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Panel Report

Appendix L - Various Approaches to Long-Term Management of Nuclear Fuel Wastes

It will examine AECL's proposed concept along with other approaches for nuclear fuel waste disposal being developed elsewhere in the world. . . . In its review, the Panel will take into consideration the various approaches to the long-term management of nuclear fuel wastes which are presently being stored at reactor sites. These long-term management approaches include long-term storage with a capability for continuing intervention in the form of monitoring, retrieval and remedial action; and the transition from storage to permanent disposal.

Terms of Reference

Elsewhere, the Terms of Reference also instruct the Panel to examine "the impact of recycling or other processes on the volume of wastes." Since treatments such as reprocessing, recycling and transmutation could form part of a long-term strategy for managing wastes, we examine them below, alongside the other options.

We were not asked to propose a different method for long-term management of spent nuclear fuel, but to be aware of the alternatives when formulating recommendations on the safety and acceptability of AECL's concept and on future steps. However, judging the safety and acceptability of one method selected in 1978, rather than deciding which of the feasible options available today was the most safe and acceptable, was problematic for both the Panel and the public.

Some participants felt that it was inappropriate or even impossible to gauge the acceptability of one option without information adequate to compare its acceptability with that of all possible options. In the words of a U.S. National Research Council panel reviewing the management of nuclear defence wastes in that country, "it is unsuitable to foreclose any technology or alternative before the various benefits, risks, and costs have been thoroughly delineated and carefully reviewed." [National Research Council, 1992, cited in Committee on Remediation of Buried and Tank Wastes, Board on Radioactive Waste Management, Barriers to Science: Technical Management of the Department of Energy Environmental Remediation Program (Washington: National Research Council, 1996), p. 9.] One participant reasoned that, since there is no good solution to the waste problem at present, "we are going to have to choose a least bad option rather than a good one." [Ann Coxworth, in Nuclear Fuel Waste Environmental Assessment Panel Public Hearings Transcripts, March 11, 1996, p. 340.] Other participants argued that it was unfair and unethical to evaluate a waste management option without examining the pros and cons of the entire nuclear fuel cycle and comparing them to those of other energy options. They also felt the Panel should address questions related to continuing nuclear power generation and to importing foreign mixed oxide (MOX) fuel or fuel wastes.

The panel's attempts to obtain information on each of the approaches, at levels of detail sufficient to permit meaningful comparisons with the AECL concept, were not entirely successful. The lack of social research and information relevant to the various approaches was particularly marked. In some cases, information did not exist or was not readily available. In other cases, participants may have been reluctant to provide it. This hesitation may have stemmed in part from the perception that, since governments had already opted to pursue disposal in plutonic rock, there was no sense in going over other options. Clearly, governments had only given AECL and Ontario Hydro the mandate to focus on deep geological disposal and interim storage, so AECL and Ontario Hydro had no obvious incentive to supply information on other approaches. Nonetheless, AECL did provide some detail on other approaches in chapters 2 and 8 of the EIS, in one of its additional information documents, [Safety Assessment Management, An International Comparison of Disposal Concepts and Postclosure Assessments for Nuclear Fuel Waste Disposal (report prepared for Atomic Energy of Canada Limited, Whiteshell Laboratories, Pinawa, TR-M-43, Undertaking 57, Additional Information 42, 1996).] and in response to specific requests from the Panel. The Hare Report, although somewhat dated, and participants' submissions and presentations were also useful.

The various approaches to the long-term management of used nuclear fuel can be viewed as falling into one of three overall types-treatment, storage or disposal-or some combination thereof. Our attention will first turn to treatment.


The key treatment approaches that have come to the panel's attention are recycling and transmutation, both of which require reprocessing in advance. These are discussed, not only in the EIS, but also in section 2.3 and Appendix A of R-Barriers.

