Water activated by fast neutrons emits both high energy gammas from 16N and delayed neutrons from 17N. The radioisotopes 16,17N are produced through the 16O(n,p)16N and 17O(n,p)17N reactions ...(thresholds about 10 MeV) and decay through the reactions 16N (T1∕2=7.13±2 s) →16O + γ (67% @ 6.13 MeV, 5% @ 7.12 MeV) and 17N (T1∕2=4.173±4 s) →17O→16O + n (37.7% @ 0.386 MeV, 0.6% @ 0.886 MeV, 49.8% @ 1.16 MeV, 6.9% @ 1.69 MeV), γ (3.7% @ 0.87 MeV), respectively. Activated water, flowing throughout a nuclear plant distributes the radioactivity to many critical components where personnel and/or instrumentation can be located thus depositing additional radiation dose which requires a proper shielding. This source of radiation represents an issue for a D-T fusion device like ITER which uses water as the main cooling fluid for components such as e.g. first wall and divertor.
Owing to the scarce experimental information available for the cross sections of the 16O(n,p)16N and 17O(n,p)17N reactions and few benchmark validations, large uncertainties are affecting the calculations of the water activation induced by DT neutrons in a tokamak. In the attempt to improve the available nuclear data Fusion for Energy (F4E) tasked ENEA to carry on a benchmark experiment to validate the water activation calculations presently performed for ITER. This benchmark experiment was carried out in the year 2019 irradiating with the 14 MeV neutrons produced by the Frascati Neutron generator (FNG) a small size ITER First Wall mock-up. Demineralized water was circulating inside the mock-up and downstream of the irradiation zone the 16N gamma-rays decay and the 17N neutrons decay were measured using proper detectors. The experiment was simulated using the MCNP and the FISPACT codes. The obtained C/E values are in a range close to unit for both 16,17N isotopes. However, due to the large uncertainty on the 16O(n,p)16N and 17O(n,p)17N reactions cross-sections, for some of the used cross-section data base, e.g. ENDF/B-VIII.0, the C/E is affected by large uncertainty. This is especially true for the case of 17N which production cross-section is affected by ±60% uncertainty. In the attempt to measure and validate the cross-section data for 16,17N production, the water activation experiment was repeated at FNG so to measure directly the 16,17O(n,p)16,17N reaction cross-sections at almost monochromatic energies. The results of this new experiment are presented in this paper and compared to the data currently used by ITER project for calculating the water activation.
A feasibility study was performed to fabricate ITER In-Vessel components by Selective Laser Melting (SLM) supported by Fusion for Energy (F4E). Almost fully dense 316L stainless steel (SS316L) ...components were prepared from gas-atomized powder and with optimized SLM processing parameters. Tensile tests and Charpy-V tests were carried out at 22 °C and 250 °C and the results showed that SLM SS316L fulfill the RCC-MR code. Microstructure characterization reveals the presence of hierarchical macro-, micro- and nano-structures in as-built samples that were very different from SS316L microstructures prepared by other established methods. The formation of a characteristic intragranular cellular segregation network microstructure appears to contribute to the increase of yield strength without losing ductility. Silicon oxide nano-inclusions were formed during the SLM process that generated a micro-hardness fluctuation in the building direction. The combined influence of a cellular microstructure and the nano-inclusions constraints the size of ductile dimples to nano-scale. The crack propagation is hindered by a pinning effect that improves the defect-tolerance of the SLM SS316L. This work proves that it was possible to manufacture SS316L with properties suitable for ITER First Wall panels. Further studies on irradiation properties of SLM SS316L and manufacturing of larger real-size components are needed.
•The mechanical properties of SS316L made by selective laser melting fulfill RCC-MR.•SLM SS316L consists hierarchical structures of high heterogeneity.•Silicon rich oxide nano-inclusions are formed unexpectedly during SLM process.•Cellular structure and oxide nano-inclusions strengthen SLM SS316L.
•Fusion reactors may experience narrow near SOL heat flux channel widths λq.•SOLPS-ITER simulation was performed for ITER with λq ∼ 1 mm.•Operational window for divertor pressure with λq∼1mm is ...rather narrow.•The inclusion of drifts increases outer target heat fluxes.
SOLPS-ITER code simulations with fluid drifts activated are used to examine the consequences for divertor performance, under burning plasma conditions, of a reduction in scrape-off layer (SOL) cross-field transport such that the outboard midplane SOL parallel heat flux width, λq is reduced to the very low values predicted by the experimental scaling in T. Eich et al., Nucl. Fusion 53 (2013) 093031 for high plasma current operation on ITER. The decrease of λq from the standard value (~3.5 mm) used in the ITER SOLPS modeling database, to λq ~ 1–2 mm expected from the scaling, leads to a strong narrowing of the operational window in terms of divertor heat loading limits. To maintain similar levels of sub-divertor neutral pressure, pn (one of the key divertor operational parameters) as those obtained with standard transport, higher levels of neon impurity seeding are required when transport is reduced, yielding higher Zeff at the upstream separatrix and requiring further integrated modelling to assess the impact on confinement. The simulations also demonstrate that the strong increase in in-out target peak power loading asymmetry at low pn seen for standard transport when drifts are switched on in the code is preserved, and in fact worsens, for low transport. This significantly reduces margins for power handling control at lower pn if heat flux channels will be narrow on ITER.
Abstract
Time-dependent SOLPS-ITER simulations have been used to identify reduced models with the sparse identification of nonlinear dynamics (SINDy) method and develop model-predictive control of ...the boundary plasma state using main ion gas puff actuation. A series of gas actuation sequences are input into SOLPS-ITER to produce a dynamic response in upstream and divertor plasma quantities. The SINDy method is applied to identify reduced linear and nonlinear models for the electron density at the outboard midplane
n
e
,
s
e
p
O
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and the electron temperature at the outer divertor
T
e
,
s
e
p
d
i
v
. Note that
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,
s
e
p
d
i
v
is not necessarily the peak value of
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along the divertor. The identified reduced models are interpretable by construction (i.e. not black box), and have the form of coupled ordinary differential equations. Despite significant noise in
T
e
,
s
e
p
d
i
v
, the reduced models can be used to predict the response over a range of actuation levels to a maximum deviation of 0.5% in
n
e
,
s
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p
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and 5%–10% in
T
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,
s
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d
i
v
for the cases considered. Model retraining using time history data triggered by a preset error threshold is also demonstrated. A model predictive control strategy for nonlinear models is developed and used to perform feedback control of a SOLPS-ITER simulation to produce a setpoint trajectory in
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e
,
s
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p
O
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using the integrated plasma simulator framework. The developed techniques are general and can be applied to time-dependent data from other boundary simulations or experimental data. Ongoing work is extending the approach to model identification and control for divertor detachment, which will present transient nonlinear behavior from impurity seeding, including realistic latency and synthetic diagnostic signals derived from the full SOLPS-ITER output.
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