Advanced Fusion Reactor Design using Remountable HT" SC Magnet

Transcription

1 J. Plasma Fusin Res. SERIES, Vl. 5 (2002) Advanced Fusin Reactr Design using Remuntable HT" SC Magnet HASHIZUME Hidetshi, KITAJIMA Sumi, ITO Satshi, YAGI Kenjir, USUI Yshiaki, HIDA Yujin and SAGARA Akir Thku University, Sendai , Japan I Natinal Institute fr Fusin Science, Tki , Japan (Received: 12 December 2001 / Accepted: 18 June 2002) Abstract A new cncept f fusin reactr design is prpsed using remuntable high critical temperature (HTc) supercnducting (SC) magnet. There are tw advantages using this system. First ne is that the magnet system can be cmpsed by parts, which means it easy t replace the damaged magnet mdule. The secnd ne is that it becmes pssible t access the reactr first wall easily. In rder t realize this system, we have perfrmed experiments using HTc SC tape. The experimental results indicate that the resistance f the jinted regin becmes abut 60 pq, which shws the feasibility f this cncept. Using this system the remutable first wall system als has the feasibility based n thermmechanical analysis. Keywrds: remuntable HT" supercnducting magnet, butt jint, remuntable first wall 1. Intrductin In rder t btain a public acceptance n fusin reactrs as pwer plants, it is crucial t prve ecnmic feasibility r at least t shw its pssibility with science and engineering develpment. As is well knwn, cst f fusin reactr designed nw is still very expensive mainly due t cnstructin fee including large SC magnet. Further the first wall f fusin reactr shuld be replaced peridically due t neutrn damage r plasma disruptin. In this paper, therefre, a new cncept f fusin reactr design is prpsed intrducing remuntable SC magnet and first wall, which can be nly achieved by using HT" SC magnet. Since the HT" SC material can be perated at relatively high temperature, the specific heat f SC material, which is prprtinal t cubic f the temperature, becmes very larger at liquid nitrgen temperature. Due t this characteristic, sme amunt f heat generatin, which is usually fatal in case f lw critical temperature SC material, is allwable as far as the heat can be remved by clant. It becmes, therefre, pssible t jint the SC tapes directly using mechanical frce, which enable us t design the remuntable magnet. This magnet system will bring the extremely attractive advantages like drastic cst reductin f SC cils and accessibility t reactr cmpnents. The first advantage is especially attractive in case f the helical reactr because the magnet system fr helical reactr can be cmpsed by cmbinatin f tw kinds f small magnet mdule. This will bring drastic reductin f cst fr the magnet system. Als it becmes easy t replace the magnet mdule damaged by, fr example, neutrn irradiatin. Therefre, it becmes pssible t treat the magnet system as a kind f cnsumer material. The secnd advantage is als attractive because it becmes pssible t access the reactr first wall easily. Crrespnding authr's by The Japan Sciety f Plasma Science and Nuclear Fusin Research 532

2 Hashizume H. et al., Advanced Fusin Reactr Design using Remuntable HT. SC Magnet Since the magnet mdules are directly cnnected by mechanical frce, we can remve the magnet system t repair r repla(re the first wall as undergne in peridical inspectin fr iissin pwer plants. 2. Remuntalbe HT" SC Magnet Fundamental experiment fr butt jinting methd: Thrugh ur previus study [1], ne f the mst prspective jintirrg methds is t apply butt jinting methds fr HT" S(l tape. The experimental results, hwever, shwed relatively large electric resistance abut 300 mw. Since this value is nt small enugh t design the remuntable magnet frm the viewpint f heat generatin, we perfrm ther experiments, where the crss sectin f HT, tape is cnditined by surface lapping. Figure I shv,s the experimental device used in this study. Ag-Mn ally / Bi-Pb-Sr-Ca-Cu-O supercnductr tape is used as a test piece. Silver rati t the SC material is 2.7. The width and the thickness f this tape are 3.98 mm and').261 mm, respectively. Critical current density f this supercnductr is 6.45x107 Nr* at17 K, prvided that SC state is defined as l0-r3 Clm. Cmpressive frce acting n the crss sectin f tape is btained by using difference f thermal expansin cefficient f the tape and vinyl chlride used as base fundatin. The experiment is carried ut at 7l K fr three cases (case l,'.t, and 3) f surface treating. In case 1 the tape is cut by nipper and then the crss sectin is grund by grinding paper (#1000). In cases 2 and 3, the tapes are fixed by plastic and then cut by diamnd cutter. In case 2, water resist paper up t #2000 is used t make the surface fla! while in case 3, lapping file up t #8000 is used t btain flatter surface. Figure 2 shws micrscpe image f the tape crss sectin fr cases 2 and 3. The black regin is crrespnding t HT" SC material. By treating the surface with the #8000 lapping film, the surface is plished mre flatly. Vinyl Chlride Vnyl Chlride Prcrcctive Resistuce Supercnducring Tapes NMw Gap Fig. 1 Experimental apparatus Case 2 (#2fi)0) Case 3 (#800O) Fig. 2 Micrscpe image f crss sectin 533

