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Economic Assessment of Tokamak Fusion Reactor Plants
Copyright © IFAC Energ\' Systems. Manage ment and Economics . '('ok m, .Japan I ~IH~I
ECONOMIC ASSESSMENT OF TOKAMAK FUSION REACTOR PLANTS T. Nanahara*, K. Yamaji*, S. Akita*, T. Takuma**, Y. Fukai***, A. Hatayama***, N. Asamit and M. Kasai* *Central Resea rch IlISlilute of Electric POWeT Industry, 2-11-1 Iwatokita , Komae-shi, Tokyo 201, Japan **Graduale School of Engineering Sciences, Kyushu Universily, Kasuga-shi, Fukuoka 816 , Japan ***Toshiba Cmporalion, 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo 100, Japan t Mitsubislzi Hem ,)' Indu stries, 2-4 -1 Shibakouen, M inato-ku, Tokyo 105, japan tMitsubishi Alomic Power Industries, 2-4-1 Shibakouen, Minato-ku, Tok,Vo 105, Japan
Abstract. As the R&D of nuclear fusion technology makes steady progress, it becomes important to examine with what perspective and toward what direction further steps should be taken. This paper dis cusses the prospect of commercial nuclear fusion power reactors principally from the viewpoint of electric utilities, namely its potential users. Based upon conceptual designs of pure fusion reactors and fusion fission hybrid ~eactors, generation costs (cost of electricity) of the reactors are evaluated. Two different approaches are employed in the design because much uncertainty still remains in the future characteristics of fusion power reactors. The generation costs for the above two approaches show a fair similarity. The evaluated costs of the hybrid reactors are significantly lower than those of the pure fusion r e actors. Keywords. Power ge neration; nuclear plants; system analysis; sensitivit y analysis; economics; nuclear fusion; commercialization.
feasibility of commercialization of the reactors for electric power generation is studied mainly through economic assessment. The assessment, however, inevitably includes much uncertainty in various aspects because many problems still remain unsolved with the reactors. Thus, based upon two different design schemes, this paper makes two conceptual designs for commercial reactors. It discusses fusion fission hybrid reactors, which could bring the early commercialization of the nuclear fusion technology, as well as pure fusion reactors.
1, I NTRODUCTION Great R&D efforts have been devoted to challenge physics and engineering related subjects on nuclear fusion, an "energy of dream". Although R&D has been conducted for many types of fusion including newly found cold fusion, the Tokamak type would be considered as the most advanced one. That is, for the Tokamak, large-scale experimental facilities, such as JT-60 in Japan, have given the p romising results suggesting th e potential ac hieve ment of the break -even condition that would be a milestone of its commercialization.
2. METHOD FOR ECONOMIC ASSESSMENT
As commercialization is now within scope, development stage of fusion may move from scientific verification phase to engineering demonstration one. On the other hand, R&D experience to date has revealed that there still remain many problems to be resolved even with the Tokamak type. Taking into account the prospect that the development of a commercial reactor will require enormous cost for a long period, it becomes important to examine with what perspective and toward what direction we should make our furt her step.
Few analyses on the economics of nuclear fusion power reactors were carried out in Japan mainly because of the much uncertainty in the performance of commercial fusion power reactors. But in the U.S.A., Schulte et a1. (1978,1979) provided a guideline for the economic assessment of fusion power reactors; Backer et al. (1980), Sheffield et al. (1986) and others made the assessment following the guideline. The results of these assessments cannot be, however, directly applied to the cases in Japan since many factors in the assessment, such as evaluation method and cost conditions, are considerably different between the two
This paper presents the results of our analyses on t he perspectives of a commercial fusion power reactor from the viewpoint of electric power utilities, namely its potential users. In the analyses,
435
T. Nanahara et al.
436 countries.
