The heat output from high level radioactive waste buried in hard rock can give rise to groundwater convection currents. These flows can change the natural groundwater flows for thousands of years after the decommissioning and sealing of a depository. This paper presents the results of some recent calculations of this effect and discusses the possible consequences for water-borne leakage of radionuclides back to the biosphere. INTRODUCTION One of the proposed options for disposing of radioactive waste from the nuclear power industry is to bury it in depositories deep in hard rock (KBS. 1977; Roberts. 1979). The heat generated by the decaying radionuclides in high level waste would be dissipated largely by thermal conduction using the rock mass as a heat sink. For a depository' containing a three-dimensional array of waste canisters, the resulting temperature field would extend several hundred meters into the rock, and rise and fall on a timescale of centuries (Beale, Bourke and Hodgkinson. 1979). The most likely way in which radioactivity could reach Man from such a depository is by groundwater leaching radionuclides from the waste and transporting them to the biosphere. This leakage path is inhibited by a number of in-series barriers including the high leach resistance of the waste form. its containment in a corrosion resistant canister and the impermeability and absorptivity of the rock mass (Hill and Grimwood. 1978). This paper addresses one aspect of this problem namely the perturbation of the existing groundwater flow paths by buoyancy flows driven by the above temperatures. NATURAL GROUNDWATER FLOW A vertical section through a hypothetical region, is used to illustrate the hydrogeological effects of a high level waste depository on its surroundings. The rock mass is treated as a porous medium with constant values of permeability (10 −16 m 2 ) and flowing porosity (10 −4 ) chosen to be representative of those measured in fractured hard rock masses (Axelsson and Carlsson. 1979; Davison. 1979; Lundstrom and Stille. 1978). It is assumed that precipitation far exceeds the infiltration into this low permeability rock mass so that the water table is always coincident with the land surface which therefore acts as a constant pressure boundary. THERMAL EFFECTS The temperature field around a depository will cause water in the fractures of the rock to rise because of buoyancy effects. Such upward flows are of concern because they could shorten the time taken by radionuclides, leached from the waste, to reach the surface. Temperature profiles along the vertical centreline of a depository are shown. The temperature rise near the centre of the depository reaches a maximum of 6l °C after about a century and then slowly decays as heat is distributed over an ever increasing volume of rock. However, the total amount of heat contained in the rock mass has not started to decay at the times shown. This heat energy has the potential to cause buoyancy flows long after the temperature rise at the centre of the depository has fallen to a fraction of its maximum value.

Economic and engineering evaluations of energy-storage potential in certain USA aquifers are being conducted. Particularly detailed evaluations have been made for compressed air energy storage (CAES), using off-peak power from nearby nuclear power stations. In ''current studies, we are examining thermal energy storage and utilization prospects, using solar power or, alternatively, off-peak, low-cost nuclear power as the heat source. Economic and energy-saving aspects of selected combinations of sources, storage media, and uses are ranked with respect to various selection criteria. INTRODUCTION The current U.S. interest in underground storage of energy grows out of a number of environm7ntal, economic, and political factors. Environmental considerations create particular difficulties for nuclear power and coal. Economic and political problems are clouding the prospects for continued supply of energy needs from outside sources of petroleum. According to the National Academy of Sciences, nuclear-fusion, solar, and geothermal energy remain at present in a primitive state of development. This and other conclusions of a four-year study are set forth in a report "Energy in Transition, 1985–2010," recently published by the Academy''s Committee on Nuclear and Alternative Energy Systems. The study also concluded that conservation and energy efficiency are essential elements of the national energy policy. Efficiency can be realized through generation of energy at a time when surplus capacity is available and storing it for use when demand exceeds capacity. One such procedure involves storage of energy in aquifers, which constitute convenient natural near-surface reservoirs for fluid storage and recovery. AQUIFER STORAGE Although aquifer storage has been primarily employed