Helium-Cooled Lithium Compound Suspension Blanket Concept for ITER

This blanket concept uses a dilute suspension of fine solid breeder particles (Li₂O, LiAlO₂, or Li₄SiO₄) in a carrier gas (He) as the coolant and the tritium breeding stream. A small fraction of this stream is processed outside the reactor for tritium recovery. The blanket consists of a beryllium multiplier and carbon/steel reflector. A steel clad is used for all materials. A carbon reflector is employed to reduce the beryllium thickness used in the blanket for a specific tritium breeding ratio. The breeder particle size has to exceed a few microns (≥ 2 microns) to avoid sticking problems on the cold surfaces of the heat exchanger. The helium gas pressure is in the range of 2–3 MPa to carry the solid breeder particles through the blanket and the heat exchanger loop. The solid breeder concentration in the helium stream is 1 to 5 volume percent. A high lithium-6 enrichment is used to produce a high tritium breeding ratio and to reduce the breeder concentration in the helium gas. At a lithium-6 enrichment of 90%, the local tritium breeding ratio is 2.03 based on a one-dimensional poloidal model. The total thickness of the helium stream is only 4 cm out of the 50 cm total blanket thickness. The blanket uses 35 cm of beryllium for neutron multiplication. A simple multi-layer design is employed where the blanket sector has the helium coolant flowing in the poloidal direction. The blanket concept has several unique advantages which are very beneficial for fusion reactors including ITER. The key advantages are listed below:

• The blanket operation can be switched between nonbreeding and breeding modes without hardware changes in the reactor.
• The blanket performance can be adjusted during reactor operation by changing the breeder concentration, lithium-6 enrichment, helium pressure, or helium velocity.
• The blanket has a very low tritium inventory.
• The tritium breeding ratio is adjustable during operation in the range of 0 to 2.03.
• The coolant loop operates at low to medium pressure (2 to 3 MPa).
• The addition of µ-sized solid particles in the helium gas improves its heat transfer and transport properties.
• The blanket can be designed to operate in any temperature range suitable for an optimum structure performance.
• The afterheat source in the blanket is very low because of the low steel fraction and the absence of the solid breeder.
• The blanket has no impact on the reactor configuration, and it can be designed for vertical or horizontal maintenance schemes.
• The blanket has very low design uncertainties in its performance.
• The blanket concept has the potential to extrapolate to power reactor conditions.

The main features, key technical issues, and design analyses of this blanket concept are summarized in this paper. ^a Work supported by the U.S. Department of Energy, Office of Fusion Energy.