- Email: [email protected]
Fusion-driven transmutations of nuclear waste—a misconception or an incentive for promotion of fusion energy?
Fusion Engineering and Design 41 (1998) 455 – 460
Fusion-driven transmutations of nuclear waste—a misconception or an incentive for promotion of fusion energy? Stefan Taczanowski *, Graz; yna Doman´ska, Jerzy Cetnar Faculty of Physics and Nuclear Techniques, Uni6ersity of Mining and Metallurgy, 30 059 Cracow, Poland
Abstract A fusion-driven system of transmutation of nuclear waste is presented. The main positive aspect of this fusion power option, thanks to energy release from fission, is the prospect of a radical reduction of necessary plasma energy gain, Q, to levels achievable in relatively simple mirror devices. Further advantages of the system include lower FW load and homogeneous heating distribution. The proposed application of the concept is as a fuel self-sufficient symbiont reactor co-operating with a number of serviced LWRs, for the regeneration of the spent fuel with incineration of external Pu. The doubling of burnup, i.e. halving the high level waste from symbiotic LWRs can easily slow down its build-up without any mechanical or chemical intervention in the fuel. In conclusion, the present option might facilitate the development and then launching of fusion power reactors. © 1998 Elsevier Science S.A. All rights reserved.
1. Introduction Worldwide anti-nuclear phobia has not left the field of nuclear fusion untouched. On the part of the fusion community, one has observed few studies on fission – fusion hybrids and the absence of respective publications. The reason seems to be the avoidance of mentioning any relationship of fusion to fission. Yet, the specialist, though aware of the important differences between theses two forms of nuclear energy, cannot perceive fusion as having no problems with radioactivity. Thus, we are sceptical about the effectiveness of opposing the fission to fusion energy so as to encourage the public to accept the latter. We believe that there * Corresponding ftj.agh.edu.pl
author.
E-mail:
taczanowski@novell.
are other, better arguments to demonstrate that fusion power can be an environmentally benign energy source. The proposal is the use of a fusion reactor as a device for safe incineration of the waste produced by fission based nuclear energy, [1], since the persistence of fission based nuclear energy (LWRs) within the foreseeable future, seems assured. In view of the limits to future world hydrocarbon production, future generations, instead of being protected from the harmful influence of spent nuclear fuel, may need to utilize its actinides—the world cumulative amount for the year 2000 is 200000 t containing 4000 t of fissile ones—as the only significant and available energy source. The LWR costs (the fuel cycle back-end costs included) should determine the future electricity prices. This factor, together with
0920-3796/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PII S0920-3796(98)00310-X
456
S. Taczanowski et al. / Fusion Engineering and Design 41 (1998) 455–460
high investment costs of the fusion reactor, put in doubt whether its mere energy production, even at reduced radioactive waste level, proves sufficient for making it economically competitive. But an additional application of fusion, namely (as free of criticality dangers) transmutation (i.e. fissioning) of actinides in a fusion-driven device, can resolve this question. Discussed below is a system of several LWRs with a symbiotic fusion-driven transmuter (FT) to handle their spent fuel. The concept as partitioning-free is a non-oriented one. Thus, in this way an attractive picture of fusion appears —a means to solve the problems inherent to fission based nuclear energy.
2. Fusion-driven transmutations A transmutation system in general is an externally driven subcritical assembly where neutrons are used for inducing desired nuclear reactions in various materials. Since the only definitive abatement of actinides is fissioning — a process inseparable from energy release of physically fixed intensity—there is a defined limit to the actinide transmutation rate (per energy unit). It amounts to 1 nuclide per 200 MeV: 1200 kg/3 GWth · per year and so is directly determined by the power of the device. Therefore, a satisfactory rate of incineration with a fusion-driven subcritical system requires a high value of the product of its plasma energy gain Q (determining the number of source neutrons) times the blanket energy gain G which is approximately proportional to the inverse of 1− keff. The keff is the neutron multiplication factor of the system (Taczanowski [2]). A high transmutation rate is difficult to achieve as high Qs pose a problem, and the required high values of keff may seem — for safety reasons— controversial. Yet, its upper limit can be theoretically set by designing the system to remain subcritical under any conceivable operating scenario. The unavoidable step-wise changes in the keff following for example, a fuel shuffling or simply reloading, indicate that lower values of keff are always safer and thus preferable. Therefore, a clear objective appears: the maximization of G at
Fig. 1. Model of the fusion-driven transmutation assembly. (1,2,3-fissile containing zones).