Reprocessing and Recycling

Reprocessing is a chemical separation process used to extract valuable materials, such as plutonium and uranium, from spent nuclear fuel. One or both of the extracted materials can then be recycled by fabricating them into fresh enriched uranium or mixed oxide (MOX) fuels. The process results in high- and low-level radioactive waste products and can result in excess quantities of separated plutonium and uranium that require storage. The high-level liquid wastes are immobilized by incorporating them into a solid host matrix. For instance, they can be immobilized through vitrification, which involves dissolving them in molten glass and casting them into a solid block. The low-level wastes come in various physical states and also require immobilization. While the immobilized wastes represent a smaller long-term radioactive hazard than the original spent fuel, they still require storage or disposal.

In the EIS, AECL compared the volumes of wastes requiring disposal if 63,400 CANDU fuel bundles were disposed of directly and if they were reprocessed. For direct disposal in the reference case study containers, the total volume of filled containers would be 622 cubic metres. Reprocessing would produce 107 cubic metres of containers filled with vitrified high-level wastes, 746 cubic metres of less radioactive wastes, 185 cubic metres of separated uranium and an unspecified volume of low-activity liquids. Further developments in technology could reduce the vitrified waste volumes from 107 cubic metres to about 21 cubic metres and the volumes of less radioactive wastes from 746 cubic metres to about 135 cubic metres. Thus, waste volumes could be reduced at best from 622 cubic metres to 156 cubic metres overall, and from 622 cubic metres to 21 cubic metres for high-level wastes only, if the separated uranium was recycled into new fuel. While these estimates are quite promising, AECL points out that the inventory of heat-generating fission products in the high-level vitrified wastes would not be reduced. Given thermal design constraints, the size of the disposal vault required for the vitrified wastes alone would be about the same as for direct disposal of the spent fuel. [Atomic Energy of Canada Limited, Environmental Impact Statement, pp. 31-32.]

Reprocessing and recycling raise a number of unanswered questions. How would the less radioactive wastes be disposed of? Where would a reprocessing plant be located and what would its effects be? What are the implications of burning enriched uranium or mixed oxide (MOX) fuels? To what degree would these processes increase the exposure of workers and the public? How safe would the handling and disposal of all the products be? For example, short-term experiments by AECL on solidified high-level waste forms indicate that contaminants would dissolve very slowly. However, the long-term performance of solidified wastes is not yet well understood. [L.H. Johnson et al, R-Barriers, p. 45 and p. 341.] A recent AECL long-term comparative safety assessment of the radionuclide release rates of Scottish spent fuel and derived vitrified reprocessing wastes found that release rates were greater for vitrified wastes, even for radionuclides whose initial inventories were much lower in the vitrified wastes. For some radionuclides, release rates were greater by up to six orders of magnitude. [P. McKay, D.S. Kendall, E.G. Watt and D.M. Wuschke, "Assessment of the direct disposal of spent AGR fuel," in S. Slate, F. Feizollahi and J. Creer, editors, Proceedings of the Fifth International Conference on Radioactive Waste Management and Environmental Remediation ICEM '95, Volume 1, Cross-cutting Issues and Management of High-level Waste and Spent Fuel (Undertaking 61, Additional Information 73), pp. 215-219.]

Reprocessing is carried out in India, Russia, Japan, the United Kingdom and France; the latter two countries also do it on a commercial basis for several other countries. In total, between 25 per cent and 30 per cent of the spent fuel produced world-wide is expected to be reprocessed. [B.A. Semenov, "Disposal of spent fuel and high-level radioactive waste: Building international consensus," IAEA Bulletin, Volume 34, Number 3 (1992), pp. 2-6, cited in Safety Assessment Management, An International Comparison of Disposal Concepts and Postclosure Assessments for Nuclear Fuel Waste Disposal, p. 6.] This widespread application is due to the inclusion of fuel reprocessing and recycling in those nations' nuclear energy policies and systems. With the "once-through" CANDU reactor fuel cycle, the relatively low cost of natural uranium and the excess of plutonium on world markets, there are currently no economic incentives for reprocessing in Canada, nor are there any plans to implement it. Even if it were adopted, AECL states that, for used CANDU fuel, reprocessing and immobilization technologies remain to be determined.