3 Hashizume H. et al., Advanced Fusin Reactr Design using Remuntable HT" SC Magnet Figure 3 shws the experimental results n the electric resistance when the strain f HT" tape varies by changing the initial gap length between tw tapes. The strain is evaluated by using thermal expansin cefficient f vinyl chlride and silver. The magnitude f transprt current in determining the resistance is 60 A (abut 90 7 f the critical current). The value f resistance at 10 A, fr example, becmes 90 V at 60 A, which may be caused by flux flw effect r difference f temperature rise due t jule heating. The result shws that the resistance decreases by increasing the strain and then reaches sme limit value. This means that the tape bending ccurs and that the stress acting n the tape des nt increase ver 0.2 V strain regin. Arund this regin, the data fr case 3 culd nt be btained because the tapes were piled up after slipping. T imprve the perfrmance, the experimental system shuld be mdified t suppress the bending f tapes. Fr cases I and 2, we can reduce the resistance frm the previus result f 300 pa t 60 po. In case 3, hwever, the resistance is nly reduced 260 pcl even thugh the tape crss sectin is much flatter than thse fcases 1 and2 as apprved frm Fig. 2. There must be sme reasns fr this relatively large resistance. One reasn can be that the cmpressive stress acting n the surfaces is nt large because the cntacting area becmes larger due t the flat surface. This is caused by the limitatin f cmpressive frce we can apply t the surface by this experimental system. Therefre there is large pssibility t reduce the resistance by imprving the experimental system. In the real magnet we can use the large electrmagnetic frce acting the SC cable by ptimizing the gemetry f cable crss sectin and the structure f casing. Outline f the magnet: In fabricating I T magnet f 5 m radius based n the present data, the ttal number f tums is calculated t be l.2x10s using 67 A critical current (1") tape. Then the ttal resistance f magnet becmes 14 C), which will causes 63 kw heat generatin. This value is still large and therefre the perfrmance f butt jinting methd shuld be imprved ne rder mre in terms f electrical resistance, whse gal is nt far frm the present results. 3. Remuntable First Wall System Cncept f the remuntalbe first wall: In the present design, the first wall shuld be replaced peridically due t neutrn damage and plasma disruptin. T avid this replacement, many researches have been perfrmed frm bth viewpints f material develpment and reactr designing such as liquid first wall cncept prpsed by APEX prgram [2]. On the ther hand, when the remutable magnet system is successfully achieved, the remuntable first wall cncept cari be acceptable, which enable us t replace the first wall as is dne in fuel (a) Cncept Case 1 A Case 2 O Case 3 E q 0< Strain (V) Fig.3 Dependence f resistance n strain (b) Crss sectin fchannel Fig. 4 Remuntable first wall 534

