ISSN 10637788, Physics of Atomic Nuclei, 2015, Vol. 78, No. 10, pp. 1138–1147. © Pleiades Publishing, Ltd., 2015. Original Russian Text © S.S. Ananyev, A.V. Spitsyn, B.V. Kuteev, 2014, published in Voprosy Atomnoi Nauki i Tekhniki. Seriya: Termoyadernyi Sintez, 2014, Vol. 37, No. 4, pp. 11–21.
Fuel Cycle for a Fusion Neutron Source S. S. Ananyev, A. V. Spitsyn, and B. V. Kuteev National Research Center Kurchatov Institute, Moscow, Russia email:
[email protected];
[email protected];
[email protected] Received October 21, 2014
Abstract—The concept of a tokamakbased stationary fusion neutron source (FNS) for scientific research (neutron diffraction, etc.), tests of structural materials for future fusion reactors, nuclear waste transmuta tion, fission reactor fuel production, and control of subcritical nuclear systems (fusion–fission hybrid reac tor) is being developed in Russia. The fuel cycle system is one of the most important systems of FNS that pro vides circulation and reprocessing of the deuterium–tritium fuel mixture in all fusion reactor systems: the vacuum chamber, neutral injection system, cryogenic pumps, tritium purification system, separation system, storage system, and tritiumbreeding blanket. The existing technologies need to be significantly upgraded since the engineering solutions adopted in the ITER project can be only partially used in the FNS (consider ing the capacity factor higher than 0.3, tritium flow up to 200 m3Pa/s, and temperature of reactor elements up to 650°C). The deuterium–tritium fuel cycle of the stationary FNS is considered. The TCFNS computer code developed for estimating the tritium distribution in the systems of FNS is described. The code calculates tritium flows and inventory in tokamak systems (vacuum chamber, cryogenic pumps, neutral injection sys tem, fuel mixture purification system, isotope separation system, tritium storage system) and takes into account tritium loss in the fuel cycle due to thermonuclear burnup and β decay. For the two facility versions considered, FNSST and DEMOFNS, the amount of fuel mixture needed for uninterrupted operation of all fuel cycle systems is 0.9 and 1.4 kg, consequently, and the tritium consumption is 0.3 and 1.8 kg per year, including 35 and 55 g/yr, respectively, due to tritium decay. Keywords: fusion neutron source DEMOFNS, tokamak, hybrid reactor, fuel cycle, tritium. DOI: 10.1134/S1063778815100026
INTRODUCTION To develop hybrid nuclear power engineering that combines nuclear and thermonuclear technologies, the NRC Kurchatov Institute has proposed a program for development of tokamak based fusion neutron sources. The program is developed for creation of a number of experimental and demonstration facilities and test benches and an experimental industrialscale hybrid plant (PHP). In particular, it is planned to build a demonstration fusion neutron source (DEMO FNS) for testing the key systems of the fusion neutron source (FNS) for operation in the steadystate regime and the GlobusM3/FNSST compact spherical tokamak for physical substantiation of the possibility of attaining FNS parameters by a compact system. If the DEMOFNS project is successfully implemented, an experimental industrialscale hybrid facility (PHP) with a fusion power of 40 MW and total thermal power of 500 MW will be built to demonstrate the possibility of producing electric power from nuclear fuel and ren dering radioactive waste disposal services in commer cial scale. The parameters of these facilities are pre sented in Table 1. The FNS is a key system of the hybrid reactor and must provide a steadystate flow of thermonuclear neutrons with a power of 10 to 50 MW, which is close
to the parameters of the JET and JT60U facilities [1, 2]. Unlike the case in a pure thermonuclear reactor without fissionable materials, the necessary power of the thermonuclear reaction can be a factor of 100 lower because the energy is mainly released in the Table 1. Parameters of the FNSST and DEMOFNS/EIHF Parameter R, m R/a Ip, MA BT, T n, 1020 m–3 Eb, keV Pb, MW Number of injectors of neutral atoms PEC, MW Swall, m2 Vpl, m3 Pn/S, MW/m2
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FNSST/Glo busM3
DEMO FNS/PHP
0.5 1.66 1.5 1.5 1–2 130 10 4
2.5–2.7 2.5–2.7 5 5 1 500 30 6
— 13 2.5 0.2
6 130–188 103–113 0.2/0.3
FUEL CYCLE FOR A FUSION NEUTRON SOURCE
blanket that contains fissionable materials. Therefore, the FNS is not required to run a selfsustained fusion reaction, which appreciably decreases the require ments on the plasma parameters and materials. Development of DEMOFNS involves the choice of steadystate operating modes for the tokamak; tests of the structural and functional materials and compo nents, fuel cycle system, neutral beam injection (NBI) system, and electroncyclotron resonance heating of plasma; and demonstration of liquid salt technologies for the hybrid reactor blanket. DEMOFNS is a stationary facility with a super conducting magnet system. The plasma temperature is 1 to 10 keV. The reaction is maintained by beams of neutral atoms with a total power of up to 30 MW injected with a downward shift of the