A method for energy analysis using electricity as basis of evaluation: applied to a Swedish nuclear power plant

UPTEC ES 09022

Examensarbete 20 p Augusti 2009

A method for energy analysis using electricity as basis of evaluation

applied to a Swedish nuclear power plant

Anna-Maria Carstensen

Teknisk- naturvetenskaplig fakultet UTH-enheten

Besöksadress:

Ångströmlaboratoriet Lägerhyddsvägen 1 Hus 4, Plan 0

Postadress:

Box 536 751 21 Uppsala

Telefon:

018 – 471 30 03

Telefax:

018 – 471 30 00

Hemsida:

http://www.teknat.uu.se/student

Abstract

A method for energy analysis using electricity as basis of evaluation

Anna-Maria Carstensen

Presently the world's energy supply consists to a large extent of finite resources. Even when producing energy from “renewable” sources, fossil fuels are consumed

indirectly to some extent. The dependency on limited resources motivates the comparison of energy systems with respect to efficiency in resource usage.

There exist different methods for analysing energy efficiency, of which three are energy-, exergy- and emergy analysis. These methods take different properties of energy resources into con-sideration. In order to analyse the efficiency of energy systems it is important to consider that some forms of energy are more easily used than other. For example, electricity is more useful than heat. Another example is that wooden chips cannot replace petrol in a vehicle without energy demanding

conversion. The usefulness of energy resources is not comprehensively dealt with by existing methods.

In this thesis a new methodology for the assessment of energy efficiency in energy supplying systems is developed. Central in the methodology is how useful energy resources are. The use-fulness of a resource is in this work technically determined and defined in terms of how much electricity it can provide within a power plant.

Electricity is used as base for the calculations be-cause it is an energy carrier easily convertible into any other form of energy and therefore strongly linked to wealth.

The objective of the method is to compare the yield of electricity from an energy system to the potential to electricity production in resources used directly and indirectly by the system. In this thesis the method is applied to a Swedish nuclear power plant. It was found that the nuclear power plant is a very good net provider of electricity equivalents to the society, the return on investment ration being

approximately 10.

UPTEC ES 09022

Examinator: Ulla Tengblad

Ämnesgranskare: Michael Österlund

Handledare: Henrik Sjöstrand

Sammanfattning

Energitillförseln i världen är för närvarande i stor utsträckning beroende av ändliga resurser.

Även energiutvinning från förnyelsebara källor är beroende av begränsade resurser så som fossi- la bränslen eller jordbruksmark. Beroendet av begränsade resurser motiverar en jämförelse av energisystem utifrån hur effektivt de använder naturresurser.

För att analysera resursanvändningen i energisystem finns flera olika metoder, bland annat ener- gianalys, exergianalys och emergianalys. Dessa metoder skiljer sig åt med avseende på hur olika egenskaper hos energiresurser hanteras. Problematiken består främst i att hantera det faktum att olika energiformer har olika kvalitet. Energianalysen värderar energiresurser utifrån deras vär- mevärde, men tar inte hänsyn till deras kvalitet och användbarhet. Exergianalysen värderar ener- giresurser utifrån deras teoretiska potential till mekaniskt arbete och innefattar därmed ett teore- tiskt kvalitetsmått på energi, men måttet har ingen koppling till resursens användbarhet i ett tek- niskt system. Emergianalysen värderar energiresurser utifrån hur mycket energi det har gått åt i naturen och i samhället för att framställa dem. Även den energi som använts av människor som arbetat med förädlingen av en resurs inkluderas. I emergianalysen räknas all resursanvändning om till dess värde i form av solenergi som ursprungligen har gått åt i formandet av resurserna.

Därmed relateras samtliga resurser till flödet av förnyelsebar energi, vilket torde vara relevant då energianvändningen på mycket lång sikt är hänvisad till förnyelsebara flöden. När det kommer till bedömning av system som hanterar kärnkraft samt fossila bränslen är detta emellertid inte så relevant för systemens effektivitet idag, då dessa system använder energi som härör från solens respektive andra solars tidigare aktivitet, vilken inte har ett alternativt värde idag. Den energi som under lång tid möjliggjort att fossila bränslen formats i naturen motsvarar heller inte den energi som skulle åtgå för att producera motsvarande resurs i teknologiska system idag.

Intressantare är att värdera energiresurser med ett mått som relaterar till energins samhälleliga värde. Elenergi hänger, genom sin vida användbarhet, starkt ihop med välfärd. I detta examens- arbete har därför en ny metod för energianalys som värderar energiresurser utifrån deras tekniska potential till elproduktion utvecklats. Energiresurser värderas i elekvivalenter utifrån det alterna- tivvärde som de hade kunnat tillföra samhället om de använts för elproduktion. Tillämpad på ett kraftverks bränslecykel, kan metoden användas för att jämföra kraftverkets elproduktion med den potential till elproduktion, som finns i de energiresurser kraftverket har använt sig av direkt och indirekt vid till exempel bränsleförädling, elgenerering och avfallshantering. Därmed kan metoden användas för att svara på hur stort netto av elekvivalenter som kraftverket tillför eko- nomin.

I metoden föreslås att systemgränserna skall dras så att såväl direkt som indirekt använd energi inkluderas i analysen av ett energisystem. Även den energi som åtgått för upprätthållandet av arbetskraft inkluderas i analysen.

Metoden har tillämpats på ett svenskt kärnkraftverk och dess bränslecykel. Information om

kärnkraftverkets resursanvändning har hämtats från en emergianalys som i sin tur bygger på en

livscykelanalys. Energianvändningen är aggregerad i posterna fossilbränsleanvändning, elan-

vändning och kostnader för arbetskraft och kapital. All använd energi har räknats om till elekvi-

valenter. Värdet av de fossila bränslena har räknats som den nettoelproduktion som bränslet hade

kunnat ge upphov till vid förbränning i ett fossilbränsleeldat kraftverk. Indirekt energianvänd-

ning för arbetskraft har beräknats utifrån kostnaderna för att driva de olika processerna i kärn-

bränslecykeln. Även kostnaderna för inspektion har inkluderats. Motivet till att utgå ifrån kost-

nader för att värdera arbetskraft är att pengar betalas till människor men aldrig till naturen. Kost-

naderna utgör på så vis ett mått på hur mycket arbetskraft som åtgått. Kostnaderna har multipli-

cerats med ett index för hur mycket energi en krona motsvarar. Indexet har beräknats genom att

dividera Sveriges BNP med landets användning av energi under ett år omräknad till elekvivalen- ter.

