Estimation of Tritium Recovery from a Molten Salt Blanket of FFHR

Transcription

1 US/Japan Workshop on Power Plant Studies and Related Advanced Technologies with EU Participation, April 6-7, 2002 (San Diego, CA) Estimation of Tritium Recovery from a Molten Salt Blanket of FFHR Dept. Applied Quantum Physics and Nuclear Engineering, Kyushu University Satoshi FUKADA

2 1. Background study : Characteristics of Flibe as a self-cooled blanket Advantages (1) liquid blanket, low reactivity with air or water (2) low MHD effect (3) TBR >1 with addition of Be and low tritium solubility FFHR or HYLIFE-II Disadvantages (1) less Flibe-facing structural materials under neutron irradiation (2) unknown tritium behavior or recovery in Flibe is not studied. (3) possibly high tritium leak to the environment (4) issues of Be safety JUPITER-II Relating to this study

3 Design activities in NIFS Collaboration Ignition access O.Mitarai (Kyusyu Tokai Univ.) Helical core plasma K.Yamazaki (NIFS) Core Plasma 14MeV neutron Thermo-mechanical analysis T.Yamamoto, H.Matsui (Tohoku Univ.) Structural Materials Pro tecti on w all P h =0.2 MW /m2 P n =1.5 MW /m 2 Nd =4 50 dp a/30 y Sel f-coo led T breeder TBRlo cal > 1.2 Be Liquid / Gas Rad iatio n shi eld redu ctio n > 5 o rd ers Thermal shi eld shielding materials. Blanket system S,Tanaka (Univ. of Tokyo ) Blanket Vac uum vess el & T bou ndary SC mag net Now, on going cf. NIFS annual repo. Safety & Cost Helical reactor design / Sytem Integration A.Sagara (NIFS) surface heat flux In-vessel Components Thermofluid Thermofluid system S.Toda (Tohoku Univ.) Advanced thermofluid T.Kunugi (Kyoto Univ.) Purifi er Pump Ta nk high temp. Chemistry HX T-diseng ager 20 C Pump T st orage Turbine Heat exchanger system A.Shimizu (Kyusyu Univ.) Device system code H.Hashizume (Tohoku Univ.) Tritium T-disengager system S.Fukada, M. Nishikawa (Kyusyu Univ.) May 21, 2001, A.Sagaar

4 1. Background study : Tritium recovery from Flibe relating to the things (1) Physical Properties (Underlined properties are not available or not reliable) Tritium solubility (TF or T 2 ) Tritium diffusivity, permeation coefficient or mass-transfer coefficient Viscosity, thermal diffusivity or heat-transfer coefficient Phase diagram, vapor pressure, free energy change of fluoride formation Estimated from H 2, D 2 or other data (2) Affecting factors Chemical forms of tritium in Flibe, T 2, TF or T 2 O, or Flibe purification REDOX control condition, change from TF to T 2 Corrosive HF or TF in Flibe Isotopic effect and coexistent components to use purified Flibe and REDOX control by Be

5 1. Background study : Necessary conditions imposed on apparatus of tritium recovery from Flibe All tritium generated in a blanket is recovered Very low tritium leak to the environment Simple apparatus and easy to operate Operation over melting temperature High operation safety and material compatible with HF M+nHFMF n +(n/2)h 2 Operated under low water vapor condition BeF 2 +2H 2 OBe(OH) 2 +2HF, LiF+H 2 OLiOH+HF Permeation window, He-Flibe counter-current column, Vacuum disengager

6 2. Design study : Design of tritium-recovery apparatus for FFHR Assumptions Based on FFHR design Steady-state operation Tritium generated in a blanket is transferred by Flibe and is recovered by a tritium recovery apparatus. No isotope effect in properties No decomposition of Flibe by VxB We focused on whether or not tritium can be recovered by a realistic scale of apparatus. Table 1 FFHR parameters on tritium recovery. Fusion power 1GWt Tritium generation 190g-T/day rate Coolant LiF(64%)-BeF 2 (36%) Coolant flow rate in blanket Colant inlet temperature Coolant outlet temperature Tritium leak rate Major radius 2.3m 3 /s Ci/day 10 m Neutron wall loading 1.7 MW/m 2 TBR >1.2 What is the rate-determining step of tritium recovery

