Heat-resistant refractory materials are used throughout the core to allow the pebble-bed system to operate much hotter than the 300 degree Celsius temperatures typically produced in today’s light-water-cooled (Generation II) designs. The helium working fluid, exiting the core at 900 degrees C, is fed directly into a gas turbine/generator system that generates electricity at a comparatively high 40 percent thermal efficiency level, one quarter better than current lightwater reactors.
The comparatively small size and the general simplicity of pebble-bed reactor designs add to their economic feasibility. Each power module, producing 120 megawatts of electrical output, can be deployed in a unit one tenth the size of today’s central station plants, which permits the development of more flexible, modest-scale projects that may offer more favorable economic results. For example, modular systems can be manufactured in the factory and then shipped to the construction site.
The pebble-bed system’s relative simplicity compared with current designs is dramatic: these units have only about two dozen major plant subsystems, compared with about 200 in light-water reactors. Significantly, the operation of these plants can be extended into a temperature range that makes possible the low emissions production of hydrogen from water or other feedstocks for use in fuel cells and clean-burning transportation engines, technologies on which a sustainable hydrogen-based energy economy could be based.
These next-generation reactors incorporate several important safety features as well. Being a noble gas, the helium coolant will not react with other materials, even at high temperatures. Further, because the fuel elements and reactor core are made of refractory materials, they cannot melt and will degrade only at the extremely high temperatures encountered in accidents (more than 1,600 degrees C), a characteristic that affords a considerable margin of operating safety.
Yet other safety benefits accrue from the continuous, on-line fashion in which the core is refueled: during operation, one pebble is removed from the bottom of the core about once a minute as a replacement is placed on top. In this way, all the pebbles gradually move down through the core like gumballs in a dispensing machine, taking about six months to do so. This feature means that the system contains the optimum amount of fuel for operation, with little extra fissile reactivity. It eliminates an entire class of excess-reactivity accidents that can occur in current water-cooled reactors. Also, the steady movement of pebbles through regions of high and low power production means that each experiences less extreme operating conditions on average than do fixed fuel con-figurations, again adding to the unit’s safety margin. After use, the spent pebbles must be placed in long-term storage repositories, the same way that used-up fuel rods are handled today.
Water-Cooled Reactors Even standard water-cooled nuclear reactor technology has a new look for the future. Aiming to overcome the possibility of accidents resulting from loss of coolant (which occurred at Three Mile Island) and to simplify the overall plant, a novel class of Generation IV systems has arisen in which all the primary components are contained in a single vessel. An American design in this class is the international reactor innovative and secure (IRIS) concept developed by Westinghouse Electric.
Housing the entire coolant system inside a damage-resistant pressure vessel means that the primary system cannot suffer a major loss of coolant even if one of its large pipes breaks. Because the pressure vessel will not allow fluids to escape, any resulting accident is limited to a much more moderate drop in pressure than could occur in previous designs.
To accomplish this compact configuration, several important simplifications are incorporated in these reactors. The subsystems within the vessel are stacked to enable passive heat transfer by natural circulation during accidents. In addition, the control rod drives are located in the vessel, eliminating the chance that they could be ejected from the core. These units can also be built as small power modules, thereby allowing more flexible and lower-cost deployment.
Designers of these reactors are also exploring the potential of operating plants at high temperature and pressure (more than 374 degrees C and 221 atmospheres), a condition known as the critical point of water, at which the distinction between liquid and vapor blurs. Beyond its critical point, water behaves as a continuous fluid with exceptional specific heat (thermal storage capacity) and superior heat transfer (thermal conductance) properties. It also does not boil as it heats up or flash to steam if it undergoes rapid depressurization. The primary advantage to operating above the critical point is that the system’s thermal efficiency can reach as high as 45 percent and approach the elevated temperature regime at which hydrogen fuel production can become viable.
