Tagged: Transatomic Power

Reactor reuses nuclear waste

Reactor reuses nuclear waste

Two Massachusetts Institute of Technology doctoral candidates are designing a nuclear power plant that would convert nuclear waste from conventional reactors into electricity — a plant you could walk away from, they said, without the risk of a radioactive leak like the meltdown last year that crippled parts of Japan.

Leslie Dewan and Mark Massie, co-founders of Transatomic Power, have developed the WAMSR, or Waste-Annihilating Molten Salt Reactor, a 400- to 500-megawatt plant that would convert high-level nuclear waste into electric power, at a price competitive with fossil fuels.

“About two years ago, we got really excited about nuclear power because we saw so much potential in the industry to improve the design of reactors and stretch the limits of the technology,” said Dewan, 27.

The two researched different designs and settled on a molten salt reactor, Massie said, because other types of reactors have not been economically viable.

They estimate the WAMSR could convert the waste produced by conventional nuclear reactors each year into $7.1 trillion worth of electricity, at 10 cents per kilowatt-hour.

At full deployment, the two said, their reactors could use existing stockpiles of nuclear waste to satisfy the world’s electricity needs through 2083, all the while reducing the majority of the waste’s radioactive lifetime from hundreds of thousands of years to hundreds of years, thereby decreasing the need for permanent repositories such as Yucca Mountain in Nevada.

Most importantly, they said, the WAMSR would differ from conventional reactors like the Fukushima I nuclear power plant — which melted down after the March 2011 earthquake and tsunami disaster in Japan — in that it would not require electric power or water to cool it in the event of an accident.

The WAMSR’s efficient modular design also could be manufactured economically at a central location and transported by rail to the reactor site. And utilities could use the profits from the first plant installed to fund construction of additional ones.

Dewan and Massie already have designed the reactor core and are now working on designing the rest of their plant.

With E Ink founder Russ Wilcox as their CEO, their goal is to have a prototype ready in the next five years and a commercial reactor ready within the next 10 years.

Source: Boston Herald

Nuclear Plant Powered by Spent Fuel

Nuclear Plant Powered by Spent Fuel

Reactors could use existing stockpiles of nuclear waste to produce electricity for the world through 2083.

Radioactive sites like this one deep inside the Yucca Mountain Nuclear Waste Repository in Nevada would be almost unnecessary because a salt reactor reduces the majority of nuclear waste’s radioactive lifetime. David Howells / Corbis Images

An old nuclear technology is getting another look, and it could clean, emission-free electricity, while at the same solving the problem of nuclear waste. It’s called a molten salt reactor, and it’s an idea that dates to the late 1950s. A start-up called Transatomic Power, based in Cambridge, Mass., is working on a newer version that uses nuclear waste as fuel. Transatomic’s founders are Russ Wilcox, formerly the CEO of E-Ink, and Leslie Dewan and Mark Massie, two MIT students.

The reactor still makes waste, but what comes out is radioactive for only 300 years, as opposed to millennia. Transatomic calls it a Waste Annihilating Molten Salt Reactor, or WAMSR.

“It’s stuff that is in the middle of the periodic table,” said Dewan, Transatomic’s chief science officer. “It’s a lot easier to isolate.”

A big selling point of this design is that it would help deal with the nuclear waste problem. The Nuclear Energy Institute says there are some 67,000 metric tons of uranium from fuel in the United States alone. It can also be built smaller at lower costs out of modular parts.

The WAMSR can do this because unlike current reactors, it doesn’t need to use enriched uranium as fuel, and the fuel itself doubles as a coolant. No need to build this near a water source like an ocean or river that can ultimately flood and cause damage.

But first a bit about how nuclear plants work: In commercial nuclear reactors, a core houses fuel rods that contain uranium oxide pellets. The radioactivity from the uranium produces heat. To make electricity, water is piped into the core and turned into steam, which is then used to drive generators. This is called the “light water” design.

 To produce enough heat for the steam, the uranium needs to be highly radioactive. That requires purified or enriched uranium. For a power plant that means that up to about 20 percent of it has to be U-235, an isotope that makes up less than 1 percent of the naturally occurring uranium. (Most of the time the enrichment percentage is lower, on the order of five percent — the higher levels are used in research reactors and naval vessels).

