Science/DGR Canisters at the Finnish DGR


Written for Canadian Community News by Mike Sterling

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An interesting part of Mr. Jackson's talk at the April 7th meeting at the Southampton Town Hall sponsored by SRA and SOS was directed at disagreement about certain issues in the Deep Geologic Repository studies. 


Feature  Town Hall meeting in Southampton looks at nuclear storage Read More

Mr Jackson the guest expert said:

"There is no doubt that safety is now a world issue," Jackson pointed out, "but when it comes to materials for canisters, etc., it's still a debate.   We have computerized predictions and models but the problem is, we don't have the real life experience of dealing with high level radioactive waste to predict what the impact will be.  It becomes guess work not based on reliable experience. "

Later he said "Don't be fooled by the science ... it is not clear and there is a real diversityOne assumes this is a general comment and not directed at a single issue, but he did bring up canisters.

Looking at the Data

I have been intrigued by the now in progress effort by Finland to establish their own DGR for only their  waste.  I had noticed that they were using thick, pure copper containers for the DGR storage of their own waste.

Video Explaining Finnish DGR

Note the huge white canister that is much like those used at the Bruce to store waste fuel after some six years in water storage and the copper container that the Finnish have selected for their DGR.

This led me to think about that selection and ask myself why copper?  Maybe Jackson's talking about that?  He was not specific, but it won't hurt to see what others say about the Finish selection.

Before I dove into the research, I decided to think about copper relative to what I  knew about it.  Jackson never mentioned copper, but he did mention the material of the container as you can see from the above quote.

My question to myself was: "Why copper and why not some other more exotic alloy or metal for the Finnish project?  How about some sort of composite?

I began to list things I know about copper:

  • It's mined at depth and comes out for our use.

  • The Chantry Island Lighthouse Lantern Room top is made of it and it's lasted since 1859.

  • It's been in the ground more than a 100,000 years for sure, so no problem there.

  • The mining industry must know a lot about copper.  After all it does not come shrink wrapped from WalMart.  They must know how other chemicals effect copper in situ.

  • I've done a weathervane Venturi made of copper and it created a nice patina and changed colour.  Where I used screws made of steel with it, they are a mess, but the copper is fine out in the elements, but that's just 12 years so far for me.

  • A large copper ingot was discovered north of the Saugeen by my friend Jim Seaton.  It must have been brought here by Lake Superior traders hundreds of years ago.  It rested in the water ever since.  I see it all the time at the Bruce County Museum.  It has that same patina and looks great.

  • They used to use copper for eaves because they stood up over time.

Ok, so what?  That's all silly nonsense, with no specifics and I can't trust my eyes and intuition.  

We're not talking about 12 years or 200 years, we're dealing with 100,000 years in the case of the design specs for the Finish DGR.

I did not want to jump into Google in general because I'd get too many hits, so I decided to go to the NWMO site to see what they had to say about copper relative to 100,000 years and a DGR.  I entered the single word 'copper'

I was surprised, but I guess I should not have been.

They have a great search engine on the NWMO site.   Wow!  I got 225 results in 1/3 of a second. 

The very first reference was entitled:

"Status of Corrosion Studies for Copper Used Fuel Containers Under Low Salinity Conditions"

Wow again!  I struck pay dirt and its from June 2011.  Here is what followed:

Abstract (by Gloria M. Kwong)

Copper has been studied as a corrosion resistant material for used fuel containers in the Canadian nuclear waste management program. Over the past 20 years, many studies have been carried out on the corrosion behaviour of copper under anticipated low salinity conditions that could be found in a deep geological repository in crystalline rock. The subject of copper corrosion has also been extensively studied in the Swedish and Finnish nuclear waste management programs as copper is also specified in their canister designs.

This report summarizes the state of understanding of the long-term behaviour of copper under low salinity conditions from these studies and what the implications are for the predicted service life of the container in a deep geological repository. The key findings include:

  • Copper will corrode under atmospheric conditions (at a relative humidity > 50-70%) and the rate and mechanism of corrosion will be affected by the presence of atmospheric contaminants.
  •  A copper used fuel container in a deep geological repository will experience an initial
    short period of uniform corrosion leading to some surface roughening under aerobic conditions, but once long-term anaerobic conditions are established, it will become
    thermodynamically stable in the absence of sulphide.
  • Stress corrosion cracking on a copper used fuel container is unlikely due to the lack of:

(i) the required threshold concentration of stress corrosion cracking agents;
(ii) a suitable interfacial pH, and
(iii) the required corrosion potential on the copper surface. The elevated Cl and initially the elevated temperature will also lower the probability of stress corrosion cracking.

  • Microbiologically influenced corrosion is expected to be controllable through the use of compacted bentonite to suppress microbial activity in the near field. The knowledge gained over the past 20 years from studies on the corrosion of copper has allowed predictions of the lifetime of a copper used fuel container in a deep geological repository. Under low salinity groundwater conditions, a realistic estimate of copper corrosion from all processes is about 1.27 mm in 1 million years in a deep geological repository.

Therefore, the lifetime of a copper used fuel container is expected to exceed 1 million years in a deep geological repository in crystalline rock. This finding is consistent with the predicted container lifetime for the Swedish deep geological repository in crystalline rock.

End of Ms. Kwong's Abstract

That's good!  1 million years.

The paper continues with formulas and many references to other studies world-wide.  This type of study gets published and is peer reviewed as one can gather by reading the entire article and references at the end.  Does anybody disagree world-wide?  I don't know.

So, now I see why Finland selected copper.  But, back to Mr. Jackson's point. 

Could there be disagreement with other scientists?  I suppose so, but the biggest issue has to do with the digging of core samples in a selected site, so scientists would be cautious about copper without the data of the questioned site and they would want to know things like the pH of water at the depth of the intended DGR and other contaminants.  The Finnish scientists did all that for their proposed site.

See more in the 2nd column

Mr. Jackson's strong statement "Don't be fooled by the science ... it is not clear and there is a real diversity" was not near his thoughts about materials.  I have to assume this is a general statement.

He did say, however ....  "but when it comes to materials for canisters, etc., it's still a debate.

I don't know whether he meant in general for sites not core sampled or for sites with the wrong pH or whatever.  He just had no detail that he presented.  Maybe it was because of the general audience, which is ok or maybe he had not studied the site in Finland for that kind of detail.  He had no obligation to bring up Finland at all, other than it is the most advanced site in the world now.

Based on what Ms Kwong says, it seems that the science is full blown and robust, however.  Do I believe her?  Yes, I guess I do.  I can't do the experiments myself, so does this mesh with what I know about copper.  Yes, it does.  I prefer to leave my intuition at the door, however, and believe what she says.

Would  NWMO select copper?  This is not at all clear due to what the samples would look like and the state of the research at the time of any build at any site.  Maybe there is another metal or alloy that would be better.

It does explain in part NWMO's lengthy site selection criteria.

The advantage of copper is that given the chemical conditions, there is a vast amount of data from the mining industry about it from its in situ position. The chemistry is well known and experiments have been done all over the world.  That's good news for not 100,000 years for the Fins, but a Million years. 

I need to study the NWMO site in more detail and other sites from other countries.

I think before we move away from canisters, we should examine the above ground ones that are used at the Bruce.  Most industry experts say that they are not good for use in a DGR, nor are they certified for above ground storage untouched for hundreds of years.  They need close monitoring and this is to be expected.

Next we'll look at above ground storage because that was Mr. Jackson's strong recommendation.  We'll see how that meshes with what the scientific community says.  Stay tuned ... 

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Friday, April 13, 2012