Tritium Fuel Cycle System Modeling with ASPEN -ISS and FCU Haibo Liu Fusion Science and Technology Center, UCLA Scott Willms Los Alamos National Lab FNST/PFC/MASCO Meeting at UCLA August 2-6, 2010

Objective Residence time based linear differential equation model to calculate the tritium inventory and required TBR in fusion reactor had been studied by Prof. Abdou and other researchers. To get a new model for FNSF or the future reactor required TBR evaluation with commercial chemical engineering software. In this presentation, the TSTA scale Isotope Separation System (ISS) modeling will be introduced and some of the dynamic characteristics are shown. The Fuel Cleanup Unit (FCU) is also modeled.

Non Built-in Hydrogen Molecules Definition Modeling of HD, HT, DT, T2 in Aspen+: Four of the hydrogen molecules are missing from A+, which have to be defined by user. The Molecular Weight, Boiling Point, Critical Temperature, Critical Pressure, Critical Volume, Triple Point Temperature, Liquid Molar Volume, Heat of Fusion, and vapor pressure formula are Given (from Hydrogen Properties for Fusion Energy by P. Clark Souers). But the ASPEN doesn’t know that there are two atoms in these molecules, and so the chemical reaction rates calculation has to be done with the known kinetics.

ISS Flowsheet for Steady-State heater heater heater heater reactor reactor The Isotope Separation System (ISS) has been modeled in A+ for steady state simulation. The design parameters are referred from TSTA. This system has four distillation columns and two reactors. The four product (HD, D2, DT, T2) purities are optimized in steady-state running mode.

Steady-State Input Feed Stream: 50% DT + 25%T2 + 24%D2 + 1% H2 Extra Feed Stream: 80% D2 + 10% H2 + 5% HD + 5% HT Feed Temperature: 20K Feed Pressure: 1 atm Feed Flow Rate: 2mol/min Chemical reactor operation Temperature: 25oC Products: H2&HD, D2, DT, T2 Blocks: 4 Columns, 2 Reactors, 4 Heaters, 2 Mixers Column 1: reflux ratio (25), distillate rate (0.5mol/min), number of stages (80), feed stage (50), column packed height (4.11m), column I.D. (29mm), drum&sump (H:34cm, D: 6cm, 15% liquid volume fraction), pressure (condenser: 0.9atm, stage pressure drop: 0.002atm) Column 2: reflux ratio (150), distillate rate (0.3mol/min), number of stages (80), feed stage (55), column packed height (4.06m), column I.D. (19mm), drum&sump (H:34cm, D:4cm, 15% liquid volume fraction), pressure (condenser: 0.7atm, stage pressure drop: 0.003atm) Column 3: reflux ratio (8), distillate rate (1mol/min), number of stages (65), feed stage (30), column packed height (3.20m), column I.D. (23.2mm), drum&sump (H:34cm, D:4cm, 15% liquid volume fraction), pressure (condenser: 1.04atm, stage pressure drop: 0.0007atm) Column 4: reflux ratio (8), distillate rate (1.75mol/min), number of stages (80), feed stage (40), column packed height (4.11m), column I.D. (38mm), drum&sump (H:34cm, D:8cm, 15% liquid volume fraction), pressure (condenser: 0.8atm, stage pressure drop: 0.003atm)

Product Stream Results Stream HD Stream D2

Product Stream Results (continue) Stream DT Stream T2

Comparison for Column I Steady- State Composition Profile SS Component Profile in C1 The stage is counted from the top in APD. the stage is counted from bottom Dimosthenis, Sarigiannis, Ph.D Thesis, UCB 1994.

ISS Flowsheet for Dynamics The dynamic simulation has to be performed for getting the tritium inventory. Lots of controls have to be given to the system before dynamic running, including pressure control, temperature control, product purity control, etc.

Dynamic Response after Feed Flow Rate Ramp Increase Feed & Product Flow Rates Component Purities In Steady-state, Total tritium inventory in ISS: ~ 260gT Tritium processing time in ISS: ~ 80 min Between 1.36~1.45 hour, the T2 purity is decreased from 99% to 95% under the ramp increase of the D-T feed flow rate. The feed flow rate is about 0.17kmol/h at that time interval. This column design could not keep the T2 purity under the feed flow rate higher than 0.16kmol/h and the columns have to be re-optimized to stand this increase. Tritium Inventory

Column Startup Simulation Startup operating sequence: 1) Purge with inert gas (this is done by the Empty script); 2) Charge the specified amount of feed into the column sump and then stop feed; 3) Increase reboiler temperature and buildup the drum holdup till specified level and then start the column reflux; 4) Continue increase reboiler temperature 5) Add some more feed until sump level reaches specified value and stop the feed; 6) Increase the reflux rate to the final value; 7) Start the column feed to final steady-state. The control has to be given to the system to realize the startup operating sequence. This startup sequence can be changed according to the existed experiment, like TSTA or the ITER/FNSF design later.

Startup Tritium Inventory Buildup and He&Products flow rate Tritium Inventory Buildup during Startup/ kmol Purge Gas and products Flow Rate/ kg/hr

Temperature and Pressure Profile in Column Column Temperature Profile Column Pressure Profile

FCU Dynamics Flowsheet Purification Recovery An Aspen Custom Modeler (ACM) user defined permeator has been modeled with instantaneous assumption. Because lack of the reaction kinetics factors, the dynamics for this sub-system has not been finished. But this sub-system will have relative small tritium inventory, so the dynamics simulation will be simplified.

Summary The ISS is simulated for steady-state and dynamics operation modes. Four absent hydrogen molecules are modeled in A+. The dynamic response of the system from feed change is studied. The rough tritium inventory and processing time are obtained for ISS after this simulation. Also the one column startup simulation is performed. The time and the amount of the tritium inventory buildup in the system during the startup should be considered for how it will affect the required TBR model. After the tritium inventories and total processing time are obtained, the reactor required TBR model will be updated with these chemical engineering based calculation results.

Future work 1) Startup and pulsed operation simulation will be performed for the four column ISS and the whole fuel cycle system. 2) The storage + fueling + plasma chamber + cryopump + FCU + ISS loop will be first evaluated for this loop’s total tritium processing time. With the sub-system’s tritium inventory results together, the required TBR model would be updated. 3) The tritium decay effect has to be included in the later model. 4) The user-defined hydrogen molecules should be reviewed. 5) The property method used here is “Ideal”. Which existed method should be used in the calculation and what’s the effect on the results should be evaluated.

Thank you for your attention!