR reactors (472 MWe) will almost exactly match one 445 MWE coal-fired boiler. Close enough for environmental mitigation.

The reactor-gas turbine package PBMR is selling has the reactor set up to take in helium at 932°F and put it out at 1,652°F. I think the best way to match Big Bend's boilers is to design a PWR-type steam generator that will duplicate the boilers exactly. Hence, the use of supercritical water to heat the turbine's steam generator. I suspect pebbles run best at the temperatures PBMR has set up since they also own the pebble factory. The supercritical water is 1,150°F at 3,200 psi.

This means a helium-to-supercritical water heat exchanger that's not too efficient (500 degree loss across the exchanger's metal) if we want to keep those gas turbine inlet and outlet temperatures for the reactor. There is plenty of reserve temperature on tap. A more reasonable approach is to back off to a couple hundred degree differential across the exchanger's metal by reducing the reactor's neutron flux. At the other end of the hot water line, we have 150 degrees delta-t across the steam generator's metal to match the 1,000°F superheated steam specification.

I'm actually visualizing a common header with isolating valves for all 12 of the Big Bend reactors so that they can pool their heat in a trunk line as needed. At the other end, isolating valves could bypass unneeded steam generators. If you think you have a better way of duplicating a coal fired boiler, I'd like to hear about it. If you think I have something wrong, I'd certainly like to hear about it.

Let's see if Clean Coal's "Coal Carbon Capture and Sequestration (Storage)" folks can top that claim.

"Combustion of fossil fuels coupled with sequesterization of the carbon dioxide is unsustainable and immoral because it burdens future generations with the responsibility for protecting the earth from our irresponsible carbon dioxide build-up." --- Laurence Williams, author of: “Global Warming Can Be Conquered” (ISBN 07 414 426 8 X)

1. Today's Conventional Nuclear Reactors are often three or more times more powerful than today's fossil fuel boilers.

2. Fossil Fuel and Conventional Nuclear Reactor power plants operate in different steam temperature-pressure domains.

Fossil fuel boilers produce "SUPERHEATED" (dry) steam - typically 1,000°F, with typical pressures around 2,600 psi (1,500 BTU, 0.30 Ft³ per pound).

Conventional nuclear reactors produce "SATURATED" (wet) steam - typically 550°F, with typical pressures around 1,000 psi (1,200 BTU, 0.45 Ft³ per pound).

(For further discussion of the steam temperature compatibility problem and why conventional reactors can't be used, see end of this section)

These temperatures and pressures are way out of a conventional reactor's league and taking on these very hot monsters with a pebble bed reactor will be a challenge, not so much from a temperature standpoint, but, rather, from the enormous volume of heat the pebbles will have to deliver. "King Coal" can give even nuclear energy a very good run for the money. Most of the world's fossil fuel steam plants are of the smaller superheated type.

If we were to use a conventional reactor to power a coal-burning power plant, we would have to by-pass the high pressure stage of the turbine array, giving up about 1/3 of the electricity generating capacity of the power plant. Unacceptable, especially in a time of national electricity shortages while facing additional air conditioning, plug-in hybrid automobiles, and water desalination loads.

FOSSIL FUEL CAN EASILY PRODUCE A 2,000°F FLAME - that's "Hard Workin' Heat" and a good reason to like 'Old King Coal' a lot.

Several different Very High Temperature Reactors (VHTRs) with core temperatures that go above 1,800°F can replicate a fossil fuel fire.

The Very High Temperature Reactor (VHTR) choice, Pebble Bed reactors and their siblings, the Prismatics, being Doppler-Broadening temperature limited, are safe, simple, and completely developed reactor types that can deliver great volumes of heat at over 1,800°F. Both have a very high level of inherent safety, including a strong negative temperature coefficient whereby fission slows as temperature rises - a natural result of the Doppler Broadening effect. While the reactors themselves are less expensive, the Pebble and Prism fuels are more expensive for the heat they provide and will never be quite as cheap as conventional nuclear fuel. http://en.wikipedia.org/wiki/Pebble_bed_reactor and http://en.wikipedia.org/wiki/Gas_turbine_modular_helium_reactor