Hence, we assess the economy of fusion reactors following the Japanese fashion as far as possible. In the assessment, we did not include such cost items that are taken into account in the U.S.A., but not in Japan -- e.g. contingency allowance, etc.. The assumptions for various cost data are determined by examining the current prices of materials and cost data for the present commercial light water reactors in Japan. In the conceptual designs of fusion power reactors, we try to depend on the recent databases in order to avoid too optimistic assumptions. In the study, capital cost and generation cost of fusion power reactors are assessed. The generation cost (cost of electricity) presented here is the levelized bus-bar cost over its legal life, composed of annual capital cost, operation and maintenance cost, and fuel cost. The generation cost C is given by the following equation:
selected results of the sensitivity analyses are presented because of the limitations of space. See Takuma et al. (1989) for details of the analyses. The economic assessment is executed both for pure fusion reactors and for fusion fission hybrid reactors; the fusion driver of the hybrid reactor is assumed to be the Tokamak type in the study. Fig. 1 depicts the outline of the studied fusion reactors. 3. ECONOMIC ASSESSMENT #1 The study performed by Backer et al. (1980) on the STARFIRE, which evaluated relevant design factors relatively in detail, gives a good example of economic assessment of fusion reactors. In this chapter, the cost of the STARFIRE is reassessed in the Japanese fashion using the latest Japanese data as far as possible. 3.1 Pure Fusion Reactor
cc x (af
+ ao&m ) + FC (1 )
C
8760 x CF x (1 - h) x MW where, CC : capital cost, af : annual fixed charge rate, ao&m : annual operation and maintenance (O&M) charge rate, FC annual fuel cost, CF capacity factor, h rate of power used in the plant, MW gross electric output. Since this evaluation inherently requires forecasts of many uncertain factors, we have conducted a number of sensitivity analyses by varying the forecasted conditions. In the following chapters, only
Blanket (With fissile fuel for hybrid reactor)
The STARFIRE is a Tokamak type fusion reactor with major radius 7 [m] and net electric output 1200 [MW]; steady-state operation is achieved with lower hybrid RF heating in this reactor. The design of the STARFIRE is somewhat optimistic from the viewpoint of betavalue (see Fig. 2) because they assumed the beta-value to be independent of the other plasma parameters. We hence introduce the Troyon scaling law (see Appendix) to the assessment model, which we developed by partly modifying the Generic Reactor Model proposed by Sheffield et al. (1986), in order to incorporate the effects of other plasma parameters on the beta-value. In the model, first, the
Coil
~ Turbine
Gross Electric Output
In·plant Power
Fig.l
Nuclear Fusion Power Reactor
Net Electric Output
Tokamak Fusion Reactor Plants
0
6
Design Point in STARFIRE
5
~ 4
J
3 2
OL-~
3
__- L_ _~_ _L-~__~ 4 5 6 Aspect Ratio
Fig.2 /3m" v.s. Aspect Ratio
plasma parameters that give the specified net electric output are determined. The costs are then evaluated based upon the required volumes of material (SUS, copper, etc.) and other supplementary data. The capital cost was calculated by summing up those for the following three sections: fusion island equipment, structures and site facilities, and BOP (balance of plant) equipment. For the equipment that would constitute a major part in the capital cost -- e.g. shield and magnet --, the cost is evaluated in detail considering the practical experience to date in design and construction of similar equipment. On the other hand, for other less-costing equipment, the
437
cost is computed simply by converting the STARFIRE costs into Japanese yen. Fig. 3 exhibits the generation cost for the reactor when the Troyon scaling law (Le. maximum beta-value) is taken into account. In the figure, the generation cost is, for instance, 25 [ yen/kWh j for aspect ratio of 3.5. If the law is not considered as in the original STARFIRE design, the cost decreases to 19 [yen /kWhj , 30% lower than the above value. This is because, without the constraints of the Troyon scaling law, the size of the reactor becomes smaller due to higher beta-value. Fig. 4 shows the contribution of major items to the costs. It reveals that 70% of the generation cost comprises the fixed cost; the capital cost of the reactor strongly affects the economics because it is almost proportional to the fixed cost. The shield and magnet, which are major components in weight, also take a large portion in the capital cost: the shield accounts for 33% and the magnets for 35% of the capital cost. 3.2 Hybrid Reactor
An electric-power-producing hybrid reactor, which places major accent on power generation, is analyzed. The parameters of the reactor core discussed here are basically those presented in the paper by Kelly, et al. (1980), but those for the blanket were examined by the authors. In the study, we adapt a design to cause nuclear fission by fast neutrons. The blanket loaded with U0 2 as fissile fuel and Li 2 0 as tritium breeding material is
Fuel Cost
I
T 0& M Cost
Annual Capital Cost 70.5%
3.8
%
25.7 %
(a) Generation Cost
40 Fusion Island System/ Equipment 54.4 %
.....o if)
o
(b)
Capital Cost
30
U
BOP 26.4 %