for natural gas, storage of compressed air for use in the generation of electrical energy is in an active stage of development. Also, thermal storage, by means of hot or cold water injection, is under serious consideration, with initiation of experimental studies funded by the U.S. government anticipated at several locations in 1980. Texas A&M University and Auburn University are operating small thermal storage projects at present. Porosity and permeability are critical rock characteristics in storage considerations. Porosity is a measure of the volume available for fluid storage, expressed in percent of the total volume of solids plus voids for a representative portion of the storage medium. Permeability is a measure of the ability of fluids to flow through the aquifer. It is usually expressed in terms of darcys or millidarcys (mD), with the higher numbers indicating greater permeability -- that is, greater ease with which a given rock will accept, transmit, and deliver fluids. For example, natural gas is stored in aquifers having permeabilities from 7 mD up to about 7,000 mD. For compressed air storage, reservoirs with very high permeability are desirable -- several thousand millidarcys, if possible. ILLINOIS AQUIFERS Two aquifers in southern Illinois have been acquired for energy-storage purposes by the URS Corporation. These are anticlinal structures in Devonian-age carbonate rocks, at depths of about 600 ft, as shown in Fig. 1. Characteristics, as determined from well logs and other geologic data, are set forth in Table 1.

The Stripa mine test site, located approximately 200 km west-northwest of Stockholm, Sweden, is the focal point of a detailed fracture-hydrology study. Preliminary results from three of the five main components of this program are discussed in this paper. These three components are a detailed borehole testing program to determine the directional permeabilities of the fractured granite, a macro permeability experiment - an attempt to measure the average permeability of a large volume of the fractured granite, and a detailed study of the groundwater geochemistry to determine the origin and age of the groundwater both in and around the immediate mine area. Preliminary analysis of the borehole tests gave equivalent porous media hydraulic conductivities that ranged from 10 −5 to 10 −10 cm/sec. Preliminary results from the macro permeability experiment suggests bulk rock mass hydraulic conductivities of about 10–9cm/sec. Environmental isotope and chemical analysis of waters collected from water bearing fractures in the granite show that the groundwaters are many thousands of years old and their salinity increases with depth. It is not yet clear whether the deep groundwaters (>338m) belong to local or regional flow systems. INTRODUCTION Fractured crystalline and argillaceous rocks have been proposed as alternative host rocks for storage or disposal of high-level radioactive waste. To evaluate this proposal, one must obtain an accurate description of the hydrology of fractured rocks. Thus, one must begin to develop data bases that permit one to answer questions such as: what is the role of fractures in determining the nature (isotropic or anisotropic) of fractured rock permeability? and under what conditions, if any, can fractured rock masses be treated as porous media or equivalent porous media? The first question dictates that we must develop methods of characterizing a fracture system and its role in determining the hydrology of fracture systems in order to provide a framework within which to interpret local and large scale flow systems in fractured rock masses. Answers to the second question determine the type of borehole testing programs that will be undertaken in concept verification studies. Borehole testing programs must provide the data needed to develop hydraulic parameters that clearly describe how fluids move and the rate at which they move through fractured rocks. based on porous media concepts will not provide sufficient data if, as is permeability of fractured rocks is highly anisotropic. Borehole testing programs generally agreed, the The volumes and rates of groundwater movement through fractured rock masses, predicted from borehole tests, must be supported by data obtained from other field studies. Such supporting data can be obtained from large-scale tunnel or shaft pumping tests, that perturb a volume of the rock mass many times larger than that tested by a single borehole, and through detailed studies. of the geochemistry and isotopic composition of the groundwaters. Groundwater flow systems configuration, calculated from measured distributions of permeabilities, porosities and hydraulic head boundary conditions, must be consistent with data of the evolution of groundwater geochemistry in fractured rocks and the distribution of ages inferred from isotope analysis.

