A Review of the Swedish KBS-3 Plan for Final Storage of Spent Nuclear Fuel (1984) / Chapter Skim
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'Adequacy of Treatment of Geology and Hydrogeochemistry'
'Adequacy of Treatment of Geology and Hydrogeochemistry'
Pages 14-29
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From page 14... ...
The purpose of this chapter is to take a fresh look at the KBS-2 report conclusions in the light of research over the past five years. REPOSITORY SITES Can bodies of crystalline bedrock be found in Sweden of sufficient size and sufficiently low permeability to serve as repository sites?
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From page 15... ...
The KBS authors concluded that the number and permeability of fractures at three of the areas made them questionable as repository sites, but the Karlshamn area appeared to have a volume of sound rock large enough, although barely so, to accommodate a repository. The NRC subcommittee concurred in this evaluation of the geologic data.
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From page 16... ...
Hydraulic conductivities -- both specific values for individual fracture zones and average values for large volumes of rock -- are measured by standard techniques on sections of the boreholes isolated by packers. Application of these various techniques by Swedish geologists and geophysicists, as described in KBS-3 and its supporting technical documents, is fully up-to-date and consistent with modern practice in other countries.
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From page 17... ...
To demonstrate that suitable repository sites can be found, therefore, requires that detailed information be acquired about amounts, movement, and chemical composition of groundwater at each candidate site. Efforts to obtain such information have been a major part of the KBS project, assigned by the KBS staff to geologists, hydrologists, and geophysicists of the Swedish Geological Survey.
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From page 18... ...
The authors of KBS-2 were well aware of the difficulties they faced in predicting groundwater conditions at depth from surface and borehole observations, and critics of the KBS-2 plan identified this as one of its most vulnerable parts. The NRC subcommittee, after extensive review of the technical documents and conversations with the KBS investigators, decided that the geological and hydrological work was well done, that enough conservative assumptions had been made to compensate for the uncertainties, and that the measurements were "adequate to ensure that the quantity of water reaching the copper canisters in a well constructed repository will not be damaging." The additional work reported in KBS-3 is not qualitatively different from that done earlier, but the methods of measurement have been refined and abundant new data have been gathered.
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From page 19... ...
The curves permit estimates of average hydraulic conductivities for different depth ranges in the rock, but many points deviated considerably from the averages indicated by the curves.
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From page 20... ...
This includes unpublished analyses of measurements at the four recently studied sites (Hans Carlsson, KBS, personal communication, 1984) and an additional unpublished study at the Stripa experimental facility (Leif Carlsson, Swedish Geological Survey, personal communication, 1983)
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From page 21... ...
To calibrate and validate numerical models, extensive field data are needed, especially data on groundwater heads over time. Such data were not available prior to preparation of the KBS plan.
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From page 22... ...
Thus, in the Panel's opinion, the flow rates calculated in KBS-3, although subject to a good deal of uncertainty, are derived by reasonable methods of calculation using the available data. Studies of groundwater chemistry, like studies of groundwater motion, have added little that is new between KBS-2 and KBS-3, but they have introduced significant refinements of method and have added greatly to the data base (KBS-3, p.
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From page 23... ...
Uncertainties still remain about interpretation of the widely variable values for hydraulic conductivity and about the validity of using Darcy's law for calculating flow in fractured rock; but the uncertainties have been narrowed by comparing results of different measurement methods, and they can be partially compensated for by use of conservative values. The panel agrees with the KBS scientists that the accumulated evidence at most of the sites selected for detailed study points strongly to groundwater behavior and groundwater composition favorable to the location of waste repositories of the kind envisioned in the KBS-3 plan.
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From page 24... ...
indicated that recent experimental work at Stripa has verified earlier predictions that the very localized fracture enhancement near shafts and tunnels would not greatly compromise the low hydraulic conductivities of the rock matrix and thereby disrupt the existing regional flow. A recent study of thermal circulation by means of a mathematical model (TR 80-19)
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From page 25... ...
; and where resulting fault displacement from individual quakes can be found, it is limited to a few centimeters, again on a few of the ancient fault lines. From such evidence, the KBS-2 authors concluded that repositories placed well within the stable blocks are in little danger of disruption by tectonic movement -- either slow deformation or the sudden displacements accompanying earthquakes -- and the earlier NRC subcommittee agreed that evidence for the conclusion was convincing.
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From page 26... ...
Bath noted also that seismic activity is concentrated in a zone running north-northeast through central and eastern Sweden, close to the Baltic shore north of Stockholm. It is doubtful that earthquakes would appreciably damage a repository built within a stable block, even if it were located in this seismic zone (as it would be at Gidea or Kamlunge)
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From page 27... ...
Bath speculated that this is a region where plate motion eastward from the Mid-Atlantic Rift abuts motion southward from rifts in the Arctic Ocean. In any event, these faults are far from any of the studied repository sites except Kamlunge, and no post-Pleistocene displacements nearly this large are known in other parts of Sweden.
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From page 28... ...
Not only were the expectable surface erosion and deposition by the ice and its accompanying meltwaters a subject of exhaustive study, but also the effects on groundwater, the effects of the weight of ice on bedrock at depth, the bowing down of the land suface beneath a thick ice cap and the consequent probable incursion of seawater, and the generation of earthquakes by the shifts in mass as the ice waxed and waned. The general conclusion was that a repository, properly located and constructed, would not be adversely influenced by any of the phenomena accompanying advance and retreat of an ice sheet, or even by the many advances and retreats that can be anticipated during the next million years.
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From page 29... ...
Such possibilities seem remote, but to prove them completely out of the question is difficult. The KBS scientists further considered the influence of the ice front, in an effort to derive possible consequences and to set rough limits, but they concluded that loosely constrained variables are so numerous that the effort is futile (Leif Carlsson, Swedish Geological Survey, personal communication, 1983)
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