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. 2023 May 26;23(11):5104.
doi: 10.3390/s23115104.

Neutronics Simulations for DEMO Diagnostics

Raul Luís  1 , Yohanes Nietiadi  1 , Antonio Quercia  2 , Alberto Vale  1 , Jorge Belo  1 , António Silva  1 , Bruno Gonçalves  1 , Artur Malaquias  1 , Andrei Gusarov  3 , Federico Caruggi  4 , Enrico Perelli Cippo  4 , Maryna Chernyshova  5 , Barbara Bienkowska  5 , Wolfgang Biel  6
Affiliations

Neutronics Simulations for DEMO Diagnostics

Raul Luís et al. Sensors (Basel). .

Abstract

One of the main challenges in the development of a plasma diagnostic and control system for DEMO is the need to cope with unprecedented radiation levels in a tokamak during long operation periods. A list of diagnostics required for plasma control has been developed during the pre-conceptual design phase. Different approaches are proposed for the integration of these diagnostics in DEMO: in equatorial and upper ports, in the divertor cassette, on the inner and outer surfaces of the vacuum vessel and in diagnostic slim cassettes, a modular approach developed for diagnostics requiring access to the plasma from several poloidal positions. According to each integration approach, diagnostics will be exposed to different radiation levels, with a considerable impact on their design. This paper provides a broad overview of the radiation environment that diagnostics in DEMO are expected to face. Using the water-cooled lithium lead blanket configuration as a reference, neutronics simulations were performed for pre-conceptual designs of in-vessel, ex-vessel and equatorial port diagnostics representative of each integration approach. Flux and nuclear load calculations are provided for several sub-systems, along with estimations of radiation streaming to the ex-vessel for alternative design configurations. The results can be used as a reference by diagnostic designers.

