In 1976, the U.S. Department of Energy (DOE) established the National Waste Terminal Storage (NWTS) program. The objective of this program is to develop and provide the capability for the long-term disposal of high-level and transuranic nuclear wastes. The present U.S. nuclear waste disposal strategies envision the isolation of such wastes in deep underground geologic repositories. Technology development in support of the NWTS program includes the formulation and management of a strong basic science program to develop an appropriate data base to aid in understanding the key geological processes and other related phenomena involved in this undertaking. A site selection for the repository is to be made in the mid-1980''s and repository operation could begin in the 1990''s. Several geological environments encompassing a number of emplacement media will be examined before final site selections are made.
Radioactive wastes are produced in a variety of ways. Major sources of such wastes are the mining of uranium ore, defense-related nuclear activities, and the operation of commercial nuclear power reactors. Other sources include the nuclear wastes generated in various research investigations and in medical diagnostics and therapy with radio-pharmaceuticals. The disposal of radioactive wastes is perceived to be a significant problem. Radioactive wastes are generally subdivided into five categories:
(1) High Level Wastes (HLW) -- These wastes are either intact nuclear fuel assemblies or the wastes generated during fuel reprocessing. The reprocessing wastes contain virtually all fission products and actinides not separated during reprocessing.
(2) Transuranic Wastes (TRU) -- These wastes also arise in reprocessing of fuel or in weapons'' fabrication. They are currently defined as material containing more than 10 nanocuries of transuranic activity per gram of material.
(3) Low Level Wastes (LLW) -- These wastes contain less than 10 nanocuries of transuranic activity per gram or they may be free of transuranics altogether. (4) Uranium Mine & Mill Tailings -- These are residues from mining and milling operations.
(5) Gaseous Effluents -- These wastes are usually released into the biosphere and thus become diluted and dispersed. In Table I, estimates for the current U.S. nuclear waste inventories and projections through the year 2000 are given. Waste quantities are given in units of volume (thousands of cubic meters). Uranium mine and mill tailings and explicit estimates of decontamination and decommissioning (D&D) wastes are not included in the table. D&D wastes pose special technical and occupational exposure problems. The disposal requirements for this class of wastes cannot be simply specified since they will differ for particular sites and facilities. Evaluations will have to be done on a case-by-case basis. By far the most challenging aspect of the radioactive waste management problem deals with the disposal of high-level and transuranic nuclear wastes, including spent fuel elements from commercial power reactors. To develop and provide the capability for the long-term disposal of these high-level nuclear wastes, the U.S. Department of Energy (DOE) established the National Waste Terminal Storage (NWTS) program in 1976.
The paper describes the geological and geotechnical investigations and engineering design and execution for the construction of an LPG underground storage in an impermeabilized rock cavern in silicified chalk above the watertable. It explains the ecological, technical, economical and safety reasons which are the basis for this novel approach for hydrocarbon underground operational storage.
A small operational storage in the vicinity of a suitable pipe network is under construction to supply the Jerusalem district and surrounding areas with LPG. Techno-economical, safety, security and ecological reasons made a novel approach for this task necessary. Terms of reference were to find a site for the excavation of cavern in suitable geological and hydrological conditions for the storage of 7,500 tons of LPG. The investigation of rock formations and hydrological conditions of Mesilat Zion area was made to find a suitable location for the excavation of a cavern in suitable rock. The area of study is located at the foothills of the Judean Mountains, 20 km west of Jerusalem, between two highways leading from Tel Aviv to the Capital. (Fig. 1). The landscape is built of rounded, nari encrusted, chalky hills of about 300-380 m height, covered with planted woods. Many dirt roads cross the area and accessibility is very good. Westwards, the hills become lower and gradually disappear into the Coastal Plain. Eastwards, there is a steepening of the slope into a prominent escarpment, building the west flank of the Judean Mountains. The area of study is part of Hashephela, which means in Hebrew, low land.
