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1 INTRODUCTION Current plans for the development of nuclear energy in Sweden call for a total of 12 reactors to operate for a limited period. All reactors are to be decommissioned by 2010, and at about this time entombment of high-level waste in a repository or repositories constructed in Swedish bedrock is expected to begin. No decision has been reached as to whether the waste will consist largely of spent fuel rods or solidified reprocessing waste, but plans are being developed for handling both kinds. After the first six reactors were in operation, questions arose about the safety of contemplated waste disposal techniques, and the Swedish Parliament in 1977 passed a law (the "stipulation law") mandating that an "absolutely safe" method of disposal be demonstrated before governmental permission would be granted for the loading of fuel into any additional reactors. To assist in complying with the law, the Swedish nuclear power util- ities set up a special organization, Karnbranslesakerhet (KBS). The organization has since become a department of the Swedish Nuclear Fuel Supply Company (Svensk Karn- brMnslef6rs6rjning (SKBF)), which is jointly owned by the utilities. The KBS organization, enlisting the aid of scientists and engineers from academia, industry, and government agencies, put together in remarkably short time two reports with accompanying technical documents intended to show that safe disposal could indeed be accomplished. The reports are Handling of Spent Nuclear Fuel and Final Storage of Vitrified High Level Reprocess- ing Waste, known as KBS-l, dealing with vitrified reprocessing waste (late 1977), and Handling and Final Storage of Unreprocessed Spent Nuclear Fuel, known as KBS-2, dealing with spent fuel elements (late 1978). On the basis of KBS-1 and supplementary material the govern- 8
ment granted permission for loading fuel into four additional reactors. Of the planned dozen, therefore, 10 reactors are now in operation, and it is planned that the two remaining reactors (Forsmark 3 and Karlshamn 3) will be ready for fueling in 1984. Because the KBS-2 documents are now five years old, the government requested KBS to prepare a new report to update the demonstration that safe disposal of radioactive waste is possible, before permission for fuel loading is given. This new report is entitled Final Storage of Spent Nuclear Fuel, and is known as KBS-3. According to changed legislation, expected to take effect in early 1984, the requirement for demonstration in the new report is not quite as stringent as for the earlier ones: rather than requiring "absolute safety," the government can now decide to grant a fueling license if the waste-handling plan presented by the plant owner "... offers a point of departure which, after carrying out appropriate research and development activities during the next few decades, is certain to provide a safe method for spent-fuel and reactor-waste management and final disposal" (Jan Magnusson, Swedish Ministry of Industry, personal communication to Peter B. Myers, staff director of BRWM, 1983). Actually, the change makes little difference, because in practice the stipulation law has been interpreted along the lines of the new legislation. To help in evaluating the conclusions reached in KBS-1 and KBS-2, the Swedish government invited reviews from many individuals and institutions both in Sweden and abroad. The National Research Council (NRC) agreed to make such a review of KBS-2, assigning the task to a subcommittee of the Board (then Committee) on Radioactive Waste Management (BRWM) and the review prepared by this subcommittee (NRC, 1980) was published in 1980. With their publication of KBS-3 in May of 1983, the Swedish authorities again sought external evaluations, and the NRC again agreed to undertake a review. The review was entrusted to a new panel of the BRWM, and the current report is a product of this panel's study. To ensure that the review would be consistent with the earlier one and with current thinking about waste management and disposal in the BRWM, the panel was set up to include two members from the KBS-2 subcommittee and two from the BRWM panel that prepared the recently published Study of the Isolation System for Geologic Disposal of Radioactive Wastes (NRC, 1983).
10 Like the KBS-2 review, the current review was limited in scope by the shortness of time within which it had to be completed. According to the Panel's charge, . . . review time and resources (should) be applied principally to a review of those portions of the report which relate to the geological repository features of the disposal system. This would include consideration of overall canister and repository design, as well as the calculations and supporting data related to waste-form dissolution and to radionuclide migration from the point of emplacement through the surrounding geosphere. Excluded from consideration here are many parts of the KBS-3 plan: technical details of handling and storing the waste, the separate facility for irradiated metal parts of fuel assemblies, the interim storage facility, and costs. The panel's focus was on the long-term integrity of a bedrock repository in Sweden, the long-term integrity of copper canisters enclosed in a bentonite buffer, the movement of groundwater, and the movement of radionuclides in groundwater in the event that a canister is prematurely breached. These topics, in the opinion of the BRWM, are critical to a judgment about the functioning and effec- tiveness of the waste-isolation system. Because the KBS-3 report is largely an update of KBS-2 with a substantial amount of new material added, this review of KBS-3 is in effect a supplement to the KBS-2 review. There seems little need to repeat here the back- ground material from the earlier review or those parts of the earlier document where neither the KBS data nor the reviewers' opinion regarding them has changed appreciably. Emphasis in this review is on the considerable expansion of the technical data base by Swedish scientists and engineers since KBS-2 appeared, especially on an evalua- tion of the extent to which this recent work has filled gaps in data and supplied additional evidence about questionable aspects of the earlier conclusions. The general outline of the present review follows closely that used for the review of KBS-2, and much of the argument here depends on evidence presented more fully in the pages of the earlier document. It should be emphasized here, as it is in the KBS-2 review, that the task undertaken by the authors of the KBS plans was not to describe how and where an actual repository should be constructed, nor to devise the best