Kärnkraftverkets elproduktion har jämförts med den totala resursåtgången i kärnkraftverkets bränslecykel omräknad till elekvivalenter. Elproduktionen under ett år uppgick till 24 TWh sam- tidigt som resursanvändningen för att åstadkomma denna elproduktion motsvarade 2.2 TWh el- ekvivalenter. Kärnkraftverket försåg alltså ekonomin med 21.8 TWh elekvivalenter netto. Re- sultatet, presenterat som kvoten mellan nettoproduktionen av elekvivalenter och investerade el- ekvivalenter, blev att för varje elenergiekvivalent som ekonomin investerar i kärnkraftverkets bränslecykel, så tillför kärnkraftverket ca 10 elekvivalenter netto till ekonomin. Det studerade kärnkraftverket är alltså med god marginal en nettoproducent av elekvivalenter.

Metoden som utvecklats i detta arbete är användbar för att avgöra om och i vilken utsträckning ett energisystem är en nettoproducent av elekvivalenter. Detta bör utgöra ett användbart mått i beslutssituationer då olika energisystem jämförs. Ett energisystem som inte ger något nettotill- skott av elekvivalenter till samhället bör väljas bort. Jämförelsen bör kompletteras med en jämfö- relse av energisystemens miljöpåverkan, effektivitet i användning av andra resurser än energirå- varor samt vilka risker energisystemen för med sig.

Metoden bör tillämpas med lika valda systemgränser på samtliga energitillförande system i sam-

hället. Detta skulle, förutom en jämförelse av energisystemens effektivitet, möjliggöra en utvär-

dering av metoden. För att utvärdera metoden vore det också intressant att jämföra de resultat

som uppnås med denna metod, med de resultat man får med andra analysmetoder.

Table of Contents

1 Introduction ... 3

1.1 Purpose ... 3

1.2 Theoretical background ... 4

1.2.1 Energy analysis ... 4

1.2.2 Exergy analysis ... 5

1.2.3 Emergy analysis ... 6

1.2.4 Life cycle assessment ... 8

1.3 Choice of direction ... 9

2 Method ... 11

2.1 System description ... 11

2.2 The electricity equivalent ... 12

2.2.1 Fuels ... 12

2.2.2 Electricity ... 12

2.2.3 Uranium ... 13

2.2.4 Services ... 13

2.3 Discussion of the methodology ... 13

3 Data and calculations ... 15

3.1 Data on the nuclear fuel cycle ... 15

3.1.1 Extraction, Conversion, Enrichment and Fuel fabrication ... 15

3.1.2 Electricity generation ... 16

3.1.3 Management and storage of nuclear waste ... 17

3.1.4 Transports in the nuclear fuel cycle ... 18

3.1.5 Limitations of data ... 18

3.2 Calculation of transformities ... 19

3.2.1 Fuels transformity ... 19

3.2.2 Electricity transformity ... 20

3.2.3 Energy per monetary unit index ... 20

3.2.4 Limitations ... 22

3.3 Calculations of the nuclear fuel cycle ... 22

4 Results ... 24

4.1 Sensitivity analysis ... 26

4.2 Impact of the system boundaries ... 27

4.3 Comparison with Emergy analysis of a Swedish nuclear power plant (1) ... 28

5 Discussion ... 29

2

6 Conclusion and outlook ... 31

Acknowledgements ... 32

References ... 33

Appendix A. Calculations of the energy per monetary unit index ... 34

Appendix B. Feedback in the nuclear fuel cycle ... 36

Appendix C. The Swedish nuclear power process ... 39

3

1 Introduction

Wealth, today and tomorrow, is primarily dependent on access to energy. Energy usage is there- fore strongly linked to sustainability both because energy dense resources are scarce and energy extraction and conversion cause environmental impact. Access to energy as such is not a limiting factor, because e.g., solar energy is flowing into the biosphere with 10 000 times more energy than is consumed through the use of fuels in the technosphere each year. Because solar energy is not easily transformed into useful work, energy quality is still a limited resource. Energy quality is in this work a measure of how useful an energy source is within a technological system and defined as the mechanical work it can perform in a power plant. To upgrade energy quality, technological, societal and ecological systems together with more energy are needed. All sys- tems for upgrading of energy make use of limited resources, e.g., metals, fossil energy and lim- ited land resources. Different methods have evolved to assess the use of resources and environ- mental impacts from energy systems. Assessments of energy systems often deal with their envi- ronmental impacts. Considering sustainability it is also important that energy systems give large energy returns and use the resource base efficiently. Energy systems often use different energy resources of different quality. As already mentioned, the energy quality is of greater interest than the energy quantity. This motivates the use of a common unit of account based on energy qual- ity, for comparison of energy used and yielded in energy systems. In this thesis a new measure of energy quality is suggested. The measure is based on electric energy. A methodology using this measure is developed and applied to a nuclear power system.

1.1 Purpose

The purpose of this work is to develop a new methodology for the assessment of energy resource usage in energy production systems. The methodology aims to assess energy systems by compar- ing their use and yield of energy. Since energy resources are of different usefulness a quality measure is developed for the comparison of different resources. The quality measure is based on the ability of a resource to perform mechanical work in a technological system and resources are valued from how much electricity they can yield in a real power plant. This is to give a realistic and technologically determined view on the quality of resources.

The choice of mechanical work or electricity as a calculation base comes from the assumption that mechanical work, because of its universal usefulness, is the basis of economical wealth. All kinds of production processes make use of mechanical work, which corresponds to an increase in economical value of the product. An energy system makes use of energy resources that could have been useful elsewhere in the society as well. The ability of a resource to perform mechani- cal work determines how useful it would have been elsewhere in the society. It is outside the scope of this work to determine the validity of this assumption.

The methodology aims to be applicable to any energy production system. However, in this thesis it is applied to a Swedish nuclear power plant. Data on the nuclear fuel cycle are taken from an emergy analysis of a generic Swedish nuclear fuel cycle (1), based mainly on an Environmental Product Declaration (EPD) for the Forsmark nuclear power plant (2) performed by Vattenfall.

The purpose has not been to present new data on energy use. Using the same data as the emergy

analysis enables the comparison of the results achieved with the different methods, and hence a comparison of the methods.

The aim of this work is to develop a method, which can assess the energy efficiency of a system.

Environmental and health impacts of the system are, although important, not covered by the method.

1.2 Theoretical background

In order to perform sustainable development several methods have been developed for assessing production processes with respect to resource use and environmental impact. This chapter intend to give a brief description of a selection of methods evolved to assess resource use and environ- mental impact. The methodologies and applications of them differ in many aspects. The most important aspect for the subject of this thesis is how they measure energy flows; in terms of thermal energy, energy quality, energy embodied through natural work or just in terms of mass of a resource. Other differences consist of how time and room boundaries are set and whether natural work and human services are assessed or not. Because of these differences the method- ologies complement each other and are useful for different purposes. This chapter describes the scope and limitations of the methods.

1.2.1 Energy analysis

In energy analysis the requirements of energy for production of goods or services is estimated.