Superheated steam is steam hotter than 708°F (one of those magic water temperatures, like 32°F, and 212°F). Above 708°F, steam behaves like a dry gas, and, being dry, contains no water micro-droplets that cause erosion of the generator turbine blades. Conventional nuclear reactors use much greater volumes of steam to compensate for their lower temperatures (about 550°F) and pressures (about 1,000 psi) along with a "steam dryer" to protect their turbine blades. http://en.wikipedia.org/wiki/Boiler http://en.wikipedia.org/wiki/Steam_drum

1,000+ psi reactor steam pressures are why reactors are kept in "containment" buildings to keep radioactive particles from escaping in the event of a steam explosion. While a steam explosion is always possible any time you have high pressure steam, nuclear reactors lack the ability to make nuclear explosions. Nothing can contain a nuclear explosion. The explosion of your neighborhood fossil fuel power plant superheated steam boiler is of no public consequence.

Again. Conventional nuclear power plant reactors all produce steam temperatures that max out at about 550-600°F. That isn't hot enough to replace the 1,000+°F superheated steam produced by all modern fossil-fuel fired boilers and needed by their turbine-generators which have a high-pressure stage designed to run only on superheated steam.

So, you can't power your neighborhood fossil fuel power plant with your neighborhood nuclear reactor.....

Water is a wonderful way to turn heat energy into mechanical energy because when you turn water into steam, it expands its volume 1,600 times. If steam is not allowed to expand in volume, its pressure will go up drastically. That's where all that piston-pushin power in a steam locomotive comes from.

Below: How a pebble bed steam boiler power plant is set up. Compared to conventional nuclear, pebble nuclear silos would be considered 'light.'

Pebble bed reactors are much better suited for "load following" than conventional reactors and should approximate a coal boiler's load following abilities in a superheated steam application. Steam control for load following (not shown in this drawing) will come from a computer coordinated feedwater throttle valve, a variable-speed "reactor gas circulating blower", a variable steam generator (boiler) gas bypass valve, and some bypass piping to return the hot gas directly to the reactor. Temperature and flow sensors to keep the computer and the operator informed of how things are going are also necessary. To repeat, strange as it sounds, running the hot gas directly back into the bed of pebbles and making them even hotter causes pebbles to reduce their atomic activity. Doppler Broadening (a nano-technology phenomenon if there ever was one) will make pebbles go toward, but not quite to, zero atomic activity as they approach their "hot idling" temperature. (A retrofit to an existing coal-fired plant might also show an economizer http://en.wikipedia.org/wiki/Economizer .)

Because pebbles are so hot, a gas - usually helium, nitrogen, or carbon dioxide - is used to carry the pebble's heat to the power plant's steam boiler. Water's supercritical temperature - where it stops behaving like a vapor and begins behaving like a gas - is around 700°F.

Inlet temperature of a pebble bed reactor is about 950°F, and its outlet temperature is almost 1,700°F. That duplicates the 1,000°F superheated steam produced by coal fire while running the pebbles in their thermal "sweet spot."

Note: The pebble bed power plant shown in the drawing is set up as a conventional coal-fired superheated steam boiler power plant. 750°C = 1382°F, 530°C = 986°F, 250°C = 482°F, 35°C = 95°F, 25°C = 77°F. I suspect this drawing may have been inspired by the now decommissioned German THTR-300 - a thorium-powered high-temperature pebble bed nuclear reactor rated at 300 MW electric that actually powered the German grid during the 80's. http://en.wikipedia.org/wiki/THTR-300

BOILERS: Modular pebble bed reactors were designed from the start to be inexpensively mass-produced in factories and shipped in standard shipping containers. There could be a variety of boiler types but current fossil-heated designs may be best for rapid power plant conversion - since speed, rather than efficiency is the most important issue. Boiler design will depend upon whether the boiler has reheat stages in addition to the typical drum with superheater stages. A supercritical pressurized water system, much like a conventional PWR reactor, but at supercritical temperatures and pressures is also a possibility since we have working temperatures as high as 1,700°F.

The German THTR-300 thorium pebble bed (above) had a boiler (actually, a ring of small boilers) designed for steam but they used helium pressurized to about 1,300 psi instead at low or no pressure to carry the heat from the pebbles to the boiler. In a fossil-fuel burning plant, these velocities are determined by the combined efforts of the forced draft and the induced draft blowers. While boiler design and fabrication is a routine heavy industry activity involving at least several months, the first pebble bed heated supercritical water heater will likely take more design and fabrication time since doing anything the first time takes longer. http://www.iaea.org/inisnkm/nkm/aws/htgr/abstracts/abst_iwggcr15.html IWGGCR-15: Technology of steam generators for gas-cooled reactors.

