Monte Carlo coupled calculations are used for modelling functionals of neutron flux in the research reactor experimental devices. On the first step, the device is replaced by black body (BB) and the surface source is obtained by interrupting each neutron path having crossed BB. On the second step, BB is replaced by the device and the coupled transport problem is then solved with stored neutrons as a source. The method is realized on the basis of the MMKFK code system. 16 refs.; 2 figs.