Neutron transport calculations in support of neutron diagnostics at JET

At JET the primary diagnostic for monitoring the neutron emission is a set of fission chambers. These are calibrated using the neutron activation tech nique. A second independent measurement of the neutron yield can be obtaine d from the neutron profile monitor. Both measurements depend on neutron tra nsport calculations and at JET this has been done using the neutron transpo rt code MCNP. The introduction of tritium into JET plasmas provided an oppo rtunity to check the modeling by comparing the activation of different mate rials. The calculation of the neutron spectrum at a re-entrant irradiation position was found to be consistent with measurements and an accuracy of <7 % in the neutron yield measurement was obtained. Neutron transport calculat ions of the effective collimator correction and attenuation for the profile monitor are also described. (C) 1999 American Institute of Physics. [S0034 -6748(99)59001-1].