On Valentine’s Day, a small puff of radioactivity exited the only deep geologic repository for nuclear waste operating in the world, the Waste Isolation Pilot Project near Carlsbad, New Mexico. A slab of rock most likely fell from the ceiling, smashing some drums, and getting a small spot on WIPPs’ 15-year spotless record.
Immediately, cries of the ceiling is falling, the ceiling is falling progressed promptly to we need to find a new place, even though there will be no impact to anyone’s heath or the environment from this event. Articles appeared quickly offering new places to put this stuff, like “How about shale? We got plenty of that!” (Bloomberg).
But before we throw the baby out with the bathwater, and start re-inventing the wheel, let’s review what options for nuclear waste disposal have been proposed over the last 70 years. Then, I invite readers’ thoughts about what you would do with, or where you would choose to put, this material. I would appreciate only a single comment from each person for the first 24 hours so as to lay out the field of possibilities first before we get into the more animated discussion that often drowns out all but the thickest-skinned among us.
Nuclear waste really begins with WWII and the making of the Bomb. The production and reprocessing of fuel from weapons reactors to make Pu resulted in the first significant amount of nuclear waste beginning in 1944. We had no idea what this stuff was, let alone anything about environmental science, so we built million-gallon tanks at Hanford in WA State, among other places, to store this material while we won the war. Then we ramped up weapons production to win the Cold War.
With the advent of commercial power reactors in the 1950s, and the increasing frenzy of weapons production, it became obvious that we needed a real strategy for long-term disposition of nuclear waste. The federal government commissioned the National Academy of Sciences to come up with the best strategy and, in 1957, they reported that deep (half-a-mile or so) geologic disposal was best, and that massive bedded salt was the best rock type (National Academies Press). This led directly to WIPP. A splinter strategy in the 1970s, involving retrievability of spent nuclear fuel from the depths, then led to Yucca Mountain.
This is where we are today. Yucca Mountain is in stasis, and we’re all atwitter about the blip of a first incident at WIPP. But in the 1970s, there was a push to investigate alternatives to geologic disposal since it was becoming obvious we wouldn’t soon agree on any location. Significant time was spent on evaluating these ideas (Mark Holt, Congressional Research Service), and the most reasonable included:
- Shoot it into the Sun (did I say reasonable?)
- Transmute it by bombarding it with high energy particles (alchemy with an accelerator)
- Sail it out to a deep ocean trench and drop it in (Exxon Valdez 21st Century)
- Drill deep (miles) boreholes in a thick Ice Sheet and drop in everyone’s canisters (Exxon Valdez on Ice)
- Drill deep (miles) boreholes in each State that has waste and drop in the canisters (distributed liability)
There were others, but these were seriously considered, and some of them still are.
Shoot it into the Sun. While theoretically correct (the Sun is a huge nuclear reactor that would completely consume this waste) the extreme cost, and risks of an accident, speaks for itself. Plus, the giggle factor was just too much to get over. But in all fairness, we had recently landed on the Moon so space was in our thoughts and, originally being a planetary geologist, I thought this idea was a gas.
Transmutation. Bombarding the waste, or individual components of it, in nuclear reactors or linear accelerators, can transmute radioactive elements into less hazardous and non-radioactive elements. Take two of the bad boys, technetium-99 and iodine-129, both of which dissolve easily and can move with the groundwater, and represent a major dose early in most performance assessment models. Each isotope absorbs a neutron if you bombard them. Tc-99 becomes Tc-100, which quickly decays into stable ruthenium, and I-129 transforms into stable xenon. You might imagine how very expensive and time consuming this process would be, even if we had enough accelerators and reactors for this purpose.
Sail it out to a deep ocean trench and drop it in. This is not a bad idea geologically – cold impermeable, oxygen-free, self-sealing ooze that will eventually get dragged down into the trench formed between two colliding crustal plates. But trenches are in international waters, and if you thought getting 50 States to agree on a single solution was hard, just think 193 sovereign nations.
Ice Sheets. Given global warming, not sure this is cool. The Greenland sheet no longer suffices in terms of stability or ice depth. The Arctic is too thin as it sits mostly over water. West Antarctica is also too thin and covers a huge archipelago that may soon emerge from below to above sea level. Only East Antarctica is thick enough and will be for millennia. Again, international unclaimed lands that are extremely dangerous and expensive to get to.
Deep borehole disposal. Bore miles deep into the crust and put in many packages. This is not a bad idea at all, but is really only for commercial waste, since the boreholes would be drilled in each State that has the waste itself, few populations would accept other States’ waste, and no one would accept the weapons waste (Sandia National Labs; Bates, et. al. 2014. Energy Policy (in press, http://dx.doi.org/10.1016/j.enpol.2014.03.003i). Although some technology development is needed (we’ve only drilled really deep holes to diameters not yet 12-inches), it appears doable. Assuming some favorable breaks, the cost would be in the ballpark of proposed traditional geologic repositories, and may even get down to that of just expanding WIPP. But you’d then have over thirty nuclear waste sites spread out over the entire country. Would that be good? Would it be bad? More equitable?
But it is most likely that we will stick with moderately deep (half-a-mile) geologic disposal, in one or more places, e.g., WIPP and Yucca Mt. So what are the characteristics of an ideal deep geologic nuclear waste disposal site? (New Mexico Academy of Science, Conca et al p.13-23)
- a simple hydrogeology (we know how the water moves here),
- a simple geologic history (we know what happened here),
- a tectonically interpretable area (we know what’s going on here),
- isolation robustly assured for all types of wastes (we don’t want the form to matter),
- minimal reliance on engineered barriers to avoid long time extrapolation of models for certain types of performance (we don’t know how long we can make anything last),
- performance that is independent of the canister, i.e., canister and container requirements are only for transportation, handling and the first several hundred years of peak temperature after emplacement in a repository (we don’t know how strong we can make something when put up against the Earth), and
- a geographic region that has an existing and sufficient sociopolitical and economic infrastructure that can carry out operations without proximity to a potentially rapidly growing metropolis (we don’t want a lot of people around it but need enough to make it happen).
Deep crustal rocks meet these criteria, but two more shallow rock types that fit these characteristics are argillaceous rocks (claystones and shales) and bedded salts (Dave Savage). Many studies have focused on argillaceous sites, particularly in Canada and Europe with some strong technical arguments for their suitability in those that are sufficiently massive and non-clastic. Similarly for salt deposits. Although many salt deposits exist throughout the world, many are not sufficiently massive, have too many clastic interbeds, are tectonically affected, or are near population centers. Salt domes and interbedded salts are less optimal than massive bedded formations from a hydrologic standpoint, particularly within the United States where diapiric movement (doming) can exceed 1 mm/yr, and spline fractures can act as hydraulic conduits. Still, there are many viable salt deposits globally that meet these criteria, the best being the Permian Salado Formation, WIPP’s host rock.
So… what choice do we have?