Public concern about nuclear power goes beyond an accident at a live plant. What do we do with the nuclear waste? If nuclear is to grow to become a major replacement for oil and gas the question must be answered. James Conca reviews the different methods that have been seriously considered: shooting it into space, burying it in deep sea trenches or under ice sheets, transmutation, or simply digging it even deeper underground.
Nuclear waste disposal presents a frustrating problem far beyond its actual danger. Nuclear waste from commercial nuclear power operations is neither particularly hazardous nor hard to manage relative to other toxic industrial wastes. It’s a solid that can’t leak, it’s strictly monitored, is all in one place and the regulators, like the IAEA or the NRC, know where that place is. Contrast that with agricultural fertilisers, toxic coal waste, and many chemical wastes that are spread across continents, factory sewage that may or may not be disposed of properly depending on how seriously the host nation takes the environment, and consumer plastics that find their way from our very hands into the guts of endangered whales in the Pacific. Defense-generated waste can be more difficult to handle than commercial waste but only the United States and Russia have significant amounts of defense waste.
In addition, the amount of radioactive waste is very small relative to any other waste stream. Waste produced by fossil fuel electricity generation from coal is about eleven million times greater than nuclear per kWh produced. All nuclear waste in the world could fit into one repository, although that is highly unlikely considering the public’s fear and international politics.
But we do have to find a final resting place for nuclear waste as it decays away back to the levels of the ore from which it came.
The history of nuclear waste
The creation of nuclear waste really begins with WWII and the making of the Bomb. The production and reprocessing of fuel from weapons reactors to make Pu (Plutonium) resulted in the first significant amount of nuclear waste beginning in 1944. We had no idea what this stuff was, let alone anything about the environmental, so the United States just built million-gallon tanks at Hanford in Washington State, among other places, to store this material while we won the war.
There are several types of nuclear waste. Low-Level Waste (LLW), Intermediate-Level (ILW, in Europe and most of the rest of the world, not the U.S.), Transuranic (TRU, only in the U.S. and only bomb waste without much Cs-137 or Sr-90), High-Level (HLW) and Spent Nuclear Fuel (SNF, from commercial power plants only).
In the U.S., HLW is only bomb waste with lots of Cs-137 and Sr-90, it does not include SNF. In Europe, where there is little bomb waste, HLW includes SNF and the separated waste from reprocessing of SNF to make new fuel.
In Europe, exempt waste and very low level waste (VLLW) contains radioactive materials at a level which is not considered harmful to people or the surrounding environment. LLW is generated from hospitals and industry, as well as parts of the nuclear fuel cycle. ILW contains higher amounts of radioactivity and requires some shielding.
In the U.S., TRU, HLW and SNF require deep geologic disposal by law. In Europe, ILW and HLW require deep geologic disposal by law.
The U.S., along with the Soviet Union, ramped up weapons production during the Cold War. Other countries, like Britain, France, China, Israel, India, South Africa, Pakistan and now North Korea, joined the weapons race, but the amount of weapons waste is tiny anywhere except the U.S. and Russia.
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 U.S. 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 makes sense. I love the Pyramids, but only the Earth makes things that last millions of years. Humans don’t.
Waste Isolation Pilot Project (WIPP): the first deep repository
The NAS’ choice of massive salt (not thin salt like Asse, or domed salts that can move over time) led directly to the Waste Isolation Pilot Project (WIPP), the first deep geologic repository to open in the world. WIPP was designed and built for all nuclear waste of any type.
A U.S. splinter strategy in the 1970s, involving retrievability of spent nuclear fuel from the depths, led to the Yucca Mountain project for SNF and HLW, and a narrowing of WIPP’s mission to just TRU waste disposal.
This is where we are today. Yucca Mountain is in stasis, and WIPP is continuing operations. Along with the U.S., France, Sweden and Finland are farthest along in their nuclear waste programs.
France, Sweden and Finland
Finland has a policy of direct disposal of nuclear waste without reprocessing of SNF. Their disposal program started in 1983 and they have two spent fuel storage sites in operation. Posiva Oy was set up 1995 to implement deep geological disposal. Their underground research laboratory, Onkalo, is under construction, and the repository planned from this work, near Olkiluoto, is scheduled to open in 2023.
Sweden has a policy of direct disposal of nuclear waste without reprocessing of SNF. The central spent fuel storage facility – CLAB – has been in operation since 1985. Their underground research laboratory at Aspo is for developing a HLW repository. The Osthammar site has been selected for the repository and is a public volunteered location. It is scheduled to open in 2028.
France has a policy of reprocessing SNF for new nuclear fuel followed by disposal of the resulting ILW. France also has a nuclear weapons program that has generated significant ILW. Their underground rock laboratories are in clay and granite. The French Parliament confirmed deep geological disposal for nuclear waste in 2006, and the waste containers are to be retrievable and the policy “reversible”. This leads to significantly higher costs.
Alternatives to half-mile deep geological disposal
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 or Country 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 starting out as 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 repository 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 in the U.S. to agree on a single solution was hard, just think 193 sovereign nations.
Ice Sheets. Given global warming, I’m 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, these are international unclaimed lands that are extremely dangerous and expensive to get to.
Deep borehole disposal. Bore miles deep into the crust and put the waste 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). Although some technology development is needed to drill larger holes deeper, 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 U.S. and dozens more in separate countries. Would that be good? Would it be bad? More equitable? That deep in the crust means that overlying features, such as aquifers, don’t matter. There is no mechanism or geologic process to get anything up from that depth in less than a million years as long as you don’t put it under a volcano or along a huge fault.
…or more of the same: half-mile deep
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 Mountain.
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 in southeastern New Mexico and west Texas, WIPP’s host rock.
So… where would you put it?
Dr. James Conca is an earth and environmental scientist and a contributor to Forbes magazine.