DESCRIPTION OF REQUIREMENTS
The rock formation required should have the following features :
Thickness of Layer
Thickness of relevant layer should be about 60 m, including a cover of 50 m over the hanging wall.
The rock formation should be in the range of at least 100 kg/cm unconfined compressive strength, in order to achieve an economically viable profile without support. The rock quality should be suitable for mechanical mining without blasting.
The cavern should be located above any existing aquifers and above any clay layers with excessive swell factors.
General Geological Setting
The area of study is located in the centre of Hashephela Syncline flanked to the east by the prominent Judean Anticline and to the west by the Kefar Uriyya undulation (Fig. 2). The strata in the area are horizontal to subhorizontal (3°- 4°). Upper Cretaceous rock (Cenomanian, Turonian, Senonian and Maastrichtian) crop out at both highs, east and west of the area, whereas Tertiary rocks (Paleocene and Eocene) comprise the selected site. The upper Cretaceous rocks are of no direct interest for building the storage, nevertheless, they are of interest while discussing water levels, aquifers and the question of preventing active aquifer pollution. The area is considered to be stable tectonically and seismically, only few faults are observed in the margins of the area (2-3 km southwards).
The reasons to store sand in in-rock bunkers are described. A case history on the planning and excavation of the Malmi sand bunkers is presented. A complete state of stress-measurement was carried out and the whole structure was analyzed with a finite-element method. The results of these investigations verified assumptions based on previous experiences. The construction was carried out by me ns of long-hole drilling from above simultaneously with tunnelling from below.
Sanding is a well-known and widely used method of improving trafficability and traffic safety on snowy and icy roads. Under heavy traffic sand tends to fly up from the road surface and that''s why salt is mixed with the sand. The salt solution forms a membrane around the sand grain. This membrane melts a hole in the ice and snow and the sand grain will stay on the road. However, when much salt is used, it causes increased corrosion in cars. In order to make sanding as efficient as possible, the sand used must be non-frozen and readily available. The sanding must be done within a short period after a snowfall, or when the roads are wet and the temperature below 0ºC. The need for speed is the main reason for storing the sand near the place where it is needed.'' Sand can be stored in various ways:
The rationale for using subsurface space applies to developing nations but very little has been done. Using mined-out space for food storage may help solve the serious problems of post-harvest food losses and hunger. Much of the mined-out space in the developing nations is unsuited to secondary use but investigations are needed to determine what and where the potential is.
In exploring the concept of using underground space for storage in the developing countries of the world, certain observations became apparent. Underground development is gaining great momentum in business, academic, and governmental circles. Even the public, in parts of the United States, is developing earth-sheltered housing at an astonishing rate. A new regard for basic resources has caused attention to be focused on earth-sheltered housing. They cost less to build, to heat, to cool, and to maintain. Today, we must move from a philosophy of waste and exploitation of non-renewable resources towards conservation. It was inevitable that sooner or later we would begin to truly and appropriately value the basic resources on this planet, including subsurface space. This symposium has as its focus three primary advantages of subsurface space. I would like to look at these for a moment and consider how they might apply to the developing countries.
We tend to think of the developing countries as having low-energy economies, and compared to the industrialized nations, this is true. But the high cost of energy of the past few years has hit the developing nations very hard. It has caught them when popular expectations were beginning to rise with standards of living. Now, high-cost energy is draining their treasuries of the precious foreign reserves and capital required to maintain their economic growth. Agricultural development, industrial and technical advances, and improved social services are also being impaired. During this century, the process of modernization has been largely subsidized by cheap energy. Except for the oil-rich, this is no longer possible; and yet for the present, we have no replacement. So while it is true that long and quick-tempered lines at the gas pump will probably not appear in the villages of Zambia, Thailand, and Honduras, it is also true that energy conservation is as important in the developing countries as in the industrialized nations.
