1. Concept development of compact DEMO reactor Kenji Tobita for DEMO Plant Design Team Japan Atomic Energy Research Institute Special thanks: F. Najmabadi (UCSD), C.P.C. Wong (GA), K. Okano(CRIEPI) IEA/LT Workshop (W59) combined with DOE/JAERI Technical Planning of Tokamak Experiments (FP1-2) 'Shape and Aspect Ratio Optimization for High Beta Steady-State Tokamak'

2. OUTLINE 1. ABC of Fusion Reactor Study 2. Compact reactor study at JAERI 3. DEMO design study at JAERI Started in 2003 Focus on the possibility of an economically attractive reactor in low-A (= 2-2.9), left behind in fusion reactor study previously - 2 -

3. 1. ABC of Fusion Reactor Study Direction of fusion reactor studies Necessity to pursue economic fusion energy - 3 -

4. (A) Reactor study seeks for an economic reactor concept Design Year COE (¢/kWh) SSTR (16 ¥/kWh) ARIES-I ARIES-RS ARIES-AT CREST (12.5 ¥/kWh) Cost-of-Electricity of Fusion COE of other sources fission~5¢/kWh coal-fired~6¢/kWh [1992 JA price basis] - 4 -

5. (B) In fusion energy, 60~70% of COE is capital cost COE (¢/kWh) = C c + C F + C OM P e 8760 (h/yr) f av Capital FuelOperation & maintenance Capital53.87 B¥/yr Fuel0.04 B¥/yr Operation19.77 B¥/yr Maintenance17.95 B¥/yr Costs of CREST (discount rate 2%) Availability output To reduce COE 1) Capital cost 2) Thermal efficiency 3) Availability - 5 -

6. (C) Much lower construction cost required for commercialization of FE Const. CostElectricity Share SSTR~4,500 $/kW ARIES-RS3,770 $/kW Default3,440 $/kW0 ~ 6% Low Cost2,400 $/kW4~11% - 6 - Fusion share assessment in 2100 4% ~ 1,500 plants Share depends on COE of other sources CO 2 -emission standards, etc. The estimated fusion cost may not be competitive in market Tokimatsu (2003)

7. Exploration of compact reactor USA Najmabadi (2000) JAERI SSTR (1990) A-SSTR2 (1999) R p = 7 m R p = 6.2 m - 7 -

8. How to compensate for reduced V p in compact reactor  low recirculating power by high bootstrap  higher thermal efficiency  higher  N  higher B max ARIES JAERI High  to reduce B max Moderate  at high B max - 8 -

9. 2. Compact reactor study at JAERI What led us to low-A compact reactor concept? - 9 -

10. JAERI’s approach toward compact reactor R p = 7 m B max = 16.5 T  N = 3.5 R p = 6.2 m B max = 23 T  N = 4 A-SSTR2 VECTOR SSTR Higher B max and  N - 10 -

11. High B T can make it heavy SSTR A-SSTR2 7.0 mRpRp 6.2 m 16.5 TB max 23 T 136 GJW TFC 181 GJ 11,200 tonsTFC Weight14,640 tons TFC weight is significant part of reactor: ~ 45% in SSTR - 11 -

12. JAERI’s approach toward compact reactor R p = 7 m B max = 16.5 T  N = 3.5 R p = 6.2 m B max = 23 T  N = 4 R p = 3.5 m B max = 20 T  N = 5.5 A-SSTR2 VECTOR SSTR High B max with slim TFC - 10 -

13. Reduce W TFC by small R TF ITER B max = 13T W TFC = 41 GJ SSTR B max = 16.5T W TFC = 140 GJ VECTOR B max = 19T W TFC = 10 GJ High W TFC Low W TFC Massive TFC Slender TFC R TF - 12 -