Structure & Site Facilities 19.2%
Current Dri ve Supporti ng Hea Structure Tra nsfer
I
r" T 7 Blanket 12 .5%
20L-;--';--;;-+--+---+----:!:----+---l:---,.J 3 5 6 7 8 9 10 Aspect Ratio Fig.3 Generation Cost v.s. Aspect Ratio
Shield 33.0 %
Magnet 35.l %
7.5 5.3 6.6 % % %
(c) Capital Cost for Fusion Island
Fig.4
Major Cost Items in Economic Assessment # 1
438
T. Nanahara et al. 25,--------------------------, 0: Capacity Factor= 75% t:; : Capacity Factor Affected by Operation (Blanket Exchange) Cycle 20 Exchange of Blanket at 110% Output
15
------().--
.....o
Exchange of Blanket at 120 % Output
eno
u
;3 (% )
Fig.5
Generation Cost of Power- Producing Hybrid Reactor (;; 1)
[N ote)
Aspect rati o is 5.0
cooled by helium gas. It is designed so that the reactor will show good performance as a power reactor: that is, high energy multiplication in the blanket with its small variation in its operation cycle. Suppressing variation of energy multiplication is difficult because fissile plutonium increases in the blanket during the operation. The net electric output of the reactor is
1200[MW] and that value is assured at the beginning of the cycle. The method of cost assessment is principally the same as for the pure fusion reactor, except that it evaluates the hybrid blanket cost and credit for the plutonium produced in the blanket. The blanket cost is evaluated based upon weight and unit price of materials, while the plutonium credit is computed by multiplying the produced plutonium volume by its unit price. Fig. 5 shows the generation cost for various beta-values and exchange-cycles of the blanket. In the study, the capacity factor of the reactors is assumed ei ther to be determined by the exchange cycle of the blanket, or to be constant at 75%. This figure reveals that the generation cost for the beta-value of 5% is, for example, 16 or 18 [ yen /kWh] if the blanket is assumed to be exchanged at 120% or 110% output, respe c ti v ely. Those costs are much low e r than the cost 25 [yen/kWh] for the pure fusion reactor in the preceding section. This is because, due to the energy mu ltiplication of more than 5.7 in the blanke t, th e fusion output can be smaller and the fusion island can be compacted. Th e cost for additional engineered safet y features in the hybrid reactor do e s not cancel out the benefit. The figure also t e lls that the cost gets cheaper as the design condi tions become severer - - i. e . as t h e beta valu e s and maximum neutron fluence on the first wall get bigger. This result also applies to a pure fusion r e act o r. 3.3 Sensiti v ity Analys i s The sensitivity of generation cost of a pure fusion reactor i s depi c t e d in Fig. 6 for the changes i n capacit y factor, efficiency of current dri v e e quipment, eff icienc y of st ea m turbine, current densit y in super con ducti ve coils, and
Base Value /1 7% lI'all Loading 3.6MW/m' Capacity Factor 75% E fficiency () f Cu r r ent drive
60%
G e ne ra tlon
36%
EffLciency
:-' lilX . :\ l a J,( nc t ic Fi e ld
Fig. 6
Results of Sensiti v ity Anal y sis
JU T
Tokamak Fusion Reactor Plants
439
TABLE I TYPICAL RESULTS OF ECONOMIC ASSESSMENT #2
Pure Fusion reactor
Hybrid [Un it ] Reactor
(I) Reactor Performance - - Major Radius
-----
Minor Radius Plasma Current Fusion Output Total Thermal Output - - Gross Electric Output - - Net Electric Output - - /3 Value - - Wall Loading
(2 ) Capital Cost - - Fusion Reactor Equipment - - Other Reactor Equipment -- Balance of Plant (3 ) Levelized Busbar Cost
8. 19 2. 30 20 . 44 3500 4669 1556 976 5. 16 2.47
6. 20 I. 50 10.84 668 2948 1179 979 4. 44 O. 94
1279
780
[m] [m] [MA ] [MWt 1 [MWt 1 [MWe ] [MWe l [Xl [MW/ m'l [b ill ion yen l
53X
40X
[Xl
16X 29X
22r.
[X]
38%
[Xl
27.6
16 . 9
[yen / kWh ]
over Legal Life [Note) If the coefficient in the Troyon law is to be twic e of the current experimental value as in the case o f th e STARFIRE, the generation cost of pure fusion reactors decreases to 17 [yen/kWh).
maximum magnetic field. Reference design in the figure is the one described in s e ction 3.1 as the case of not considering the Troyon law; the generation cost for the reference design is thereby 19 [yen/kWh). This study is also performed with the model described in section 3.1. The figure makes clear that, in general, these factors strongly affect the generation cost. The reasons for the influence are briefly summarized in the following. The current drive efficiency and current densit y in coils have a great influence mainly on the power requirement in the plant and on the size of coils, respectively. The magnetic field bears a physical relation to the fusion output -- that is, to the reactor dimensions if the output power is kept constant. The capacity factor and turbine efficiency directly affect generated electric energy and accordingly generation cost. 4. ECONOMIC ASSESSMENT #2 In this chapter, the design and cost estimation are executed using the system analysis code "NEW-TORSAC" developed by Kasai et al. (1987). This code provides a means for determining plasma parameters, structure of equipment, and performance of required auxiliar y equipment. The design is carried out by modifying the reference reactor design, which is input in advance, to adjust its characteristics to the specified values; blanket characteristics are also given to the code as input data. This code incorporates the Troyon scaling law in examining the design.
