One tonne of nuclear fuel produces energy equivalent to two to three million tonnes of fossil fuel. [Suzuki (1993), cited in Lehman (1996), p. 138.] Burning 1 kilogram of firewood can generate 1 kilowatt hour of electricity; 1 kg of coal, 3 kWh; 1 kg of oil, 4 kWh. But 1 kg of uranium fuel in a modern lightwater reactor generates 400,000 kWh of electricity, and if that uranium is recycled for maximum burnup, 1 kg can generate more than 7,000,000 kWh. These spectacular differences in volume of fuel per unit of energy produced largely determine the differing environmental impacts of nuclear versus fossil fuels from mining or extraction, through transportation, to environmental releases and the disposal of waste. Generating 1,000 MW of electricity for a year requires 2,000 train cars of coal or 10 supertankers of oil, but only one 10 cubic-meter fuel assembly of uranium. [IAEA (1997), P. 32.] Out the other end of such fossil fuel plants even with abatement systems operating come thousands of tonnes of noxious gases, particulates and heavy-metal-bearing (and radioactive) ash plus solid hazardous waste: up to 500,000 tonnes of sulfur if coal, more than 300,000 tonnes if oil and 200,000 tonnes if natural gas. In contrast, a 1,000 MWe nuclear plant releases annually no noxious gases or other pollutants, [5]  and trace radioactivity many times less per person than airline travel, a home smoke detector or a television set. It produces about 30 tonnes of high-level waste (spent fuel) and 800 tonnes of low- and intermediate-level waste about 20 cubic meters in all when compacted (roughly, the volume of two passenger cars). [6]  [IAEA (1997), pp. 32-34.]

[snip]

Photovoltaic cells are large semiconductors; their processing produces a highly toxic waste stream of metals and solvents that requires special disposal technology. A 1,000 MWe solar electric plant using photovoltaics would generate 6,850 tonnes of hazardous waste over a thirty-year lifetime from metals finishing alone. A comparable solar thermal plant (mirrors focussed on a central tower) would require primary metals that would generate 435,000 tonnes of manufacturing waste, of which 16,300 tonnes would be contaminated with lead and chromium and considered hazardous. [Lehman (1996), pp. 53-54.]

Notes:

IAEA (1997). Sustainable Development and Nuclear Power. Vienna, International Atomic Energy Agency.

Lehman, L. L. (1996). Nuclear Fear: The Environmental Cost. Prior Lake MN, Technical & Regulatory Evaluations Group, Inc.

Excerpts from: Richard Rhodes, Denis Beller, "The Need for Nuclear Power", Foreign Affairs, Jan/Feb 2000  http://www.nci.org/conf/rhodes/index.htm

In about 40 years of operation, commercial nuclear power in the US has generated about 70,000 tonnes of spent nuclear fuel.