safe keff. Simultaneously, one should remember that low Qs draw behind excessive energy consumption for fusion neutrons generation. But the energy-rich fission reactions can assist the insufficient energy yield from fusions, while the fissile material deeper in the blanket extends the volume of nuclear heating, thus allowing for sufficient system power at radically reduced size of the device. Moreover, lowering Q to a level achievable with the use of a tandem mirror device, thus allowing for replacement of the much more expensive tokamak (Badger et al. [3]) would be a qualitative advantage. One of the most promising options of the fusion-driven incineration systems (all the other feasible variants not excluding) is the regeneration of spent nuclear fuel from several symbiotic LWRs (Taczanowski [4]). In this concept of FT, the fuel
Fig. 2. Neutron multiplication in successive neutron generations.
S. Taczanowski et al. / Fusion Engineering and Design 41 (1998) 455–460
457
Fig. 3. Blanket composition and distribution of nuclear heating.
fertile nuclides are transmuted into fissile ones, some radioactive fission products into stable ones, and external fissile materials, necessary for achieving a sufficient FT power at low Q, are also fissioned. The re-use of spent fuel reduces the amount of high level waste per produced energy by half, thus approximately halving the environmental impact of all the symbiotic LWRs fuel cycle. This thanks to simply doubling the amount of energy extracted from the fuel. The other benefits of the concept are: possibility of incineration of external fissile materials (e.g. Pu), reutilization of unburned fissile nuclides and halving the demand for uranium (Taczanowski et al. [5 – 7]). At this point a comparison to alternative transmutation options should be done. The most developed and reasonable approaches are (1) heightening of the burnup in LWRs; (2) burning of Pu in LWR in the form of the MOX fuel, and (3) burning of Pu in FBRs. One can state effectively: 1. the effect is limited, since generally doubling of the burnup requires excessive initial enrichments; 2. this mature idea requires fuel reprocessing and thus it is not a non-proliferation oriented one; 3. again fuel reprocessing is required, plus there is a very strong opposition to fast critical systems which put in doubt serious developments of FBRs.
As concerns other emerging solutions, the advantages of tokamaks—that remain physically insuperable in the race towards reactor conditions of nuclear fusion—lose their significance at relaxed requirements well below the breakeven, i.e. at plasma parameters achievable in simpler devices e.g. mirrors. The tokamaks of toroidal geometry, giving rise to a formidable engineering problems (access, handling, etc.) do not seem competitive against cylindrical systems of much easier access and manufacturing. Instead, accelerator-driven systems remain their true competitors, (Taczanowski [7]). 3. Calculations and results In order to illustrate the present concept some neutron transport calculations showing improved results (as compared with our recent works [2,6– 8]) have been carried out with the MCNP4a (criticality) and modified BISON1.5 (transmutations & heating) codes. Respectively, the RMCCS1 and JENDL-3 based (burnup), libraries have been used. The model of calculation geometry is presented in the Fig. 1, illustrating also the configuration of collapsed assembly, now considered for the first time. This way, in addition to the normal operation, the most crucial item for the evaluation of system safety was analysed—system criticality in circumstances of the maximum credible accident.
458
S. Taczanowski et al. / Fusion Engineering and Design 41 (1998) 455–460
Table 1 Performance of the fusion-driven transmuter Gross thermal power Net power Gross plasma heat power Efficiency Of plasma heating Plasma Q FW neutron loading TBR
3000 (MWt) 1000 (MWe1) 150 (MWe1) 0.5 0.33 0.4 (MW m−2) 1.06
0.94 80 (W g−1) 97.7 (t) 86.6 (t) 1.0 (t year−1) 9 (months) 3
keff PuO2 rod specific power HM inventory: Spent fuel inventory Pu incineration rate Fuel rejuvenation time Symbiotic LWRs
˚ 3). Composition of blanket materials: (atoms/A SF: 238U 2.3−2, 235U 2.2−4, 239Pu 1.711−4, 237Np 1.49−5, O 4.712−2, F.P. 8.82−4. PuO2: 238Pu 3.659−4, 239Pu 1.359−2, 240Pu 5.148−3, 241Pu 3.049−3, 242Pu 1.34−3, 237Np 9.020−4, O 4.879−2. LiPb: 6Li 3.64−4, 7Li 4.53−3, Pb 2.39−2. PbO: Pb 2.48−2, O 2.48−2. SS: Cr 1.255−3, Ni 9.8486−3, Mo 1.5757−2, Fe 5.7272−2.