4.1 Pure Fusion Reactor The net electric output of the d e signed reactor is 1000 [MW) a c hi e ving stead ystate operation with RF curr e nt drive. The major radius of th e rea c tor is 8[m), which is a little larger than that of the STARFIRE. Table 1 list s the gene ration cost and other re c tor characteristics for the t y pical reactor designed. The generation cost of the pur e fusi o n r e actor , in the table is 28 [ yen / kWh), slightly higher than that d e scribed i n section 3.1. Since this design d e pends on the recent database for th e c urrent drive efficiency adopted b y t he I NTOR (1988), it requires large in-pl ant power mainl y used for current drive. The cal c ulated in-plant energy rate here is 37%, which is considerably greater than 17% in sec tion 3.1. If we assume the c o e f fi c ient in the Troyon law to be twice of th e current experimental v alue, the generation c ost decreases to 17 [yen /kWh); this assumption approximatel y corresponds to the original design conditions of th e STARFIRE. As for the capital cost calculated, the fusion island takes a large share. Among components in the fusion island, the current drive equipment and magnet are especially costly. The same reason that explains the greater in-plant energy rate makes the cost in Table 1 higher than in the STARFIRE. 4.2 Hybrid Reactor In the simi lar way to section 3.2,
we
440
T. Nanahara et al.
examine the economics of an electricpower-producing hybrid reactor. In the reactor, molten salt (flibe) is selected as blanket coolant, and U3 Si as fissile fuel, and Li 2 0 as tritium breeding material. Basic design of the reactor is that described in the paper by Matsuoka et a1. (1987). In this reactor, fast neutrons are used for nuclear fission. The reactor allows 4.9 times energy multiplication in the blanket. Its fusion output is, accordingly, only one fifth of that of the pure fusion reactor discussed in the previous section, and the plasma dimension is about 30% smaller than that of the pure fusion reactor. The required plasma current is only half of that in the pure fusion reactor, resulting in the improved in-plant energy rate of 17%; this value is much lower than 37% for the pure fusion reactor. Table 1 also shows the typical results of economic assessment for the hybrid reactor. The capacity factor of the reactor is assumed to be 75% through this analysis. The evaluated generation cost of the hybrid reactor is 17 [yen/kWh) for the case shown in Table 1. As can be observed in the table, the hybrid reactor requires capital cost as large as 61% of that for the pure fusion reactor, while it has fusion output as small as about one-fifth of that of the pure fusion reactor. This result suggests that a considerable scale-merit is expected particularly for fusion island equipment. 5. CONCLUSION The major findings of the paper are as follows: (1) The generation cost calculated for the two different economic assessments shows a good similarity. The generation costs are about 27 [yen/kWh) for pure fusion reactors and about 17 [yen/kWh) for electric - power-producing hybrid reactors when we take the Troyon scaling law into account. (2) The above generation cost for the pure fusion reactor is significantly higher than that of the present light water reactors -- about 10 [yen/kWh). It should be noted that the generation cost is calculated for the commercial fusion reactors that have already sol v ed the forth-coming technological problems such as those for steady state operation. More break-throughs would be required to develop economically viable commercial reactors. (3) The major part of the generation cost of a fusion reactor is the fixed cost, much of which is attributed to the capital cost for the blanket, magnets, shields, and current drive equipment. (4) The capacity factor, maximum magnetic field, current density in coils, and other factors possess a vital influence on the economy of fusion reactors.
(5) The hybrid reactor might be a promising option because it could realize power generation at lower cost with relatively conservative designs for nuclear fusion. (6)
For
commercialization of nuclear reducing the size of a reactor by 1ncreas1ng the beta-value or by other means is indispensable. It is also required to improve the current driving technology in order to lessen the inplant power burden. ~usion,
Acknowledgment We would like to thank our colleagues concerned with this study for their invaluable assistance. REFERENCES Backer C.C., et a1.(1986), STARFIRE, A Commercial Tokamak Fusion Power Plant Study, ANL/FPP-80-1. INTOR GROUP(1988), International Tokamak Reactor: Phase Two A, Vienna, IAEA. Kasai,M.,et a1. (1987), Development of Tokamak Reactor System Analysis Code, JAERI-M 87-103. Kelly J.I. ,et al.(1980),Conceptual Design of a Commercial Tokamak Hybrid Reactor(CTHR), Final Report, WFPS:TME-80012. Matsuoka,F.,et a1.(1987), Conceptional Design of a Hybrid Power Reactor(THPR), 12th Symp. on Fusion Eng. of IEEE, Oct.1987, Monterey U.S.A. Schulte,S.C. ,et al.(1978), Fusion Reactor Design Studies - Standard Accounts for Cost Estimates, PNL-2648. Schulte,S.C.,et al.(1979), Fusion Reactor Design Studies - Standard Unit Costs & Cost Scaling Rules, PNL-2987. Sheffield,J., et al. (1986), Cost Assessment of a Generic Fusion Reactor, Fus10n Technology, 9, 199-249. Takuma,T., et a1. (1989), Prospects of Realizing Nuclear Fusion Reactors, CRIEPI Report, to be published (in Japanese) . [Appendix) Troyon Scaling Law This experimental law tells that the maximum beta-value BET~ax realizable is given by the following equation: I BET~ax
(A.1 )
g
a
B
where, I plasma current (MA), plasma minor radius (m), a B troidal magnet field (T), and g constant (the experimental value at present is about 3.5).
