After the coated CFC wall to ITER-Like Wall (Beryllium/Tungsten/Carbon) transition in 201011, confirmation of the neutron yield calibration will be ensured by direct measurements using a calibrated 252Cf neutron source deployed by the in-vessel remote handling boom and Mascot manipulator inside the JET vacuum vessel. The paper describes preliminary calculations and the results of numerical study of the effect of source holder on neutron detector response. The source baton was designed in such a way, that it does not significantly affect the neutron spectrum, angular neutron flux distribution or activation detector response. All effects are approximately equal to or less than 1%. The largest disturbance to the neutron flux angular distribution and to the neutron spectrum arises from the source capsule. Hence one should obtain as much information as possible about the capsule and the 252Cf source material in order to avoid additional systematic errors.
COBISS.SI-ID: 26263847
JET made a transition from Carbon wall to ITER-Like Wall (Beryllium/Tungsten/Carbon) during 2010-11. Measurement of the resulting neutron yield calibration is being ensured by direct measurements using a calibrated 252Cf neutron source (NS) deployed by the in-vessel remote handling (RH) boom and mascot manipulator inside the JET vacuum vessel [1]. This activity will allow direct measurement of the calibration of the 3 sets of external fission chambers (FC) system which was the original JET standard [2] and provide the first direct calibration of the JET activation system inside the torus. A key objective of the calibration is to achieve at least 10 % accuracy in absolute calibration of the JET external neutron monitors. The paper investigates the effect of the JET Remote Handling System (RHS) on the external neutron monitor response. It is found the most affected external neutron detector is the one which is closest to the RHS entrance port, as the port is blocked by the massive RHS boom. The two external neutron detectors further from the RHS entrance port are affected to a much lesser extent. The effect of the JET RHS on the response of the external monitors at individual positions of the NS can be substantial, i.e. up to 30 %, but this occurs in locations which have low importance in the global response, integrated for all NS positions round the torus. Hence the total effect due to the RHS is less than 5 % in the most affected detector.
COBISS.SI-ID: 26436647