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18 Comments
Add CommentIn retrospect it’s too bad our environmental friends gave the “man made global warming” treatment to nuclear power in the 60’s by using superstition and scare tactics to intimidate people with bad information. I’m sure they thought they we’re justified in their views at the time but now we realize the extreme damage of their ignorance. If we had gone nuclear 40 years ago we could have averted spewing gigatons of tons of carbon into our atmosphere and averted the “tipping” point we find our climate in today. Not to mention we could have spent the last 40 years making nuclear power safer and more efficient and the United States less reliant on fossil fuels. This is just one example of how environmentalist can do incalculable damage to our nation and to our climate when they start screaming before they know what they’re talking about.
Reply | Report Abuse | Link to thisThe Next Generation Nuclear Plant will be a demonstration of the technical, licensing,operational, and commercial viability of the high temperature gas-cooled reactor (HTGR) technology for the production of process heat, electricity, and hydrogen. This nuclear based technology can provide high-temperature process heat that can be used as a substitute for the burning of fossil fuels for a wide range of commercial applications.
Reply | Report Abuse | Link to thisThe substitution of a high temperature gas-cooled reactor for burning fossil fuels conserves these hydrocarbon resources for other uses, reduces the vulnerability to the cost and supply of natural gas and oil, and eliminates the emissions of greenhouse gases attendant with the burning of these fuels. The HTGR is an inherently safe nuclear reactor concept with an easily understood safety basis that permits substantially reduced emergency planning requirements and improved siting flexibility. For more information about this project log onto to nextgenerationnuclearplant.com .
My main concern as a laymen is the waste that is produced in this process. Where does it go? What do we do with it? Time and time again, I see reports of waste storage facilities that contaminate the land and environment near them. Also, this waste is transported via the rail system. What happens when the disposal cars go off the tracks and dump reactor waste over well-trafficked areas? I am willing to accept nuclear power, but I don't think we can contain the waste products in a responsible way. Please prove me wrong.
Reply | Report Abuse | Link to thisI fear the next generation of nuclear plant will run into the same financial problems that hamper the conventional nuclear units. The proposed high temperatures, which greatly complicate the design and small output (appears to be around 300 mW(e)) appear to cause the next generation to be simply too costly from a commercial viability standpoint.
Reply | Report Abuse | Link to thisSafe storage or disposal of used nuclear fuel is purely a political issue, NOT a technical one. First of all, used nuclear fuel is not waste. It is extremely valuable slightly burned fuel. When removed from a reactor the used fuel still contains about 95% of energy content it had when new. The day will come when the USA will want to reprocess used fuel and burn it again. Until then it is completely safe stored at existing nuclear plants. In fact, it makes no economic sense to expend resources to transport used fuel thousands of miles to an underground storage location only to have to repeat the process in reverse in a few years when we decide to reprocess it. Consider this: with nuclear energy 100% of the hazardous by-products are contained and controlled and paid for by the utilities. Contrast that with other forms of energy that exhaust toxic emissions and CO2 into the air with no regard for the health or environmental impacts, and no financial accountability for the eventual consequences!
Reply | Report Abuse | Link to thisAre all you proponents completely insane?!!! Nuclear power might not produce carbon emissions but it does produce NUCLEAR WASTE! In addition, the naturally occurring elements spent during this energy production are responsible for sustaining the Earth's magnetic field and the more fuel we manipulate the more we alter said field. The truth is we no longer need ANY power companies at all. The future is without carbon emission, without ever increasing or maintaining failing infrastructure and without the bloated, wasteful expenditures of despotic energy consortia. Modular energy or "point of need" production and consumption models are the only sustainable plans and they are in truth the most readily available and easiest to upkeep.
Reply | Report Abuse | Link to thisWhen it comes to Nuclear Waste it is just better to make less of it.
Reply | Report Abuse | Link to thisThorium Molten Salt Reactors make dramatically less nuclear waste.
It is not necessary for us to leave a mountain full of radioactive contaminants in Nevada as our legacy to our children’s children.