14. VECTOR 18.2m RpRp 3.2 mIpIp 14 MA a1.4 m NN 5.5 A2.3HH1.3  2.35n/n GW 0.9 B max 19 Tq MHD 6.5 BTBT 5 TP fus 2.5 GW Physical features  CS-less  Low A (~2.3) high , high n GW, high q - 13 - Remove CS to shorten R TF and reduce W TFC Concept of VECTOR Slender CS Low-A

15. Difference between VECTOR and ST conventional VECTOR ST CS removed Cu coil SC coil A ~ 2.5 A ~ 1.5 Power reactor VNS w. n-shield w/o. n-shield A = 3-4 - 14 -

16. VECTOR, likely to have economical and environmental advantages Reactor weight (t) Power / Weight (kW th /t) Low const. cost Resource-saving Economical - 15 -

17. Radwaste of VECTOR, ~4,000 t LLW, vulnerable point of fusion (usually, ≥ 10,000 t) PWR ~ 4,000 t Clearance Reinforced shield Recycle Reuse Compactness Resources (t) Disposal waste (t) 0 10,000 20,000 Clearance Low level Medium level SSTR DEMO2001VECTOR Reuse LiPb TiH 2 Recycle Be 12 Ti Li 12 TiO 3 - 16 -

18. Remarks on VECTOR VECTOR concept on TFC system breaks new ground of power reactor design in low- A ST 12345 2 4 6 8 ARIES-ST ARIES-AT ARIES-RS ARIES-I A-SSTR2 SSTR PPCS(B) PPCS(A) PPCS(C) PPCS(D) CREST VECTOR VECTOR-opt conventional A NN What is sure Open question Is the optimal design point for cost-minimum really A ~ 2.3 for the VECTOR concept? Assumed parametric dependence of  N (A) is uncertain. - 17 -

19. 3. DEMO design study at JAERI  How to fit VECTOR concept to DEMO  Three DEMO options - 18 -

20. JA Strategy for FE commercialization IFMIF Commercial. DEMO ITER Tech.R&D NCT  1 GWe output  Year-long continuous op.  Economical feasibility DEMO must be compact and have high power density - 19 -

21. Tradeoff between size and feasibility small as possible to reduce W TFC CS RemoveInstall CompactLarge R p More feasible + difficult + Size plasma Based on roles of CS, three DEMO options are under consideration VECTOR concept - 20 -

22. Difficulties caused by CS-less  I p rise/control Ex) CS-less Ip ramp-up Exp. (JT-60U, etc) will be resolved  Shaping triangularity is limited (  x ~ 0.3) problematic in confinement in high n/n GW suppression of giant ELMs giant ELM grassy ELM JT-60U - 21 -

23. Best effort to raise  w/o CS RpRp 5.1 m a2.1 m IpIp 17.5 MA pp 2.5 lili 0.8  up 2.0  up 0.3 A far distance between plasma and PF coils makes the shaping difficult. - 22 -

24. Three DEMO options shaping I p ramp CSsize “Full CS” 1.5 m (dia.) ~30 Vsec  x ~ 0.45 15 MAlarge Option C “CS-less” small  x ~ 0.3  Option A 0.7m (dia.) ~10 Vsec “Slim CS”  x ~ 0.4 ~ 5 MA medium Option B challenging conservative - 23 -

25. Preliminary design parameters CS-lessSlim CSFull CS R p (m)5.15.56.5 a (m)2.152.1 A2.42.63.1  2.082.01.9  ~0.30.40.45 B T /B max (T)5.4 / 18.26.0 / 16.46.8 / 14.6 I p (MA)18.116.715.0 q 95 5.75.45.3 NN 4.64.34.1 HH1.3 f BS 0.760.770.79 n/n GW 0.950.981.0 P fus (GW)3.13.0 P n (MW/m 2 )3.63.53.0 Q495254 Weight (tons)15,70017,50023,900 - 24 -