Since the keff after assembly collapse remains well under 1, there is no risk of uncontrolled supercriticality. Thus, the main requirement of safety has been achieved. An additional premise for lower keff results from greater demand for excess neutrons in cases of incineration of minor actinides and transmutation of long lived fission products (both beyond this work), since more than one neutron/nuclide is then used. Therefore, at high blanket energy gain, a lowering of keff also for neutron savings is desirable. The substitution for high keffs by intensified fast fission and (n, 2n) reactions effectively induced by the 14 MeV neutrons can be shown through the neutron multiplication in the successive generations. The results of respective calculations are presented in Fig. 2. The above effect of increasing the neutron multiplication without affecting final keff allows also a more radical decrease in the 14 MeV neutron flux at the FW with unchanged power of the whole system. It fructifies, in turn, in a reduction of FW radiation damage. However, intense fissioning at
the FW threats an excessive energy release there. Thus, in designing the system one is limited again by the admissible power density and its peaking (Fig. 3). As can be concluded from the Figs. 2 and 3, the proposed configuration is still not optimum. The neutron multiplication in the second generation might be more intense and the power density distribution, though much more uniform than in a blanket of pure fusion reactor, still could be improved. The results of calculations are summarized in the Table 1. All the above results show significant technological progress Table 2. The proposed concept, in spite of its advantages, obviously is not free of certain drawbacks. The large amount of fissile and fissionable materials in the system seems to be a primary concern. However, one should be aware that there is no possibility of destroying nuclear waste without manipulating it at all. Though the hazard caused by the FT alone is higher than that stemming
Table 2 A comparison of fusion-driven transmuter with pure fusion reactor
Device (1Gwel) Plasma Q FW area FW load
Pure fusion reactor
Fusion-driven transmuter
Reduction factor
Tokamak 30–50 1200 m2 2.5 MW m−2
Tandem mirror 0.2 – 0.5 60 m2 0.3 – 0.5 MW m−2
– 60 – 250 20 5–8
S. Taczanowski et al. / Fusion Engineering and Design 41 (1998) 455–460
from a pure fusion reactor, the global environmental load of the whole system: LWRs+ transmuter is reduced. Also some specific material problems may appear as an indirect result of reduced size of the system, i.e. of higher nuclear heating rate. Namely, for safety reasons (LOCA), instead of He, the liquid metal coolant Li17Pb83, often proposed for fusion systems, (e.g. Oda et al [9]) will be necessary. Liquid Li17Pb83 is corrosive. The combating of corrosion may require some additives in the coolant, not sufficiently explored as yet. On the other hand, the much lower FW load assures less troubles with the first wall and all the 14 MeV neutron induced damage, e.g. gas production in the threshold (n, p), (n, a), etc. reactions. Summarizing, the benefits of a fusiondriven transmuter clearly prevail over its imperfections.
459
chanical nor chemical intervention into the fuel. The latter signifies that the concept does not draw behind directly any partitioning, and thus is a nonproliferation-oriented one. Since LWRs do not seem yet menaced with extinction, just such a symbiotic transmuter system can most efficiently and timely slow down the increase in global stock of high level waste. Such a symbiont based upon the existing LWRs significantly reduces the investment for an environmentally benign electricity supply. Summarizing, the present concept of symbiotic system fusion reactor-LWRs with a significant relaxation of requirements regarding plasma Q at simultaneous Pu incineration allows for seeing the realization and then launching of the fusion energy as more near ones.
Acknowledgements 4. Conclusions The main result of the discussed option of fusion power is the prospect of a radical reduction of plasma Q to levels achievable in mirror systems with simultaneous Pu abatement. In this way significant economical savings can be achieved thanks to the replacement of a tokamak by simpler, cheaper, and more easily engineered mini tandem mirror device (Badger et al. [3]). In addition to this, the application of fusion to spent fuel regeneration should help in deployment of fusion energy as an attractive way of reducing nuclear environmental impact a point of particular social importance. These newly carried-out detailed calculations, as compared with the earlier ones, have brought further improvement of the system: lower plasma Q and FW load and more uniform heating distribution with strong neutron multiplication in the first generation. The exemplary application of the present concept of FT is a symbiotic nuclear energy system, consisted of a fusion-driven, deeply subcritical assembly and a number of serviced LWRs. The regeneration of spent fuel allows for its recycling and so halves the waste volume with neither me-
This study was sponsored by KBN (National Committee for Scientific Research).