The hydrogeological survey was executed in a small granite island for the construction of underground oil storage caverns. In spite of many cracks and fissures, the permeability of the bedrock was relatively low (10 −4 to 10 −6 cm/sec.) and thus the level of groundwater table was very high. As for the groundwater flow, the authors measured the groundwater pressure in the bore holes and described the potential distribution. The measuring result of environmental tritium concentration in groundwater also supported the existence of the groundwater flow from center to circumference of the island. Furthermore, the potential distribution of groundwater was calculated by the numerical analysis of finite element method using the measured permeability distribution and the estimated rate of recharge from the water balance calculation, and the reasonable groundwater flow enough to account the actual measurement was reproduced. The authors also investigated the environmental influence of the drawdown of groundwater in excavating of the caverns. In case that there exists the relatively permeable layer near the ground surface such as weathered zone of the present study and also that the rate of recharge is relatively large in a humid climate like Japan, the influence of the drawdown by excavation is seemed to be very little. INTRODUCTION The conservation of an oil material in underground caverns using its surrounding groundwater has been carrying out for long period. In this case, the role of groundwater in the bedrock is very important but there is almost no systematic measurement regarding the movement of this groundwater and a number of unclarified problems are still existed. In the bed rock, there exist many cracks and fissures originated from crust diastrophism. The groundwater is stored in them or moves downwards through them by a gravity. Cracks and fissures in the bedrock have very different shapes such as tubular or plate-type, and they cross, expand and connect each other making a very complex structure. Nevertheless from a macroscopic point of view the network of these cracks and fissures compose the storage zone or pervious layer. In case that many irregular and non-homogeneous fissures exist in the bedrock and make a network of fissures, it may be reasonable to consider this bedrock hydraulically homogeneous. As for the groundwater flow in isotropy and homogeneous media, Hubbert (1940) solved the groundwater flow analytically. After then, Toth (1962) and Freeze and his co-workers (1967) tried to estimate the flow in the more complex pervious layer using computer simulation. However, the actual measurement of the groundwater flow was observed only that by Meyboom (1966) in an aluvium deposit, and the groundwater flow in the bedrock has not been measured by now. The purpose of the present study is to understand the regime of the groundwater in the bedrock by the actual measurement and mathematical modeling, and also to estimate the influence on the environment by excavation. In the present study, the authors investigated the flow characteristics of the groundwater in bedrock using the potential distribution measured by double packered groundwater pressure measuring apparatus, and the concentration of environmental tritium containing in the groundwater. study is shown in Fig. 1.

In unlined underground rock caverns, liquid petroleum and petroleum gas can be stored by making use of natural or artificial ground water pressure. In case of applying the unlined underground storage caverns to the cracky rock mass, it seems to be most important that the behaviour of the ground water through the rock mass surrounding the caverns is studied in advance. This study, therefore, discusses the following subjects concerning unlined underground oil storage caverns. The numerical study on the effects of natural ground water pressure on the storage caverns. The numerical study on the effects of artificial ground water pressure on the storage caverns. Model experiment about gas leakage into the crack of rock mass. INTRODUCTION Unlined underground storage system of petroleum has been proven to be efficient in the effective exploitation, environmental preservation, safety and economy. The system has already many past references in Europe and America. However, in case when the said system is adopted to the cracky rock mass, it is necessary to study and examine the nature of the rocks, the structure of fuel storage tank and the influence over the environment. This report is intended to describe the results of the analysis and experiments on the seepage flow made in relation to the matters most important for the construction of the unlined underground storage tank for petroleum, that is to say, the water pressure required for preventing leakage of oil and gas, the lowered level of ground water liable to give influence over the environment, and the water leakage volume indispensable for determining the capacity and the economy of the equipments and apparatuses to be involved. NUMERICAL STUDY ON THE EFFECT OF NATURAL GROUND WATER PRESSURE ON THE STORAGE CAVERNS The petroleum like heavy oil and light oil having low vapor pressure can be stored under the atmospheric pressure when the underground caverns are not found in the state completely covered with ground water. This is to say, there happens no gas leakage and no oil leakage even if the ground water level reaches the cavern. On the other hand, when the underground caverns are excavated in the rock mass beneath the natural ground water level, the seepage flow into the caverns through the surrounding rock mass will be happened. Consequently, it is worried that the ground water level on the upper part of the caverns will fall down after the excavation of the cavern. Therefore, it is necessary to understand the behaviour of natural ground water around the cavern in case when heavy oil, light oil, etc. are to be stored under natural ground water only. In this chapter the behaviour of ground water around the cavern will be analyzed through two dimensional analysis of seepage flow in saturated-unsaturated porous media (Komada, 1978) and the possibility of unlined underground storage under natural ground water only will be examined.