Note: In the past, some high temperature gas-cooled reactors have used multiple small boilers arranged in a ring around the reactor vessel. This produces a very large surface area for the volume that contains the heat exchanging surfaces. I don't know what current thinking is on this design detail but, since the amount of heat is large and supercritical water, rather than steam is involved, I'm inclined to think that as there are efficiency constraints (there's a lot of heat to be lost and we want it to run as cool as possible) rather than size constraints, a large single unit might be the appropriate design starting place for both ends of the hot water loop.

(Photograph of the interior of a pebble bed reactor silo from a January, 2002, Scientific American magazine article by J. A. Lake, et al.) Not unlike a huge charcoal grille with air blowing down through it. Aerodynamically, pebbles behave somewhat like a sintered metal air filter and have acceptably low drag.

REACTOR CONTAINMENT: For a power plant conversion, pebble bed reactors should be installed in individual underground silos instead of above ground. The moisture in the earth provides a good radiation barrier along with being a good heat sink, something pebble beds need. PBMR pebble bed reactors are 8 foot in diameter tubes, about 30 feet tall, made of thick, radiation-proof sheet metal, capable of running at very high temperatures like a boiler, are hermetically sealed in very heavily reinforced underground concrete silos. Since nothing in direct contact with radioactive materials is under pressure, the traditional concrete and steel steam explosion containment vessels needed by conventional reactors are unnecessary, thereby providing a huge saving in both cost and construction time.

Pebble beds do not have a fuel cycle as such. Pebbles are circulated through the pebble bed reactor in much the same manner as a fluid. Each pebble is checked individually for how strong it is and is removed and replaced when too "tired". 10 to 15 trips through the reactor over a two to three year time are said to be typical. Additional "Moderating" pebbles containing only graphite are also added to "dilute" the critical mass to fine-tune the reactor's heat output and burnup rate.

Tired pebbles are removed pneumatically and transported to a central storage area where they are kept spaced from each other to keep a critical mass from forming and automatically packaged in thermally insulated, radiation-proof casks for shipment to a recycling plant.

(Left) From MIT's pebble bed reactor web site. Pneumatic pebble handling system that removes, measures for remaining energy, and then either returns a useable, removes a spent pebble or removes fragments of a broken pebble. A broken pebble was a problem in the 1980's-era German THTR-300 pebble bed reactor. http://web.mit.edu/pebble-bed/

As with conventional fission nuclear fuel, only about 5% of a pebble's atomic energy is actually consumed during a power run, so pebbles will have to be crushed to powder like quarry rocks and recycled for their remaining energy as is done world-wide with conventional nuclear waste.

Illustrating the Coal Yard Nuke idea (as applied to TECO's Big Bend power plant), above is an anatomically correct simplified coal burning power station schematic diagram from Wikipedia. This sketch shows how I think PBMR would like to see their reactor used in this sort of application. The reactor is the tank at the extreme right, with helium in it circulating clockwise through a helium-to-water hot water heat exchanger. The red exit water is supercritically hot and would need to be over 3,200 pounds per square inch to remain water at 1,150 °F. As a gas turbine driver, the PBMR puts out 1,652 °F so it should be plenty hot enough to make supercritical water. The gas turbine version of the PBMR takes in helium at 932 °F, (a delta-t of 720 °F), way hotter than an estimated 400 °F (an almost identical delta-t of 750 °F) from the 40 foot tall supercritical water heat exchanger.

Note that as a gas turbine driver, the PBMR is pressurized to 1,323 psi. While gas under pressure has greater density and thus heat carrying capacity, this is less important as a heat exchanger driver. A strong circulating blower is needed here. Because of this, a much less expensive reactor vessel could be used instead.