References [1] L.M. Lidsky, Fission – fusion systems: hybrid symbiotic and augean, Nucl. Fusion 15 (1975) 151 – 172. [2] S. Taczanowski, Fusion – fission coupling — a hindrance or an incentive for promotion of fusion energy?, Proc. 2nd Int. Conf. Plasma 95%, Warsaw, June 1995, pp. 209– 216. [3] B. Badger, et al., TASKA-A: a low cost near term tandem mirror device for fusion technology testing, KfK 3680, 1984. [4] S. Taczanowski, Neutronic considerations for direct enrichment and spent fuel regeneration in hybrids without reprocessing, Atomkernenergie/Kerntechnik 45 (1984) 50 – 54. [5] S. Taczanowski, Significance of the resonance self-shielding in fissile breeding blankets, Nucl. Eng. Des./Fus. 3 (1985) 103 – 111. [6] S. Taczanowski, G. Domanska, P. Gronek, J. Cetnar, A study on the Environmentally Benign Fusion BreederTransmuter, Proc. ICENES 93%, September 1993, Tokyo, World Scientific, pp. 184 – 188. [7] S. Taczanowski, Neutronic Study of Nonproliferation Oriented Options of Fusion- and Accelerator-driven Transmutation Systems, Proc. ICENES 96% Obninsk, June 1996, pp. 701 – 712.
460
S. Taczanowski et al. / Fusion Engineering and Design 41 (1998) 455–460
[8] G. Domanska, S. Taczanowski, J. Cetnar, P. Gronek, J. Janczyszyn, A small Tandem Mirror Hybrid Reactor as a Safe and Economical Solution for Spent Fuel Rejuvenation and Fissioning of Plutonium, Proc. ICENES 96%, Obninsk, June 1996, pp. 419–426.
.
[9] A. Oda, et al., Tritium Breeding in Inertial Confinement Fusion Blankets: Effect of Source Neutron Energy Spectra, Proc. of ICENES 93%, September 1993, Tokyo, World Scientific, pp. 213 – 217.
.
Fusion-driven transmutations of nuclear waste—a misconception or an incentive for promotion of fusion energy? Stefan Taczanowski *, Graz; yna Doman´ska, Jerzy Cetnar Faculty of Physics and Nuclear Techniques, Uni6ersity of Mining and Metallurgy, 30 059 Cracow, Poland
Abstract A fusion-driven system of transmutation of nuclear waste is presented. The main positive aspect of this fusion power option, thanks to energy release from fission, is the prospect of a radical reduction of necessary plasma energy gain, Q, to levels achievable in relatively simple mirror devices. Further advantages of the system include lower FW load and homogeneous heating distribution. The proposed application of the concept is as a fuel self-sufficient symbiont reactor co-operating with a number of serviced LWRs, for the regeneration of the spent fuel with incineration of external Pu. The doubling of burnup, i.e. halving the high level waste from symbiotic LWRs can easily slow down its build-up without any mechanical or chemical intervention in the fuel. In conclusion, the present option might facilitate the development and then launching of fusion power reactors. © 1998 Elsevier Science S.A. All rights reserved.
1. Introduction Worldwide anti-nuclear phobia has not left the field of nuclear fusion untouched. On the part of the fusion community, one has observed few studies on fission – fusion hybrids and the absence of respective publications. The reason seems to be the avoidance of mentioning any relationship of fusion to fission. Yet, the specialist, though aware of the important differences between theses two forms of nuclear energy, cannot perceive fusion as having no problems with radioactivity. Thus, we are sceptical about the effectiveness of opposing the fission to fusion energy so as to encourage the public to accept the latter. We believe that there * Corresponding ftj.agh.edu.pl
author.