7 Flibe blanket 2. Design study : Flow of Flibe and tritium He cooling cylindrical support helical coils vacuum chamber divertor target Be pebbles Flibe flow rate 2.3m 3 /s self-cooling Flibe T-breeder core plasma 9 10 m R pump thermal insulation radiation shield & reflector poloidal coils 470C Tritium generation rate (1 GWt) 190 g-t/day = 1.8 MCi/day 570C x in ( = K H p in or = K S p in 0.5 ) Tritium leak rate K p A in p in 0.5 Tritium recovery system Tritium storage Tritium permeation barrier x out ( = K H p out or = K S p 0.5 out ) Tritium leak rate K p A out p out 0.5 Bypass ratio a Tritium recovery system Heat exchanger Tritium permeation barrier Tritium leak rate to the environment 10 Ci/day K p A in p in K p A out p out others

8 2. Design study : Evaluation of tritium leak If there is no barrier for tritium leak, Q leak = 2x10-3 mol-t/s = 5 MCi/day huge tritium leak (A=10 2 m 2, p T2 =10 3 Pa, K p =3.15x10-11 mol/mspa 0.5 (ferrite), t=5mm) impossible to lower the tritium leak rate, < 10-8 Pa If the heat exchanger or the tritium recovery system is surrounded by a stagnant Flibe (or Flinak) ) layer (barrier), Q leak = 6x10-10 mol-t/s = 1.6Ci/day allowable tritium leak (A=10 2 m 2, p T2 =10 3 Pa, D T =5x10-9 m 2 /s, K H =3.2x10-7 mol/m 3 Pa, t=50cm ) First wall Self-cooled Radiation shield Vacuum vessel T breeder & & 450 C 550 C Thermal shield T boundary coolant in coolant out 20 C Other reliable tritium barrier with a factor of 10 6 is OK, if available (e.g. alumina) Plasma SOL LCFS 0 Flibe Be (60 vol.%) JLF-1(30vol. %) Carbon 10 ~ 20 JLF-1 + B4C (30 vol.%) 100 cm SC magnet

9 2. Design study : Material balance of tritium in Flibe 10 1 Outlet T pressure in Flibe, p out [Pa] Q T = aw Flibe C Flibe (x T,in - x b T, out ) b x T,out = ax T,out + ( 1- a )x T,in Inlet T concentration in Flibe, x in [ppm] a=0.1 a=1 allowable 10Ci/day limit Inlet Tritium pressure in Flibe, p in [Pa] p T,in = K H x T,in p T,out = K H x T,out Q leak = K p Ap T,in + K p Ap T,out Necessary conditions Q T =1.8MCi/day Q leak <10Ci/day Design of economic apparatus Outlet T concentration in Flibe, x out [ppm] a=0.1 is possible Fig. 2 Relation between c in and c out if 50cm shield is present

10 Permeation window He out Tritium getter Permeation material Flibe in Tritium permeation Flibe out He in Tritium permeation barrier (stagnant Flibe) Fig. 3 Permeation window system

11 2. Design study : Tritium transfer process in Flibe-facing material Processes include (1) Tritium (TF or T 2 ) generation rate in Flibe (2) Tritium (TF or T 2 ) diffusion in Flibe (3) Tritium (TF or T 2 ) solution in Flibe (4) Tritium migration from Flibe surface to metal surface (impurity layer) (5) Tritium (T) permeation through metal (6) Desorption or absorption of tritium (TF or T 2 ) from Flibe (7) Tritium (TF or T 2 ) diffusion in gas (8) Tritium recombination on metal surface ( ) unique to Flibe gaseous phase Flibe (6) desorption or absorption (1) generation (2) diffusion (3) solubility (7) diffusion oxide or scale Flibe facing metal (4) interface migration (5) permeation If H 2 or H 2 O coexists in Flibe, HT or HTO is also present. (8) recombination Fig. 4 Mass transfer processes from Flibe to gas phase

12 2. Design study : Rate-determining step of permeation window clean dirty Oxide migration factor, K O /t O [mol-h2/m 2 s] Flibe film diffusion Ni permeation Metal impurity layer migration Tritium pressure in Flibe, p [Pa] j = 2k M ( c F,B - c F,1 ) = 2K O ( p t 1 - p 2 ) O = K p ( p 2 - p 3 ) t p = 2k d c 2 S,3 Fluid Flibe film Impurity migration Permeation Fig. 5 Rate-determining step of the overall tritium permeation

13 2. Design study : Design equations of permeation window Permeation material : Ni, or ferritic steel Upstream side : (purified) Flibe Downstream side : He purge Overall resistance of mass-transfer of tritium permeation 2.3m 3 /s 1 k L,0 H T2 2 = 1 k L H T2 2 + t s K p p ,in p 2 ln 0.5 p 1,out p ,in p p 1,out p 2 p Diffusion in Flibe Permeation through wall k L d = r d v L D L m L Tritium generated in blanket, Q T, is all recovered by permeation window. 0.8 m L r L D T 1 3 m L,b m L,w 0.14 c 1,in H T2 p 2 c 1,out H T2 p 2 Q T = A k L,0 c 1,in H T2 p 2 ln c 1,out H T2 p 2 Fig. 5 Permeation window tritium recovery system

