The tritium aspects of the DT fuel cycle embody some of the most challenging feasibility and attractiveness issues in the development of fusion systems. The review and analyses in this paper provide important information to understand and quantify these challenges and to de ne the phase space of plasma physics and fusion technology parameters and features that must guide a serious R&D in the world fusion program. We focus in particular on components, issues and R&D necessary to satisfy three ‘principal requirements’: (1) achieving tritium self-suf ciency within the fusion system, (2) providing a tritium inventory for the initial start-up of a fusion facility, and (3) managing the safety and biological hazards of tritium. A primary conclusion is that the physics and technology state-of-the-art will not enable DEMO and future power plants to satisfy these principal requirements. We quantify goals and de ne speci c areas and ideas for physics and technology R&D to meet these requirements. A powerful fuel cycle dynamics model was developed to calculate time-dependent tritium inventories and ow rates in all parts and components of the fuel cycle for different ranges of parameters and physics and technology conditions. Dynamics modeling analyses show that the key parameters affecting tritium inventories, tritium start-up inventory, and tritium self-suf ciency are the tritium burn fraction in the plasma ( fb), fueling ef ciency (ηf), processing time of plasma exhaust in the inner fuel cycle (tp), reactor availability factor (AF), reserve time (tr) which determines the reserve tritium inventory needed in the storage system in order to keep the plant operational for time tr in case of any malfunction of any part of the tritium processing system, and the doubling time (td). Results show that ηf fb > 2% and processing time of 1–4 h are required to achieve tritium self-suf ciency with reasonable con dence. For ηf fb = 2% and processing time of 4 h, the tritium start-up inventory required for a 3 GW fusion reactor is ∼11 kg, while it is <5 kg if ηf fb = 5% and the processing time is 1 h. To achieve these stringent requirements, a serious R&D program in physics and technology is necessary. The EU-DEMO direct internal recycling concept that carries fuel ∗ Author to whom any correspondence should be addressed. 1741-4326/20/013001+51$33.00 1 © 2020 IAEA, Vienna Printed in the UK Nucl. Fusion 61 (2021) 013001 Review directly from the plasma exhaust gas to the fueling systems without going through the isotope separation system reduces the overall processing time and tritium inventories and has positive effects on the required tritium breeding ratio (TBRR). A signi cant nding is the strong dependence of tritium self-suf ciency on the reactor availability factor. Simulations show that tritium self-suf ciency is: impossible if AF < 10% for any ηf fb, possible if AF > 30% and 1% 6 ηf fb 6 2%, and achievable with reasonable con dence if AF > 50% and ηf fb > 2%. These results are of particular concern in light of the low availability factor predicted for the near-term plasma-based experimental facilities (e.g. FNSF, VNS, CTF), and can have repercussions on tritium economy in DEMO reactors as well, unless signi cant advancements in RAMI are made. There is a linear dependency between the tritium start-up inventory and the fusion power. The required tritium start-up inventory for a fusion facility of 100 MW fusion power is as small as 1 kg. Since fusion power plants will have large powers for better economics, it is important to maintain a ‘reserve’ tritium inventory in the tritium storage system to continue to fuel the plasma and avoid plant shutdown in case of malfunctions of some parts of the tritium processing lines. But our results show that a reserve time as short as 24 h leads to unacceptable reserve and start-up inventory requirements. Therefore, high reliability and fast maintainability of all components in the fuel cycle are necessary in order to avoid the need for storing reserve tritium inventory suf cient for continued fusion facility operation for more than a few hours. The physics aspects of plasma fueling, tritium burn fraction, and particle and power exhaust are highly interrelated and complex, and predictions for DEMO and power reactors are highly uncertain because of lack of experiments with burning plasma. Fueling by pellet injection on the high eld side of tokamak has evolved to be the preferred method to fuel a burning plasma. Extrapolation from the DIII-D penetration scaling shows fueling ef ciency expected in DEMO to be <25%, but such extrapolations are highly uncertain. The fueling ef ciency of gas in a reactor relevant regime is expected to be extremely poor and not very useful for getting tritium into the core plasma ef ciently. Gas fueling will nonetheless be useful for feedback control of the divertor operating parameters. Extensive modeling has been carried out to predict burn fraction, fueling requirements, and fueling ef ciency for ITER, DEMO, and beyond. The fueling rate required to operate Q = 10 ITER plasmas in order to provide the required core fueling, helium exhaust and radiative divertor plasma conditions for acceptable divertor power loads was calculated. If this fueling is performed with a 50–50 DT mix, the tritium burn fraction in ITER would be ∼0.36%, which is too low to satisfy the self-suf ciency conditions derived from the dynamics modeling for fusion reactors. Extrapolation to DEMO using this approach would also yield similarly low burn fraction. Extensive analysis presented shows that speci c features of edge neutral dynamics in ITER and fusion reactors, which are different from present experiments, open possibilities for optimization of tritium fueling and thus to improve the burn fraction. Using only tritium in pellet fueling of the plasma core, and only deuterium for edge density, divertor power load and ELM control results in signi cant increase of the burn fraction to 1.8–3.6%. These estimates are performed with physics models whose results cannot be fully validated for ITER and DEMO plasma conditions since these cannot be achieved in present tokamak experiments. Thus, several uncertainties remain regarding particle transport and scenario requirements in ITER and DEMO. The safety standard requirements for protection of the public and release guidelines for tritium have been reviewed. General safety approaches including minimizing tritium inventories, reducing tritium permeation through materials, and decontaminating material for waste disposal have been suggested.

https://iopscience.iop.org/article/10.1088/1741-4326/abbf35/pdf

Physics and technology considerations for the deuterium–tritium fuel cycle and conditions for tritium fuel self sufficiency

In this work, hydrogen isotopes in the form of protium and deuterium were rapidly desorbed from magnetic-hydride iron oxide-palladium (Fe2O3-Pd) hybrid nanomaterials using an alternating magnetic f...

Controlled Release of Hydrogen Isotopes from Hydride-Magnetic Nanomaterials

The recent Thermal Cycling Absorption Process (TCAP) advances at Savannah River Site (SRS) include compressor-free concept for heating/cooling, push and pull separation using an active inverse column, and compact column design. The new developments allow significantly higher throughput and better reliability from 1/10th of the current production system’s footprint while consuming 60% less energy. Various versions are derived in the meantime for external customers to be used in fusion energy projects and medical isotope production.

/pdf/recent-advances-in-srs-on-hydrogen-isotope-separation-using-1lm8q91d4a.pdf

Recent Advances in SRS on Hydrogen Isotope Separation Using Thermal Cycling Absorption Process

One of the main design drivers of the EU-DEMO fuel cycle is to avoid unnecessary hydrogen isotope separation. In the tritium plant, this implies a novel functionality for isotope rebalancing (IR) a...

Technology Development for Isotope Rebalancing and Protium Removal in the EU-DEMO Fuel Cycle

Dynamic simulation of Thermal Cycling Absorption Process with twin columns for hydrogen isotopes separation

The Thermal Cycling Absorption Process (TCAP) was further studied with a new configuration. Previous configuration used a palladium packed column and a plug flow reverser (PFR). This new configuration uses an inverse column to replace the PFR. The goal was to further improve performance. Both configurations were experimentally tested. The results showed that the new configuration increased the throughput by a factor of more than 2.

/pdf/tcap-hydrogen-isotope-separation-using-palladium-and-inverse-3636dgvz66.pdf

Tcap hydrogen isotope separation using palladium and inverse columns

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Tcap hydrogen isotope separation using palladium and inverse columns