Verification of neutron transport calculations for nonstandard pressure vessel surveillance positions in the VVER-1000 Novovoronesh-5

Activation measurements results at non-standard surveillance positions of the VVER-1000 Novovoronesh-5 have been used to verify neutron fluence calculations for pe-ripheral reactor regions with large flux gradients. Fluence integrals and activities of irradiated detectors and specimens had been calculated by three laboratories using different transport calculation methods: 2D/1D-SN synthesis, 3D-SN and the Monte Carlo method. The results obtained by different calculations and by activation measurements have been compared. The differences between measured and calculated activities as well as between the different calculation results were reasonable. Possible causes of discrepancies are discussed.