equatorial plane axis. The plasma current is maintained by noninduction methods. Neutron flows are expected to be 0.2 MW/(m2 s). The project involves a steadystate operating regime of the facility with capacity factor = 0.3. The Lawson criteria for the FNS can be nτE ~ 1019 m–3 s, which is much lower than for a thermonu clear reactor [3], but the DEMOFNS will operate near the Lawson criteria nτE ~ 1020 m–3 s. Implementation of DEMOFNS project requires all systems of the facility (magnet, plasma heating, blanket, fuel cycle (FC), diagnostics, remote control) to demonstrate steadystate operation. In addition, serviceability of structural and functional materials in expected thermal and neutron flows should be dem onstrated. DEMOFNS fuel cycle specifications include steadystate operation for up to 5000 h, remote maintenance, and considerable inventory and con sumption of tritium. The fuel cycle systems must provide injection of fuel into the plasma, exhaust of fusion and plasma–wall interaction products, sepa ration and purification of the exhausted fuel, enrichment of the fuel mixture to the prescribed concentration, and storage. The problems of thermonuclear fuel supply and tri tium reprocessing in thermonuclear facilities were examined in many countries, in particular, for the JET and TFTR facilities and also within the ITER project [4–6]. At the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP), the hybrid reactor FDSMFX [7–9] was proposed as a multifunctional experimental facility to support the DEMO hybrid reactor. The existing technologies need substantial upgrad ing because the engineering solutions chosen for the ITER, FDSMFX, and JET projects can only partially be used in such facilities in view of the installed capac ity utilization factor over 0.3, tritium flows up to 200 m3 Pa/s, steadystate operating regime of all sys tems, and high temperature of some DEMOFNS ele ments. PHYSICS OF ATOMIC NUCLEI
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FNS FUEL CYCLE To maintain thermonuclear combustion, fuel is injected into the FNS plasma using neutral atom injection and pellet injection systems and gas valves. The deuterium–tritium fuel mixture, fusion reaction products, and impurities are pumped out from the vacuum chamber divertors and the neutral beam injec tion system. The fuel mixture is purified from impuri ties by a cryotrap and a membrane filter. The impuri ties containing tritium in the form of chemical com pounds are fed into the purification system consisting of a system for catalytic decomposition of hydrogen compounds and a system for separation of super heavywater compounds. After the purification, a small fraction of the fuel mixture undergoes separation for removing the protium impurity and reenrichment to the prescribed deuterium–tritium ratio and then is admitted to the longterm isotope storage system [10]. The fuel cycle system is designed in such a way that a single circulation of the fuel takes no longer than one to three hours depending on the size of the facility and the amount and type of impurities. The isotope sepa ration system is only used to remove protium and helium impurities from the fuel mixture because all FNS systems use a deuterium–tritium mixture with equal D and T content. Protium results from the D–D reaction and nuclear reactions of neutrons with the structural materials and also comes to the vacuum chamber from its materials and through its body. The isotope separation system thus reprocesses 0.5 to 5% of the total fuel flow, which leads to a decrease in the total amount of tritium in the fuel system and accord ingly in the tritium loss due to β decay. After the fueling of the facility, there should be fuel enough to ensure the steadystate operation of all FC system for 24 h and thus the smooth performance of the facility. The system for longterm storage of hydro gen isotopes uses storage getters. It is planned to breed tritium using (Li, n) reactions in the blanket. Figure 1 presents a general diagram of the FNS fuel cycle. Pipeline vacuum pumping system. The system for vacuum pumping of pipelines is used during the heat ing and degassing of the pipelines that connect the fuel cycle facilities. With additional equipment, it can be used for mass spectrometry of the gas composition of the mixture in the pipelines during the operation of the facility and for detecting leakage in the pipelines. Since there is a high risk of losing tritium into atmo sphere, two independent pumping systems are built into the FNS, one for tritiumcontaining gas mixtures and the other for tritiumfree gas mixtures. Tritium containing mixture exhaust pipelines (and other FNS systems) have double walls to prevent tritium leaking into atmosphere by penetrating through the wall of the internal pipeline. FNS exhaust system. The system for collection and prepurification of gases from the facility receives gas from the outlet of the FNS exhaust system, transports
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ANANYEV et al. D2 + HT, T2, DT
T:D = 1:1, H < 0.5% 6
9 ~2% H2, HD
D ,T ,D T 2 ,H ,2 T D H H
~98% ,
H2, T2, He ...