Generally the aim is to investigate the potential to reduce energy costs or to compare energy use in different processes giving the same product. The production process is seen as a system com- prising the main process and supporting processes for material production and machinery pro- duction. The system perspective is described hierarchically with respect to energy requirements as illustrated in Figure 1. Direct energy from fuels used in the processes is traced backwards to the primary energy sources so that energy used for the extraction and refining of the fuels is ac- counted for. The back system boundary is drawn at a level where additional inputs are supposed to be negligible. In industrial processes, level one and two in Figure 1 often account for more than 90% of the total primary energy required for the whole process. (3)(4)

Figure 1. The system hierarchy in energy (process) analysis, ref. (3) and (5).

One problem in energy analysis is that different forms of energy have different usability. In en- ergy analysis, the discussion has been whether the heating value of a fuel or the Gibb’s free en- ergy, i.e., the chemical potential of a fuel to do work, should be used to determine the value of

4

the fuel. According to ref. (3), Gibbs free energy is recommended as a measure of energy content in fuels, when the analysis is concerned with depletion of the resource base. However it is a de- manding work to calculate the free energy of a resource and for energy intensive fuels the differ- ence between the calorific heating value and Gibbs free energy is often less than 10% (3). Gibbs free energy is also a limited concept, very useful for chemical reactions, but of little value when dealing with for example nuclear energy or potential energy. In general an energy analysis uses the calorific heating value as a measure of energy, and the energy quality is not accounted for.

The system boundaries depend on the aim of the study. Generally the energy contained in energy rich materials, such as plastics or wood, that are used for non-energy purposes are not accounted for. Consequently the energy analysis is limited to cover the process and therefore often called process analysis. Whether sunlight and labour should be accounted for in an energy analysis or not is a disputed question, generally it is not accounted for. (4) (3)

1.2.2 Exergy analysis

Exergy analysis is a further development of the energy analysis where the quality of energy re- sources is taken into account. The production process is viewed in the same way as in energy analysis and basically the same data are needed but instead of valuing an energy resource from its heating value it is valued from how much work it theoretically can give, i.e., the exergy. Ex- ergy is a concept in thermodynamics which refers to the potential to perform work. While energy cannot be destroyed, only converted into other forms of energy, exergy is the qualitative property that is destroyed in these conversions. The driving force of all processes is the difference be- tween a system and its environment. Exergy is a measure of how much a resource or a system deviates from equilibrium with its surrounding and is always defined relative to a specified ref- erence environment. Compared to Gibbs free energy, mentioned in section 1.2.1, exergy is a more general concept, useful not only in closed physical/chemical systems, but also in open macro systems (e.g., economic, technical or ecological systems). Table 1 shows the exergy con- tent in different forms of energy. (4)(6)

Table 1. Quality factors for different forms of energy. The quality factor tells how much exergy one unit of energy corresponds to. (7)

Form of energy Quality factor

Mechanical 1.00

Electrical 1.00

Sun light 0.95

Nuclear energy 1.00

Chemical energy 0.90

Thermal energy and thermal radiation at 300

C 0.49

100

C 0.21

40

C 0.06

20

C 0.00

The exergy concept can also be used for other resources than energy resources. The exergy of a mineral in an ore, is one example, and is determined from the difference in chemical potential and concentration between the ore and the reference environment. Energy resources can also contain exergy constituted of other qualities than the energy content. Such qualities are the struc- ture of fibres that makes wood usable as a building material, and the micro-structure in amino acids that makes food useful not only as metabolic energy but also for building the body. Exergy is then not only a measure of a resource’s ability to do work but also the alternative physical work, that would be required if all inputs were taken from a standard state environment, instead of being supplied by the actual resource. The entity exergy can therefore be used for the meas-

5

6 urement of quality of all kinds of natural resources within the same unit. This means that in an assessment of, for example, a power plant, all resources used in the system can be measured as exergy in Joules or kWh. The result of the assessment can then be an over-all efficiency for the power plant. (6)

Exergy analysis indicates how far a system deviates from its theoretical potential to do work.

The method is useful to locate and quantify losses of energy quality in processes (4). This is a help to optimise the use of resources with respect to their quality, in order to use energy more efficiently in a process or in the society as a whole (6). Yet the value of the quality measure ex- ergy is limited, as for example one joule of nuclear energy cannot perform the same work in a technological system as one joule of electricity, which has the same quality factor. Another ex- ample is that one joule of sunlight cannot perform the same work in our bodies as one joule of chemical energy in food (8).

1.2.3 Emergy analysis

Emergy analysis deals with the quality aspect of energy from another perspective than exergy analysis. Instead of a quality measure from the user’s perspective it offers a quality measure from the producer’s perspective. The producer can be the environment and/or the economy. The quality or value of a resource is the amount of energy that has been required to form the resource through processes in the environment and in the economy. Such processes are, for example, geo- logical, ecological and technological. Energy required for the formation of a resource is called embodied energy or energy memory, abbreviated emergy. The emergy is measured in units of energy of one kind. Generally solar energy is chosen as base for the calculations. Thus all energy required to form a resource is referred back to its origin as solar energy. Energy forms not origi- nating from solar energy are compared to, and given a value referring to, solar energy. Other energy flows than solar energy that are concerned are tidal energy and crustal heat. Different energy forms are related to solar energy by “transformities”. A transformity tells how much of solar energy, measured in solar emergy joules (sej), it has taken to form one joule of the actual energy form. (9)

The emergy analysis was developed within a system ecology context and differs from energy and exergy analysis, in that it includes environmental processes in the system of study (see Figure 2). Emergy evaluation deals with energy flows in ecological and economical systems in interaction. In this interaction natural resources are extracted and processed to become useful for the economy. This requires the use of human labour and already extracted natural resources. One objective of an emergy analysis could be to compare the input of emergy contained in the ex- tracted resource with the emergy used in the extraction process, in order to determine how effi- cient a system uses the emergy. This comparison is eased by the system perspective of the emergy analysis described in Figure 2.

In the system perspective of emergy analysis resources needed by a system are divided on two flows; the “input from nature” (I) and the “feedback from society” (F). The input from nature (I) consists of the emergy in the resource extracted by the system; for a nuclear power plant this is the uranium. The feedback from society (F) contains the emergy in resources required in the ex- traction process; those are human labour, and already extracted natural resources in the form of goods, fuels and electricity. The emergy in the final product is called the emergy yield (Y) and is calculated as the sum of the input I and the feedback F.

Y = I + F

Figure 2. The system perspective of emergy analysis (5). The diagram is drawn with symbols from the “energy systems language” used in emergy analysis and described in ref. (9). Energy is lost in the conversions as showed by the arrows. The emergy is not lost, but accumulated.