Some review participants advocated reprocessing and recycling to eliminate the portion of fissile plutonium in spent fuel (about 0.3 per cent for CANDU fuel [C. R. Frost, Current Interim Used Fuel Storage Practice in Canada, p. 63.] ) and the risk of future terrorists mining such plutonium from a disposal vault. Others were more concerned that the separated plutonium yielded by reprocessing would be vulnerable to terrorism and that it had the potential for criticality.

We believe that, although reprocessing and recycling would reduce the volume of high-level wastes, the many other factors discussed here could negate that benefit at present.

Reprocessing and Transmutation

As described in the EIS, transmutation is a nuclear process using specialized nuclear reactors or particle accelerators to transform some long-lived radionuclides into either stable or shorter-lived nuclides. It requires reprocessing of the spent fuel to separate its components according to the transmutation method they require. Thus, it has many of the drawbacks of reprocessing, including the need to dispose of long-lived wastes. Although the U.S., Japan and France are studying transmutation, AECL maintains that it is not a currently available or readily achievable technology. On the other hand, one participant cited a recent report as proof that the feasibility of transmutation had been established. [P.J. Richardson, Examining the "International Consensus" on Nuclear Fuel Waste Management and Disposal (North Bay: Northwatch, PH3Pub.088, February 1997), p. 1.] Nevertheless, various studies over the last two decades have concluded that there are no safety or cost incentives associated with transmutation. An analysis by Ramspott et al. (1992) of the potential of transmutation to reduce U.S. spent fuel wastes concluded that the total volumes of wastes produced may not differ significantly from those arising from reprocessing. In addition, many of the long-lived fission products, the major contributors to long-term risk, would not be eliminated. [L.H. Johnson et al, R-Barriers, p. 48.] Similar information was not provided for Canadian or other types of spent fuel.

A number of participants put forward transmutation options that were not discussed in the EIS. None of these transmutation technologies appears to be either technically or economically viable in the short term. In addition, reprocessing-a prerequisite to classical transmutation-has uncertain benefits and risks for Canada.


For our purposes, storage is defined as the safekeeping of used fuel with the intention of possible future use or disposal. As opposed to disposal, storage relies on continual monitoring and remediation, when necessary, and permits easy waste retrieval. These features, combined with fear and uncertainty about the long-term safety of disposal and hopes for a future technological solution to the waste problem, made long-term storage the option preferred by many participants. Any long-term storage option gives future generations more choices for retrieving and managing the wastes than disposal does. However, long-term storage forces future generations to make a choice, and transfers to them the responsibilities and risks of caring for the wastes. The Panel heard that there would over time be an unpredictable but increasing risk of the loss of institutional control over the wastes, due to social or economic collapse. Even without full-scale collapse, there would be a risk that the required funds or expertise might not be available if and when they were needed for disposal. For these reasons, critics, notably from the scientific community, felt that the wastes must not be allowed to accumulate indefinitely in storage.

Current interim storage practices in Canada are described in section 2.2 of the EIS and in an Ontario Hydro document entitled Current Interim Used Fuel Storage Practice in Canada. [C. R. Frost, Current Interim Used Fuel Storage Practice in Canada.] At present, about 1.2 million used fuel bundles are stored either in water-filled pools (wet storage) or in concrete canisters (dry storage) on the surface at nuclear generating sites. The AECB regulates and licenses these facilities. In Ontario, the sites have enough space to accommodate all the wastes that the existing nuclear reactors will produce until the year 2035, which is the end of all their life cycles. [C. R. Frost, Current Interim Used Fuel Storage Practice in Canada, p. 17.] These wastes will total 3.3 million fuel bundles. [Ken Nash, in Nuclear Fuel Waste Environmental Assessment Panel Public Hearing Transcripts, March 11, 1996, p. 51.]

