1. Implications of tritium burn fraction on fuel cycle Dai-Kai Sze, UCSD FNST Meeting August 18-20, 2009 UCLA, LA, Ca

2. ITER Burn fraction ITER is reported to have a tritium burn fraction of 0.3%. It was not clear if this is the tritium brun fraction, or fuel cycle capacity for ITER. It also was not clear how this value was obtained. ITER fueling is based on tritium pellet, and deuterium gas puffing.

3. Questions How is the 0.3% value was obtained? Does DEMO has similar burn fraction? Is 0.3% burn fraction acceptable to both ITER and DEMO? What burn fraction will we need? How can a higher burn fraction can be achieved? How can this be demonstrated?

4. Typical reactor parameters Fusion power 3000 MW Tritium burn rate (456 g/FPD) or 1.06X10(21) #/s Tritium fueling rate (with 0.3%) 3.53X10(23) #/s Plasma volume 400 M3 Ion Density 1.2X10(20) #/m3 Number of tritium in plasma 2.4X10(22) Plasma temperature 17 KeV

5. Energy Balance Large amount of T (and D) have to be fed into plasma. The fueling materials are in room temperature. Those materials have to be heated up to the plasma temperature, or the plasma will cold down. To heat 7.06X10(23) #/s (D+T) to 17 Kev will require 2000 MW power. We maybe able to afford 200 MW heating power (still very painful), which will require to increase the burn fraction to 3%.

6. Fueling cycle residence time The residence time for TSTA is 24 hours. The design residence times for both ITER and Demo are one hour. This residence time has to cover the croy pump, the ISS, and the fuel factory. It is difficult to reduce the tritium residence time to much lower than 1 hour.

7. Allowable tritium inventory The allowable releasable tritium inventory from each unit is 80g from safety considerations. Since the fuel cycle has many independent units, it is assumed that the total tritium inventory is 1 Kg. This is the total tritium inventory in the cryo pump, the ISS and the fuel factory.

8. Tritium mass balance Allowable tritium inventory is 1 Kg. With 0.3% burn fraction, the tritium throughput is 152 Kg/d. If the tritium residence time is 1 hour, the tritium inventory in the fueling system is 6.3 Kg. To reduce the tritium inventory to1 Kg, the residence time needs to be reduced to 10 minutes.

9. Burn fraction required To limit tritium inventory to 1 Kg, and keep the tritium residence time to 1 hour (which is not easy), the tritium burn fraction needs to be increased to >3%

10. Pellet fueling considerations The total number of tritium in plasma is 2.4X10(22). The fueling rate is 3.53X10(23) #/s. If we limit each pellet will contain no more than 10% of the T in the plasma, the fueling rate for each pellet needs to be less than 2.4X10(21). We will need to inject 150 pellets/s. This high pellet fueling rate will cause many design and operation issues.

11. What burn fraction will we need? There are many reasons that 0.3% burn fraction is not acceptable. This is my suggestion 0.3% not acceptable 3% marginal 10% desirable >10% perferable

12. Help Please let me know that I am wrong!!! What plasma do we need to attain high burn fraction? Is high recircling divertor a possible solution to get high burn fraction?