H. Date

K. Katayama

K. Uehara

N. Ashikawa

S. Fukada

T. Honda

National Institute for Fusion Science (NIFS-Repository)

    Transient critical heat fluxes of subcooled water flow boiling in a SUS304-tube caused by a rapid decrease in mass velocity from nucleate boiling regime is necessary to investigate the reliability of a divertor in a nuclear fusion facility at a loss of flow accident for Fusion Reactor Safety (FRS). The nuclear fusion facility has two operation modes. One is the steady-state operation mode, and the other is the transient one. The plasma facing material in transient operation mode is exposed to a heat load three times larger or more than during steady-state operation for several seconds. The knowledge of high heat flux heat removal during various decelerations caused by the rapid decreases in velocity (flow transients) becomes especially very important to take the heat out of the plasma facing material for short pulse high heat flux test mode.  Figure 1 shows typical example of the time variations in the inlet and outlet pressures, Pin and Pout, the inlet and outlet liquid temperatures, Tin and Tout, heater inner surface temperature, Ts, heat flux, q, and inlet flow velocity, u, for the initial flow velocity, u0=7.09 m/s, the initial heat flux, q0=15.73 MW/m2, which is equivalent to the CHF measured by exponentially increasing heat input (Q0 exp(t/W), W=around 8 s) at the flow velocity of 4 m/s and deceleration caused by a rapid decrease in velocity, D=-1.771 m/s2, at initial outlet pressure, Pout0=801.37 kPa, initial inlet subcooling, 'Tsub,in0=145.83 K. The values of Pin, Pout, Tin, Tout, Ts, q and u keep almost constant until the beginning of a decrease in flow velocity. The pump input frequency was linearly reduced to 0 Hz at a deceleration time setting, td, of 20 seconds by the inverter function. As soon as the inlet flow velocity decreases, the Pin and Pout oscillate violently and the Tout has started to increase. At the elapsed time of 6.35 seconds, that is, the flow transient CHF, qcr,sub, the heater inner surface temperature, Ts, rapidly increases, although the heat flux keeps constant to near the flow transient CHF point. The current for the heat input to the test tube was automatically cut off when the measured average temperature increased up to the preset temperature,                which was several tens of Kelvin higher than corresponding flow transient CHF surface temperature. This procedure avoided actual burnout of the test tube. The heat flux, the outlet pressure, Pout, the flow velocity, ucr, and the deceleration caused by a rapid decrease in velocity, D, at the flow transient CHF were measured 17.726 MW/m2, 703.29 kPa, 4.56 m/s and -1.771 m/s2 in this run (1).  The flow transient CHFs, qcr,sub, at the initial heat flux, q0=(qcr,sub,st)u=4m/s, which is equivalent to the CHF measured by exponentially increasing heat input (Q0 exp(t/W), W=around 8 s) at the flow velocity of 4 m/s, for the decelerations caused by a rapid decrease in velocity, D, ranging from -5.444 to -0.326 m/s2 are shown as green and orange open circle symbols with the initial flow velocities, u0, of 6.9 and 9.9 m/s, respectively, in Fig. 2. Most of the flow transient CHF data are within -18.8 to 15.0 % differences of the values calculated from the steady-state CHF correlation against inlet subcooling for the circular test tube, Eq. (1) (1). 34.0Re2)/(1.03.01.01 **CdCdLcr ScedLWeDCBo¹¸·©¨§  ('Tsub,int40 K) (1) The ratios of flow velocity at flow transient CHF point to flow velocity calculated from Eq. (1) with initial heat flux, q0, by a try-and-error method, ucr/ucr,st, and those of flow transient CHF, qcr,sub=q0, to steady-state critical heat flux calculated from Eq. (1) with the flow velocity at flow transient CHF point, (qcr,sub/qcr,sub,st), for the SUS304 circular test tube of d=6 mm and L=59.5 to 59.7 mm with inlet liquid temperatures, Tin, of 290.12 to 308.51 K at the initial flow velocities, u0, of 6.9 and 9.9 m/s are shown versus the deceleration caused by a rapid decrease in velocity, D, at initial heat flux, q0, which is equivalent to the CHF at the flow velocity of 4 m/s, (qcr,sub,st)u=4m/s, in Fig. 3. The experimental data of ucr/ucr,st and qcr,sub/qcr,sub,st for the SUS304 test tube of d=6 mm with the rough finished inner surface can be expressed for the D ranging from -5.444 to -0.326 m/s2 by the following correlations (1):  794.0275.0, Dstcrcruu     (2) 038.105.0,,,  Dstsubcrsubcrqq  (D-0.75 m/s2)    (3)  1) Hata, K., et al.,  Proceedings of ICONE22  (2014) 1-12.           