Studies show that used fuel with undamaged sheaths should maintain its integrity in either type of storage for at least 100 years, and that fuel with damaged sheaths should maintain its integrity for at least 50 years. The dry storage canisters should last at least 50 years, and could be replaced with new ones as needed. To make the transition from storage to disposal, Ontario Hydro plans to transfer the fuel bundles into special shipping containers, transport them to a disposal site and transfer them there to another container for disposal. Bundles with defective sheaths would require special treatment. According to Current Interim Used Fuel Storage Practice in Canada, with continued maintenance and monitoring, current storage practices should continue to provide safe, economic and retrievable waste management for as long as needed. [C. R. Frost, Current Interim Used Fuel Storage Practice in Canada, p. 67, cited in Atomic Energy of Canada Limited, Environmental Impact Statement, p. 51.] Thus, although there may be insufficient storage space at existing sites after 2035 if nuclear power generation is maintained, continuing current storage practices could be viewed as a possible long-term approach to managing wastes.

During the hearings, representatives from Ontario Hydro stated that they have no reason to believe that extended surface storage is not technically feasible. However, they pointed out that neither an optimized design nor sufficient information has been developed that would allow them to conclude that relying solely on such storage over the long term is an acceptable strategy. A number of factors would have to be considered: regulatory and public expectations; location; design alternatives; safety under normal, accident and security threat conditions; fuel integrity during storage and handling; transition to disposal or other options; impact on reactor decommissioning plans; and maintenance and cost considerations. [Ken Nash and Frank King, in Nuclear Fuel Waste Environmental Assessment Panel Public Hearing Transcripts, November 21, 1996, pp. 24-34.]

In terms of risks to human health and the environment,current storage practices normally pose a fraction of the risk posed by nuclear power generation, which itself falls well within regulatory limits. However, wastes at the earth's surface are more vulnerable to man-made and natural hazards, such as terrorism and earthquakes, than wastes stored or disposed of underground. Some existing storage sites are located in densely populated areas, which may make them potentially more attractive to terrorists and of more concern when considering collective or population dose and the effects of increasing waste inventories over time. Communities may not necessarily accept the idea of keeping the wastes indefinitely.

On the other hand, some participants have argued that continuing on-site storage would justifiably locate the wastes near the beneficiaries of nuclear energy; keep the wastes near the seats of government, thereby avoiding the "out of sight, out of mind" mentality; eliminate the problems and costs of finding a disposal site; and preclude transportation and handling, and their associated risks. The Panel cannot resolve the question of who does or does not benefit from nuclear energy.

France, Scotland, South Korea, the Netherlands and others are considering long-term storage as part of their waste management strategies. Furthermore, interim centralized underground storage is being used in Sweden and has been proposed in the U.S. Underground storage would help to isolate the wastes from the biosphere and from surface hazards such as terrorism and earthquakes (which have greater effects at the surface). However, according to the EIS, it would also increase used fuel handling, construction hazards and costs. Compared to current practices, centralized storage offers no clear engineering, safety or economic advantages, according to studies cited in the EIS. [Atomic Energy of Canada Limited, Environmental Impact Statement, p. 333.]

However, if a centralized underground storage facility could be easily converted to disposal, it would significant-ly reduce the cost of disposal for future generations. In addition, such a facility would permit the monitoring of performance and the integration of scientific advances before any final commitment to disposal, and would be safer than surface storage in case of a lapse of institutional controls. It may be a useful compromise between maximizing choice for future generations and minimizing the responsibility placed on them. In any case, it is worth considering in the event of either a delay in implementing disposal or a decision to continue with storage for the medium or long term.

At the panel's request, AECL considered underground storage that could be readily adapted to disposal without any need to re-handle the used fuel. Initially, this option would be the same as AECL's disposal concept up to the end of the operation stage, when the wastes would be emplaced and rooms would be backfilled and sealed with concrete bulkheads. Afterwards, tunnels, shafts and some monitoring boreholes would remain open. A number of design and related safety issues would have to be resolved, but no feasibility problems were identified. AECL estimated that this option would entail a workforce of about 110 people and annual costs of at least $20 million (1991 dollars) once the rooms had been sealed. [Ken Dormuth, in Nuclear Fuel Waste Environmental Assessment Panel Transcripts, November 21, 1996, pp. 11-14.]


