FNST Meeting UCLA, August 12 th -14 th, 2008 Brad Merrill 1, Phil Sharpe 1, Dai-Kai Sze 2 1 INL Fusion Safety Program 2 UCSD Tritium Permeation in HCLL/DCLL

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

ARIES-CS Design Parameters Fusion Thermal Power in Blanket2480 MW Typical Module Dimensions~4 m 2 x 0.62 m Tritium Breeding Rate~400 g/d PbLi Inlet/Outlet Temperatures464/737°C PbLi Inlet Pressure1 MPa Typical Inner Channel Dimensions0.26 m x 0.24 m Average PbLi Velocity in Inner Channel~0.04 m/s Fusion Thermal Power removed by PbLi1323 MW PbLi Total Mass Flow Rate25,910 kg/s Maximum PbLi/FS Temperature472°C He Inlet/Outlet Temperatures385/460°C He Inlet Pressure10 MPa Typical FW Channel Dimensions (poloidal x radial)2 cm x 3 cm He Velocity in First Wall Channel46 m/s He Inlet/Outlet Temperatures385/460°C Total Mass Flow Rate of Blanket He3559 kg/s Maximum Local ODS/RAFS Temperature at FW654/550°C Layout of ARIES-CS Power Core ARIES-CS Power Parameters

ARIES-CS Tritium Extraction All PbLi component models (blanket gaps, pipes, permeator, and HTX) account for turbulent enhanced transport of tritium in the PbLi Correlation a proposed by Scott Willms used to model turbulent mass transport enhancement: Tritium solubility and diffusivity correlations developed by Reiter b and Teria c Vacuum Q Pb-17Li C T,I Niobium Membrane T2T2 T2T2 Q vacuum Q Pb-17Li C T,O Vacuum Permeator Concept C T,Bulk Q Pb-17Li C T,S1 Or C T,S3 based on molecular recombination C T,S2 Membrane diffusion Pb-17Li mass transport a Harriot and Hamilton, Chem Engr Sci, 20 (1965) 1073 b Reiter, FED 14 (1991) c Teria, J. Nucl. Mater. 187 (1992)

Schematic of ARIES-CS DCLL TMAP Model Concentric pipes PbLi Permeator PbLi core He/He FS HX Non-Hartmann Gaps Hartmann Gaps First wall Second wall Rib walls Back plate Tritium cleanup system Helium pipes Shield Manifolds Intermediate Helium Cycle He/PbLi Nb HX He/H 2 O Al HX

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 K s-Reiter 100 x K s-Reiter FW Implantation K m /5 Tritium source~400 g/d ~940 g/d~400 g/d Inventory Structure g86 g2500 g1850 g PbLi1.0 g11.5 g2.6 g3.0 g Release g/a0.03 g/a3.4 g/a g/a 3 Permeator overall efficiency70%7.7%73%26.5% Tritium pressure PbLi0.17 Pa1.3x10 -3 Pa0.86 Pa1.1 Pa Helium1.4x10 -2 Pa9.0x10 -4 Pa0.9 Pa0.5 Pa Tritium global balance Permeator99.8%99.9%98.2%96.7% Helium cleanup system0.15%2.0x10 -2 %1.7%2.4% Leaked1.0x10 -2 %2.0x10 -3 %0.1%0.2% Permeates to VV4.0x10 2 %8.0x10 -3 %0%0.7% Permeation into Rankine cycle Intermediate helium cycle360 Ci/a 5 93 Ci/a2160 Ci/a Ci/a 5 Direct (required reduction) 4/5 47 /4.7x /2 1.7x10 3 /1.7x x10 3 /1.1x % of this inventory is in the Nb alloy HTX and because reactor has 6 sectors only 1/6 th is at risk during most accident 2 99% ventilation flow cleanup is assumed 3 Limit is < 1 g/a 4 Based on CANDU water concentration of ~1 Ci/kg (34,000 Ci/a allowed into Rankine cycle) 5 Based on US PWR water concentration of ~ 1 mCi/kg (340 Ci/a allowed into Rankine cycle)

Melodie * Results used to Investigate Extraction Column Tritium Removal for an ARIES-CS HCLL Blanket * N. Alpy, et al., FED, (2000) Sulzer Column (not a 750 Y series) 20 cm Structured packing 80 cm 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 m 2 /m 3

Melodie Experimental Loop Results for Sulzer Extraction Column and Application to ARIES-CS 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., Melodie type extractors) – an occupational radiation exposure problem based in DCLL TBM analyses The counter flow gas rate per column set at 100 Ncm 3 /min A film thickness of 0.2 mm was used to give an efficiency of ~25% per stage in this TMAP PbLi flow Packing Plate Gas flow C T2 = P T2 /kT C T = K s (P T2 ) 1/2 Melodie Results Schematic of TMAP Extractor Model

Tritium Inventory and Permeation Results For HCLL 1 95% 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 2 99% ventilation flow cleanup is assumed 3 99% of this permeation is from extraction columns 4 Limit is < 1 g/a 5 Based on CANDU water concentration of ~1 Ci/kg (34,000 Ci/a allowed into Rankine cycle) 6 Based on US PWR water concentration of ~ 1 mCi/kg (340 Ci/a allowed into Rankine cycle) 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 K s 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 K s-Reiter 100 x K s-Reiter FW Implantation Tritium source~400 g/d ~910 g/d 1 Inventory Structure g274 g455 g PbLi60 g864 g60 g Release g/a 3,4 95 g/a 3,4 145 g/a 3,4 Extractor overall efficiency80%3.6%80% Tritium pressure PbLi2900 Pa60 Pa2925 Pa Helium2 Pa14 Pa130 Pa Tritium global balance Extraction columns81.5%55.5%33% Helium cleanup system7.3%30.0%60% Leaked9.2%6.5%7.0% Permeates to VV2.3%8.0%0% Permeation into Rankine cycle Intermediate helium cycle2890 Ci/a Ci/a 6 12,060 Ci/a 6 Direct (required reduction) 5/6 3.1x10 3 /3.1x x10 4 /1.3x x10 4 /5.3x10 6

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

Postscript On Melodie Results 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 PbLi flow Packing Plate Gas flow C H2 = P H2 /kT C H = K s (P H2 ) 1/2 Schematic of TMAP Extractor Model Conservation of mass between phases: Conservation of mass in liquid and diffusion: Substituting the above and solving for film thickness:

Postscript On Melodie Results (cont.) Given the volume of the Melodie column (V=2.26x10 -3 m 3 ), a packing fraction of 80%, and a packing area density of 750 m 2 /m 3, the packing (film) surface area is ~ 1.4 m 2 PbLi flow Packing Plate Gas flow C H2 = P H2 /kT C H = K s (P H2 ) 1/2 Schematic of TMAP Extractor Model Given the other parameters of where, K s-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 K s fits Melodie results and using Melodie saturation pressures and efficiencies gives: P H2 sat (Pa)  (mm) K s-max /K s-Reiter K s-  =0.15 mm /K s-Reiter

Schematic of ARIES-CS HCLL TMAP Model

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