26. Comparison of Options 0 100 200 300 010,000 20,00030,000 ITER ARIES-RS ARIES-ST SSTR A-SSTR2 DREAM VECTOR Economical Low const. cost P fus / weight (kW/t) Reactor weight (t) Option A CS-less R p ~5.1m Full CS R p ~6.4m Option C shaping, I p ramp Slim CS R p ~ 5.5m Option B shaping Higher B max ,  N margin Adv. n-shield - 25 -

27. Key parameters in reactor design inboard SOL Gap BLK n-shield VV th-insulator RpRp R TF B max  TF 1.3 m Rule of thumb TFC CS Minimum shield thickness enough to protect TFC from neutron damage Four key parameters : R p, B max, R TF,  TF To use B T effectively, the inboard SOL width should be small - 27 -

28.  SOL in, expected to increase with A  SOL in usually assumed to be 10 cm but expected to decrease with A.  SOL out ~ Roughly, defined by the width of heat flux in SOL ( assumed to be 3 cm) - 28 -

29. Low-A requires a wide inboard clearance, especially for “CS-less”  For A~3  SOL in ~ 10 cm, good approx.  For A < 2.5 must be careful about  SOL in Determined from the flux surface corresponding to  SOL out = 3cm - 29 -

30. R CS R TF  TF a RPRP Separate TFC design B ma x CS TFC Selection of design parameter ｓ - 30 -

31.  N, B T Selection of design parameter ｓ R CS R TF  TF a RPRP Separate TFC design B ma x CS TFC 75% of  78% of  N Wong’s formula ( ,  N ) - 30 -

32. Selection of design parameter ｓ  N, B T R CS R TF  TF a RPRP Separate TFC design B ma x CS TFC 75% of  78% of  N Wong’s formula ( ,  N ) HH (=1.3) I P, q   V P, P fus, P CD, f GW, …. Check consistency - 30 -

33. Optimal design point (“Slim CS”) P fus = 3GW ←P e net = 1 GWe Weight minimum  Optimal range, rather wide optimal –– less dependent on A (or R TF ) fat TFC & high-A slender TFC & low-A - 31 -

34. Breakdown of weight A= 2.2 A= 2.8 Weight (t) lightheavy Higher A Torus comp. PFC TFC Lower A TFC Torus comp. PFC - 32 -

35. Problem in parameter selection:  N (A) is not sure Kessel (ARIES-AT, -RS) Wong (based on Miller’s stab.DB) A  (A)  N (A,  )  -dependence hidden   N vs  curve, depends on    N, less dependent on  in our conditions Our conditions 100% BS-driven plasma Our systems code uses this - 33 -

36. How does the optimal design point change when  N is independent on  ? Original assumption Alternative assumption to check an impact of  N (  ) Based on Wong’s formula Kessel-like (but not incl. dependence of  N on A) - 34 -

37. A ~ 3 optimum when  N (A,  ) = const Original design Constant  N  N = 4 optimal Optimal Slight increase in R p - 35 -

38. Present understanding on DEMO With slim CS, DEMO seems to succeed in adopting the VECTOR concept with plasma shaping capability. At the optimum design point, DEMO can have low-A (= 2.5-3) which is unexplored A in previous power reactor study before VECTOR. ST 12345 2 4 6 8 ARIES-ST ARIES-AT ARIES-RS ARIES-I A-SSTR2 SSTR PPCS(B) PPCS(A) PPCS(C) PPCS(D) CREST VECTOR VECTOR-opt conventional A NN DEMO - 36 -

39. Summary VECTOR concept Removes CS to shorten R TF and reduce W TFC, leading to slim TFC system compatible with high B max Suggests a possibility of power reactor with A = 2-3 DEMO CS will be necessary for shaping. “Slim CS”, i.e., modified VECTOR concept, enables us to envision DEMO with A = 2.5-3 To make the proper footing of DEMO, dependence of  N on A and  should be investigated in the range of A = 2.5-4, hopefully through international cooperation - 37 -