E-mail:
taczanowski@novell.
are other, better arguments to demonstrate that fusion power can be an environmentally benign energy source. The proposal is the use of a fusion reactor as a device for safe incineration of the waste produced by fission based nuclear energy, [1], since the persistence of fission based nuclear energy (LWRs) within the foreseeable future, seems assured. In view of the limits to future world hydrocarbon production, future generations, instead of being protected from the harmful influence of spent nuclear fuel, may need to utilize its actinides—the world cumulative amount for the year 2000 is 200000 t containing 4000 t of fissile ones—as the only significant and available energy source. The LWR costs (the fuel cycle back-end costs included) should determine the future electricity prices. This factor, together with
0920-3796/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PII S0920-3796(98)00310-X
456
S. Taczanowski et al. / Fusion Engineering and Design 41 (1998) 455–460
high investment costs of the fusion reactor, put in doubt whether its mere energy production, even at reduced radioactive waste level, proves sufficient for making it economically competitive. But an additional application of fusion, namely (as free of criticality dangers) transmutation (i.e. fissioning) of actinides in a fusion-driven device, can resolve this question. Discussed below is a system of several LWRs with a symbiotic fusion-driven transmuter (FT) to handle their spent fuel. The concept as partitioning-free is a non-oriented one. Thus, in this way an attractive picture of fusion appears —a means to solve the problems inherent to fission based nuclear energy.
2. Fusion-driven transmutations A transmutation system in general is an externally driven subcritical assembly where neutrons are used for inducing desired nuclear reactions in various materials. Since the only definitive abatement of actinides is fissioning — a process inseparable from energy release of physically fixed intensity—there is a defined limit to the actinide transmutation rate (per energy unit). It amounts to 1 nuclide per 200 MeV: 1200 kg/3 GWth · per year and so is directly determined by the power of the device. Therefore, a satisfactory rate of incineration with a fusion-driven subcritical system requires a high value of the product of its plasma energy gain Q (determining the number of source neutrons) times the blanket energy gain G which is approximately proportional to the inverse of 1− keff. The keff is the neutron multiplication factor of the system (Taczanowski [2]). A high transmutation rate is difficult to achieve as high Qs pose a problem, and the required high values of keff may seem — for safety reasons— controversial. Yet, its upper limit can be theoretically set by designing the system to remain subcritical under any conceivable operating scenario. The unavoidable step-wise changes in the keff following for example, a fuel shuffling or simply reloading, indicate that lower values of keff are always safer and thus preferable. Therefore, a clear objective appears: the maximization of G at
Fig. 1. Model of the fusion-driven transmutation assembly. (1,2,3-fissile containing zones).
safe keff. Simultaneously, one should remember that low Qs draw behind excessive energy consumption for fusion neutrons generation. But the energy-rich fission reactions can assist the insufficient energy yield from fusions, while the fissile material deeper in the blanket extends the volume of nuclear heating, thus allowing for sufficient system power at radically reduced size of the device. Moreover, lowering Q to a level achievable with the use of a tandem mirror device, thus allowing for replacement of the much more expensive tokamak (Badger et al. [3]) would be a qualitative advantage. One of the most promising options of the fusion-driven incineration systems (all the other feasible variants not excluding) is the regeneration of spent nuclear fuel from several symbiotic LWRs (Taczanowski [4]). In this concept of FT, the fuel
Fig. 2. Neutron multiplication in successive neutron generations.
S. Taczanowski et al. / Fusion Engineering and Design 41 (1998) 455–460
457
Fig. 3. Blanket composition and distribution of nuclear heating.
fertile nuclides are transmuted into fissile ones, some radioactive fission products into stable ones, and external fissile materials, necessary for achieving a sufficient FT power at low Q, are also fissioned. The re-use of spent fuel reduces the amount of high level waste per produced energy by half, thus approximately halving the environmental impact of all the symbiotic LWRs fuel cycle. This thanks to simply doubling the amount of energy extracted from the fuel. The other benefits of the concept are: possibility of incineration of external fissile materials (e.g. Pu), reutilization of unburned fissile nuclides and halving the demand for uranium (Taczanowski et al. [5 – 7]). At this point a comparison to alternative transmutation options should be done. The most developed and reasonable approaches are (1) heightening of the burnup in LWRs; (2) burning of Pu in LWR in the form of the MOX fuel, and (3) burning of Pu in FBRs. One can state effectively: 1. the effect is limited, since generally doubling of the burnup requires excessive initial enrichments; 2. this mature idea requires fuel reprocessing and thus it is not a non-proliferation oriented one; 3. again fuel reprocessing is required, plus there is a very strong opposition to fast critical systems which put in doubt serious developments of FBRs.