We define disposal as the permanent placement of used fuel with no intention of future use. It has the goal of achieving long-term safety without the need for continuing intervention. If achieved, this goal is the major advantage of disposal over storage. Compared to wastes in storage, wastes in disposal would be more isolated and their retrieval and long-term monitoring would be difficult or impossible. If all goes as planned, disposal would reduce the responsibilities and risks of future generations, but it would also reduce their degree of choice in re-using, monitoring or otherwise managing the wastes.

Supporters of disposal argue that the current generation, as the originator and beneficiary of the wastes, has a moral obligation to produce the technology, site and resources necessary to dispose of it safely. Depending on the precise option chosen, disposal does not necessarily preclude other options. Its implementation could span many decades, during which time better alternatives could arise and be used. Natural Resources Canada also reasoned that disposal would make nuclear energy more sustainable by not passing costs on to future generations and by closing the nuclear fuel cycle.

Opponents of disposal counter that closing the nuclear fuel cycle would perpetuate and even expand nuclear power generation and waste production, resulting in an ever-increasing waste inventory and hazard from both on-site storage and disposal facilities. Since the long-term safety of disposal is uncertain, they feel that we owe it to future generations to stop producing wastes, to keep a close watch on existing inventories and to await the development of a safer alternative. Concerns about long-term safety could possibly be partially addressed through disposal approaches that permit small-scale demonstrations of disposal and long-term monitoring.

Several means of disposal have been considered over the years and are discussed in Chapter 9 of the EIS and in the Hare Report. This appendix discusses disposal in space, in ice sheets, on or beneath the seabed, and underground in geological formations.

Space Disposal

Disposing of used fuel by sending it into space has been considered since before the Hare Report. A number of people advocated this approach during the review. Of all disposal methods, it has the greatest potential to isolate the wastes permanently from the biosphere. Accordingly, it would not permit waste retrieval. Although we know that it is technically possible, we also recognize that its costs would be very high. Studies cited in the EIS indicate that, since the number of flights required to transport the existing volume of spent fuel would be impractical, space disposal could be feasible only for a smaller volume of reprocessed high-level wastes. This would entail all the advantages and disadvantages of reprocessing, including the need to manage intermediate- and low-level wastes in some other way. AECL reported that the risk of catastrophic accidents was about one per cent per flight, and thus that the radiological risk of disposal in space would be higher than that of geological disposal. Combined with the fact that Canada has neither the required facilities nor international approval to dispose of nuclear wastes in this manner, it does not appear to be a viable or acceptable solution at this time.

Ice Sheet Disposal

While disposing of spent nuclear fuel in ice sheets has been suggested for quite some time and appears to be feasible, it has not been extensively researched. This concept would have the advantage of situating the wastes in a slowly changing environment, devoid of living organisms. If it used an anchored emplacement technique, it could permit waste retrievability for up to a few hundred years. Unfortunately, Canadian glaciers are too small for this method, so ice sheets in Greenland or the Antarctic would have to be employed. Correspondingly, the wastes would have to be transported over great distances. As neither of these regions is part of Canadian territory and because Canada interprets its treaty obligations as precluding disposal in the Antarctic, this cannot currently be regarded as an acceptable option.

Seabed Disposal

Proposals for seabed disposal range from placing used fuel on or beneath deep oceanic plains, far from continental margins, to placing it in zones of subsidence along continental margins such as the Pacific coast. The former proposal was studied over 10 years and partially demonstrated by an international seabed working group, including AECL and the Geological Survey of Canada. Many scientists consider it to be the best disposal option. It is potentially safe, except for transportation accidents where containers could not be recovered. Preliminary estimates suggest that its costs could compare favourably with those of other disposal methods. [Organization for Economic Co-operation and Development, Nuclear Energy Agency, Faisabilité de l'évacuation des déchets de haute activité sous les fonds marins. Volume 1: Bilan des recherches et conclusions (Paris: Organization for Economic Co-operation and Development, 1988), p. 41.] Sites away from the continental margins have the advantages of being located in geologically and geochemically stable areas, as well as being well removed from areas of human habitation or intrusion, and areas of important biological and mineral resources.

