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Home , Nuclear weapon, Tokamak

TO THE CHOICE OF THE WORK SCENARIO OF COMPACT -REACTOR WITH TRANSMUTATION AND PURE BLANKET

E.A.Azizov1, E.P.Velikhov2, V.N.Dokuka1, V.A.Korotkov3, V.A.Krylov3, A.V.Lopatkin4, A.B.Mineev3, N.A.Obysov5, N.B.Rodionov1, J.S.Strebkov4, O.G.Filatov3, R.R.Khayrutdinov1, V.E.Cherkovets1

1SRC RF TRINITI, , 142190, region, Troitsk 2RRC "", Russia, 123182, Moscow Kurchatoiv Sq. 1 3Efremov Institute, Russia,196641, St. Petersburg, NIIEFA 4ENTEK, Russia, 107140, Moscow, M. Krasnoselskaya ul., build. 2/8 5Federal Agency for Atomic , Russia, 119017, Moscow, B.Ordynka, 24/26

The concept of using of the low aspect ratio (A≤ 2) for creation of thermonuclear power blocks is not new. Earlier it was considered in works [1, 4]. In these works, on basis of physical predictions based on impressing results obtained on the START device [4, 5] and the analyses of MHD stability for the low aspect ratio configurations with high elongation [6], the detailed estimation of parameters for such power units has been implemented. The obtained estimations shows, that creation of compact power units with clear blanket having sufficient high efficiency and required resources will in principle be possible, if basic assumptions about physical model and also MHD stability of plasma configuration (guarantying to operate at high βN values ), a possibility of achievement of high bootstrap current fraction, an opportunity of a maintenance of stationary operation regime are confirmed. The following problems compared in complexity with physical ones, are a maintenance of stationary regime operation of electromagnetic system, hardiness of materials for coils and isolation of electromagnetic system, development of effective blanket and providing of the breeding. Separately one should consider a problem of efficacious utilization of the heating produced by thermonuclear in blanket for producing of electric power, and of heating transferred by liquid cooling the electromagnetic system. A contribution of the last can substantially increase general efficiency of compact power units. The present work is devoted to discussion of opportunity to create the thermonuclear power unit (TPU) on the basis of enough conservative physical prerequisites concerning processes in the thermonuclear plasma. The main points of proposed concept can be worded as follows: 1. The density of plasma does not exceed Greenwald limit; 2. The obtained value of βN is to satisfy the scaling βN ≤ 5 li; 3. The energy confinement time is calculated taking into account an enhancement multiplier

HIPB98(y,2) = τЕ/τIPB98(y, 2); 4. The needed stationary plasma current is to be provided by bootstrap-current and current drive. The last should be generated by using NB injection of ; 5. Aspect ratio А=2; 6. Single-null plasma configuration with an elongation κ = 1.7. The simplified scheme of the compact power unit is presented on the Fig. 1. The basic dimensions of power units are given in Table 1.

Contact area Central solenoid Central post of TMS

Two shell vacuum Outer part of TMS chamber

Poloidal field coil

Fig. 1. Schematic of Geometrical Configuration of TPU

Table 1. Main parameters of TPU

Version R0, m a, m hts, m tсs, m b, m I 2 1 6.32 2.7 1.20 II 3 1.5 9.48 4.05 1.8 III 4 2 12.64 5.4 2.4