ECONOMIC ASSESSMENT OF TOKAMAK FUSION REACTOR PLANTS T. Nanahara*, K. Yamaji*, S. Akita*, T. Takuma**, Y. Fukai***, A. Hatayama***, N. Asamit and M. Kasai* *Central Resea rch IlISlilute of Electric POWeT Industry, 2-11-1 Iwatokita , Komae-shi, Tokyo 201, Japan **Graduale School of Engineering Sciences, Kyushu Universily, Kasuga-shi, Fukuoka 816 , Japan ***Toshiba Cmporalion, 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo 100, Japan t Mitsubislzi Hem ,)' Indu stries, 2-4 -1 Shibakouen, M inato-ku, Tokyo 105, japan tMitsubishi Alomic Power Industries, 2-4-1 Shibakouen, Minato-ku, Tok,Vo 105, Japan
Abstract. As the R&D of nuclear fusion technology makes steady progress, it becomes important to examine with what perspective and toward what direction further steps should be taken. This paper dis cusses the prospect of commercial nuclear fusion power reactors principally from the viewpoint of electric utilities, namely its potential users. Based upon conceptual designs of pure fusion reactors and fusion fission hybrid ~eactors, generation costs (cost of electricity) of the reactors are evaluated. Two different approaches are employed in the design because much uncertainty still remains in the future characteristics of fusion power reactors. The generation costs for the above two approaches show a fair similarity. The evaluated costs of the hybrid reactors are significantly lower than those of the pure fusion r e actors. Keywords. Power ge neration; nuclear plants; system analysis; sensitivit y analysis; economics; nuclear fusion; commercialization.
feasibility of commercialization of the reactors for electric power generation is studied mainly through economic assessment. The assessment, however, inevitably includes much uncertainty in various aspects because many problems still remain unsolved with the reactors. Thus, based upon two different design schemes, this paper makes two conceptual designs for commercial reactors. It discusses fusion fission hybrid reactors, which could bring the early commercialization of the nuclear fusion technology, as well as pure fusion reactors.
1, I NTRODUCTION Great R&D efforts have been devoted to challenge physics and engineering related subjects on nuclear fusion, an "energy of dream". Although R&D has been conducted for many types of fusion including newly found cold fusion, the Tokamak type would be considered as the most advanced one. That is, for the Tokamak, large-scale experimental facilities, such as JT-60 in Japan, have given the p romising results suggesting th e potential ac hieve ment of the break -even condition that would be a milestone of its commercialization.
2. METHOD FOR ECONOMIC ASSESSMENT
As commercialization is now within scope, development stage of fusion may move from scientific verification phase to engineering demonstration one. On the other hand, R&D experience to date has revealed that there still remain many problems to be resolved even with the Tokamak type. Taking into account the prospect that the development of a commercial reactor will require enormous cost for a long period, it becomes important to examine with what perspective and toward what direction we should make our furt her step.
Few analyses on the economics of nuclear fusion power reactors were carried out in Japan mainly because of the much uncertainty in the performance of commercial fusion power reactors. But in the U.S.A., Schulte et a1. (1978,1979) provided a guideline for the economic assessment of fusion power reactors; Backer et al. (1980), Sheffield et al. (1986) and others made the assessment following the guideline. The results of these assessments cannot be, however, directly applied to the cases in Japan since many factors in the assessment, such as evaluation method and cost conditions, are considerably different between the two
This paper presents the results of our analyses on t he perspectives of a commercial fusion power reactor from the viewpoint of electric power utilities, namely its potential users. In the analyses,
435
T. Nanahara et al.
436 countries.
