Core Fueling of DEMO by Direct Line Injection of High-Speed Pellets From the HFS

Frattolillo, A.; Baylor, L. R.; Bombarda, F.; Combs, S. K.; Day, Christian; Lang, P. T.; Migliori, S.; Pégouriè, B.; Ploeckl, B.

doi:10.1109/tps.2018.2798502

Cited by 5 publications

(8 citation statements)

References 25 publications

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“…However, compared to conventional arrangements that make use of curved guide tubes, the DLS injection scheme allows in principle to inject pellets at significantly higher velocities; this peculiarity does indeed help to recover sufficient fuelling performance, despite a potentially less favorable layout. Preliminary simulations carried out using the HPI2 code indicate indeed that there are possible OHFS injection configurations providing performance (in terms of fuel deposition depths and fuelling efficiency) comparable to those achievable by pellets injected at 1.3 km/s through a curved guide tube featuring a curvature radius R = 6 m, provided that the OHFS injection location does not exceed a distance z inj of  2.5 m from the equatotial midplane [11]. A more detailed investigation is still ongoing, aimed at optimizing the injection location, and will be published elsewhere as soon as the results will become available.…”

Section: Hfs Injection Of High-speed Pellets Along "Direct-line-of-si...mentioning

confidence: 97%

“…Options using the upper vertical port have been explored first, since they represents by far the simplest approach. However, the position of the vertical port in DEMO is such that pellets injected through it are predicted to not yield sufficiently deep fuel deposition for the injections velocities available with current technologies [11,12], so HFS injection is being presently investigated, since this scheme is predicted to provide better fuelling performance [11]. Due to the interference with the central solenoid (CS), DLS injection paths from the HFS must be necessarily oblique, a configuration which is referred to as Oblique High Field Side (OHFS) injection, that might lead, as in the case of curved guide tubes, to make compromises on the possible injection configurations, particularly as the angle that the pellets trajectory forms with the magnetic surfaces is concerned.…”

Section: Hfs Injection Of High-speed Pellets Along "Direct-line-of-si...mentioning

confidence: 99%

“…These preliminary tests have been carried out using an existing high-speed pellet injector, originally designed for the Ignitor experiment and therefore named "IPI" (Ignitor Pellet Injector). This facility, developed in collaboration between ENEA and ORNL, has been described exhaustively elsewhere [20,21]; the four-barrels "pipe gun" cryostat of the IPI has been recently upgraded, resulting in a significant improvement of the injector performance [11,12]. The specific arrangement used for scatter cone measurement, the analysis of the experimental data, and the results are also reported in detail in ref.…”

Section: Angular Dispersion Of Free-flight High-speed Pelletsmentioning

confidence: 99%

“…For instance, after a free-flight of  20 m (which is a realistic value for DEMO), a hole with a diameter of  24 cm would be required in the BB. The adoption of a straight guide tube, able to confine the trajectories of the pellets within a much narrower DLS duct, could get rid of this issue [11]. So far, high-speed cryogenic pellets have always been launched across pipes featuring a sufficiently large cross section to ensure "free-flight" conditions, for fear of destroying the projectiles by collisions.…”

Section: Preliminary Experiments Using a Dls Guide Tubementioning

confidence: 99%

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Injection of high-speed solid D2 pellets using a “Direct-Line-of-Sight” (DLS) guide tube

Frattolillo

Baylor

Day

et al. 2021

Fusion Engineering and Design

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Section: Hfs Injection Of High-speed Pellets Along "Direct-line-of-si...mentioning

confidence: 97%

Section: Hfs Injection Of High-speed Pellets Along "Direct-line-of-si...mentioning

confidence: 99%

Section: Angular Dispersion Of Free-flight High-speed Pelletsmentioning

confidence: 99%

Section: Preliminary Experiments Using a Dls Guide Tubementioning

confidence: 99%

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Injection of high-speed solid D2 pellets using a “Direct-Line-of-Sight” (DLS) guide tube