The electromagnetic system includes 16 toroidal coils, the sectionalized central solenoid and poloidal coils for providing the control of plasma shape and equilibrium. To minimize looses, copper was selected as a conductor material. The cooling of all coils is proposed to implement by water with on input no more 100°C. Central solenoid is used at the initial stage of plasma current ramp-up only. After this it is removed from irradiation zone. In this way the CS is used as "so-called" solenoid-starter Heating of plasma up to thermonuclear is provided by injection of two neutral beams with 400 and 500 keV. The main aim is a calculation of stationary steady state of compact power unit with fusion factor Q>1. In calculations it is accepted, the initiation and ramp-up of plasma current up to the value IP = 2.5 МА is produced with using of the central solenoid which provides necessary toroidal electric field and required supply of magnetic flux. The achievement of steady state for plasma current is reached by combinations of inductive current, a bootstrap-current, and driven current [7]. Numerical calculations are carried out with the use of 1.5D DINA code. There is a certain sense to consider two alternatives in the development of the compact thermonuclear power unit: 1. With blanket, containing dividing materials not representing dangers for spreading of nuclear . Such a way allows solving, in addition to power problems, ecological problems of utilization of minor (МА), which are highly active long-living components of nuclear waste. 2. With a pure blanket in which absorption of neutrons leads to heating a component of blanket up to the temperatures necessary for using a traditional cycle of transformation of thermal energy into electricity. As in the first and second case, it is necessary to include a compound into blanket components for getting full reproduction of tritium. For the above version of the thermonuclear power unit (TPU) with transmutation blanket it is enough to have a plasma with confinement multiplier HIPB98(y,2)=1.6. The main parameters of such a power unit with major plasma radius R0=2 m and elongation κ=1.7 are given in Table 2.

Table 2.ТРU with MA blanket, R0= 2 m, A= 2, κ=1.7, D:T= 0.3:0.7, Bt(R0)=3.9 T, HIPB98(y,2)=1.6 I II

Plasma current Ip, MA 5.00 5.3

Poloidal , βp 1.2 1.3

Energy confinement time, τE, ms 412 427 -3 Average density, ne20, m 1.0 1.0

Neutral beam power, PNBI, MW 45. 45.

Electron temperature on axis Te(0), keV 18 22

Ion temperature on axis Ti(0), keV 20 26

Average temperature, Тe, keV 6.8 7.1

Average temperature, Ti, keV 7.1 7.5

Safety factor on axis, q0 2.9 1.4

ne/nGW 0.638 0.604

Internal inductance, li 0.585 0.746

Ibs, MA 2.542 2.181

Thermal plasma energy, Wp, MJ 20.900 22.153

Fraction fast , ffast, % 17.485 25.631 2 loading Гn, MW/m Γn 0.311 0.352 Fusion gain factor, Q 1.217 1.374

Normalized beta, βN 3.189 3.550

Beam-target interaction, PBTI, MW 25.429 28.204

α-particles power, Pα, MW 7.818 8.849

Neutron Power Pn, MW 46.587 52.732

Bootstrap current fraction, fbs 0.5089 0.4142

Beam-driven current efficiency, γNB, A/W 0.0546 0.0690 Neutral beam energy, ENB, keV 200. 300.

In presented calculations, the at R0 is accepted equal to 3.9 T. Tangential injection of neutral deuterium with energies ENB = 200 keV, 300 and 400 keV and total power PNB = 45 MW is applied for auxiliary plasma heating and providing required meaning of current drive. 2 Having provided the required average neutron loading Γn about 0.3 MW/m on internal surface of blanket we can get the necessary thermal power due to fission reactions of MA. The design of transmutation blanket containing minor actinides (MA) is shown on fig. 2. Compound of transmutation blanket zones is presented in Table 3. The resume of the main characteristics of such a power unit is done in the Table 4.

1.5cm 5 cm 15 cm 50 cm Plasma 1 2 3 4

Fig. 2. Sketch of transmutation blanket with water-cooling

Table 3. Structure of blanket zones Zone 1 50 % steel, 50 % heat-transport medium (liquid lithium) Zone 2 15 % steel, 35 % МА, 50 % heat-transport medium (liquid lead) Zone 3 15 % steel, 45 % МА, 40 % heat-transport medium (water) Zone 4 75 % steel, 25 % water

Table 4. Integrated characteristics of blanket and speed of МА fission

Parameter Variant 2 (Li) Variant 3 (H2O) The number of fission per 1 DT neutron Zone 2 1.87 0.66 Zone 3 5.17 1.23 Total 7.04 1.89

Keff 0.96 0.86 Integral characteristics Averaged specific power of MA fission, MW/m3 211 56.7 Thermal power of fission, MW 4627 1243

