nuclear-news

One way to dispose of SOME of the nuclear waste burden

Can’t We Just Throw Our Nuclear Waste Down A Deep Hole?  http://www.forbes.com/sites/jamesconca/2015/03/05/cant-we-just-throw-our-nuclear-waste-down-a-deep-hole/  James Conca 5 Mar 15 Um…yes, we can. It’s called Deep Borehole Disposal and is pretty easy for some nuclear waste. Especially some highly radioactive materials that have sat in some fairly small capsules for almost 40 years.

This was exactly the topic of discussion in Washington this week when Secretary of Energy Ernest Moniz answered questions from Rep. Dan Newhouse (R-WA) at a House Science, Space and Technology committee hearing (Tri-City Herald).

The answer from Moniz was positive. He discussed a pilot project that would demonstrate the idea of deep borehole disposal using these capsules.

Deep borehole disposal is simple. Drill a very deep hole – 3 miles or so – put the waste in it and fill it up with some special layers, but mainly crushed rock and cement. As geologists, we know how many millions of years it takes for anything to get up from that depth in the Earth’s crust.

As long as you don’t put it under an active volcano!

The nice thing about deep borehole disposal is that it doesn’t matter where you put it in the country. At that depth, you’re so deep in the crust that the overlying rocks don’t matter. The water table doesn’t matter. The climate doesn’t matter. Human activities don’t matter.

But why these capsules? Because the material, cesium-137 and strontium-90 chloride salts (137CsCl and 90SrCl2), is in an easy waste form compared to that sludgy gooey stuff that makes up most of the tank waste left over from weapons production. These capsules are dry solid material in relatively small containers – less than 3-inches in diameter and only 2-feet long – very small compared to the large spent fuel assemblies and high-level waste glass logs usually discussed in geologic disposal plans.

Deep borehole disposal for the larger waste containers is trickier and more expensive because we haven’t yet drilled large-diameter holes that deep. Like all technological advances, we will (Sandia National Labs; Ethan Bates et al 2014). But these capsules are less than 3-inches wide, and we’ve drilled 6 and 8 inch holes that deep many times, so nothing really new needs to be developed for this project.

There are 1,936 capsules filled with radioactive 137CsCl and 90SrCl2 that are stored underwater at the Waste Encapsulation Storage Facility at DOE’s Hanford site in Washington State. Because these radionuclides, left over from plutonium production for weapons, are the primary heat-generator in nuclear waste, they were separated from the rest of the waste almost 40 years ago to reduce heat in the tanks, as well as to use in research.

But there is a time-sensitive nature to these capsules. Although CsCl doesn’t melt until 645°C (1,193°F), it goes through a bizarre solid-state phase change at 450°C (842°F). This means that without melting it’s atoms change their arrangement in space from one structure to another with a very different density. So as the temperature changes across this boundary, the material swells and shrinks. And that tends to degrade the containers it’s in.

The existing containers are beginning to get a little degraded, so best to get rid of them as soon as possible. They’re small, so deep borehole disposal would be cheap and easy.

Since there isn’t much of this boutique nuclear waste, only 5 cubic yards, and it’s in a great form, this is a perfect opportunity to demonstrate deep borehole disposal and clean out this facility.

Like all really hot nuclear waste, these capsules were destined for the proposed deep geologic nuclear waste repository at Yucca Mountain, Nevada, which was halted in 2010. Since a new permanent federal repository for high-level waste won’t be chosen for decades, we need to rethink our nuclear disposal program.

And this is a good idea, one of the few looked at by thePresident’s Blue Ribbon Commission on America’s Nuclear Future that was formed to come up with a new strategy in the wake of Yucca Mountain’s closure. Their recommendations were basically to pick disposal options suited to the waste and the need. And to get everyone to buy off on them before you start!

These capsules “could be very well suited perhaps for much earlier disposal through a borehole approach,” Moniz said. “We have to drill — we have to do the demonstration project, do the science, which is what we want to do in 2016.”

Budget proposal documents show $2 million for technology development to support plans in fiscal 2016 for what is anticipated to be a multi-year test using a non-radioactive waste substitute. Since Yucca Mountain was projected to cost over $200 billion, this is a steal.

The test would demonstrate technology for sealing the borehole, tools to characterize waste in the borehole and controls on waste isolation. DOE has also sought communities interested in being the site for the borehole test.

March 6, 2015 Posted by Christina Macpherson | Reference, USA, wastes | Leave a comment