D2
T2
Ne
He
2
4
10
3
5
14
1
CnHm, He, Ne, N2 + D2 + T2
2
7
8 FeO
n
11
13
12 C, N2, Ne, He
He3
O2
Fig. 1. General diagram of the fuel cycle systems: (black lines and arrows) gas mixture (including tritium) pipelines; (⋅⋅⋅⋅⋅⋅) deute rium–tritium (1 : 1) mixture pipelines; (gray lines and arrows) D2, T2, He, and other gas pipelines; (1) diverter pumping system; (2) neutral particle injector pumping system; (3) vacuum chamber and the first wall; (4) blanket; (5) cryotraps and membrane gas sepa ration system; (6) longterm isotope storage system; (7) system for catalytic decomposition of hydrogen compounds; (8) superheavy water compound reprocessing system; (9) hydrogen isotope separation system; (10) gas puffing system; (11) pellet injection system; (12) neutral injection system; (13) membrane filter; (14) plasma.
it to the fuel cycle system, and prepurifies it from hydrocarbon fractions. The system receives gas from 24 cryogenic pumps and transports it to the fuel cycle system for further purification from hydrocarbons on the same principle as a nitrogen trap. The system is designed for a gas flow rate of up to 200 m3/s. Cryogenic pumps of the vacuum pumping system. They are intended for evacuating the FNS vacuum chamber, being the main pumping devices as the plasma burns. The cryogenic pumps are arranged into groups and operate in an uninterrupted mode. Two key points that govern their regeneration cycle are the drop in the sorption ability of the cryogenic panels when a frozen layer of some width arises on them and the safety (critical tritium concentration in a room). Facility for cryogenic prepurification of exhaust. It is intended for separating compounds and impurities with a condensation temperature above 77 K from the gas mixture and transporting to the facility for catalytic decomposition of chemical compounds. To ensure steadystate operation of the fuel cycle system, the facility consists of two identical chambers (as one is operation, the other is under regeneration). Membrane filtering facility. It is intended for mem brane purification of hydrogencontaining gas mix tures from impurities using a diffusion palladium filter. Membrane filters effectively operate with an excess pressure at the inlet surface of the membrane, which is ensured by a system of receivers and force pumps. On this basis, we assume that a quasistationary gas flow
comes into the system. All systems will be made mod ular to allow scaling in accordance with the required flows. Facility for catalytic decomposition of hydrogen compounds. It is intended for chemical purification of the fuel mixture by separating gases that contain hydrogen isotopes and removing auxiliary gases (Ne, Ar) from the mixture. The operation of the facility is based on continuous catalytic decomposition of the methane series hydrocarbons with premethanation of carbon oxides and removal of water by zeolites. Since the system for catalytic decomposition of chemical compounds has a characteristic separation cycle time, the gas should be puffed into the system periodically (identical to the periodicity of the gas mixture dis charge from the system). The gas mixture not passing through the membrane filters will be stored in the buffer receiver. Facility for reprocessing of superheavywater hydro gen compounds. The facility for reprocessing of heavy water waste (superheavy water and tritiumcontaining molecules) is intended for decomposing hydrogen compounds to allow chemical purification of the fuel mixture by separating gases that contain hydrogen iso topes. The operation of the facility is based on presep aration, continuous catalytic decomposition of water with oxidation of metals, and extraction of hydrogen isotopes in the gas phase. Isotope separators. There are several isotope sepa rators used in the FNS FC for detritization of water,