Cleaner, superior, less waste generating nuclear technology exists.
Thorium Fuel Cycle Molten Salt Reactors are better technology and deserve your investigation and support.
Conventional Technology LWR reactors burn 35 metric tons of enriched Uranium-235/Uranium-238 fuel to generate 1 gigawatt of energy and in that process generate 35 metric tons of high level waste all of which has to be stored for ~25,000 years in Yucca Mountain repository.
Thorium Molten salt reactors burn 1 metric ton of Thorium-232/Uranium-233 fuel to produce 1 gigawatt of energy and in that process generate 1 metric ton of fission product waste all of which decay to benign levels within 400 years (83% of the fission products decay to the benign level of the natural radioactive background in 10 years) and only approximately 30 grams of the original 1 metric ton of Thorium fuel becomes Plutonium-239 which may be burned as reactor fuel or stored in Yucca Mountain. The 1 ton of fission product waste would not require storage in the long term Yucca Mountain repository. When the fission products are first removed from the TMSR they are very radioactive but the material decays very rapidly to where only 17% of the fission products remain radioactive after 10 years. All of the fission products decay to benign levels in less than 400 years.
The majority of the spent fuel rods produced as waste by current technology LWRs contain (96.5%) good unburned U-238 and Pu-239 fuel . LWR reactors are only about 3% efficient at burning their nuclear fuel. Thorium Molten Salt Reactors burn in excess of 98% of their Thorium Fuel while making energy and shorter lived fission products. It is even possible to configure Molten Salt Reactors to run on LWR spent fuel waste dissolved into the molten fuel salt and burn the remaining 96% of the unburned LWR Uranium fuel in the Molten Salt reactor producing dramatically more (3200%) useful energy than was produced through the first burning of the fuel rod in the current technology LWR. Using Thorium Molten Salt Reactors to burn LWR spent fuel from old fuel rods extracts much more energy value from the LWR fuel. Running the Molten Salt Reactor on Uranium spent nuclear fuel from old fuel rods would generate a significant amount of Transuranic waste however.
Yes, someone here is "insane". but it doesn't appear to be the proponents. I think the alteration of the magnetic field is affecting the function of your cerebral aura.
Reply | Report Abuse | Link to thisAnd say hi to Amory Lovins, that old fraud, for us.
Someone here is demonstrating signs of "insanity", but it doesn't look like the proponents. Maybe the atomically-induced alteration of the magnetic field is playing havoc with your cerebral synapses. Or maybe you are just a natural-born anti-nuke loon.
Reply | Report Abuse | Link to thisRegardless, say hi to that old fraud Amory Lovins for us.
Dennis Earl Baker
Reply | Report Abuse | Link to this103 - 66 Duncan avenue west
Penticton British Columbia V2A6Z3
Phone/Fax 778-476-3673
25/11/2009
The Copenhagen Diagnosis, 2009: Updating the world on the Latest Climate Science. Has again indicated urgency in action is imperative. Here's my solution and immediate areas of impact.
dennisbaker2003@hotmail.com
RE : The solution to climate change.
( human excrement + nuclear waste = hydrogen )
The USA discharges Trillions of tons of sewage annually, sufficient quantity to sustain electrical generation requirements of the USA.
Redirecting existing sewage systems to containment facilities would be a considerable infrastructure modification project.
It is the intense radiation that causes the conversion of organic material into hydrogen, therefore what some would consider the most dangerous waste because of its radiation would be the best for this utilization.
I believe the combination of clean water and clean air, will increase the life expectancy of humans.
The four main areas of concern globally are energy, food,water and air!
The radiologic decomposing of organic materials generates Hydrogen
By using our sewage as a source of energy we also get clean air , clean water, and no ethanol use of food stocks. Eat food first, create energy after.
Simply replacing the fossil fuel powered electrical generating facilities with these plants, would reduce CO2 emissions, and CH4 emissions, to acceptable levels, globally.
