Tritium Permeation in HCLL/DCLL

1. Tritium Permeation in HCLL/DCLL Brad Merrill1, Phil Sharpe1, Dai-Kai Sze2 1INL Fusion Safety Program 2UCSD FNST Meeting UCLA, August 12th-14th, 2008

2. Presentation Overview • This presentation examines Dual Cooled Lead Lithium (DCLL) and Helium Cooled Lead Lithium (HCLL) blanket tritium inventory and permeation rates as impacted by tritium: • Solubility in PbLi • First wall (FW) implantation • Reduced turbulent mass transport in PbLi • The results are based on a TMAP model developed for the ARIES-CS DCLL design, with the model modified to give an intermediate helium cooling system to Rankine cycle in place of ARIES-CS Brayton cycle • This TMAP model was also modified to simulate a HCLL blanket in ARIES-CS based on Melodie experimental results • Conclude with a summary

3. ARIES-CS Design Parameters ARIES-CS Power Parameters Layout of ARIES-CS Power Core

4. Qvacuum T2 Vacuum Niobium Membrane T2 QPb-17Li CT,I QPb-17Li CT,O ARIES-CS Tritium Extraction Vacuum Permeator Concept • All PbLi component models (blanket gaps, pipes, permeator, and HTX) account for turbulent enhanced transport of tritium in the PbLi • Correlationa proposed by Scott Willms used to model turbulent mass transport enhancement: • Tritium solubility and diffusivity correlations developed by Reiterb and Teriac Membrane diffusion Pb-17Li mass transport CT,S2 CT,Bulk QPb-17Li Or CT,S3 based on molecular recombination CT,S1 aHarriot and Hamilton, Chem Engr Sci, 20 (1965) 1073 bReiter, FED 14 (1991) 207-211 cTeria, J. Nucl. Mater. 187 (1992) 247-253

5. Schematic of ARIES-CS DCLL TMAP Model Non-Hartmann Gaps Manifolds PbLi core Shield He/PbLi Nb HX Permeator First wall He/H2O Al HX Second wall Rib walls Intermediate Helium Cycle Back plate Concentric pipes PbLi Hartmann Gaps He/He FS HX Helium pipes Tritium cleanup system

6. Tritium Inventory and Permeation Results For DCLL • Based on TMAP results, increasing the solubility of tritium in PbLi by 100 increases the PbLi tritium inventory by ~12, but surprisingly reduces the reactor structural inventory and permeation rate • This is due to the fact that the concentration jump at all PbLi/metal interfaces drops by 100 while the PbLi concentration increase of ~12 produces a balance between tritium production and extraction • Tritium release is at or near allowable 198% of this inventory is in the Nb alloy HTX and because reactor has 6 sectors only 1/6th is at risk during most accident 299% ventilation flow cleanup is assumed 3Limit is < 1 g/a 4Based on CANDU water concentration of ~1 Ci/kg (34,000 Ci/a allowed into Rankine cycle) 5Based on US PWR water concentration of ~ 1 mCi/kg (340 Ci/a allowed into Rankine cycle)

7. Structured packing 80 cm 20 cm Sulzer Column (not a 750 Y series) Melodie* Results used to Investigate Extraction Column Tritium Removal for an ARIES-CS HCLL Blanket • The extractor column used in Melodie experiments was a Sulzer Mellapak 750 Y series • The extraction column was 60 mm in diameter, 800 mm in height, and had an area packing of 750 m2/m3 *N. Alpy, et al., FED, 49-50 (2000) 775-780.

8. Schematic of ARIES-CS HCLL TMAP Model PbLi/He HX Poloidal Gaps Manifolds PbLi core Shield 823 K 673 K First wall Packed Columns Second wall He/H2O Al HX Purge gas PbLi Pipes Rib walls Back plate Intermediate Helium Cycle He/He FS HX Radial Gaps Helium pipes Tritium cleanup system

9. Melodie Experimental Loop Results for Sulzer Extraction Column and Application to ARIES-CS Melodie Results • Melodie measured extractor efficiencies were ~25% based on concentration, i.e. • For this TMAP model, the reactor PbLi processing flow rate is assumed to be 300 kg/s, giving a change out rate of eight times per day • All external volumes (PbLi - manifolds, pipes, HTX) were scaled to the 300 kg/s (from the DCLL 26,000 kg/s) and all turbulent mass transport terms set to diffusion only • Extractor PbLi flow rate per column was set at 50 l/h • ARIES-CS will require ~2430 parallel extractor column paths, and at an efficiency of ~25% will also need five stages per path (i.e., 12150 Melodie type extractors) – an occupational radiation exposure problem based in DCLL TBM analyses • The counter flow gas rate per column set at 100 Ncm3/min • A film thickness of 0.2 mm was used to give an efficiency of ~25% per stage in this TMAP Schematic of TMAP Extractor Model PbLi flow Packing Plate CT = Ks (PT2)1/2 CT2 = PT2/kT Gas flow