PROTECTION OF THE URBAN ENVIRONMENT
Since World War II, probably the greatest human migration in history has been occurring in the developing countries--the migration from the countryside to the cities. It goes on still, creating gigantic urban centers where once only large towns stood. New Delhi has increased its population over 400% in this period. No wonder they are thinking of building an underground transit system. Calcutta''s, by the way, is already under construction. Trying to deal with such logistical problems on the surface was really quite out of the question. So I don''t think there is any doubt that the great cities of the developing world will be looking underground to solve some of their problems. In fact, architect Jannson of Sweden (1974) predicts that urban subsurface construction will double every ten years in both the developed and developing countries.
The Spent Fuel Test-Climax (SFT-C) is a test of dry geologic storage of spent nuclear reactor fuel. The SFT-C is located at a depth of 420 m in the Climax granitic stock at the Nevada Test Site of the U.S. Department of Energy. Eleven canisters of spent commercial PWR fuel assemblies are to be stored for 3 to 5 years. Additional heat is supplied by electrical heaters, and more than 800 channels of technical information are being recorded. The measurements include rock temperature, rock displacement and stress, joint motion, and monitoring of the ventilation air volume, temperature, and dewpoint.
The Lawrence Livermore National Laboratory (LLNL) as a participant in the Nevada Nuclear Waste Storage Investigations (NNWSI) program is responsible for the technical direction of a test of geologic storage of spent reactor fuel. This test (generally referred to as the Spent Fuel Test-Climax or SFT-C) is at a depth of 420 m in the Climax granite at the Nevada Test Site. The NNWSI is part of the commercial waste management activities of the National Waste Terminal Storage (NWTS) program of the U.S. Department of Energy (DOE). At the time the SFT-C was authorized in June 1978, there was no high level nuclear waste in deep geologic storage, even at a demonstration or pilot scale. Furthermore, the only previous such test, Project Salt Vault (Bradshaw and McClain, 1971), was in bedded salt, and no actual experience with deep geologic storage in other rock types existed. At the Nevada Test Site (NTS) of the DOE, there existed facilities both for encapsulating spent fuel assemblies in canisters suitable for underground storage and for a test layout near previously mined workings at a depth of 420 m.
Therefore, a test was planned which would have both educational and demonstration value as well as address technical issues of rock response to the waste. The technical concept for the SFT-C (Ramspott and others 1979) provides a simulation of the thermal field of a large repository within a 15-m x 15-m repository model cell. The heat sources are 11 canisters of spent commercial PWR fuel assemblies and 6 electrical fuel-simulators in a central canister storage drift. These are supplemented by 10 electrical heaters in each of 2 adjacent heater drifts (Fig. 1). By comparison of the electrical simulators with the spent fuel, it is possible to evaluate the effects of heat alone with heat plus ionizing radiation. Work performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48. Spent fuel emplacement was completed by May 28, 1980, at which time the decay heat from each fuel assembly was about 1550 W. Following encapsulation at a facility about 75 km from the storage site, the canistered fuel was transported and emplaced with a system designed specifically for this test. No hot cell was built at the site, and although sufficiently shielded for personnel access at all times, operations at the Climax site were remotely controlled.
Albrecht, H. (Bundesanstalt fur Geowissenschaften and Rohstoffe (BGR), Hannover, Federal Republic of Germany) | Langer, M. (Bundesanstalt fur Geowissenschaften and Rohstoffe (BGR), Hannover, Federal Republic of Germany) | Wallner, M. (Bundesanstalt fur Geowissenschaften and Rohstoffe (BGR), Hannover, Federal Republic of Germany)
The temperature rise resulting from the radioactive decay of high level waste may cause geochemical and geomechanical reactions within the host rock, which are important for the development of final design criteria of a radioactive waste repository. A realistic and acceptable concept for a convincing safety analysis can be derived from the principle of multiple barriers:
1. separate analysis of the effectiveness of the individual barriers,
2. analysis of the physical and geochemical processes, which arise as a result of the interrelation between the barriers of different systems,
3. comprehensive safety analysis of the final repository by identification and evaluation of the combined effects of all barriers under certain theoretically imaqinable events.
