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GeoPoll: What should we do with radioactive waste?

GeoPoll: What should we do with radioactive waste?

I don’t think it is any secret that the world is facing an imminent energy crisis. We are trying to generate more power than ever before, but at the same time, we now realize we have to do it in a sustainable way that does not harm the environment or exacerbate any existing issues such as climate change. The problem is these two goals are often mutually exclusive. Most of our power generation methods have environmental implications or are simply at the early technology stage and cannot be relied upon the produce the juice that we all need. Thus, we’re stuck between a rock and a hard place when it comes to generating power. Therefore, the question becomes: we need more power, but at what cost? What are we willing to compromise to generate the energy? The answer is generally something in the environment protection aspect. We now accept that in generating the power we need we will have to affect the environment either to obtain the natural resources required or use huge tracts of land. The trick is how do we best manage the risks and impact of power generation?

The Bruce Nuclear Generating Station in Ontario, Canada. The largest nuclear plant in the world. (Wikipedia Commons – User: Cszmurlo)

This post isn’t about energy policy though. Instead, I would like to write about how we manage the risks of nuclear power, specifically the waste? One of the big knocks against nuclear energy is what do we do with the potentially dangerous and long lived waste that it generates? Over the years a huge range of ideas have been proposed, some silly, and some practical.  In this post I intend to explore some of these proposals and see which ones make the most sense given that this is a problem the world is facing now and is going to face for the foreseeable future, especially, if nuclear energy generation expands. One important point is that most radioactive waste is classified as low/intermediate level. This is essentially everything that is not heat generating fuel. The high level waste is the left over fuel. For all intents and purposes the disposal options aren’t different it’s just that high level waste seems scarier and has the potential to cause more environmental or human health damage if it escapes. Either way the waste, no matter what variety, has got to stay isolated essentially forever.

What are the key features that every storage solution must have?

1. Must be immobile/isolated from the environment and people for at least 100,000 to 1,000,000 years.

The reason for this requirement is pretty obvious. Nuclear waste is dangerous and therefore, it must be isolated from the environment for long periods of time. The reason it must be completely isolated for so long is because the half lives of the isotopes within the waste vary greatly. Thus even though the most highly radioactive isotopes decay to almost nothing within the first 1,000 years there are others, like iodine-129, which have long half lives and remain radioactive for millions of years.

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This shows the relative activity of each major isotope in high level radioactive waste and how it decays overs time. The top red line shows the total radiation over time. This way you can easily see which isotopes are contributing the most to the total radioactivity of the waste over long time scales.

2. Must be potentially recoverable.

The reason that the waste must be potentially recoverable is two-fold. Should there be a problem with the repository it must be possible to remove the waste and either fix the problem or relocate it. The second reason is that as nuclear technologies advance it may become feasible to re-use the waste for energy generation or some other purpose. Therefore, the waste must remain isolated yet accessible during the lifetime of the repository.

3. Must be able to withstand every possible circumstance for incursion.

This one is clearly a key characteristic of a repository. This waste can be used for potentially nefarious reasons and thus it cannot be simple to access. Furthermore, given that the lifetime of the repository is far greater than human civilization has already existed it must also be able to withstand unintentional incursions by future generations. For example, future generations may not use existing languages. Therefore, it must be communicated unmistakably that you should not dig here.

Deep Geologic Repositories (DGR’s) 

The most popular of all solutions for long term disposal of radioactive was these day has to be deep geologic repositories. The idea behind this solution is to bury the waste hundreds of metres underground in an engineered space in a geologically impermeable and stable location. Almost every nation around the world with a nuclear program is investigating this means of disposal. This solution, while certainly expensive, meets the above criteria on all counts. The waste will be isolated for geological time scales. The site evaluation will use a wide variety of methods to confirm this. The waste will be recoverable as it is not that deeply buried and is still on land. In fact, some proposals I have seen for these repositories include an underground lab as well so people will actually be working at the repository site. Finally, the hundreds of metres of solid rock and engineered barriers will withstand attempts to access the waste. Most of these site investigations are looking at igneous rock, however, there is a strong case to be made that sedimentary sites may even be better. The current Canadian site under evaluation for low and intermediate level waste is in sedimentary rock and shows excellent potential as an environment that has been isolated for the last 400 million years.

