7.4 Tritium Breeding and Recovery

Tritium breeding is crucial for sustaining fusion reactions in nuclear reactors. It involves producing tritium within the reactor to replenish the fuel consumed during fusion. This process is essential for long-term reactor operation, as tritium is rare and has a short half-life.

The breeding process uses lithium-containing blankets to produce tritium when bombarded with neutrons from fusion reactions. Various materials and methods are employed for tritium production, recovery, and management. Optimizing the tritium breeding ratio is key to achieving reactor self-sufficiency.

Tritium Breeding Fundamentals

Concept of tritium breeding

Top images from around the web for Concept of tritium breeding

• 

  Deuterium–tritium fusion - Wikipedia View original

  Is this image relevant?

• 

  Deuterium–tritium fusion - Wikipedia View original

  Is this image relevant?

1 of 1

Top images from around the web for Concept of tritium breeding

• 

  Deuterium–tritium fusion - Wikipedia View original

  Is this image relevant?

• 

  Deuterium–tritium fusion - Wikipedia View original

  Is this image relevant?

1 of 1

• Tritium breeding produces tritium in a fusion reactor to replenish consumed tritium in the deuterium-tritium (D-T) fusion reaction $D + T \rightarrow {}^4He (3.5 MeV) + n (14.1 MeV)$
• Breeding tritium in-situ is essential for sustaining the D-T fuel cycle and enabling long-term operation of fusion reactors since tritium is a rare isotope with a short half-life of 12.3 years making external sourcing challenging

Materials for tritium production

• Lithium-containing blankets commonly used for tritium breeding due to lithium's ability to produce tritium when bombarded with neutrons from the fusion reaction
• Tritium breeding reactions with lithium: ${}^6Li + n \rightarrow {}^4He + T + 4.8 MeV$ and ${}^7Li + n \rightarrow {}^4He + T + n - 2.5 MeV$
• Blanket materials include lithium ceramics (Li2O, Li4SiO4, Li2TiO3) embedded in a neutron multiplier (beryllium, lead) or liquid lithium and lithium-containing molten salts (LiF-BeF2, LiPb)

Tritium Recovery and Management

Tritium recovery methods

• Permeation processes involve tritium diffusing through the blanket material and being collected by a purge gas (helium) driven by concentration gradient and temperature
• Extraction processes for liquid lithium blankets use molten salt extraction or getter beds, while molten salt blankets use gas sparging or electrolytic processes
• Tritium recovery technologies include cryogenic molecular sieve beds, palladium-based membrane reactors, and getter beds (titanium, zirconium)

Impact of tritium breeding ratio

• Tritium breeding ratio (TBR) is the number of tritium atoms produced per tritium atom consumed in the fusion reaction, with TBR > 1 indicating self-sufficiency and TBR < 1 requiring external tritium
• Factors affecting TBR include neutron multiplier efficiency, lithium enrichment (higher ${}^6Li$ content increases TBR), blanket coverage and thickness, and structural materials' neutron absorption cross-sections
• A TBR ≥ 1.1 is typically targeted to account for losses and ensure self-sufficiency, with higher TBR allowing for a larger tritium inventory buffer against breeding performance fluctuations

Optimization of tritium breeding

• Challenges include ensuring uniform tritium production across the blanket, minimizing tritium permeation into structural materials, controlling inventory and preventing release, and maintaining blanket integrity under high neutron fluence and thermal stresses
• Optimization strategies involve:

1. Advanced blanket designs with optimized neutron multipliers and lithium compounds
2. Developing low-activation structural materials with reduced tritium permeation
3. Implementing efficient tritium extraction and recovery systems
4. Real-time monitoring and control of tritium inventory and breeding performance
5. Establishing a robust tritium fuel cycle with effective storage, handling, and safety protocols