Sustainability of uranium sources

Smith and Storm van Leeuwen (SSL, 2005) point out that the growth of the energy requirements for uranium mining and milling at decreasing ore grades will cause the output of the nuclear energy chain to become negative at uranium contents in the ore below 100 - 200 ppm. They conclude that an expiration of uranium will occur by 2076 in a business-as-usual scenario and by about 2050 when a 2.5 % annual growth of the consumption is assumed. The high relevance of this issue is the motivation for a detailed review of these results. The concept of a limiting ore grade was introduced by Chapman already in 1975. His model has been fitted to the performance data of the Roessing mine in Namibia operating at low grade, which makes further extrapolations more reliable. The performance data published in open literature allows quantifying the energy requirements for the removal of the waste rock separately from those for the mining of the ore, which is one of the concepts of Chapman. It is shown that the amount of waste rock to be removed per unit ore has a strong effect on the energy consumed in the mine. The limiting ore grade is much lower than the one predicted by SSL and much higher amounts of uranium are predicted for a continuation of the utilization of nuclear power. Despite of the fact that SSL cite the paper of Chapman (1975), they decide to develop an own oversimplified model based on a reciprocal proportionality of the energy requirements to the ore grade alone, which is a significant step back. SSL even cite a statement of Chapman directly, saying that the stripping ratio can influence the energy requirements of uranium mining 'by a factor of five', without drawing the right conclusions. Furthermore, neither a comparison to more recent mine data, nor any kind of an uncertainty analysis is presented. The approach of SSL must therefore be disqualified as unscientific and their results discarded. (authors)