As concerns other emerging solutions, the advantages of tokamaks—that remain physically insuperable in the race towards reactor conditions of nuclear fusion—lose their significance at relaxed requirements well below the breakeven, i.e. at plasma parameters achievable in simpler devices e.g. mirrors. The tokamaks of toroidal geometry, giving rise to a formidable engineering problems (access, handling, etc.) do not seem competitive against cylindrical systems of much easier access and manufacturing. Instead, accelerator-driven systems remain their true competitors, (Taczanowski [7]). 3. Calculations and results In order to illustrate the present concept some neutron transport calculations showing improved results (as compared with our recent works [2,6– 8]) have been carried out with the MCNP4a (criticality) and modified BISON1.5 (transmutations & heating) codes. Respectively, the RMCCS1 and JENDL-3 based (burnup), libraries have been used. The model of calculation geometry is presented in the Fig. 1, illustrating also the configuration of collapsed assembly, now considered for the first time. This way, in addition to the normal operation, the most crucial item for the evaluation of system safety was analysed—system criticality in circumstances of the maximum credible accident.
458
S. Taczanowski et al. / Fusion Engineering and Design 41 (1998) 455–460
Table 1 Performance of the fusion-driven transmuter Gross thermal power Net power Gross plasma heat power Efficiency Of plasma heating Plasma Q FW neutron loading TBR
3000 (MWt) 1000 (MWe1) 150 (MWe1) 0.5 0.33 0.4 (MW m−2) 1.06
0.94 80 (W g−1) 97.7 (t) 86.6 (t) 1.0 (t year−1) 9 (months) 3
keff PuO2 rod specific power HM inventory: Spent fuel inventory Pu incineration rate Fuel rejuvenation time Symbiotic LWRs
˚ 3). Composition of blanket materials: (atoms/A SF: 238U 2.3−2, 235U 2.2−4, 239Pu 1.711−4, 237Np 1.49−5, O 4.712−2, F.P. 8.82−4. PuO2: 238Pu 3.659−4, 239Pu 1.359−2, 240Pu 5.148−3, 241Pu 3.049−3, 242Pu 1.34−3, 237Np 9.020−4, O 4.879−2. LiPb: 6Li 3.64−4, 7Li 4.53−3, Pb 2.39−2. PbO: Pb 2.48−2, O 2.48−2. SS: Cr 1.255−3, Ni 9.8486−3, Mo 1.5757−2, Fe 5.7272−2.
Since the keff after assembly collapse remains well under 1, there is no risk of uncontrolled supercriticality. Thus, the main requirement of safety has been achieved. An additional premise for lower keff results from greater demand for excess neutrons in cases of incineration of minor actinides and transmutation of long lived fission products (both beyond this work), since more than one neutron/nuclide is then used. Therefore, at high blanket energy gain, a lowering of keff also for neutron savings is desirable. The substitution for high keffs by intensified fast fission and (n, 2n) reactions effectively induced by the 14 MeV neutrons can be shown through the neutron multiplication in the successive generations. The results of respective calculations are presented in Fig. 2. The above effect of increasing the neutron multiplication without affecting final keff allows also a more radical decrease in the 14 MeV neutron flux at the FW with unchanged power of the whole system. It fructifies, in turn, in a reduction of FW radiation damage. However, intense fissioning at
the FW threats an excessive energy release there. Thus, in designing the system one is limited again by the admissible power density and its peaking (Fig. 3). As can be concluded from the Figs. 2 and 3, the proposed configuration is still not optimum. The neutron multiplication in the second generation might be more intense and the power density distribution, though much more uniform than in a blanket of pure fusion reactor, still could be improved. The results of calculations are summarized in the Table 1. All the above results show significant technological progress Table 2. The proposed concept, in spite of its advantages, obviously is not free of certain drawbacks. The large amount of fissile and fissionable materials in the system seems to be a primary concern. However, one should be aware that there is no possibility of destroying nuclear waste without manipulating it at all. Though the hazard caused by the FT alone is higher than that stemming
Table 2 A comparison of fusion-driven transmuter with pure fusion reactor
Device (1Gwel) Plasma Q FW area FW load
Pure fusion reactor
Fusion-driven transmuter
Reduction factor
Tokamak 30–50 1200 m2 2.5 MW m−2
Tandem mirror 0.2 – 0.5 60 m2 0.3 – 0.5 MW m−2
– 60 – 250 20 5–8
S. Taczanowski et al. / Fusion Engineering and Design 41 (1998) 455–460
from a pure fusion reactor, the global environmental load of the whole system: LWRs+ transmuter is reduced. Also some specific material problems may appear as an indirect result of reduced size of the system, i.e. of higher nuclear heating rate. Namely, for safety reasons (LOCA), instead of He, the liquid metal coolant Li17Pb83, often proposed for fusion systems, (e.g. Oda et al [9]) will be necessary. Liquid Li17Pb83 is corrosive. The combating of corrosion may require some additives in the coolant, not sufficiently explored as yet. On the other hand, the much lower FW load assures less troubles with the first wall and all the 14 MeV neutron induced damage, e.g. gas production in the threshold (n, p), (n, a), etc. reactions. Summarizing, the benefits of a fusiondriven transmuter clearly prevail over its imperfections.
