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Nuclear power, energy security and CO2 emission

May 2012

 

Summary

Nuclear power is claimed to be indispensable for energy security and climate control, as part of the future world energy supply. Energy security and climate control are physical issues at global scale. Therefore a physical analysis of the lifetime energy and material balance of the nuclear energy system is essential to assess these issues.

This study, with a global perspective and a long time horizon, comprises a full life cycle assessment (LCA) of a nuclear power plant combined with an energy analysis. The LCA charts the complete sequence of industrial processes needed to generate nuclear power, called the nuclear energy system or the nuclear process chain, from cradle to grave. The energy analysis examines all inputs and outputs of materials and energy of the nuclear energy system, applying a reliable methodology developed in the 1980s by a large international group of scientists and economists.

The climate footprint of nuclear power encompasses not only the emission of carbon dioxide CO2, but also the emission of other greenhouse gases. Virtually no data are available on the emission of greenhouse gases other than CO2 by the nuclear energy system, so this study limits its scope to the analysis of the emission of CO2.

The nuclear CO2 emission is assumed to be caused by burning fossil fuels and some chemical reactions (e.g. cement and steel production) in the nuclear chain. The electrical inputs are assumed to be provided for by the nuclear system itself.

This study is based on a reference Light-Water Reactor (LWR) in the once-through mode, which may considered a model for the newest currently operating power reactors and a model for virtually all nuclear power plants under constuction or in the planning stage. Closed-cycle reactor systems (breeders), if ever possible are unlikely to come on line before 2050.

The nuclear process chain comprises three main components, each consisting of a sequence of separate processes: front end, mid-section and back end. The processes of the front end and the mid-section may be considered technologically mature.

The back end imposes a heavy burden on the society, due to a unique and dominant feature of nuclear power: the generation and mobilisation of huge quantities of man-made radioactivity, inextricably and irreversibly. Each year a 1 GWe nuclear reactor generates as much radioactivity as 1000 exploded nuclear bombs of 15 kt, about the yield of the Hiroshima bomb.

Radioactivity is extremely dangerous to man and cannot be destroyed nor made harmless, so it has to be immobilised and isolated from the biosphere forever. The vital processes of the back end, needed to achieve a safe situation with regard to the man-made radioactivity, are systematically passed on to the future. No new technologies are needed to finish the nuclear process chain, just vast amounts of materials and energy. The timescale to finish the back end of a given nuclear power station is unprecedented: 100 years or more.

The energy analysis in this study quantifies the direct and indirect energy investments, required to construct and operate the nuclear energy system and for completing the back end: the definitive storage of the radioactive wastes, including the closed down reactor. The energy investments of the yet non-existing processes of the back end are approximated by analogy with similar, existing, processes.

Major findings of the energy analysis are, among other:

• At an operational lifetime of 25 full power years (3-4 FPY more than the current world average) the mean energy return on energy investments over the cradle-to-grave (c2g) period is EROEI = 2.01.

• Energy investments for construction and decommissioning plus dismantling are fixed energy investments, which are assumed not to depend on the operational lifetime of the reactor. Both quantities cannot be estimated accurately, due substantial uncertainties and spread in the basic data. This analysis comes to a mean value of 200 PJ 80 PJ, about half of the c2g energy investments of the nuclear power plant.

• The specific energy consumption of the fuel chain (front end + back end) increases with decreasing grade of the uranium ore feeding the nuclear system and starts rising exponentially at grades below 0.3% uranium. Consequently the lifetime net energy delivered by the nuclear power plant to the consumer declines as the average ore grade declines. When fed by uranium from ores at grades below 0.02% uranium the EROEI of the nuclear system approaches unit, meaning that the nuclear energy system becomes an energy sink instead of an energy source. The rapid decline of the net energy production at low grades is called the energy cliff and turns out to be nearly independent on the height of the fixed energy investments (construction and dismantling) and independent on the performance of the nuclear energy system as a whole.

• If no new rich uranium resources of significant size are discovered during the next decades, the nuclear system will fall off the energy cliff in the period 2050-2080, within the lifetime of new nuclear build, depending on the capacity of the world nuclear capacity.

• The chance of discovering of new rich uranium ore deposits of significant size are unknown. During the past few decades no significant discoveries have been reported.

• Basically the depletion of uranium resources as source of useful energy is a thermodynamic notion.

• The specific CO2 emission of the baseline nuclear system in this study is 84 -130 gCO2/kWh, if supplied by uranium ore at a grade of 0.13% U. At a grade of 0.05% U, about the current world average, the emission is 98-144 gCO2/kWh. The large spread in the emission figures is caused by uncertainties in the data used to calculate the emission. These figures are higher than the results of other studies, due the choice of the system boundaries: this study includes all processes of the c2g period. No other studies has done so.