Calculations on the thermomechanical effects on the geological barrier and the proof of the integrity of the salt dome over long times are an important part of the safety analysis. A simplified model has been used for non site specific calculations. Some results of the calculation of the thermo-mechanical stress and strain field around the repository are discussed and their importance for the structural stability of the repository and the salt dome will he illustrated.
The safe disposal of radioactive wastes is one of the most important problems of modern technology. In no other engineering project do safety aspects have such a foremost role as they do in waste disposal of atomic power plants. This requires the equal efforts of geo-scientists and engineers. The, in part, controversial and emotionally loaded public discussion on the problem of final storage .of radioactive wastes has given rise to the impression that decisive problems of this complex question were not recognized and that the scientists and experts were suddenly and without preparation confronted with this problem. This impression is wrong. The truth is, that geologists - also engineering geologists and rock mechanical engineers - have been working resolutely and systematically for more than ten years on the concept of final storage. In the Federal Republic of Germany the main emphasis of the research work was placed early upon a final storage in the diapiric salt structures of Northern Germany. This paper is a contribution to the discussion of the feasibility of the final storage concept. The special properties of rock salt, upon which the suitability for a long term safe final storage is based, are presented. Furthermore, unanswered questions and problems will at least be explained by means of examples, a concept for an extensive safety analysis will be presented and also on the basis of a calculation of thermo- mechanical effects, methods of solving the problems will be indicated.
SUITABILITY OF SALT DOMES FOR THE FINAL STORAGE OF RADIOACTIVE WASTES
In the following, final storage is understood to be the maintenance free, safe storage of radioactive wastes. Every final storage concept must therefore, fulfill the requirement that the wastes remain isolated from the biosphere until the activity of the separate radionuclides has subsided to an acceptable level. Depending on the composition of the waste products, this means a period between 103 and 106 years.
This paper describes how a rather conventional rock cavern will be used for intermediate storage of spent nuclear fuel from the Swedish nuclear power stations. The plant and the spent fuel handling is generally described. The design requirements for the rock cavern postulate very high safety demands. An extensive reinforcement will therefore be carried out in order to guarantee the stability of the rock cavern. The cost of the rock cavern will be reasonably low, in spite of the extended costs of reinforcement, compared to the advantages which are obtained by this type of sub-surface storage.
In order to increase present spent fuel storage capacity available at the Swedish nuclear power stations, the Swedish Nuclear Fuel Supply Company (SKBF) is planning to erect an intermediate spent fuel storage facility (CLAB). Oskarshamnsverkets Kraftgrupp Aktiebolag is assisting SKBF in realising the CLAB project, and the Swedish State Power Board (SSPB) is designing the building constructions. The other main consultants engaged in the project is Asea-Atom (Sweden) and Societe Generale pour les Techniques Nouvelles (France).
CLAB will be located close to the Oskarshamn nuclear power station. All permits required to the facility were obtained in 1979. CLAB was then the first licensed spent fuel storage facility of its kind in the western world.
The fuel elements will be stored in a rock cavern, which provides very good protection against external impacts such as acts of war and sabotage. The bedrock will also protect the environment by isolating the fuel in the unlikely event of any internal impact taking place. The advantages of this sub-surface storage are obtained at a reasonably low cost compared to the cost of a storage building on the surface designed to resist the same impacts.
The rock cavern will be constructed using well-known techniques. This paper will describe how a rather conventional rock cavern can be used in combination with techniques for nuclear fuel handling. The description of the design and construction work is based on knowledge of the existing rock mass on the site.
THE CLAB FACILITY - GENERAL DESCRIPTION AND LAYOUT
The CLAB design is based on a storage capacity of 3000 metric tonnes of uranium, with provisions to permit an expansion of this capacity to 9000 tons. In terms of function, the CLAB facility can be divided into three main parts: fuel reception, storage and auxiliaries.