The result of an emergy analysis can be presented as the quotient Y/F, telling to what extent the production contributes with emergy to the economy, relative to the amount of emergy it con- sumes from the economy. Also the quotient I/F, which is the same as (Y-F)/F, is of interest, as it tells how much free emergy the economy has gained from the nature, relative to how much emergy that has been invested from the economy. Another result of interest is the total emergy in the final product that is the emergy yield (Y). (9) (1)

Extraction of natural resources requires, in addition to fuels and goods, also human labour or services. As human labour also requires natural resources for its maintenance, it could be re- ferred to solar energy and measured in terms of emergy. Yet it is not self-evident to what extent the emergy in labour maintenance should charge a production process; e.g., it could be all the emergy consumed by the family of the labourer, or just the emergy in the food metabolised by the labourer during work. Another difficulty is to obtain data on the use of labour, especially as labour is used indirect in the production of goods, fuels and machines, that are used in the proc- ess. The solution to these problems, suggested in the emergy analysis, is to derive emergy flows from money flows. Since money is only paid to humans for their work, and never to the nature, costs can be seen as a representation of labour. Money is then related to emergy by dividing the emergy flow by the corresponding money flow for a region. In practice this can be done by di- viding a nation’s total emergy consumption by its gross domestic product, resulting in an index showing the emergy buying power of money in that country. (9)

Emergy analysis has been used for very different purposes, such as evaluation and understanding of energy flows, and energy hierarchies, in ecological and geological systems, and for assessing use of resources in economical systems. One application has been to set a numerical value on finite resources, such as fossil fuels, derived from the environmental work gained in the forma- tion of them (9). Emergy analysis offers the possibility to derive the “renewable” energy flow behind the use of natural resources. This could in principle be valuable information in decision making, since in the very long run only “renewable flows” are available. However the result of emergy analysis is not always relevant for this decision making on usage of resources. Work already done by nature must not necessarily equal the work that will be needed for the environ- ment or the society to recreate a resource. One example of this is that the amount of solar emergy joules yielded in diesel produced through gasification of biomass does not equal the emergy yielded in diesel derived from crude oil, although both products are identical from the user per-

7

8 spective. Also the renewable energy, during long time embodied in fossil resources, has no alter- native value for the economy today; it is already used by the nature in the formation of fossil resources. Another thing affecting the usefulness of emergy analysis in decision making is the fact that it is not necessarily so that a high emergy yield is of good with respect to resource con- servation, as it is not related to the useful work a resource can perform. This could be exempli- fied by electricity production that can take place in different systems, such as hydro power, nu- clear power, solar cells etc. One kWh of electricity from these systems do not have the same emergy value. Depending of the feedback, the emergy analysis can give the highest emergy re- turn on investment to the system that actually demands the most work from the environment.

Hence emergy analysis with solar emergy as base is not easily used in decision making con- cerned with sustainability. Furthermore, the accuracies of the solar emergy transformities are limited because of insufficient knowledge about the environmental work (4).

An alternative base for emergy analysis has been used in ref. (1), where the base unit is biomass, when standing untouched in the field. The value of a fossil or non renewable resource is esti- mated to the emergy that it takes to create a resource with the same quality or usability from biomass with today’s technology. One example is that the emergy from diesel is calculated to the amount of biomass joules required to produce diesel through gasification of willow. When calcu- lating the emergy content in bio-diesel, the energy use in all parts of the production, on the wil- low field as well as in the gasification plant, is considered and assumed to be bio-energy deriva- tives. In ref. (1) this method has been used for the assessment of a Swedish nuclear power plant.

The uranium has been valued from the amount of electricity it can give rise to within the actual nuclear power plant. The bio-emergy joules in the uranium is estimated to the amount of biomass joules that would have been required to produce the same amount of electricity in a power plant fuelled by willow. The result of the methodology is more easily interpreted for a bio-energy sys- tem, for which the result would be the net yield of bio-emergy. If the net yield of bio-emergy is positive, this means that the system provides more bio-energy than is consumed internally, and hence is a sustainable energy system.

Considering sustainability in energy systems based on mainly renewable resources, the emergy analysis with bio-emergy joules as base is a useful methodology, because all energy resources are referred to real-time flows of renewable energy. It measures energy resources in terms of its production cost, and provides a more relevant sustainability measure than traditional emergy analysis with solar emergy as base unit. This method also takes into consideration the quality aspect of energy resources from a users perspective, when considering the replacement of a fossil fuel with an alternative bio-fuel. However, the unit of bio-emergy joules is not directly telling the usefulness of an energy resource.

1.2.4 Life cycle assessment

The methodology of life cycle assessment (LCA) has evolved in parallel with energy analysis and is concerned with emissions, wastes and use of resources. Comparative studies of packaging materials were the first object of study. The concern with waste makes the life cycle perspective, from cradle to grave central. Important is also that LCA does not only assess a product or service but also the function of the product or service in a given context.

Unlike the other methods presented here, the LCA methodology is standardised (within the ISO 14040 –series). LCA comprises the steps of

- goal and scope definition

- inventory analysis

- impact assessment.

9 In the step of goal and scope definition, the context and purpose of the study is stated and the system boundaries are figured out. The function of the studied product is quantitatively ex- pressed as a functional unit, to which the whole assessment is related. The inventory analysis consists of building a flow model of all included processes and to validate relevant flows, i.e., of harmful substances and especially scarce resources. Often the production system produces more than one product. When this is the case, an allocation of resource use and environmental impact must be done; alternatively a system expansion can be performed. In the impact assessment the results of the inventory is aggregated in environmental impact categories, e.g., acidification, eu- trophication and global warming potential. The relative impacts of different emissions are weighted with indexes based on scientific models of cause-effect chains in the natural system.

The impacts is sometimes further weighted into one aggregated value for environmental impact, carried out with methods based on ethical values. (10)

The fact that the method is standardised makes it valuable because it is easy to see to what extent assessments are comparable and makes it also quite easy to build up and make use of databases.

LCA does not account for labour, neither is it concerned with risk. It is useful for comparison of different products/services, but with the same function or comparison of different production processes for a product. LCA can then be used both for internal work on efficiency and environ- mental improvements, but also externally for marketing or political decision making. (10) The disadvantage with LCA is that it does not regard processes as interactions in a system, im- plying a restriction in seeing whether an energy system is a net contributor or not to wealth. Nei- ther does LCA assess the quality of primary fuels.

1.3 Choice of direction

The method developed in this thesis is an energy analysis with electricity as base and it has evolved from the methodologies described in chapter 1.2. The objective of the method is to as- sess energy systems ability to generate useful work in relation to their use of mechanical work.

Since an energy system use different resources, and since these resources have different abilities to perform mechanical work, a common unit of account is needed that makes the resources com- parable. The purpose of the unit is to be a measure of the quality in energy resources determined from their potential to do work within a technological system. This is to give a realistic view on the quality of resources. The assessment is further eased by using the system perspective of the emergy analysis, and dividing resources into the parameters input (I), feedback (F) and yield (Y).