ll possible or most cost-effective repository, but rather to show that development of a safe method for disposing of radioactive waste in Sweden is possible. This means that reviewers need not be concerned with costs of the proposed disposal method, except in a very general way, or with comparisons of the Swedish method with others that might be better, or with suggestions for possible improvements. The problem for reviewers is to judge how effectively the KBS authors have marshaled technical and scientific evidence in support of their conclusion that a repository for the safe disposal of high-level waste can be con- structed in Swedish bedrock. Like the KBS-2 subcommittee, the present KBS-3 panel has had to depend for its information almost entirely on sources provided by SKBF that are favorable to the KBS program. The sources are voluminous: they include the five volumes of the KBS-3 report itself ("Summary," "General," "Geology," "Barriers," and "Safety"), the supporting KBS technical documents published since 1979 (25 in 1980, 16 in 198l, 28 in 1982, and more than 70 in 1983), reports from the research program at the Stripa mine (formerly a Swedish-American cooperative venture, now an international research program), and articles in the standard scientific literature. In addition, the panel benefited from a day-long question-and-answer ses- sion with eight of the principal authors of the technical documents and from subsequent telephone conversations. One panel member had follow-up conversations with indi- viduals. The Panel had no first-hand contact with Swedish laboratories or repository sites, although two of its members had visited Sweden earlier as part of the KBS-2 subcommittee. Although one critic provided written material and met with the panel, the panel had no other opportunity to question individuals, Swedish or foreign, who are critical of some of the KBS-3 conclusions. The heavy dependence on data and opinions from enthusiastic advocates could easily lead to unconscious bias, but the panel tried to avoid this by maintaining a hearty skep- ticism, by perusing critical comments in previous reviews of KBS-1 and KBS-2, and by querying the Swedish experts as to their own opinions of weaknesses in the program. Because the quantitative data could not be directly checked, this review necessarily consists, like its predecessor, primarily of the panel's subjective evalu- ation of the quality and completeness of the Swedish research and the logic used in relating the research to the conclusions drawn.
12 In its general outline the KBS-3 plan for disposal is no different from that described in KBS-2: spent fuel rods are to be stored for a 40-year cooling-off period in an intermediate facility a few tens of meters below the ground surface and then moved to a repository site where they will be encapsulated in copper canisters; the can- isters will be lowered into a bedrock cavity some 500 m under the surface, placed in holes drilled into the floor of the cavity, and surrounded with blocks of compacted bentonite; and, finally, the cavity, shafts, and boreholes will be filled and sealed with mixtures of bentonite and sand. Principal reliance for isolation of the radio- nuclides is placed on the durability of the copper can- isters for very long periods, in an environment where the temperature remains below 100Â°C, where groundwater is noncorrosive, and where the flow of water past canister surfaces is negligibly small. The geologic surroundings are also expected to retard effectively the movement of radionuclides to the biosphere, but only as a sort of insurance against early breaching of many canisters. A few specific changes in the KBS-3 plan are noteworthy: walls of the canisters are to be 0.1 m thick rather than 0.2 m, copper is suggested as an alternative to lead for filling the canisters around the fuel rods, and the addition of ferrous phosphate to bentonite backfill as a control on redox potential of the groundwater has been eliminated. A more important new aspect of KBS-3 and its technical support documents is not a specific change, but simply the wealth of additional detail that has been supplied in support of conclusions about the availability of suitable repository sites, the durability of copper canisters under repository conditions, and the slow move- ment of radionuclides that may escape into groundwater should some of the canisters be breached. An evaluation of these new results of continuing research is the main objective of this review. This review, like its predecessor, is organized around three major topics: the adequacy of technical and scien- tific data on the geology and hydrogeochemistry of the sites suggested as suitable for repository construction; the adequacy of metallurgical data on the mechanical properties and corrosion resistance of the copper canis- ters in the expected geologic environment; and the adequacy of the data describing the possible movement of radionuclides in groundwater when the canisters are ultimately breached. These topics are considered in the following three chapters of the review.
13 The five-volume KBS-3 report in which the disposal plan is decribed, "Final Storage of Spent Nuclear Fuel," is referred to in this review simply as KBS-3; its 1978 two-volume predecessor, "Handling and Final Storage of Unreprocessed Spent Nuclear Fuel," is referred to as KBS-2. References to the KBS technical documents on which this report is based are given in the form TR 82-1l, the first two digits of the number indicating the year in which the document was written. References to standard literature are given in the name-date form (e.g., Ander- son, 1979), and complete references are listed at the end of the review. Two differences in nomenclature between KBS-2 and KBS-3 should be noted: "permeability" in KBS-2 (and in the KBS-2 review) is changed to "hydraulic con- ductivity" in KBS-3, and the "bentonite overpack" is changed to "bentonite buffer." Both of these changes are in accord with current international usage, and the new terms are used in this review.