Yucca Mountain Nuclear Storage on Ice. Now What?

March 04 2009 / by joelg
Category: Energy   Year: 2009   Rating: 4

By Joel Greenberg

Yucca MountainThe Obama administration recently announced their proposed budget with an interesting nuclear wrinkle:  they are no longer funding Yucca Mountain, the underground repository for nuclear wastes in Nevada, 90 miles Northwest of Las Vegas.  "Unfunding" effectively kills the project.  Supporters view Yucca Mountain as a reasonable solution to storing nuclear waste for the long term.  Critics call it a boondoggle based upon flawed science.

Nuclear waste is a byproduct of generating electricity in the 104 nuclear reactors currently running in the US.  It's highly toxic with some elements remaining dangerous for hundreds of thousands of years. It's currently being stored on-site at each reactor, which are running out of room to store the waste.  While Yucca Mountain had room for the existing waste from these 104 reactors, it did not have room for the future waste from the reactors that are now planned as a result of the Energy Policy Act of 2005, which has kicked off a renaissance of nuclear power in the US after 30 years of dormancy.

Surprised?

"No," says Dr. Mike Kotschenreuther, a senior research scientist at the Institute for Fusion Studies at the University of Texas, "We've known that President Obama said he was going to discontinue Yucca Mountain for some time.  We're still going to need a solution to nuclear waste, even if Yucca Mountain is no longer a viable project, so we've been doing our best to come up with a solution."

Hybrid ReactorKotschenreuther's colleague, Dr. Prashant Valanju adds, "There's going to be a mix of various types of energy that are going to play a role.  Nuclear energy is going to be quite a player.  In that case, we're going to have to face up to the waste problem."

Their team's solution is a recently announced fusion-fission hybrid reactor that "burns" nuclear waste.  The result is a small volume of less radioactive material. "We can enormously reduce by a factor of a hundred.  You enormously reduce the number of repositories you need. You reduce the long lived radiotoxicity.  The resulting fission products decay in a few hundreds of years instead of in a few hundreds of thousands of years," says Kotschenreuther.  It's far easier to store a small amount of waste for a few hundred years than football fields of waste for hundreds of thousands.

The hybrid design consists of a fusion reactor surrounded by a blanket of the radioactive waste all enclosed within the fission reactor.  The fission reactor powers the fusion reactor.  This "reactor in a reactor" design not only burns nuclear waste, it generates electricity, just like conventional reactors.  Indeed, the fission reactor is based upon the so called "Generation IV" nuclear reactor designs, which are currently being developed. 

Generation I reactors were early prototypes; Generation II reactors are "light water" reactors that make up the existing US fleet;  Generation III reactors are Advanced Light Water Reactors currently being considered for new reactors that the industry hopes to begin building in the next few years, some of which are permitted to be built by the Nuclear Regulatory Commission and some of which have yet to receive permits; and Generation IV reactors are currently being designed to be more economical, minimize waste, and reduce the chance of proliferation, but aren't expected to be built until 2030.

"Light water" refers to normal water, H20, as opposed to "heavy water." The hydrogen nucleaus in normal water consists of one proton and one neutron.  If an additional neutron is added to the hydrogen nucleus through a nuclear reaction, the resulting H20 is called "deuterium."  If two additional neutrons are added to the hydrogen nucleus, the resulting H20 is called "tritium."  Deuterium and tritium are known as "heavy water" because the H20 molecule is in reality heavier due to the additional neutrons.

The Texas team's fusion-fission hybrid reactor destroys waste by bombarding it with neutrons.  The fusion reactor creates the stream of neutrons.  Because a neutron is electrically neutral (hence it's name), it can sail past electrons, which deflect charged particles.  Crashing into the nucleus of the atoms that make up the radioactive waste, the neutrons split the protons and neutrons of the nucleus.  Doing so transforms the material.  This transformation ultimately reduces the volume and radioactivity of the nuclear waste.

Valanju continues, "Because the neutron source is strong, the fission reactor can be made to run better because you have a strong neutron source.  That's why we can burn this waste." 

The waste isn't destroyed by the fusion reactor directly, it's destroyed by the neutrons created by the fusion reactor.

The team's two major innovations are the ability to create a compact fusion neutron source and the ability to move the heat away from the fusion reactor so that it doesn't consume itself.  The team calls the piece of technology that performs that neat thermodynamic trick a Super X Diverter.  Says Kotschenreuther, "The diverter is a way of using magnetic fields to disperse the heat and let the energy exhaust cool down so you don't damage the vessel around the fusion reactor.  That allows you to get a very high power in a very small volume.  Because the energy that is coming out is in millions of degrees, you have to do it with magnetic fields and that's what's new about it."

The UT team are fusion physicists. But what will it take to make the reactor a reality?  "We usually say something in the range of $1 to $2 billion dollars," says Kotschenreuther. "To put that in context, Yucca Mountain was $96 billion dollars.  If the scale of the problem your dealing with is $100 billion, this is cost effective."

But it won't go online next year. "This would be a substantial project.  If the government really wanted to go into a Manhattan style project, then we should have a prototype running in 10 or 20 years," says Kotschenreuther.

"The timescale is more dependent on the committment of the resources," says Valanju.   But how many hybrid reactors would we need to burn the waste generated by a fleet of reactors?  "For 100 light water reactors, we'll need six to seven of our hybrids," says Valanju.

The scientists have additional reasons for why they'd like to see this project become a reality, other than the huge benefits of being able to burn radioactive waste. "The reason we're doing this is to find an application for fusion that is much easier to do than a full blown fusion reactor.  However, this would be a good, intermediate milestone enroute to fusion.  To make this compact fusion neutron source  reactor work, you have the same problems as a regular fusion reactor, it's just that the problems are easier.  By making it, you've started the process of solving the problems in the real world.  You'd have real fusion reactors in the real world and we really don't have that now," says Kotshcenreuther.  One aspect that makes this easier:  not requiring the fusion reactor to be a net energy producer.

There's something else.  'What motivates us in our heart of hearts to do this is that we want to help in the global warming problems and we think nuclear energy will be a solution to that," says Kotschenreuther, "Everyone says they don't like nuclear energy because of the waste.  So we're trying to solve that problem so that nuclear energy can be used to help solve global warming."

But there's a timeline for global warming.  Some scientists say we need to eliminate all coal fired electricity by 2040 or 2050.  "You can begin to destroy the waste in 20 to 30 years," says Kotschenreuther.

Maybe doing so will make Nuclear truly "safe."

For more information:
The team's original article is titled "Fusion–Fission Transmutation Scheme—Ef´Čücient destruction of nuclear waste", by M. Kotschenreuther, P.M. Valanju, S.M. Mahajan, E.A. Schneider in Fusion and Engineering Design. Volume 84, Issue 1, January 2009, Pages 83-88.
 
University of Texas Article on the hybrid fusion-fission reactor.

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