Tritium Permeation Issue, Plan and Progress Dai-Kai Sze University of California, San Diego Presented at the ITER TBM Project Meeting UCLA, Feb , 2004

Statement of Problem  Fusion blankets have high tritium partial pressure.  The temperature of the blanket is high.  The surface area of the heat exchanger is large, with thin wall.  Those are the perfect conditions for tritium permeation.  The allowable tritium loss rate is very low.

Typical tritium partial pressure For LiPb Pa a For flibe 380 Pa a For Li 2.6X10 -8 Pa b For solid breeder 0.6 Pa c The tritium partial pressure increase per coolant path. Assuming tritium concentration of 1 ppm. With a purge gas flow rate of 10 4 liter/s.

Tritium Permeation Typical parameters of heat exchangers are: Temperature 500C Surface area 2.5X10 4 m 2 Wall thickness 1 mm Tritium permeability in FS = 0.46 mol T 2 -mm/d-m 2 -atm 0.5 If the tritium partial pressure is 1 Pa, the tritium permeation rate will be 218 g

Methods to reduce Tritium Permeation  Develop efficient tritium recovery system from the breeding material.  Develop high performance tritium diffusion barrier.  Convert tritium from elementary form to oxide form.  Secondary tritium clean up from the intermediate coolant.  Tritium clean up from the power conversion medium.

Canada Experience  CANDU loss about 10 Kg/hr coolant water, and 2- 5 Kg/hr of moderator water  About 95% of the water is recovered.  About 50% of the tritium emission is from the water loss.  Only about 5-10% of the emission is caused by tritium permeation.

Tritium loss from fusion  Permeation is a much important path for tritium loss for fusion than for CANDU, because tritium is in elementary form.  Tritium loss caused by coolant loss, either water or He, has to be included.  CANDU losses about 200 Ci/d, and it has a much smaller tritium throughput than fusion.  Is it reasonable to expect fusion can achieve a loss rate close to 1 Ci/D?

Where are we?  Tritium recovery processes from breeder materials are in good shape.  Tritium diffusion barrier development did not obtain the required performance.  Tritium oxidation kinetics has been studied, but results vary.  Some efforts, mainly for safety concerns, have been spent to develop an intermediate heat exchanger.

Where are we? (Cont.)  The leakage of the coolant, especially water and He, needs to be carefully assessed.  The economy of the tritium clean up system depends strongly on the coolant leakage rate.  Loss coolant recovery rate, was 95% of the CANDU system, will have major impact on the tritium loss rate.  SR tritium loss rate is about 4 g/y (100Ci/d), while the CANDU reactor loss about 200 Ci/d, is it reasonable to limit the tritium loss rate to a fusion power plant to between 1 to 30 Ci/D?  It will be useful for us to get back the last VG for further discussion.