Fluence calculation and reaction rates determination at the reactor pressure vessel Kola 3

In this work, different geometric positions which have influence on the radiation conditions of the samples are investigated. Thus, the uncertainties can be determined in the fluence values of surveillance specimens. The fluence calculations were carried out by the codes TRAMO and DORT. This study was accompanied by ex-vessel neutron dosimetry experiments at at Kola NPP, Unit 3 (VVER-440/213), which provide the basis for validation of calculated neutron fluences. The main neutron-activation monitoring reactions were 54Fe(n,p)54Mn and 58Ni(np)58Co. The activity measurements were carried out by SEC NRS.
Good agreement as between the deterministic and stochastic calculation results and between the calculations and the ex-vessel measurements was found. The average difference between measured and calculated values is 5%. The influence of the channels for surveillance specimens and the shielding effect of a baffle rib on the monitors and on the Monte-Carlo calculated results was studied.
The differences of fast neutron fluences in the depth of surveillance specimens could be up to 30% depending on the direction to the core. Based on these calculations the lead factor of specimens is very large and has high uncertainty. The maximum fluence of RPV may be achieved after two cycles. These uncertainties should be taken into account during validation of calculated results by SS neutron dosimetry.