Klik på foto for artikler om Covra - Hollands langtidsmellemlager for radioaktivt affald

tirsdag den 9. juni 2015

Atomaffald: Om Mellemlager og Slutdepot af Gerhard Schmidt Öko-Institut

I forbindelse med resuméet af Sundhedsministeriets møde med de kommunale kontaktpersoner 22. maj 2015 har den tyske ekspert ingeniør Gerhard Schmidt fra Öko-Institut i Darmstadt sendt følgende kommentar:

Searching for a new location for interim storage should not be confused with the question of long-term storage or disposal. Because the Risoe storage is insufficiently flood-protected and because siting, planning and construction of a repository requires in any case longer than twenty or thirty years, another storage location is necessary in any way. Whether this storage is called "long-term" or "guarded" or whatever is completely irrelevant. As both, 20 or 30 years long storage as well as e.g. 100 year storage, require the ability to repair packages, to overpack those or to repackage them, such handling facilities are necessary either way. So, selling this as a concept is a little bit overstated.

And of course, barrels or containers are at best good for 20 years of storage. Inner and outer corrosion limit the lifetime. If they are coated with >1 mm of plastic on the inside they might as well withstand inner corrosion for some more years. But only if the waste product is chemically inert and does not release too much water. Outer corrosion depends from the thickness/quality of the cover layer (mostly paint), the handling and processing defects in that layer as well as the ageing of that layer, from water evapotranspiration and dew (day/night temperature swings) and from the chloride concentration in the ambient air. Enhanced corrosion prevention requires expensive package material and quality.

Corrosion of barrels/containers is at first a problem of later handling of that packages. If seriously corroded packages are handled, the package can fail massively and release its content. Most of the Danish wastes are in a form that does not aggressively release gases or aerosols or dust particles, but massive corrosion can increase those radioactive losses to the ambient air in the storage facility.

The main problem in the discussion is the confusion that is made in Denmark on final disposal. As their final disposal definition includes disposal at surface- or in a low depth and no further requirements than respecting an individual dose limit are set, there is no real substantial difference between interim storage and final disposal. Most of the confusion results from this inappropriate discrimination between the two basic concepts. As long as they advocate for this inappropriate "repository" concept ("in any case at small depth") they can as well name it "interim storage". Nobody, including themselves, really understands the difference then. So, the meetings, on and on, will circle around a myth, will neverendingly produce questions, will be more and more confusing and will further go away from the center of the basic questions and obligations.

It is so easy:

Q1. Question: Are the Danish wastes short-lived, that is: do they decay to below safe levels within a period of 500 years.
A1: Answer: No, 17 of 19 of the waste types are not short-lived, only 2 of the 19 are.
C1. Consequence: The wastes require geologic disposal. That is: their long-term enclosure has to be guaranteed by a geological isolation system.

Q2: Are the Danish wastes decayed to below safe levels before the next massive ice age is to be expected? (10,000 to 15,000 years)
A2: No, 17 of the 19 waste types are not decaying to below safe levels within this time period. (If in a future ice age, e.g., packages would reach the surface or would destroy isolation layers, this would have unacceptable radiological consequences.)
C2: The geological isolation systems have to be inert against future ice ages in Denmark to guarantee safe enclosure over the long term.

Q3: Are geologic isolation systems potentially available in Denmark that were not affected by past ice ages and will be inert against future ice ages?
A3: Yes, there are such promising layers. Generally, Danish geology was affected by past ice ages down to approximately 100 m depth. Below this depth well-isolating clay layers are available. 
And: the deeper the clay layer the more consolidated is the clay and the easier is it to drill shafts and tunnels. There is no need to look at heavily fractured bedrock or other layers.
C3: It is possible and appropriate to search for such isolation layers, to characterise them for their suitability for final disposal and finally to construct a repository.

Q4: Is it possible to place all different waste types into a single geological isolation system or do different waste types require specific solutions?
A4: If the selected isolation system is geologically stable and able to enclose the five most relevant waste types, it can also enclose all other waste types as well.
C4: Denmark needs only a single repository for its waste and there is no need to explorate specific solutions for single waste types.

Q5: What is the advantage to store these wastes in a surface facility over a longer time period?
A5: Interim storage allows for a thorough selection, planning and construction of a repository and to perform the associated consultation processes. The wastes should not be stored over periods beyond that necessary time, because their extended decay has no relevant radiological advantage and only increases the risk of package corrosion and massive release events.
C5: As a geological repository for the waste is necessary in any way and unavoidable, the time necessary to set-up the repository should determine the necessary storage period. Arbitrarily selected storage periods point the focus away from the necessity for a repository.

Confusion is, if one ignores Q1 and Q2 completely. Then all following answers are: "Anything goes", "Do what you want", or "We are just playing around a bit with those wastes, with no clue on what is really to be done with them".






Ingen kommentarer:

Send en kommentar