Absolute neutron yield measurement using divertor NFM Kaschuck Yu.A., Krasilnikov A.V., Prosvirin D.V., Tsutskikh A.Yu. SRC RF TRINITI, Troitsk, Russia ITPA-10 Troitsk, Moscow reg., Russia

ITER neutron diagnostic system for total neutron yield measurements System Type of measurements Problems Activation direct No time resolution, absolute calibration Neutron Flux Monitor Absolute calibration RNC, VNC constrained Plasma core horizontal and vertical shifts Neutron tomography RNC&VNC Unfolding procedure, calibration Neutron spectrometry Plasma shift, source profile, time resolution

Neutron sources for ITER neutron diagnostic calibration Initial calibration Radionuclide neutron sources: Cf, Am-Be – well-know neutron spectrum, constant neutron yield, isotropic emission Neutron generators: compact switchable fusion neutron source (d-t, d-d) Running cross-calibration Plasma core as “certified” neutron sources - ITER discharges with well-know plasma parameters: total neutron yield, plasma position, ion temperature and fuel density profile, etc.

Neutron sources for ITER neutron diagnostic calibration 252 Cf neutron sources = 2.14 MeV  Y n up to 2  n/s  m Cf ~ 8.5 mg   Y n ~ 1-2%  size:  7  25 mm Commercial available 252 Cf neutron sources produced by “Research Institute of Atomic Reactor”, Dimitrovgrad, RF

Neutron sources for ITER neutron diagnostic calibration DT neutron generators: DT neutron generators: neutron yield up to n/s; sealed tube lifetime hours; mass kg; size  200  1000 mm  anisotropic emission due to neutron backscattering at the NG construction;  target water cooling is necessary for NG with neutron yield higher n/s  on-line neutron flux monitoring is necessary due to neutron yield variation during operation;

Neutron generator emission anisotropy NGM-17, TRINITI Yn ~ n/s TFTR DT neutron generator Yn ~ 10 8 n/s A. L. Roquemore 9 ITPA Daejeon, Korea, Oct 2005

Divertor Neutron Flux Monitor DNFM conception: Arrangement of high sensitive 235 U and high purity 238 U fission chambers meet ITER requirements Arrangement of high sensitive 235 U and high purity 238 U fission chambers meet ITER requirements Design features: 238 U FC has a B 4 C thermal neutron shielding 238 U FC has a B 4 C thermal neutron shielding 235 U FC surrounded by water moderator 235 U FC surrounded by water moderator both FC has low and high sensitive volume (1:10 3 ) both FC has low and high sensitive volume (1:10 3 ) blank chamber for background measurements blank chamber for background measurements 3 similar DNFM modules located toroidal around the ITER VV to provide cross calibration 3 similar DNFM modules located toroidal around the ITER VV to provide cross calibration

Divertor Neutron Flux Monitor DNFM calibration analysis with MCNP 4C code: Model includes full torus vacuum vessel and shielding blanket modules Model includes full torus vacuum vessel and shielding blanket modules Simulation of point sources (14 MeV and 252 Cf) moving toroidally along the plasma axis Simulation of point sources (14 MeV and 252 Cf) moving toroidally along the plasma axis Fast neutron group fluxes (1  14 MeV) at the divertor level were analyzed Fast neutron group fluxes (1  14 MeV) at the divertor level were analyzed

Divertor Neutron Flux Monitor DNFM calibration: neutron group fluxes produced by 14MeV neutron source moving along VV axis

Divertor Neutron Flux Monitor DNFM calibration: neutron group fluxes produced by 252 Cf source moving along VV axis

Divertor Neutron Flux Monitor DNFM calibration: fast and direct neutron fluxes vs toroidal angle for point DT neutron source moving along VV axis

Divertor Neutron Flux Monitor DNFM calibration: relative count rate in case 1,2 and 3 NFM at the divertor for 14 MeV neutron source along VV axis

Calibration scenario Test level Type testComprehensive calibrationOperation check and laboratory test FactoryNTAIn-situ Running cross calibration NTAWorkplace Absolute sensitivity; Response linearity over all required fluence rate range Absolute sensitivity, Response linearity in limited range Absolute sensitivity vs toroidal angle Cross calibration of neutron emission rate: 1)among another NFM 2)with RNC&VNC 3)with activation system Cross calibrati on in case of replace ment or modific ation Random Confirm correct operation and long term stability

Calibration scenario Crossing of factory test, NTA calibration and operation range for NFM based on fission chambers.

Calibration scenario Requirements for in-vessel calibration special handling tools and certified container for operation with radionuclide source neutron source mechanical support in the machine additional detectors for neutron flux measuring support execution time schedule of calibration

Conclusions Both types of neutron sources DT generator and 252 Cf are necessary for DNFM calibration Source intensity ~10 10 n/s is enough for DNFM calibration:  252 Cf is commercial available  DT generator has less anisotropy emission Source moving in range  90  is enough for one DNFM detector calibration, but movement around full torus is required for two or three detectors to guarantee further cross-calibration MCNP calculation support for initial calibration and further running cross-calibration is necessary to take into account calibration source spectrum and anisotropy NTA has significant importance for neutron filed simulation, initial test and running cross-calibration