The water then goes to another heat exchanger, a supercritical water-to-superheated steam heat exchanger, (located in the power plant) where it makes both superheated steam (1,000 °F and 2,400 pounds per square inch) for the high pressure stage of the generator turbine where it is either by-passed or expanded through the turbine and then returned to the steam generator to become intermediate pressure steam (1,000 °F, 552 psi) for the intermediate pressure turbine. After leaving the intermediate pressure turbine the steam, now expanded to low pressure, goes immediately into the low pressure turbine and then exits at near atmospheric pressure and just above 212 °F into the condensing tub. There, the low pressure steam will flash condense into boiler feed water so it can be turned into steam again. The condensing tub is kept cool by a loop of cooling water from the cooling tower (extreme left).

Notice the 88 foot tall reactor is underground and that the supercritical water never touches the radioactive pebbles. If damaged, the reactor vessel will just loose helium like your car tire looses air. There is no possibility of the reactor exploding. Supercritical water was first used in the "Benson Boiler" as a way to reduce the catastrophic consequences of steam explosions in power plants during the twenties.

So we have a no-explosion device (the PBMR reactor) driving a reduced explosion hazard device (the supercritical heat exchanger pair) driving a standard power plant steam turbine from a steam generator that has less than the usual steam plant's typical amount of water in the steam state. I think this is as safe as a power plant can ever be made. Converted power plants will be a little safer than when they were when running on coal.

Thermal Efficiency: This design runs 500°F hotter than a conventional nuclear reactor and does not have the stack heat losses of a coal fired power plant. It's got to be more efficient than either a nuclear or fossil fuel power plant. The latest information (12/07) posted on PBMR's web site says: The reactor is designed for 930°F helium in, 1,700°F out, has about 452,000 pebbles that are expected to last 3 years. They are claiming 40% thermal efficiency and their reactor-generator combination is listed at 165 megaWatt electrical by PBMR and 180 MWe by the NRC.

Generation IV reactors hold wonderful promise of compact conversion units for coal power plants. Conventional uranium fuel pellet reactors and pebble bed reactors have been around for some time. You can buy conventional reactors from a surprisingly wide variety of vendors right now. Pebble bed and prism reactors have only a few vendor-wannabes at the moment. They are waiting for acceptance of their differing designs by various government nuclear authorities around the world.

Modern large power plants are huge, serious machines, costing serious amounts of money, putting out serious amounts of electrical energy, and emitting serious amounts of Global Warming CO2, uranium, radon, and other forms of air pollution.

When you look at a fossil fuel power plant, you are looking at the major cause of Global Warming CO2. You are looking at where the problem of Global Warming will be successfully mitigated. Since mankind can never give up the electricity that keeps his mega-cities alive, after every possible energy gizmo has proven itself of no great value in ending the 10 billion tons of CO2 produced by coal burning power plants each year, we will do what we have to do.

The typical maximum thermal energy needed for converting a large coal-fired generating unit to pebble bed nuclear would be about 1,600 megaWatts of heat. This would drive a 550 megaWatt electrical generator. This is larger than any silo type high temperature reactor being proposed today and going in a direction not being advocated by pebble bed reactor companies. I see multiple pebble silo units, perhaps 200 megaWatts thermal in size, running in tandem as the most practical way to use either pebbles or prism/compacts.

Also, these silo type high temperature reactors are all designed to work with gas turbines rather than work with a heat exchanger such as a boiler. A case can be made for producing a larger modified silo, perhaps incorporating some characteristics of the German thorium pebble THTR-300 which was designed to work with a boiler right from the beginning.

I think a variant, perhaps a ruggedized combination of the best features of both commercially available reactors, is possible that would be optimized for Coal Yard Nuke service. Both the PBMR and the GT-MHR reactors are helium instead of nitrogen reactors. They both appear sophisticated and seem intended for silk-glove "Nuclear Quality" environments rather than the more rough and tumble world of fossil fuel power plants.

What keeps going around in my mind is a pebble bed reactor equivalent of the DC-3 airplane. A rugged, economical, 'simple elegance' example of a high-tech machine - a definitive "Coal Yard Nuke." Perhaps made by one of the big boiler companies. The metal working capabilities are an excellent fit. A company that doesn't already have a heavy investment in the nuclear technology of the past, and big enough to acquire or hire the necessary expertise. One that could produce pebble bed reactors and their boilers as a single, highly integrated system, in the spectrum of sizes needed to supply the entire fossil fuel power plant market. A single, perfected pebble handler, used with perhaps 5 different sized superheated steam generators - 50 to 600 MWe.

