www.uic.com.au/nip57.htm
Energy Analysis of Power Systems UIC Nuclear Issues Briefing Paper # 57 January 2004 * Life Cycle Analysis, focused on energy, is useful for comparing net e nergy yields from different methods of electricity generation. If the financial c ost of building and operating the plant cannot profitably be recouped by selling the electricity, it is not economically viable. But as energy i tself can be a more fundamental unit of accounting than money, it is als o essential to know which generating systems produce the best return on the energy invested in them. Analysing this energy balance between inputs and outputs, however, is com plex because the inputs are diverse, and it is not always clear how far back they should be taken in any analysis. For instance, oil expended to move coal to a power station, or electricity used to enrich uranium for nuclear fuel, are generally included in the calculations. But what abou t the energy required to build the train or the enrichment plant? And ca n the electricity consumed during enrichment be compared with the fossil fuel needed for the train? Many analyses convert kilowatt-hours (kWh) t o kilojoules (kJ), or vice versa, in which assumptions must be made abou t the thermal efficiency of the electricity production. Some inputs are easily quantified, such as the energy required to produce a tonne of uranium oxide concentrate at a particular mine, or to produc e a tonne of particular grade of UF6 at a uranium enrichment plant. Simi larly, the energy required to move a tonne of coal by ship or rail can b e identified, although this will vary considerably depending on the loca tion of the mine and the power plant. Moving gas long distances by pipel ine is surprisingly energy-intensive. Other inputs are less straightforward such as the energy required to buil d a 1000 MWe power plant of a particular kind, or even to construct and erect a wind turbine. But all such energy inputs, as with cash inputs by way of capital, need to be amortised over the life of the plant and add ed to the operational inputs. Also the post-operational energy requireme nts for waste management and decommissioning plants must be included. As well as energy costs, there are external costs to be considered, those environmental and health consequences of energy production which do not appear in the financial accounts. Recent studies have plausibly quantif ied them in financial terms, and I will comment on those at the end. Many energy analysis studies done in the 1970s seem to have assumed that a rapid expansion of nuclear generating capacity would lead to a tempora ry net energy deficit in an overall system sense. However, this requires dynamic analysis of whole systems, and is not considered here. Studies were also driven by a perception that primary energy sources including u ranium would become increasingly difficult and expensive to recover, and would thus require undue amounts of energy to access them. The figures in Table 1 are based as far as possible on current assumption s and current data for enrichment, mining and milling, etc. Where curren t data is unavailable, that from earlier studies is used. For nuclear po wer, enrichment is clearly the key energy input where the older diffusio n technology is used - it comprises more than half the lifetime total. H owever, with centrifuge technology it is far less significant than plant construction. There is an overall threefold difference in energy ratio between these two nuclear fuel cycle options. As yet, no figures seem to have been tabulated for a closed fuel cycle wi th reprocessing, such as is UK policy (and upsetting some Irish observer s), although this would probably reduce the energy inputs for nuclear po wer production somewhat *. It is also important to recognise that precis e energy figures for plant construction are not readily available, altho ugh several studies use a factor converting monetary inputs to energy. The only data available for storage and disposal of radioactive wastes, n otably spent fuel, suggests that this is a minor contribution to the ene rgy picture. This is borne out by personal observation in several countr ies - spent fuel sitting quietly in pool storage or underground is not c onsuming much energy. Decommissioning energy requirements may be conside red with wastes, or (as Vattenfall) with plant construction.
On the same basis, Cogema's McClean Lake mine there input 56 TJ and two Cogema mines in Niger in 2000 input 37 TJ. Note that if ore of 001% U is envisaged, the Ranger data would give 58 P J for the centrifuge option. Comparison with ERDA 76/1: The Ranger data (1997-98) x 34 years shows onl y 20% of the mining & milling energy use but excludes plant construction . The diffusion enrichment data above (on higher tails assay, burn-up, and capacity factor) gives only 66% of the ERDA figure but excludes plant construction. ERDA notes that "the centrifuge process is expected to reduce the direct requiremen t for electricity by a factor of ten", in fact today it is better than t hat. for conversion: 167 PJ (Chapman 1975), 9 PJ (Perry et al 1977, table IV) . for fuel fabrication: 042 PJ (Chapman 1975), 5 PJ (Perry et al 1977, tab le IV). for waste facilities in Sweden: 019 PJ for decommissioning: Bruce A 52 PJ, Bruce B 43 PJ, Darlington 45 PJ, P ickering A 57 PJ, Pickering B 62 PJ. If 30 PJ or 25 PJ is taken for diffusion and centrif uge enrichment respectively as the energy capital cost of setting up, th en at 75 PJ/yr output the initial energy investment is repaid in 5 month s or 4 months respectively at full power. Table 2 Life Cycle Energy Ratios for Various Technologies Source R3 Energy Ratio. These figures show that energy ratios are clearly sensitive not only to t he amount of energy used, but also to capacity factors, particularly whe re there are significant energy inputs to plant. Just as with cash input s to plant construction, the higher the input cost the more output is ne eded to amortise it. With technologies such as wind, this is inevitably spread over a longer period due to lower capacity factors. The LNG figures quoted are for natural gas compressed cryogenically and s hipped to Japan and used largely for peak loads. The solar and wind figu res relate to intermittent inputs of primary energy, with inevitably low capacity utilisation and relatively high energy costs in the plant (for silicon manufacture in the case of solar cells, or steel & concrete for wind turbines). Unlike some others in use, the R3 energy ratio converts between electrica l and thermal energy, including a thermal efficiency factor. Nevertheles s the reciprocal percentage seems more meaningful. The Swedish utility Vattenfall has undertaken a thorough life cycle asses sment of its Forsmark nuclear power station, which has three boiling wat er reactors totalling 3100 MWe net. The energy analysis figures (transport included, 40 y r plant life, with PJ figures calculated from percentage on basis of 327 2 PJ output) were: input as % of output PJ Mine 044 14 Refining & conversion 318 104 Enrichment (80:20 centrifuge:diffusion) 300 98 Fuel fabrication 134 44 Plant operation 028 92 Plant build & decommission 027 88 Waste management 011 36 Waste build & decommission 001 Total life cycle: 870 % 285 PJ (This Vattenfall 2000 LCA study tracks energy inputs further back than ot hers, hence it is only comparable with data based on similar methodology . Wind and solar, however, are under 10 because of their lower energy density. Vattenfall (1999) mentions that the production of pure silicon for solar photovoltaics (PV) requires large energy inputs and accounts for most re source consumption in solar cell manufacture. Voss (2002) shows hydro, wind and nuclear with inputs less than 7% of lif etime outputs, then gas and coal between 17 and 30%.
Life cycle analysis: external costs and greenhouse gases A principal concern of life cycle analysis for energy systems today is th eir likely contribution to global warming. If all energy inputs are assumed to be from coal-fired plants, at about o ne tonne of carbon dioxide per MWh, it is possible to derive a greenhous e contribution from t...
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