Frattolillo

Baylor

Day

et al. 2021

Fusion Engineering and Design

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“…Unfortunately, fuel deposition simulations performed using the HPI2 code predict that vertical injection may be effective, to some extent, only if pellets are injected from radial positions well inboard the magnetic axis of the plasma [6], so that DLS injection paths routed across this vertical duct are expected to result in very poor fueling efficiency. High-speed injection through oblique inboard "DLS" paths, not interfering with the CS, are instead predicted to yield good fueling performance, provided that the trajectories intercept the separatrix at a distance from the equatorial mid-plane ≲ 2.5 m [6]. Their integration in the design of DEMO need therefore to be investigated.…”

Section: Identification Of Dls Injection Paths Using the Vertical Uppmentioning

confidence: 99%

Addressing the feasibility of inboard direct-line injection of high-speed pellets, for core fueling of DEMO

Frattolillo

Baylor

Bombarda

et al. 2019

Fusion Engineering and Design

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Pellet injection represents, to date, the most promising option for core fuelling of the EU-DEMO tokamak. Simulations with the HPI2 pellet ablation/deposition code indicate, however, that sufficiently deep fuel deposition requires injection from the High Field Side (HFS) at velocities ≳1 km/s. Two complementary inboard injection schemes are being explored: one makes use of guide tubes with curvature radii  6 m in the attempt of preserving pellet integrity at speeds of  1 km/s; the other is investigating the feasibility of injecting high-speed ( 3 km/s) pellets along "direct line of sight" (DLS) trajectories, from either the HFS or a vertical port. Options using quasivertical DLS paths routed across the upper vertical port have been explored first, as they can be more easily integrated; Unfortunately, the radial position of the available vertical access (≳ 9 m from the machine axis) turns out to be unfavorable; further simulations with the HPI2 code predict indeed that vertical injection may be effective only if pellets trajectories are well inboard the magnetic axis. High-speed injection through oblique inboard "DLS" paths, not interfering with the Central Solenoid (CS), are instead predicted to yield good performance, provided that the injection location is ≲ 2.5 m from the equatorial mid-plane. The angular spread of high-speed free-flight pellets, recently measured using an existing facility, turns out to be enclosed within ~ 0.7°. This scatter cone may require significant cut off volume of the Breeding Blanket (BB). Moreover, DLS in-vessel conical penetrations may increase the neutron flux outside of the bio-shield, and also result in a significant heat load in the cryogenic pellet source.These issues are being investigated, to identify suitable shielding strategies; preliminary results are reported. The suitability of straight guide tubes to reduce the scatter cone, and hence the corresponding open cross section on BB penetration and the neutron streaming, will be explored as a further step.

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

et al. 2020

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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 define 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-sufficiency 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 define specific 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 flow 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-sufficiency are the tritium burn fraction in the plasma (f b), fueling efficiency (η f), processing time of plasma exhaust in the inner fuel cycle (t p), reactor availability factor (AF), reserve time (t r) which determines the reserve tritium inventory needed in the storage system in order to keep the plant operational for time t r in case of any malfunction of any part of the tritium processing system, and the doubling time (t d). Results show that η f f b > 2% and processing time of 1–4 h are required to achieve tritium self-sufficiency with reasonable confidence. For η f f b = 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 η f f b = 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 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 significant finding is the strong dependence of tritium self-sufficiency on the reactor availability factor. Simulations show that tritium self-sufficiency is: impossible if AF < 10% for any η f f b, possible if AF > 30% and 1% ⩽ η f f b ⩽ 2%, and achievable with reasonable confidence if AF > 50% and η f f b > 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 significant 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 sufficient 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 field side of tokamak has evolved to be the preferred method to fuel a burning plasma. Extrapolation from the DIII-D penetration scaling shows fueling efficiency expected in DEMO to be <25%, but such extrapolations are highly uncertain. The fueling efficiency of gas in a reactor relevant regime is expected to be extremely poor and not very useful for getting tritium into the core plasma efficiently. 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 efficiency 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-sufficiency 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 specific 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 significant 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.

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Core Fueling of DEMO by Direct Line Injection of High-Speed Pellets From the HFS

Cited by 5 publications

References 25 publications

Injection of high-speed solid D2 pellets using a “Direct-Line-of-Sight” (DLS) guide tube

Injection of high-speed solid D2 pellets using a “Direct-Line-of-Sight” (DLS) guide tube

Addressing the feasibility of inboard direct-line injection of high-speed pellets, for core fueling of DEMO

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

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