{ Tritium Breeding Blanket Part I: Background, Choice of design, Choice of breeder, Tritium permeation and separation Matt Torrico NRE 4610: Intro to Fusion Dec. 7 th, 2015 Introduction The DD fuel cycle requires ion temperatures ~10x greater than DT to reach ignition. Worldwide T reserves < 22 kg [1]. A 1GWe 30% conversion assuming steady- -state would consume this in a matter of 2-3 months [2]. SignificanceValue DEMO T Consumption Rate43 75% online time Desired TBR>1, ideally 1.15 1.20 Min. T Inventory for 1000MW6.2 kg for 30 days One Shell or Two? Full BlanketOutboard Only Surface Area m^ m^2 Volume184.6 m^ m^3 Ideally we wish to maximize the S/F ratio for breeding economy. However, the presence of the shielded TF coils and CS preclude service routes to the inboard side. Our calculations assumed outboard only. Cube-Square Law Solid, or Liquid.? Solid Breeder! PROSCONS No flowing metalsT Recovery Harder Still! Fewer problems w/ corrosionMicrostructure defects due to temp and rads Less complex plumbingMore complex cell design! PROSCONS Dual breeder/coolant!Liquid state must be maintd Simplified cell designLiq. metal embrittlement Online T processing!High temp encourages T diffusion Liquid Breeder! Li-17Pb Properties 83 at % in Pb allows for (n,2n). Pb captures fast ns, spits out thermal Liquid state must be maintained- -even when offline! Lower limit on T set by Li- 17Pb solidification temperature. Upper limit set by structural material (ODS). Hence our effective coolant range is 500 800 K. Thermal ns are only absorbed by Lithium-6, imposing an enrichment requirement (>75% Li-6)!! Breeding Cell Design [4] Breeding Cell Design Tritium and its Properties Chemically, Tritium = Hydrogen. Very difficult to passivate. T(1/2) = 12.3 years. (Dose!!) Regulatory limit: 1-3 g/yr max. tolerable losses (public health) 1 g Tritium ~ 9,600 Curies. How to minimize loss of T through SiC and/or structural- -mats? Use an oxide coat! Erbium Oxide 0.7 micron coatings have- -been investigated. Gas bubbles in steel can lead to cavitation, sintering, and loss in yield strength (see inset image). It is imperative that essentially none of the T is allowed to enter the structural materials. Permeation increases w/ pressure according to Sieverts Law, Use of Erbium Oxide [6] Er2O3 shows promise as a Tritium-Permeation Barrier (TPB). 0.7 micron Erbium Sesquioxide coatings have shown ~650x Reduction in losses! Er2O3 TPB has been prepared on RAFM steel. How to prepare on SiC/ODS? How will these materials withstand irradiation? Will Erbium be affordable? [The authors] have demonstrated that crack formation in the coating above 900 K greatly increase tritium permeation, making the useful range of temps for the coating similar to the breeder range ( K). Tritium Isolation A well-studied approach for T sequestering is to use a liquid Li loop flowing past a hot [solid] yttrium target, which sorbs the T. Tritium diffusion through yttrium is the rate-limiting-step in the process. The IFMIF will be used partly to explore the validity of this approach via irradiation of the H2 that enters the loop (see insert). Trace amounts of ambient nitrogen can contaminate the loop and reduce its effectiveness. Solid titanium targets for N adsorption as part of the Li loop are being explored. Tritium Isolation is Tough! Tritium must be chemically removed from the Y target using HF. A purge gas (Argon) passing through/over the breeder fluid is necessary based on current designs. Future breakthroughs may obviate the need for such complex plumbing. Sieverts Constant (for gas solubility) in Li-17Pb is low, making the use of the Er2O3 coating a necessity to avoid losses in the SiC or steels. We must learn to exploit the low solubility of T in metals. Tritium breeding and separation has proven to be one of the most significant economical and engineering challenged associated with D/T reactors. Gas solubility decreases with Temperature! Citations 1.) ITER website.accessed on Nov. 10 th 2015.www.iter.org 2.) McMorrow, D. Jason Technical Report on Tritium. MITRE Corp. Nov ) Jauch, U, et al. Thermophysical Properties in the System Li-Pb. Institut fr Material-und-Festkrperforschung. Sep ) Wong, CPC, et al. An overview of dual coolant Pb-17Li breeder Fusion Engineering and Design 81 (2006). 5.) Stacey, W.M. Fusion Textbook 6.) Chikada, T, et al. Deuterium permeation through erbium oxide Journal of Nuclear Materials 443 (2013). Citations (cont.) 7.) Katekari K, Hatachi Y, Edao Y, and Fukada S. Hydrogen Isotopes Recovery from Journal of Energy and Power Engineering 6 (2012). 8.) Wu. CH. The Solubility of Deuterium in LiPb Alloys. Journal of Nuclear Materials 114 (1983). 9.) Segev, M. Analysis of (n,2n) Multiplication in Lead. Am. nucl. Energy Vol 11, No. 4 (1984).