October 13, 2005
Uranium Pellet Design Allows Longer Lower Temperature Burning
Purdue University researchers have discovered a way to operate uranium pellets in nuclear reactors at lower temperature which also will allow the pellets to last longer before needing replacement.
WEST LAFAYETTE, Ind. – Purdue University nuclear engineers have developed an advanced nuclear fuel that could save millions of dollars annually by lasting longer and burning more efficiently than conventional fuels, and researchers also have created a mathematical model to further develop the technology.
New findings regarding the research will be detailed in a peer-reviewed paper to be presented on Oct. 6 during the 11th International Topical Meeting on Nuclear Reactor Thermal Hydraulics in Avignon, France. The paper was written by Shripad Revankar, an associate professor of nuclear engineering; graduate student Ryan Latta; and Alvin A. Solomon, a professor of nuclear engineering.
The research is funded by the U.S. Department of Energy and focuses on developing nuclear fuels that are better at conducting heat than conventional fuels. Current nuclear fuel is made of a material called uranium dioxide with a small percentage of a uranium isotope, called uranium-235, which is essential to induce the nuclear fission reactions inside current reactors.
Better heat conduction allows cooler internal operating temperature and hence less cracking and longer life. This could reduce the interval between refuelings, allowing reactors to have more up-time and also reduce fuel consumption.
"Although today's oxide fuels are very stable and safe, a major problem is that they do not conduct heat well, limiting the power and causing fuel pellets to crack and degrade prematurely, necessitating replacement before the fuel has been entirely used," Solomon said.
Purdue researchers, led by Solomon, have developed a process to mix the uranium oxide with a material called beryllium oxide. Pellets of uranium oxide are processed to be interlaced with beryllium oxide, or BeO, which conducts heat far more readily than the uranium dioxide.
This "skeleton" of beryllium oxide enables the nuclear fuel to conduct heat at least 50 percent better than conventional fuels.
"The beryllium oxide is like a heat pipe that sucks the heat out and helps to more efficiently cool the fuel pellet," Solomon said.
A mathematical model developed by Revankar and Latta has been shown to accurately predict the performance of the experimental fuel and will be used in future work to further develop the fuel, Revankar said.
Pellets of nuclear fuel are contained within the fuel rods of nuclear fission reactors. The pellets are surrounded by a metal tube, or "cladding," which prevents the escape of radioactive material.
Longer lasting fuel also translates into less waste generated.
Because uranium oxide does not conduct heat well, during a reactor's operation there is a large temperature difference between the center of the pellets and their surface, causing the center of the fuel pellets to become very hot. The heat must be constantly removed by a reactor cooling system because overheating could cause the fuel rods to melt, which could lead to a catastrophic nuclear accident and release of radiation – the proverbial "meltdown."
"If you add this high-conductivity phase beryllium oxide, the thermal conductivity is increased by about 50 percent, so the difference in temperature from the center to the surface of these pellets turns out to be remarkably lower," Solomon said.
Revankar said the experimental fuel promises to be safer than conventional fuels, while lasting longer and potentially saving millions of dollars annually.
"We can actually enhance the performance of the fuel, especially during an accident, because this fuel heats up less than current fuel, which decreases the possibility of a catastrophic accident due to melting," Revankar said. "The experimental fuel also would not have to be replaced as often as the current fuel pellets.
"Currently, the nuclear fuel has to be replaced every three years or so because of the temperature-related degradation of the fuel, as well as consumption of the U-235. If the fuel can be left longer, there is more power produced and less waste generated. If you can operate at a lower temperature, you can use the fuel pellets for a longer time, burning up more of the fuel, which is very important from an economic point of view. Lower temperatures also means safer, more flexible reactor operation."
Solomon said a 50 percent increase in thermal conductivity represents a significant increase in performance for the 103 commercial nuclear reactors currently operating in the United States.
A small group of academic researchers figured out how to reduce uranium consumption, increase reactor performance, and reduce waste generation and all in one fell swoop. Pretty impressive. Nuclear reactor technology continues to advance just as other energy technologies advance.
Even if oil production peaks in the next 10 years I do not see the economies of developed countries being slowed down for long. Too many good minds would react to necessity and demonstrate once again that it really is the mother of invention.
Safe nuclear power will provide the transition between fossil fuel dependency and a more long term renewable energy scheme. Pseudo-environmentalists have scared everyone away from nuclear for decades. This has retarded the research into safer and more economical nuclear power sources. The global warming scare has the potential to be even more destructive toward long term energy strategies in its emphasis on avoidance of energy use rather than concentrating on resourceful and inventive approaches to energy production. Environmentalism and politics is a deadly mix.