The yield of mechanical work (Y) can then easily be related to the mechanical work “fed back”

(F) to the system within the resources required in the processes of electricity production.

Similarly to energy analysis and the LCA methodology the system boundaries are set so that the use of energy, directly and indirectly, in all the processes related to energy extraction, are as- sessed. The system boundaries are though extended to assess also the use of human services.

Like in the exergy and emergy analysis, all resources are accounted for in one base, in order to

compare inputs and outputs. Considerations of energy quality are made, as in exergy analysis,

but not with a theoretical quality measure based on entropy. Instead real efficiencies in power

plants are used for assessing resources ability to do work. This is to give a more realistic view on

the quality of resources. The system perspective of the emergy analysis, described in Figure 2

above, is chosen, dividing resources into the parameters input, yield and feedback. However, in

contrast to the emergy analysis, the method assumes that work done by nature has no alternative

value for the economy other than the electricity that can be produced from resources formed by

nature. Therefore the environmental input is estimated to this amount of electricity. The focus is

on how useful a resource is to the economy. The approach of usability makes it suitable to

choose an energy carrier instead of an energy source as a base for the calculations. Electricity is

10 used as base because it is an energy carrier convertible into any form of energy and therefore strongly linked to wealth. Mechanical work is equalized to electricity and thermal energy is re- calculated to electric energy with the methodology of the Clausius-Rankine cycle, since this process at present is the main process for electricity production.

Labour and services also demand energy. The role of increased use of energy has been to replace human labour by machines, why it is reasonable to compare energy consumption from labour with energy consumption by machines. As more labour is freed in one sector, the wealth can be increased because more work can be carried out in another. The energy required for labour and services is calculated with a methodology developed in the emergy analysis.

The energy analysis with electricity as base is primarily concerned with efficient use of energy

resources. Environmental impact is not directly assessed. An assessment of the environmental

impact is a necessary complement.

11

2 Method

In this chapter the method of performing an energy analysis, when using electricity as a base for the calculations is described. To exemplify how the method can be used it is described when applied to the nuclear fuel cycle of a Swedish nuclear power plant. In section 2.1 the system studied is described and delimited and the perspective on the system described. In section 2.2 the base for the calculations is defined as the electricity equivalent. Here the procedure of calculating the electricity equivalent of different resources is described. The design of the methodology is not obvious, which motivates a discussion on the methodology performed in section 2.3.

2.1 System description

The system studied contains the fuel cycle of uranium in the Swedish nuclear power process. A process tree showing the nuclear fuel cycle can be found in Appendix C. The nuclear fuel cycle comprises the activities of:

- extraction, conversion, enrichment and fuel fabrication (upstream processes) - electricity production in the nuclear power plant (NPP)

- handling and storage/disposal of the radioactive waste - inspection.

Energy spent directly in the fuel cycle is included as well as energy required to extract that en- ergy and other products used. Also indirect energy used by supporting structures for labour and services is contained in the system. The process of formation of the uranium ore in nature is not included.

The system perspective used is taken from the emergy analysis, as described in section 1.2.3.

Inputs to the system containing the uranium cycle are divided into two categories; input from nature (I) and feedback from society (F). The category input from nature contains the uranium.

The category feedback from society contains resources previously extracted and already brought into the economy, which could have had an alternative value for the economy. These are fuels, electricity and human services. The gross electricity yielded from the system is denoted the gross yield (Y).

It is assumed that work done by nature is of no value for the economy other than through the electricity that can be produced from the resources formed by the nature. Hence, the environ- mental input (I) is estimated to be the net yield of electricity equivalents from the input of ura- nium in the system. The net yield (I) of electricity equivalents is a function of the feedback (F)

ss yield (Y) and is calculated as and the gro

.

The efficiency of the system with respect to energy use is determined as the quotient I/F, i.e., the energy return on investment.

In order to relate the parameters Y, F and I to each other, the energy resources must be recalcu-

lated to a comparable form. Mechanical work, or equivalently electricity, lays the ground for this

analysis. The value of a resource is determined from its ability to perform mechanical work or to

12 produce electricity within a technological system. The base used for comparison of different sources is the electricity equivalent, defined in chapter 2.2.

2.2 The electricity equivalent

The electricity equivalent of an energy resource is calculated as the amount of electricity that can be produced out of it within a commercial technological system. The technological system is, though commercial, chosen to be as efficient as possible and at the forefront of technological development. A fuel’s ability to do mechanical work is estimated as the net electricity produc- tion; that is the gross production in a given power plant minus the electricity equivalents used for the operation of the plant supplied in the form of energy wares and services.

The electricity equivalent is defined at the power plant used as reference and losses due to sup- posed transfer of electricity are included only in the cases where transfer occurs within the sys- tem boundaries of the nuclear fuel cycle. Transfer of electricity to the final consumer is not in- cluded within the system borders. The factor used for calculating the electricity equivalent from a given amount of fuel is called transformity.

Energy systems also make use of other resources than energy, such as building materials, chemi- cals and labour. The electricity equivalent for other resources than fuels is the same as the elec- tricity equivalent for the sum of the fuels used in the production and maintenance of these re- sources.

2.2.1 Fuels

The electricity equivalent of a fuel used by a system is, as described above, the amount of elec- tricity technically possible to generate from the fuel. The electricity equivalent is calculated from the actual quality of the fuel that is used by the system. The gross electricity production is calcu- lated from the efficiency in an appropriately chosen power plant. The internal use of electricity equivalents in the chosen power plant is subtracted from the gross production to form the net production.

Fuels used by the system are secondary fuels, meaning that they have been extracted and refined before entering the system. As mentioned in section 2.1, the energy for extraction of energy re- sources is included within the system boundaries. This is done by increasing the transformity of the fuel, so that the electricity equivalent of a fuel also contains the mechanical work used to transform the resource into the actual form and quality used by the system.

2.2.2 Electricity

Electricity used in the system gets the transformity one, so that one unit of electricity used in the system is valued as one electricity equivalent, regardless the actual source of the electricity, re- sulting in that all electricity used is valued as if it is generated in the system itself; i.e., in the nuclear power plant. This need not always be the case because all processes in the fuel cycle are not taking place at the power plant site, not even inside the extent of the grid that is fed by the power plant. However this is a reasonable assumption since the aim of this work is to relate the amount and quality of the energy yielded to the amount and quality of the energy used by a sys- tem. The electricity fed into the nuclear fuel cycle could have been produced in the nuclear power plant as well.

The transformity of electricity is adjusted according to the losses that occur in the cases where

electricity is transferred. Losses due to transfer of electricity are assumed to be compensated for

by an increase of the amount of electricity needed.