A conceptual diagram for the proposed DGR in southern Ontario

A conceptual diagram for the proposed DGR in southern Ontario – Source: NWMO (2011), Descriptive Geosphere Site Model

Dilution in the ocean/Sub seafloor burial

This option is likely not going to be the most popular in my poll below, but in order to give equal treatment to all of the proposals I feel that it should be mentioned. The basics behind this idea are best described by the old and oft-repeated quote “dilution is the solution to pollution”. In essence, the idea is simple: drop the waste into the deep ocean where it can slowly disperse, decay and dilute. Obviously for high level waste this is a bad idea and is certainly not popular among the international community. However, while it may seem that this idea is ludicrous there are numerous operating nuclear facilities that currently release radioactive isotopes into the ocean. In fact, the nuclear fuel reprocessing facilities of Sellafield and La Hague are allowed to release a certain amount every year. These radioisotopes are then dispersed in the ocean currents and diluted. They are released at extremely low levels to begin with. However, their presence has afforded oceanographers the opportunity to use these isotopes as tracers of ocean currents.

Burial of the waste beneath the ocean floor has also been proposed as an option. It bears a similarity to deep geologic disposal, however, in a more remote and isolated environment. This slant does have some merit as long as the waste could still be recovered, however, the cost would be extremely high build the repository and recover the waste. Furthermore, this solution still has the problem of potentially releasing radionuclides into the ocean only with the added difficulty that fixing a leak would involve working hundreds of metres underwater. That said a leak of a small amount of radionuclides would be diluted within the ocean and would be unlikely to result in significant contamination unless it was very large.

Deep sea trenches/Subduction zones

This option might seem kind of similar to the sub seafloor burial option since trenches and subduction zones are part of the seafloor. However, the idea with this option is that the waste would eventually get subducted into the mantle and return to whence it came. Basically this idea is kind of like composting the waste, which admittedly seems appealing. However, this idea has all of the drawbacks of sub seafloor disposal and would certainly make the waste unrecoverable…at least once it had started its journey through the crust.

Blast it into space

This solution certainly meets the permanently isolate criteria as well as withstanding accidental incursion. 2 out of 3 ain’t bad, right? However, it does fall down when it comes to waste recovery for obvious reasons. This is a solution, that while appealing on the surface never really gained significant traction. One of the biggest reasons for this is the extremely costly nature of shuttle launches. The other major issue is where do we aim the rocket? Towards another planet? Into the vastness of space? Into the sun? All of these options are fraught with difficulties. Finally, if the launch should fail there is a possibility that the waste could be released into the local environment as well.

Disposal in ice sheets

Disposal of radioactive waste in ice sheets has been considered as well, although never very seriously. Continental ice sheets, such as the Antarctic and Greenland ice sheets, have been stable for many thousands of years. Additionally, as high level wastes are heat generating storage in glaciers would provide in situ cooling. Win-Win right? At least that was the early logic on the proposal when it came out the 70’s. In practice, this is clearly a pretty bad idea, especially since as the climate warms the long term stability of continental ice sheets is not as certain as it was when this idea was proposed. Furthermore, the heat generating capability of high level waste does not go away quickly, as the figure above shows, meaning that the waste could potentially melt its way out of the ice sheet or mix with the meltwater that was produced spreading radioisotopes. Thus, ensuring the waste’s stability for millions of years into the future is uncertain at best with this storage solution.

A composite satellite image of Antarctica. Source: Wikimedia Commons

Long term above ground storage

The final choice is store the waste in an engineered facility on the surface of the Earth. Generally, this disposal option is considered temporary or only for low-level radioactive waste. However, it has been investigated as a long term solution as well. The idea is the the waste is placed together in a constructed facility that has been engineered to isolate it from the environment and withstand any attempts at incursion. At the same time the facility would still be easy to access and make waste recovery very simple.One issue with this option is that since the waste is on the Earth surface it is impossible to truly seal it. Thus, future generations would also have to be responsible for maintaining the facility and ensuring the waste remained isolated.