In recent years interest in gas escape phenomenon from unlined mined rock caverns has increased considerably. This phenomenon is most critical to the feasibility of Compressed Air systems, closed surge chambers, and underground storage of hydrocarbons. It is of further interest in the long term sealing of radioactive waste repositories and in the potential siting of underground nuclear plants. All previous studies used extremely simplified analytical models and/or laboratory tests and attempted to define a "critical gradient" at which "bubble escape" would cease to occur. The predicted critical gradients ranged from 0.4 to 1.0. These ideas were sometimes translated into practice in the form of elaborate tunnel schemes with radiating pressurized boreholes in order to maintain sufficient gradients both during cavern construction and during use. This paper describes detailed laboratory experiments which were conducted to study two-phase countercurrent flow through simulated rock fractures. A modified Hele-Shaw parallel plate model was built which allowed variation of fracture aperture and orientation with respect to the pressurized cavity. Also, different entrance geometries were simulated to delineate their importance as far as bubble or slug initiation is concerned. An array of sensitive pressure transducers were used to obtain any small variation in the pressure field during bubble propagation. The deformation and volume of the bubbles were recorded via a high speed camera. The data is analysed in light of existing two-phase flow theories developed in the chemical and nuclear engineering fields. Engineering implications are discussed in detail. INTRODUCTION Gas escape from unlined rock caverns involves two distinct problems: the fundamental initiation and motion of gas "bubbles" through rock fractures, and, the calculation of overall gas losses from storage caverns. Solutions to the latter problem, at present, are best handled using an equivalent porous medium approach as suggested by Barton (1972) and Berg and Noren (1969). However, this provides no insight into the fundamental mechanism and parameters controlling the initiation of gas escape. It is this problem that the present research addresses. Interest in two-phase flow in the geotechnical area was originally restricted to the petroleum engineering field where drillstem and two-phase porous medium problems have received considerable attention. A phase is simply one of the states of matter and can be either a gas, a liquid, or a solid. The term two-component is sometimes used to describe flows in which two phases are not of the same chemical substance. Since the mathematics describing two-phase or two component flows are identical, it does not matter which definitions are chosen. Increasing use of underground space has aroused significant interest in developing a better understanding of single-phase and to a lesser extent of two-phase fracture flow. Recently Willet (1979a, 1979b) has given an excellent review of the history and present status of the economic use of the underground. Two-phase fracture flow may be a very important, if not critical, parameter in each of the following areas: nuclear power plants sited underground, crude oil and petroleum product storage.