Keywords: DEMO; MCNP; diagnostics; neutronics; nuclear fusion; tokamaks.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Representation of one DEMO sector and foreseen locations for diagnostics, represented in red (for visualization only—diagnostics will be distributed in different sectors). DSC: Diagnostics Slim Cassette (red). EP: Equatorial Port (red). UP: Upper Port (red). BB: Breeding Blanket (blue—inboard and pink—outboard). DIV: Divertor (red). VV: Vacuum Vessel (green).
Figure 2
Figure 2
DEMO MCNP reference model used for the simulation of in-vessel diagnostics (excluding port diagnostics). Left: Plane y = 10.5 cm. Right: Plane z = 0.
Figure 3
Figure 3
Reference model used in the simulations of the ex-vessel Faraday sensors.
Figure 4
Figure 4
MCNP reference model used in the simulations of equatorial port diagnostics. Left: Plane y = 28 cm. Right: Plane z = 10 cm.
Figure 5
Figure 5
Detail of the MCNP reference model used in the simulations of equatorial port diagnostics, showing the EP and the bioshield plug.
Figure 6
Figure 6
Weight windows used in the simulations. Left: Faraday sensors, installed on the outer layer of the VV. Right: EP diagnostics.
Figure 7
Figure 7
MCNP model of the DSC, containing the antennas and WGs designed for reflectometry. Left: Plane y = 10.5 cm. Right: Plane y = 6 cm.
Figure 8
Figure 8
MCNP model of the DSC (plane z = 0).
Figure 9
Figure 9
Left: Detail of the DSC, highlighting the cells used to tally fluxes, heat loads and dose rates (plane z = 0). Right: The 60 poloidal positions around the plasma foreseen for magnetics sensors.
Figure 10
Figure 10
Neutron flux spectra (n cm−2 s−1) and statistical error fraction behind the DSC and WCLL blanket.
Figure 11
Figure 11
Detail of the meshes used in the simulations.
Figure 12
Figure 12
Neutron fluxes (n cm−2 s−1) and statistical errors behind the WCLL blanket in plane y = 10.5 cm.
Figure 13
Figure 13
Neutron fluxes (n cm−2 s−1) and statistical errors behind the WCLL blanket at 60 poloidal locations in plane y = 10.5 cm.
Figure 14
Figure 14
Left: Neutron flux ratios (with DSC/without DSC) in plane y = 10.5 cm. Right: Values at 60 poloidal locations.
Figure 15
Figure 15
Gamma fluxes (γ cm−2 s−1) and statistical errors behind the WCLL blanket at 60 poloidal locations.
Figure 16
Figure 16
Left: Gamma flux ratios (with DSC/without DSC) in plane y = 10.5 cm. Right: Values at 60 poloidal locations.
Figure 17
Figure 17
Left: dpa/FPY behind the WCLL blanket. Right: dpa/FPY behind the DSC.
Figure 18
Figure 18
Left: Location of the FOCS in the MCNP model. Right: Poloidal positions used in the simulations to tally fluxes and energy deposition.
Figure 19
Figure 19
Neutron fluxes (n/cm2/s) and statistical errors (%) in 4 FOCS positions (WCLL blanket).
Figure 20
Figure 20
Gamma fluxes (γ/cm2/s) and statistical errors (%) in four FOCS positions (WCLL blanket).
Figure 21
Figure 21
EP configuration with the X-ray spectroscopy (light blue), divertor monitoring (X-point and outer divertor tangential line-of-sight in purple, outer divertor surface views in red) and pellet monitoring (green) systems.
Figure 22
Figure 22
Possible radiation shielding locations proposed for the EP (units in mm).
Figure 23
Figure 23
CAD model of the EP used in the simulations.
Figure 24
Figure 24
CAD model of the EP used in the simulations with transparent cells, showing the diagnostic ducts.
Figure 25
Figure 25
X-ray spectroscopy ducts along the EP.
Figure 26
Figure 26
MCNP model of the EP. Left: X-ray spectroscopy ducts. Right: Near-ultraviolet (bottom) and visible (top) divertor spectroscopy ducts (poloidal view, plane y = −15 cm).
Figure 27
Figure 27
Materials used in the MCNP model of the equatorial port.
Figure 28
Figure 28
Neutron and gamma fluxes (cm−2 s−1) in plane y for the configuration with diagnostics in the EP.
Figure 29
Figure 29
Neutron and gamma fluxes (cm−2 s−1) in plane z for the configuration with diagnostics in the EP.
Figure 30
Figure 30
Statistical errors of the neutron fluxes, for the planes y = 80 cm and z = 0.
Figure 31
Figure 31
Neutron flux (n/cm2/s) and statistical error 2 m behind the bioshield plug (x = 2400 cm, y = 70 cm, z = 0), for a circular duct with r = 1.5 cm.
Figure 32
Figure 32
Gamma flux (γ/cm2/s) and statistical error 2 m behind the bioshield plug (x = 2400 cm, y = 70 cm, z = 0), for a circular duct with r = 1.5 cm.
Figure 33
Figure 33
Neutron flux variation with the cross-sectional area, for rectangular ducts.
Figure 34
Figure 34
CAD model of the neutron and gamma cameras.
Figure 35
Figure 35
CAD model of the core radiated power and soft X-ray intensity system.
Figure 36
Figure 36
Neutronics model used in the simulations of the neutron/gamma cameras and core radiated power and soft X-ray intensity system (plane y = 50 cm).
Figure 37
Figure 37
CAD model of the EP used in the simulations with transparent cells, showing the pre-reflectors and the diagnostic ducts of the X-ray spectroscopy system.
Figure 38
Figure 38
MCNP model of the EP, showing the X-ray spectroscopy ducts (plane z = 1 cm).
Figure 39
Figure 39
Neutron (n cm−2 s−1) and gamma (γ cm−2 s−1) fluxes in plane y with the alternative X-ray spectroscopy ducts.
Figure 40
Figure 40
Neutron (n cm−2 s−1) and gamma (γ cm−2 s−1) fluxes in plane z with the alternative X-ray spectroscopy ducts.
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