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An example of a long term above ground storage facility and its engineered barriers. This facility is planned for low-level waste in Port Hope, Ontario. Source

 

Ultimately, the legacy of nuclear power generation has to be dealt with in a safe and responsible manner for thousands to millions of years into the future. As a society we recognize this and the ideas outlined above range from the practical to the fantastic. I would like your opinion this question. Which of these solutions do you prefer? If the answer is none of above please comment below and encourage discussion on this topic!

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Modelling the Vadose Zone…What fun!

Modelling the Vadose Zone…What fun!

Sometimes our projects take stage and unexpected turns down pathways that we have no experience in whatsoever. My project on the input of Fukushima iodine-129 into groundwater has taken one of those turns. This is not a bad thing, but it is a time consuming one, as these deviations often are. However, instead of bemoaning my new lot in life as modeller of the unsaturated (vadose) zone, I thought I’d share a bit of what I’m doing. By the way, if any of you reading this have any experience modelling the vadose zone I’d love to talk in greater detail with you.

Modelling is an interesting field. The basic idea behind modelling is to try and make a computer program predict what is happening in reality by putting in a bunch of experimental or estimated parameters in and letting the model work through calculations that predict what would happen in nature. This is terrific since it is impossible for me to actually observe what is happening in the vadose zone of my field site. Sure I can do a bunch of experiments to try and empirically measure what is happening over time in the field. However, the cost and time is simply too prohibitive and there is no guarantee that I could even sample in such a way as to get good data back. This is the sort of circumstance where the model really comes into its own.

Models are great, but it is important to remember they do not provide the final answer. It doesn’t matter what is being modelled, the real world is orders of magnitude more complex than the model. Therefore, drawing conclusions based solely on the results of modelling is risky and certainly provides and incomplete picture of reality. Furthermore, models provide such pretty pictures and simple explanations for complex phenomena that it is easy/tempting to fall into the trap of over concluding from the model results. Therefore, when using a model to try to simulate reality is it very important to take the conclusions and results with a grain of salt whether you are the modeller, reviewer or reader.

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A picture from my model showing 129I transport in grams. The height of the column is proportional to depth.

The beautiful column of blue and green above shows a very preliminary attempt by me to model the transport of iodine-129 through the vadose (unsaturated) zone of an aquifer over a period of time in 2011. The way the model works is I input a bunch of data (educated or even not so educated guesses) on the soil conditions such as porosity, hydraulic conductivity, moisture content and much more. Then I add in the amount of rain that fell on my study area that has a known concentration of iodine. I then let the model run and watch the 129I infiltrate into the ground. When it gets to the bottom that means it has reached the water table. I can then look through the dataset that the model produces and see the number of grams of 129I that have travelled through the vadose zone and how long it took for them to do so.

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A graph of the model output showing concentration with depth. Each line represents a different snapshot in time. e.g. 7 represents 7 days.

The next step once the model produces a scarily large table of numbers is to try and make some sense of what happened. The blue-green thing is nice, but it doesn’t give a whole lot of information about what is happening over time at different depths. With this table I can then make graphs showing the movement of my iodine over time into the vadose zone. As you can see the “peak” migrates downwards pretty rapidly and within just over a month has moved 7 metres! Of course, this result makes us all think that iodine infiltrates into groundwater really rapidly. The actual truth is not nearly so black and white however. In fact, if I tweak the parameter that controls how iodine sticks to soil I can prevent it from ever getting past the ground surface. This is why all models should be taken with several grains of salt. The input control the outputs, however, a small change in the input can result in a radically different output. Which is the truth??? Only observation and more modelling can tell us!

 

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#AESRC2014 Highlights

Well, AESRC is done for another year and with it my role as co-chair of the organizing committee! Thank goodness for that! Hopefully, I can finally get some actual thesis related work done in the coming months…and maybe get back to blogging a bit as well. However, as grateful as I am that AESRC is done, I have to say that it was a fantastic conference this year with a host of terrific talks from keynotes and grad students alike.