As the fuel is “burned,” the uranium decays into other elements, including plutonium, zirconium, cesium, xenon and iodine. Eventually, enough other elements mix in with the uranium that the nuclear reactions slow down, reducing the efficiency of boiling the water. The fuel is then called “subcritical,” or spent, and is put into a waste storage facility.

That’s where the WAMSR comes in. Spent fuel from other reactors is dissolved in fluorine to make a molten “salt,” a chemical whose elements are bound together by their positive and negative charges. The molten salt is pumped out of the core and into a heat exchanger, where the water is boiled to drive a turbine. Since the heat energy is being transferred to the water, the fuel cools down.

This type of reactor was first proposed as a way of powering a bomber; in the 1960s and 70s there was one operated at the Oak Ridge National Laboratory. But the nuclear industry had settled on the light water reactors, and that became the industry standard.

Small May Be Beautiful For Nuclear Power

Because the molten salt behaves like a liquid, it’s easier to get it into a shape that allows for self-sustaining reactions, Dewan said. The shape matters because to make sure that neutrons and nuclei hit others (and sustain the fission) it’s necessary to reduce the surface area of the fuel as much as possible. A sphere is the perfect shape, but a cylinder works as well. The fission reactions in the molten salt “burn” more of the uranium in it, so eventually much more turns into other elements that don’t stay radioactive for so long.

The radioactivity dies down more quickly, too, so it’s easier to build containment facilities. Designing a structure to last a few centuries has been done (think of the average cathedral). But to build one that will last ten or a hundred times as long is much harder; let alone figuring out how to warn future people of the danger when it isn’t likely anyone will speak English — or even remember that English existed.

The fuel is also safer. When accidents have happened in power plants, such as at Fukushima in Japan, it was because the cooling systems failed. At Fukushima the generators that powered the water pumps were flooded by a tsunami. The heat built up in the reactor core until there was a meltdown. The result was a release of hydrogen, which exploded.

The WAMSR’s core is “plugged” with a chunk of solid material that is actively cooled. If that cooling fails, then the plug melts and the molten salt drains out into a pool Once outside of the reactor vessel it will simply cool off and eventually solidify – and since it isn’t in the right shape anymore, the fission reactions won’t be self-sustaining. A failure of the cooling system power would stop the reactor, rather than leading to a meltdown.

With all these pluses, outside experts say there are still some problems. Transatomic isn’t releasing the details of its design, though Dewan and Massie outlined the basics in a TEDx talk on Nov. 1. She said some of these issues have been addressed.

First is the process of taking the fuel out of the reactor vessel, and replacing it. A number of the fission products in nuclear waste are gases — notably radioactive iodine, xenon, and cesium. “It’s one thing to deal with the solids, it’s another to deal with the gaseous fission products,” said Jim Malone, chief nuclear fuel development officer at Lightbridge, a company that is working on a thorium reactor design. He said there has to be some method of containment.

Dewan said the fuel would be processed by draining off some of it and removing the “poisons,” or elements that slow the nuclear reactions down. But that requires a lot of heavy-duty chemical processing.

As one of the selling points of this kind of reactor is that it would be cheaper to build, having that type of processing plant on-site might alter that calculation, said Tanju Sofu, department manager of the nuclear engineering division at Argonne National Laboratory. “You’d probably need a fuel cycle facility attached to the plant,” he said.

Sofu also noted that molten salt needs to be pumped around, and any moving parts have to function for a long time. Many metals when exposed to radiation — especially the neutrons produced in a reactor — become brittle over time. Replacing parts inside the core raises the same containment problems that processing the fuel does.

Metallurgy and materials science have come a long way since 1959, and Dewan says there is a lot of experience in industry with pumping molten fluoride salts and doing maintenance on complex systems

Perhaps the biggest issue will be getting the nuclear fuel itself. Technically, nuclear waste is all property of the Department of Energy, said Mike Mayfield, director of the division of advanced reactors and rulemaking at the Nuclear Regulatory Commission. So there would need to be some discussion of how the fuel is getting processed and working out an agreement to get it.

Even with those obstacles, the WAMSR is still a worthwhile innovation, Sofu said. “In the 1990s the DoE did a study of next generation designs,” he said. “The molten salt reactor was one of the four or five most promising concepts. It has a lot of advantages in fuel cycle consideration and resource utilization.”

