Status of the divertor neutron flux monitor design and integration

1. Status of thedivertor neutron flux monitor design and integration Kaschuck Yu.A., Krasilnikov A.V., Prosvirin D.V., Tsutskikh A.Yu. SRC RF TRINITI, Troitsk, Russia 10.04.2006 ITPA-10 Moscow, Russia

2. Neutron Flux Monitoring System as a tool for ITER fusion power measurement Requirements : Total neutron strength 1014 - 51020 n/s Accuracy 10% Temporal resolution1 ms Proposed NFM System consists of: External NFM – set of 235U fission chambers Internal NFM – 235Umicro fission chambersDivertor NFM – 235U and 238U FC Key FC properties: - high radiation resistance - wide dynamic rangeof measurements - low sensitivity to gamma radiation- high temperature operation - technology availability- long-time experience of application in fission reactor

3. NFM Systems Integration • Integration : • Micro fission chambers – behind blanket modules inside tokamak • External NFM - set of FC in moderator at the radial port plug (limiter) • Divertor NFM – set of FC inside divertor cassette • Issue of the integration: • meet ITER requirements • provide absolute calibration

4. Divertor Neutron Flux Monitor Conception: • Analysis of present NFM system operation and integration shows the necessity of high sensitive neutron flux monitor at the divertor level to provide diagnostic requirements and possibility of absolute calibration • Arrangement of high sensitive 235U (~1.5g) and high purity 238U (~1.5g) fission chambers will meet required accuracy and temporal resolution for neutron flux dynamic range over 7 orders of magnitude • In both case the proposed fission chamber is a combination of low and high efficient chamber with sensitivity difference 1:103

5. Divertor Neutron Flux Monitor • Design features: • 238UFC has a B4C (~1g/cm2 of 10B) thermal neutron shield to reduce transmutation changes of efficiency • 235UFC will be surrounded by water moderator (thickness 5-7 cm) to increase sensitivity. Water can be used from cassette cooling system • Additional blank chamberwill be used for background contribution measurements (EM noise, gammas, etc) • Divertor NFM system includes three similar modules located toroidal around the VV to increase sensitivity and guarantee a cross calibration

6. Specification of DNFM Fission Chambers * - including water moderator

7. Divertor NFM Integration

8. Divertor NFM Integration

9. MCNP Analysis of DNFM Operation • DNFM response analyzed using MCNP 4C code: • the simplest model includes full torus vacuum vessel and shielding blanket modules (SS+H2O) with elliptic cross-section • monoenergetic (14 MeV) toroidal symmetric neutron source with poloidal distribution and peaking factor 13 • Neutron flux (114MeV)at the divertor level has been calculated • Detection efficiency variations were analyzed for vertical and horizontal plasma core shift • Fast neutron fluxes for calibration point source moving toroidally along the VV axis were calculated • Detection efficiency variation versus neutron source peaking factor is under analysis now (in progress)

10. MCNP analysis results:neutron group fluxes at the divertor level

11. MCNP analysis results:DNFM efficiency variations for vertical and horizontal plasma core shift

12. DNFM integration in the new divertor cassette

13. DNFM integration in the new divertor cassette

14. Conclusions We are planning to continue DNFM activity: • Improve the MCNP model including a divertor cassette with T dome support • Development of DNFM fission chamber prototypes for ITER relevant tests (high temperature operation, wide neutron flux range measurement etc.) • Integration in the novel divertor cassette • Advance calibration scenario including DNFM • DNFM official status needs to update (at the moment - RFvoluntary task as not credit diagnostic)