Analysis of data from the table 4 leads to conclusion, that in the case of the power unit with transmutation blanket, there are no principle problems which hinders achievement of the required parameters for generating thermal power more than 1 GW and 4 GW for water and lithium coolants correspondingly. However, a vigilance of world community to systems containing trans- elements, which is connected to a problem of non-spreading of the , is known. Therefore, the opportunity of creation of the thermonuclear power unit on the basis of compact low aspect ratio tokamak with a pure blanket is of interest. As a prototype can be chosen a blanket for DEMO-C providing both transformation of neutrons energy into heating and reproduction of tritium. Total thickness of a blanket placed outside of external plasma boundary is 0.5-0.75 m. The basic materials of ceramic blanket are supposed to be steel as constructional element, ortosilicate lithium for breeding of tritium and for multiplication of neutrons. under pressure 10 МP is to use as a heat-transport liquid. Having thermonuclear neutron loading Γn about 1.3 MW, such a blanket can generate thermal power from 1.5 GW up to 2.8 GW. In tables 5 and 6 the data of plasma-physical calculations of the power unit for two different sizes of major plasma radius R0 = 3 m and R0 = 4 m are given. The plasma density profile is approximated by a curve close to the parabolic with power 2 and the ratio nb/n0 = 0.2. It is known, a creation and a support of necessary density profile is rather a complex problem. To solve it, we have to pay attention to development of appropriate controllers and tools, which allow us to change local density of plasma. The power of neutral beams injected in plasma and the ratio of beams power with different energies are assumed as the basic variable parameters. The magnetic field on R0 in all simulated variants is considered to be equal to 3.9 T and the confinement multiplier НIPB98(y,2) is equal to 2. From the obtained results of calculations follows that for the power unit with major plasma radius R0=3 m, the fusion gain factor Q = 10 is achieved by using injected power РNB = 60 MW of neutral beams with energies 400 keV and 500 keV in ratio of 20 MW and 40 MW correspondingly. Plasma current is equal to 10.8 MA. The contribution of a bootstrap-current makes up about 0.71⋅Ip and fraction of a driven current is 0.29 with current drive efficiency been equal to γNB = 0.052А/W. Increasing of injected power up to 100 MW leads to significant growth of plasma current (up to 15.4 МА) and negligible increase of fusion gain factor Q (about 25 %).

For the power unit with major radius R0 = 4 m, the meaning of fusion gain factor being equal to

Q = 19 is achieved for variant with plasma current Ip = 13 МА, averaged plasma density ⎯ne = 19 9⋅10 m-3 and total power of neural injection PNBI = 51 MW provided by beams with energies 400/500 keV and powers 20/31 MW correspondingly.

Table 5. ТРU with pure blanket, R0= 3 m, A= 2, κ=1.7, D:T= 0.5:0.5, Bt(R0)=3.9 T, HIPB98(y,2)=2 I II

Plasma current Ip, MA 10.792 11.918

Poloidal beta βp 1.228 1.210

Energy confinement time τE, ms 1328.54 1189.72 -3 Average density, ne20, m 1.364 1.375

Electron temperature on axis, Te(0),keV 22.05 30.75

Ion temperature on axis, Ti(0), keV 21.34 30.36

Average electron temperature, Тe keV 8.96 10.10

Average ion temperature, Ti, keV 8.74 9.92

Safety factor on axis, q0 2.33 1.78

ne/nGW 0.893 0.815

Internal inductance, lj 0.733 0.809

Thermal plasma energy, Wp, MJ 174.76 211.54

Fast particles fraction, ffast, % 6.65 5.97 2 Neutron loading Гn, MW/m 1.6551 2.2573 Fusion gain factor, Q 10.871 11.863

Normalized beta, βN 4.655 5.075

Beam-target interaction PBTI, MW 27.12 35.846

α-particles power, Pα, MW 93.73 127.84

Neutron Power Pn, MW 558.54 761.83

Bootstrap current fraction, fbs 0.7117 0.6943

Beam-driven current efficiency, γNB, A/W 0.0516 0.0483 Neutral beam power PNB, MW 20/40 20/55

Neutral beam energy ENB, keV 400/500 400/400

Table 6. ТРU for pure blanket, R0= 4 m, A= 2, κ=1.7, D:T= 0.5:0.5, Bt(R0)=3.9 T, HIPB98(y,2)=2 I II