• Note that the unit geqCO2/kWh should not be applied here, because only the nuclear CO2 emission is known, excluding other greenhouse gases. There are reasons to suppose that the nuclear process chain emits also other greenhouser gases, in view of the large amounts of fluorine and chlorine and their compounds being used in the nuclear process chain. These emissions are a well-kept secret of nuclear power. However, 'no data' does not mean 'no emission'.

• A rising specific energy consumption of the nuclear chain with decreasing ore grades causes a rising specific CO2 emission per kilowatt.hour. When the nuclear system is fed by uranium from ores at grades below 0.02% uranium, the specific CO2 emission of nuclear generated electricity surpasses that of gas-fired and even coal-fired electricity generation. This phenomenon is called the CO2 trap.

• If no new rich uranium resources of significant size are discovered during the next decades, the nuclear system will get stuck in the CO2 trap in the period 2050-2080, within the lifetime of new nuclear build, depending on the capacity of the world nuclear park.

• About half of the c2g energy requirements has not been invested at the moment of closedown of the reactor, but has irrevocably to be invested in the century thereafter. This 'mortgage' is called the energy debt of the nuclear system. The energy debt refers to the activities to be done in order to keep the human environment habitable and avoid societal and economic disruption: final disposal of all radioactive wastes, including the reactor and associated equipment.

Novel notions introduced by this study are: energy cliff, CO2 trap and energy debt. In addition to the introduction of these novel notions this study is distinct from other studies by the choice of the system boundaries of the analysis: all processes and activities causally related to the generation of nuclear power are included. This implies, among other, an exceedingly long time horizon of 100-150 years. Other studies deleted one or more processes from the process chain and/or ignored the indirect energy investments. Another distinction is that this study relies on empirical data where possible and on proven technology, not on concepts only existing in cyberspace. As a consequence many figures with regard to energy requirements and CO2 emissions are higher than in other studies.

A number of references are dating from the 1970s and 1980s. The concerned technologies have virtually not been changed since. Besides, the information flow in the open literature from the nuclear industry on relevant matters has become increasingly meager during the past few decades.

The cost of nuclear power will rise very likely in the future, due to a combination of several factors, among other:

• energy will become more expensive

• uranium will become more expensive and its recovery more energy intensive

• materials (construction, auxiliary) will become more energy intensive

• unavoidable deterioration of materials of temporary storage facilities.

 

[download pdf full report]

 

Contents

Summary

1 Introduction

Complexity

System boundaries

Major differences with other studies

2 The nuclear energy system

2.1 Reference reactor

2.2 Nuclear process chain

2.3 Cradle to grave: the c2g period

3 Energy analysis, the method

3.1 Usefulness and work

3.2 Energy cost vs monetary cost

3.3 About the method

Process analysis

Fossil fuel and electric inputs separated

3.4 Input/output analysis

Basic concept

3.5 Energy return on energy investment (EROEI)

3.6 CO2 emission of nuclear power

3.7 Emission of other greenhouse gases: a well-kept secret

4 Front end: from uranium ore to nuclear fuel

4.1 Front end processes

4.2 Uranium recovery from ore

Dilution factor

Extraction yield

Specific energy consumption

Coal equivalence

4.3 Uranium resources Economic view Known uranium resources

4.4 Thermodynamic quality of uranium resources

5 Nuclear power plant

5.1 Operational lifetime

Full-power year FPY

Load factor

Effective operational lifetime

5.2 Construction

5.3 Operation, maintenance and refurbishments (OMR)

6 Back end: immobilising radioactive waste

6.1 Unique feature of nuclear power

Nuclear bomb equivalents

6.2 Spent fuel

6.3 Mine rehabilitation

Energy consumption

6.4 Decommissioning and dismantling

6.5 Immobilising radioactivity

7 Results

7.1 Contributions to the energy investments

7.2 EROEI

7.3 Climate footprint of nuclear power

Nuclear CO2 emission

Other greenhouse gases

Radioactive emissions

8 World nuclear outlook

8.1 Energy debt

8.2 Depletion of uranium resources: a thermodynamic notion

8.3 Energy security: scenarios

Scenario 1: constant nuclear capacity

Scenario 2: constant nuclear share

8.4 Energy cliff

Energy cliff and other commodities

8.5 CO2 trap

Conclusions

Inadequate information flow to politicians and public

Available reactor technology

Energy security and nuclear power

Energy cliff

Climate control and nuclear power

CO2 trap

System boundaries

Energy debt

Annex A Present state

A.1 World gross energy production

A.2 Nuclear contribution

Annex B Reactor technology

B.1 Reference reactor LWR with MOX fuel

B.2 Breeders

B.3 Thorium

Thorium breeder scenario

Feasibility

Annex C Uranium extraction

C.1 Yield and entropy

C.2 Mineralogical barrier

Annex D Radioactive heritage of nuclear power

D.1 Mobilisation and generation of radioactivity

Generation of man-made radioactivity

Nuclear bomb equivalents

D.2 Radioactivity and health effects

D.3 Immobilising radioactivity

Annex E Monetary cost trends

References

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