The disparity between energy production and demand has led to increased research into the use of aquifers for the long-term, large-scale storage of thermal energy. Currently, there are several field experiments and feasibility studies under way in which the technical, economic, and environmental aspects of aquifer storage are being researched. The present paper surveys the recent theoretical efforts in aquifer storage research and the impact their results may have on these field projects. Major work is highlighted according to three categories: semianalytic studies, numerical modeling studies, and site-specific studies. INTRODUCTION The need for energy storage arises from the disparity between energy production and demand. The development of viable storage methods will play a significant role in our ability to implement alternative energy technologies and use what is now waste heat. The ability to provide heat at night and during inclement weather is a key factor in the development of solar energy. Conversely, winter cold, in the form of melted snow or water cooled to winter air temperatures, can be used as a coolant or for air-conditioning. Practical storage systems would also allow us to capture the heat that occurs as a by-product of industrial processes and power production. Industrial plants and electric utilities generate tremendous amounts of waste heat, which is usually dissipated through an expensive network of cooling towers or ponds to avoid thermal pollution. Because periods of heat demand do not generally coincide with electricity generation or industrial production, a viable storage method is essential if this heat is to be used. Such a method would not only provide for the use of what is now waste heat, but would significantly decrease the necessary investment in cooling and backup heating systems. In recent years, aquifers have been studied as a very promising means for the long-term, large-scale storage of thermal energy. Aquifers are porous underground formations which contain and conduct water. Confined aquifers are bounded above and below by impermeable clay layers and are saturated by water under pressure. They are physically well suited to thermal energy storage because of their low heat conductivities, large volumetric capacities (on the order of 109m 3 ), and their ability to contain water under high pressures. Aquifers are also attractive storage sites because of their widespread availability. Aquifer storage is not a new concept. Over the last few decades aquifers have been used to store fresh water, oil products, natural gas, and liquid wastes. However, it has only been in recent years that their use for thermal energy has been suggested. Initial studies were conducted by Rabbimov, Umarov, and Zakhidov (1971), Meyer and Todd (1972), Kazmann (1971), and Hausz (1974). A good source of information about more recent work is the proceedings of the Thermal Energy Storage in Aquifers Workshop (Berkeley, 1978). Current research and development activities are reviewed in the quarterly ATES Newsletter prepared by Lawrence Berkeley Laboratory. Recent work includes field experiments at Mobile, Alabama (USA), Gaud (Fance), Bonnaud (France), College Station (USA).

The field testing requirements of nuclide transport models are changing The existing methods of measuring hydraulic conductivity in-situ are reviewed and their relevance to modelling requirements assessed. Within the field of multiple borehole methods, some techniques, suitably adapted from the original oilfield environment, are suggested. The limited methods available to carry out three dimensional testing are supplemented with a new method based on propagating a sinusoidal pressure pulse. The distances over which testing could be accomplished are assessed together with the range of the rock parameters within which the test is practical It is concluded that the new method has interesting possibilities and could provide a series of hydraulic diffusivity vectors. INTRODUCTION The last ten years have seen the increasing use of computer models and techniques within hydrogeology in general, and solute transport investigations in particular. The nuclide transport models produced so far are still in their infancy but show a trend towards increasing complexity which is likely to continue. The tendency is to add more and more effects, such as thermally induced flows, radioactive decay and rock stress effects, onto the basic groundwater flow model. As yet most groundwater flow models are of the porous medium type and assume that Darcys law broadly applies within the scale of interest. Some work though, has been carried out on a model involving flow through a system of blocks bounded by shear zones, and the results (Axelsson and Carlsson, 1979) differ considerably from the homogenous case (Stokes, 1979). Whatever the particular type of model involved, all require field measurements of those factors which delimit the velocity and direction of groundwater movements within quite large volumes of rock. In the simpler models, where groundwater is assumed to flow horizontally in response to a regional hydraulic gradient, equivalent to the average dip of a water table, the field measurements required are straight forward. However, as the models become more complex, the requirements on field investigations become more exacting and, although the basic hydrogeological parameters of hydraulic conductivity, hydraulic potential, porosity and dispersivity are still relevant, the nature of their variation is coming under closer scrutiny. It is the intention here to examine the changing methods relating to the field measurements of hydraulic conductivity in fractured crystalline rocks and their likely relevance. EXISTING SINGLE BOREHOLE TECHNIQUES Average values of hydraulic conductivity are the usual basis of most porous medium models and can be obtained by either injecting or abstracting water from a completely open borehole. In an attempt to measure the variation of hydraulic conductivity with depth, straddle packer systems are currently being employed by many investigators (e.g. Davison, 1980, BRGM, 1979 and Carlsson,1979). These packer results tend to apply to individual fractures near the borehole, and only by averaging large numbers of results, is it possible to infer a depth-dependent permeability relationship. The use of short spacing straddle packer measurements does mean however, that the spatial variability of hydraulic conductivity can be deduced.