4 Hashizume H. et al., Advanced Fusin Reactr Design using Remuntable HT. SC Magnet replacement f fissin reactrs. Figure 4(a) shws the cncept f remuntable first wall, which is divided int upper and lwr parts. The end feach part is welded t the main structure, while the ribs are nt welded. Therefre fr maintenance r replacement, the magnet is remved at first and then the first wall is detached frm the uter struclure by slving the welded regin. Finally the uter main structure is remved easily t access the fist wall. Thermmechanical evaluatin: Figure 4(b) shws the crss sectin f channel whse gemetry is assumed t be a square. lllibe is chsen as clant material t reduce the MI{D pressure drp since the large inner pressure f clant is nt allwable in this design. The parameters used in thermmechanical evaluatin are listed in Table 1. The first wall design is determined by cnsidering maximum stress induced in the first wall, buckling pressure f arch and maximum temperature f the wall. The maximum stress induced in the first wall is evaluated as a functin f the thickness f first wall lb and the span f channel Z by cnsidering thermal and mechanical stress. Figure 5 shws the result, where the clant pressure is assumed 2 atm, which causes mechanical stress. When the 16 is smaller than 6 mm in case f 350 MPa, the mechanical stress is dminant and therefre by increasing the thickness, larger length t becmes acceptable. When the /5 becmes larger, the thermal stress rncreases and then the mechanical stress shuld be reduced by decreasing the length l,. Frm the result, the allwable maximum thickness /6 in case f 350 MPa is evaluated abut 6 mm. Since the maximum temperature in the first wall increases with using thicker wall, we chse 5 mm as the first wall thickness. where the maximum l, becmes abut 0.2 m fr 350 MPa. Figure 6 shws the critical pressure f buckling fr shell structure evaluated by the fllwing equatin [3]; P"=EI(P_D/R3 (1) where E, I R and r are Yung's Mdulus, mment f inertia f area, radius f curvature and a cnstant depending n the central angle (K= 2 fr n), respectively. In the figure, tr crrespnds t half f the lib thickness 0.25 c..j 0.2!.rs T cf.t ?3 E z.s a. 9.2 f I t.s El.t <i.s F--sf'\ l-.8. =275[i I --*- d=300[l\ --.. =325[t\ I --*- =351-[ --:: IHAJ Thickness f first wall f6 [mmj Fig. 5 Maximum stress induced in the first wall = 3.0[mm] s/ :4. = 4.0[mm] 'G,.8 F;z 4Fz '{.,"- /..Ez ' Channel width I [m] Fig. 6 Critical pressure fr buckling g {? 0.3 Table 1 List f parameters and material prperties 4 (heat flux) 0.6 (MWm) R 4 (m) B 10 (r) E wr-g 180 (GPa) H'-g 26 (W/m/K) ^ d lpt'r-g il.8 x10-6 (K,') P n,u" 2020 (kg/m3) vnre 9.26 xl0-1mz/s) t n'u" (Wm/K) driu 155 (S/m) d 0.08 E \ ; 0.04 = $.z Clant velcity l [m/s] Fig. 7 Pressure drp in channel 535

5 Hashizume H. et al., Advanced Fusin Reactr Design using Remuntable HT. SC Magnet as defined in Fig. 4(b). Frm the results the length l, shuld be greater than 0.1 m because the clant pressure is assumed t be 2 atm and the half thickness, /., des nt affect the critical pressure s much. Finally by cnsidering the structural integrity discussed in Fig. 5, we chse 0.2 m as the channel width and 2.5 mm as half f the rib thickness t make the wall thickness f channel becme 5 mm. In Fig. 7, pressure drp in the channel is pltted with the Z as parameter. The pressure drp includes the pressure lss alng the arch and 40 m straight pipe with 6 elbws using equatins given by ref. [4]. The criterin fr transitin t turbulent flw is RelHa = 150 as given by ref. [4]. Since the clant pressure is assumed 2 atm, which means the allwable pressure rise is I atm frm the atmsphere, the allwable maximum velcity is evaluated 2 mlsec. Using this value the maximum first wall temperature becmes abut 1080 K. 4. Cnclusin Thrugh this study the fllwing results are btained. 1) By using the butt methd fr HT" SC tape with surface treatment, the electric resistance is reduced t 60 pq at 90 7 f the critical current 1". By cntrlling the surface cmpressive stress, there is pssibility t reduce the resistance mre. 2) Based n the thermmechanical analysis, the remautable first wall als has pssibility and ne example design is demnstrated. 3) In this analysis, MHD effect is ignred. This effect shuld be cnsidered in future wrk because the clant channel prpsed in this study is pen ne and therefre it is very easy t cat the channel surface by electrical insulatr r t cut the electric circuit cmpsed frm the clant and wall. 4) Thrugh mre experiments, the cncept shuld be evaluated, which will bring breakthrugh in the fusin reactr design. Acknwledgement The authr wuld like t express thank t Prf. K. Abe f Thku University wh helped us fr the surface treating f HT" SC tape. References tll S. It et al.,lnt. J. f Applied Electmagnetics and Mechanics (2002), (in press). t2l M. Abdu and The APEX Team, Fusin Eng. Des. 54, 181 (2001). [3] Timshenk S.P. and Gere J., The thery f elastic stability (McGraw-Hill, 196l ). [4] JSME, JSME Mechanical Engineers' Handbk (in Japanese). 536