related to the longevity (timescale of availability) of the primary energy source in the current fossil-based global energy pathway (Hall, 2004).

Both renewables and nuclear can meet the longevity and environmental friendliness criteria for sustainable development. Renewable energy sources are indigenous and abundant. Solar and wind power are inexhaustible as long as the sun shines and it does so unevenly. Hydroelectric power is the world’s largest source of renewable electricity, with considerable unexploited potential. Less than a ...fth of technically exploitable hydropower has been used to date (WEC, 2007). Much of the potential for new development is in Asia, Latin America, Africa, and the former Soviet Union. Uranium is present at a concentration of 2 - 3 parts per million in the Earth’s crust which is about 600 times greater than that of gold. The total known global uranium reserves which can be mined at less than $US 130 are estimated to be around 4.7 million tonnes. At current rates of usage, in a once-through cycle these uranium resources would be adequate to supply the world’s nuclear power stations for at least 100 years. Deployment of fast breeder reactors and recycling of transuranic from recycled spent fuel could lengthen this period by 50-fold or more and thus increase the long-term availability of nuclear energy to several thousand years. It should also be noted that in recent years, growing demand and higher prices have spurred increased investment in exploration activities and led to substantially larger identi...ed uranium resources. Indeed, the identi...ed world reserves of uranium have risen by over 50% since the end of 2003. In Russia alone, proven uranium reserves have reached 545,000 metric tons, a 275 percent increase from 2006. Speculative uranium resources, i.e. deposits that are likely to be discovered on the basis of the geological characteristics of already identi...ed resources, have risen to over 10.5 million tonnes (NEA, 2008).

Renewable technologies and nuclear power have signi...cant environmental bene...ts compared to fossil fuel based electricity generation. Under normal operating conditions, wind, solar, and nuclear plants produce almost none of the residual fossil fuel pollutants which include particulate matter, sulfur dioxide, nitrogen oxides, and a variety of heavy metals— mercury being the most prominent. In the case of nuclear power, small quantities of radioactive gases are emitted under controlled conditions imposed and supervised by regulatory authorities and pose no signi...cant threat to plant workers or surrounding populations. Moreover, numerous LCA cradle-to-grave studies point to a very substantial gap between coal, oil and gas at the high end and wind, hydro, solar, and nuclear at the low end, in terms of their CO2 emissions per unit of electricity generated–the average estimates being 1.2 kg CO2/kWh for coal, .4 kg CO2/kWh for gas, .06 kg CO2/kWh for solar PV, .011 kg CO2/kWh for wind (onshore), .008 kg CO2/kWh for nuclear, and .005 kg CO2/kWh for hydro (OECD/NEA, 2008).

# 5.2 Capacity to Deliver Net Excess Energy

There is substantial variance across the di¤erent electricity generation options in terms of their lifetime capacity to deliver net excess energy. With the exception of hydro, renewables 18