Spent fuel from Ringhals, Barseback and Forsmark nuclear power stations will arrive at the harbour of the Oskarshamn power station on a ship specially designed for this purpose. The fuel elements will be transported in containers called casks. These casks are designed to provide adequate protection against damage during transport. The casks will be transported on a special vehicle from the ship or from Oskarshamn power station to the CLAB facility. The vehicle will bring the cask to the fuel reception building at CLAB. In this building, the casks will be cooled down and then placed in an unloading pool. The fuel elements will be unloaded under water, which provides protection against radiation, and then placed in special canisters.
Cities all over the world are confronted with ever growing problems in keeping alive and functioning. This means that at an ever increasing speed the underground has got to be used where there are no good solutions anymore above ground for many vital elements. Subsurface construction used to be too expensive in many cases but now gives a much wider scope because of new developments in building techniques and because of a growing awareness of what should be put underground to preserve precious space above ground for people to use to its best advantage. Problems to be solved both in hardrock and in soft ground are often very big since the city has got to remain functioning and both construction as well as maintenance should be done as un-obstrusively as possible. Examples from Oslo Norway, and Amsterdam Netherlands will be given. HARDROCK, THE OSLO EXPERIENCE
The City of Oslo, surrounded by hills, is situated at the end of the Oslo fjord(Fig. 1). The built up areas of the central part of Oslo consist mainly of 4-5 storeyed buildings which were erected in the later half of the 19th century. The greater part of these buildings are founded on clay deposits. Newer buildings can be considerably higher, but are then founded on rock. As in most established cities planning and building of new highways, a public transport system, and transportation systems for sewage and storm water drainage confronts the city planners and engineers with many problems. Very often the only solution is subsurface constructions. This chapter will deal with the more important aspects of rock constructions under urban areas with reference to experience gained by various public works departments in the Municipality of Oslo. Especially in two fields much new practical knowledge has been obtained recently, i.e. in the use of full face tunnel boring machines (TBM) and in grouting techniques against ground water leakage.
1.2. Geological conditions.
The geological conditions in Oslo are known to be very complex(Fig. 2). The rocks originate from three different geological periods. The oldest are the pre-Cambrian gneisses (1800 million years old). We find these mainly in the eastern parts of town, but they also form the foundation for Akershus Castle which lies in the centre of the town. The cillnbro-silurian sedimentary rocks arc about 570 to 350 million years old. These rocks consist mainly of different kinds of shale and limestone. These appear in the western and central part of town. The youngest rocks are the permian rocks which are about 250 million years. During the permian age the area around Oslo underwent great changes including large volcanic activities. The rocks from this period consist of java, basalt, syenite and porphyrite. These igneous rocks are found in the northern part of the town and also in the form of sills and dykes penetrating the sedimentary rocks and even the pre-cambrian bed-rock. There are large differences in the compressive strength of the different types of rocks. Some examples will show this:
For the past 20 years almost all new storage plants in Finland, Norway and Sweden installed for crude oil and refined products have been constructed in mined, unlined caverns. This has proved to be the cheapest and safest way. However, the promotion of this technology in other countries has been more complicated than expected. Many obstacles have appeared e.g. less favorable geophysical conditions, fears about environmental damage, laws etc. not related to underground storage. Another major obstacle is the present uncertain state of the petroleum world market. The various obstacles we have encountered are discussed in this paper. BACKGROUND
The method of storing crude oil and refined products in mined, unlined caverns is, in Finland, Norway and Sweden, the cheapest and safest way provided that the quantities are not too small. This is confirmed by the fact that during the two last decades nearly all new storage facilities - both commercial and strategic - have been constructed underground. More than 100 plants with a total storage capacity of more than 25 million cubic meters (160 million barrels) have been completed. With this experience and knowledge of all the advantages, considerable efforts have been made to introduce this technology in several other countries. But what was simple and easy in the three countries mentioned above has proved to be more complicated and has taken much longer than expected. We are surprised and somewhat disappointed that this technique has not been generally accepted in other countries and we have difficulties in understanding the reasons for this. Based on the experience of several pre-investigations and feasibility studies executed in South and Central Europe, North America, Africa and Asia the different causes of the obstacles met with are discussed here.