10. Tritium Inventory and Permeation Results For HCLL • An increase in solubility by 100 increases the PbLi inventory by ~16 and increases HTX permeation, with the helium cleanup system now removing a large fraction of the tritium • A tritium inventory of 0.9 kg for high Ks case could represent a radioactive release hazard for ex-vessel PbLi spills • Tritium airborne releases are above allowable • When implantation is considered, most of the implanted tritium remains in the helium cycles 195% in of this inventory is in austenitic steel of extraction columns, and because there are 12,150 columns very little tritium is at risk in most accidents 299% ventilation flow cleanup is assumed 399% of this permeation is from extraction columns 4Limit is < 1 g/a 5Based on CANDU water concentration of ~1 Ci/kg (34,000 Ci/a allowed into Rankine cycle) 6Based on US PWR water concentration of ~ 1 mCi/kg (340 Ci/a allowed into Rankine cycle)

11. Summary • Based on the present models, an increase in tritium solubility above that measured by Reiter would increase the tritium inventory in the PbLi, decrease extraction efficiencies, but could reduce the structural tritium inventory and permeation rates in DEMO reactors • Most of the tritium in a DCLL concept will be in the PbLi/helium HTX tube walls, and because Nb is a getter accidents that result in HTX cooling will not release significant quantities of tritium • For the HCLL concept, the majority of the tritium inventory and permeation is associated with the extractor columns, which could be reduced by a better design or selection of column materials. In addition, the HCLL has a much higher PbLi tritium inventory, making ex-vessel PbLi spills a tritium release concern • Tritium permeation into a simulated Rankine power cycle was compared against equilibrium tritium concentrations in CANDU and US PWRs, it appears to be difficult to maintain an equilibrium concentration of 1 mCi/kg (PWR concentrations) by permeation barriers and/or material heat exchanger choice • Regardless of the blanket concept employed, FW tritium implantation represents a significant problem for a Rankine cycle; a FW coating is need on the plasma side • However, these result are based on the assumption that a sufficient understanding of tritium behavior in the PbLi, at PbLi/metal or PbLi/gaseous interfaces is presently known. Based on present experimental information this is clearly not the case • What can be inferred from these results is that fusion reactors tritium inventories and permeation rates are highly dependent on this information, and thereby the ability to predict accidental and routine release of tritium from fusion reactors

12. Postscript On Melodie Results • Conservation of mass between phases: Schematic of TMAP Extractor Model PbLi flow Packing Plate CH = Ks (PH2)1/2 • Conservation of mass in liquid and diffusion: CH2 = PH2/kT Gas flow • If the simple TMAP extractor model is correct, then data from Melodie can be used directly to determine if Reiter’s solubility coefficient is reasonable for Melodie conditions, at least based on simple conservation equations • Substituting the above and solving for film thickness:

13. Postscript On Melodie Results (cont.) • Given the other parameters of Schematic of TMAP Extractor Model PbLi flow Packing Plate CH = Ks (PH2)1/2 CH2 = PH2/kT and using Melodie saturation pressures and efficiencies gives: Gas flow • Given the volume of the Melodie column (V=2.26x10-3 m3), a packing fraction of 80%, and a packing area density of 750 m2/m3, the packing (film) surface area is ~ 1.4 m2 where, Ks-max is the largest solubility that still results in a film for the TMAP extractor model, which is found by setting the term in brackets in the film thickness equation to zero => Reiter Ks fits Melodie results

14. Poloidal Gaps Manifolds PbLi core Shield Tritium cleanup system PbLi/He HX 823 K First wall 673 K Pressure boundary Brayton Cycle Packed Columns Second wall PbLi Pipes Rib walls Purge gas Back plate Inter-cooler Radial Gaps Helium pipes Schematic of ARIES-CS HCLL TMAP Model

15. Non-Hartmann Gaps Manifolds PbLi core Shield Tritium cleanup system PbLi/He Nb HX Permeator First wall Pressure boundary Second wall Brayton Cycle Rib walls Back plate Concentric pipes PbLi Inter-cooler Hartmann Gaps Helium pipes Schematic of ARIES-CS DCLL TMAP Model