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air, and technical gases and oils to a purity level of 99.9% and for removal of protium from the fuel mix ture since protium can decrease the neutron yield. The separator used for the latter purpose is able to separate 1 to 5% of the total fuel mixture flow. The isotope sep aration systems comprise buffer receivers for storing gas (and other) mixtures between periodic charges of separation columns. Since the gas mixture of hydro gen isotopes from the catalytic decomposition system must also undergo separation (deprotization), the sep arator has several modules. Main deuterium and tritium storage devices. A stor age getter is intended for collecting and storing hydro gen isotopes for their further reprocessing and use in the FNS. All storage getters are duplicated to ensure uninterrupted operation of the fuel cycle stands. The system for longterm storage of hydrogen isotopes should allow storage of all the fuel mixture for loading into the FNS FC systems. When the FNS operates in the steadystate regime, the storage getter keeps only the reserve fuel supply. The fuel mixture comes into the system from the membrane separator and from the isotopic separation systems in a periodic steadystate regime. The flow rate through the system is up to 300 m3 Pa/s. Pelletinjector. The injector is intended for fuelling thermonuclear plasma and controlling the discharge by injecting impurity macroparticles. It comprises lightgas guns, a differential pumping system with fast electromagnetic valves to cut the accelerating gas flow into the facility, gas/electromagnetic injectors of the frozen gas mixture (with a characteristic fuel pellet injection velocity of up to 10 km/s), and a fuel pellet production plant. Gas supply to the neutral particle injector. The DEMOFNS will use six injectors of neutral atoms with an energy of 500 keV, while the FNSST will use two injectors of atoms with an energy of 130 keV. For the neutral injection system to operate, it is necessary to fuel the ion sources and gas neutralizers. TCFNS CALCULATION CODE The TCFNS code was developed to estimate the tritium distribution in the hybrid reactor systems and tritium plant elements. It allows fuel flows and inven tories to be calculated in the FNS systems and ele ments, such as the vacuum chamber, cryogenic pumps, neutral injection system, fuel mixture purifi cation and isotope separation system, and tritium stor age system. The input parameters for the code are the parameters of the tokamak and its subsystems: geo metrical dimensions of the tokamak, particle confine ment time, plasma density, fusion power, hydrogen accumulation in the vacuum chamber materials, energy and power of neutral atom beams, number of injectors, operating regimes of cryogenic injectors of the tokamak and injectors, duration of the fuel purifi cation cycles, and efficiency of fuel mixture injection PHYSICS OF ATOMIC NUCLEI
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Table 2. Main input parameters Input parameter
FNSST
DEMOFNS
2.5 103 Vacuum chamber volume, m3 Area of vacuum chamber 13 130 walls, m2 Plasma density n, m–3 5 × 1019 1 × 1020 Fusion power Pf, MW 3 30 Particle confinement time 50 200 τpl, ms Number of neutral atom 4 (2 + 1 + 1) 6 (4 + 1 + 1) injectors Total power of neutral atom 10 30 injectors Pnbi, MW Energy of neutral atoms 130 500 E, keV Efficiency of injection of fuel mixture particles in plasma, %: injection of neutral atoms 100 100 injection of fuel pellets 90 90 gas puffing 20 20 Gas flow into the isotope 2 2 separation system (for pro tium removal), % (of total)
into the tokamak plasma. The operating regimes of the FC systems are built into this code for calculating the tritium inventory in the elements of these systems. Tri tium loss in the fuel cycle due to thermonuclear bur nup and β decay in all systems is taken into account. Table 2 presents the input parameters used for cal culating fuel mixture (tritium) flows in various FC sys tems for the FNSST and DEMOFNS versions under consideration. The FNS systems shown in Fig. 2 will be consided separately. In the FNS exhaust systems, it is proposed to use 24 (12 + 12) pumps operating in a continuous cycle mode. While four pumps are in the regeneration state, the other 20 operate. At each instant of time, four out of six neutral atom injectors operate, while the other two are shut down for regeneration of cryogenic panels and routine maintenance (Fig. 3). This operat ing regime allows the quasistationary mode of opera tion for all systems (Fig. 4). For safety reasons, the amount of tritium in each room must not be higher than the critical value, which is now taken to be 100 g [11]. Consequently, the amount of tritium in the exhaust systems of the upper and lower diverters separately must not exceed this value. For this reason of the maximum time between regenerations of cryogenic pumps will be 2 h. The amount of tritium in all 24 pumps is accordingly lim ited to 200 g.