300400500T in, Tout, Ts (K)Tin5 102468100.111010010000FT8359SUS304d=6 mmL=59.5 mm  Pout=703.29 kPa  'Tsub,in=144.06 K  u=4.56 m/s  D=-1.771 m/s2u (m/s), P in/100, Pout/100 (kPa)time (s)PinPoutCHF pointqTsq (MW/m2 )uTout50 100 1500.511.520(q cr,sub,st)exp/(q cr,sub,st) cal'Tsub,in   (K)Horizontal Orientation  SUS304  RF  d=6 mm  L=59.4 mm  L/d=9.9  Pin=786.26-960.93 kPa +15%-15%(qcr,sub,st)exp : experimental value(qcr,sub,st)cal : calculated value            u 4.0 m/s 6.9 m/s 9.9 m/s 13.3 m/s            u 4.0 m/s 6.9 m/s 9.9 m/s 13.3 m/sVertictal Orientation  d=6 mm  L=66 mm  L/d=11Current Study Vertical      Orientation  d=6 mm  L=59.5-       59.7 mm  L/d=9.92-9.95  Pin=743.7-       994.1 kPa  q0=  (qcr,sub,st)u=4m/s           u0 6.9 m/s 9.9 m/s-7 -6 -5 -4 -3 -2 -1 000.511.522.533.5u cr/u cr,st, qcr,sub/qcr,sub,stD (m/s2)Flow Transient Data  SUS304 Tube    d=6 mm    L=59.5-59.7 mm    L/d=9.92-9.95    Pin=717.6-1448.7 kPa    'Tsub,in=150 KEq.(2) Eq.(3)  u0 (m/s)6.9    9.9  ucr/ucr,st qcr,sub/qcr,sub,st+10 %-10 %u0+25 %-25 %Fig. 1 Time variations in Pin, Pout, Tin, Tout, Ts, q and u for u0=7.09 m/s, q0=15.73 MW/m2 and D=-1.771 m/s2 at Pout0=801.37 kPa and 'Tsub,in0=145.83 K Fig. 2 Ratios of CHF data for the inner diameter of 6 mm to the values derived from the inlet CHF correlation, Eq. (1), versus 'Tsub,in at inlet pressures of 743.7 to 994.1 kPa Fig. 3 Relationship between ucr/ucr,sub,st and D and that between qcr/qcr,sub,st and D with u0=6.9 and 9.9 m/s at q0=(qcr,sub,st)u=4m/s W/m2 for Pout=800 kPa and Tin=290.12 to 308.51 K  Mass Flow ControllerMass Flow ControllerArH2 or D2Thermo couple 1Thermo couple 2FanFan HeaterRubber stopperCoolantQuartz tubeSamplePressure gaugeTurbomolecularpumpRotarypumpStainless steel tube & flangeMolecularSieveFig.1 The schematic diagram of the experimental apparatus.NiNi with W depo.Fig.2 The pressure rise by hydrogen permeation. 1.0 1.5 2.010-1610-1510-1410-1310-1210-1110-101000 800 600 400 200Frauenfelder3This work 100%H2 100%D2Zakharov4Temperature[ºC]㻌Permiability[mol·m/m2 ·s·Pa1/2]1000/T[K-1]㻌Fig.3 Hydrogen and deuterium permeability. It is necessary to understand isotope exchange reaction for the evaluations of tritium inventory and permeation because the flux of hydrogen isotopes from plasma is changed by fuel control. Deposition layers, which will grow on the surface of plasma facing components may affect hydrogen isotope behavior because the structure of deposition layers will be different from that of original materials. Some reports have shown that metal deposition layers formed under hydrogen isotope plasma can trap a certain amount of hydrogen isotopes in the deposition process1,2). However, basic behaviors such as dissolution, diffusion and surface recombination of hydrogen isotopes on tungsten (W) deposition layers have not been understood quantitatively so far. In this work, W deposition layers, which were formed on nickel substrate by hydrogen plasma sputtering, were exposed to hydrogen or deuterium gas and the permeation behavior was observed. By hydrogen plasma sputtering at 100 W RF power, 10 Pa H2 pressure and 307 hours deposition time, tungsten deposition layer was formed on circular substrates of nickel, 20 Pm in thickness and on square substrates of quartz, 1 mm in thickness. From SEM observation of the cross-section of the W deposition layer formed on the quartz substrate, thickness of the deposition layers were measured to be 970 nm. From the deposition weight and the volume, the porosity was estimated to be 0.37. By EDX analysis, the layer contained oxygen at 20~30 at%. The permeation experimental device was shown in Fig.1. The sample substrate separates a hydrogen supply side (primary side) and a hydrogen permeation side (secondary side). The secondary side connecting to a pressure gauge was closed in a vacuum before pure hydrogen gas or pure deuterium gas was supplied to the primary side. The permeation flux was obtained from the pressure rise in the secondary side. Fig.2 shows the pressure rise by hydrogen permeation at 244 oC through the nickel substrate with and without W deposition layer. This result implies that the rate-controlling step of hydrogen permeation through the nickel substrate with the W deposition layer is hydrogen transfer in the W deposition layer. Therefore the permeability of hydrogen and deuterium through the W deposition layer was obtained ignoring the permeation in the nickel substrate. As shown in Fig.3, hydrogen permeability and deuterium permeability in the W deposition layer corresponded and were higher than that in bulk tungsten3,4). From the analysis of the permeation curve by Time-Lag method, it was found that the diffusivity of hydrogen isotopes in W deposition layer is considerably smaller than that in bulk tungsten. 1) Katayama, K., et al., J. Nucl. Mater., 438 (2013) 1010. 2) Temmerman, G.De, et al., J. Nucl. Mater., 389 (2009) 479. 3) Frauenfelder, R.J., Chem. Phys., 48 (1968) 3955. 4) Zakharov, A.P., et al., Sov. Mater. Sci., 9 (1973) 149. 351§32. Study on Hydrogen Isotope Exchange in Deposition Layer of Plasma Facing MaterialKatayama, K., Date, H., Honda, T., Uehara, K., Fukada, S. (Kyushu Univ.),  Ashikawa, N.

Study on Hydrogen Isotope Exchange in Deposition Layer of Plasma Facing Material

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Study on Hydrogen Isotope Exchange in Deposition Layer of Plasma Facing Material

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