<p dir="ltr">The estimation of local irradiation conditions is a complex and crucial task with significant implications for reactor safety, operation, and spent nuclear fuel management. This study aims to investigate the feasibility of using measurements of a limited number of nuclides taken at the time of discharge to infer local irradiation conditions. Specifically, the focus is on determining the local operating power, void fraction, and burnup. These factors are required to calculate the isotopic composition of discharged reactor assemblies. Existing methods often struggle with substantial uncertainties when estimating these local conditions, leading to inaccuracies in isotopic calculations. Therefore, markedly different, this research aims to establish a relationship between local conditions and isotopic measurements, benefiting from the low uncertainty associated with experimental isotopic measurements. To achieve this goal, a two-step approach is employed. First, a mathematical inference procedure is developed to correlate the isotopic composition of discharged fuel with the local irradiation conditions. Second, given a certain prediction accuracy, efforts are made to minimize the number of isotopic measurements required at the time of discharge. To do so, this work develops an inference algorithm employing a simplified depletion model of a single pin in a BWR assembly using SCALE Polaris module. Polaris module generates the virtual measurement of 29 nuclides including actinides and fission products with assumed power and void fraction histories provided to SCALE Polaris as inputs. Employing these virtual measurements, a similarity measure metric is employed to minimize the number of nuclides to estimate irradiation conditions, and the inference method used to estimate the irradiation conditions is the ordinary least squares method.</p>

DYN3D is an best estimate advanced code for the three-dimensional simulation of steady-states and transients in light water reactor cores with quadratic and hexagonal fuel assemblies. Burnup and poison-dynamic calculations can be performed. For the investigation of wide range transients, DYN3D is coupled with system codes as ATHLET and RELAP5. The neutron kinetic model is based on the solution of the three-dimensional two-group neutron diffusion equation by nodal expansion methods. The thermal-hydraulics comprises a one- or two-phase coolant flow model on the basis of four differential balance equations for mass, energy and momentum of the two-phase mixture and the mass balance for the vapour phase. Various cross section libraries are linked with DYN3D. Systematic code validation is performed by FZR and independent organizations.

DYN3D is an best estimate advanced code for the three-dimensional simulation of steady-states and transients in light water reactor cores with quadratic and hexagonal fuel assemblies. Burnup and poison-dynamic calculations can be performed. For the investigation of wide range transients, DYN3D is coupled with system codes as ATHLET and RELAP5. The neutron kinetic model is based on the solution of the three-dimensional two-group neutron diffusion equation by nodal expansion methods. The thermal-hydraulics comprises a one- or two-phase coolant flow model on the basis of four differential balance equations for mass, energy and momentum of the two-phase mixture and the mass balance for the vapour phase. Various cross section libraries are linked with DYN3D. Systematic code validation is performed by FZR and independent organizations.