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ANANYEV et al. Ne, Ar, ... Cryogenic pumps of upper diverter
Pellet injectors
Gas valves He3
Gas valves
NBI systems
Storage getters
Receivers
Pd filters
Cryogenic pumps of lower diverter Separation of hydrogen isotopes H2 HD and HT
Getter
D2
Catalytic decomposition of hydrogen compounds
T2
He3 + He4 + Ne + Ar + ... H2 HD and HT
Fig. 2. Block diagram of functional elements of the fuel cycle.
Limiting the amount of tritium in each injector neutral beam to 100 g, we obtain the time between cryogenic panel regenerations of 50 min and the amount of tritium in all injectors of 300 g. According to the calculations, the cryogenic panels of an injector lose their sorption ability owing to accumulation of a layer of atoms on their surface later than the time of accumulation of a critical amount of tritium in the sys
Upper diverter exhaust 20 pumps simultaneously in operation Neutral beam injector
Lower diverter exhaust
4 pumps simultaneously under regeneration Operating injectors Regeneration of cryogenic panels
Fig. 3. FNS exhaust system.
tems of this injector. Figure 5 shows the time diagram of the operating regime of the neutral injection system. The gas mixture from the exhaust systems passes through the cryosorption traps and enters the mem brane filtering system, which requires excess pressure over the membrane surface for its effective operation (Fig. 6). We assume that this pressure will be attained using a system of receivers and pumps which will pro vide a quasistationary gas flow (Fig. 7). It is important that all FC systems have a modular design to allow scaling in accordance with required flows. The isotope mixture not passing through the mem brane filter is sent to the catalytic decomposition sys tem for purification and separation (Fig. 8). After undergoing cyclic purification in the catalytic decomposition system, the mixture is fed into the superheavywater compound reprocessing system, where it also undergoes cyclic purification. The mixture of auxiliary gases purified from hydro gen isotopes is admitted to the separation and storage system for these gases. The tritiumcontaining gas mixture is stored in the storage getter, from which it comes to the module of the isotope separation system. Since these systems operate in periodical regime, the gas will be puffed into the systems on a periodic mode. To
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1−4 5−8 9−12 1−4 5−8 9−12
N (tritium)
N (tritium)
Exhaust
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Total inventory in system 200 g Time Fig. 4. Time diagram of the exhaust system operation.
Regeneration
1 2 3 4 5 6 N (tritium)
N (tritium)
Exhaust
Total inventory in system 300 g Time Fig. 5. Time diagram of the neutral beam injection system operation.
P1 > P2
Receivers
Pumps Filter
N (tritium)
Fig. 6. Block diagram of the membrane separation system.
Gas mixture deliver from diverter exhaust system
Time
Gas mixture deliver from neutral injection system
Time
Total supply of gas mixture to system Time Fig. 7. Time diagram of the membrane separation system operation. PHYSICS OF ATOMIC NUCLEI
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ANANYEV et al. Superheavywater waste reprocessing Catalyst
Mg/Fe
Catalyst
Getter
Catalyst
Catalytic decomposition of hydrogen compounds Sorbent Blower
Receiver
Gas mixture accumulation receiver
Receiver
Fig. 8. Block diagram of the gas mixture purification systems.
Gas puffing and tritium accumulation in system N (tritium)
N (tritium)
Gas storage for delivering gas mixture to system Time
Gas puffing period
Gas puffing and tritium accumulation in system
Time
Gas puffing period
Gas transport to hydrogen isotope separation system
Time
Time
Gas puffing period
Fig. 9. Time diagram of the catalytic decomposition sys tem operation.
Fig. 10. Time diagram of the superheavywater waste reprocessing system operation.