The present paper presents methods for injection of brine solution into the subsurface investigated under the Compressed Air Energy Storage Project of the Department of Energy in the United States of America. The principal objectives in this investigation were two fold: Prevention of any possible pollution of ground water by the injected brine solution. Avoidance of over pressurizing the solution-deposit zone by the injection operation which will result in: induced undesirable fractures in both upper and lower confining formations, and inefficient and uneconomical injection operation. INTRODUCTION The continental United States has many rock salt deposits, as well as salt lakes and natural brines. Salt is found in 4 major basins as well as several minor basins (Fig. 1). Taken together, this means that over one half of the states contain salt deposits (Lefond, 1969). The injection of brine into geologic formations can cause contamination of existing portable ground water. The contamination is due to either extensive lateral spreading or vertical upward of downward movement of the brine. The direction and magnitude of brine movement is a direct function of the total geologic environment surrounding the injection point. The total geologic environment embraces the rock types, fractures, rock strengths and permeabilities, in situ state of stress, ground water regime(s), and geochemistry. During brine injection containment is ideally obtained by ensuring that the suitable injection sequence, which is highly permeable, is over/underlain by impermeable rocks. These rocks restrict both the vertical upward and downward movement of the brine. The lateral extent is dependent on the uniformity, isotropic aspects, of the injection formation. The operating fluid pressures active within the migrating brine, must be known to ensure that they do not cause either, a) tensile fractures or b) extend pre-existing fractures within the over/underlying confining rocks. The promotion of fractures markedly increases the permeability of the low permeability confining rocks, and consequently contamination of previously isolated ground water by the brine. CRITERIA FOR INJECTION FORMATION The injection formation should be: an extensive sedimentary formation: unfractured sandstone, limestone, dolomite, and unconsolidated sands are the general lithologic types used for injection; at least several hundred feet thick; hundreds of square miles in extent in order to minimize injection pressures and to provide a buffer zone against migration of brine to discharge areas; an area of relatively simple geologic structure without complex folds and faults (synclinal sedimentary basins are favorable; high formation pressures are unfavorable); of uniform hydraulic properties with high enough permeability so that excessive injection pressures can be avoided (according to Warner in 1977, a porosity of at least 10% to 20% and permeability greater than 100 millidarcys, or 0.2 ft/day, is required for large-scale brine injection); of low or negligible lateral movement of formation fluids, to a discharge point (grouting may be necessary to lower the permeability so that lateral confinement is maintained); a zone that is below the level of fresh-water circulation with the surface

In the safety assessment of the underground siting of a nuclear power plant, it is necessary to know the transport behavior of gaseous fission products in rock. A new in-situ experimental method has been developed in order to obtain the parameters governing the air movement in rock. The experimental results obtained with this method have made it possible to explain the transport behavior. The preliminary analyses has shown that the gaseous fission products, when leaked underground, would be kept and contained there to a fairly hi~h degree. INTRODUCTION Japan has an area of 377 thousand square kilometers covered by 70 percent of mountainous area and a population of 112 million. The flat parts are therefore densely populated and intensively utilized for various purposes. Under these circumstances, underground siting of nuclear power plant (NPP) is thought to be attractive from the view point of effective land use. Recently, a committee established by the Ministry of International Trade and Industry (MITI) pointed out that it is essential to comprehend the behavior of gaseous fission products in rock and seismic characteristics of underground structures in order to realize underground NPP construction. As for behavior of gaseous fission products in rock, however, there are few field data to be applicable for analyses. This paper describes a new method to determine the