A Review of the Swedish KBS-3 Plan for Final Storage of Spent Nuclear Fuel (1984) / Chapter Skim
Currently Skimming:
'Adequacy of Treatment of the Physical and Chemical Stability of the Canisters and Buffer'
'Adequacy of Treatment of the Physical and Chemical Stability of the Canisters and Buffer'
Pages 30-41
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 30... ...
Major considerations are the feasibility of canister construction, the mechanical behavior of canisters enclosed in compacted bentonite, the resistance of the canisters to corrosion and to stress-corrosion cracking, and the ability of the bentonite buffer to control access 30
|
From page 31... ...
Instead of molten lead, copper powder would be used to fill the remaining space in the canisters, after which they would be sealed and the copper powder compacted by hot-isostatic pressing. This process uses a combination of high temperature and isostatic gas pressure (usually an inert gas)
|
From page 32... ...
Whether this method or the molten lead method will ultimately be favored remains uncertain, but KBS scientists in conversation (September 1983) expressed a preference for the copper powder method.
|
From page 33... ...
While agreeing with Pusch that uncertainty about the response of tightly held canisters to sudden displacement is a real weakness in the KBS program, the panel notes that the probability of rock movement in precisely the right orientation and of the right magnitude and suddenness to do appreciable damage is exceedingly slight. Earthquakes in Sweden are uncommon, and recorded rock displacements of the last million years that can reasonably be ascribed to earthquake activity are nearly all along planes that are steeply inclined rather than horizontal.
|
From page 34... ...
. Dissolved oxygen will be significant for a time after repository closure, because of residual air in all unfilled openings and in interstices of the backfill; but after natural groundwater conditions are reestablished, dissolved oxygen content will be kept very low by reaction with minerals containing ferrous ion in the surrounding rock.
|
From page 35... ...
Earlier, the addition was intended to ensure that groundwater in the repository would remain reducing. Omission of the reductant in KBS-3 is in part the result of calculations showing that ferrous ion derived from iron minerals in the bedrock is sufficient to maintain reducing conditions, and in part a response to concern that addition of yet another chemical species to the repository environment would complicate its chemistry unduly (TR-83-36)
|
From page 36... ...
The ability of canisters surrounded by compacted bentonite in Swedish bedrock to last for a million years and more seems adequately documented -- provided, of course, that the canisters are made according to rigid specifications and that the subsurface environment is not subject to radical change. STRESS CORROSION CRACKING Will the canisters be immune to stress corrosion cracking for a million years?
|
From page 37... ...
(TR 83-06) , however, showed that the electrochemical conditions necessary to stimulate cracking of pure copper in dilute sodium nitrite solutions are so remote from conditions expected in a repository that they eliminate stress corrosion cracking of the canisters as a source of concern.
|
From page 38... ...
. As noted in the section in Chapter 3 entitled "Mechanical Capability," the protection against slow moderate displacement is adequate, but a question remains about possible rupture of a canister by rapid horizontal rock movement of more than 0.01 m.
|
From page 39... ...
give experimental values for hydraulic conductivity: With 10 percent bentonite, at a density of 2.1: 10~9 m/s With 20 percent bentonite, at a density of 2.1: I0-10 m/s In similar experiments, Peterson and Kelkar found With 10 percent bentonite, at a density of 1.98: 6.1 x 10~9 m/s With 30 percent bentonite, at a density of 2.29: 2.2 x 10~12 m/s The agreement is satisfactory, and the range of values is similar to that for the matrix of granitic rock between major fractures. This finding indicates that the backfill in tunnels and shafts will have a permeability comparable to that of its surroundings.
|
From page 40... ...
The composition of bentonite can be somewhat modified, if desirable, by currently available commercial processes: sodium may be substituted for calcium, and much of the sulfide and organic impurity can be removed by several hours of oxidative heating to about 400°C. At the time of the KBS-2 plan, Pusch had reservations about the possible effect of heating bentonite to 400°, on the grounds that its structure might be irreversibly altered and its expansive properties impaired; but results of recent experiments have convinced him that the change in properties is minor if the heating is not continued too long.
|
From page 41... ...
41 nical documents effectively support the KBS claims that, in the system of copper canisters plus bentonite, the canisters are adequately protected from corrosion and stress. The swelling pressure, bearing capacity, and plasticity of the bentonite will provide good mechanical protection; its low hydraulic conductivity will serve as a barrier to active groundwater flow and will maintain a controlled low-corrosion environment immediately adjacent to the canisters.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.