The Generation IV Lead-Cooled Fast Reactor ( http://en.wikipedia.org/wiki/Lead_cooled_fast_reactor ) which is supposed to be able to run as hot as 800°C (1,500°F) strikes me as a strong candidate but Generation IVs are intended to be future technology. Lead-cooled fast reactors have seen extended practical service in the Russian Navy. From Wikipedia: "LFR reactors OK-550 and BM-40A, capable of producing 155 MW of power, have been applied on soviet Alfa class submarines. They were significantly lighter than typical water-cooled reactors and had an advantage of being capable of quickly switching between maximum power and minimum noise operation modes, but lacked reliability, as solidifying of lead-bismuth solution turned the reactor inoperable."

The commercially available pebble bed reactors coming into service now are being made in what turns out to be excellent "small" and "medium" sizes for our conversion purposes. For our "large" size, we shouldn't overlook what the now-decommissioned German thorium-powered pebble bed reactor, the THTR-300, has to offer. Equipped much as the proposed fossil-fuel power plant conversions, it actually drove the German power grid for about 2 years (423 days at full load) during the late 1980s. Of interest to us is a 500 MWe successor reactor that was also designed. It would exactly match the boiler needs of modern large fossil-fuel power plants such as Big Bend, providing a one-for-one conversion match. http://en.wikipedia.org/wiki/THTR-300

WESTINGHOUSE-ESKOM: It will take 12 of the South African Westinghouse-ESKOM's (U.S. NRC designation) 180 MWe pebble bed high temperature gas cooled reactors to replace those 4 coal-fired monster boilers at Big Bend. Three reactors running in tandem, each with their own boiler for radioactive pebble dust containment, per generator, would provide an additional 100 MWe of extra power per boiler over the old, existing coal boilers. Reminiscent of those old three-engine airplanes.

<---- Left: Drawing of an approximately 88 foot high, 20 feet in diameter, pebble bed reactor vessel by PBMR. In a steam plant conversion such as the Big Bend rapid-conversion, the tubes coming out of the bottom of the underground reactor would be run vertically to a superheated steam-producing heat exchanger (A.K.A. boiler) located above ground. The reactor is basically just a high-temperature-sheet-metal, graphite-lined silo. The heat transfer gas (either helium, nitrogen, or carbon dioxide) is circulated around by a blower. The heat transfer gas simply flows between the spherical pebbles in the bed of pebbles, gets hot, flows to the supercritical hot water heater, then is cooled off by the water in the supercritical water heater, then returns to the bed of pebbles to be heated again. Simple eh? That's the whole reactor cooling loop. (Extracted from an image on ESKOM's PBMR web site)

GENERAL ATOMICS: Or, instead, it would take 8 of the competing American made General Atomics GT-MHR (U.S. NRC designation) 325 MWe "Prismatic" high temperature gas cooled reactors. With two running in tandem per superheated steam generator, they would provide an excess of about 200 MWe of extra power per boiler over the old, existing coal boilers. Prismatics use stationary prism-shaped ceramic high-temperature fuel elements. GT-MHRs use both natural Doppler Broadening temperature limiting and control rods for precise "cruising" heat adjustment and to provide a rapid cold shut-down capability.

Like a pebble bed, its heat is carried to the steam boiler with unpressurized circulating helium so it is incapable of explosion. Also like the pure pebble bed, the HT-MHR has a Level 1 safety designation: "LEVEL 1: No need for active systems in event of subsystem failure. Immune to major structural failure and operator error." (While General Atomics also has pebble expertise, the U.S. seems to be more interested in developing the South African Westinghouse-ESKOM pebble bed reactor at this time.) From G.A. site -->

General Atomics, like Westinghouse, has a foreign affiliate. In their case: "In 1993, General Atomics (GA) and the Russian Federation Ministry for Atomic Energy (MINATOM) initiated a joint cooperative program to develop the Gas Turbine - Modular Helium Reactor (GT-MHR). In 1994, the primary emphasis of the program was refocused on development of the GT-MHR for disposition of surplus Russian weapons-grade plutonium. In 1996 and 1997, Framatome and Fuji Electric, respectively, also became partners in this program. The scope of the program includes construction of a GT-MHR plant at Seversk (formerly Tomsk-7) to destroy a portion of the Russian inventory of surplus plutonium and to produce electricity for the surrounding region." - From the General Atomics GT-MHR web site.