Hence, we assess the economy of fusion reactors following the Japanese fashion as far as possible. In the assessment, we did not include such cost items that are taken into account in the U.S.A., but not in Japan -- e.g. contingency allowance, etc.. The assumptions for various cost data are determined by examining the current prices of materials and cost data for the present commercial light water reactors in Japan. In the conceptual designs of fusion power reactors, we try to depend on the recent databases in order to avoid too optimistic assumptions. In the study, capital cost and generation cost of fusion power reactors are assessed. The generation cost (cost of electricity) presented here is the levelized bus-bar cost over its legal life, composed of annual capital cost, operation and maintenance cost, and fuel cost. The generation cost C is given by the following equation:
selected results of the sensitivity analyses are presented because of the limitations of space. See Takuma et al. (1989) for details of the analyses. The economic assessment is executed both for pure fusion reactors and for fusion fission hybrid reactors; the fusion driver of the hybrid reactor is assumed to be the Tokamak type in the study. Fig. 1 depicts the outline of the studied fusion reactors. 3. ECONOMIC ASSESSMENT #1 The study performed by Backer et al. (1980) on the STARFIRE, which evaluated relevant design factors relatively in detail, gives a good example of economic assessment of fusion reactors. In this chapter, the cost of the STARFIRE is reassessed in the Japanese fashion using the latest Japanese data as far as possible. 3.1 Pure Fusion Reactor
cc x (af
+ ao&m ) + FC (1 )
C
8760 x CF x (1 - h) x MW where, CC : capital cost, af : annual fixed charge rate, ao&m : annual operation and maintenance (O&M) charge rate, FC annual fuel cost, CF capacity factor, h rate of power used in the plant, MW gross electric output. Since this evaluation inherently requires forecasts of many uncertain factors, we have conducted a number of sensitivity analyses by varying the forecasted conditions. In the following chapters, only
Blanket (With fissile fuel for hybrid reactor)
The STARFIRE is a Tokamak type fusion reactor with major radius 7 [m] and net electric output 1200 [MW]; steady-state operation is achieved with lower hybrid RF heating in this reactor. The design of the STARFIRE is somewhat optimistic from the viewpoint of betavalue (see Fig. 2) because they assumed the beta-value to be independent of the other plasma parameters. We hence introduce the Troyon scaling law (see Appendix) to the assessment model, which we developed by partly modifying the Generic Reactor Model proposed by Sheffield et al. (1986), in order to incorporate the effects of other plasma parameters on the beta-value. In the model, first, the
Coil
~ Turbine
Gross Electric Output
In·plant Power
Fig.l
Nuclear Fusion Power Reactor
Net Electric Output
Tokamak Fusion Reactor Plants
0
6
Design Point in STARFIRE
5
~ 4
J
3 2
OL-~
3
__- L_ _~_ _L-~__~ 4 5 6 Aspect Ratio
Fig.2 /3m" v.s. Aspect Ratio
plasma parameters that give the specified net electric output are determined. The costs are then evaluated based upon the required volumes of material (SUS, copper, etc.) and other supplementary data. The capital cost was calculated by summing up those for the following three sections: fusion island equipment, structures and site facilities, and BOP (balance of plant) equipment. For the equipment that would constitute a major part in the capital cost -- e.g. shield and magnet --, the cost is evaluated in detail considering the practical experience to date in design and construction of similar equipment. On the other hand, for other less-costing equipment, the
437
cost is computed simply by converting the STARFIRE costs into Japanese yen. Fig. 3 exhibits the generation cost for the reactor when the Troyon scaling law (Le. maximum beta-value) is taken into account. In the figure, the generation cost is, for instance, 25 [ yen/kWh j for aspect ratio of 3.5. If the law is not considered as in the original STARFIRE design, the cost decreases to 19 [yen /kWhj , 30% lower than the above value. This is because, without the constraints of the Troyon scaling law, the size of the reactor becomes smaller due to higher beta-value. Fig. 4 shows the contribution of major items to the costs. It reveals that 70% of the generation cost comprises the fixed cost; the capital cost of the reactor strongly affects the economics because it is almost proportional to the fixed cost. The shield and magnet, which are major components in weight, also take a large portion in the capital cost: the shield accounts for 33% and the magnets for 35% of the capital cost. 3.2 Hybrid Reactor
An electric-power-producing hybrid reactor, which places major accent on power generation, is analyzed. The parameters of the reactor core discussed here are basically those presented in the paper by Kelly, et al. (1980), but those for the blanket were examined by the authors. In the study, we adapt a design to cause nuclear fission by fast neutrons. The blanket loaded with U0 2 as fissile fuel and Li 2 0 as tritium breeding material is
Fuel Cost
I
T 0& M Cost
Annual Capital Cost 70.5%
3.8
%
25.7 %
(a) Generation Cost
40 Fusion Island System/ Equipment 54.4 %
.....o if)
o
(b)
Capital Cost
30
U
BOP 26.4 %
