Shielding design and neutronics calculation of the GDT based fusion neutron source ALIANCE

https://doi.org/10.1016/j.fusengdes.2020.112221Get rights and content

Highlights

  • Shielding of GDT based fusion neutron source ALIANCE has been designed and analyzed.

  • The nuclear heating and fast neutron fluence of MC2 is the highest, the values are about 300 W/m3 and 9 × 1018 n/cm2.

  • Additional WC shielding layer can protect the mirror coils more effectively than SS shield.

  • The structural materials’ specific activities will decrease to 4 × 1011 Bq/kg in one year after shutdown.

  • All structural materials of ALIANCE can be recycled by different recycling technologies.

Abstract

This paper presents the high flux neutron shielding design and extensive neutronics calculations of GDT based fusion neutron source ALIANCE. Neutron distribution of ALIANCE is strongly inhomogeneous along the axis: significant portion of the neutron flux is generated near the two mirrors, while the rest of it is spread over the remaining central volume of plasma. The shielding design includes 40 cm stainless steel as the main shielding layer and an additional 5 cm tungsten carbide shielding layer at mirror plugs to protect superconducting coils from neutron damage and reduce nuclear heating. The simulations have been carried out by using Monte Carlo transport code SuperMC with nuclear data library FENDL 3.1. Results show that the nuclear heating on the mirror coils can be reduced by more than two thirds with additional tungsten carbide shield, and fast neutron fluence by 30 %. The highest nuclear heating and the highest fast neutron fluence zones are located at the mirror coils, and the values are about 300 W/m3 and 9 × 1018 n/cm2 respectively, which meets the threshold of ITER superconducting coils. The specific activities of shielding layers are of order of 1012 Bq/kg. The structural materials’ specific activities will decrease to 4 × 1011 Bq/kg in one year after shutdown, and their decay heat will quickly drop below 2 kW/m3 after one day. Besides, all the structural materials of ALIANCE can be recycled by different recycling technologies. The modeling and calculations reported in this paper will be beneficial for the pre-conceptual engineering design of ALIANCE.

Introduction

R&D of the low activation materials and the reliability of components in fusion environment at a long operation time is one of the key issues for the realization of the commercial fusion reactor. For that reason, a fusion neutron source, which can qualify materials and large components under high intensity neutron flux is in urgent demand. A gas dynamic trap is an axially symmetric magnetic plasma confinement device with magnetic mirrors. Its distinct features in comparison to other linear devices are the high mirror ratio (R>>1) and mirror-to-mirror length L greatly exceeding the effective length of ion scattering into the loss cone [1,2]: L >> λeff = λ·ln(R)/R, where λ is a mean free path of ion-ion collision. Recent experiments on the GDT device have also demonstrated [1] confinement of plasma with parameters that would correspond to a transient mode with L ∼ λeff. A fusion neutron source based on GDT is suitable to serve as a fusion material and components test facility, which has the advantages of moderate technical difficulty, compact structure, good economy and flexible operation scenario [[3], [4], [5], [6], [7], [8], [9], [10]].

The Axisymmetric LInear Advanced Neutron sourCE (ALIANCE) is a GDT based fusion neutron source, aiming to produce 1018 of D-T neutrons per second and to provide a large testing volume required for fusion materials and components testing. A similar neutron source could also be valuable in the long run for medical isotopes production and as a driver of sub-critical fission reactor. ALIANCE is an international mega-science cooperation project, jointly initiated by the Institute of Nuclear Energy Safety Technology (INEST HFIPS CAS), and the Budker Institute of Nuclear Physics (BINP SB RAS) in 2018, and the conceptual design activities of ALIANCE have been on-going in collaboration with other institutions [11,12].

