CAD-Based Shielding Analysis for ITER Port Diagnostics

The purpose of TNS spectrometer is to measure spectra of neutrons flying in tangential direction as a collective D-T plasma rotation. In result to estimate the Doppler energy shift of the neutron spectrum emission. Problem was noise of neutrons coming from other Diagnostics.


Stages of CAD-to-MC models geometry conversion to CSG model of MCNP:
1) Geometry simplification -remove the unnecessary details 2) Approximation of free-form and spline surfaces to 1 st and 2 nd order surfaces of MCNP 3) Material definition with homogenization setting up the material mixtures for the simplified cells, such as steel-water shield 60 vol.% steel -40 vol.% water.
Tallying procedure in MCNP models with lost particles • CAD-to-MC geometry conversion of tokamaks (ITER, DEMO) with all their complex engineering and diagnostic systems is performed with some level of approximation. Approximations could couse geometry errors and as the consequence -lost paricles. • Big problem with lost particles: If one of particles in a history is lost, MCNP cancels all tallies calculated during the history and all banked particles are erased.

Summary and Recommendations
• Neutronics analysis was performed in the MCNP Local model of EPP17 included only the apertures of two Diagnostics: TD-monitor and CIXS. • The results include neutron and gamma fluxes and nuclear heating on 7 mirrors of the TD-monitor, neutron fluxes and SDDR estimated in spherical detectors and with 3D distributions in EPP17: • Nuclear heating on mirrors is up to 0.77 W/cm 3 (cooling might be required).
• SDDR in spherical detectors at the bottom of TD-monitor shield box (at 30 cm from Closure Plate) reaches 210 microSv/h, with a contribution of 17 microSv/h from TD-monitor. • Shield block behind the TD-monitor contribute to a decrease on 7 microSv/h -gamma shadow effect. • These are relative SDDR values of Local MCNP model. Final values request inclusion of all the tenants of EPP17 (TD-monitor, CIXS, Vis/IR system, and Divertor Thermography) -future task of EPP17 port plug integration, with inclusion of all the sorts of the gaps, radiation cross-talks between the ports, and environmental effects in global MCNP C-lite model.

Recommendations for TD-monitor design improvement:
• Increase vertical shift (M4-M5) of the dog leg inside the port plug -to prevent possible direct neutron streaming.

Possible neutron streaming
• Shield block behind the TD-monitor optical box appears as a "neutronic relevant option".
Vertical cut of MCNP model Horizontal cut In-port radiation cross-talks Example 2: Tangential Neutron Spectrometer (TNS) inside the EPP #8 with 7 Diagnostics in C-lite v.2

Tangential Neutron Spectrometer (TNS) integrated inside the Diagnostic Equatorial Port Plug (EPP) #8
Diamond detectors and fission chambers are instaled in TNS as neutron detectors. High fluxes (10 9 n/cm 2 s -10 10 n/cm 2 s) will allow at least 100 ms spectroscopy time resolution.
Top view on ITER vacuum vessel 2 neutron detectors of Tangential Neutron Spectrometer (TNS)

Task: eliminate radiation cross-talk from the Fast Ion Loss Detector (FILD or Lost Alpha -LAM) to Tangential Neutron Spectrometer (TNS) in EPP #8
The purpose of TNS spectrometer is to measure spectra of neutrons flying in tangential direction as a collective D-T plasma rotation. In result to estimate the Doppler energy shift of the neutron spectrum emission. Problem was noise of neutrons coming from other Diagnostics.
Photon heating (W/cm 3 ) for EPP8 (7 diagnostics included in EPP#8) -impact of Lost Alpha Monitor (LAM) on neutron energy spectrrum in two Detectors of TNS

Plasma Plasma
Investigation was carrying on for the Central TNS detector.
In the original EPP #8 model the distance between TNS and 1 st leg of FILD was 10 cm, in the turned model it is 60 cm.
Turning upside-down of the FILD pathway helps to increase the 14-MeV peaking factor in energy resolution of the central TNS detector.
Turned FILD configuration stops neutron streaming from the FILD pathway to the Central TNS detector.
For measuring of n-spectrum in Central Det. #2 the turned FILD option is an equivalent to one of its absence -option of totally filled FILD (LAM -as FILD called before): "TNS-no-LAM" case on the spectra plots next slide.