Measurements of gamma emission rates from Fe and Cu dosimeters extracted from a boiling water reactor-type reactor vessel were carried out to determine their total activity. The dosimeter's activity is related to the neutron flux at that location by taking into account the reactor material's embrittlement caused by neutron bombardment. The dosimeters were taken out after the first reactor operation cycle. From gamma radioactivity measurements of these dosimeters, neutron flux and fluence were calculated. These parameters are used in the determination of the shift and adjusted reference temperature values needed for the development of pressure-temperature curves used during reactor operation.