13 2.2.3 Uranium

The input (I) of uranium is valued on the basis of net electricity possible to generate out of it with the technique used by the system, i.e., the actual nuclear power plant. The net electricity production is calculated from the gross yield (Y) of electricity from the system minus the energy

) from the economy, that is feedback (F

.

The input (I) is then the net yield and must exceed zero for the system to be considered good.

The higher the value of parameter I, the better the system is in producing a net yield of electricity equivalents.

2.2.4 Services

Labour and services also demands energy, as motivated in section 1.3. A system uses services both directly in the form of labour and indirectly by purchasing products and services. The indi- rect services are difficult to assess because the number of people contributing to them are un- known. However, the cost of these services is known. It is assumed that money counts for ser- vices but not for direct use of energy and other natural resources, since money is never paid to nature but only to people (9). Money can therefore be used to trace the distribution of energy into services. Therefore services are assessed on the basis of costs. This is done with an energy per monetary unit index; that is a transformity for costs. The index is calculated as the quotient of the total use of electricity equivalents in a country in a year and the Gross Domestic Product from the same year. The index multiplied with the cost of a resource gives the amount of electricity equivalents required for the processing of the resource through the work done by labour.

All energy used by the economy, regardless if it is seen as essential for the survival or not, is seen as supporting the final consumer; that is the labourer. The total energy use in Sweden dur- ing one year is here limited to the energy embodied in used fuels. Energy embodied in imported and exported goods, as well as in energy rich goods from domestic extraction (for example in forestry and plastic products), are not assessed, because of lack of data. One could expect that energy bound into energy rich goods, is released and exploited through waste incineration, and included this way, though with a time delay.

2.3 Discussion of the methodology

It has proved difficult to make this method deal with all inputs in a consistent way, and still an- swering the question of how much electricity equivalents are yielded compared to how much electricity equivalents are consumed. In this section three problems are discussed, all concerning how the calculations of electricity equivalents of inputs relate to the system boundaries.

In the described methodology, the electricity equivalents are calculated differently for the re- sources in the feedback (F) and in the input (I):

- electricity equivalents in the input (I) are calculated as the net yield of electricity equiva- lents in a fuel cycle. The net yield is calculated as the gross yield minus the feedback of electricity equivalents needed throughout the whole fuel cycle; that is from cradle to gate - electricity equivalents in the feedback (F) are calculated as the net yield of electricity

equivalents in a power plant using the actual secondary fuel. The net yield is calculated

as the gross yield minus the feedback of electricity equivalents needed in the power plant

alone, that is from gate to gate in the power plant.

14 This difference may seem inconsistent, but is considered the most reasonable. The alternative of calculating the electricity equivalents in the feedback by subtracting the use of electricity equiva- lents before the power plant gate, would make a fuel requiring more energy in the refining step to seem better, i.e., meaning a smaller F and giving a larger I, than a fuel requiring less energy in these steps.

Furthermore, the boundaries for the system studied are set so that the energy needed for extrac- tion of the resources in the feedback to the system is accounted for. Indirect use of energy is also seen as being caused by the system, i.e., the nuclear fuel cycle. Hence, this energy is also valued in terms of electricity equivalents and added to the feedback. The adding of indirect use of en- ergy to the feedback may seem inconsistent, because the electricity equivalent is defined as the possible yield of net electricity from a fuel, and because the indirect energy can never be avail- able as electricity to a grid. However, if the indirect energy would not be accounted for, the as- sessment would not be sensitive to unsustainable conditions in the system where the feedback energy is produced. To illustrate this, one can think of what the result would be if one makes the extreme assumption that the extraction of a fuel fed back to the nuclear fuel cycle would con- sume more energy than yielded by the nuclear power plant. The method would not detect this unsustainability, unless indirect use of energy is accounted for in the feedback. The method would hence answer another question than the one asked, namely: ‘How much electricity could be produced from the resources in the feedback when used in an alternative power producing system?’

There is also a difference in how primary energy is handled for electricity and fuels in the feed- back. The feedback of electricity is seen as coming from the system under study, i.e., the nuclear power plant, and contains only the actual use of electricity plus compensation for grid losses.

The feedback of fuels also contains the electricity equivalents of the extraction of the fuels. If the fuels were treated in the same way as the electricity, the method would answer the question:

‘How much electricity is yielded compared to the amount of electricity that would have been needed in the nuclear power plant, if all resources were replaced by the use of electricity in- stead?’ This question is not as interesting, because all resources are probably not possible to re- place by electricity.

To summarise the discussion, the method could be developed to be able to answer three different questions, where the yield of electricity is compared to:

- the mechanical work or potential to mechanical work in resources used directly and indi- rectly by the system

- the possible amount of electricity that could be produced from the resources used directly in the system, when used in an alternative power producing system

- the amount of electricity that would have been needed in the nuclear power plant if all re- sources were replaced by the use of electricity instead.

The different questions imply differences in how the primary energy of a resource in the feed-

back should be calculated. The question chosen for this work is the first one: What is the yield of

electricity compared to the potential to mechanical work in resources used directly and indirectly

by the system?

15

3 Data and calculations

In this chapter the feedback (F) of resources into the nuclear fuel cycle of a Swedish nuclear power plant is presented and calculated as electricity equivalents. The input to the calculations comes from data on the use of energy and services in the different steps of the nuclear fuel cycle that are presented in section 3.1. The transformities between the resource usage and their elec- tricity equivalent are presented in section 3.2. The calculation of the feedback in terms of elec- tricity equivalents is presented in section 3.3. The data and the calculated amounts of electricity equivalents are presented in more detail in Appendix B.

Data on the nuclear power process are taken from refs. (1) and (2). The energy feedback has been calculated with transformities developed in accordance with the method described in sec- tion 2. Where no other reference is given the information is collected from ref. (1). In some cases the original reference is given although the data is collected from ref. (1). The reference year of the data in ref. (1) are mainly 2004 and in some cases 2002. All economical data are from 2004 and hence, exchange rates from this year are used. In order for this study to be comparable with ref. (1) it is assumed that the technical service life of the nuclear power plant is 40 years.

3.1 Data on the nuclear fuel cycle

The data on the nuclear fuel cycle are taken from an emergy analysis of a Swedish nuclear power plant (1). This emergy analysis is based on the uranium consumption for the Forsmark nuclear power plant as presented in the Environmental Product Declaration (EPD) (2). However, the data in the EPD, concerning use of primary energy, are considered to be too aggregated for the emergy analysis. Hence, a Nuclear Fuel Energy Balance Calculator, ref. (11), have been used to calculate the amounts of fuel and electricity needed in the production process of the actual amount of nuclear fuel derived from the EPD. This implies that the data on the use of fossil fuels and electricity in the processes of extraction, conversion, enrichment and fuel fabrication are not the real data but are instead generic. Data on the use of fuel and electricity as well as costs at the power plant are taken from the Annual Report of Forsmark (12). Data on the handling of nuclear waste was mainly collected from SKB.