D H2 HD and HT
Storage receiver
Separation columns
D2
Pump
T2 H2 He3, 4
Storage tank in superheavywater waste reprocessing system
HD and HT
Fig. 11. Block diagram of the hydrogen isotope separation system.
maintain the steadystate operating regime of other FC systems, the gas mixture will be allowed to accumulate in receivers for subsequent loading into the purification sys tem. The total amount of the fuel mixture in these sys tems will involve the fuel accumulated in the buffer receiver, the fuel in water reprocessing system and in catalitic decomposition system, and the fuel in the storage getter (Figs. 9, 10).
Almost all of the mixture passing through the membrane filter is admitted to the FNS injection sys tems. To remove protium from the fuel mixture in order to avoid a possible decrease in the neutron yield, an isotope separation system separates only 0.5 to 5% of the total flow in the steadystate operating regime (Fig. 11). Thus, the total amount of the fuel mixture in the FNS FC decreases. Similar to the catalytic decomposition and super heavywater compound reprocessing systems, the iso
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Gas storage for delivering gas mixture to system Time
Gas puffing period
Gas puffing and tritium accumulation in system Time
Gas puffing period
Gas transport to storage getter and output tritium flow Time
Gas puffing period
Fig. 12. Time diagram of the hydrogen isotope separation system operation.
To FNS injection systems
Storage getters
D2 puffing Fuel mixture reenrichment receivers
T2 puffing From membrane filtering system
From isotope separation system
N (tritium) N (tritium) N (tritium)
Fig. 13. Block diagram of the isotope storage system.
Gas mixture delivery to system from membrane filter Gas transport from hydrogen isotope separation system (catalytic decomposition system) and output gas flow
Time
Time
Gas puffing period
Gas transport from hydrogen isotope separation system and output gas flow
Gas puffing period
Time
Fig. 14. Time diagram of the isotope storage system operation.
tope separation system requires that the gas mixture be periodically loaded into it. And the total amount of the tritiumcontaining mixture will consist of T accumu lated in the buffer receiver and T in the system (Fig. 12). PHYSICS OF ATOMIC NUCLEI
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The fuel mixture from the membrane purification system and isotope separation system(s) delivered to the storage getter (Fig. 13). The longterm hydrogen isotope storage system is responsible for inventory full
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Table 3. Fuel flows through the FNS systems
Table 4. Tritium inventory in FNS systems
FNSST, g/s
DEMOFNS, g/s
Neutral injection system
7.50 × 10–2
1.38 × 10–1
Pellet injection system
3.13 × 10
–2
3.09 × 10
Gas valve system
–2
Fuel cycle systems
–4 –4
4.23 × 10
1.28 × 10
FNS plasma
–4
3.13 × 10
2.58 × 10
Vacuum pumping system
1.93 × 10–3
4.55 × 10–2
Membrane filtering system
6.57 × 10–2
1.74 × 10–1
Catalytic decomposition system
6.57 × 10
1.74 × 10
Superheavywater waste reprocessing system
6.24 × 10–4
1.65 × 10–3
Isotope separation system
1.30 × 10
3.44 × 10
Storage getter
6.57 × 10
–4
–3 –2
FNSST, g
DEMO FNS, g
Neutral injection system
200
300
Vacuum pumping systems
200
200
Cryotrap and membrane gas separation system
27
27
Hydrogen isotope storage system
112
178
Hydrogen isotope separa tion system
74 + 37
198 + 100
Catalytic decomposition system
84
225
Superheavywater waste reprocessing system
84
225
124
124
0.0003
0.03
Total
882
1372
Annual tritium burnup
283
1817
Amount of tritium in FNS chamber
400
500
Fuel cycle systems
–2
–3
–3
Main lines, receivers, pumps, etc.