As I mentioned in my conference opening post AESRC is the only conference in Ontario, maybe Canada for all I know, that is organized by and for graduate students. The entire organizing committee is composed of graduate students and all of the talks, with the exception of keynotes, are given by graduate students. AESRC is meant to be a place where new and experienced grads alike can talk about their work in a less nerve-racking environment. We encourage in progress research or research that does not even have results yet. The idea is that every graduate student can feel comfortable, practice presenting to an educated audience and hopefully enjoy themselves and meet their colleagues from across the province.

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This AESRC was by far the most well attended in the past 10 years, with over 100 delegates attending from 8 different universities. The conference kicked off with the Icebreaker at a campus pub, where we all got meet each other or reconnect in many cases, while watching hockey and drinking beer. A nice relaxing end to the week and prelude to the science of the weekend. On a personal note, it is always worth attending the Icebreaker at every conference I have been to. More often than not there is free food and drink, but it is a great opportunity to meet new people, spot that keynote you want to talk with and introduce yourself. I try to make of point of meeting at least one new person at every Icebreaker I go to.

Saturday started with some great talk on Environmental Geoscience (my session) and Sedimentology and Petroleum Geology. We had two keynote speakers on Saturday: Paul Mackay from the Canadian Society of Petroleum Geologists and Dr. Jack Cornett from uOttawa. The video of Jack’s talk is below.

 

To summarize, in case you didn’t watch the entire video, Jack discusses the incredible range of radionuclides that are found naturally occurring on Earth and the vast range of geologic problems these nuclides can be applied to. He also talks about how we can use accelerator mass spectrometry to measure these radionuclides at incredibly low levels, which is how we are able to apply them to geologic questions. To illustrate this point Jack discussed the case study of chlorine-36 in the Cigar Lake uranium mine in Saskatchewan, Canada.

Saturday concluded with a fantastic dinner at the nearby National Arts Centre and another terrific keynote by Dr. Becky Rogala on the challenges of extracting bitumen from the oil sands and the importance of having an accurate understanding of the sedimentology to ensure maximum efficiency of SAGD recovery. There was also quite a bit of beer.

Sunday started nice and early with the Geophysics session as well as the Paleontology and Tectonics sessions as well. Our keynote for the geophysics session was Dr. Glenn Milne from uOttawa, who was an author on the most recent IPCC report and is an expert on sea level change.

 

We also had another great keynote from uOttawa in the tectonics session in Dr. Jon O’Neil. The video of his talk on the oldest rocks on Earth (4.4 billion years old) is coming soon! That pretty much wraps up AESRC2014! It was a great weekend, there was lots of great science and I am really glad its over. I likely won’t be around for next year’s AESRC at Queens University (fingers crossed), however, I am sure it will be great.

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Yours truly giving his talk on iodine-129 fallout from Fukushima. (Photo: Viktor Terlaky)

 

 

 

The Most Epic Unboxing Ever

The Most Epic Unboxing Ever

There is a strange phenomenon on the internet called unboxing. Unboxing is when a person receives a new package of something and takes a video or pictures of the process of opening it for the first time and posts it online.  Mostly, from what I can see, people “unbox” electronics or hockey cards or things of that nature. However, what I have today could be called the granddaddy of all unboxings; I have a series of photos of the unboxing and, initial stages of set-up of the University of Ottawa’s new, 3 million volt, accelerator mass spectrometer (AMS), which cost 5 million dollars. This takes opening your new laptop or that Sidney Crosby rookie card to a whole new level!!! The AMS will be housed in uOttawa’s new Advanced Research Complex.

The accelerator portion in its shipping container being transferred into our new building. (Photo: Dr. Liam Kieser)

The accelerator portion in its shipping container being transferred into our new building. (Photo: Dr. Liam Kieser)

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Easy does it. Now pivot!!! (Photo: Dr. Liam Kieser

Since I am showing pictures of this incredible piece of equipment being installed I’ll explain a bit about what it is an how it is used as well. I use the AMS in my own work to analyze iodine-129, chlorine-36 and once or twice carbon-14. In short, tools that can be used for groundwater dating. However, the AMS is capable of analyzing for a huge range of isotopes and this allows its use a wide variety of disciplines from health science to homeland security.