Disposal in subduction zones (areas along some continental margins where the oceanic plate is subsiding below the adjacent continental plate) has not been thoroughly investigated, but was promoted by one participant advocating a concept involving access from land by underground tunnel to a sub-seabed repository located in or near a subduction zone. This approach does not share the locational advantages of the other proposal, but has the unique capability to carry the wastes deeper into the earth's core over time. This participant contended that, if implemented on an international, aggregate basis, this approach would be less expensive than multiple national land-based disposal facilities. [J.R. Baird, Subductive Waste Disposal Method, Comments on the Environmental Impact Statement (Nanaimo: March 31, 1994), p. 12.] Retrieval of the wastes is presumed to be difficult if not impossible with either form of seabed disposal.

Since Canada interprets its obligations under the London Dumping Convention (1972) as prohibiting seabed disposal, these approaches would require renegotiated international acceptance and an international regulatory framework, neither of which is currently being pursued. The Canadian Environmental Protection Act (CEPA) prohibits "ocean dumping" (better described as disposal executed at sea) and thus would appear to preclude seabed disposal. The subduction disposal advocate argued that, since such disposal would occur within Canada's 200-mile economic coastal zone, it could not be reasonably interpreted as a violation of the London Convention. For instance, Sweden is building a repository for low- and intermediate-level radioactive wastes 50 metres beneath the Baltic Sea. We also note that, since the subduction proposal does not involve disposal executed at sea but via an access tunnel running beneath the seabed, the CEPA may not apply to it either. Nonetheless, the Panel is not in a position to investigate these assertions or the merits of the proposal any further.

Land-based Geological Disposal

Land-based geological disposal involves burying spent fuel deep underground in one of several feasible types of rock and vault configurations. As such, it can be based in part on existing mining technologies. Geological disposal is the long-term management option being pursued by most other countries with nuclear fuel wastes. It is supported by the International Atomic Energy Agency (IAEA) and the Nuclear Energy Agency of the Organization for Economic Co-operation and Development (OECD/NEA). Extensive research and development have been devoted to it, and there is a strong scientific consensus that it is feasible. AECL's concept for deep disposal in plutonic rock is one variation of this approach.

Compared to space, ice sheet or seabed disposal, land-based geological disposal would make it easier to monitor or retrieve wastes. A room-and-pillar vault design, such as that used in the AECL concept, would be superior to deep borehole or other vault designs in terms of ease of retrieval or other intervention. Although participants' preferences for storage over geological disposal could be addressed, in part, by improving postclosure monitoring and retrieval capabilities, these improvements could also compromise the passive safety objective of disposal. While less vulnerable to natural and man-made hazards than surface facilities, an underground repository could be prone to risks arising from a borehole being inadvertently left open, accidental or deliberate human intrusion, earthquakes, glaciation and long-term environmental change.

The various geological media considered for underground disposal include clay, volcanic tuff, basalt, plutonic rock (granite, gabbro), salt and shale. Since Canada reportedly has suitable deposits only of the latter three, [Atomic Energy of Canada Limited, Environmental Impact Statement, pp. 328-329.] and since the Hare Report named these as the top three choices respectively for Canada, we shall limit our consideration to them. Neither salt nor shale have undergone field investigation as part of the Canadian Nuclear Fuel Waste Management Program. Tuffaceous rock is being pursued as a disposal medium in the U.S. Thick clays have been selected in Belgium and are being studied in France, Spain and Switzerland.