The data used in ref. (1) have here been complemented with data on energy use in the construc- tion and decommissioning phase with data from the LCA of Forsmark carried out by Vattenfall (13). This data corresponds to only 1% of the energy use in the fuel cycle.

3.1.1 Extraction, Conversion, Enrichment and Fuel fabrication

Energy use in the upstream processes of the nuclear fuel cycle vary widely depending on the

uranium content in the ore, the nature of the ore body and the techniques used. The data used in

this work are taken from ref. (1) and are based on calculations with the Nuclear Fuel Energy

Balance Calculator and the Nuclear Fuel Cost Calculator from World Information Service on

Energy (WISE) and the WISE Uranium Project (11)(14). The calculator is developed for educa-

tional purpose only and is not intended for commercial use. The calculator only covers the en-

ergy used for the operation of the plants. Energy used for the construction and decommissioning

of the plants as well as energy used for the production of raw materials required, is not included.

The data takes into consideration direct energy used in the processes.

The energy use refers to open-pit and underground mining only, because the technique of in situ leaching is not covered by the calculator. An underlying assumption for the calculations is that enrichment is carried out in centrifuges and not in gaseous diffusion plants that are more energy demanding. This assumption is reasonable, because the centrifugation technique is dominating today and will be even more so in the close future.

The data on the costs from the Nuclear Fuel Cost Calculator, are based on prices of U

O

, con- verted UF

and enriched UF

. Prices are given in US dollars and converted to SEK with the ex- change ratio valid for the reference year, 1 USD = 6.96 SEK (1).

The data on the upstream processes are presented in Table 2.

Table 2. The energy consumption and costs for the processes of Extraction, Conversion, Enrichment and fuel fabri- cation presented per year and per kWh of gross electricity production in the NPP. Data regard direct energy use in the process and not primary energy.

16

Fuel (J) Electricity (J) Costs (SEK) Fuel (kWh) Electricity (kWh) Costs (SEK)

Yearly flows Flows per kWh

Extraction 1,37E+15 1,18E+14 4,81E+08 1,59E-02 1,37E-03 2,00E-02

Conversion 6,31E+14 2,34E+13 3,85E+07 7,30E-03 2,70E-04 1,60E-03

Enrichment 1,78E+14 4,67E+13 2,42E+08 2,06E-03 5,40E-04 1,01E-02

Fuel fabrication 1,84E+14 7,37E+13 1,44E+08 2,13E-03 8,52E-04 5,99E-03

3.1.2 Electricity generation

In Table 3, data on costs and energy use for the Forsmark nuclear power plant during one year is presented. The data are collected from ref. (1) with some exceptions. The technical service life of the nuclear power plant is assumed to be 40 years.

The data on energy use consists of energy use during operation, energy used during the construc- tion phase and estimates of the energy need during the decommissioning phase of the nuclear power plant. The net electricity generation in the year of 2002 was 23,074 GWh (2) and the use of electricity for the operation of the power plant was 944 GWh in the same year (12). The use of diesel as reserve fuel varies a lot from year to year. In the year 2004 the use of diesel as reserve fuel was 1.38 GWh according to ref. (1).

Data on the energy use for construction and decommissioning of the nuclear power plant stems from ref. (13). The energy use is allocated to the electricity production from the assumed total electricity production during the life time of the power plant. The energy use allocated to the year of 2002 amounts to 23.9 GWh of fuels, mainly fossils, and 17.3 GWh of electricity.

The real construction costs of existing Swedish nuclear power plants are difficult to determine

because the power plants are old and the building was part of a governmental program. However,

it is of great interest to assess the cost of building new power plants, because this type of analysis

is especially useful when investigating possible future use of nuclear power. Hence, the projected

construction cost of the new Finnish reactor, Olkiluoto 3, has been used to estimate the capital

costs for a nuclear power plant. The price Finland has to pay for the new reactor is 3.2 billion

Euros (15). In 2004, that is the reference year of this report, the exchange rate was 1 EUR = 9.1

SEK. In ref. (1), the capital costs did not include any interest rate. In this study, the capital costs

have been calculated using the annuity method. The calculations are based on an interest rate of

6% and the estimated service life of Olkiluoto 3 that is 60 years. Furthermore, the capital cost

has been normalised to the power of Forsmark. Olkiluoto 3 will have the net electric power of

1600 MW (16) and the net electric power of Forsmark was 3090 MW in the year of 2004 (2).

The costs related to administration, operation and maintenance, inspection, liability insurance and decommissioning are the same as used in ref. (1). The costs for operation and maintenance regard the costs for wages paid by Forsmark and administration costs for inspection carried out by the Swedish nuclear power inspectorate (SKI) and the Swedish radiation protection authority (SSI)

. The inspection costs are collected from the annual reports from SSI and SKI and the costs that Forsmark is responsible for is allocated from how much of the services that are carried out at Forsmark. (1)

Future costs for decommissioning of the nuclear power plants in Sweden will be covered by the Swedish Nuclear Waste Fund. All the Swedish nuclear power plants contribute to the fund rela- tive to their electricity generation. In 2004 the share of the fund’s assets allotted to the Forsmark NPP was 29%. Hence, 29% of the total estimated costs for the decommissioning of Swedish nu- clear power plants have been allocated to Forsmark. In the calculations the costs have been dis- tributed equally to each year of operation through dividing the decommissioning cost with the assumed service life of Forsmark, i.e., 40 years.

Table 3. Data on the costs, use of electricity and fossil fuels in the nuclear power plant.

Item Flows/year Flows/kWh

Fuel 9,12E+13 J 1,05E-03 kWh

Electricity 3,46E+15 J 3,99E-02 kWh

Operation and maintenance costs 1,13E+09 SEK 1,31E-08 SEK Investment (Olikiluoto 3) 5,62E+10 SEK 6,49E-07 SEK Economic lifetime (Olikiluoto 3) 60 Years

Interest rate 6%

Capital costs 3,48E+09 SEK 4,02E-08 SEK

Insurance costs 3,31E+07 SEK 3,82E-10 SEK

Decommissioning costs 9,61E+07 SEK 1,11E-09 SEK Total power plant costs 4,74E+09 SEK 5,47E-08 SEK

3.1.3 Management and storage of nuclear waste

The facilities for management and storage of nuclear waste are Slutförvar för radioaktivt driftavfall (SFR), Centralt mellanlager för använt bränsle (CLAB), facilities for capsule manu- facturing and encapsulation and deep repository. The waste facilities are shared by all the Swed- ish nuclear power plants. Therefore, an allocation of the energy use and costs must be done. For CLAB the allocation is not trivial because of the time delay between the electricity production in the nuclear power plant and the energy consumption and generation of costs in the storage, where the nuclear fuel is stored for approximately 30 years. Another aggravating factor is that presently, only prototypes for the encapsulation facility and the deep repository exist and hence, data relies on estimates.

