Keywords: fluence calculation, BWR surveillance, boiling water reactors, fixed source distribution, neutron source, safety related structures, NPPs, nuclear power plants, nuclear energy, 3D neutron flux distribution, DORT code
A computational set of tools developed for fluence calculation as support for BWR's surveillance programme
The determination of a neutron source for the RPV fluence calculation is a key factor to detect and prevent degradation of safety–related structures of a NPP. A 3D neutron fluence calculation can be very challenging if all the source details are considered. Several options are possible in order to address the problem, being the most direct the use of 3D transport codes; however, strategies that reduce calculation times are sometimes the preferred. A fast methodology has been developed in order to simplify the calculations without losing accuracy. The methodology relies on the use of DORT together with the synthesis method for having a 3D neutron flux distribution. A set of auxiliary modules for the calculations of the fixed source distribution has been developed. Comparisons of the calculated neutron fluxes against the measurements from the surveillance capsules of the NPP Laguna Verde show maximum relative differences up to 6.81% by far within the 20% difference required by regulation.