Plutonic rock is being pursued as the disposal medium of choice in Finland and Sweden and is being studied by France, Japan, Spain, Switzerland, Argentina and India. AECL has proposed using plutonic rock in the Canadian Shield for its disposal concept, and has been studying such rock for the last 18 years. The Canadian Shield is widely distributed across central and eastern Canada. Plutonic rock also exists elsewhere in Canada, buried beneath sedimentary strata. Its wide distribution, especially in Ontario where most of the wastes are produced, allows for more choice in siting than do salt and shale. Other beneficial characteristics of plutonic rock in the Canadian Shield include geological stability; low topographic relief conducive to slow groundwater movement; low or partially known and avoidable economic mineral potential; and the known existence of units of sufficient size to contain a vault and possessing suitable physical and chemical properties. Among its disadvantages are the occurrence at repository depths of saline groundwater that could cause container corrosion in the presence of oxygen; fractures that may extend to the surface and serve as conduits for contaminant transport; and, in unfractured bodies, high stresses requiring special design measures.

Salt has been selected for disposal use in Germany, Russia and Ukraine, and investigated in Spain, the Netherlands and the U.S. The Hare Report recommended it as Canada's second choice. In Canada, salt deposits exist in Ontario, the Hudson Bay area, the prairie provinces and the Northwest Territories, and on the Atlantic coast. Databases exist for many of these deposits. Only the Ontario deposit lies within a province that generates nuclear power, but its distribution there is limited and its location in the southwest of the province places it near high population densities and the international border.

In addition to indicating the long absence of groundwater, salt has low permeability and high thermal conductivity, which make it conducive to nuclear waste disposal. Its unfavourable properties are corrosiveness, high solubility and low sorption capacity. Salt's plasticity renders it less vulnerable to geological instability than other rock, but could create difficulties in maintaining a stable repository. The frequent association of salt with potash or hydrocarbon deposits and its value as a commodity in itself renders it incompatible with AECB Regulatory Document R-72, which states that "there should be little likelihood that the host rock will be exploited as a natural resource." This requirement is intended to reduce the probability of future inadvertent human intrusion into the repository.

Shale was recommended as Canada's third choice in the Hare Report. Thick shale formations can be found in the same regions of the country as salt, with the exception of the Atlantic coast, and are more widely distributed in southern Ontario. The advantages of shale are its low permeability and excellent sorption characteristics. Detracting from these are its low strength, its variable composition and properties, and its association with hydrocarbons or with rock carrying large amounts of groundwater. The same conclusions can be drawn for shale as for salt with respect to its geographic distribution and its proximity to exploitable natural resources.

A number of participants suggested a variation on land-based geological disposal: disposal below the nuclear power stations where the wastes are currently stored. Even theHare Report raised this possibility, noting that an attractive feature of shale was its presence directly beneath most of the stations in existence at that time in Ontario. The EIS states that none of the current sites has been investigated for technical suitability, nor is any site located on the Canadian Shield. However, they are all either situated on plutonic rock of the same age as the Shield lying beneath sedimentary strata, or located near the Shield or other younger plutonic rock. Nonetheless, if we exclude sites outside seismic zones 0 and 1, as AECL suggests, the reactor sites in Quebec and New Brunswick would not be suitable (see Figure 5 in Chapter 3 of this report).

On-site disposal is a decentralized approach that would have many of the advantages and disadvantages of on-site storage. However, AECL estimates that the cost of implementing two facilities, each capable of disposing of five million fuel bundles, would be 30 per cent greater than the cost of building one 10-million-bundle facility. The already substantial cost of building just one facility is likely the primary reason why no country has selected decentralized disposal.

Other related options put forward by participants aredisposal in abandoned mines or in natural caves. We have not received much information on either of these options, but abandoned mines have been used to dispose of some types of radioactive wastes. We assume that such sites may not be technically suitable due to the type and properties of the host rock; their proximity, especially in the case of abandoned mines, to mineral deposits and hence their potential for intrusion via mineral exploration; and the presence of natural or man-made fractures or cavities in the rock, which could be unsafe. These drawbacks may reduce the effectiveness of the geosphere as a component of a multi-barrier system. On the other hand, there are many known sites. The chances of finding a suitable site seem slim, but the cost and time savings in site identification, characterization and excavation may warrant further investigation of this approach.