1.74 × 10–1
FNS plasma
amount of all the fuel mixture into FNS FC systems. When the FNS operates in the steadystate regime, it holds an amount that ensures uninterrupted operation of all FC systems (approximately 20% of the total amount). The circulating fuel mixture will be enriched to the required concentration (D : T = 1 : 1) and deliv ered to the FNS injection systems without entering the longterm storage system (Fig. 14). The total amount of the tritiumcontaining mix ture in the FC main lines and pipelines should also be taken into account. In addition, going into further details of the fuel cycle systems reveals the necessity of considering the air, water, technical gas and oil, and lithium detritization systems for closing the FC. The ITER experience will probably help us with these problems. Tables 3 and 4 present fuel flows and tritium inven tories in the FC systems calculated for the FNSST and DEMOFNS. For the facility versions under consideration, the amount of the fuel mixture needed for uninterrupted operation of all FC systems is 0.9 and 1.4 kg. The tri tium consumption will be 0.3 and 1.8 kg per year, including 35 and 55 g/yr due to tritium decay for the FNSTS and DEMOFNS, respectively. CONCLUSIONS The deuterium–tritium fuel cycle of stationary FNS with a fusion power of 3 to 50 MW is considered. It consists of the systems for vacuumpumping exhaust of contaminated fuel (pumping of the vacuum cham ber, diverters, and neutral atom injectors), purification of the evacuated fuel (cryogenic, membrane filtering), removal of impurities and protium (catalytic decom position of compounds, isotope separation), and re
enrichment of the fuel mixture to the prescribed con centration and its storage and also of the equipment for injection of fuel (neutral injection, pellet injection, gas valves) and impurities (argon, neon, helium). Complete circulation of the fuel in the system takes one to three hours depending on the size of the facility. After passing through the vacuum chamber of the tokamak, the fuel is purified and enriched in the steadystate regime. Fuel flows in the systems are expected to be as high as 200 m3 Pa/s. The isotope sep aration system is used only to remove the protium impurity from the fuel mixture because all FNS sys tems use a deuterium–tritium mixture with equal D and T contents, which allows decreasing both the load on this system, which processes 0.5 to 5% of the total flow, and the total amount of tritium in the fuel system. In turn, a decrease in the amount of tritium in the sys tem allows decreasing the tritium loss due to β decay. A TCFNS code is developed for calculating the tritium distribution in the hybrid reactor systems and tritium plant elements. The code allows fuel flows and inventories in the tokamak systems to be calculated with consideration of the tritium loss in the fuel cycle due to thermonuclear burnup and β decay in all sys tems. Flows and inventories of tritium are calculated for the spherical FNSST version and the currently existing DEMOFNS version. The amount of the fuel mixture needed for uninterrupted operation of all fuel cycle sys
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tems is 0.9 and 1.4 kg. The tritium consumption for the fusion reaction together with losses will be 0.3 and 1.8 kg/yr, including 35 and 55 g/yr due to tritium decay in all FNS systems. The amount of tritium in the FNSST chamber will be 400 and 500 g, respectively. For comparison, the amount of tritium in the ITER vacuum chamber (mainly adsorbed in the dust) can be as large as 1 kg [11]. The concept and the draft design of the DEMOTIN tokamak fuel system are developed. REFERENCES 1. D. Barbier, P. Batistoni, P. Coad, et al., in Proceedings of the 26th Symposium on Fusion Technology (SOFT), Porto, Portugal, 2010. 2. M. Ishikawa, T. Nishitani, Y. Kusama, et al., Plasma Fusion Res. 2, 019 (2007). 3. B. V. Kuteev et al., Nucl. Fusion 51, 073013 (2011). 4. C. Day and T. Giegerich, Fusion Eng. Des. 88, 616 (2013).
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5. M. Glugla et al., Fusion Eng. Des. 81, 733 (2006). 6. S. Maruyama et al., in Proceedings of the 23rd IEEE/NPSS Symposium on Fusion Engineering, SOFE 2009, June 1–5, 2009. 7. Y. Wu et al., Plasma Sci. Technol. 3, 1085 (2001). 8. Y. Wu et al., Fusion Eng. Des. 81, 2713 (2006). 9. Y. Wu et al., “The fusion–fission hybrid reactor for energy production: a practical path to fusion applica tion,” in 22nd Intern. Conf. on Fusion Energy (FEC22), Geneva, Switzerland, October 13–18, 2008. 10. S. S. Anan’ev et al., Fusion Science and Technology (in press). 11. N. Taylor, D. Baker, G. Cattaglia, et al., “Key issues in the safety and licensing of ITER,” in IAEA, 9th Techni cal Meeting “Fusion Power Plant Safety”, Vienna, Aus tria, 15–17 July 2009, CDROM proceedings, Thursday 2009715.
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Translated by M. Potapov