Source – Discovery News

A Pair of MIT Scientists Try to Transform Nuclear Power

A Pair of MIT Scientists Try to Transform Nuclear Power

 

Leslie Dewan and Mark Massie are Ph.D. students in nuclear engineering at MIT.  For most of their peers, the options upon graduating are pretty simple: teach, or work for one of the national labs.  Dewan and Massie, though, decided on an unconventional path: like a couple of Stanford grads, they’ve formed a start-up.  Incorporated in 2011, it’s called Transatomic Power, and its mission is to transform the nuclear power industry.

Transatomic’s product is called a “Waste Annihilating Molten Salt Reactor.” If you’ve read my book, SuperFuel, you’ll recognize it as an update on an old reactor technology that was pioneered at Oak Ridge National Laboratory, in the 1950s and 60s.  SuperFuel focused on another type of molten salt reactor, a Liquid Fluoride Thorium Reactor, or LFTR.  Dewan and Massie’s design is fuel-agnostic in the sense that it can run on either uranium or thorium; as the name implies, its signal feature is that it can consume spent fuel from conventional light-water reactors.  Transatomic joins a growing list of start-ups, including Flibe Energy, that are trying to revolutionize nuclear power by bringing back alternative fuels, including thorium, and alternative reactor designs.

(A quick note on the uranium fuel cycle: Most uranium in the ground is the isotope uranium-238 (U238), which is not fissile, and thus is no good for producing power.  Conventional reactors require fuel in which the percentage of the isotope U235 has been enriched up to 3% to 5%, or “reactor-grade” uranium.  Uranium that is enriched to around 20% U235 is weapons-grade.  That’s why it’s a relatively easy step for countries with enrichment capability, like Iran, to build nuclear weapons programs.  Thorium requires no enrichment.)

‘A Leapfrog Move’

“Nuclear power is in a cul de sac,” Russ Wilcox, the CEO and co-founder of Transatomic, told me in a phone interview.  “The nuclear industry knows it’s in trouble, it’s not quite sure what to do, and it’s just trying to survive for the moment.  It’s a fabulous time to do a leapfrog move.”

Wilcox was one of the founders of E Ink, which commercialized electronic paper materials originally developed at MIT’s Media Lab and ended up licensing the technology to Amazon, for the Kindle, to Barnes & Noble’s Nook, and so on.  (Wilcox also points out that the ink for E Ink-based readers continues to be made at a state-of-the-art facility in Boston that employs around 100 skilled workers.)  E Ink was sold to Taiwanese company Prime View for nearly half a billion dollars in 2009.  Transatomic’s plan is to build a prototype reactor in 5 years, commercialize the technology in 15 years, and have reactors come online by around 2030.  The company doesn’t plan to build and operate nuclear power plants, but to license its reactor technology.

Molten salt reactors (MSRs) can achieve much higher burn-up factors than conventional uranium reactors.  In other words, while conventional reactors harness only around 3% of the available energy in a given volume of uranium, MSRs can capture much higher percentages – up to 98%, according to Transatomic (I should note that the nuclear experts I consulted for SuperFuelbelieve that burn-up factors of 50% are more realistic).  Beyond that, the company is not releasing details of its patented reactor technology.

Liquid-fuel reactors, such as MSRs, also offer inherent safety advantages: because the fuel is liquid, it expands when heated, thus slowing the rate of nuclear reactions and making the reactor self-governing.  Also, they’re built like bathtubs, with a drain in the bottom that’s blocked by a “freeze plug.”  If anything goes wrong, the freeze plug melts and the reactor core drains in to a shielded underground container.  Essentially, if Transatomic’s design works as advertised, MSRs could solve the two problems that have bedeviled the nuclear power industry: safety and waste.

Noting that China plans to build a liquid-fuel reactor (likely powered by thorium) within 5 years, Wilcox says that he and Dewan and Massie – currently the entire staff of Transatomic – would prefer to build the prototype MSR in the United States, but will consider another country if the licensing or financing proves too difficult here.  (The Nuclear Regulatory Commission recently licensed a two-reactor nuclear plant in Georgia, the first new reactors to be licensed in this country since 1978.  The reactors are conventional light-water uranium powered models.)

In SuperFuel I noted that the nuclear power industry has a generational problem: most of the leading executives in the industry are now in their 60s.  It will take a new generation of scientists and technologists to spark a revival in nuclear power technology.  Transatomic Power is an encouraging sign that this is beginning to happen.

Source – http://www.forbes.com/sites/pikeresearch/2012/09/27/a-pair-of-mit-scientists-try-to-transform-nuclear-power/