14 2. Design study : Estimation of permeation window area Tritium recovery is easy at high tritium pressure (concentration) high tritium leak Tritium recovery is difficult at low tritium pressure (concentration) large apparatus Operation at around x T =0.2 ppm satisfies 10Ci/day limit and 190g/day recovery Resistances of Flibe-film diffusion is controlling and permeation gives a small effect Tritium molar fraction in Flibe [-] ferrite-steel permeation window T=843K, Q T =190g -T /day, W Flibe =2.3m 3 /s 10 6 Fluid film diffusion controlling Fluid-film diffusion + permeation Permeation controlling Permeation area [m 2 ] Fig. 6 Permeation window area (a=1, t=1mm) Tritium leak Tritium partial pressure [Pa] Large apparatus

15 Counter-current extraction tower Raschig ring packing Flibe in Perforated plate He out Tritium getter Downward Flibe flow Upward He flow Flibe out He in Tritium permeation barrier (stagnant Flibe) Fig. 8 Flibe-He counter-current extraction tower

16 2. Design study : Design equations for He extraction tower Material balance equation Ldy = Gdx k L a v g S ( y - y i )dz = k G a V c t ( x - x i )dz Gas-phase height transfer unit 2 Ê G ˆ H G Á = = 3.07 G0.32 Ê n G ˆ 3 Á Ë k G a V c t L 0.51 Ë D G Flibe-phase height transfer unit Ê L ˆ H L Á = = Ê L ˆ Ê n Á L ˆ Á Ë k L a V g S 430Ë m L Ë D L Concentration profile (Solution) y y in = È Ê exp 1- K CLˆ Á Î Í Ë G È Ê exp 1- K L ˆ Á C Î Í Ë G z H 0, L h H 0, L - K C L G - K L C G 0.5 c T2,out /c T 2,in [-] h/htu 0,L =1 h/htu 0,L =10 h/htu 0,L = LH T2 p/g [-] Fig. 9 Concentration change in extraction tower Rate-determining step is liquid phase diffusion.

17 2. Design study : Tritium concentration in He extraction tower Tritium concentration in He almost increases logarithmically. Tritium concentration in Flibe almost decreases logarithmically of DF for Flibe-tritium system is possible by 5 m extraction tower. 190 g/day tritium can be recovered by one extraction tower. Values of H L are unsure because they are not determined by Flibe experiment but by water-hydrogen system. (HTU) L >> (HTU) G Fig. 10 Tritium concentration in He extraction tower (a=0.1)

18 2. Design study : Analysis of vacuum disengager Assumptions Flibe drops free fall from the top and dissolved tritium is desorbed by a vacuum pump. d p =2mm, h=10m, a=0.1 Surface recombination resistance is ignored. Drop formation energy 1.4kW Pumping power for perforation 160kW Flibe in Gas out Tritium out Tritium concentration in Flibe [appm] Vacuum disengager a=0.1, W=2.3m 3 /s, d p =2mm Distance from the top [m] 1.6x Fig.11 Concentration profile in disengager Tritium pressure in Flibe [Pa] Flibe out x T,out = 6 1 x T,in p 2 n exp(- 4Dn2 p 2 t  ) 2 d 2 n=1 t = 2h g Q T = aw Flibe c Flibe ( x T, in - x T,out ) Vacuum pump Tritium permeation barrier

19 2. Design study : Conclusions from design study Need a tritium barrier to control tritium leak below 10Ci/day As long as the tritium leak rate is lower than the permissible level (e.g. by stagnant Flibe), arranging the tritium recovery system in a by-pass line is effective. In that case, the recovery systems of the permeation window, extraction column and vacuum disengager are a realistic- scale apparatus. Diffusion in fluid Flibe is the rate-determining step in the permeation window and He-Flibe counter-current column. In order to raise the accuracy of the design, the mass-transfer coefficient from Flibe to extraction gas should be clearly determined.

20 2. Design study : On Flinabe as a blanket material (LiF-NaF-BeF 2 ) advantages Low melting point (=240C?), low operation temperature TBR>1 may be possible with addition of Be. Other physical properties may be similar to Flibe disadvantages Activation of Na (formation of 22 Na or 24 Na) There are no data available on tritium mass-transport More data are necessary for the design of the tritium recovery system