Plasma current Ip, MA 12.934 11.876

Poloidal beta βp 1.186 1.2764

Energy confinement time τE, ms 2033.15 1932.37 -3 Average density, ne20, m 0.9078 0.906

Electron temperature on axis, Te(0),keV 23.258 25.441

Ion temperature on axis, Ti(0), keV 22.503 24.679

Average electron temperature, Тe keV 10.374 8.857

Average ion temperature, Ti, keV 10.127 8.664

Safety factor on axis, q0 2.523 2.160

ne/nGW 0.882 0.959

Internal inductance, lj 0.728 0.819

Thermal plasma energy, Wp, MJ 329.24 300.19

Fast particles fraction, ffast, % 5.118 4.608 2 Neutron loading Гn, MW/m 1.3863 1.2708 Fusion gain factor, Q 19.045 16.188

Normalized beta, βN 4.032 3.990

Beam-target interaction PBTI, MW 26.942 26.773

α-particles power, Pα, MW 139.575 127.948

Neutron Power Pn, MW 831.75 760.47

Bootstrap current fraction, fbs 0.7391 0.7508

Beam-driven current efficiency, γNB, A/W 0.0660 0.0535

Neutral beam power PNB, MW 20/31 20/35

Neutral beam energy ENB, keV 400/500 400/400

For the first variant the neutrons flux is equal to 1.65 MW/, and for the second one the flux is about 1.4 MW/m2, this allows to achieve the necessary thermal power in the pure blanket. It is necessary to pay attention to the supplying of electrical power for toroidal magnetic system. The calculations of the power consumed by toroidal magnetic system (TMS) for devices with major radii R0 = 2 m, 3 m and 4 m are given in the table 7. In the same table the currents, voltages in ТМС and the water consumption for removing thermal output are presented too. Table 7. TF magnetic coil parameters

Major radius, R0, m 2 3 4 Current density, j, MA/m2 21.40 14.25 11.05 Total current, I, MA 39.05 58.51 78.10 Total voltage, U, V 441.6 441.6 441.6

Toroidal magnetic field, Bt, T 3.9 3.9 3.9 Power of heating, P, MW 88.9 135.1 177.8 2 of water channels, SH2O, m 0.249 0.560 1.126

Total rate of water flow, GH2O, kg/s 204.57 329.68 409.07

Water speed, VH2O, m/s 0.82 0.57 0.33

Radiation hardiness of warm electromagnetic system can be provided by using an alloy CuCrZr and ceramic isolation. Another way is to use a protective shield placed between central part of toroidal leg and vacuum vessel.

Conclusion The existing base of experimental data, the numerical and theoretical analysis, and the advanced allows us to draw the following: ♦ Creation of the compact thermonuclear power unit on base of tokamak with А=2 and warm electromagnetic system and technically is possible both for transmutation blanket and for "clean" one ♦ The cost of the stationary power unit with transmutation blanket and thermal power up to 1,3MW with a full cycle of transformation of energy will not exceed one billion USA dollars ♦ There are no physical and technological problems standing in the way of creation of the power unit with "pure" blanket and thermal power up to 2 GW

References 1. M. Peng, J.Hicks. Proc. 16th Symposium on Fusion Technology, , Sept, 1990 2. E.A. Azizov, N. Ya Dvorkin, O.G. Filatov et al., JUST: Concept Development and Status Proc. Ind. Workshop on Spherical Torus V.I Abingdon, Dec., 1996 3. D.C. Robinson, R. Akers, S. Allfrey et al., Fusion Technology application of the , Proc. 17 IAEA Fusion Energy Conference Yokohama, Oct. 1998 4. R. Stanbaugh, V. Chan et al., Fusion on Technology, 33, 1, 1998 5. A. Sykes et al., Plasma Phys Control. Fusion 39, (1997), 247 6. A. Morris, R. J Akers et al., Plasma Phys. Control. Fusion, 41, (Suppl 12B), 1999, B191- B207 7. Miller R.L., 2001, ARIES Team, Fusion Technol., 39, 439-443