A Google Earth® photo of TECO's Big Bend power plant in Tampa Bay shows that the dark coal yard area is large enough to build a big shopping mall - ample room for twelve 50-foot-in-diameter 180 MWe PBMR pebble bed reactor silos. Perhaps in a circle 250 feet in diameter for the silo centerlines. They could be arranged in 4 groups of three reactors each with each reactor having its own boiler radiating outward from the outer edge of the reactor silo ring like spokes on a wheel.

The ring should be sized for 2 extra reactor silos to allow for an access road to the reactor control/support building located in its center. The access opening would be facing away from the power plant to allow an open interconnect area on the other side for the steam and feedwater piping. The extreme outer edges of the boilers might form a ring 400 feet in diameter or, at most, the length of the ocean-going coal barge tied up at the bay end of the coal yard. A linear layout might be about 700 feet by 300 feet.

PBMRs at Big Bend are a worst-case situation, using the lowest-power pebble bed available to power a very high power coal-burning generating plant. At the other end of the spectrum, the entire J. R. Whiting plant in Michigan, three 100 MWe boilers, could be powered by a single General Atomics 325 MWe GT-MHR pebble bed reactor.

For scale, notice the diameter of the smoke stack bases - they're also about 50 feet in diameter. In winter, manatees hang out in the warm water that's being discharged just below the stack plumes.

I think the Hillsborough county desalination plant is in the upper right corner. It produces 25% of the county's drinking water. It is no coincidence the desalination plant is located next to a power plant. Desalination for mega-cities and mega-suburbs like the Tampa Metro area requires massive amounts of energy regardless of which method is used.

Multiple pebble bed reactor installations can be a circle of underground silos - one reactor per silo, somewhat like a missile silo complex - around an above ground central control building having an underground pebble monitoring and replacement facility as its basement.

Cooling water in the form of a lake or river is almost always present at power plant sites. This means ground water is usually present only a few feet below ground level. This is a plus when it comes to buried pebble beds since the moisture in the ground acts both as an additional radiation shield and also would carry away any 'afterheat' that would be present in the reactor in the event of an abrupt loss of coolant or coolant circulation. All underground facilities constructed below water levels have to be water tight and some means for sump drainage provided. A well known example of this type of construction are the subways of New York City. Being within a few feet of sea level, anything underground at Big Bend will need that type of construction. In addition, despite the fact the silos are hermetically sealed to keep radioactive materials contained, a mesa-like mound, perhaps 30 feet high, should be provided for the entire reactor facility to guarantee it will never be immersed in water during a storm surge from a hurricane.

For a steam power plant conversion installation, the pebble-heated supercritical water from the underground reactors would heat the new conversion superheated steam generator located in the power plant building. See the 6 unit Ludington, Michigan, (Consumers Energy) pumped water energy storage site photo (at right - Visit ) for an example of how this type of equipment can be arranged. Note the tall overhead equipment crane (right) that runs on tracks. Easy way to remove and replace entire pebble bed reactors.

The supercritical water heated steam generator's output lines would be run to the existing coal boiler steam discharge pipes, through a new isolating valve, and then via the original steam lines to the electricity generating turbine set.

Having valved feedwater and steam lines, along with not removing the plant's coal boilers and their coal handling/pulverizer/precipitator systems, is quickest, shortest shut-down, least costly, and gives the plant a "Flex-Fuel" capability.

Of course, we should convert only one of the four coal-fired boilers first to make certain everything works as planned and to fine-tune the design's details for the remaining three units.

Adding pebble bed reactors has no effect whatsoever on the water used by a power plant. In the case of Big Bend's manatees, this is a very good thing.

Long superheated steam lines are unusual for a power plant but not for an oil refinery complex.

Per coal boiler, we would have one supercritical water pipeline connecting its reactor set and the new steam generator. There is no reason all 12 supercritical water heaters could not be connected in parallel for operational flexibility. And Big Bend's four coal-burning boilers are silent, their smoke stacks cold. Simple, eh?

There are many ways to upgrade a power plant. Every power plant in the world is somewhat different from all the others. These are just general overview thoughts that come to mind without knowing the intimate details of this particular plant, how it's being operated or what its owner's future plans for it are.