Uranium evaluation and mining techniques

Full text: Report on an IAEA/NEA/IANEC international symposium, Buenos Aires, Argentina, 1-5 October 1979. The symposium was attended by 162 participants from 35 countries and five international organizations, with 35 observers also registered. Twenty-nine papers and two informal discussions were presented in seven sessions. Planning nuclear power programmes is fraught with a very wide range of uncertainties, some of which are the uncertainties associated with rising costs and ever-lengthening lead times, the uncertainties of the rate of growth of nuclear energy, the uncertainties caused by anti-nuclear activities, and the uncertainties of uranium resources and availability of uranium supplies. Present known resources, not all of which may actually become uranium supply before the year 2025, are slightly less than 5 million tonnes uranium. Even if all these resources could be produced, production rates from them would drop seriously in the mid-1990s. It is, therefore, most important that the uncertainty of uranium resources and availability of supply be dealt with promptly. In this respect many countries of the world have begun national programmes either to determine their uranium potential, or to explore for uranium deposits. The symposium held in Buenos Aires at the invitation of the Government of Argentina sought to provide these countries with a state-of-the-art report on the various methods of uranium resource evaluation. Developments and improvements in both new and old techniques of mineral assessment proliferate. Notable among the 'newer' methods are geostatistical estimation of ore reserves, a sophisticated method which, although still under development, has gained wide recognition. In the domain of objective measurements and sample-based estimation procedures, the older classical methods also yield acceptable estimates when properly used. But uranium ore reserves are always inadequate for long-range planning, seldom exceeding a few years' demand. An accurate, comprehensive, and understandable appraisal of the world's potential uranium resources, and the ability to discover, develop and produce these resources within an acceptable time frame are absolutely essential to making meaningful decisions in relation to the future supply of nuclear fuel. Therefore, the methods used to appraise undiscovered uranium resources were examined and compared in the light of the needs of the world nuclear power industry as a whole. Notable among these methods is one based on interactive genetic models. It is currently being developed to reduce the amount of subjectivity inherent in most of the currently used appraisal techniques The goal is to use more geologic data and depend less on the intuition and experience of the estimator. The more esoteric statistical techniques based on past production rates, prices, rates of increase or decrease in reported reserves or resources, etc., while of unknown or unproved value, were not discussed at the symposium. The symposium provided a forum for discussion of closely related subjects as well. One of the major problems in reporting internationally in uranium resources is classification of the resources into various categories and defining those categories. Conceptually, among earth scientists, there is general agreement, but defining these concepts is a difficult task. At least three organizations have undertaken to develop classifications and definitions to satisfy the needs of international reporting. Two of these were described at the symposium. (The third has been used by the joint NEA/IAEA Working Party on Uranium Resources but was not described.) The techniques of winning uranium from its several sources include, besides mining by conventional open pit or underground methods, in situ leaching of low-grade ores in special environments, and from ores left in mines In addition, virtually all marine phosphates contain some uranium that can be recovered as a by-product in the manufacture of phosphoric acid in fertilizer plants This is being done at several plants in North America, and is gaining favour in many other parts of the world. Uranium is also recovered from copper leach liquors as a by-product and from gold ores in South Africa as a co-product. The symposium also noted that as prices for uranium concentrates increase, lower grade ores can be mined, but lower grade ores contain less uranium per ton of ore and result in lower recovery of uranium in the ore processing plant. Both of these factors require increased rates of mining and processing in order to maintain uranium production schedules and consequently the problem of grade control in the mine increases. Grade control is accomplished by three principle methods: by probing the blast holes in the mine to define the location of ore and waste before the holes are loaded, by pre-processing the ore using radiometric-mechanical means at the mine before sending it to the processing plant, or by radiometric bulk sampling to determine if it should be directed to the dump, stockpile or ore processing plant The final session of the symposium was devoted to production capability. The uncertainty of uranium supply cannot be dealt with only by development of resources. The capability of the industry to produce from those resources at a rate necessary to satisfy the demand must also be considered. This requires careful analysis of the ability of the mines to produce the ore and of the mills to process it. (author)