Structure & Site Facilities 19.2%
Current Dri ve Supporti ng Hea Structure Tra nsfer
I
r" T 7 Blanket 12 .5%
20L-;--';--;;-+--+---+----:!:----+---l:---,.J 3 5 6 7 8 9 10 Aspect Ratio Fig.3 Generation Cost v.s. Aspect Ratio
Shield 33.0 %
Magnet 35.l %
7.5 5.3 6.6 % % %
(c) Capital Cost for Fusion Island
Fig.4
Major Cost Items in Economic Assessment # 1
438
T. Nanahara et al. 25,--------------------------, 0: Capacity Factor= 75% t:; : Capacity Factor Affected by Operation (Blanket Exchange) Cycle 20 Exchange of Blanket at 110% Output
15
------().--
.....o
Exchange of Blanket at 120 % Output
eno
u
;3 (% )
Fig.5
Generation Cost of Power- Producing Hybrid Reactor (;; 1)
[N ote)
Aspect rati o is 5.0
cooled by helium gas. It is designed so that the reactor will show good performance as a power reactor: that is, high energy multiplication in the blanket with its small variation in its operation cycle. Suppressing variation of energy multiplication is difficult because fissile plutonium increases in the blanket during the operation. The net electric output of the reactor is
1200[MW] and that value is assured at the beginning of the cycle. The method of cost assessment is principally the same as for the pure fusion reactor, except that it evaluates the hybrid blanket cost and credit for the plutonium produced in the blanket. The blanket cost is evaluated based upon weight and unit price of materials, while the plutonium credit is computed by multiplying the produced plutonium volume by its unit price. Fig. 5 shows the generation cost for various beta-values and exchange-cycles of the blanket. In the study, the capacity factor of the reactors is assumed ei ther to be determined by the exchange cycle of the blanket, or to be constant at 75%. This figure reveals that the generation cost for the beta-value of 5% is, for example, 16 or 18 [ yen /kWh] if the blanket is assumed to be exchanged at 120% or 110% output, respe c ti v ely. Those costs are much low e r than the cost 25 [yen/kWh] for the pure fusion reactor in the preceding section. This is because, due to the energy mu ltiplication of more than 5.7 in the blanke t, th e fusion output can be smaller and the fusion island can be compacted. Th e cost for additional engineered safet y features in the hybrid reactor do e s not cancel out the benefit. The figure also t e lls that the cost gets cheaper as the design condi tions become severer - - i. e . as t h e beta valu e s and maximum neutron fluence on the first wall get bigger. This result also applies to a pure fusion r e act o r. 3.3 Sensiti v ity Analys i s The sensitivity of generation cost of a pure fusion reactor i s depi c t e d in Fig. 6 for the changes i n capacit y factor, efficiency of current dri v e e quipment, eff icienc y of st ea m turbine, current densit y in super con ducti ve coils, and
Base Value /1 7% lI'all Loading 3.6MW/m' Capacity Factor 75% E fficiency () f Cu r r ent drive
60%
G e ne ra tlon
36%
EffLciency
:-' lilX . :\ l a J,( nc t ic Fi e ld
Fig. 6
Results of Sensiti v ity Anal y sis
JU T
Tokamak Fusion Reactor Plants
439
TABLE I TYPICAL RESULTS OF ECONOMIC ASSESSMENT #2
Pure Fusion reactor
Hybrid [Un it ] Reactor
(I) Reactor Performance - - Major Radius
-----
Minor Radius Plasma Current Fusion Output Total Thermal Output - - Gross Electric Output - - Net Electric Output - - /3 Value - - Wall Loading
(2 ) Capital Cost - - Fusion Reactor Equipment - - Other Reactor Equipment -- Balance of Plant (3 ) Levelized Busbar Cost
8. 19 2. 30 20 . 44 3500 4669 1556 976 5. 16 2.47
6. 20 I. 50 10.84 668 2948 1179 979 4. 44 O. 94
1279
780
[m] [m] [MA ] [MWt 1 [MWt 1 [MWe ] [MWe l [Xl [MW/ m'l [b ill ion yen l
53X
40X
[Xl
16X 29X
22r.
[X]
38%
[Xl
27.6
16 . 9
[yen / kWh ]
over Legal Life [Note) If the coefficient in the Troyon law is to be twic e of the current experimental value as in the case o f th e STARFIRE, the generation cost of pure fusion reactors decreases to 17 [yen/kWh).
maximum magnetic field. Reference design in the figure is the one described in s e ction 3.1 as the case of not considering the Troyon law; the generation cost for the reference design is thereby 19 [yen/kWh). This study is also performed with the model described in section 3.1. The figure makes clear that, in general, these factors strongly affect the generation cost. The reasons for the influence are briefly summarized in the following. The current drive efficiency and current densit y in coils have a great influence mainly on the power requirement in the plant and on the size of coils, respectively. The magnetic field bears a physical relation to the fusion output -- that is, to the reactor dimensions if the output power is kept constant. The capacity factor and turbine efficiency directly affect generated electric energy and accordingly generation cost. 4. ECONOMIC ASSESSMENT #2 In this chapter, the design and cost estimation are executed using the system analysis code "NEW-TORSAC" developed by Kasai et al. (1987). This code provides a means for determining plasma parameters, structure of equipment, and performance of required auxiliar y equipment. The design is carried out by modifying the reference reactor design, which is input in advance, to adjust its characteristics to the specified values; blanket characteristics are also given to the code as input data. This code incorporates the Troyon scaling law in examining the design.