Very interesting. More fuel to be burned is going to be more cost effective, and have less waste.
Also in the future we will probably have commercial breeder reactors to use up a lot of the waste as well. So one way to judge nuclear's progress should be to look at the total amount of energy produced versus the amount of waste.
I'm assuming this is intended for increased effeciency of current LWR's. Still something like the IFR is needed in the coming decade or so to really stretch supplies. If memory serves the IFR would have had nearly a 20% burndown before fuel elements would have needed in-house reprocessing. Also it can take and burn the spent fuel from the traditional LWR's. I find it funny that the biggest argument against breeder reactors in general was worries of plutonium proliferation. It's actually easier to get proper P239 from a normal LWR or CANDU than from the breeder which tend to produce a mixed bag of P239, P240 etc. which is not really feasible for weapons production and is a huge pain to isotopically seperate.
Aside: You know what would really lower the cost of nuclear power? Faster reactor construction.
Reactors that are partially built represent huge amounts of capital tied up and doing nothing. Unproductive capital has to get paid for when the capital finally enters production.
A poster in a comment here some time back said that reactors take a long time to build in part because the concrete has to cure (or whatever it is called) and that something so massive has to sit there a long time.
So could a new type of concrete be developed that would cure faster?
I'm not sure how feasible that would be. The formulas are advancing every year so perhaps it's possible. As an example I actually saved money last year having the parking lot redone by going with the more expensive newer blends. Half the thickness needed on the pour and no requirement for rebar due to the fiber material mixed in. Minimal expansion joints yet with a spread of -50F to +95F last year still no cracking.
Now newer designs using liquid metals etc. shouldn't need the same level of containment engineering and might reach requirements through subsurface emplacement since a pressure dome to contain a powerfull steam explosion event wouldn't be needed.
The concrete argument sounds like BS to me. Concrete develops most of its strength within weeks, and is typically rated at 28 days; if you need the margin of strength earlier, you can always make things thicker and pay a bit more.
It was my impression that the big delays in reactor construction were for permits and inspections.
Cut down the length of many regulatory stages and you are still left with several years to build a nuclear reactor? Maybe not.
Can the AP-1000 really get built in 3 years?
The Westinghouse AP-1000, scaled-up from the AP-600, has now received final design approval from the NRC and is expected to gain full design certification in 2005. It represents the culmination of a 1300 man-year and $440 million design and testing program. Overnight capital costs are projected at $1200 per kilowatt and modular design will reduce construction time to 36 months. The 1100 MWe AP-1000 generating costs are expected to be below US$ 3.5 cents/kWh and it has a 60 year operating life. It is under active consideration for building in China, Europe and the USA, and is capable of running on a full MOX core if required.
Ditto for a new Canadian design:
The ACR-700 is 750 MWe but is physically much smaller, simpler and more efficient as well as 40% cheaper than the CANDU-6, giving projected overnight capital cost of US$ 1000/kWe and operating costs of 3 cents/kWh. It will run on low-enriched uranium (about 1.5-2.0% U-235) with high burn-up, extending the fuel life by about three times and reducing high-level waste volumes accordingly. Regulatory confidence in safety is enhanced by negative void reactivity for the first time in CANDU, and it utilises other passive safety features. Units will be assembled from prefabricated modules, eventually cutting construction time to three years.
I'd love to know how long construction times took for the most recently constructed reactors.
Actually ~36 months would be really cooking along if that also included inspection/certification processes. Also consider the additional building code/OSHA requirements since the mid seventies. I would'nt be surprised it it didn't take 5 years minimum for the first unit with unforseen construction problems/material supply/court challenges to contend with. Hell a couple of borderline welds discovered during the x-raying procedures could add a couple of weeks to the total.
Hmm your reference to the CANDU. High burn up? Would that be due to the richer (compared to the origional CANDU design) U235 percentage?
Nuclear Plant Has Flaw Undetected for 19 Years
By THE ASSOCIATED PRESS
Published: October 14, 2005
PHOENIX, Oct. 13 (AP) - "A potential problem with the emergency reactor core cooling system at the nation's largest nuclear power plant went undetected from 1986, when the plant began producing electricity, until last week, the Nuclear Regulatory Commission and the plant operator confirmed Thursday.
"The issue, a design flaw, was identified when engineers at the plant, the Palo Verde Nuclear Generating Station, did an analysis after commission overseers raised questions at a detailed inspection early last week. The analysis showed that the emergency cooling system might not operate as expected to provide water to reactor cores after a small leak in the reactor cooling lines, said a commission spokesman, Victor Dricks."