A preliminary schematic view of the ALIANCE facility is shown in Fig. 1. The total heating power of neutral beam injection (NBI) will reach 50 MW to achieve the high neutron flux. The vacuum mirror ratio (Bmax/Bmin) of the device will be as high as R = 27.4 (25.8 T/0.94 T). Distance between two mirror plugs is 20 m, which brings the total length of the device to ∼ 30 m. The diameter of the central vacuum vessel section is determined by the fairly large radius of plasma of ∼ 30 cm, which was selected to cover a wide range of discharge regimes. We choose wide range of discharge regimes because there are still uncertainties in optimal operation regimes of ALIANCE both due to lack experimental data from continuously operating volumetric neutron source [11] and due to approximations used in plasma simulations (namely, the use of 1D-code DOL [13] for simulations). Therefore, the effects related to more realistic radial profiles of plasma are neglected at present. For that reason, we have to leave a room for further optimization of plasma parameters in ALIANCE. The plasma parameters of ALIANCE are shown in Table 1. For such a 3 MW fusion neutron source, we plan to arrange the tritium proliferation blanket in the corresponding location to verify its tritium breeding capability. In addition, there is no need to achieve TBR > 1 for the GDT based fusion neutron source as it in the fusion reactor and fusion-fission hybrid reactor.

As a high flux fusion neutron source with high availability that is expected to reach 80 %, extensive neutronics analysis should be performed in order to guarantee the reliable operation of key components and safety of occupational staff during the operation of ALIANCE.

In this paper, we present a suitable shielding design and assessment of the safe operation of ALIANCE as an intense fusion neutron source. Firstly, we give a description of the neutronics calculation model of the facility. Next, we present a detailed evaluation of the shielding design. Finally, the activation of structural materials is considered to ensure safety after final neutron source run.

Section snippets

Methodology

To evaluate the neutronics characteristics of the ALIANCE with respect to its safe operation, neutronics calculations were performed using the SuperMC (Super Multi-functional Calculation Program for Nuclear Design and Safety Evaluation) [14] code with the nuclear data from the FENDL 3.1 nuclear data library [15].

Fusion neutron source

The deuterium and tritium (50:50) atomic beams with particle energy of 70 keV are injected to the plasma column near the middle plane of the device. Due to the ionization and

Nuclear analysis

The neutron spectrum is the most important neutronics characteristic of ALIANCE. Neutron spectrum of the first wall in testing zone has been calculated (as shown in Fig. 4). This is a typical fusion neutron spectrum which is similar to neutron spectra of the HCPB blanket of fusion DEMO reactor [18] that can be applied to test materials and components. Consequently, the interpretation of the results after irradiation of samples and components does not require compensation for spectral

Conclusions

This paper focuses on the shielding design and the activation analysis of the GDT based volumetric fusion neutron source ALIANCE. The shielding design includes 40 cm stainless steel as the main shielding layer and an additional tungsten carbide shielding layer at the mirror plugs to protect superconducting coils from neutron damage and reduce nuclear heating. Simulations have shown that this shielding design of ALIANCE could meet the nuclear heating and radiation threshold, which was set by

CRediT authorship contribution statement

Wenjie Yang: Conceptualization, Methodology, Software, Writing - original draft, Writing - review & editing. Qiusun Zeng: Conceptualization, Writing - original draft, Writing - review & editing. Chao Chen: Software, Writing - original draft, Writing - review & editing. Zhibin Chen: Resources. Jun Song: Investigation. Zhen Wang: Resources. Jie Yu: Resources. Dmitry Yakovlev: Methodology, Writing - original draft, Writing - review & editing. Vadim Prikhodko: Software, Writing - original draft,

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the IAEA Coordinate Research Project under contract F13018-22776. The views and opinions herein do not necessarily reflect those of IAEA, which is not liable for any use that may be made of the information contained herein. This work was also funded by the Anhui Provincial Natural Science Foundation under the Grant Nos. 202004b11020032 and 1908085MA17. China-Ukraine science and technology cooperation project under the Grant No. CU03-24. Besides, the authors would like

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