4.1 Pure Fusion Reactor The net electric output of the d e signed reactor is 1000 [MW) a c hi e ving stead ystate operation with RF curr e nt drive. The major radius of th e rea c tor is 8[m), which is a little larger than that of the STARFIRE. Table 1 list s the gene ration cost and other re c tor characteristics for the t y pical reactor designed. The generation cost of the pur e fusi o n r e actor , in the table is 28 [ yen / kWh), slightly higher than that d e scribed i n section 3.1. Since this design d e pends on the recent database for th e c urrent drive efficiency adopted b y t he I NTOR (1988), it requires large in-pl ant power mainl y used for current drive. The cal c ulated in-plant energy rate here is 37%, which is considerably greater than 17% in sec tion 3.1. If we assume the c o e f fi c ient in the Troyon law to be twice of th e current experimental v alue, the generation c ost decreases to 17 [yen /kWh); this assumption approximatel y corresponds to the original design conditions of th e STARFIRE. As for the capital cost calculated, the fusion island takes a large share. Among components in the fusion island, the current drive equipment and magnet are especially costly. The same reason that explains the greater in-plant energy rate makes the cost in Table 1 higher than in the STARFIRE. 4.2 Hybrid Reactor In the simi lar way to section 3.2,
we
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T. Nanahara et al.
examine the economics of an electricpower-producing hybrid reactor. In the reactor, molten salt (flibe) is selected as blanket coolant, and U3 Si as fissile fuel, and Li 2 0 as tritium breeding material. Basic design of the reactor is that described in the paper by Matsuoka et a1. (1987). In this reactor, fast neutrons are used for nuclear fission. The reactor allows 4.9 times energy multiplication in the blanket. Its fusion output is, accordingly, only one fifth of that of the pure fusion reactor discussed in the previous section, and the plasma dimension is about 30% smaller than that of the pure fusion reactor. The required plasma current is only half of that in the pure fusion reactor, resulting in the improved in-plant energy rate of 17%; this value is much lower than 37% for the pure fusion reactor. Table 1 also shows the typical results of economic assessment for the hybrid reactor. The capacity factor of the reactor is assumed to be 75% through this analysis. The evaluated generation cost of the hybrid reactor is 17 [yen/kWh) for the case shown in Table 1. As can be observed in the table, the hybrid reactor requires capital cost as large as 61% of that for the pure fusion reactor, while it has fusion output as small as about one-fifth of that of the pure fusion reactor. This result suggests that a considerable scale-merit is expected particularly for fusion island equipment. 5. CONCLUSION The major findings of the paper are as follows: (1) The generation cost calculated for the two different economic assessments shows a good similarity. The generation costs are about 27 [yen/kWh) for pure fusion reactors and about 17 [yen/kWh) for electric - power-producing hybrid reactors when we take the Troyon scaling law into account. (2) The above generation cost for the pure fusion reactor is significantly higher than that of the present light water reactors -- about 10 [yen/kWh). It should be noted that the generation cost is calculated for the commercial fusion reactors that have already sol v ed the forth-coming technological problems such as those for steady state operation. More break-throughs would be required to develop economically viable commercial reactors. (3) The major part of the generation cost of a fusion reactor is the fixed cost, much of which is attributed to the capital cost for the blanket, magnets, shields, and current drive equipment. (4) The capacity factor, maximum magnetic field, current density in coils, and other factors possess a vital influence on the economy of fusion reactors.
(5) The hybrid reactor might be a promising option because it could realize power generation at lower cost with relatively conservative designs for nuclear fusion. (6)
For
commercialization of nuclear reducing the size of a reactor by 1ncreas1ng the beta-value or by other means is indispensable. It is also required to improve the current driving technology in order to lessen the inplant power burden. ~usion,
Acknowledgment We would like to thank our colleagues concerned with this study for their invaluable assistance. REFERENCES Backer C.C., et a1.(1986), STARFIRE, A Commercial Tokamak Fusion Power Plant Study, ANL/FPP-80-1. INTOR GROUP(1988), International Tokamak Reactor: Phase Two A, Vienna, IAEA. Kasai,M.,et a1. (1987), Development of Tokamak Reactor System Analysis Code, JAERI-M 87-103. Kelly J.I. ,et al.(1980),Conceptual Design of a Commercial Tokamak Hybrid Reactor(CTHR), Final Report, WFPS:TME-80012. Matsuoka,F.,et a1.(1987), Conceptional Design of a Hybrid Power Reactor(THPR), 12th Symp. on Fusion Eng. of IEEE, Oct.1987, Monterey U.S.A. Schulte,S.C. ,et al.(1978), Fusion Reactor Design Studies - Standard Accounts for Cost Estimates, PNL-2648. Schulte,S.C.,et al.(1979), Fusion Reactor Design Studies - Standard Unit Costs & Cost Scaling Rules, PNL-2987. Sheffield,J., et al. (1986), Cost Assessment of a Generic Fusion Reactor, Fus10n Technology, 9, 199-249. Takuma,T., et a1. (1989), Prospects of Realizing Nuclear Fusion Reactors, CRIEPI Report, to be published (in Japanese) . [Appendix) Troyon Scaling Law This experimental law tells that the maximum beta-value BET~ax realizable is given by the following equation: I BET~ax
(A.1 )
g
a
B
where, I plasma current (MA), plasma minor radius (m), a B troidal magnet field (T), and g constant (the experimental value at present is about 3.5).