Our team came together to conduct a neutronic analysis of tritium breeding blankets within a fusion stellarator. This project was proposed to our mentors by a third party, and seeks to develop the next generation of reactors, to include fusion reactors. This project is unique from our peers’ projects, because it seeks to provide answers to questions within the field of nuclear science and engineering that has yet to be answered. Due to this, this project has been challenging and time consuming, but the experience has been very rewarding.
We are looking to maximize the production of tritium, because tritium is a multipurpose, radioactive isotope that is a primary fuel source for fusion reactors. It is also used for DNA tracers in Biomedical Research, consumer products, nuclear weapon stockpile stewardship, and it has luminescence properties. Tritium is seen in the D-T fusion reaction (D + 3H → 4He + n) which uses 17.6 MeV neutrons, but for our design we are using D-D fusion reactions (D + D → 3He + n or D + D → 3He + p) which uses 2.5 MeV neutrons.
The primary objectives of this design are:
- Identify material compositions that can be used in a fusion stellarator breeding blanket, which will efficiently absorb heat, produce tritium, and reduce neutron flux.
- Use MCNP 6.2 & Python to conduct a neutronic analysis of chosen material compositions and design.
- Maximize the amount of tritium produced for the chosen material composition, using the developed codes.
- Develop models to explain the key components of final design.
Limitations and Assumptions:
- Thermal Efficiency
- MCNP 6.2 cannot perform any heat transfer calculations.
- Heat transfer will be generally quantified but not thoroughly analyzed
- Resources
- Real Experimental Data
- Limited operable stellarators
- Time Constraints
- Strict deliverable timeline
Results:
The flux as a function of design thickness (flux profile) for each blanket material:
Assuming a neutron wall load (NWL) of 0.5 MW/m2, a source strength of 2.94 * 1019 neutron/sec was calculated, which is agreeable with other stellarator systems. An integral operation time of 1 second is assumed. T(t) is plotted as a function of thickness, and the outer shield is 1 cm thick of 304L carbon steel. Due to such an extreme source strength and high reaction rates, all the 6Li is depleted almost immediately. Below is a graph demonstrating the amount of tritium produced in a single 1 cm thick section of the blanket material.
Cost Analysis and Discussion:
The average price of tritium per gram is $30,000. Using the price per gram of each material in the spherical model, a one-cycle cost figure can be calculated.
| Material | System Cost | Tritium Revenue |
| Li2ZrO3 | $2M | $593.2M |
| Li2TiO3 | $474k | $411.3M |
| Li4SiO4 | $13.3M | $695.6M |
It should be noted that cost of electricity, downtime between blanket replacements, and labor costs are outside the scope of this project, but can add considerable cost to each system.
For each lithium composite, all blankets deplete their 6Li and produce near maximum amounts of 3H. The income generated far exceeds the material costs for all designs. These results determine that producing tritium in stellarators using Li2ZrO3, Li2TiO3, and Li4SiO4 is not a limiting factor and can be a viable and profitable endeavor. The Li4SiO4 blanket generates the most revenue per cycle, generating $682.6M in net income. Future work is encouraged for more detailed analysis regarding structural integrity and heat transfer, as these may introduce limits to the geometry of the breeder blanket and affect tritium production.