459
chanical nor chemical intervention into the fuel. The latter signifies that the concept does not draw behind directly any partitioning, and thus is a nonproliferation-oriented one. Since LWRs do not seem yet menaced with extinction, just such a symbiotic transmuter system can most efficiently and timely slow down the increase in global stock of high level waste. Such a symbiont based upon the existing LWRs significantly reduces the investment for an environmentally benign electricity supply. Summarizing, the present concept of symbiotic system fusion reactor-LWRs with a significant relaxation of requirements regarding plasma Q at simultaneous Pu incineration allows for seeing the realization and then launching of the fusion energy as more near ones.
Acknowledgements 4. Conclusions The main result of the discussed option of fusion power is the prospect of a radical reduction of plasma Q to levels achievable in mirror systems with simultaneous Pu abatement. In this way significant economical savings can be achieved thanks to the replacement of a tokamak by simpler, cheaper, and more easily engineered mini tandem mirror device (Badger et al. [3]). In addition to this, the application of fusion to spent fuel regeneration should help in deployment of fusion energy as an attractive way of reducing nuclear environmental impact a point of particular social importance. These newly carried-out detailed calculations, as compared with the earlier ones, have brought further improvement of the system: lower plasma Q and FW load and more uniform heating distribution with strong neutron multiplication in the first generation. The exemplary application of the present concept of FT is a symbiotic nuclear energy system, consisted of a fusion-driven, deeply subcritical assembly and a number of serviced LWRs. The regeneration of spent fuel allows for its recycling and so halves the waste volume with neither me-
This study was sponsored by KBN (National Committee for Scientific Research).
References [1] L.M. Lidsky, Fission – fusion systems: hybrid symbiotic and augean, Nucl. Fusion 15 (1975) 151 – 172. [2] S. Taczanowski, Fusion – fission coupling — a hindrance or an incentive for promotion of fusion energy?, Proc. 2nd Int. Conf. Plasma 95%, Warsaw, June 1995, pp. 209– 216. [3] B. Badger, et al., TASKA-A: a low cost near term tandem mirror device for fusion technology testing, KfK 3680, 1984. [4] S. Taczanowski, Neutronic considerations for direct enrichment and spent fuel regeneration in hybrids without reprocessing, Atomkernenergie/Kerntechnik 45 (1984) 50 – 54. [5] S. Taczanowski, Significance of the resonance self-shielding in fissile breeding blankets, Nucl. Eng. Des./Fus. 3 (1985) 103 – 111. [6] S. Taczanowski, G. Domanska, P. Gronek, J. Cetnar, A study on the Environmentally Benign Fusion BreederTransmuter, Proc. ICENES 93%, September 1993, Tokyo, World Scientific, pp. 184 – 188. [7] S. Taczanowski, Neutronic Study of Nonproliferation Oriented Options of Fusion- and Accelerator-driven Transmutation Systems, Proc. ICENES 96% Obninsk, June 1996, pp. 701 – 712.
460
S. Taczanowski et al. / Fusion Engineering and Design 41 (1998) 455–460
[8] G. Domanska, S. Taczanowski, J. Cetnar, P. Gronek, J. Janczyszyn, A small Tandem Mirror Hybrid Reactor as a Safe and Economical Solution for Spent Fuel Rejuvenation and Fissioning of Plutonium, Proc. ICENES 96%, Obninsk, June 1996, pp. 419–426.
.
[9] A. Oda, et al., Tritium Breeding in Inertial Confinement Fusion Blankets: Effect of Source Neutron Energy Spectra, Proc. of ICENES 93%, September 1993, Tokyo, World Scientific, pp. 213 – 217.
.