The geophysical conditions in our countries are in general favorable for subsurface constructions. Most of the bedrock consists of very competent granite or gneiss. Decomposed and weathered rock was removed during the last big ice age which means that it is easy to reach the bedrock without any major excavation of overburden. However, it should not be assumed that all rock in these countries is of good quality; now and then we also encounter bad rock conditions. Special methods and equipment have been developed to be used in such cases and the projects can still be completed on a sound economic basis for the owner. The ground water situation is also favorable and it is usually easy to find a stable groundwater table, the level of which is secured and proved by proximity to the sea or lakes. The lack of active seismic zones is also important. It is quite obvious that it is not possible to find places all over the world with this favorable combination of conditions. However, there are several places with similar, good conditions in many areas of the world. Simple estimates also show that there are considerable economic advantages to be gained in constructing storage facilities even in less favorable rock masses; such plants are still able to compete on an economic basis with steel tank storage systems.
Funcken, R. (Tractionel Engineering, Brussels, Belgium) | Mayence, M. (Tractionel Engineering, Brussels, Belgium) | Heremans, R. (CENISCK, Mol, Belgium) | Manfroy, P. (CENISCK, Mol, Belgium) | Vanhaelewyn, R. (CENISCK, Mol, Belgium)
The construction of a shaft and a experimental gallery has started under the site of the Centre d''Etude de l ''Energie Nucleaire (C.E.N./S.C.K.) at Mol in Belgium. The shaft, excavated by means of freezing technique, will be 225 m deep and will give access to anhorizontal gallery 30 meters long with circular cross section, excavated in plastic clay at a depth of -220 m. The C.E.N./S.C.K. will take advantage of the shaft sinking to implant a series of measuring devices in the clay in order to assess certain geomechanical parameters of the in situ clay as well of the resistance characteristics of the shaft lining. This geotechnical campaign will allow to get experience about frozen clay at that depth and to test the measuring devices prior undertaking a long term extensive experimental campaign in the gallery.
Since the end of 1973, the Centre d''Etude de l ''Energie Nucleaire (C.E.N./S.C.K.) at Mol, Belgium, has been working on an R&D-program for the disposal of conditioned radioactive wastes in geological formations. In the scope of this program, the Geological Survey of Belgium has helped in drawing up an inventory of the formations of the Belgian subsoil that would be suitable for that purpose. One of the selected formations is a clay layer at medium depth underneath the C.E.N./S.C.K. facilities (Fig. 1). In Belgium this formation is known as "Boom clay". A drilling campaign along with high accuracy seismic survey have allowed definition of the structure of the formations while intensive laboratory experiments with samples taken in situ during drilling work have led to specifying the physical, chemical, mineralogical and mechanical properties of the clay. A conceptual and feasability study of a facility to dispose conditioned wastes in the clay was carried out. This study yielded a number of plausible burial facilities and a number of plugging techniques. It also evidenced that a large number of major questions would remain unanswered as long as there would not be any experimental facility in the selected layer. C.E.N./S.C.K. therefore undertook preliminary digging work early this year. The whole facility is scheduled operational by the end of 1982.
GEO-TECHNICAL MEASUREMENTS CAMPAIGN
The foreseen underground facilities will be composed of a vertical access shaft, an intermediate room and an horizontal gallery (Fig. 2). The shaft will be cylindrical and will have an inner diameter of 2.65 m. The tunneling of the horizontal gallery will begin from a circular intermediate room at the low end of the shaft. The gallery will have an inner diameter of 3.50 m. its centerline will be at 220 m depth, approximately at mid-depth of the host layer. Its length will be about 25 to 30 m. The shaft, gallery and intermediate room will be used as underground laboratories where a series of in-situ tests will be carried out on the clay (mechanical properties, heat transfer, migration, corrosion, etc.) as well as on the lining material (resistance, deformation, permeability, corrosion, etc.) and where technological drilling tests in the clay core can be made.