The necessity of detailed multi-dimensional transport calculations in LWR pressure vessel surveillance and for MTR irradiation

For two typical German PWR's (1300 and 800 MWsub(el) power) the fast neutron fluxes and spectra outside the core have been determined. In a first step the commonly used group cross section libraries VITAMIN/C and EURLIB have been compared and checked with a 271-fine-group library showing acceptable small differences. The perturbation of the neutron field caused by a surveillance capsule has been analysed in detail. Reaction rates obtained from a fine mesh S sub(n)-calculation were confirmed by a Monte-Carlo calculation and by measurements. The flux synthesis method can be used outside the core barrel to get the three-dimensional distribution with sufficient accuracy. Transport calculations have been performed also for several MTR irradiation experiments. Compared with LWR surveillance and pressure vessel positiones the neutron spectra are much softer suggesting the use of DPA instead of flux greater 1 MeV as a measure for neutron exposure. (author)