Yep, I say pump those nuclear puppies out as fast as we can. After all, we've proved that they're inherently safe, nothing can really go wrong, and their designers and construction crews always work to the highest standards possible.
Nuclear flaw discovered after fifteen years? Oh, the horror! And do the new designs contain the same flaw? No, of course not. But still--oh, the horror!
And the human body has flaws that are being discovered daily after millions of years. Deal with it and move on. That's the difference between engineering and catastrophe mongering. The engineer is constantly on the lookout for flaws, even years and decades after implementation.
Yep pump 'em out. We need the power and the world's factories, hospitals, schools and homes will not be powered by some Gia worshipper trying to brew hydrogen with a couple of old plastic pop bottles and a homemade wooden windmill.
Joseph: Have you been looking in gmoke's backyard?
Gmoke: Just kidding.
Curing concrete time is less important than a requisite number of plants. If your design willbe state of the art for 20-30 yrs (like the Saturn V still is today?)you can build hundreds over that time with logarithmic reductions in the costs per unit at some point. Assume that each plant is capable of 40-50 yrs of operation at an average of 85% operational capacity (achieved with 1970's plants that assumed only 65% op capacity at the time -- see article in IEEE)and you've got a doable nuclear economy.
but I have questions. First, breeder reactors could assume importance rapidly as natural U235 ore diminishes in quantity, grade (5% U by content in Canadian ore, to 1-2% elsewhere). Thorium could triple energy supplies, but the breeders would be huge. How huge, and could we justify such large reactors, on the order of the late Superfenix project in France (which continues to cost hundreds of millions of dollars in remediation costs)?
Next, what are the alloying properties of the BeO-U mix over time? A truly efficient fuel cycle will produce massive amounts of daughter nuclides -- at least high enough to reprocess with dividends -- such as Americium and Protactinium, which are feasible as fuels in their own right. Would your fuel rods be susceptible to cracking and explosions? Could they be heat treated? (which is what you would probably have to do with U metal alloy, Engineer-Poet)
Also, is Beo-U really intended for fast breeder reactors, which must operate at temperatures hot enough to melt Sodium?
The rest of the story about the "undetected flaw" at Palo Verde:
There was no flaw, just careful evaluation of a concern. A concern that was noted because of strict regulation.
The use of nuclear power by a capitalist republic is the safest form of power production yet devised. That is a proven fact. It gets safer every year.
Yeah, we'll just power up the nuclear plants that we've built, and charge up the batteries of our fleet of 200 million electric cars, electric trailers, and electric barges, and it'll be business as usual. Oh, and we'll flip the switch on the electric methane and oil generators to make the cheap feedstock for our fertilizers and plastics, and turn on the electric furnaces that were installed in every home, office, and foundry in America to replace all the oil and gas furnaces. And use all those electric trains to shuttle people from city to city, since nobody uses those fuel-guzzling airplanes anymore. Oh, and those electric aircraft carriers, tanks and bombers that are so vital to our national defense. And the electric mining equipment used to get the uranium out of the ground in the first place.
It's a good thing that private industry, the government, and individual citizens are sinking the $trillions needed to convert the oil- and gas-based segments of our infrastructure into electric versions, so we will be prepared for the chronic increases in fossil fuel prices that are expected to occur in the next 10 to 30 years. Because if it's one thing our country has shown, it's how prepared we are for problems that were predicted decades ago.
But don't worry! If we can't convert this country to an electric economy in the next few decades, we can always convert everything to run on our other long-term energy source; coal.
First, breeder reactors could assume importance rapidly as natural U235 ore diminishes in quantity,
This isn't obvious to me. Today, the value of plutonium for power generation is negative, and that's after it's been separated. The price of uranium would have to rise to $300/lb or more for reprocessing to start to make sense; breeders would require even higher prices. I think it's likely that high-efficiency once-through cycles (U-Th, say) and seawater U extraction could delay economical reprocessing and breeding for centuries, even for an all-nuclear global economy.
Yep keep making it better. Once the general public figures out that the radiation released from a nuclear plant is less than the background radiation in denver nuclear power will really start leaping forward.
What is the name of the company that supported the Beryllium mixed with uranium to form the pellet for the rods, that has been studied by Prudue and Texas A&M ?
What is the name of the company that supported the Beryllium mixed with uranium to form the pellet for the rods, that has been studied by Prudue and Texas A&M ?