parameters governing the air movement in rock, the result of the in-situ measurements which, taken under the auspices of MITI, are the basis of the parameters, and the analytical result under the condition of a hypothetical accident of underground NPP. BEHAVIOR MODEL OF FISSION PRODUCTS IN ROCK. At a hypothetical accident such as a loss-of-coolant in an underground NPP, atmospheric pressure and temperature within the reactor cavern will increase and a part of fission products such as noble gas and iodine will be released from the reactor core. Therefore the gaseous fission products will leak into the surrounding rock from the reactor cavern. In this case it may be thought that these fission products will be transported to ground surface dominantly through gaseous phase rather than liquid phase. The behavior of gaseous fission products in rock can be generally expressed by Eqs. (1) and (2) (the Japan Society of Civil Engineers, 1974). EXPERIMENT CONCERNING CONTAINMENT OF GASEOUS FISSION PRODUCTS There are several reports concerning the flow of compressed air through rock (Binggeli, Verstraete and Sutter, 1964; Bernell and Lirdbof, 1965; DiBiageo and Myrvoll, 1972). However there still remain many problems to be solved regarding rock properties such as air permeability coefficient, effective porosity of rock, effective diffusion coefficient of fission products in rock, absorption and adsorption coefficients of rock for fission products, etc. In December 1978, an in-situ experiment was performed at Numappara Pumped-Storage Hydro Electric Power Station to examine those rock properties. Fig. 1 shows the experiment site and the geological profiles. Experiment Facility Testing holes. The experiment site is located about 100 m inward from the adit entrance and 50 m beneath the ground surface.

Ground water flow through an underground repository for nuclear waste located 500 m below the ground surface as proposed by Swedish authorities may be considerably reduced by surrounding the repository with a zone of constant potential like Faraday's cage in electricity. The zone consists of tunnels and boreholes between them. INTRODUCTION It is proposed that nuclear waste from Swedish power plants be permanently stored in an underground repository. This should consist of a system of storage tunnels located 500 metres below the ground surface; and the nuclear waste should be enclosed in special canisters surrounded by compacted bentonite. The canisters are calculated to last for many thousands of years. However, if the canisters should be destroyed, radioactive material would be transported with groundwater to the biosphere in wells, rivers and lakes, or the sea. Therefore, the requirement is that the rock as the last barrier should have such very low permeability that the movement of the groundwater should take many hundreds or thousands of years from the storage to the biosphere. The Swedish Government has approved this project and accepted the judgement by the State Nuclear Power Safety Board that acceptable rock for a storage of nuclear waste is available. However, many people have protested against this decision, and different opinions exist about rock quality and the long-term effect of the storage. HYDRAULIC CAGE In primary rock such as granite etc. there exist small micro-cracks along mineral particles. Therefore, it is true that groundwater flow will occur in such rock but only to a very small extent. The permeability of such as homogeneous considered rock is very low, in fact so low that the rock can be considered to be impervious, and that the ground water flows in open cracks only. If the cracks are distributed evenly in different directions and the distance between the cracks is not too great, we may calculate the groundwater flow by using Darcy''s formula: q = k.S m 3 /s per m 2 area (1) where k = coefficient of permeability, m/s S = hydraulic gradient, m/m The velocity of the water in the system of cracks is v = q/n = 1/n. k. s m/s (2) where n = effective porosity. The effective porosity is not equal to the total porosity of the rock. The porosity of. the "homogeneous" rock should not be included, and neither cracks running laterally to the direction of the groundwater flow. The porosity, n, is difficult to determine at the site, but may be assumed to be between 0.001 and 0.0001 for very good hard rock. The formulae show that the intensity of the groundwater flow is proportional to the hydraulic gradient. A method to reduce the groundwater flow and its velocity and thereby to reduce the requirement regarding the permeability of the rock is to reduce the hydraulic graient around the repository.