The AMS works on the same principles and a regular mass spectrometer, but it has a few key differences that make it extremely powerful.

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Lots of boxes to open. (Photo: Dr. Liam Kieser)

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Once the boxes have been unloaded the building begins. It is like building an IKEA desk, but somehow more… (Photo: Dr. Liam Kieser)

The process of AMS analysis begins with the preparation of the samples, which involves large amounts of lab time in extremely clean conditions. Contamination of samples with unwanted isotopes is a real problem in AMS so great care has to be taken to prepare good samples. The sample is then mixed with niobium powder and pressed into a steel cartridge. The cartridge then gets loaded into the ion source where cesium ions get fired at the sample like shooting a gun. The Cs ions physically break bits of the sample off the cartridge and these get negatively ionized and accelerated out of the ion source towards the first magnet. 

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Xiao-lei carefully taking the glass rings that are in the accelerator. These are to kill any free electrons that could escape from the stripper canal as well as keep the ions on a stable flight path. X-rays charged to 3 million volts are very bad! (Photo: Dr. Liam Kieser)

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The glass rings all put together with the stripper canal in the centre. The stripper canal is where electron get stripped off the negative ions turning them into positive ions as well as keeping the ions on a straight and even flight path. (Photo: Dr. Liam Kieser)

This is what the ion source looks like. Up to 200 samples sit in the big wheel waiting their turn. The AMS control room is those windows in the background.

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Our fancy new SO-110 ion source. (Photo: Matt Herod)

Once the samples leave the ion source they are accelerated to the first bending magnet which can bend an incredible range of masses. From tritium to plutonium tri-fluoride.

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The first magnet looking towards the accelerator. (Photo: Matt Herod)

The next step is firing the ion into the particle accelerator that carries a charge of 3 million volts! Inside the accelerator is a passage called a stripper canal that pulls electrons off the ions turning them from negative into positive ions. The reason for this is that this allows us to get rid of interferences that normal mass spectrometers face. For example, chlorine-36 has an interference with sulphur-36 making it impossible to analyse using normal mass specs. Actually, our AMS has another modification that makes 36Cl analysis possible on a 3MV machine, which is generally considered too small for this isotope. Usually, 36Cl needs a much larger accelerator however, our isobar separator for anions (ISA) allows this. Once the ion leaves the stripper canal it is accelerated at very great speed into the next magnet.

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Dunh, dunh, dunh. This is the A in AMS! (Photo: Matt Herod)

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This is the biggest magnet I have ever seen!! It is over 3m long and weighs 18 tonnes! This is why the room needs an overhead crane. (Photo: Matt Herod)

Once the ions are redirected and isotopes are further separated by the magnet they are ready to be analyzed in either the Faraday cups for the common isotopes or the gas ionization detector for rare isotopes.

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Me, touching the Faraday cups. (Photo: Laurianne Bouchard)

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The gas ionization detector. This bad boy literally counts atoms as they come around yet another magnet and through a silicon nitride window. Once they enter the detector which is filled with gas they ionize it which leads to pulses of electricity that are counted. This is the end of the AMS!!! (Photo: Matt Herod)

Once the atoms are counted in the gas ionization detector their trip around the AMS is over! It is quite a journey and full of positives and negatives (haha, a little pun there). Seriously, though this gigantic instrument is used to quantify the smallest of small quantities and can very literally count atoms. The AMS has a massive number of possible uses and I’ll likely be posting about these as this new facility starts to ramp up in the next few months. In addition to the AMS we also have an SEM, microprobe, stable isotope equipment, two noble gas mass spectrometers, ICP-MS, LA-ICP-MS, ICP-AES and a host of other MS’s as well. There will be very few types of isotopes that we cannot analyze for and this facility will be one of the best in the world for this type of geological research. Stay tuned for further developments as we start to move in soon!

Cheers,

Matt