This would require a completely new reactor facility capable of converting human waste into hydrogen and then burning the hydrogen to generate electricity on site.
This solution is sellable to citizens because of all the side issue solutions. I've been able to convince most simply with concept of using nuclear waste to a productive end.
Superbugs ( antibiotic resistant ) apparently are created in the waters sewage is discharged into, which is one more side issue solution.
Anything not converting into hydrogen will potentially be disposed of using Transmutation.
The water emitted from hydrogen burning will have uses in leaching heavy metals from other contaminated site clean ups.
I thank you for your consideration, please feel free to contact me anytime.
Dennis Baker
Thorium Molten Salt reactors would be great but they face more technical hurdles before they are ready.They say the High Temp Gas reactors won't have a prototype until 2021.I would like to see the timetable sped up.Barak has done nothing to educate or sell these systems.It is so ignorant to call this waste. The oxygen you breathe was excreted .
Reply | Report Abuse | Link to thishttp://www.neatorama.com/2010/04/02/us-military-developing-poop-powered-nuclear-reactors/
Reply | Report Abuse | Link to thishttp://www.neatorama.com/2010/04/02/us-military-developing-poop-powered-nuclear-reactors/
Reply | Report Abuse | Link to thisI read once that large coal fired power stations emit large amounts of radioactivity in the form of thorium in the ash.
Reply | Report Abuse | Link to thisIs thiss true?
people yacking, hollering and worring about nuclear power plant wast and its contanment schould get their head out of there ass and take a lock at the millions of tons of hot nuclearer wast barried in las vegas nevade's back yard. go to google maps about a hunderad or so miles north of vages and have a look for yourself at the thousand pluse underground nuclear boom creaters in the nevada proving gorunds count. them your self. it was estmated that the booms droped on japan and the lettle boy tested at trinty in new mexieco all produced about a 1,000 tons or more of raido active wast each with no storage contanment and they were smale ones. talk about being worried about containment of recator wast in a nevada mounton at least its in containers first. that stuff under nevada proving grounds is only in the ground water and with all hinds of raido active gases seaping up into the air every day. belive you, me i would much rather have the clostest house that is bilt to a nuclear powerplant then live enywhere in southeren nevada. as i read some where that the deployment of proper breader reactors that brun wast as well as create new fuel would take some where around 30,ooo years to produce as much nuclear wast as our world wide testing of nuclear booms and inefecint powerplants have already produced.
Reply | Report Abuse | Link to thisYes cold fired power plants do release radioactive in their ash but not just thoruim but all kinds of other raidioactives that are buried with the coal. they also releace smale amounts into there ehust stacks into the air. due to the large number of coal plants world wide it is estmated that the total amount of raidioactive elements released into the inviroment by coal plants far exceds and may be by servial times the amount released by the world nuclear power plants. although this raidioactive release is a bad thing. the release of sulferdioxide, forming acide rain is servial million times worse to the envirment and our lungs. along with co2 emisions make coal plants the worst for the enviroment as my grandparence said about coal its dirty and nasiy. their is no such thing as clean coal. wona know about raidioativiy of coal ass just take a gigercounter to the blocks in a cinder block building then compair to a wood fram building.
Reply | Report Abuse | Link to thisThe push for nuklear power is by the corporations that will benefit from the building of the plants. Last time, people were paid to not work in order to get that 15% guaranteed profit, no matter how much the overcosts were. Geo thermal woworks better and is much cheaper. This is why the corporations don't want geo--too cheap to make! Geo have very little danger, also.
Reply | Report Abuse | Link to thisPerhaps. But there are still lots of caveats to uranium-based nuclear that have yet ( maybe never?) to be worked out. But here's something that was achievable - fuel efficiency. If North America had taken efficiency to heart after the '73 embargo, it would have prevented the spewing of gigatonnes of CO2 AND kept TRILLIONS of dollars in American pockets. Truly a crying shame - now a financially devastated economy, a fractured political system and can't get anything done.
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