The data used here are the same as in ref. (1). Forsmark’s share of the electricity and fuel use, as well as the costs are, in accordance with the argument in the previous section, assumed to be 29% of the total values for electricity usage, fuel usage and costs in the nuclear waste facilities.

For SFR and CLAB the annual values on electricity usage, fuel usage and operation and mainte- nance costs are used. This is a simplification, valid for the SFR storage. Considering CLAB, this assumption would be correct if the lifetime of the power plant would be the same as the time of storage of the nuclear waste in CLAB, and if the system consisting of the power plant and the waste facility would be in equilibrium, implying that the amount of waste stored at CLAB were constant. The first criterion is satisfied, but the second is not.

17

1 The Swedish radiation protection authority (SSI) and the Swedish nuclear power inspectorate (SKI) have been merged into the Swedish radiation safety authority (SSM).

Of the total capital costs for the waste facilities 29% have been allocated to the Forsmark NPP.

The capital costs include an interest rate of 6% and are calculated using the annuity method.

Only the capital costs for facilities already constructed are included. The costs have been equally distributed over the 40 years of electricity production that will take place in the Forsmark NPP, without considering differences in electricity production between the years. Also, no considera- tion has been given to the fact that investments are done at different times.

The energy use for the construction and decommissioning of waste facilities stems from ref.

(13). Allocation of energy use has been done with respect to assumed energy consumption for all waste facilities that are built and will be built and from the electricity production in all the Swed- ish nuclear power plants that have been and will be produced within their life time. The energy use for 2004 has been calculated from the energy use per kWh for the construction and decom- missioning of the waste facilities and the electricity production for Forsmark during the reference year.

Table 4 shows the sum of the resources allocated to Forsmark that are used in the waste facilities during the year 2004. In Appendix B it is shown how the resources are shared between the dif- ferent facilities.

Table 4. Required resources for handling of radioactive waste generated during one year in Forsmark.

18

Item

Fuel 6,67E+13 J 7,72E-04 kWh

Flows/year Flows/kWh

Electricity 5,84E+13 J 6,75E-04 kWh

Costs 4,39E+08 SEK 5,08E-09 SEK

3.1.4 Transports in the nuclear fuel cycle

Transports represents only a small share of the resources contained in the feedback (F) to the nuclear fuel cycle. The estimated resources required for transports in all the steps of the nuclear fuel cycle are presented in Table 5 and stems from ref. (1). In Appendix B it is shown how the transports are shared by the different steps in the system.

Table 5. Energy use and costs for transportation in the nuclear fuel cycle.

Item

Motor fuel 1.93E+13 J 2.23E-04 kWh Costs 6.87E+06 SEK 7.95E-11 SEK

Flows/year Flows/kWh

3.1.5 Limitations of data

For some parts of the nuclear fuel cycle data has not been available for all resources used. The costs are however covered for most activities. The energy use for the production of chemicals and durable goods is not included in the analysis. For the upstream processes data is missing regarding energy use for the construction and decommissioning of the facilities. Direct energy use for inspection activities is assumed to be negligible. The energy use and the costs for the restoration of mines are also not included.

Comparing the data on the upstream processes, that are calculated with the Nuclear Fuel Energy Balance Calculator (11), with data from the EPD of Forsmark (2), the data on electricity and fuel use presented here are about twice as large. Although the EPD by Vattenfall covers the processes in more detail, the use of primary energy resources is less there than calculated here.

The reason for this is that the energy usage in upstream processes is very sensitive to the tech-

niques used and hence, varies widely. This is also were most of the energy is used, except for the

use of electricity in the power plant.

19 In this work as well as in ref. (1), the service life of the power plant of Forsmark is assumed to be 40 years. Because of new investments, the technical service life of the reactors in Forsmark is presently assumed to be 50 years. This has little effect on the results, because the main use of resources stems from the operation. The longer life time implies less allocation of energy to the reference year. However, the longer life time also implies more investments.

3.2 Calculation of transformities

In order to calculate the amount of electricity equivalents in different resources, transformities are used. A transformity describes the relation between a resource and its corresponding electric- ity equivalent. The calculations of the transformities are based on the possible net production of electricity equivalents in power plants using different fuels.

Data on the feedback (F) in the nuclear fuel cycle (presented in section 3.1 above) are divided into three categories: fuels, electricity and services. To calculate the electricity equivalents of the energy used by these categories, three transformities are needed: the transformity of fuels, trans- formity of electricity and the energy per monetary unit index. The calculation of the transformity of fuels is presented in section 3.2.1. The calculation of the transformity for the use of electricity is presented in section 3.2.2. In section 3.2.3 the Swedish economy is analysed in terms of its use of electricity equivalents and the energy per monetary unit index is calculated; that is, the trans- formity of costs.

3.2.1 Fuels transformity

The fuels used in the nuclear fuel cycle are assumed to be only fossil fuels, mainly oil products.

The amounts of fuels presented in section 3.1 represents the direct use of fuels in the nuclear fuel cycle. As described in chapter 2, the feedback also contains the energy required to provide the nuclear power plant with the fuels, that is, the primary energy. The primary energy is calculated from the primary energy conversion factor for fossil oil. Primary energy conversion factors are normally used in an energy analysis and describe how much extra energy of the actual fuel that is needed for the extraction of the fuel. The extraction process for a fossil fuel requires typically 10% extra of the fuel and hence, the primary energy conversion factor is 1.1.

The amount of electricity equivalents in the fuel is calculated from the net electricity efficiency in a condensing power plant. Also the services used in the power plant used as reference requires electricity equivalents and these are subtracted to form the net electricity equivalents. The trans-

used in the nuclear power plant is calculated using the formula formity for the fossil fuels

(eq. 1)

where P is the primary energy conversion factor, is the net electricity efficiency, is the en- ergy per monetary unit index, and is the cost for the electricity production per unit electricity.

Typically the net electricity efficiency of a 400 MW condensing power plant fuelled by coal is 47% (17). This efficiency is assumed to be valid for electricity production from oil as well and has been used to determine the fuel transformity. Ultimately the net electricity efficiency should be compensated for energy fed back to the power plant. This would require that an energy analy- sis using electricity as base is carried out for a fossil fuelled plant as well. In this work the net electricity efficiency is not compensated for the feedback of other resources than the internal electricity use, which is a simplification.

The costs estimated for electricity production in a 400 MW condensing power plant is 0.28

SEK/kWh

, excluding the cost of the fuel (17). The costs are multiplied with the energy per

monetary unit index, calculated in section 3.2.3.