Snowmass Hot Topic

Chamber Science and Technology

 

Key Question number 6

Potential for Achieving Tritium Self-Sufficiency

 
Mohamed Sawan (UW) and Scott Willms (LANL)
  Description: Attaining tritium self-sufficiency is necessary for self-sustaining fusion plants operating on the D-T fuel cycle. Tritium is bred in a lithium-containing blanket surrounding the plasma. The achievable tritium breeding ratio determined from neutronics calculations depends on the type of the breeding material as well as the coolant and structural materials used in the FW/blanket subsystem. The calculated achievable TBR should account for the 3-D geometrical configuration of the chamber including penetrations. Hence, in addition to dependence on the blanket type, the achievable TBR might depend on the plasma confinement concept considered. Moreover, the geometrical and spectral differences of the neutron source in MFE and IFE chambers affect the achievable TBR. The calculated achievable TBR for a given FW/blanket concept is uncertain due to the uncertainty associated with system definition and the inaccuracies in predicting the TBR. The latter includes the uncertainty associated with the geometrical modeling, calculational methods, and basic nuclear data. The required TBR in a fusion system must exceed unity by a margin that accounts for calculational uncertainties, tritium losses and radioactive decay during the period between production and use, tritium inventory in the plant components, and supplying inventory for startup of other fusion plants. To accurately determine the required TBR, one has to consider the entire fuel cycle for the D-T plant. The tritium fuel cycle will involve many subsystems. Simulation of this cycle, including the dynamic behaviour is required for accurate evaluation of tritium build-up and consumption/losses in this closed cycle. The required tritium breeding margin depends on many system parameters. These include the desired doubling time, tritium inventory in the different components, and the tritium extraction and processing system utilized. In addition, tritium fractional burnup in the plasma impacts the tritium inventory in some of the components, such as the plasma fueling system, and hence affects the required tritium breeding ratio. The required TBR, therefore, depends on the plasma confinement concept used, the breeding blanket concept, and the tritium extraction and processing system. To attain tritium self-sufficiency, the calculated achievable TBR must exceed the required TBR. Uncertainties in predicting both the achievable and required TBR should be addressed. The potential of the plasma confinement concepts in both MFE and IFE and the breeding blanket concepts for attaining tritium self-sufficiency will be investigated. Possible plasma and technology R&D required to reduce the uncertainties and increase the potential for achieving tritium self-sufficiency need to be identified. The first generation of fusion ignition machines are designed without tritium breeding blankets and rely on the available tritium resources for supplying their fuel. These resources are decreasing due to radioactive decay and reduced production rate. An important issue that needs to be addressed is whether there is a time window for the availability of tritium to supply the tritium requirements for the ignition machines. This time window will impact the schedule for developing tritium producing chamber technologies.

Subtopics:

(1) What is the achievable TBR in different plasma confinement and breeding blanket concepts?     How does TBR vary for different breeding blanket concepts?    - Effect of breeding material    - Effect of neutron multiplier    - Effect of coolant    - Effect of structural material
     What is the impact of chamber configuration in different confinement concepts on achievable TBR?    Is there significant difference in size of penetrations required in different confinement concepts and how does this impact the achievable TBR?    Is there significant difference between achievable TBR in MFE and IFE systems?    How large are the current uncertainties in predicting the achievable TBR and what can be done to reduce them?    - Nuclear data    - Modeling    - Calculation methods

(2) How large a tritium breeding margin above unity is required?     What are the most important parameters influencing the required  TBR?   What is the potential for achieving high tritium fractional burnup in the plasma for both MFE and IFE confinement concepts?  How does the tritium inventory depend on the chamber technology concept?    How does the method and time needed for tritium extraction and processing affect the required TBR?    How does achieving high reliability and reducing level of complexity of various components of the cycle affect the required TBR?    How does achieving higher safety requirement could affect the required TBR?    What are the uncertainties in determining the required TBR?

(3) Do we expect that present candidate blanket materials can breed sufficiently, or is this an issue where more innovative ideas for chamber technology concepts are needed to achieve tritium self-sufficiency?

(4) Does any of the current and alternate confinement concepts have clear advantage in achieving tritium self-sufficiency?

(5) What are the R&D needs to increase the potential for tritium self-sufficiency?- Plasma R&D- Technology R&D

(6) By the time an ignition machine is built, such as ITER, will there be enough tritium available in the world to supply its initial and operating multi-kg tritium requirements? What are the implications on the schedule for the development of tritium-producing chamber technology?

Core Working Group: Mohamed Sawan (UW)Scott Willms (LANL)Laila El-Guebaly (UW)Mahmoud Youssef (UCLA)Edward Cheng (TSI)Dai-Kai Sze (ANL) W. Nevins (LLNL) Suggested assignment for addressing the 6 subtopics is as follows:

    (1)  M. Sawan, L. El-Guebaly, E. Cheng, M. Youssef, W. Nevins
    (2)  S. Willms, D-K. Sze, W. Nevins
    (3)  All
    (4)  All
    (5)  S. Willms, W. Nevins, D-K. Sze, M. Youssef, E. Cheng
    (6)  S. Willms, D-K. Sze

Plan for the 2 Hour Session at Snowmass: The session will start with a 10 min presentation by the question leader describing the topic and subtopics to be addressed. The session will be divided into several time slots to address each of the subtopics. For each subtopic, a brief introduction will be given followed by discussion.
Report Outline: The report will have sections each corresponding to one of the subtopics listed above. Members of the core group will provide input to the writeup as outlined above. The lead responsibility for writing each section will be as follows:
M. Sawan: 1,3,4 and S. Willms: 2,5,6